FR3142468A1 - SELENIUM IMMOBILIZED ON POROUS CARBON IN THE PRESENCE OF OXYGEN, METHOD FOR MANUFACTURING AND USES OF SELENIUM IMMOBILIZED IN A RECHARGEABLE BATTERY - Google Patents

Abstract

SELENIUM IMMOBILIZED ON POROUS CARBON IN THE PRESENCE OF OXYGEN, METHOD FOR MANUFACTURING AND USES OF SELENIUM IMMOBILIZED IN A RECHARGEABLE BATTERY In one method of preparing a selenium immobilized system or body, a selenium - carbon - oxygen mixture is formed. The mixture is then heated to a temperature above the melting temperature of selenium and the heated mixture is then cooled to ambient or ambient temperature, thereby forming the immobilized selenium system or body. Figure for abstract: None

Description

SELENIUM IMMOBILIZED ON POROUS CARBON IN THE PRESENCE OF OXYGEN, PROCESS FOR MANUFACTURING AND USES OF IMMOBILIZED SELENIUM IN A RECHARGEABLE BATTERY Field of invention

The present application relates to the field of high energy density lithium secondary batteries. More particularly, the application relates to a method for preparing carbon-selenium nanocomposite materials and applications thereof. The present invention also relates to immobilized selenium comprising selenium and carbon. It also relates to a method for manufacturing and the utility of the immobilized selenium. One of the uses of the immobilized selenium is in a rechargeable battery. The present invention also relates to a rechargeable battery which can perform a discharge-charge cycle at a rapid rate (e.g., at a rate of 10 C) with a minimal level of capacity loss, while being capable of substantially recovering its electrochemical performance, such as specific capacity, when charged at a low rate, for example, at a rate of 0.1 C.

Description of the state of the art

With the increase of human energy demand, secondary batteries with high mass energy density and high volumetric energy density, such as lithium-sulfur and lithium-selenium batteries, have attracted great interest. Elements in group 6A of the periodic table, such as sulfur and selenium, have shown two-electron reaction mechanisms in the electrochemical reaction process with lithium. Although the theoretical mass specific capacity of selenium (675 mAh/g) is lower than that of sulfur (1675 mAh/g), selenium has a higher density (4.82 g/cm3) than sulfur (2.07 g/cm3). Therefore, the theoretical volumetric energy density of selenium (3253 mAh/cm3) is close to the theoretical volumetric energy density of sulfur (3467 mAh/cm3). At the same time, compared with sulfur, which is close to an electrically insulating material, selenium is an electrical semiconductor and has better electrical conduction properties. Therefore, compared with sulfur, selenium can demonstrate a higher activity level and better utilization efficiency even at a higher charge level, leading to battery systems with high energy and power density. In addition, a selenium-carbon composite can exhibit further improvement in electrical conductivity compared with a sulfur-carbon composite to obtain an electrode material with higher activity.

As described in Patent Publication No. CN104393304A, by passing hydrogen selenide gas through a graphene dispersion solution, the heat of the solvent reduces graphene oxide to graphene, while oxidizing hydrogen selenide to selenium. The thus prepared selenium-graphene electrode material is coupled with an ether-based electrolyte system, 1.5M lithium bis-trifluoromethane sulfonimide (LiTFSI) / 1,3-dioxolane (DOL) + dimethyl ether (DME) (volume ratio 1:1); the specific charge capacity reaches 640 mAh/g (approaching the theoretical specific capacity of selenium) in the first cycle. However, in the charge-discharge process, polyselenide ions dissolve in the electrolyte, showing a significant degree of shuttle effect, which consequently causes a decrease in capacity. At the same time, the preparation procedures of graphene oxide raw material used in this process are complicated and are not suitable for industrial production.

Patent CN104201389B discloses a cathode material for a lithium-selenium battery, using a nitrogen-containing layered porous carbon composite current collector, which has been compounded with selenium. When preparing the nitrogen-containing layered porous carbon composite current collector, a nitrogen-containing conductive polymer is first deposited or grown on the surface of a piece of paper and followed by alkali activation and high-temperature carbonization, producing a nitrogen-containing layered porous carbon composite current collector where a carbon fiber constitutes a network structure that supports itself. This nitrogen-containing layered porous carbon composite current collector is then mixed with selenium. The deposition process for preparing a conductive polymer is complicated, and the film formation or development process is difficult to control. The preparation process is complicated, which is accompanied by undesirably high costs.

In addition, the demand for a long-lasting, high-energy-density, high-power-density rechargeable battery that can be charged and discharged at a rapid rate is growing in electronics, electric/hybrid vehicles, aerospace/drones, submarines, and other industrial, military, and consumer applications. Lithium-ion batteries are examples of rechargeable batteries in the above-mentioned applications. However, the need for better performance and cycling capability has not been met by lithium-ion batteries as lithium-ion battery technology has matured.

Atomic oxygen has an atomic weight of 16 and has a capacity of 2 electron transfers. A rechargeable lithium-oxygen battery has been studied with the aim of making high energy density batteries. When a battery has an oxygen cathode that is coupled with lithium or sodium metal as anode, it has the highest stoichiometric energy density. However, most of the technical problems of the Li//Na-Oxygen battery are still unsolved.

Elemental sulfur is also a member of the oxygen group and has the second highest energy density (after oxygen) when combined with a lithium or sodium metal anode. A lithium-sulfur or sodium-sulfur cell has been extensively studied. However, the polysulfide ions (intermediates) that form during the discharge process of Li-S or Na-S batteries dissolve in the electrolyte and “shuttle” from the cathode to the anode. Upon reaching the anode, the polysulfide anions react with the lithium or sodium metal, resulting in a loss of energy density, which is undesirable for a battery system. In addition, sulfur is an insulator, requiring a high charge level of the carbon materials to achieve a minimum level of electrical conductivity. Due to the extremely low electrical conductivity of sulfur, a rechargeable Li/Na-S battery is very difficult to discharge or charge at a rapid rate.

Provided is a process for preparing a two-dimensional carbon nanomaterial, which has a high degree of graphitization. The two-dimensional carbon nanomaterials are mixed with selenium to obtain a carbon-selenium composite material, which is used as a cathode material that combines with a lithium-containing anode material, producing a lithium-selenium battery that has a high energy density and stable electrochemical performance. A similar process can be used to further assemble a pouch cell that also has excellent electrochemical properties.

Also provided is a method for preparing the selenium-carbon composite material with readily available raw materials and simple preparation procedures.

The selenium-carbon composite material described herein can be obtained from a preparation process which comprises the following steps:

(1) Carbonizing organic salts of alkali metals or organic salts of alkaline earth metals at high temperature, then washing them with dilute hydrochloric acid or other acids, and drying them to obtain two-dimensional carbon material;

(2) Mixing the two-dimensional carbon material obtained in step (1) with selenium in organic solution, heating and evaporating the organic solvent, and then carrying out the mixing of selenium with the two-dimensional carbon material by a multi-step thermal ramp-up and hot stabilization procedure to obtain a carbon-selenium composite.

In step (1), the organic alkali metal salt may be selected from one or more of potassium citrate, potassium gluconate and sodium salt of sucrose acid. The organic alkaline earth metal salt may be selected from one or both of calcium gluconate and calcium salt of sucrose acid. The high-temperature carbonization may be carried out at 600-1000°C, preferably 700-900°C; the carbonation time is 1-10 hours, preferably 3-5 hours.

In step (2), the organic solvent may be selected from one or more of ethanol, dimethyl sulfoxide (DMSO), toluene, acetonitrile, N,N-dimethylformamide (DMF), carbon tetrachloride and diethyl ether or ethyl acetate; the multi-stage thermal ramp-up and heat stabilization procedure may be referred to as a ramp-up rate of 2 to 10°C/min, preferably 5-8°C/min, to a temperature of 200 to 300°C, preferably 220 to 280°C, followed by temperature stabilization for 3-10 hours, preferably 3-4 hours; then continued heating to 400-600°C, preferably 430-460°C, followed by stabilization for 10-30 hours, preferably 15-20 hours.

Also provided is a lithium-selenium secondary battery that comprises carbon-selenium composite materials. The lithium-selenium secondary battery may further comprise: a lithium-containing anode, a separator, and an electrolyte.

The lithium-containing anode may be one or more of lithium metal, a lithiated graphite anode, and a lithiated silicon-carbon anode (by assembling the graphite and silicon-carbon anode materials and the lithium anode into a half-cell battery, and discharging to prepare the lithiated graphite anode and the lithiated silicon-carbon anode materials). The separator (membrane) may be a commercially available membrane, such as, but not limited to, a Celgard® membrane, a Whatman® membrane, a cellulose membrane, or a polymer membrane. The electrolyte may be one or more of a carbonate electrolyte, an ether electrolyte, and ionic liquids.

The carbonate electrolyte may be selected from one or more of diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC); and the solute may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), and lithium bis-fluorosulfonylimide (LiFSI).

For the ether electrolytic solution, the solvent may be selected from 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (DME), and triethylene glycol dimethyl ether (TEGDME); and the solute may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), and lithium bis(fluorosulfonyl)imide (LiFSI).

For ionic liquids, the ionic liquid may be one or more of room temperature ionic liquids [EMIm] NTf2 (1-ethyl-3-methylimidazolium bis trifluoromethane sulfonimide salt), [Py 13] NTf2 (N-Propyl-N-methylpyrrolidine bis trifluoromethane sulfonimide salt), [PP13] NTf2 (N-propylmethylpiperidine alkoxy-N-Bis trifluoromethane sulfonimide salts); and the solute may be selected from one or more of lithium hexafluorophosphate (LiPF6), bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), and lithium bis-fluorosulfonylimide (LiFSI).

The present invention also describes a lithium-selenium pouch cell battery which comprises the carbon-selenium composite material.

Compared with the prior art, with regard to the preparation method of the selenium-carbon composite material disclosed in the present paper, the two-dimensional carbon material has the following advantages: the raw materials are readily available at low cost, the preparation method is simple, highly convenient and suitable for mass production, and the obtained selenium-carbon composite material has excellent electrochemical properties.

This document also describes immobilized selenium (an immobilized selenium body) comprising selenium and a carbon skeleton. The immobilized selenium comprises at least one of the following: (a) requires sufficient energy to be gained for a selenium particle to reach a kinetic energy of ≥9.5 kJ/mole, ≥9.7 kJ/mole, ≥9.9 kJ/mole, ≥10.1 kJ/mole, ≥10.3 kJ/mole, or ≥10.5 kJ/mole to escape the immobilized selenium system; (b) a temperature of 490°C or more, ≥500°C, ≥510°C, ≥520°C, ≥530°C, ≥540°C, ≥550°C, or ≥560°C is required for the selenium particles to acquire sufficient energy to escape the immobilized selenium system; (c) the carbon skeleton has a surface area (with pores less than 20 angstroms) ≥500 m2/g, ≥600 m2/g, ≥700m2/g, ≥800 m2/g, ≥900 m2/g, or ≥1,000 m2/g; (d) the carbon skeleton has a surface area (for pores between 20 angstroms and 1,000 angstroms) of 20% or less, 15% or less, 10% or less, 5% or less, 3% or less, 2% or less, 1% or less of the total surface area.

This document also describes a cathode or rechargeable battery comprising immobilized selenium. Selenium may be doped with other elements, such as, but not limited to, sulfur.

This document also describes a composite comprising selenium and carbon having a platelet morphology with an aspect ratio ≥1, ≥2, ≥5, ≥10, or ≥20.

The present document also describes a cathode comprising a composite comprising selenium and carbon having a platelet morphology with an aspect ratio of ≥1, ≥2, ≥5, ≥10, or ≥20. The present document also describes a rechargeable battery comprising a composite of selenium and carbon and having a platelet morphology with the aforementioned aspect ratio.

This document also describes a rechargeable battery comprising a cathode, an anode, a separator and an electrolyte. The rechargeable battery can be charged at 0.1 C, 0.2 C, 0.5 C, 1 C, 1.5 C, 2 C, 3 C, 4 C, 5 C, 6 C, 7 C, 8 C, 9 C, 10 C or more rapidly. The cathode can comprise at least one element of a chalcogen group such as selenium, sulfur, tellurium and oxygen. The anode can comprise at least one element of an alkali metal, alkaline earth metals and one or more metals of group III A. The separator can be composed of an organic separator or an inorganic separator whose surface can be optionally modified. The electrolyte may comprise at least one alkali metal, alkaline earth metal and one or more group III A metals. The solvent of the electrolytic solution may comprise organic, carbonate, ether or ester solvents.

The rechargeable battery may have a specific capacity of 400 mAh/g or more, 450 mAh/g or more, 500 mAh/g or more, 550 mAh/g or more, or 600 mAh/g or more. The rechargeable battery may be capable of undergoing electrochemical cycling of 50 cycles or more, 75 cycles or more, 100 cycles or more, 200 cycles or more, etc. The rechargeable battery can maintain a specific battery capacity of more than 30%, more than 40%, more than 50%, more than 60%, more than 70% or more than 80% of the specific capacity of second discharge at a cycling rate of 0.1C after performing a high C-rate charge-discharge cycle (e.g., 5 cycles at 0.1C, 5 cycles at 0.2C, 5 cycles at 0.5C, 5 cycles at 1C, 5 cycles at 2C, 5 cycles at 5C and 5 cycles at 10C). The rechargeable battery can have a Coulomb efficiency of ≥50%, ≥60%, ≥70%, ≥80%, or ≥90%. The rechargeable battery can be used for electronics, an electric or hybrid vehicle, an industrial application, a military application such as a drone, an aerospace application, a marine application, etc.

There is a 50,000X scanning electron microscope photograph of the carbon material of Example 1;

There is a 0.1 C charge and discharge curve of the lithium-selenium battery of Example 1;

There is a 0.1 C charge and discharge curve of the lithium-selenium battery of Comparative Example 2;

There is an optical image of the pouch cell battery of Example 1;

There is a 0.05 C charge and discharge curve of the pouch cell battery of Example 1;

There is a flowchart of a process for manufacturing immobilized selenium;

There is a scanning electron microscope image of a carbon skeleton prepared by the process of Example 9;

There represents the X-ray diffraction patterns for the carbon skeleton prepared by the process of Example 9;

There is the Raman spectrum of the carbon skeleton which was prepared by the process of Example 9;

There is a graph of the cumulative and incremental surface area of the carbon skeleton prepared by the process of Example 9;

There is a graph of cumulative and incremental pore volumes for the carbon skeleton prepared by the process of Example 9;

There is a graph of the ATG analysis for immobilized selenium that was prepared by the process of Example 10;

There is a graph of the ATG analysis for non-immobilized selenium samples prepared by the process of Example 10 using a Se-Carbon Black Super P composite and a Se-graphite composite;

There is a graph of the ATG analysis of the non-immobilized selenium sample prepared using the Se-Carbon Black Super P composite ( ) under an argon gas flow and at heating rates of 16°C/min and 10°C/min;

There is a graph of rate constants for non-immobilized selenium (solid line of Se-Carbon Black Super P composite), and 2 different immobilized selenium samples (228-110 (dotted line) and 115-82-2 (dashed line)) prepared by the process of Example 10;

There is a graph of the Raman spectrum of immobilized selenium prepared by the process of Example 10;

There is a graph of X-ray diffraction patterns for immobilized selenium prepared by the process of Example 10;

There is an SEM image of immobilized selenium prepared by the process of Example 10;

There is an exploded view of a button cell including a cathode prepared according to the process of Example 11 or Example 13;

Figure 16 shows graphs of the cycling test results for a first lithium-selenium button cell (0.1C) ( - left) and a second lithium-selenium button cell (0.1C, then 1C) ( - right) of the type illustrated in the , which were prepared according to the process of Example 12;

There presents cycling test graphs for a lithium-selenium coin cell of the type shown in , which was prepared according to the process of Example 12 at different cycling speeds;

There presents graphs of the results of the 0.1 C cycling test of a sulfur-doped lithium-selenium button cell of the type indicated in , manufactured according to example 13 with a polymer separator;

There presents graphs of the results of the 1 C cycling test of a sulfur-doped lithium-selenium button cell of the type indicated in , manufactured according to example 13 with a polymer separator.

There presents SEM images of a three-dimensional interconnected thin-walled porous carbon nanomaterial produced from glucose;

There represents the BET N2 isotherms (a) and pore size distribution (c) for three-dimensional interconnected thin-walled porous carbon nanomaterials, which are produced from glucose;

There presents SEM images of a three-dimensional interconnected thin-walled porous carbon nanomaterial produced from soybean grinds; and

There represents the BET N2 isotherms (b) and pore size distributions (d) for three-dimensional interconnected thin-walled porous carbon nanomaterials, which are produced from soybean grinds.

DESCRIPTION OF THE INVENTION

In connection with the specific examples, the present invention will be described in more detail below. Unless otherwise indicated, the experimental methods presented in the following examples are all conventional; the reagents and materials are all commercially available.

Example 1:

(A) Preparation of selenium-carbon composite material

After crushing and grinding, an appropriate amount of potassium citrate is calcined at 800°C for 5 hours in an inert atmosphere and then cooled to room temperature. It is washed with dilute hydrochloric acid at neutral pH, filtered and dried to give a two-dimensional carbon nanomaterial ( ); according to the mass ratio of 50/50, the two-dimensional carbon material and selenium should be weighed, and then stirred and mixed evenly with the selenium solution in ethanol; after evaporation of the solvent, the mixture should be dried in a dry oven; the dried mixture was heated at 5°C/min to 240°C and was heat-stabilized for 3 hours, then was heated again at 5°C/min to 450°C, was heat-stabilized for 20 hours and cooled to room temperature to give the selenium carbon composite material.

(B) Preparation of selenium-carbon composite cathode

The above prepared selenium-carbon composites are mixed with Super P carbon black (TIMCAL) and CMC/SBR binder (weight ratio 1:1), as well as water by fixed formulation through paste forming, coating, drying and other processes to obtain selenium-carbon composite cathode.

(C) Assembly of a lithium-selenium battery

The above-prepared selenium-carbon composite cathode was assembled with a lithium film as an anode, a Celgard® membrane as a separator, and a 1m solution of LiPF6 in EC/DMC as an electrolyte to form a lithium-selenium button cell and a lithium-selenium pouch cell battery ( ).

(D) Lithium-selenium battery test

A charge-discharge apparatus should be used to conduct a constant current charge-discharge test on the lithium-selenium button cell and the lithium-selenium pouch cell battery. The voltage range used for the test is 1.0 to 3.0 V and the test temperature is 25°C. The specific discharge capacity and the charge-discharge current level are calculated in a standard manner based on the mass of selenium. The charge-discharge current is 0.1 C or 0.05 C. The charge and discharge curve of lithium-selenium button cells is shown in , the results of the specific tests are presented in Table 1 below. The results of the tests on lithium-selenium pouch cell batteries are presented in .

Example 2:

The conditions are the same as in Example 1, except that the carbonized raw material used for the two-dimensional carbon is sodium citrate. The battery test results are summarized in Table 1 below.

Example 3:

The conditions are the same as in Example 1, except that the raw carbonized material used for the two-dimensional carbon is potassium gluconate. The battery test results are summarized in Table 1 below.

Example 4:

The conditions are the same as in Example 1, except that the high temperature carbonization for the carbon material is 650°C. The battery test results are summarized in Table 1 below.

Example 5:

The conditions were the same as in Example 1, except that the dried mixture was heated at 5°C/min to 300°C and stabilized at this temperature for 3 hours. The battery test results are summarized in Table 1 below.

Example 6:

The conditions were the same as in Example 1, except that the dried mixture was heated at 5°C/min to 240°C and stabilized at this temperature for 3 hours, then continued to be heated to 600°C, and stabilized at this constant temperature for 20 hours. The battery test results are summarized in Table 1 below.

Example 7:

The conditions are the same as in Example 1, except that the lithium-Se battery is assembled with a lithiated graphite anode, instead of the lithium anode film. The battery test results are summarized in Table 1 below.

Example 8:

The conditions are the same as in Example 1, except that the lithium-Se battery is assembled with a lithium silicon carbon anode, instead of a lithium anode film. The battery test results are summarized in Table 1 below.

Comparative example 1:

The conditions are the same as in Example 1, except that polyacrylonitrile is used as the base material. The battery test results are summarized in Table 1 below.

Comparative example 2:

The conditions are the same as in Example 1, except that a one-step compound preparation method is used to prepare the selenium-carbon composite. In this example, the dried selenium-carbon mixture was heated at 5°C/min to 500°C and stabilized at this temperature for 23 hours to obtain a selenium-carbon composite material. The charge-discharge curve of a battery made from the selenium-carbon composite material thus obtained is shown in ; the battery test results are summarized in Table 1 below.

Table 1 summarizes the battery test results.

Numeration First cycle discharge capacity (mAh/g) First cycle charge capacity / first cycle discharge capacity (%) Capacity at the 50th cycle
(mAh/g) Example 1 1,050 78.1 756 Example 2 940 74.6 672 Example 3 962 75.3 683 Example 4 987 72.1 680 Example 5 936 73.2 653 Example 6 972 70 661 Example 7 836 72.5 580 Example 8 910 73 600 Comparative 635 55 350 Example 1 Comparative 980 40.8 386 Example 2

Having thus described a process for preparing a selenium-carbon composite material, a process for manufacturing immobilized selenium and the use of immobilized selenium, for example in a rechargeable battery, will be described.

Selenium is an element in the same group as oxygen and sulfur, namely group 6 of the periodic table of elements. Selenium can be advantageous over oxygen and sulfur due to its very high electrical conductivity. US Patent 2012/0225352 describes the fabrication of rechargeable Li-selenium and Na-selenium batteries, with good capacity and cycling ability. However, a certain level of polyselenide anions shuttle between the cathodes and anodes of these batteries, resulting in additional electrochemical performances that need to be significantly improved to be used in practice. The literature in this area includes the following:

“Electrode materials for rechargeable batteries,” Ali Aboulmrane and Khalil Amine, U.S. patent application 2012/0225352, September 6, 2012.

“Lithium-selenium secondary batteries with nonflammable electrolyte,” Hui He, Bor Z. Jang, Yanbo Wang, and Aruna Zhamu, U.S. Patent Application 2015/0064575, March 5, 2015.

“Electrolyte solution and sulfur-based or selenium-based batteries with electrolyte solution,” Fang Dai, Mei Cai, Qiangfeng Xiao, and Li Yang, U.S. Patent Application 2016/0020491, Jan. 21, 2016.

“A New Class of Rechargeable Lithium-Sodium Batteries Based on Selenium and Selenium-Sulfur as Positive Electrode,” Ali Abouimrane, Damien Dambournet, Kerena W. Chapman, Peter J. Chupa, Wei Wang, and Khalil Amine, J. Am. Chem. Soc. 2012 134/45054508

“A self-supporting and ultra-long-life lithium-selenium battery cathode enabled by a 3D mesoporous carbon/graphene hierarchical architecture,” Kai Han, Zhao Liu, Jingmei Shen, Yuyuan Lin, Fand Dai, and Hongqi Ye, Adv. Funct. Mater., 2015, 25, 455–463.

“Carbon-selenium cathodes derived from micro- and mesoporous carbide for high-performance lithium-selenium batteries”, Jung Tai Lee, Hyea Kim, Marin Oschatz, Dong-Chan Lee, Feixiang Wu, Huan-Ting Lin, Bogdan Zdyrko, Wan II Chao , Stefan Kaskel, and Gleb Yushin, Energy Mater. 2014, 1400981.

"High-performance lithium-selenium battery with microporous carbon composite cathode and carbonate-based electrolyte", Chao Wu, Lixia Yuan, Zhen Li, Ziqi Yi, Rui Zeng, Yanrong Li and Yunhui Huang, Sci. China Mater. 2015 58/-97

“Advanced Se-C Nanocomposites: A Bifunctional Electrode Material for Li-Se and Li-ion Batteries,” Huan Ye, Ya-Xia Yin, Shuai-Feng Zhang, and Yu-Guo Guo, J. Mater. Chem. A., May 23, 2014.

“Lithium Iodide as a Promising Electrolyte Additive for Lithium-Sulfur Batteries: Advanced Mechanisms for Performance Enhancement,” Feixiang Wu, Jung Tae Lee, Naoki Nitta, Hyea Kim, Oleg Borodin, and Gleb Yushin, Adv. Mater. 2015, 27, 101–108.

“Se/C composite as cathode material for rechargeable lithium batteries with good electrochemical performance,” Lili Li, Yuyang Hou, Yaqiong Yang, Minxia Li, Xiaowei Wang, and Yuping Wu, RSC Adv. 2014, 4, 9086-9091.

“Elemental selenium for electrochemical energy storage,” Chun-Peng Yang, Ya-Xia Yin, and Yu-Guo Guo, J. Phys. Chem.Lett. 2015, 6, 256–266.

“Mesoporous carbon-selenium composite with superior storage capacity of lithium and sodium,” Chao Luo, Yunhua Xu, Yujie Zhu, Yihang Liu, Shiyou Zheng, Ying Liu, Alex Langrock, and Chunsheng Wang, ACSNANO, Vol. 7, No. 9, 8003-8010.

This document also describes immobilized selenium comprising selenium and carbon. The immobilized selenium may comprise elemental selenium or compound selenium. The selenium may be doped with another element, such as, but not limited to, sulfur. The immobilized selenium allows elemental selenium atoms to be located that function properly electrochemically without being "transported" between a cathode and anode of a battery. The immobilization of selenium allows an elemental selenium atom to gain two electrons during a discharge process and form a selenide anion at the location where the selenium molecule/atom is immobilized. The selenide anion can then give off two electrons during a charge process to form an elemental selenium atom. Therefore, the immobilized selenium can function as an active electrochemical agent for a rechargeable battery which has a specific capacity of up to a stoichiometric level, can have a Coulomb efficiency of ≥95%, ≥98%, or even 100%, and can achieve significantly improved sustainable cycling capability.

In a battery made with immobilized selenium, the electrochemical behaviors of elemental selenium atoms and selenide anions during charging are well-functioning processes. Carbon skeletons with Sp2 carbon–carbon bonds have delocalized electrons distributed on a six-membered conjugated aromatic ring with π bonds on graphene-like local lattices of the G-band, which are bounded by the D-band carbon. In the presence of an electric potential, these delocalized electrons can flow with little or no electrical resistance in the carbon skeleton. Selenium immobilization can also compress the Sp2 carbon–carbon bonds of a carbon skeleton, resulting in stronger carbon–carbon bonds, which can improve the conductivity of electrons within the carbon skeleton lattice. At the same time, the immobilization of selenium can also lead to compression of the selenium particles, resulting in stronger selenium-selenium chemical and physical interactions, which can lead to improved electrical conductivity between the immobilized selenium particles. When the carbon-carbon bonds and Se-Se bonds are strengthened due to the immobilization of selenium, the carbon-selenium interactions are also strengthened by the compression, in addition to the presence of a stabilized selenium moiety to which the carbon skeleton can bind. This selenium moiety can act as an interface layer for a carbon skeleton to successfully immobilize the stabilized selenium moiety. Therefore, electrons can flow with minimal electrical resistance between the carbon skeleton and the immobilized selenium, after which the electrochemical charge/discharge processes can operate efficiently in a rechargeable battery. This allows the rechargeable battery to maintain a near stoichiometric specific capacity and to be able to cycle at almost any rate, with a low level of deterioration in the battery's electrochemical performance.

A carbon skeleton may be porous and may be doped with another composition. The pore size distribution of the carbon skeleton may vary from less than one angstrom to a few microns or a pore size that a pore size distribution instrument can characterize using nitrogen, argon, CO2, or another absorbent as a molecular probe. The porosity of the carbon skeleton may include a pore size distribution having a peak in at least one of the following ranges: from less than one angstrom to 1000 angstroms, or from one angstrom to 100 angstroms, or from one angstrom to 50 angstroms, or from one angstrom to 30 angstroms, and or from one angstrom to 20 angstroms. The porosity of the carbon skeleton may further include pores having a pore size distribution with more than one peak in the ranges described in the preceding statement. The immobilized selenium may favor a carbon skeleton having small pore sizes in which electrons can be rapidly supplied and captured with minimal electrical resistance, which may enable the selenium to have better electrochemical behavior in a rechargeable battery. The small pore size also allows for an increase in the surface area of the carbon skeleton on which the first portion of the selenium can form a first interface layer for the second portion of the selenium immobilization. In addition, the presence in a carbon skeleton having a portion of medium pore sizes and a portion of large pore sizes may also be beneficial to efficient delivery of solvent lithium ions from a solvent bulk to a low porosity region where the lithium ions can lose coordinated solvent molecules and be transported into the lithium selenide solid phase.

The pore volume of the carbon skeleton can be as low as 0.01 ml/g and as high as 5 ml/g, or can be between 0.01 ml/g and 3 ml/g, or can be between 0.03 ml/g and 2.5 ml/g, or can be between 0.05 ml/g and 2.0 ml/g. The volume of pores having a size of less than 100 angstroms, or less than 50 angstroms, or less than 30 angstroms, or less than 20 angstroms can be greater than 30%, or greater than 40%, or greater than 50%, or greater than 60%, or greater than 70%, or greater than 80% of the total measurable pore volume that can be measured using a BET instrument with nitrogen, CO2, argon, and other gaseous molecular probes. The carbon surface area determined by the BET method may be greater than 400 m2/g, or greater than 500 m2/g, or greater than 600 m2g, or greater than 700 m2/g, or greater than 800 m2/g, or greater than 900 m2/g, or greater than 1000 m2/g.

Carbon can also be substantially amorphous, or it can have the characteristic of a very broad peak centered at a d spacing around 5 angstroms.

The carbon may include Sp2 carbon-carbon bonds, having Raman peak shifts showing a D band and a G band. In one example, the carbon-carbon Sp2 bonds of the carbon exhibit a D band centered at 1364±100 cm-1 with an LMH of about 296±50 cm-1 and a G band centered at 1589±100 cm-1 with an LMH of about 96±50 cm-1 in the Raman spectrum. The area ratio of the D band to the G band may vary from 0.01 to 100, or from 0.1 to 50, or from 0.2 to 20.

The carbon may be of any morphology, such as, for example, a platelet, a sphere, a fiber, a needle, a tube, an irregular, interconnected, agglomerated, discrete morphology or any solid particle. Platelets, fibers, needles, tubes or a certain morphology having a certain level of aspect ratio may be beneficial in achieving better contact between particles, which results in better electrical conductivity, which may improve the performance of rechargeable batteries.

Carbon can be any particle size, with a median particle size of one nanometer to a few millimeters, or a few nanometers to less than 1000 microns, or 20 nm to 100 microns.

The property of a carbon skeleton can affect the immobilization of selenium and the interactions between the surface of the carbon skeleton and the selenium particles can affect the performance of a rechargeable battery. The localization of Sp2 carbon in a carbon skeleton can aid in the immobilization of Se. The Sp2 carbon of the small pores of the carbon skeleton may be preferred, which can be quantified by the NLDFT surface area method, as shown in Example 9. The surface area of the pores of the carbon skeleton smaller than 20 angstroms may be ≥500 m2/g, ≥600 m2/g, ≥700 m2/g, ≥800 m2/g, ≥900 m2/g, or ≥1000 m2/g. The pore areas of the carbon skeleton between 20 angstroms and 1000 angstroms may represent 20% or less, 15% or less, 10% or less, 5% or less, 3% or less, 2% or less, or 1% or less of the total surface area of the carbon skeleton.

Immobilized selenium may include selenium that vaporizes at a temperature higher than that of elemental selenium, by referring to the following definition of selenium vaporization: Elemental selenium in a Se-Super P carbon black composite loses 50% of its weight at a temperature of 480°C; elemental selenium in a Se-Graphite composite loses 50% of its weight in contained selenium at a temperature of 471°C. Immobilized selenium loses 50% of its weight at a temperature above 480°C, for example at a temperature of ≥490°C, ≥500°C, ≥510°C, ≥520°C, ≥530°C, ≥540°C, ≥550°C, ≥560°C, ≥570°C, or ≥580°C or higher. Selenium in immobilized selenium may require kinetic energy ≥9.5 kJ/mole, ≥9.7 kJ/mole, ≥9.9 kJ/mole, ≥10.1 kJ/mole, ≥10.3 kJ/mole, or ≥10.5 kJ/mole or more to overcome the binding forces and/or intermolecular forces in the immobilized selenium system and escape to the gas phase. In one example, the last portion of the immobilized selenium that vaporizes may require kinetic energy ≥11,635 joules/mole (≥660°C) to escape from the carbon skeleton and may be critical for the immobilization of selenium and may function as an interface material between the carbon skeleton and the majority of the immobilized selenium molecules. Therefore, that part of selenium that requires kinetic energy ≥11,635 joules/mole is called interfacial selenium. The amount of interfacial selenium in immobilized selenium can be ≥1.5%, ≥2.0%, ≥2.5%, or 3.0% of the total immobilized selenium.

The immobilized selenium may include selenium that has a higher activation energy than conventional (non-immobilized) selenium that must be overcome for the selenium to escape from the immobilized Se-C composite system. The activation energy for the non-immobilized selenium (Se-Super P carbon black composite system) was determined to be approximately 92 kJ/mole according to ASTM E1641-16 laboratory test standard. The activation energy of selenium in immobilized selenium comprising selenium and carbon is ≥95 kJ/mole, ≥98 kJ/mole, ≥101 kJ/mole, ≥104 kJ/mole, ≥107 kJ/mole, or ≥110 kJ/mole. The activation energy of selenium in the immobilized selenium comprising selenium and carbon is ≥3%, ≥6%, ≥9%, ≥12%, ≥15% or ≥18% higher than that of selenium in the Se-carbon black Super P composite. The immobilized selenium may be more stable than the non-immobilized selenium, which explains why the battery comprising immobilized selenium may have a better electrochemical cycle, probably due to the minimization (or elimination) of selenium shuttling between the cathode and the anode, resulting from the immobilization of selenium in the Se-C composite.

The immobilized selenium may include selenium that may be Raman inactive or active, typically having a Raman peak at 255±25 cm-1, 255±15 cm-1, or 255±10 cm-1. The relative Raman peak intensity is defined as the area of the Raman peak at 255 cm-1 relative to the area of the D-band peak of the Raman spectrum of the carbon. The immobilized carbon may include selenium having a relative Raman peak intensity of ≥0.1%, ≥0.5%, ≥1%, ≥3%, ≥5%. Immobilized selenium may contain ≥5% selenium, ≥10% selenium, ≥20% selenium, ≥30% selenium, ≥40% selenium, ≥50% selenium, ≥60% selenium or ≥70% selenium.

Immobilized selenium may include selenium having a red shift relative to the Raman peak of pure selenium. A red shift is defined as a positive difference between the location of the Raman peak for immobilized selenium and that of pure selenium. Pure selenium typically has a Raman peak at about 235 cm-1. Immobilized selenium may include selenium that has a red shift of the Raman peak of ≥4 cm-1, ≥6 cm-1, ≥8 cm-1, ≥10 cm-1, ≥12 cm-1, ≥14 cm-1, or ≥16 cm-1. A red shift of the Raman peak suggests that there is compression on the selenium particles.

The immobilized selenium may comprise carbon which may be subjected to compression. Under compression, electrons can flow with minimal resistance, which facilitates the rapid supply of electrons to the selenium and from the selenium anions for the electrochemical processes involved during the discharge-charge processes of a rechargeable battery. The D-band and/or G-band of the Raman spectrum for the carbon-carbon Sp2 bonds of the carbon skeleton comprising the immobilized selenium may exhibit a red shift of ≥1 cm-1, ≥2 cm-1, ≥3 cm-1, ≥4 cm-1 or ≥5 cm-1.

Immobilized selenium includes selenium that may have a higher collision frequency than non-immobilized selenium. Such a high collision frequency may be due to the selenium in the immobilized Se-C system being compressed. The collision frequency of selenium in non-immobilized selenium was determined to be approximately 2.27 x 105, according to the ATSM E1641-16 laboratory test standard. The collision frequency of selenium in the immobilized selenium comprising selenium and carbon is ≥2.5x105, ≥3.0x105, ≥3.5x105, ≥4.0x105, ≥4.5x105, ≥5.0x105, ≥5.5x105, ≥6.0x105 or ≥8.0x105. The immobilized selenium may have a higher collision frequency of ≥10%, ≥30%, ≥50%, ≥80%, ≥100%, ≥130%, ≥150%, ≥180%, or ≥200% than that of the non-immobilized selenium in the Se-C composite. This may lead to better electron conductivity in the immobilized selenium system due to a greater number of collisions between the selenium species. The immobilized selenium in the Se-C composite would also have a higher collision frequency against the carbon host wall (e.g., carbon skeleton), which could result in better electron delivery or capture from the carbon skeleton during electrochemical cycling, which may lead to a battery (comprising immobilized selenium) that has improved cycling performance, such as achieving a greater number of cycles and/or cycling at a much higher C rate, which is highly desirable.

Immobilized selenium comprises selenium that is less likely to leave its host material (carbon), having a kinetic rate constant that is ≤1/5, ≤1/10, ≤1/50, ≤1/100, ≤1/500 or ≤1/1000 of the kinetic rate constant for non-immobilized/conventional selenium. In our example, immobilized selenium comprises selenium that is less likely to leave its host material (carbon), having a kinetic rate constant (at 50°C) ≤1x10-10, ≤5x10-11, ≤1x10-11, ≤5x10-12 or ≤5x10-13.

The immobilized selenium may include selenium that may be amorphous, as determined by X-ray diffraction measurements. A diffraction peak having a d spacing of about 5.2 angstroms is relatively smaller or weaker, for example, 10% weaker, 20% weaker, 30% weaker or 40% weaker, than that of the carbon skeleton.

Immobilized selenium can be prepared by physically mixing carbon and selenium, then melting and homogenizing (or mixing) the selenium molecules to achieve selenium immobilization. The physical mixture can be obtained by ball milling (dry and wet), mortar and pestle mixing (dry or wet), jet milling, horizontal milling, attrition milling, high shear mixing into pastes, conventional mixing of pastes with a blade, etc. The physical mixture of selenium and carbon can be heated to a temperature equal to or greater than the melting point of selenium and lower than the melting temperature of carbon. The heating can be carried out in an inert gas environment such as, but not limited to, argon, helium, nitrogen, etc. The heating environment can include air or a reactive environment. The immobilization of selenium can be achieved by impregnating the dissolved selenium in carbon, followed by evaporation of the solvent. The solvent for dissolving selenium may include an alcohol, an ether, an ester, a ketone, a hydrocarbon, a halogenated hydrocarbon, a nitrogen-containing compound, a phosphorus-containing compound, a sulfur-containing compound, water, etc.

Immobilized selenium can be obtained by melting a large amount of selenium in the presence of carbon and then removing the excess non-immobilized selenium.

An immobilized selenium system or body may comprise immobilized selenium at ≥30%, ≥40%, ≥50%, ≥60%, ≥70%, ≥80%, or ≥90% of the total amount of selenium in the system or body. Non-immobilized selenium may vaporize at a lower temperature than immobilized selenium.

An immobilized selenium system or body may comprise immobilized selenium that is doped with one or more other/additional elements from group 6 of the periodic table, such as sulfur and/or tellurium. The dopant level may range from 100 ppm by weight to 85% of the weight of the immobilized selenium system or body.

An example of an immobilized selenium production process is illustrated in . In this process, selenium and carbon are mixed together (S1) under dry or wet conditions. The mixture may be optionally dried into powder form (S2) and then optionally processed into dried powder pellets (S3). The results of step S1 and optionally steps S2 and S3 produce a carbon skeleton as the starting material for step S4. In step S4, selenium is fused into the carbon skeleton. The fused selenium in the carbon skeleton is allowed to dry, thereby producing the immobilized selenium of step S5. The preparation and characterization of the immobilized selenium will be described later in this document in connection with Example 10.

The immobilized selenium can be used as a cathode material for a rechargeable battery. To make a cathode, the immobilized selenium can be dispersed in a liquid medium such as, but not limited to, water or an organic solvent. The cathode comprising the immobilized selenium can comprise a binder, optionally another binder, optionally an electrical conductivity promoter and an electrical charge collector. The binder can be an inorganic or organic solvent. An organic binder can be a natural product, such as, for example, carboxymethylcellulose (CMC), or a synthetic product, such as, for example, a styrene-butadiene rubber (SBR) latex. An electrical conductivity promoter can be a type of carbon, such as small particles derived from graphite, graphene, carbon nanotubes, carbon nanofilms, carbon blacks, etc. An electrical charge collector may be, for example, an aluminum film, a copper film, a carbon film, a carbon cloth, or other metallic films. The cathode may be prepared by depositing one or more pastes containing immobilized selenium on the charge collector, followed by a conventional drying process (air drying, oven drying, vacuum oven drying, etc.). The immobilized selenium paste(s) may be prepared by a high shear mixer, a conventional mixer, a planetary mixer, a double planetary mixer, a ball mill, a vertical attritioner, a horizontal mill, etc. The cathode comprising immobilized selenium may be pressed or roll milled (or calendered) before use in a battery pack.

A rechargeable battery comprising immobilized selenium may comprise a cathode comprising immobilized selenium, an anode, a separator and an electrolyte. The anode may comprise lithium, sodium, silicon, graphite, magnesium, tin and/or an element or combination of suitable and/or desirable elements from Group I A, Group II A, Group III A, etc. of the periodic table of elements (periodic table). The separator may comprise an organic separator, an inorganic separator or a solid electrolyte separator. An organic separator may comprise a polymer such as, for example, polyethylene, polypropylene, polyester, a halogenated polymer, a polyether, a polyketone, etc. An inorganic separator may comprise a glass or quartz fiber, a solid electrolyte separator. An electrolyte may comprise a lithium salt, a sodium salt or other salt, a salt from Group I A of the periodic table, a salt from Group II A of the periodic table and an organic solvent. The organic solvent may include an organic carbonate compound, an ether, an alcohol, an ester, a hydrocarbon, a halogenated hydrocarbon, a lithium-containing solvent, etc.

A rechargeable battery comprising immobilized selenium can be used for electronics, electric or hybrid vehicle, industrial application, military application such as drone, aerospace application, maritime application, etc.

A rechargeable battery comprising immobilized selenium may have a specific capacity of 400 mAh/g active amount of selenium or more, 450 mAh/g or more, 500 mAh/g or more, 550 mAh/g or more, or 600 mAh/g or more. A rechargeable battery comprising immobilized selenium may be capable of undergoing electrochemical cycling of 50 cycles or more, 75 cycles or more, 100 cycles or more, 200 cycles or more, etc.

A rechargeable battery containing immobilized selenium can be charged at 0.1 C, 0.2 C, 0.5 C, 1 C, 1.5 C, 2 C, 3 C, 4 C, 5 C, 6 C, 7 C, 8 C, 9 C, 10 C or faster. After performing a charge-discharge cycle at a high C rate for 30 cycles or more (e.g., 5 cycles at 0.1 C, 5 cycles at 0.2 C, 5 cycles at 0.5 C, 5 cycles at 1 C, 5 cycles at 2 C, 5 cycles at 5 C, and 5 cycles at 10 C), a rechargeable battery including immobilized selenium can retain a specific capacity >30%, >40%, >50%, >60%, >70%, >80% of the specific capacity of the 2nd discharge at a cycling rate of 0.1 C.

Some examples are given below to illustrate the spirit of the inventions. However, these examples should not be interpreted restrictively.

EXAMPLES Characterization process

Scanning electron microscopy (SEM) images were collected on a Tescan Vega scanning electron microscope equipped with an energy dispersive X-ray (EDX) detector.

Raman spectra were collected using a Renishaw inVia Raman microscope (confocal). Laser Raman spectroscopy is the standard technique widely used for the characterization of carbon and diamond, and provides easily distinguishable signatures of each of the different forms (allotropes) of carbon (e.g. diamond, graphite, fullerenes, etc.). When combined with photoluminescence (PL) technology, it provides a non-destructive means of studying various diamond properties, including phase purity, crystal size and orientation, defect level and structure, impurity type and concentration, and stress and strain. In particular, the width (full width at half maximum or FHM) of the Raman peak of a first-order diamond at 1332 cm-1, as well as the Raman intensity ratio between the diamond peak and the graphitic peaks (D band at 1350 cm-1 and G band at 1600 cm-1), is a direct indicator of the quality of diamond and other carbon materials. In addition, stress and strain levels in diamond or other carbon grains and films can be estimated from the shift of the diamond Raman peak. It has been reported that the shift rate of the diamond Raman peak under hydrostatic stress is about 3.2 cm-1/GPa, with the peak shifting to a lower wavenumber under tensile stress and a higher wavenumber under compressive stress. The Raman spectra reported here were collected using a Renishaw inVia Raman spectroscope with a 514 nm excitation laser. Further information on the use of Raman spectroscopy to characterize diamond can also be found in (1) A. M. Zaitsev, Optical Properties of Diamond, 2001, Springer and (2) S. Prawer, R. J. Nemanich, Phil. Trans. R. Soc. Lond. A (2004) 362, 2537-2565.

BET surface area and pore size distribution data of carbon samples were measured by nitrogen absorption and CO2 absorption with a 3Flex (Micromeritics) equipped with a Smart VacPrep sample degassing preparation system. The sample is typically degassed in Smart Vac-Prep at 250°C for 2 hours under vacuum before measuring CO2 and N2 absorption. Nitrogen absorption is used to determine the BET surface area. Nitrogen absorption data and CO2 absorption data were combined to calculate the pore size distribution of a carbon sample. For more details on combining N2 and CO2 adsorption data to determine pore size distributions of carbonaceous materials, see “Dual gas analysis of microporous carbon using 2D-NLDFT heterogeneous surface model and combined adsorption data of N and CO2,” Jacek Jagiello, Conchi Ania, Jose B. Parra, and Cameron Cook, Carbon 91, 2015, page 330-337.

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) data for immobilized selenium samples and control samples were measured by a Netzsch thermal analyzer. TGA analysis was performed under an argon flow of ~200 mL/min at a heating rate of 16°C/min, 10°C/min, 5°C/min, 2°C/min, 1°C/min, and other heating rates. For consistency, the typical amount of immobilized selenium sample used for TGA analysis was approximately 20 mg.

The activation energy and collision frequency of immobilized and non-immobilized selenium were determined by TGA according to the procedures described in the ASTM E1641-16 test standard.

X-ray diffraction results for different samples of carbon, SE-carbon and immobilized selenium were collected on a Philip diffractometer.

The cycling performance of rechargeable batteries containing immobilized selenium was tested on Lanhe CT2001A battery cycling tester. The charge and discharge currents of rechargeable batteries containing immobilized selenium were determined by the amount of selenium contained in the immobilized selenium and the cycling speed (0.1C, 0.5C, 1C, 2C, 3C, 4C, 5C, 10C, etc.).

Example 9: Synthesis and characterization of the carbon skeleton.

To form a first residue, a 260 g charge of potassium citrate was included in a crucible and the crucible was placed in a quartz tube inside a tube furnace. A stream of argon gas was introduced into the furnace and the furnace was heated at 5°C/min from room temperature (~20-22°C) to 600°C. The furnace was held at this temperature for 60 minutes, then the furnace was stopped and the charge was removed from the crucible after the furnace had cooled, recovering 174.10 grams of treated residue. To form the second and third treated residues, the same process described for the first residue was repeated for 420 and 974 grams of potassium citrate charges, separately. The second and third processed residues weighed 282.83 grams and 651.93 grams, respectively.

1108.9 grams of these three treated residues were combined together in a crucible, which was placed in the quartz tube inside the tube furnace and a flow of argon gas was injected into the furnace. The furnace was heated at a rate of 5°C/min to 800°C. The furnace was maintained at 800°C for 1 hour. The furnace was allowed to cool, then the crucible was removed from the quartz tube and it was possible to recover 1085.74 grams of a first final residue.

Following the same procedure described in this example (800°C), a charge of 120 grams of potassium residue introduced into the furnace produced approximately 77 grams of a second final residue (800°C).

The combination of the first and second final residues produced approximately 1163 grams of a third final residue.

The 1163 grams of the third final residue were then mixed with 400 ml of water to form a paste which was separated approximately equally into four two-liter beakers. The pH of each paste was measured to be greater than 13. Next, a concentrated hydrochloric acid solution was added to each beaker with a violent evolution of carbon dioxide, which subsided to a pH of less than about 5. Additional hydrochloric acid solution was added to obtain a pH of about 1.9. Next, the pastes were filtered and washed to obtain filter cakes which were dried in an oven at 120°C for about 12 hours and then vacuum dried at 120°C for 24 hours, yielding four carbon skeleton samples, totaling about 61.07 grams.

These carbon skeleton samples were characterized by SEM, XRD, Raman and BET/pore size distribution. The SEM result for a carbon skeleton is shown in . The surface morphologies of typical carbon skeleton particles prepared in the process described in this Example exhibited interconnected angle film morphologies with a sample thickness between 500 nm and 100 nm and a width (or length) between 0.5 and 2 µm, thus having an aspect ratio (defined as the ratio of the largest dimension of the sample width (or film length) to the sample thickness) ≥1, for example an aspect ratio ≥5 or more, or an aspect ratio ≥10.

X-ray diffraction patterns of a carbon skeleton, presented at , show that the carbon skeleton is essentially amorphous in phase. However, it shows a broad diffraction peak centered at about 2θ of about 17°, indicating a d spacing of about 5.21 angstroms.

The results of Raman scattering spectroscopy for a carbon skeleton are presented in , showing the Sp2 carbon having a D band at about 1365 cm-1 (curve 1) and a G band at about 1589 cm-1 (curve 2) with an LMH of 296 and 96 cm-1, respectively. Both the D band and the G band exhibit a mixture of Gaussian and Lorentian distributions; the D band has a Gaussian distribution of about 33% and the G band has a Gaussian distribution of about 61%. The ratio of the D band area to the G band area is about 3.5.

The BET surface area of a carbon skeleton was measured to be 1205 m2/g by nitrogen absorption. The incremental pore area as a function of pore width is plotted on the using the NLDFT method, showing a cumulative pore area of 1,515 m2/g. The discrepancy between the BET surface area and the NLDFT surface area may arise from the fact that the NLDFT distributions are calculated with both nitrogen and CO2 absorption data; CO2 molecules can enter smaller pores than nitrogen molecules can enter. The NLDFT surface area in pores peaking at 3.48 angstroms is 443 m2/g, at 5.33 angstroms is 859 m2/g, and at 11.86 angstroms (up to 20 angstroms) is 185 m2/g, for a total of 1,502 m2/g for pores of 20 angstroms or less, while the NLDFT surface area of pores between 20 angstroms and 1,000 angstroms is only 7.5 m2/g, and the surface area of pores of 20 angstroms or more is only about 0.5% of the total surface area.

The pore size distribution of the carbon skeleton sample was determined by nitrogen absorption and CO2 absorption. The results of nitrogen absorption and CO2 absorption were combined to produce the pore size distribution shown in . The relationship between incremental pore volume (mL/g) and pore width (angstrom) shows that there are three major peaks located at 3.66 angstroms, 5.33 angstroms and 11.86 angstroms; the relationship between the cumulative pore volume (mL/g) and the pore width (angstrom) shows that there are about 0.080 mL/g pores below the 3.66 angstrom peak, about 0.240 mL/g pores below the 5.33 angstrom peak, about 0.108 mL/g pores below the 11.86 angstrom peak, having 0.43 mL/g pores of 20 angstroms or less, 0.042 mL/g pores between 20 and 100 angstroms, and a total of 0.572 mL/g pores up to 1000 angstroms.

Example 10: Preparation and characterization of immobilized selenium.

Include 0.1206 grams of selenium (showing the bulk properties of selenium) in an agate mortar and pestle assembly and include 0.1206 grams of the carbon skeleton that was prepared in accordance with Example 9 in the same agate mortar and pestle. Hand grind the mixture of selenium and carbon skeleton for about 30 minutes and transfer the ground mixture of selenium and carbon skeleton into a stainless steel die (10 mm in diameter). Press the mixture into the die at a pressure of about 10 MPa to form a pellet of the mixture. Then, charge the pellet into a sealed container in the presence of an inert environment (argon) and place the sealed container containing the pellet in a furnace. Heating the furnace, including the sealed container containing the pellet, to 240°C (above the melting temperature of selenium) for, for example, 12 hours. However, it is contemplated that any combination of time and temperature, above the melting temperature of selenium, sufficient to cause the selenium and carbon to react, partially or completely, to form immobilized selenium having some or all of the characteristics described in this application may be used. Thereafter, discharging the pellet from the container after allowing the pellet to return to room temperature. The discharged pellet is the immobilized selenium of this Example 10.

The immobilized selenium of this Example 10 was then characterized by TGA-CDB and TGA. The results of the TGA-CDB analysis were collected for the immobilized selenium under a flow of 200 ml/min of argon gas at a heating rate of 10°C/min. There is no endothermic CDB peak observable at temperatures near the melting point of selenium (about 230°C), indicating that the immobilized selenium of this Example 10 is different from the bulk form of selenium molecules/atoms which are expected to have a melting point at about 230°C where there should be an endothermic peak.

An examination revealed that the data from the ATG-CDB analysis could be unreliable when the heating temperature reached a point where selenium molecules began to escape from the sample crucible used for the ATG-CDB (graphite or ceramic). To this end, the gas phase selenium molecules (from the sample crucible) entered the argon carrier gas stream and appeared to react with the platinum sample holder of the ATG-CDB, distorting the actual thermochemical behaviors involved in the ATG-CDB. The selenium molecules released from the sample crucible reacting with the platinum sample holder, led to a lower weight loss in this temperature region. The selenium-platinum composite in the platinum sample holder is then released into the gas phase when the heating temperature reaches a point above 800°C. Complete release of selenium can occur at 1000°C. This examination exhausted most of the immobilized selenium sample in this Example 10. Therefore, a new immobilized selenium sample (~16 grams) was prepared using the same procedure as described in the previous part of this Example 10.

The thermochemical behaviors of this new immobilized selenium sample were studied by TGA analysis, which uses a ceramic sample holder that covers a very small thermocouple used for TGA analysis. The results of TGA analysis for this new immobilized selenium sample are presented in , as well as the results of the AGT analysis ( ) for selenium-carbon composites (made with a 50-50 Se-carbon black Super P composite and Se-graphite (ground graphite)), using the same method as the preparation of immobilized selenium in this Example 10. Super P is a commercial grade carbon black widely used in the lithium-ion battery industry. The ground graphite was prepared by grinding Poco 2020 graphite. The TGA analysis data are also summarized in the following Table 2.

Comp. Se-Graphite Comp. Se-Super P Immobilized in Example 10 Median weight loss temperature Temp. at minimum of highest weight loss Final temp., AGT data. Median weight loss temperature, °C 471 480 595 660 1000 Median weight loss temperature, K 744 753 868 933 1273 Kinetic energy,
Joule/Mole 9,278 9,391 10,825 11,635 15,876

The immobilized selenium may have an initial weight loss temperature of about 400°C compared to 340°C for the Se-Super P carbon composite and the Se-Graphite carbon composite; a median weight loss temperature for the immobilized selenium may be about 595°C compared to 480°C for the Se-Super P carbon composite and 471°C for the Se-Graphite composite; the highest weight loss is completed at about 544°C for the Se-Super P composite and the Se-Graphite composite, and at 660°C for the immobilized selenium. The Se-Super P carbon composite and Se-Graphite carbon composite show a weight loss of less than 0.6% between 560°C and 780°C, while the immobilized selenium shows a weight loss of about 2.5% from the minimum to the highest weight loss (~660°C to 1000°C). These results suggest that the non-immobilized selenium (Se-Super P carbon composite and Se-Graphite G composite) has ≤1.2% of the total selenium that can escape from the composite at a temperature ≥560°C, while the immobilized selenium has about 5.0% of the total selenium that can escape from the carbon skeleton at a temperature ≥660°C. The following details are provided to provide examples to help understand the thermochemical behaviors. However, these details should not be interpreted restrictively.

Using the average weight loss temperature data of AGT as examples of thermochemical behaviors, as the heating temperature increases, the kinetic energy of selenium molecules in the Se-Super P composite and the Se-Graphite composite increases to a level at which these selenium molecules have enough energy to overcome the intermolecular interactions between selenium molecules and escape from the liquid phase of selenium. The kinetic energy here is equal to 3RT/2, where: R is the gas constant and T is the temperature in Kelvin.

It was observed that the average kinetic energy of selenium molecules for Se-Super P composite was measured to be 9,391 joules/mole when selenium molecules escape from the Se-Super P composite mixture. However, the immobilized selenium needs to gain more energy to reach an average kinetic energy of about 10,825 joules/mole for the selenium to leave the carbon skeleton and the selenium molecules to enter the gas phase. It is considered that the selenium in the immobilized selenium, in atomic form, molecular form, or any form, can chemically interact with the selenium and the carbon skeleton beyond the intermolecular interactions of selenium. Furthermore, the latter portion of the selenium that escapes from the carbon skeleton between 660°C and 1000°C has an average kinetic energy in the range of 11,635 joules/mole to 15,876 joules/mole or more. This suggests that the selenium in the immobilized selenium is more stable than the selenium in conventional selenium-carbon composites. The stabilized selenium in the immobilized selenium of this Example 10 enhances the ability of selenium, in atomic, molecular or other form, to remain within the carbon skeleton during electrochemical processes, such as during the charge and discharge cycle of a rechargeable battery made with the immobilized selenium. In one example, this latter portion of selenium may require kinetic energy ≥11,635 joules/mole (≥660°C) to escape from the carbon skeleton; it may be critical for the immobilization of selenium and may function as an interfacial material between the carbon skeleton and the majority of the immobilized selenium molecules. The share of interfacial selenium in the immobilized selenium may be ≥1.5%, ≥2.0%, ≥2.5%, or 3.0% of the total immobilized selenium.

There also shows the AGT studies of immobilized selenium with a heating rate of 16°C/min and a temperature of 628°C for the median weight loss of the selenium contained. As shown in , for the Se-Super P composite, the temperature at the median weight loss of Se content is 495°C under a heating rate of 16°C/min. With different heating rates (e.g., 16°C/min, 10°C/min, 5°C/min, 2.5°C/min and 1°C/min), the activation energy and collision frequency can be determined and calculated using known methods, such as ASTM E1641-16 and E2958-14 test standards. The temperatures at 15% weight loss for different heating rates are shown in the following Table 3.

Table 3 β(°C/min) Temperature (°C) Immobilized, prepared by the process of Example 10 (228-110) Se immobilized, prepared by the process of Example 10 (155-82-2) Se-Super Composite
P 16 590.65 570.13 471.08 10 560.82 544.86 456.61 5 535.57 515.09 413.37 2.5 506.66 493.27 397.21 1 478.48 462.18 365.02 Activation energy, kJ/mole 120.7 120.0 92.3 Frequency of collisions 12.4 x 105 18.3 x 105 2.27 x 105

The activation energy of selenium (non-immobilized or conventional) in the Se-Super P composite was determined to be 92.3 kJ/mol with a collision frequency of 2.27x105. The activation energy of immobilized selenium (228-110 above) was also determined to be 120.7 kJ/mol with a collision frequency of 12.4x105. Another sample of immobilized selenium (155-82-2 above) which was prepared according to the same procedures as those of Example 10, was also measured and showed an activation energy of 120.0 kJ/mol and a collision frequency of 18.3x105.

The kinetic rate constant of selenium is calculated using the Arrhenius equation

k = Ae

where k is the rate constant, Ea is the activation energy, A is the collision frequency, R is the gas constant and T is the temperature in Kelvin.

Regarding the , with the activation energy and collision frequency determined above, the kinetic rate constant was calculated using the Arrhenius equation at different temperatures. The shows that non-immobilized selenium (Se-Super P composite - solid line) has a much higher rate constant than immobilized selenium (228-110 (dotted line) and 115-82-2 (dashed line)), for example, about four orders of magnitude higher at 35 °C and about three orders of magnitude higher at 100 °C. For example, at 50 °C, the rate constant of non-immobilized selenium (Super P) is 2.668x10-10, while immobilized selenium has a rate constant of 7.26x10-14 (155-82-2) and 3.78x10-14 (228-110). Selenium which has a lower kinetic rate constant has less tendency to leave the host material (carbon), which can lead to better battery cycling performance.

There shows the spectrum of immobilized selenium with Raman peaks of the D band at 1368 cm-1 and the G band at 1596 cm-1, with a ratio of the D band area to the G band area of 2.8. Compared to the Raman spectrum of the carbon skeleton shown in , selenium immobilization shifts both Raman peaks to a higher wavenumber, namely a redshift of about 3 cm-1 for the D band and a redshift of 7 cm-1 for the G band, suggesting that the binding strength of the Sp2 carbon in the carbon skeleton is enhanced, with a redshift of about 4 cm-1 for the D band and a redshift of about 8 cm-1 for the G band. At the same time, the ratio of the D band area to the G band area also decreased, from about 3.4 to 2.8, suggesting that either the D band is relatively weakened or the G band is relatively strengthened. A stronger G band may be desirable, as the G band may relate to a type of carbon that allows the carbon skeleton to conduct electrons more easily, which may be desirable for electrochemical performance when used in a rechargeable battery. Bulk or pure selenium generally exhibits a very strong shift of the Raman peak to about 235 cm-1. For immobilized selenium, the Raman spectrum of the shows a broad Raman peak at about 257 cm-1 (~12.7% of the G-band area) and a broad new bump at about 500 cm-1 (~3.0% of the G-band area). Selenium immobilization is thought to alter the Raman characteristics for both the carbon skeleton and selenium, with all Raman peaks being shifted to higher wavenumbers, suggesting that both the carbon-carbon Sp2 bonds for the carbon skeleton and the selenium-selenium bonds for selenium are being squeezed.

The compression resulting from the immobilization of selenium strengthens both the carbon–carbon Sp2 bonds for the carbon skeleton and the Se–Se bonds for selenium, creating stronger selenium–selenium and carbon–selenium interactions. Therefore, more kinetic energy would be required for selenium to overcome the greater strength of the Se–Se bond and the stronger carbon–selenium interactions, which explains the AGT analysis observations of immobilized selenium compared to the Se–Super P composite and the Se–Graphite composite.

Furthermore, under compression, the carbon skeleton would then have a better capacity to conduct electrons at the bonds; and under compression, the selenium atoms or molecules would also have a better capacity to conduct electrons.

A stabilized selenium for immobilized selenium, as well as an increased electronic conductivity through the carbon skeleton and selenium may be desirable in electrochemical processes, such as, for example, an improved specific capacity for the active substance with a minimal level of shuttling, an improved cycling capacity due to immobilization, a capacity to charge and discharge at a higher rate, etc. However, this should not be interpreted in a restrictive sense.

X-ray diffraction patterns for immobilized selenium prepared according to Example 10 and presented in show a decrease in the intensity of the broad diffraction peak on the carbon skeleton with a d-spacing of about 5.21 angstroms, only about 1/3 of the intensity, suggesting that the immobilized selenium makes the carbon skeleton even more disordered, or causes further destruction of the carbon skeleton order. For example, it has been observed that this is due to the compressive forces being applied to the carbon-carbon Sp2 bonds.

There shows the SEM image for immobilized selenium that was prepared according to Example 10, showing film morphologies, as does the image of the for the carbon skeleton. Although there is about 50% selenium immobilized in the carbon skeleton, there are no observable selenium particles on the carbon skeleton surfaces, except that the connections between the films have been destroyed, resulting in high aspect ratios for many flat films. These film morphologies can be highly desirable for forming an oriented and aligned coating along the direction of the flat films, creating surface-to-surface contacts that lead to improved electrical conductivity between the films, which can translate into superior electrical performance in electrochemical processes, such as in a rechargeable battery.

Example 11: Preparation of Se cathode

In a mortar and pestle, include 56 mg of the immobilized selenium that was prepared in accordance with Example 10; 7.04 mg of Super P; 182 μL of carboxymethylcellulose (CMC) solution (which contains 1 mg of dry CMC for each 52 μL of CMC solution); 21.126 μL of SBR latex dispersion (which contains 1 mg of dry SBR latex for each 6.036 μL of SBR latex dispersion); and 200 μL of deionized water. Grind the particles, binders, and water by hand for 30 minutes to produce a cathode paste. The cathode paste was then applied to one side of a piece of electrically conductive substrate, such as a film, and air dried. For example, the conductive substrate or film may be an aluminum (Al) film. However, this is not to be construed in a restrictive sense since the use of any suitable and/or desirable electrically conductive material, of any form, is contemplated. For the exclusive purposes of the disclosure, the use of Al film to form a selenium cathode will be described herein. However, this is not to be construed in a restrictive sense.

The paste-coated Al foil was then placed in a drying oven and heated at a temperature of 55ºC for 12 hours, resulting in a selenium cathode composed of an immobilized selenium foil dried on one side of the Al film, with the other side of the Al film having no coating (bare aluminum).

The selenium cathode was then cut into cathode discs, each with a diameter of 10 mm. Some of these cathode discs were used as cathodes for rechargeable batteries.

Example 12: Assembly and testing of Li-Se rechargeable batteries

The cathode disks of Example 11 were used to assemble Li-Se rechargeable button cells as described in the following example and illustrated in . In this example, a 10 mm diameter cathode disk 4 of Example 11 was placed on a base 2 of a 2032 stainless steel button cell which functions as the positive case of the cell (the “positive case” of the ) with the immobilized selenium sheet 5 facing upwards, away from the base 2 of the positive case and with the bare Al face facing and in contact with the base 2 of the positive case. Next, a battery separator 6 (19 mm in diameter and 25 microns thick) was placed on top of the cathode disk 4 in contact with the immobilized selenium sheet 5. For example, the battery separator 6 may be an organic separator, or an inorganic separator, or a solid electrolyte separator. The organic separator may be a polymer, for example, polyethylene, polypropylene, polyester, a halogenated polymer, a polyether, a polyketone, etc. The inorganic separator may be made from glass fibers and/or quartz.

Next, 240 µl of electrolyte 7 comprising LiPF6 (1M) in ethylene carbonate (EC) and dimethyl carbonate (DMC) solvent (50-50 by weight) was introduced into the positive housing 2, then a lithium film disk 8 (15.6 mm in diameter and 250 microns in thickness) was placed on one side of the separator 6 opposite the cathode disk 4. Next, a stainless steel (SS) sleeve 10 was placed on one side of the lithium film disk 8 opposite the separator 6, then one or more foam disks 12 made of, for example, nickel were placed on one side of the SS sleeve 10 opposite the lithium film disk 8. The lithium film 8, the SS sleeve 10 and/or the foam disk 12 can serve as an anode. Finally, a 14 stainless steel 2032 case, intended to serve as the negative pole of the button cell (the “negative case” of the ), was placed on one side of the nickel foam disc(s) 12, opposite the SS sleeve 10 and on the edge of the positive housing 2. The positive housing 2 and the negative housing 14 were then sealed together under high pressure, for example at 1000 psi. Sealing the positive and negative housings (2, 14) under high pressure also had the effect of compressing together the stacked elements which comprise (from bottom to top in the ) the cathode disk 4, the separator 6, the lithium film 8, the SS sleeve 10 and the Ni foam disk(s) 12. More than a dozen button cells were assembled using the battery separators described above and the glass fiber separators. The assembled button cells were then tested under the following conditions.

Some of the assembled button cells were tested at charge-discharge rates of 0.1C and 1C using a Lanhe CT2001A battery tester. Each button cell was tested under the following conditions: (1) rest for 1 hour; (2) discharge to 1V; (3) rest for 10 minutes; (4) charge to 3V; (5) rest for 10 minutes; repeat steps (2) to (5) to repeat the cycling test.

There (left) depicts the results of cycling tests (313 cycles at a charge-discharge rate of 0.1 C) for a button cell manufactured according to Example 12 using the cathode prepared according to Example 11, which show excellent cycling stability with a specific capacity of 633.7 mAh/g after 313 cycles, representing a retention of 93.4% of the initial specific capacity. The specific capacity at first discharge was higher than the stoichiometric value, possibly due to some side reactions on the cathode and anode surfaces. From the second cycle onwards, the specific capacity initially decreased with cycling; however, the specific capacity increased slightly from about 30 cycles to about 120 cycles, before remaining stable at about 180 cycles and then decreasing. (right) also shows excellent cycle stability (100 cycles at 0.1 C, then 500 cycles at 1 C) for another coin cell with a specific capacity of 462.5 mAh/g at the 600th cycle, representing a retention of 66.0% of the 2nd cycle capacity at 0.1 C or a retention of 80.3% of the 105th cycle capacity at 1 C. The Coulomb efficiency can be ≥95%, ≥98%, or as high as 100%, suggesting that there was no detectable amount of selenium shuttling between the cathode and anode. This electrochemical performance is thought to be due to the selenium immobilized in the cathode, which prevents selenium from dissolving and moving from the cathode 14 to the anode 2.

There shows the results of cycling tests at different discharge-charge cycling rates (between 0.1 C and 10 C) for a coin cell that was assembled with a polymer separator described in Example 12. The test protocols were similar to the tests described above, except for the cycling rates (0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 5 C, and 10 C); five charge and discharge cycles were performed for each rate C; then the cycling rate was reduced to one cycle of 0.1 C. At the 0.1 C rate, the battery exhibited a specific capacity close to the stoichiometric value. In addition, the battery showed good cycling stability for cycling rates of 0.2C, 0.5C, 1C, and 2C. The battery also exhibited fast charge and discharge capability, cycling 56% of stoichiometric capacity at the 10C rate, although it showed decreasing specific capacity over cycles. In other words, at the 10C rate, the battery took 3.3 minutes to charge and discharge based on 56% of stoichiometric capacity. With such a cycling rate, a conventional battery would not survive.

The Li-Se battery comprising immobilized selenium can recover its specific capacity to 670 mAh/g, which is 98% of its full capacity when used at a rate of 0.1 C at the beginning of the test. It is considered that (1) the stabilization of selenium in the immobilized selenium cathode prevents selenium from leaving the carbon skeleton, thereby avoiding selenium shuttling between the cathode and the anode during cycling, which enables the battery to have a better cycling performance; (2) the Sp2 carbon-carbon bonds and the carbon skeleton, selenium-selenium bond, and carbon-selenium interactions can be subjected to compression so as to result in higher electrical conductivity in the carbon skeleton, in the selenium particles, and between the carbon and selenium interfaces, which may help to achieve the cycling performance observed at high C rates.

The immobilized selenium body comprising selenium and carbon prepared in accordance with the principles described herein may exhibit one or more of the following characteristics:

(a) a kinetic energy required for a selenium particle to escape from the immobilized selenium may be ≥ 9.5 kJ/mole, ≥ 9.7 kJ/mole, ≥ 9.9 kJ/mole, ≥ 10.1 kJ/mole, ≥ 10.3 kJ/mole, or ≥ 10.5 kJ/mole;

(b) the temperature required for a selenium particle to escape from the immobilized selenium may be ≥ 490°C, ≥ 500°C, ≥ 510°C, ≥ 520°C, ≥ 530°C, ≥ 540°C, ≥ 550°C, or ≥ 560°C;

(c) the carbon may have a surface area (for pores less than 20 angstroms) ≥ 500 m2/g, ≥600 m2/g, ≥ 700 m2/g, ≥ 800 m2/g, ≥ 900 m2/g, or ≥ 1,000 m2/g;

(d) the carbon may have a surface area (for pores between 20 angstroms and 1000 angstroms) ≤ 20%, ≤ 15%, ≤ 10%, ≤ 5%, ≤ 3%, ≤ 2%, ≤ 1% of the total surface area;

(e) the carbon and/or selenium may be subjected to compression. The advantages of immobilized selenium where the carbon and/or selenium are subjected to compression compared to a carbon-selenium system where the carbon and/or selenium are not subjected to compression may include: improved electron flow, reduced resistance to electron flow, or both, which may facilitate the delivery of electrons to the selenium and from the selenium anions during the charging and discharging of a rechargeable battery having a cathode comprised of immobilized selenium;

(f) the immobilized selenium may include selenium that has a higher activation energy than conventional (non-immobilized) selenium so that the selenium escapes from the immobilized Se-C composite system. For example, the activation energy of non-immobilized selenium (Se-Super P composite system) was determined to be 92 kJ/mole, according to ASTM E1641-16. In contrast, for example, the activation energy of selenium in immobilized selenium including selenium and carbon may be ≥ 95 kJ/mole, ≥ 98 kJ/mole, ≥ 101 kJ/mole, ≥ 104 kJ/mole, ≥ 107 kJ/mole, or ≥ 110 kJ/mole. In another example, the activation energy of selenium in the immobilized selenium comprising selenium and carbon may be ≥ 3%, ≥ 6%, ≥ 9%, ≥ 12%, ≥ 15%, or ≥ 18% greater than that of selenium present in the Se-Super P composite;

(g) immobilized selenium may include selenium that has a higher collision frequency than non-immobilized selenium. For example, the collision frequency for non-immobilized selenium has been determined to be 2.27 x 105, according to the ATSM E1641-16 test standard. In contrast, in one example, the collision frequency for selenium in immobilized selenium, comprising selenium and carbon, may be ≥ 2.5x105, ≥ 3.0x105, ≥ 3.5x105, ≥ 4.0x105, ≥ 4.5x105, ≥ 5.0x105, ≥ 5.5x105, ≥ 6.0x105, or ≥ 8.0x105. Immobilized selenium may have a collision frequency of ≥10%, ≥30%, ≥50%, ≥80%, ≥100%, ≥130%, ≥150%, ≥180% or ≥200% compared to non-immobilized selenium in a Se-C composite; and

(h) the immobilized selenium may comprise selenium having a kinetic rate constant of ≤ 1/5, ≤ 1/10, ≤ 1/50, ≤ 1/100, ≤ 1/500, or ≤ 1/1000 of the kinetic rate constant for non-immobilized/conventional selenium. For example, the immobilized selenium may comprise selenium having a kinetic rate constant (at 50°C) of ≤ 1 x 10-10, ≤ 5x 10-10, ≤ 1 x 10-11, ≤ 5 x 10-12, or ≤ 5 x 10-13.

With the carbon and/or selenium of the immobilized selenium under compression, the D band and/or G band of the Raman spectrum for the C-C Sp2 bonds of the carbon (or carbon skeleton defined by said carbon) present in the immobilized selenium may show a red shift (positive), for example, ≥ 1 cm-1, ≥ 2 cm-1, ≥ 3 cm-1, ≥ 4 cm-1 or ≥ 5 cm-1 relative to a carbon base.

Since the carbon and/or selenium in immobilized selenium are under compression, the selenium may exhibit a red shift (positive) relative to the Raman peak of pure selenium (235 cm-1), for example ≥ 4 cm-1, ≥ 6 cm-1, ≥ 8 cm-1, ≥ 10 cm-1, ≥ 12 cm-1, ≥ 14 cm-1 or ≥ 16 cm-1, this red shift may suggest compression on the selenium particles.

Immobilized selenium may be an elemental form of selenium and/or a compound form of selenium.

The immobilized selenium comprising selenium and carbon may also be doped with one or more additional elements from Group 6 of the periodic table (hereinafter, “additional G6 element(s)”), including, for example, without limitation, sulfur and/or tellurium. The dopant level may range from 100 ppm by weight to 85% of the total weight of the immobilized selenium. For example, the immobilized selenium may comprise 15% to 70% carbon and 30% to 85% selenium and, optionally, one or more additional G6 elements. For example, the immobilized selenium may comprise (1) 15% - 70% carbon and (2) 30% - 85% selenium + one or more additional G6 elements. In the mixture comprising selenium plus one or more additional G6 elements, the additional G6 element(s) may constitute between 0.1% and 99% of the mixture and selenium may constitute between 1% and 99.9% of the mixture. However, these ranges of selenium and additional G6 element(s) should not be interpreted restrictively.

The immobilized selenium may comprise ≥ 5% selenium, ≥ 10% selenium, ≥ 20% selenium, ≥ 30%, ≥ 40% selenium, ≥ 50% selenium, ≥ 60% selenium, or ≥ 70% selenium or more.

Immobilized selenium may optionally include another element, such as sulfur, tellurium, etc.

Immobilized selenium can be Raman inactive or Raman active. If Raman active, immobilized selenium can have a peak relative Raman intensity at 255±25 cm-1, at 255±15 cm-1, or at 255±10 cm-1.

The immobilized selenium may comprise selenium having a peak relative Raman intensity of ≥0.1%, ≥0.5%, ≥1%, ≥3%, or ≥5%; herein, the peak relative Raman intensity is defined as the area of the Raman peak at 255 cm-1 relative to the area of the D-band peak of the Raman spectrum of carbon.

The carbon composing the immobilized selenium can serve as a carbon skeleton for the immobilization of selenium. The carbon skeleton can have carbon-carbon Sp2 bonds with a Raman D band located at 1365 ± 100 cm-1 and a G band located at 1589 ± 100 cm-1; a D band located at 1365 ± 70 cm-1 and a G band located at 1589 ± 70 cm-1; a D band located at 1365 ± 50 cm-1 and a G band located at 1589 + 50 cm-1; a D band located at 1365 + 30 cm-1 and a G band located at 1589 + 30 cm-1, or a D band located at 1365 ± 20 cm-1 and a G band located at 1589 + 20 cm-1.

The immobilized selenium carbon may comprise carbon-carbon Sp2 bonds, having Raman peaks with a D band and a G band. The area ratio between the D band and the G band may vary from 0.01 to 100, from 0.1 to 50, or from 0.2 to 20.

The immobilized selenium carbon may comprise carbon-carbon Sp2 bonds, having Raman peaks with a D band and a G band. Each of the D and G bands may have a shift to a higher wavenumber -1, ≥ 2 cm-1, or more.

The immobilized selenium carbon can be doped with one or more other elements of the periodic table.

Immobilized selenium carbon can be porous. The pore size distribution of the carbon skeleton can vary from one angstrom to a few microns. The pore size distribution can have at least one peak between one angstrom and 1000 angstroms, between one angstrom and 100 angstroms, between one angstrom and 50 angstroms, between one angstrom and 30 angstroms, or between one angstrom and 20 angstroms. The porosity of the carbon skeleton can have pore size distributions with more than one peak in the preceding ranges.

The immobilized selenium carbon may have a pore volume between 0.01 ml/g and 5 ml/g; between 0.01 ml/g and 3 ml/g; between 0.03 ml/g and 2.5 ml/g; or between 0.05 ml/g and 2.0 ml/g.

The immobilized selenium carbon may comprise a pore volume (whose size is < 100 angstroms, < 50 angstroms, < 30 angstroms, or < 20 angstroms) that may be > 30%, > 40%, > 50%, > 60%, > 70%, or > 80% of the total measurable pore volume.

Immobilized selenium carbon may comprise a surface area > 400 m2/g, > 500 m2/g, > 600 m2/g, > 700 m2/g, > 800 m2/g, > 900 m2/g, or > 1000 m2/g.

Immobilized selenium carbon may be amorphous and may have a broad peak centered at a d spacing of about 5.2 angstroms.

The immobilized selenium carbon can be of any morphology, platelet, sphere, fiber, needle, tubular, irregular, interconnected, agglomerated, discrete or any solid particle. A platelet, fiber, needle, tube or certain morphology having a certain aspect ratio can be beneficial to achieve better contact between particles resulting in increased electrical conductivity (as compared to immobilized selenium having a different aspect ratio), which can be beneficial for an electrochemical cell, such as a rechargeable battery.

The immobilized selenium carbon can be of any particle size, having a median particle size between 1-9 nanometers and 2 millimeters, between 1-9 nanometers to <1000 microns, or between 20 nanometers to 100 microns.

The immobilized selenium may be amorphous, for example, as determined by X-ray diffraction. The diffraction peak of the immobilized selenium, which may have a d-spacing of about 5.2 angstroms, may be weaker than that of the carbon skeleton, for example 10% weaker, 20% weaker, 30% weaker, or 40% weaker.

As an example, a method of preparing immobilized selenium may include:

(a) a physical mixture of carbon and selenium. The physical mixture can be obtained by ball milling (dry and wet), mortar and pestle mixing (dry or wet), jet milling, horizontal milling, attrition milling, high shear mixing of pastes, conventional mixing of pastes with a blade, etc.;

(b) the physical mixture of carbon and selenium of step (a) may be heated to the melting temperature of selenium or higher. Heating of the mixture of carbon and selenium may occur in the presence of an inert gas environment such as, but not limited to, argon, helium, nitrogen, etc.;

(c) optionally, homogenizing or mixing the heated carbon and selenium to achieve immobilization of the selenium; and

(d) cooling the immobilized selenium from step (c) to ambient temperature or room temperature.

In another example, immobilized selenium can be prepared by dissolving selenium on carbon followed by evaporation. The solvent for dissolving the selenium can be an alcohol, an ether, an ester, a ketone, a hydrocarbon, a halogenated hydrocarbon, a nitrogen-containing compound, a phosphorus-containing compound, a sulfur-containing compound, water, etc.

In another example, immobilized selenium can be prepared by melting selenium on carbon and then removing additional or excess non-immobilized selenium.

As an example, a method of making immobilized selenium may include:

(a) the mixing of selenium and carbon under dry or wet conditions;

(b) optionally drying the mixture of step (a) at an elevated temperature;

(c) optionally granulating the dried mixture of step (b);

(d) fusion of selenium into carbon to produce immobilized selenium.

The immobilized selenium can be used as a cathode material for a rechargeable battery. The cathode can include an organic or inorganic binder. The inorganic binder can be a natural product, such as CMC, or a synthetic product, such as styrene-butadiene (SBR) latex. The cathode can include an optional electrical conductivity promoter, such as small particles derived from graphite, graphene, carbon nanotubes, carbon nanoparticles, carbon blacks, etc. Finally, the cathode can include a charge collector, such as aluminum film, copper film, carbon film, carbon cloth, or other metal films.

The method of manufacturing the cathode may include applying an immobilized paste containing selenium to the charge collector, followed by drying the paste-coated charge collector (e.g., air drying, oven drying, vacuum oven drying, etc.). The immobilized selenium may be dispersed in the paste, which may be prepared by a high shear mixer, a regular mixer, a planetary mixer, a double planetary mixer, a ball mill, a vertical attritioner, a horizontal mill, etc. The paste may then be coated onto the charge collector and then air or vacuum dried. The coated cathode may then be pressed or roll milled (or calendered) before being used in a rechargeable battery.

A rechargeable battery may be made using the immobilized selenium described herein. The rechargeable battery may include a cathode comprising the immobilized selenium, an anode, and a separator separating the anode and the cathode. The anode, cathode, and separator may be immersed in an electrolyte such as, for example, LiPF6. The anode may be composed of lithium, sodium, silicon, graphite, magnesium, tin, etc.

The separator may be comprised of an organic separator, an inorganic separator, or a solid electrolyte separator. An organic separator may comprise a polymer such as, for example, polyethylene, polypropylene, polyester, a halogenated polymer, a polyether, a polyketone, etc. The inorganic separator may comprise a glass or quartz fiber, or a solid electrolyte separator.

The electrolyte may comprise a lithium salt, a sodium salt or another salt of groups IA, IIA and IIIA, in an organic solvent. The organic solvent may comprise an organic carbonate compound, an ether, an alcohol, an ester, a hydrocarbon, a halogenated hydrocarbon, a lithium-containing solvent, etc.

The rechargeable battery can be used for electronics, electric or hybrid vehicle, industrial application, military application such as drone, aerospace application, marine application, etc.

The rechargeable battery may have an electrochemical capacity of ≥ 400 mAh/g active selenium quantity, ≥ 450 mAh/g active selenium quantity, ≥ 500 mAh/g active selenium quantity, ≥ 550 mAh/g active selenium quantity, or ≥ 600 mAh/g active selenium quantity.

The rechargeable battery can undergo an electrochemical cycle of ≥ 50 cycles, ≥ 75 cycles, ≥ 100 cycles, ≥ 200 cycles, etc.

The rechargeable battery can be charged at 0.1C, 0.2C, 0.5C, 1C, 1.5C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C or faster.

The rechargeable battery can maintain a thermal capacity of >30%, >40%, >50%, >60%, >70%, or >80% of the 2nd discharge thermal capacity at a cycling rate of 0.1C, after performing a high C rate charge-discharge cycle (5 cycles at 0.1C, 5 cycles at 0.2C, 5 cycles at 0.5C, 5 cycles at 1C, 5 cycles at 2C, 5 cycles at 5C, and 5 cycles at 10C).

The rechargeable battery may have a Coulomb efficiency of ≥50%, ≥60%, ≥70%, ≥80%, ≥90%, or up to about 100%.

The colorimetric efficiency of a battery is defined by the following ratio:

Or is the Coulomb efficiency (%)

is the amount of charge that leaves the battery during one discharge cycle.

is the amount of charge that enters the battery during one charge cycle.

The rechargeable battery can be charged at 0.1C, 0.2C, 0.5C, 1C, 1.5C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C or faster. A C rate is a measure of how quickly a battery is discharged relative to its maximum capacity. For example, a 1C rate means that the discharge current will discharge the entire battery in 1 hour. For example, for a battery with a capacity of 100 amp-hours, this is equivalent to a discharge current of 100 amps. A 5C rate for this same battery would be 500A, and a 0.5C rate would be 50A.

The cathode of the rechargeable battery may comprise one or more elements from a group of chalcogens such as selenium, sulfur, tellurium and oxygen.

The anode of the rechargeable battery may comprise at least one element of alkali metal, alkaline earth metals and group IIIA metals.

The separator of the rechargeable battery can be an organic separator or an inorganic separator.

The electrolyte of the rechargeable battery may comprise at least one element of alkali metals, alkaline earth metals and group IIIA metals, the solvent of the electrolyte may comprise an organic solvent, based on carbonate, ether or ester.

The rechargeable battery may have a specific capacity of ≥ 400 mAh/g, ≥ 450 mAh/g, ≥ 500 mAh/g, ≥ 550 mAh/g, or ≥ 600 mAh/g.

The rechargeable battery can undergo electrochemical cycling of ≥ 50 cycles, ≥ 75 cycles, ≥ 100 cycles, ≥ 200 cycles, etc.

The rechargeable battery may have a specific capacity of >30%, >40%, >50%, >60%, >70%, or >80% of the 2nd discharge specific capacity at a 0.1C cycle rate, after performing a high C rate charge-discharge cycle (5 cycles at 0.1C, 5 cycles at 2C, 5 cycles at 5C, 5 cycles at 1C, 5 cycles at 2C, 5 cycles at 5C, and 5 cycles at 10C).

The rechargeable battery may have a Coulomb efficiency of ≥ 50%, ≥ 60%, ≥ 70%, ≥ 80%, or ≥ 90%.

This document also describes a composite comprising selenium and carbon, said composite being able to have a platelet morphology with an aspect ratio of ≥ 1, ≥ 2, ≥ 5, ≥ 10, or ≥ 20.

The selenium in the composite may be amorphous, for example, as determined by X-ray diffraction. The selenium diffraction peak may have a d spacing of about 5.2 angstroms which may be weaker than that of a carbon skeleton, for example 10% weaker, 20% weaker, 30% weaker or 40% weaker.

For example, the method of preparing the composite may include:

(a) physical mixing of carbon and selenium. Physical mixing can be achieved by ball milling (dry and wet), mortar and pestle mixing (dry or wet), jet milling, horizontal milling, attrition milling, high shear mixing of pastes, conventional mixing of pastes with a blade, etc.;

(b) the physically mixed carbon and selenium of step (a) may be heated to the melting temperature of selenium or above and said heating may occur in the presence of an inert gas environment such as, for example, argon, helium, nitrogen, etc.

(c) the heated carbon and selenium from step (b) may be homogenized or mixed to aid in immobilization of the selenium.

In another example, the composite may be prepared by dissolving selenium on carbon followed by evaporation. The solvent for dissolving the selenium may be an alcohol, an ether, an ester, a ketone, a hydrocarbon, a halogenated hydrocarbon, a nitrogen-containing compound, a phosphorus-containing compound, a sulfur-containing compound, water, etc.

The composite can be prepared by melting selenium onto (or into) carbon and then removing additional or excess non-immobilized selenium.

For example, a composite manufacturing process may include:

(a) the mixing of selenium and carbon under dry or wet conditions;

(b) optionally drying the mixture of step (a) at an elevated temperature;

(c) optionally granulating the dried mixture of step (b);

(d) fusion of selenium into carbon to produce immobilized selenium.

The composite may be used as a cathode material for the cathode of a rechargeable battery. The cathode may include an organic or inorganic binder. The inorganic binder may be a natural product, such as CMC, or a synthetic product, such as styrene-butadiene (SBR) latex. The cathode may include an optional electrical conductivity promoter, such as small particles derived from graphite, graphene, carbon nanotubes, carbon nanoparticles, carbon blacks, etc. Finally, the cathode may include an electrical charge collector, such as aluminum film, copper film, carbon film, carbon cloth, or other metal films.

The method of manufacturing the cathode may include applying an immobilized paste containing selenium to the charge collector, followed by drying the paste-coated charge collector (e.g., air drying, oven drying, vacuum oven drying, etc.). The immobilized selenium may be dispersed in the paste, which may be prepared by a high shear mixer, a regular mixer, a planetary mixer, a double planetary mixer, a ball mill, a vertical attritioner, a horizontal mill, etc. The paste may then be coated onto the charge collector and then dried in ambient air or under vacuum. The coated cathode may then be pressed or roll milled (or calendered) before being used in a rechargeable battery.

A rechargeable battery can be manufactured using the composite described above. The rechargeable battery can be charged at 0.1 C, 0.2 C, 0.5 C, 1 C, 1.5 C, 2 C, 3 C, 4 C, 5 C, 6 C, 7 C, 8 C, 9 C, 10 C or faster.

Example 13: Preparation of immobilized sulfur-doped selenium, an electrode and its batteries.

Following the principles and procedures described in Example 10, 5 atomic percent (at%) selenium, 20 at% selenium, 35 at% selenium, and 50 at% selenium were separately replaced by sulfur in the synthesis of immobilized sulfur-doped selenium, detailed in the following Table 4. Samples of immobilized sulfur-doped selenium were synthesized with the carbon skeleton prepared in accordance with the principles and procedures described in Example 9.

Identification of samples Yes, %at. Yes, %at. Se, % by weight S, % by weight Se95S5 95 5 97.9 2.1 Se80S20 80 20 90.8 9.2 Se65S35 65 35 82.1 17.9 Se50S50 50 50 71.1 28.9

The thus prepared sulfur-doped immobilized selenium samples were then used to prepare a number of cathodes 4 comprising sulfur-doped immobilized selenium in accordance with the principles and procedures described in Example 11 for immobilized selenium.

The cathodes thus prepared comprising immobilized selenium doped with sulfur in this example were then used to prepare button cells in accordance with the principles and procedures described in Example 12.

The button cells assembled in this example were then tested in the battery tester described in Example 12, following the test protocols also described in Example 12, at charge and discharge cycle rate rates of 0.1 C and 1 C.

The results of electrochemical cycling at the cycling rate of 1 C for button cell batteries comprising a cathode composed of immobilized sulfur-doped selenium, fabricated with a sample of immobilized sulfur-doped selenium (Se50S50 in Table 4) are presented in with a discharge capacity of 821 mAh/g in the 2nd cycle and a constant Coulomb efficiency of ≥ 95%, typically ≥ 98% (which can also be considered satisfactory) and up to 100%.

Assuming that selenium has a stoichiometric specific capacity of 675 mAh/g at a cycling rate of 0.1 C, then the specific capacity of sulfur would be estimated to be about 1178 mAh/g (which is considered good for sulfur). A Coulomb efficiency of ≥95%, ≥98%, or up to 100% indicates that there is no significant amount of sulfur shuttling between the cathode and anode. The sulfur species in the sulfur-doped immobilized selenium battery perform well in an electrolyte that includes carbonate. As a general rule, sulfur would not perform well in a Li-S battery with a carbonate electrolyte; a typical Li-S battery typically uses an ether-based electrolyte. The carbonate-based electrolyte is typically used in today's lithium-ion batteries. Carbonate based electrolyte is more economical and much more widely available in the market, compared to ether based electrolyte.

The results of electrochemical cycling at the cycling rate of 1 C for button cell batteries comprising a cathode composed of immobilized sulfur-doped selenium, fabricated with a sample of immobilized sulfur-doped selenium (Se50S50 in Table 4) are presented in with a discharge capacity of 724 mAh/g in the 2nd cycle and a constant Coulomb efficiency of ≥ 95%, typically ≥ 98% and up to 100%.

If we assume that selenium has a specific capacity of 625 mAh/g at a 1 C cycle rate, then the specific capacity of sulfur would be estimated to be about 966 mAh/g (which is also unexpected). Sulfur is an insulator and has very low electrical conductivity. Typically, a Li-S battery cannot perform well at a fast cycling rate, such as at 1 C.

As can be seen, when used as a cathode material in a rechargeable battery, sulfur-doped immobilized selenium overcomes two fundamental problems associated with Li-S batteries, namely the shuttle effect and the low cycling frequency. Once these two problems are solved, a battery comprising a cathode composed of sulfur-doped immobilized selenium can have high energy density and power density in real applications.

As can be seen, in one example, a sulfur-doped selenium immobilized body or system may be formed by the method comprising the steps of: (a) mixing selenium, carbon, and sulfur to form a selenium-carbon-sulfur mixture; (b) heating the mixture of step (a) to a temperature above the melting temperature of selenium; and (c) cooling the heated mixture of step (b) to ambient temperature or room temperature, thereby forming the sulfur-doped selenium immobilized body.

The sulfur-doped immobilized selenium body of step (c) may comprise selenium and sulfur in a carbon skeleton body.

Step (a) can be carried out in dry or wet conditions.

Step (b) may include homogenizing or mixing the mixture.

Step (a) may comprise forming the selenium-carbon-sulfur mixture in a body. Step (b) may comprise heating the body to a temperature above the melting temperature of selenium. Step (c) may comprise causing or waiting for the body to cool to ambient temperature or room temperature.

Step (b) may comprise heating the mixture for a time sufficient for the selenium, carbon and sulfur to react completely or partially.

In another example, a method of preparing a sulfur-doped immobilized selenium system or body may comprise: (a) forming a carbon skeleton; and (b) fusing the selenium and sulfur into the carbon skeleton.

In another example, a method of forming a sulfur-doped immobilized selenium system or body may comprise: (a) mixing selenium, carbon, and sulfur; and (b) after step (a), dissolving the selenium and sulfur on the carbon, thereby forming the sulfur-doped immobilized selenium system or body.

The solvent for dissolving selenium and sulfur may be an alcohol, an ether, an ester, a ketone, a hydrocarbon, a halogenated hydrocarbon, a nitrogen-containing compound, a phosphorus-containing compound, a sulfur-containing compound, or water. The solvent may be added to one or more of selenium, sulfur, or carbon before step (a), during step (a), or during step (b).

The method may further include in (c) removing excess non-immobilized selenium, non-immobilized sulfur, or both, from the system or the sulfur-doped immobilized selenium body.

This document also describes a rechargeable battery comprising: a cathode composed of immobilized sulfur-doped selenium, disposed on an electrically conductive substrate; a separator disposed in direct contact with the electrically conductive substrate, and in contact with the immobilized sulfur-doped selenium; and an anode spaced from the cathode by the separator.

The rechargeable battery may further include the anode spaced from the separator by lithium. For example, the lithium may be in the form of a lithium film.

The rechargeable battery may further include the cathode, the separator, the anode and the lithium immersed in an electrolyte.

In the rechargeable battery, the sulfur-doped immobilized selenium may comprise a selenium-carbon-sulfur mixture, in which the selenium and sulfur have been fused into the carbon.

In the rechargeable battery, the separator may be made of organic material, inorganic material or solid electrolyte.

The rechargeable battery can have a Coulomb efficiency of ≥95%.

Having thus described a method of preparing a selenium-carbon composite material, a method of manufacturing immobilized selenium and the use of the immobilized selenium, for example, in a rechargeable battery, a method of manufacturing immobilized selenium in a porous carbon with the presence of a desirable level of oxygen species and the use of the immobilized selenium in a rechargeable battery will be described below.

It should be noted that selenium is one of the chalcogens including sulfur, selenium, tellurium, etc. The descriptions relating to selenium in this communication are also applicable to the rest of the chalcogen elements such as sulfur and tellurium.

In the present invention, selenium atoms or molecules are immobilized, either in their oxidized form as an element (in the charged state in a rechargeable battery), or in their reduced form as selenide (in the discharged state in a rechargeable battery). The selenium atoms are located inside the pores of a porous carbon, which allows the electrochemical reactions of a rechargeable battery to proceed properly during the discharge process and during the charging process. During the discharge process, an elemental selenium atom (neutral, Se) at the cathode is reduced and gains two electrons to become a selenide anion (Se2-), generally existing in the form of a salt, lithium selenide, Li2Se, and always located at the cathode. The chemical energy of the discharge process is effectively converted into electrical energy for the rechargeable battery, with a minimum level of conversion to heat due to the presence of the intrinsic internal electrical resistance of the battery. During the charging process of a rechargeable battery, electrical energy is also efficiently converted into chemical energy whereby a selenide anion in the form of Li2Se at the cathode is oxidized and loses two electrons to form an elemental selenium atom which is always localized at the cathode. If the selenium is not immobilized in a porous carbon, intermediate selenium species (usually in the form of polyselenide, Sen2-) can form at the cathode during the electrochemical reduction/oxidation (ReDox) process and dissolve in a liquid electrolyte of the battery system. The dissolved intermediate polyselenide species is then transported in the liquid electrolyte from the cathode to the anode, through a battery separator, where it finds metallic lithium, reacts with the metallic lithium atoms, and forms a salt composed of lithium and selenium on the surface of the lithium anode. The chemical energy generated by the reactions of the intermediate lithium and selenium species on the anode is converted into heat, not electrical energy, which is highly undesirable. Furthermore, the selenium salt formed on the anode can then be converted back to the polyselenide anion, even partially, which is then dissolved in the battery electrolyte, and transported back to the cathode where it consumes additional electrical energy by gaining electrons and is reduced back to elemental selenium. Conversion of the electrochemical energy of selenium to heat or consumption of additional electrical energy is not desirable, even if the rechargeable battery can be recycled, due to an undesirably low recycling efficiency. It should be noted that a battery with an undesirably low cycling efficiency often does not operate properly for a desirable number of cycles.

Accordingly, the present invention shows that immobilization of selenium in a porous carbon skeleton is desirable to achieve proper cycling on a rechargeable battery comprising a lithium anode, a selenium cathode, a separator, and an electrolyte. The selenium is immobilized in a porous carbon and has an activation energy that, in one example, may be ≥ 95 kJ/mole, ≥ 98 kJ/mole, ≥ 101 kJ/mole, ≥ 104 kJ/mole, ≥ 107 kJ/mole, or ≥ 110 kJ/mole. The interaction of selenium and carbon in immobilized selenium comprising selenium and porous carbon is often more frequent, having a collision frequency, for example, ≥ 2.5x105, ≥ 3.0x105, ≥ 3.5x105, ≥ 4.0x105, ≥ 4.5x105, ≥ 5.0x105, ≥ 5.5x105, ≥ 6.0x105, or ≥ 8.0x105. The kinetic rate constant (at 50°C) of immobilized selenium comprising selenium and porous carbon is, for example, ≤ 1x10-10, ≤ 5x10-11, ≤ 1x10-11, ≤ 5x10-12, or ≤ 5x10-13. The carbon skeleton plays an important role in the proper immobilization of selenium. Carbon having a certain microporosity (pore size of 20 angstroms or less) is of interest for spatially confining selenium within the micropores of the carbon skeleton to achieve immobilization of selenium with desirable levels of activation energy, collision frequency, and kinetic rate constant. The presence of some amounts of mesoporosity (pore size between 20 and 500 angstroms) and/or macroporosity (pore size greater than 500 angstroms) in the carbon skeleton is also desirable for successful transport of lithium ions into the cathode during the battery discharge process and out of the cathode during the battery charge process, although it is not critical for selenium immobilization. The amount of microporosity, mesoporosity, or macroporosity is generally characterized by the amount of pore volume (ml) per unit weight (g) of the carbon skeleton. High levels of porosity, including microporosity, mesoporosity, and macroporosity, may be necessary to spatially confine a high level of selenium within the porous carbon. The more selenium is loaded into the porous carbon skeleton (per gram of base), the more chemical energy and electrical energy can be interconverted during the cycling processes of a rechargeable battery.

The microporosity amounts of the porous carbon for selenium immobilization can be >0.3 mL/g, ≥0.4 mL/g, or ≥0.5 mL/g. The total porosity amounts, including microporosity, mesoporosity, and macroporosity are ≥0.4 mL/g, ≥0.5 mL/g, and ≥0.6 mL/g. The percentage of microporosity relative to the total porosity, including microporosity, mesoporosity, and microporosity, is between 50 and 99%, 55 and 97%, and 60 and 95%.

A short path is preferred for lithium transport between the bulk of the electrolyte and where selenium is immobilized in the micropores, while the presence of mesoporosity and macroporosity may be important for the successful transport of lithium ions in and out to access the selenium that is immobilized in the micropores, allowing the electrochemical processes to function properly during the discharge and charge processes of a rechargeable battery. One of the dimensions of the porous carbon particles may prefer to be small, possibly ≤5 µm, ≤2 µm, ≤1 µm, ≤0.5 µm, or ≤0.2 µm; the carbon particle may be relatively large in size with thin interconnected walls, or may be small relative to the particle as a whole. The dimension of porous carbon can be characterized by scanning electron microscope, transmission electron microscope, optical microscope, laser scattering particle size analyzer, etc.

Selenium is immobilized in the micropore space of the porous carbon particle which has porosity including microporosity, mesoporosity, and macroporosity. Selenium is immobilized by strong interactions between the selenium and carbon skeleton inside the pores of the porous carbon. The high surface area porous carbon may have more active sites where selenium interacts with the carbon skeleton. The porous carbon prefers to have a BET surface area of ≥600 m2/g, ≥800 m2/g, ≥1000 m2/g, ≥1200 m2/g, or ≥1400 m2/g.

Selenium is efficiently immobilized in porous carbon by chemical interactions between selenium species and the carbon skeleton surface. Oxygen-bonded functional groups in porous carbon could be the key species that determine strong chemical interactions with selenium. These strong chemical interactions can result in efficient immobilization of selenium, resulting in an increase in activation energy, a decrease in the kinetic rate constant, and/or an increase in collision frequency. To achieve the desirable level of chemical interactions between the backbone carbon atoms and the selenium atoms or molecules, the amounts of oxygen-bonded groups or species as interfaces between carbon and selenium in porous carbon may need to be high enough for effective selenium immobilization for a rechargeable battery that can function properly in electrochemical discharge and charge cycle processes. The amounts of species bound to oxygen or to the oxygen functional group, can be characterized by the amounts of oxygen contained in the porous carbon, analyzed by an oxygen analyzer (such as the LECO oxygen analyzer). The oxygen content of the porous carbon can also be characterized by other instruments that operate similarly to the LECO instruments, for example, temperature-programmed desorption (or thermogravimetric analysis known as "TGA") with a gas detector such as, but not limited to, a mass spectrometer, a thermal conductivity detector, etc.

Porous carbon for selenium immobilization should preferably have the oxygen content amounts ≥2%, ≥3%, ≥5%, or better still ≥7%.

Oxygen species in porous carbon can be categorized and characterized by temperature-programmed desorption (TPD), typically CO2-forming oxygen species, CO-forming oxygen species, and water-forming oxygen species. In a stream of inert gas such as helium, nitrogen, or argon as the carrier gas, the porous carbon sample is heated to a programmed temperature at a defined heating rate, up to a temperature of up to 1000°C. The oxygen species present in the porous carbon sample are destroyed at different temperatures, forming CO2, CO, and/or water, which are eluted by the carrier gas. For the porous carbon that is used for the immobilization of selenium, the ratio between the amounts of oxygen linked to the formation of CO2 and the amounts of oxygen linked to the formation of CO may be between 0.05 and 0.95, 0.15 and 0.85, or 0.2 and 0.8; the amount of oxygen linked to the formation of CO2 may be greater than ≥2%, ≥3%, ≥5%, or preferably ≥7%; the amount of oxygen linked to the formation of CO may be greater than ≥2%, ≥3%, ≥5%, or preferably ≥7%; the amount of oxygen linked to the formation of water may be greater than ≥2%, ≥3%, ≥5%, or preferably ≥7%.

On the other aspect, the density of oxygen species (micromole per square meter, or µmole/m2) of the backbone carbon may be critical to achieve a sufficient level of chemical interactions between the carbon surface and the selenium atoms, resulting in satisfactory immobilization of selenium for proper operation of a rechargeable battery. The porous carbon for immobilization of selenium prefers to have the amounts of oxygen content ≥0.8 µmole/m2, ≥1.0 µmole/m2, ≥1.2 µmole/m2, ≥1.4 µmole/m2, or preferably ≥1.6 µmole/m2; or the amount of oxygen related to the formation of CO2 is ≥0.8 µmole/m2, ≥1.0 µmole/m2, ≥1.2 µmole/m2, ≥1.4 µmole/m2 or preferably ≥1.6 µmole/m2; or the amount of oxygen related to the formation of CO is ≥0.8 µmole/m2, ≥1.0 µmole/m2, ≥1.2 µmole/m2, ≥1.4 µmole/m2 or preferably ≥1.6 µmole/m2.

The presence of adequate amounts of oxygen species in the carbon skeleton appears to play a critical role in the oxidation stability of the Se-C composite. Under ambient conditions, the Se-C composite that consists of a carbon skeleton with low amounts of oxygen species appears to be easy to oxidize under ambient conditions; the fresh material of this Se-C composite shows similar temperature-gravimetric behaviors as the Se-C composite with a carbon skeleton having adequate amounts of oxygen species. However, it was surprising to find that Se-C composites made with low amounts of oxygen species, aged under ambient conditions for about two years and three months, exhibit significant exothermic weight loss at temperatures of about 200-250 °C, with the total weight loss of the Se-C composite being greater than the amount of selenium that was loaded onto the carbon when they were freshly made. In another example, the magnitude of the weight loss at these temperatures appears to correlate well with the amount of carbon skeleton in the Se-C composites: the higher the amounts of carbon skeleton, the greater the exothermic weight loss at temperatures between 200°C and 250°C. In another example, the oxygen content of aged (27 months) Se-C composites made with a carbon skeleton with low amounts of oxygenated species increases to about 24%. In another example, it is also interesting to note that the density of aged Se-C composites that were made from a carbon skeleton with low amounts of oxygenated species is significantly reduced. Without limiting the scope or spirit of the present invention, the exothermic weight loss may be related to oxidation of the carbon-selenium composite by ambient oxygen species (environmental oxygen and/or humidity at ambient conditions), and/or to ambient oxygen species-assisted oxidation of carbon by elemental selenium, both of which result in the formation of the oxidized carbon species; oxidation of the Se-C composite may occur near the pore mouths of the composite; the newly formed oxidized carbon species near the pore mouths may form a closed porosity; the closed porosity is then not accessible to helium gas probing molecules during density measurements, which would result in a decrease in density for aged Se-C composite samples that were made with a carbon skeleton having a low amount of oxygen species. The decomposition products of the oxidized carbon species at temperatures between 200°C and 250°C under an inert carrier gas such as argon or nitrogen may be bound to carbon, selenium and/or oxygen, for example carbon dioxide, carbon monoxide, carbon diselenide, carbon oxyselenide, etc. It should also be noted that the free-standing carbon skeleton containing low amounts of oxygen species is stable under ambient conditions. The carbon and/or selenium present in the Se-C composite which is made with a carbon skeleton having low amounts of oxygen species appear to be susceptible to attack by oxygen species in the environment, as is the selenium. Such oxidation instability may well result in poor electrochemical cycling performance of a Li-Se rechargeable battery; It is possible that the carbon skeleton is slowly oxidized by elemental selenium in electrochemical cycling environments, as well as in ambient environments. It is undesirable to obtain the formation of oxidized carbon species in a Se-C composite. The amount of selenium in the oxidized carbon species may not participate in the electrochemical cycle of a rechargeable battery, resulting in a permanent loss of the specific capacity of a rechargeable battery. The carbon skeleton also plays a key role, in addition to accommodating selenium for immobilization, in providing an electrical conduction pathway for (1) the supply of electrons from the external circuit to the elemental selenium during the discharge process and (2) the capture of electrons from the selenium anions (Se2-) to the external circuit during the charge process. If partial amounts of carbon are oxidized by elemental selenium, forming oxidized carbon species, the electrical resistivity of the carbon skeleton can increase significantly, so that the electrical conduction pathway required for the supply and capture of electrons during each electrochemical cycle is shared, eventually reaching a level where the rechargeable battery would not function properly, not to mention the loss of electrical energy and chemical energy as heat, which is indeed undesirable for a rechargeable battery in view of the aspects of (1) low energy efficiency and (2) thermal management.

In contrast, the Se-C composite which is manufactured with a carbon skeleton having an adequate level of oxygen species shows no change in the thermogravimetric analysis (TGA) behaviors between the fresh sample and the sample aged under ambient conditions for about two and a half years; there is no exothermic weight loss at a temperature of about 200-250 °C; the total weight loss indicated by TGA is similar to the level of selenium loading (by weight) when freshly produced; there is no gain in oxygen content and there is no decrease in density. Therefore, a Se-C composite with a carbon skeleton having adequate amounts of oxygen species somehow achieves a satisfactory immobilization level of selenium by applying strong chemical interactions between carbon and selenium with the interfacial oxygen species, improving the oxidation stability of the Se-C composite.

Effective immobilization of selenium in the carbon skeleton can be achieved by the presence of adequate amounts of oxygen species in the Se-C composite, possibly in the form of interfacial species that allow strong chemical interactions between the carbon skeleton and selenium (in any chemical form). The amounts of oxygen species desirable in the immobilized selenium-carbon composite can depend on the level of oxygen species in the carbon skeleton source and the level of selenium loading (by weight) in the Se-C composite. For a selenium loading of 50% or less, the amount of oxygen species in the Se-C composite is ≥0.63 mmol/g, ≥0.94 mmol/g, ≥1.56 mmol/g, or ≥2.19 mmol/g; for a selenium loading of between 50% and 60% (including 60%), the amount of oxygen species in the Se-C composite is ≥0.5 mmol/g, ≥0.75 mmol/g, ≥1.25 mmol/g, or ≥1.75 mmol/g; for a selenium loading of 60% or more, the amount of oxygen species in the Se-C composite is ≥0.31 mmol/g, ≥0.47 mmol/g, ≥0.78 mmol/g, or ≥1.09 mmol/g.

It should be noted that the adequate amounts of oxygen species in the Se-C composite are not related to the oxygen species involved in the exothermic weight loss at temperatures between 200°C and 250°C. The oxygen related to the exothermic weight loss at temperatures between 200°C and 250°C may well result from post-oxidation of the Se-C composite under ambient conditions by oxygen species such as oxygen and/or moisture in the air.

The amount of oxygen species in the porous carbon is generally generated during a porous carbon manufacturing process, generally comprising a carbonization process in which the precursor is converted to carbon, generally at a temperature below 700°C, preferably below 650°C, preferably below 600°C, followed by an activation process in which the carbon is converted to porous carbon, generally at a temperature above 700°C, preferably above 750°C, or even at about 800°C or higher. The amount of porosity of the porous carbon depends on the degree of activation. The degree of activation is controlled by the temperature and time of activation with different activation chemicals such as steam, CO2, a base (such as NaOH, KOH, etc.), a salt (such as K2CO3, Na2CO3, ZnCl2, etc.). The more severe the activation conditions, the more the porosity of the porous carbon increases. Activation at a higher temperature, for example around 1000 °C, and/or for a certain period of time results in a porous carbon having a higher level of porosity, which is desirable. However, activation at a higher temperature and/or for a longer period of time results in a greater loss of oxygen species for a porous carbon resulting in a lower level of oxygen species in the porous carbon, which is undesirable. A higher level of oxygen species can be preserved for the porous carbon by activating it at a relatively lower temperature and/or for a shorter period of time which can result in a lower porosity, which is undesirable. The present disclosure discusses the spirit of the invention regarding the culmination of both the amounts of porosity and the amount of oxygen species for the porous carbon for the immobilization of selenium with a suitably high selenium loading level, with a suitably high immobilization level characterized by a high activation energy, a high collision frequency or a depressed level of the kinetic rate constant.

As described in the preceding paragraph, activation at a higher activation temperature and/or for a longer period of time results in a greater loss of oxygen species. One compromised approach may be activation at a relatively low temperature, for example, around 800°C and below, and for a relatively longer period of time, for example, 10 minutes or more. The present invention also includes post-treatments of the porous carbon with a suitably high level of porosity resulting from a severe activation process, which leads to an increase in the amounts of oxygen species in the porous carbon. This oxygen species-enhanced porous carbon then has desirable levels of both porosity and amount of oxygen species, as described in the preceding paragraphs.

The porous carbon may be post-treated with an oxidizing agent. The oxidizing agent may be an oxygen-containing chemical. The post-treatment(s) of the porous carbon may be carried out in the liquid phase, or in the gas phase. Liquid phase post-treatments of porous carbon may be carried out in an aqueous medium. Liquid phase post-treatments of porous carbon may also be carried out in an organic solvent which may be hydrophobic or hydrophilic in nature. Liquid phase post-treatments of porous carbon may also be carried out under salt melting conditions.

Porous carbon aftertreatments may be transported in the liquid at a relatively low temperature, for example, at or below the boiling point of the liquid medium. Under elevated pressure above atmospheric pressure, the aftertreatment temperature may be above the atmospheric boiling point of the liquid medium. Under vacuum, the aftertreatment temperature may need to be below the atmospheric boiling point of the liquid medium.

The oxidizing agent may be nitric acid, hydrogen peroxide, a persulfate salt (e.g., ammonium, sodium, or potassium persulfate), a salt of manganese, vanadium, chromium, or another transition metal-related element whose high oxidation valence state permits reduction. The oxidizing agent may be oxygen, ozone, or an organic peroxide.

Post-treatments of porous carbon in an aqueous environment can be carried out under acidic, neutral or basic pH conditions.

The post-treated porous carbon may be washed and dried. The dried porous carbon after treatment may be further treated at an elevated temperature (e.g., ≥150°C, ≥200°C, or ≥250°C) under static conditions, a gas flow, preferably an inert gas. This heat treatment may rebalance the distribution of oxygen species related to CO2 formation, oxygen species related to CO formation, and oxygen species related to H2O formation.

Post-treatments of porous carbon can increase the amount of oxygen species by ≥30%, ≥50%, ≥100%, or ≥150%.

It may be more desirable to perform the immobilization of selenium at a temperature that preserves oxygen species that can serve as a critical site that enhances the chemical interactions of the selenium and carbon skeleton. The melting temperature of selenium in the pores of the porous carbon may be equal to or greater than the melting point of selenium. Doping with other elements such as S, Te, or other impurities can lower the melting point of selenium.

Selenium (with or without dopant) can be loaded onto the carbon skeleton by an impregnation method. The selenium can be dissolved in a solvent, forming a selenium solution. The selenium solution is then impregnated onto a porous carbon, and the solvent is evaporated off, leaving the selenium inside the porous carbon. This impregnation process can be repeated to obtain a sufficient selenium loading. This method can also significantly lower the loading temperature of selenium onto the porous carbon to below the melting point of selenium.

The source of production of the porous carbon for immobilization of selenium may be from renewable carbon sources, for example, but not limited to, biomass, such as sugar, glucose, starch, protein, soybean meal, nuts, shells (walnut, rice, wheat, etc.), fibers and sawdust, or any carbon source related to nature. The source of production of the porous carbon for immobilization of selenium may be a salt that includes carbon, as described in the previous sections. The source of production of the porous carbon for immobilization of selenium may be an acid that includes carbon, such as citric acid, gluconic acid, tannic acid. The carbon source may also be from a chemical, for example a polyol, or a polymer such as polyacryonitrile or polyphenol.

Description of the carbon manufacturing process.

The carbon material described herein can be obtained from a preparation method which comprises the following steps:

(1) Mixing the different ingredients: inert salt, activating agent and carbon precursor. The mixing process may include a ball milling process or a freeze-drying process of a solution of the different ingredients.

(2) Carbonize the mixture in an inert atmosphere at high temperature, then wash it with hot water to remove inorganic salts, and dry it to obtain a three-dimensional porous material comprising thin, curved and interconnected carbon layers.

In step (1), the inert salt may be selected from potassium chloride, sodium chloride or sodium carbonate. The activating agent may be selected from potassium carbonate, potassium bicarbonate or potassium oxalate. The carbon precursor may be selected from the renewable carbon sources described above. In step (2), the high-temperature carbonization may be carried out at 800-900 ° C, preferably at 800-850 ° C; the carbonization time is 1-8 hours, preferably 1-4 hours.

The present invention embodies two main methods of manufacturing thin-walled interconnected porous carbon, namely self-assembled carbon and exo-assembled carbon.

The self-assembly process may involve the use of a salt that includes carbon and can be carbonized, for example, potassium citrate, potassium gluconate, potassium tartrate, calcium citrate, sodium citrate, etc. When the salt is heated, it first goes through a melting process that accompanies decomposition, forming water, carbon dioxide, carbon monoxide, light hydrocarbons, and certain sticky, malodorous tar-like oils that may be oxygenated hydrocarbons; as decomposition proceeds, the cation of the original salt may be in a soluble form with a newly formed carbonate and/or oxalate anion and/or another salt form; When the concentration of the newly formed carbonate, bicarbonate, oxalate and/or other anions reaches a solubility saturation point, the conditions for supersaturation of the newly formed carbonate, bicarbonate, oxalate and/or other anions begin to set in as the decomposition process proceeds. It should be noted that supersaturation of the solubility of a salt is thermodynamically quasi-stable; when it reaches a supersaturation point that is no longer kinetically stable, it results in crystallization of the newly formed carbonate, bicarbonate, oxalate and/or other anion salt. An organic carboxylate salt comprising a hydroxyl group (e.g., potassium citrate, potassium gluconate, potassium tartrate, etc.) may be a crystallization inhibitor; such a crystallization inhibitor allows a higher level of supersaturation to develop, which generally leads to a large population of small crystallites. The newly crystallized salt of carbonate, bicarbonate, or other form may have a very uniform particle size. As decomposition continues with increasing temperature and/or time, the viscosity of the melt may increase, which may uniformly coat the surface of the newly formed crystallites with carbonate, bicarbonate, oxalate, and/or other salt forms. The carbon then eventually solidifies on the surfaces of the newly formed crystallites. This carbon assembly process is described herein as a self-assembly process, a carbonization process. The temperature for the self-assembly process may be less than 700° C. This thermal self-assembly process may be accomplished by increasing the temperature at a constant rate or at a variable rate. The self-assembly process may also be accomplished by maintaining a constant heating temperature or "hot" stabilization at a temperature less than or equal to 700° C.

As the temperature increases, the self-assembled and newly formed carbon with three-dimensional interconnected thin walls undergoes an activation process by the newly formed crystallites acting as the chemical activating agent. For example, the activation process can be mainly based on the high-temperature redox reaction between carbon and the newly formed crystallites such as K2CO3 (from potassium citrate as the base material), K2CO3 + C → K2O + 2CO, which takes place at about 700 °C or higher. The consumption of carbon can cause the generation of porosity (especially microporosity) in the carbon, leading to the formation of a porous carbon with three-dimensional interconnected thin walls. The activation temperature can reach 1100 °C. The ramping rate can be less than 1 °C/min up to 100 °C/min. An inert carrier gas stream, for example, nitrogen or argon, can be used for the porous carbon manufacturing process. A reactive gas, such as CO2 and steam, can also be used separately or together for and during activation.

There may be an additional or secondary reaction contributing to the generation of carbon porosity. Some of these reaction processes may include: i) carbon gasification by CO2 produced during the carbonization and/or activation process, ii) reduction of metal oxides by carbon (e.g., K2O + C → CO + 2 K), iii) intercalation of some newly formed metal species (e.g., K) into carbon layers, or iv) a catalytic effect associated with cations, which is particularly relevant in the case of potassium. Carbon gasification (C+CO2 = 2 CO) is particularly relevant, since the CO2 generated by the decomposition of unreacted K2CO3 (K2CO3 → K2O + CO2) occurs slowly at a temperature above 800-850°C.

The exoassembly process may involve the use of exogenous particles, e.g., an activating agent (e.g., an alkali metal salt of carbonate, such as K2CO3, an alkali metal hydroxide, such as KOH), optionally with an inert salt (e.g., KC1, NaCl, etc.) to generate abundant amounts of porosity from a carbon source. The exogenous particles may be mixed with the carbon source prior to carbonation or after carbonization, more preferably, prior to the carbonization step. This mixture of exogenous particles and the carbon source may be obtained by physical mixing, optionally followed by mechanical grinding, or by recrystallization of the carbon source with the chemical substance of the exogenous particle from an aqueous solution, aqueous slurry, or the like using an organic liquid medium. The drying process for recrystallization can be done by evaporation, air drying, oven drying, spray drying or freeze drying.

When the mixture is heated in the exoassembly process, carbonization-activation of the carbon source occurs on a salt particle as a matrix, as described in the previous paragraphs for a room temperature process. During the carbonization process, the carbon source may somehow melt and decompose as the temperature increases and time passes, forming by-products such as CO2, CO, water, light hydrocarbons, and some sticky and slimy heavy hydrocarbons. The viscosity of the melt may increase, and the melt may eventually coat and solidify on the surface of the exogenous particles, forming a thin-walled, interconnected carbon coating on the surface of the exogenous particles. As the temperature continues to increase, the activation process starts and gives rise to porosity, which can be mainly based on the high temperature redox reaction, e.g. K2CO3 + C → K2O + 2CO, which occurs at a temperature of about 700°C or more.

For example, when the exogenous particles optionally include an inert salt, e.g. KC1, the melting point of an activating chemical such as K2CO3 is lowered from 891°C to about 630°C, for example. Due to the formation of a liquid phase KCl-K2CO3 system at a temperature of about 630°C, the activation of the interconnected thin-walled carbon can be significantly accelerated, perhaps due to the increased reactivity of the K2CO3 with the carbonized elements (interconnected thin-walled carbon), possibly by more intimate contacts between the activating chemical (such as K2CO3 herein) and the surface of the interconnected thin-walled carbon. This could suggest that the self-assembly process with exogenous particles comprising an activating chemical agent and, possibly, an inert salt, could indeed be a more viable strategy to achieve the synthesis of a three-dimensional interconnected thin-walled porous carbon with sufficient amounts of porosity, while preserving adequate amounts of species including oxygen (activation under less severe conditions, i.e., at a lower activation temperature). At the same time, the carbon surface can be isolated by the liquid phase of the molten KCI-K2CO3 system, preventing the side reaction of the formed CO2 and the formed interconnected thin-walled porous carbon by possibly limiting the diffusion of the CO2 gas molecules created on the surface of the solidified three-dimensional interconnected thin-walled porous carbon, which is desirable to achieve higher performance of the interconnected thin-walled porous carbon. In addition, the “monolithic” liquid phase of the molten KCI-K2CO3 system can also limit the gaseous diffusion of emitted gases such as carbon volatiles, which may result in a possibility of their redeposition on the three-dimensional interconnected thin-walled porous carbon and an increase in the performance of the interconnected thin-walled porous carbon, which is desirable.

Example 14. Three-dimensional interconnected thin-walled porous carbon nanomaterial: fabrication and characterization of carbon --- by an exo-assembly process: freeze-drying of the aqueous mixture of carbon source such as glucose, chemical activating agent such as K2CO3 and, optionally, inert salt such as KCl.

After dissolving appropriate amounts of KCl, K2CO3 and glucose in distilled water, the solution was frozen with liquid nitrogen (-196°C), then transferred to a freeze dryer and freeze-dried at a temperature of -50°C and a pressure of 0.06 mbar, which gave a solid mixture of KCl, K2CO3 and glucose. The solid mixture was then carbonized at 850°C for one hour in an inert atmosphere, then cooled to room temperature, followed by washing with hot distilled water, filtration and drying, which produced a three-dimensional interconnected thin-walled porous carbon nanomaterial, as shown in .

The surface area of the glucose-derived three-dimensional interconnected thin-walled porous carbon nanomaterial was measured to be 2316 m2/g with a total pore volume of 1.04 cm3/g and a micropore volume of 0.90 cm3/g, of which about 86% of the pores are described as microporosity and about 14% as meso and macroporosity. The N2 adsorption isotherm and pore size distribution of the three-dimensional interconnected thin-walled porous carbon nanomaterial are shown in Fig. .

In another example, soybean meal is used instead of glucose. As shown in , the macroscopic structure of the three-dimensional interconnected thin-walled porous carbon nanomaterial derived from soybean flour is similar to that of glucose. However, this material has a surface area of 2613 m2/g/g, a pore volume of 1.42 cm3/g, and a micropore volume of 1.0 cm3/g, of which about 70% of the pores are described as microporosity and about 30% as meso and macroporosity. The N2 adsorption isotherm and pore size distribution of this material are shown in . The amount of mesoporosity of this material derived from soy flour is higher than that derived from glucose. [Table 5] Carbon Precursor Activation/assembly agent Precursor/KCL/K2CO3 weighting ratio Carbonization temperature (°C) SM-K-800 KC1 1/6,7/0 800 SM-CK-800 Soy K2CO3 1/0/1 800 SM-800 grinding KCI+K2CO3 1/6,7/1 800 SM-850 KCI+K2CO3 1/6,7/1 850 GK-800 KC1 1/6,7/1 800 G-CK-800 Glucose K2CO3 1/0/1 800 G-800 KCI+K2CO3 1/6,7/1 800 G-850 KCI+K2CO3 1/6,7/1 850 Carbon Texture Properties Sbet (m2g-1) VP (cm3g-1) Vmicro (cm3g-1) SM-K-800 470 0.38 0.16 SM-CK-800 2650 1.22 1.04 SM-800 2580 1.19 0.98 SM-850 2613 1.42 1.00 GK-800 335 0.16 0.12 G-CK-800 1443 0.58 0.53 G-800 2000 0.81 0.71 G-850 2316 1.04 0.90 Carbon Chemical composition (% by weight) C O N SM-K-800 75.4 15.7 7.8 SM-CK-800 91.0 7.9 0.73 SM-800 93.6 5.6 0.46 SM-850 93.7 5.6 0.36 GK-800 G-CK-800 G-800 92.7 6.8 0.14 G-850 93.6 5.9 0.19

Table 5 above shows several different examples of three-dimensional interconnected thin-walled porous carbon nanomaterials fabricated by an exo-assembly process for different combinations of precursors, activating/assembling agent, precursor/activating/assembling agent weight ratio, and carbonization ratio - resulting in the different combinations of textural properties and chemical composition shown, where Vbet = apparent surface area, Vp = total pore volume, and Vmicro = micropore volume.

Example 15: Three-dimensional interconnected thin-walled porous carbon nanomaterial: Capabilities and performances.

The three-dimensionally interconnected thin-walled porous carbon nanomaterials of Example 14 can be used as electrodes in electrochemical capacitors. The electrode comprises an organic binder, which may be, for example, PTFE or PVDF. Optionally, the electrode also comprises an electrical conductivity promoter such as, for example, black carbon, graphene, carbon nanotubes, etc. In a typical example, a mixture of 85 wt.% active substance, 10 wt.% binder and 5 wt.% electrical conductivity promoter is prepared.

The method of manufacturing the electrodes may include preparing a paste of the various components or their dry mixture in a mortar. The paste may be deposited on a current collector or may be formed into self-supporting electrodes such as disk-shaped electrodes. The electrodes may then be pressed or roller-milled before being used in an electrochemical capacitor.

A symmetrical electrochemical capacitor can be assembled using the electrodes described above. Two electrodes of the same mass and thickness can be used. The current collectors can be made of gold, stainless steel, aluminum, nickel, etc., depending on the electrolyte used.

The electrolyte may be an acidic aqueous solution such as sulfuric acid or hydrochloric acid, a basic solution such as sodium hydroxide or potassium hydroxide, a salt such as lithium sulfate, sodium sulfate, potassium sulfate, etc., or an organic solution such as an ionic liquid such as 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium, bis(trifluoromethylsulfonyl)imide, ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, etc., or a pure ionic liquid as mentioned above.

The electrochemical capacitor can be charged at 0.2 A/g, 0.5 A/g, 1 A/g, 5 A/g, 10 A/g, 20 A/g, 50 A/g or faster. The assembled electrochemical capacitors were tested using a computer-controlled potentiostat. The tests consisted of cyclic voltammetry (CV) experiments, electrochemical impedance spectroscopic (EIS) studies, and galvanostatic charge/discharge (CD) cycling tests. The cell voltage can be up to 1 V in acidic or basic solution, up to 1.5 V in aqueous saline solution, and up to 3 V in organic and ionic liquid electrolyte solution.

As an example, a 1 M H2SO4 solution is used as the electrolyte. The electrochemical capacitor made from a three-dimensional interconnected thin-walled porous carbon nanomaterial derived from glucose (referred to as glucose-based) has an electrical capacitance of 57 F/g at 0.2 A/g, and the electrochemical capacitor made from a three-dimensional interconnected thin-walled porous carbon nanomaterial based on soybean meal has a capacitance of 60 F/g. At an ultra-large current density of 110 A/g, the electrical capacitance is 24 and 31 F/g, respectively.

In another example, a 1 M Li2SO4 solution is used as the electrolyte. The glucose-based electrochemical capacitor has a cell capacitance of 37 F/g at 0.2 A/g and the soybean-based electrochemical capacitor 39 F/g. At a current density of 20 A/g, the electric capacitance is 25 and 29 F/g, respectively.

In another example, a solution of EMImTFSI in acetonitrile (1/1 wt%) is used as the electrolyte. The glucose-based electrochemical capacitor has an electrical capacitance of 36 F/g at 0.2 A/g and the soybean-based electrochemical capacitor 39 F/g. At a current density of 30 A/g, the electrical capacitance is 28 and 30 F/g, respectively.

Figure X8 shows a Ragone type diagram of electrochemical capacitors with different electrolytes. The robustness of the electrochemical capacitors was tested by long-term cycling at 5-10 A/g for more than 5,000 cycles.

Example 16 Three-dimensional interconnected thin-walled porous carbon nanomaterial: Carbon fabrication by an open-air heating process, mixing (optionally followed by grinding) the carbon source such as sugar, glucose, soybean meal or sawdust, the activating chemical agent such as K2CO3 and, optionally, inert salt such as KCl.

Appropriate amounts of a carbon source such as sugar, glucose, soybean meal, sawdust (e.g., pine, cherry, or oak sawdust), a chemical activating agent such as K2CO3, and optionally, an inert type salt were weighed into an inclusion apparatus, then subjected to physical mixing which may involve mechanical grinding, and then transferred to a crucible which may be ceramic, steel, stainless steel, etc. Under a flow of inert gas (which is also optional), the mixture is heated at a progressive rate of less than 100°C/min, optionally to a heat stabilization temperature of 700°C or less for the time required for carbonization, or directly to an activation temperature of 700°C or more, and maintained at that temperature for the time required for activation. Throughout the ramp-up process, the carbon source goes through a carbonization process by decomposing into CO, CO2, water, light hydrocarbons, and sticky heavy and oily hydrocarbons. During the activation process, volatile CO, CO2, water and carbon can continue to form.

After activation, the mixture is mixed with water and, optionally, neutralized with an acid such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc. The carbon paste is then filtered and washed with water to a level that has a low level of electrical conductivity, for example, less than 5000 μS/cm, less than 3000 μS/cm, less than 1000 μS/cm, and, optionally with deionized or distilled water, to a conductivity of less than 300 μS/cm, less than 100 μS/cm, or even less than 50 μS/cm. The filtered elements can be dried in an oven to remove the water.

The resulting three-dimensional interconnected thin-walled porous carbon nanomaterials were then characterized by their oxygen content, SEM, XRD, Raman, TGA-CDB, BET N2 and CO2 surface area and pore size distribution.

The following Table 5 shows the elemental analysis of three-dimensional interconnected thin-walled porous carbon nanomaterials such as 237-8 (self-assembled carbon synthesized from potassium citrate), 237-51A (self-assembled carbon from potassium citrate), SKK2 (exogenously sourced carbon) and commercial carbons such as Elite C available from Calgon Carbon of Pittsburgh, Pennsylvania, USA, YP-50 available from Kruray Co. Ltd of Osaka, Japan, Ketjen carbon black available from Lion Specialty Chemicals Co. Ltd. of Tokyo, Japan and Maxsorb available from Kansai Coke and Chemicals Co. Ltd. of Hyogo, Japan. [Table 6] Identification of samples ELEMENTAL ANALYSIS (% by weight) C 0 H N S ELITE C 97.54 1.19 0.45 1.05 0.08 YP-50F 97.96 1.46 0.60 1.08 0.02 KETJEN 98.56 0.33 0.28 0.97 0.10 MAXSORB 96.99 1.33 0.28 1.36 0.01 237-8 87.62 9.29 0.57 1.24 0.01 237-51A 87.84 9.90 0.40 1.12 0.02 SKK2 94.30 5.25 0.31 0.14 - 237-101D 12%

Table 6 above shows two carbon groups, one of which is three-dimensional interconnected thin-walled porous carbon nanomaterials, such as 237-8 (self-assembled carbon synthesized from potassium citrate), 237-51A (exo-assembled carbon synthesized from glucose), 237-101D (self-assembled carbon synthesized from potassium citrate), and SKK2 (foreign carbon synthesized from sugar), which have an oxygen content of more than 1.5 wt%, more than 2.0 wt%, more than 3 wt%, or more than 4.0 wt%. X-ray research studies show that the carbon materials in the above table are all amorphous. Raman studies show that the carbonaceous materials in the table above are also amorphous in nature, showing the Raman signature of amorphous carbon scattering at both the D and G peaks.

The prepared interconnected thin-walled porous carbon is then used to prepare the selenium immobilization. Appropriate amounts of selenium and carbon are mixed together as described above, and then the selenium is melted into the interconnected thin-walled porous carbon in the presence of a high content of oxygen species, yielding the immobilized selenium of the present invention. Reference is made to the preceding description for the method of manufacturing the immobilized selenium in the presence of a high content of oxygen species to yield the immobilized selenium of the present invention. Reference is made to the preceding description for the method of manufacturing the immobilized selenium subject of the present disclosure. The immobilized selenium is then characterized by the analyses of oxygen content, XRD, Raman, SEM, TGA-CDB, etc.

Analysis table of oxygen content of selenium immobilized in three-dimensional interconnected thin-walled porous carbon nanomaterials which has an oxygen content greater than 1.5 wt%, greater than 2.0 wt%, greater than 3 wt% or greater than 4.0 wt% relative to the immobilized carbon-selenium composite which is prepared with commercial carbons which have an oxygen content less than 1.5%, less than 2.0 wt%, less than 3 wt% or less than 4.0 wt%. [Table 7] Carbon identification C-Se
ID 0 (%) Elite C 115 24 Max sorb MSP20X 259 14 Ketjen 600JD 352 0.47 237-8 301 2.6 237-51A 366 3.1 237-67 426 4.9 237-101D 483 4.8 SKK-2 385 4.8

Table 7 above shows two different groups of immobilized selenium: one group (referred to as Group I, namely Ketjen 600JD, 237-8, 237-51A, 237-67, 237-10ID, and SKK-2) having an oxygen content that is approximately half the oxygen content of the three-dimensionally interconnected thin-walled porous carbon nanomaterials, ranging from 1% to 10%, 1.5% to 9%, or 2% to 8%, and another group (referred to as Group II, namely Elite C and Maxsorb MSP20X) having an oxygen content that is at least five times the oxygen content of carbon, or greater than 8%, greater than 9%, or greater than 10%. It should be noted that Ketjun carbon is a non-porous carbon, whose carbon-selenium composite is considered as non-immobilized selenium; its oxygen content therefore remains very low, less than 1%.

Group I oxygen species of immobilized selenium may play critical roles as interfacial chemical groups in selenium immobilization, enabling strong interactions between

carbon and selenium, resulting in tighter packing of selenium atoms or species within the pores of the three-dimensional interconnected thin-walled porous carbon nanomaterials, as evidenced by an increased collision frequency, as shown in the examples of the present disclosure. These interactions between the carbon skeleton and the selenium atoms or selenium chemical species, may also be evidenced by a higher intrinsic density.

For example, a sample of immobilized selenium that is made from three-dimensional interconnected thin-walled porous carbon nanomaterials, for example self-assembled carbon synthesized from potassium citrate, in a 50-50 ratio (by weight) of carbon to selenium. It was surprising to find that its density was 3.42 g/cm3. It is worth noting that selenium has a density of 4.819 g/cm3. Using 4.819 g/cm3, the density of carbon in the immobilized selenium composite is calculated to be about 2.8 g/cm3. It is also worth noting that diamond has a density of 3.5 g/cm3, graphite has a density of about 2.3 g/cm3, and amorphous carbon has a typical density of about 2.0 g/cm3.

The immobilized selenium is then used to make a cathode of a rechargeable battery by mixing appropriate amounts of immobilized selenium, an aqueous or organic medium and at least one binder, as described above, followed by coating on a charge collector, for example aluminum foil, resulting in a cathode comprising immobilized selenium. Reference is made to the preceding description for the process of making a cathode comprising immobilized selenium in the present disclosure.

The thus obtained cathode, composed of immobilized selenium, is then used to assemble a rechargeable battery with an anode, for example, lithium, a separator, an electrolyte. Reference is made to the preceding description for the process of assembling a rechargeable battery comprising a cathode comprising immobilized selenium in the present disclosure.

The carbon sample thus obtained can be used in a process of manufacturing electrodes for a capacitor or for a rechargeable battery.

The examples have been described by reference to the figures accompanying them. Modifications and alterations will be made to others upon reading and understanding the preceding examples. Accordingly, the preceding examples should not be construed as limiting the disclosure.

Claims (20)

A process for preparing an immobilized selenium body comprising:
(a) forming a mixture comprising selenium and a self-assembled porous carbon;
(b) heating the mixture of step (a) to a temperature above the melting temperature of selenium; and
(c) cooling the mixture heated in step (b) to room temperature, thereby forming the immobilized selenium body,
wherein the self-assembled carbon is manufactured by a process which comprises:
the carbonization of a salt by fusion until supersaturation of the anions in the melt forms a crystallized salt in the melt;
increasing the viscosity of the melt until the melt covers the surfaces of the crystallites of the crystallized salt; and
solidify the carbon in the melt on the surface of the crystallites. The method of claim 1, wherein the self-assembled porous carbon comprises oxygen species. The method of claim 1, further comprising, prior to step (a), subjecting the self-assembled porous carbon to a post-treatment process to increase the amount of oxygen species in the self-assembled carbon. The method of claim 3, wherein the post-treatment process comprises reacting the self-assembled porous carbon with an oxidizing agent. The method of claim 4, wherein the oxidizing agent comprises at least one of the following:

• nitric acid;
• hydrogen peroxide;
• an organic peroxide;
• oxygen; and/or
• ozone.

The method of claim 4, wherein the oxidizing agent comprises at least one of the following in an aqueous environment:

• ammonium persulfate;
• sodium persulfate;
• potassium persulfate;
• a manganese salt;
• a vanadium salt; and/or
• a chromium salt.

The method of claim 1, wherein the mixture further comprises sulfur. The method of claim 1, wherein the mixture further comprises tellurium. The method of claim 1, wherein the mixture further comprises sulfur and tellurium. The method of claim 1, wherein the carbonized salt comprises a carbonate anion. The method of claim 10, wherein the carbonized salt is potassium carbonate. The method of claim 1, wherein the salt comprises a citrate anion. The method of claim 12, wherein the salt is potassium citrate, calcium citrate or sodium citrate. The method of claim 1, wherein the salt comprises a gluconate anion. The method of claim 14, wherein the salt is potassium gluconate. The method of claim 1, wherein the salt comprises a tartrate anion. The method of claim 16, wherein the salt is potassium tartrate. The method of claim 12, wherein the salt comprises a bicarbonate anion. The method of claim 12, wherein the salt comprises an oxalate anion. An immobilized selenium body, the immobilized selenium body being produced by a method according to claim 12.