CN111864260B

CN111864260B - Ether gel electrolyte and preparation method and application thereof

Info

Publication number: CN111864260B
Application number: CN202010858396.9A
Authority: CN
Inventors: 洪波; 赖延清; 贺亮; 张治安; 张凯; 方静; 王宁; 郑景强
Original assignee: Central South University
Current assignee: Nanning Yisida New Energy Technology Co ltd
Priority date: 2020-08-24
Filing date: 2020-08-24
Publication date: 2022-02-11
Anticipated expiration: 2040-08-24
Also published as: CN111864260A

Abstract

本发明属于锂电池电解质技术领域，具体公开了一种凝胶电解质，其由包含醚类有机溶剂、支持锂盐、锆盐和硝酸盐的溶液自聚凝胶化得到。通过锆盐和硝酸盐的协同作用，能够促使环状醚类有机溶剂发生开环聚合作用，在室温下自发地形成成分均一、性质稳定的凝胶电解质。该凝胶能够有效减少活性物质的损失，同时硝酸根能够有效保护锂负极，抑制锂枝晶的生长，提升库伦效率。所述凝胶电解质能够提升锂电池的循环稳定性以及延长电池的使用寿命。The invention belongs to the technical field of lithium battery electrolytes, and specifically discloses a gel electrolyte, which is obtained by self-polymerization and gelation of a solution comprising an ether organic solvent, a supporting lithium salt, a zirconium salt and a nitrate. Through the synergistic effect of zirconium salt and nitrate, the ring-opening polymerization of cyclic ether organic solvent can be promoted, and a gel electrolyte with uniform composition and stable properties can be spontaneously formed at room temperature. The gel can effectively reduce the loss of active materials, and at the same time, nitrate can effectively protect the lithium anode, inhibit the growth of lithium dendrites, and improve the Coulombic efficiency. The gel electrolyte can improve the cycle stability of the lithium battery and prolong the service life of the battery.

Description

Ether gel electrolyte and preparation method and application thereof

Technical Field

The invention relates to the field of lithium battery design, in particular to an ether gel electrolyte for a lithium battery and a lithium battery using the ether gel electrolyte.

Background

With the rapidly expanding market growth of reusable energy storage devices applicable to electric vehicles and portable electronic devices, there is an increasing demand for: a lithium battery as an energy storage device having high capacity characteristics and improved stability.

The lithium secondary battery is mainly a lithium ion battery and a lithium metal battery; the negative electrode of the lithium metal battery is usually a metallic lithium simple substance or an electrode containing the metallic lithium simple substance, different from a conventional lithium ion battery, and in the lithium metal battery, the negative electrode is charged and discharged in a deposition and dissolution manner instead of being inserted and removed, and the charging and discharging mechanism is as follows: charging of Li⁺+ e ═ Li; discharge Li-e ═ Li⁺. Compared with lithium ion batteries, lithium metal batteries are a brand new battery system with different mechanisms of action. Among them, Lithium Sulfur Battery (LSB) has higher theoretical energy density (2600W h kg)^-1) And theoretical specific capacity (1675mA h g^-1) It is very popular with researchers. In addition, the cathode material of the lithium-sulfur battery is a sulfur cathode which has rich sources, low price, environmental protection and low toxicity, thereby becoming one of the most promising secondary battery systems.

Practical application of lithium sulfur batteries has been hampered by a number of factors. The dissolution of long-chain polysulfide during the discharge process increases the viscosity of the electrolyte, and simultaneously, the long-chain polysulfide inevitably diffuses to the lithium negative electrode under the action of concentration gradient and electric field, is reduced to short-chain polysulfide at the lithium negative electrode, and then moves back and forth between the positive electrode and the negative electrode, so that the shuttle effect causes self-discharge, loss of active substances, reduction of coulombic efficiency and lithium metal corrosion. Insoluble insulating discharge products (Li), on the other hand₂S₂/Li₂S) deposits on the cathode surface causing passivation of the pole piece and hindering electron transport. Due to the large expansion of sulfurShrinkage leading to collapse of the cathode structure. In addition, the growth of lithium dendrites due to non-uniform deposition of lithium ions is likely to penetrate the separator, resulting in short circuits and thermal runaway.

The physical and chemical properties of the electrolyte, which is one of the important components of the lithium-sulfur battery, in the ion path between the positive electrode and the negative electrode, deeply affect the performance of the electrochemical performance of the lithium-sulfur battery. The electrolyte is modified, and the new lithium-sulfur battery electrolyte formula is provided, which is a means with simple operation and remarkable improvement. The aim of improving the electrochemical performance of the lithium-sulfur battery is fulfilled by adding a small amount of additive. Currently, the most successful additive used is lithium nitrate. Lithium ions in the lithium nitrate can increase the concentration of the lithium ions and improve the ionic conductivity, nitrate radicals can generate an SEI film on the surface of the lithium negative electrode, the lithium negative electrode is protected from being eroded by polysulfide, the growth of lithium dendrite is inhibited, and the coulombic efficiency and the cycling stability of the lithium-sulfur battery are improved. Researchers add an additive (CN202010103131.8) with an imidazolinone ring structure to reduce the polarization effect in the charging and discharging process of the lithium-sulfur battery, improve the conversion efficiency of polysulfide, promote the dissolution of short-chain polysulfide and finally obviously improve the capacity and the cycling stability of the lithium-sulfur battery. Researchers also introduce multifunctional ether additives (CN201911248701.6), so that the loss of active substances of sulfur and lithium is reduced, the cycling stability of the battery is enhanced, the chemical reaction between polysulfide and metal lithium is inhibited, and the coulombic efficiency of the battery is improved.

Disclosure of Invention

In view of the above problems, a first object of the present invention is to provide a method of gelling an electrolyte.

The second purpose of the invention is to provide a gel electrolyte prepared by the preparation method.

A third object of the present invention is to provide a solid-state lithium secondary battery manufactured by the above manufacturing method.

A fourth object of the present invention is to provide a method for manufacturing the solid-state lithium secondary battery.

In order to solve the above problems, the technical scheme adopted by the invention is as follows:

a preparation method of ether gel electrolyte comprises the steps of carrying out gelation reaction on a solution containing an ether organic solvent, a supporting lithium salt, a zirconium salt and a nitrate;

wherein the mass percent of the zirconium salt is 2-8%; the mass percentage of the nitrate is 1-2%;

the ether organic solvent comprises a cyclic ether solvent.

The research of the invention finds that the zirconium salt can induce the ring-opening self-polymerization of the cyclic ether solvent to gelate, however, even if the brand new function of the zirconium salt is known, how to really realize the preparation of the gelled electrolyte, how to improve the stability of the prepared gelled electrolyte and how to improve the electrochemical performance of the prepared gelled electrolyte are still the technical problems which need to be mainly solved.

In the invention, the combination of the zirconium salt and the nitrate is innovatively found to synergistically induce the ring-opening self-polymerization gelation of the cyclic ether solvent, and further research finds that controlling the components at the required ratio contributes to further controlling the gelation behavior, further improving the gelation form and structure and further improving the electrochemical performance of the battery. It has also been found that if the amount of the additive is not controlled within this range, for example, below the lower limit or above the upper limit, gelation is not favored and/or the gelation morphology is poor, and electrochemical performance is not favored.

Preferably, the zirconium salt is at least one of zirconyl nitrate, zirconium fluoride, zirconium chloride, zirconium acetate, zirconium basic carbonate, zirconium acetylacetonate and zirconocene dichloride; further preferred is zirconyl nitrate.

Preferably, the nitrate is at least one of lithium nitrate, copper nitrate, cobalt nitrate, nickel nitrate, potassium nitrate, ferric nitrate and magnesium nitrate; lithium nitrate is more preferable.

Preferably, the zirconium salt is zirconyl nitrate and the nitrate is lithium nitrate. The research finds that the preferred zirconium salt and nitrate are adopted and further matched with the combined control of the proportion, so that the structure and the form of the gelled electrolyte can be adjusted and controlled, and the electrochemical performance can be improved on the premise of realizing gelation.

The research of the invention discovers that the mass ratio of the zirconium salt to the nitrate is controlled to be 1-4: 1; preferably 1-2: 1; further, when the ratio is controlled to 1:1, the construction of a stable gelled solid electrolyte can be unexpectedly realized, which contributes to the improvement of the electrochemical performance of the gelled electrolyte.

The research finds that under the combined use of the zirconium salt and the nitrate and the accurate control of the proportion, the concentration in the system is further controlled, and the electrochemical performance of the gel electrolyte can be improved on the premise of successfully realizing gelation.

Preferably, the mass percent of the zirconium salt is 2-4%; more preferably 2 to 2.5%.

Preferably, the mass percent of the nitrate is 1-2%; more preferably 1.5 to 2%.

It was found that controlling the concentration of the zirconium salt and nitrate to be in the above range is advantageous for achieving gelation, but it was found that a larger concentration of the component affects the morphology of the gel and, to a certain extent, the electrochemical performance.

The cyclic ether solvent can be an ether solvent with a ring structure well known in the industry, and comprises at least one of 1, 3-dioxolane, 1, 2-epoxycyclopentane, furan, tetrahydrofuran, 2, 3-dihydrofuran, 2, 5-dihydrofuran and crown ether.

Preferably, the cyclic ether solvent further comprises a linear ether solvent, preferably at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

In the present invention, the volume ratio of the cyclic ether solvent to the linear ether solvent is, for example, 1 to 5:1 to 5.

The support lithium salt is well known in the technical field of lithium batteries and comprises lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (fluorosulfonyl) imide (LiFSI), lithium trifluoromethanesulfonate (LiTf), lithium difluorooxalato borate (liddob), lithium difluorobis (oxalato) phosphate (lidbop), lithium dioxalate borate (LiBOB), lithium hexafluorophosphate (LiPF)₆) Lithium tetrafluoroborate (LiBF)₄) Lithium perchlorate (LiClO)₄) A mixture of one or more of them.

Preferably, the concentration of the supporting lithium salt is 0.5mol/L to 2 mol/L.

In the present invention, the temperature of the gelation reaction is 0 ℃ or higher; further preferably 10-90 ℃; further preferably 15 to 75 ℃.

The gelation reaction time is more than or equal to 0.5h, preferably 1-72 h; more preferably 6 to 60 hours.

The invention also provides an ether gel electrolyte prepared by adopting the preparation method of the ether gel electrolyte.

The invention also discloses a solid-state lithium secondary battery which comprises the ether gel electrolyte.

The invention also provides a preparation method of the solid-state lithium secondary battery, which comprises the steps of compounding the positive plate, the diaphragm and the negative plate into the battery cell in sequence, filling the battery cell into the battery shell, injecting a solution containing ether organic solvent, supporting lithium salt, zirconium salt and nitrate into the battery shell by using the preparation method of the ether gel electrolyte, and carrying out gelation reaction after packaging the battery to obtain the solid-state lithium secondary battery.

According to the invention, by virtue of the synergy of the components in the solution containing the ether organic solvent, the supporting lithium salt, the zirconium salt and the nitrate and the control of the component proportion, and further matching with self-polymerization in the battery, the gel electrolyte with a uniform structure can be obtained, the contact between the positive electrode and the negative electrode can be improved, good compatibility with the positive electrode and the negative electrode can be achieved, the loss of active substances can be effectively inhibited, and compared with a pure solid electrolyte, the gel electrolyte has smaller interface impedance and faster lithium ion transmission. Meanwhile, the electrochemical performance of the lithium battery can be effectively improved by introducing zirconium salt and nitrate.

Preferably, the positive plate comprises a positive current collector and a positive material compounded on the surface of the positive current collector; the positive electrode material is obtained by solidifying slurry of a positive electrode active material, a conductive agent, a binder and a solvent.

The positive active material is one or more of elemental sulfur, sulfur-containing polymer, lithium sulfide and lithium polysulfide.

The negative plate is one of metal lithium foil, a lithium plate, a lithium alloy and a silicon-carbon compound.

A lithium battery preferably using the gel electrolyte assembly, characterized in that: comprises a positive plate, a negative plate, a diaphragm and a shell package; the diaphragm is positioned between the positive plate and the negative plate, and the positive plate, the negative plate, the diaphragm and the gel electrolyte are sealed in the battery shell package. The positive plate is formed by coating a positive active material, a conductive agent and a binder on a current collector in proportion, wherein the positive active material is one or more of elemental sulfur, a sulfur-containing polymer, lithium sulfide and lithium polysulfide. The negative plate is one of metal lithium foil, a lithium plate, a lithium alloy and a silicon-carbon compound.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

1. the zirconium salt can induce the ring-opening self-polymerization gelation of the ether cyclic organic solvent.

2. Nitrate can improve the solubility of zirconium salt in ether solvents; the combination of the zirconium salt and the nitrate can synergistically improve ring-opening self-polymerization gelation of the cyclic ether;

3. the combination of nitrate and zirconium salt enables the gelling process to proceed spontaneously. The gel electrolyte components are derived from the components of the gel electrolyte, no additional initiator is needed to be introduced, and the influence of a trace amount of initiator on the electrochemical performance of the lithium battery is eliminated. The obtained gel electrolyte has uniform components and stable structure.

4. On the basis of the synergy of the nitrate and the zirconium salt, the concentration control is further matched, which is beneficial to further controlling the gelation state, obtaining the gel electrolyte with uniform property and stable structure and further improving the electrochemical performance of the battery.

5. On the basis of the coordination of nitrate and zirconium salt and the proportion control, the temperature and time of the gelation process are controlled, and the electrochemical performance of the battery is further improved by further matching with the mode of protomorphic self-polymerization in the battery.

6. The formed gel electrolyte can suppress a self-discharge phenomenon and loss of active materials during the cycling of the battery through a physical structure. Meanwhile, nitrate can generate a layer of SEI film on the surface of the lithium cathode, so that the lithium cathode is well protected, the growth of lithium dendrites is inhibited, the cycling stability of the lithium battery is improved, and the cycle life of the lithium battery is prolonged.

7. The optimized zirconium salt has low price and stable physicochemical property, can improve the safety of the lithium battery, and has wide application in the fields of preparation of solid electrolyte, catalyst and the like. The method is simple to operate and excellent in performance, so that the method has a wide industrial prospect.

Drawings

FIG. 1 is a lithium battery charge-discharge cycle diagram of the gel electrolyte of comparative example 1;

FIG. 2 is a lithium battery charge-discharge cycle diagram of the gel electrolyte prepared in example 1;

FIG. 3 is a graph showing the effects of the gel electrolyte prepared in example 1;

Detailed Description

The following examples are intended to illustrate the invention in further detail; and the scope of the claims of the present invention is not limited by the examples.

Example 1

The lithium battery is prepared by the following method:

preparation of gel electrolyte: in an argon atmosphere glove box (H)₂O is less than 0.1ppm), mixing organic solvent ethylene glycol dimethyl ether (DME) and 1, 3-Dioxolane (DOL) in a volume ratio of 1:1 with LiTFSI (1.0M), adding 2 percent by mass of lithium nitrate and 2 percent by mass of zirconyl nitrate, and fully and uniformly stirring to obtain the productThe above-mentioned lithium battery electrolyte (solution A) was allowed to stand for gelation, and the formation of a gel electrolyte was recorded. As a result, the picture of standing at room temperature of 20-35 ℃ for 24h is shown in FIG. 3, and it can be seen that gelation was successfully achieved without an initiator and a crosslinking agent based on the control of the components and the ratio. In addition, the gel can be formed by standing for 6 hours at 50-75 ℃.

Preparing a positive electrode: mixing a sulfur/carbon composite material (the sulfur carrying amount is 75%), acetylene black and PVDF according to the ratio of 8: 1, adding N-methylpyrrolidone (NMP) with a proper volume, placing the mixture into a homogenizer, stirring for 15min, and forming stable and uniform anode slurry at the rotating speed of 15 kr/min. The slurry was coated on carbon-coated aluminum foil using a doctor blade and placed in an oven at 60 ℃ for 12h until the NMP was completely volatilized.

Assembling and testing the button cell: and (3) punching the prepared sulfur pole piece into a round pole piece with the diameter of 13mm, and drying in an oven at the temperature of 55 ℃ for 1 h. In argon atmosphere, a metal lithium sheet is used as a negative electrode, a polypropylene microporous membrane with the model of Celgard 2400 is selected as a diaphragm, an electrolyte (namely the solution A) is injected into the battery before the gel electrolyte is formed, and the liquid-sulfur ratio is controlled to be 20 mu L/mg_sAnd sequentially assembling the lithium battery CR 2025. And (3) standing the assembled battery in a greenhouse (20-35 ℃) for 24 hours to ensure that the electrolyte packaged in the battery is converted into gel electrolyte. And (3) carrying out a charge-discharge cycle test on a blue test charge-discharge tester under the test condition of a multiplying power of 0.5C (1C: 1675mAh/g) charge-discharge cycle, setting an electrochemical window to be 1.7-2.8V, and circulating for 100 circles.

Examples 2 to 3 and comparative examples 1 to 2

The differences from example 1 are only in the components added to the gel electrolyte (i.e., the content of zirconium salt in solution a is different, as shown in table 1), and other parameters and preparation methods are the same as those of example 1.

Table 1 example and comparative example gel electrolyte formulations

Example 4 and comparative examples 3 to 4

The differences from example 1 are only in the addition components of the gel electrolyte (the content of nitrate in solution a is different, and is specifically shown in table 2), other parameters and preparation method as in example 1.

Table 2 example and comparative example gel electrolyte formulations

TABLE 3 summary of test results for examples and comparative examples

It was found that as the amount of lithium nitrate added increases, the solubility of zirconyl nitrate increases. When the addition amount of zirconyl nitrate is 2 wt.%, the additive 2 wt.% lithium nitrate may form a gel; when the addition amount of lithium nitrate was increased to 4 wt.%, no gel could be formed. When the same amount of lithium nitrate was added, the zirconium oxynitrate added at 1% and 2% was almost completely dissolved after stirring for 12 hours, but gel formation was only possible at 2% content. When the addition amount of the zirconyl nitrate is 4% and 8%, the viscosity is obviously increased after stirring for 24 hours, and gel is formed quickly after standing. When the amount of zirconyl nitrate exceeds the solubility, the suspension is formed after stirring, and the gel formed from the suspension has uneven properties and an unstable structure. The gel is susceptible to structural collapse during cycling, rendering the battery system ineffective. The specific discharge capacity and coulombic efficiency of examples 2 and 3 were significantly reduced due to the influence of viscosity and gel properties. Comparative example 2 failed to gel, resulting in loss of active material and decreased capacity retention compared to example 1. The content of zirconium oxynitrate is certain, when the content of lithium nitrate is lower, gel can be formed, but the lithium nitrate is consumed in the circulation process, the protection of a lithium negative electrode is weakened, and the circulation stability is reduced; when the content of lithium nitrate is higher, gel cannot be formed, the viscosity of electrolyte can be improved, the specific discharge capacity of the first ring is reduced, and the stability and the coulombic efficiency are still kept at higher levels due to the good protection effect on the lithium cathode. When the contents of zirconyl nitrate and lithium nitrate are both 2%, a gel electrolyte having the most stable structure and the most excellent properties can be formed. The formed gel electrolyte can inhibit the self-discharge phenomenon and the loss of active materials during the cycle of the lithium battery through a physical structure. Meanwhile, nitrate radicals in the auxiliary additive can generate a layer of SEI film containing nitrogen oxide on the surface of the lithium negative electrode, so that the lithium negative electrode is protected from corrosion of polysulfide, growth of lithium dendrite is inhibited, the cycle stability of the lithium battery is improved, and the cycle life of the lithium battery is prolonged.

Examples 5 to 7

The differences from example 1 are only in the components added to the gel electrolyte (the type of zirconium salt is different, and specifically shown in table 4), other parameters, and the preparation method, which are the same as those of example 1.

Table 4 example gel electrolyte formulation

Examples 8 to 10

The differences from example 1 are only in the components added to the gel electrolyte (the types of nitrates are different, and specifically shown in table 5), the other parameters, and the preparation method, which are the same as those of example 1.

Table 5 example gel electrolyte formulation

TABLE 6 summary of test results for the examples

It was found that substitution of zirconyl nitrate for other zirconium salts such as zirconium nitrate, zirconium fluoride and zirconium chloride maintained the coulombic efficiency at a higher level due to the protection of the lithium negative electrode by nitrate and fluoride ions. The substitution of lithium nitrate for other nitrates such as cobalt nitrate, nickel nitrate and copper nitrate is not very different in average coulombic efficiency since all three are nitrates. Since copper ions may react irreversibly with sulfur species, severe loss of active species is caused, resulting in severe drop in capacity retention. In comparison with example 1, examples 5 to 10 show that, by combining zirconyl nitrate and lithium nitrate, with precise control of the ratio, a more stable gelled electrolyte can be obtained unexpectedly, contributing to unexpected improvements in electrochemical properties of the gelled electrolyte, such as cycle stability and cycle life.

Claims

1. a preparation method of ether gel electrolyte, is characterized in that, the solution that comprises ether organic solvent, support lithium salt, zirconium salt and nitrate is carried out gelation reaction and obtains;

Wherein, the mass percentage of the zirconium salt is 2-8%; the mass percentage of the nitrate is 1-2%;

The ether-based organic solvents include cyclic ether-based solvents.

2. The preparation method according to claim 1, wherein the zirconium salt comprises zirconium oxynitrate, zirconium nitrate, zirconium fluoride, zirconium chloride, zirconium acetate, basic zirconium carbonate, zirconium acetylacetonate, At least one of the chlorozirconocenes.

3. The preparation method of claim 1, wherein the nitrate comprises at least one of lithium nitrate, copper nitrate, cobalt nitrate, nickel nitrate, potassium nitrate, iron nitrate, and magnesium nitrate.

4. The preparation method of claim 1, wherein the mass ratio of the zirconium salt and the nitrate is controlled at 1 to 4:1.

5. The preparation method of claim 1, wherein the mass ratio of the zirconium salt and the nitrate is controlled at 1 to 2:1.

6. The preparation method of claim 1, wherein the mass percentage of the zirconium salt is 2-3%;

The mass percentage of the nitrate is 1-2%.

7. The preparation method according to any one of claims 1 to 6, wherein the cyclic ether solvent is 1,3-dioxolane, 1,2-epoxycyclopentane, At least one of furan, tetrahydrofuran, 2,3-dihydrofuran, 2,5-dihydrofuran and crown ether.

8 . The preparation method according to claim 7 , wherein the cyclic ether solvent further comprises a linear ether solvent. 9 .

9. preparation method as claimed in claim 8 is characterized in that, linear ether solvent is ethylene glycol dimethyl ether, glyme dimethyl ether, tripolyethylene glycol dimethyl ether, tetraethylene glycol at least one of dimethyl ether.

10. The preparation method of claim 1, wherein the supported lithium salt comprises lithium bis(trifluoromethanesulfonyl)imide, lithium bisfluorosulfonylimide, lithium trifluoromethanesulfonate, A mixture of one or more of lithium difluorooxalate borate, lithium difluorobis(oxalato)phosphate, lithium dioxalateborate, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium perchlorate.

11 . The preparation method according to claim 1 , wherein the concentration of the supporting lithium salt therein is 0.5 mol/L to 2 mol/L. 12 .

12. The preparation method according to claim 1, wherein the temperature of gelation is greater than or equal to 0°C.

13. The preparation method according to claim 12, wherein the temperature of gelation is 10-90°C.

14. The preparation method according to claim 12, wherein the temperature of gelation is 15-75°C.

15. The preparation method of claim 1, wherein the gelation reaction time is greater than or equal to 0.5h.

16. The preparation method of claim 15, wherein the gelation reaction time is 1-72 h.

17. The preparation method of claim 15, wherein the gelation reaction time is 6-60h.

18 . An ether gel electrolyte, characterized in that, it is prepared by the preparation method according to any one of claims 1 to 17 .

19 . A solid-state lithium secondary battery comprising the ether-based gel electrolyte according to claim 18 .

20. A method for preparing a solid-state lithium secondary battery according to claim 19, wherein the positive electrode sheet, the separator and the negative electrode sheet are sequentially compounded into a battery cell, the battery core is loaded into the battery case, and the battery cell is placed in the battery case. The solution described in the preparation method of claims 1 to 17 is injected, and gelation is carried out after encapsulation, and then the solution is obtained.