CN113270688A - Cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm and preparation method and application thereof - Google Patents
Cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm and a preparation method and application thereof, wherein the modified lithium-sulfur battery diaphragm comprises a basic diaphragm and a modified functional layer; the base diaphragm is a nanofiber membrane; the modified functional layer comprises a cyclodextrin layer and a graphite carbon layer which are respectively arranged on two sides of the basic diaphragm. The lithium-sulfur battery assembled by the cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm prepared by the invention has high ionic conductivity of 1.3-1.8 mS/cm and low interface impedance of 60-70 omega; under the current density of 0.2C, the first discharge specific capacity is as high as more than 1300 mAh/g.
Description
Technical Field
The invention relates to the field of material chemistry, in particular to a cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm and a preparation method and application thereof.
Background
With the continuous miniaturization of electronic equipment and the rapid development of mobile communication equipment, portable electronic information products, electric automobiles and energy storage power stations, transition metal oxides such as lithium cobaltate (LiCoO) have been traditionally used2) Lithium manganate (LiMn)2O4) And lithium nickelate (LiNiO)2) Lithium ion batteries, which are positive electrode materials, have not been able to meet the overall development requirements, particularly the requirements of high specific capacity and high energy density. The theoretical specific capacity of the lithium-sulfur battery is about 5 times that of the lithium-ion battery, and the lithium-sulfur battery becomes a candidate for the next-generation high-energy-density secondary battery.
The active substance sulfur has rich natural resources, low toxicity and low cost, and can be used as a positive electrode material to ensure that the mass and the volume energy density of a lithium-sulfur battery system consisting of the active substance sulfur and metallic lithium respectively reach 2600 Wh.kg-1And 2800Wh kg-1And has an Ah.g of 1675m-1The theoretical specific capacity of (a). The high capacity and chargeable and dischargeable performance of elemental sulfur is derived from S8Electrochemical cleavage and re-bonding of the S-S bond in the molecule is a multi-step electron-gain-loss redox reaction.
Compared with the traditional lithium ion battery, the multi-electron reaction characteristic of sulfur molecules brings the high-capacity characteristic of an electrode material, but the lithium sulfur battery system has more problems. During charging and discharging processIn the lithium-sulfur battery, soluble polysulfide as an intermediate product of redox reaction in the lithium-sulfur battery is dissolved in ether electrolyte, and because the pore diameter of a commercial diaphragm is far larger than the size of polysulfide, the polysulfide can shuttle between a positive electrode and a negative electrode through the diaphragm to form a shuttle effect, and meanwhile, the shuttle reaches the negative electrode and can react with metal lithium to generate insoluble Li2S2Or Li2S is deposited on the electrode, which not only corrodes the lithium cathode to destroy the SEI film, but also causes the loss of active substances, reduces the utilization rate of S, and causes the rapid attenuation of the battery capacity, poor cycle performance and short service life of the battery. In addition, the lithium ion deposition process is easily influenced by uneven electric field distribution, and the charge-dense deposition speed at the bulge is higher, so that dendritic crystals are formed to cause potential safety hazards.
In order to suppress the polysulfide shuttle effect, the current research is mainly to control the shuttle effect by three methods, namely physical adsorption, chemical adsorption and electrostatic repulsion. The physical adsorption method mainly utilizes van der waals force between a porous carbon material with high specific surface area and lithium polysulfide to inhibit shuttle action, and the long-cycle requirement of the battery is difficult to meet because the van der waals force is relatively small and the polysulfide cannot be effectively adsorbed. Electrostatic repulsion mainly utilizes the repulsion between negatively charged sulfonic acid groups, carboxyl groups and the like and polysulfide anions to limit the anions in a positive electrode area, but the limited number of negatively charged functional groups cannot meet the electrostatic inhibition of polysulfide generated by repeated circulation, so that a certain polysulfide shuttling problem is caused. Neither physical adsorption nor electrostatic repulsion effectively solves the shuttling problem of polysulfides. The chemisorption method is the most widely used method for capturing polysulfides, but the capture of polysulfides must ensure the presence of polar groups and depends on the amount of bond energy formed between the polar groups and the polysulfides, and thus the chemisorption method has limitations.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm and a preparation method and application thereof. The cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm prepared by the invention can improve the rate capability of the lithium-sulfur battery, improve the affinity between the diaphragm and electrolyte, effectively block the shuttle of polysulfide, improve the utilization rate of active substances, improve the cycle performance and the service life of the lithium-sulfur battery, and ensure that the lithium-sulfur battery has good safety performance.
The technical scheme of the invention is as follows:
a cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm comprises a basic diaphragm and a modified functional layer; the base diaphragm is a nanofiber membrane; the modified functional layer comprises a cyclodextrin layer and a graphite carbon layer which are respectively arranged on two sides of the basic diaphragm.
The nanofiber membrane is prepared from cellulose acetate through electrostatic spinning, has a three-dimensional reticular structure and is 18-22 mu m thick; the cellulose acetate is one or more of cellulose monoacetate, cellulose diacetate and cellulose triacetate.
The cyclodextrin layer is a molecular sieve membrane formed by an interfacial polymerization method, and the aperture is 0.6-0.9 nm.
The graphite carbon layer is prepared by a magnetron sputtering physical deposition method, and the thickness of the graphite carbon layer is 50-100 nm.
A preparation method of a cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm comprises the following steps:
(1) weighing cellulose acetate, adding the cellulose acetate into a mixed solution of acetone and N, N-dimethylacetamide, stirring, standing and defoaming to obtain a cellulose acetate solution;
(2) placing the cellulose acetate solution prepared in the step (1) into an injector, installing the injector on an injection pump, setting spinning voltage to be 14-18 KV, receiving distance to be 10-20 cm and propelling speed to be 0.8-1.2 mL/h, and turning on the injection pump to carry out electrostatic spinning to obtain a basic diaphragm;
(3) weighing cyclodextrin and NaOH, and preparing a solution by using deionized water;
(4) placing the basic diaphragm prepared in the step (2) above a culture dish, slowly pouring the solution prepared in the step (3) onto the surface of the basic diaphragm, absorbing and removing the solution after impregnation, dropwise adding a trimesoyl chloride solution onto the upper surface of the basic diaphragm, absorbing and removing redundant solution after reaction, washing with water to remove the redundant trimesoyl chloride solution on the upper surface of the basic diaphragm and the cyclodextrin solution on the lower surface of the basic diaphragm, taking out the basic diaphragm, naturally airing, and drying to obtain the basic diaphragm with one cyclodextrin modified side;
(5) and (3) mounting the base diaphragm which is prepared in the step (4) and is modified by cyclodextrin and the graphite carbon target material on one side in a vacuum chamber of magnetron sputtering equipment, setting sputtering parameters, introducing argon, and opening the magnetron sputtering equipment for sputtering to obtain the cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm.
Further, the mass concentration of the cellulose acetate is 12-15%; the mass ratio of the acetone to the N, N-dimethylacetamide is (1-2): 1; the stirring speed is 120-150 r/min, and the stirring time is 36-48 h; the standing time is 1-2 h.
Further, in the step (2), the electrostatic spinning time is 24-36 h; the diameter of a single fiber of the electrostatic spinning is 180-240 nm; in the solution obtained in the step (3), the mass concentration of cyclodextrin is 0.3-0.4%, and the mass concentration of NaOH is 0.45-0.55%.
Further, in the step (4), the size of the culture dish is smaller than that of the basic diaphragm; the dipping time is 20-40 min; the mass concentration of the trimesoyl chloride solution is 0.1-0.4%; the reaction time is 3-10 min; the natural airing time is 0.5-1 h; the drying temperature is 50-70 ℃, and the drying time is 10-12 h.
Further, in the step (5), the surface of the basic diaphragm which is not modified by the cyclodextrin is opposite to the graphite carbon target material; the sputtering parameters are as follows: sputtering power is 50-100 w, and working pressure is 0.5-1.0 Pa; the vacuum degree of the vacuum chamber is 7 x 10-4～6*10-4Pa, the introducing speed of the argon is 25-35 cm3Min; the sputtering time is 20-40 min; the thickness of the sputtered carbon layer is 50-100 nm; the thickness of the cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm is 18.2-22.2 microns.
A lithium sulfur battery prepared with the cyclodextrin/graphitic carbon-modified lithium sulfur battery separator comprising: the lithium-sulfur battery comprises a positive electrode, a negative electrode, a cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm and electrolyte; the positive electrode comprises a carbon material and a sulfur active substance, wherein the carbon material is acetylene black; the sulfur active substance is sublimed sulfur; the negative electrode is a lithium sheet; the cyclodextrin layer of the cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm faces the cathode, and the graphite carbon layer faces the anode; the electrolyte consists of 1, 3-dioxolane, ethylene glycol dimethyl ether, lithium bistrifluoromethylenesulfonate imide and lithium nitrate.
The beneficial technical effects of the invention are as follows:
(1) according to the method, a substance with a molecular sieve structure is modified on a diaphragm, and a nanometer pore channel of the substance is utilized to realize selective passing of lithium ions, wherein the pore diameter of the molecular sieve pore structure is far larger than that of the lithium ions and smaller than the size of polysulfide, so that the polysulfide is completely blocked on the cathode side of a battery; by utilizing the strong interaction between chemical groups on the membrane and polysulfide, the shuttle of the polysulfide can be effectively inhibited; the molecular sieve barrier is cooperated with a chemical adsorption method, polysulfide is captured by double effects, and shuttle effect can be inhibited to the maximum extent.
(2) The nanofiber membrane with high porosity can promote the rapid transfer of ions in the charging and discharging processes, and realize rapid charging and discharging, so that the rate performance of a lithium-sulfur battery is improved; the cellulose acetate nano-film rich in polar hydroxyl groups improves the affinity between the diaphragm and electrolyte, and can form strong interaction with polysulfide to adsorb the polysulfide chemically.
(3) The aperture of the basic diaphragm modified by cyclodextrin on one side prepared by the method is 0.6-0.9 nm, is larger than the size of lithium ions (0.076nm) and smaller than the size of polysulfide (1.2-1.7 nm), so that shuttling of polysulfide can be physically blocked, the utilization rate of sulfur active substances is improved, and the cycle performance and the service life of the lithium-sulfur battery are improved.
(4) The graphite carbon layer prepared by the method has high electric and thermal conductivity, can promote lithium to be uniformly deposited, and reduces the growth of lithium dendrites; the coating prepared by the magnetron sputtering technology has the advantages that the nano-scale coating thickness does not cause the increase of interface impedance, so that the lithium-sulfur battery has good safety performance.
(5) According to the invention, the electrostatic spinning nanofiber membrane is adopted to improve the porosity and electrolyte affinity of the diaphragm, and effectively promote the transmission rate of ions in the charge and discharge processes; the prepared cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm effectively inhibits shuttling of polysulfide through a physical barrier and chemical adsorption method, simultaneously solves the problems of growth and uneven deposition of lithium dendrite, and further promotes the cycle performance and rate performance of the battery.
(6) The lithium-sulfur battery assembled by the cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm prepared by the method has high ionic conductivity of 1.3-1.8 mS/cm and low interface impedance of 60-70 omega; under the current density of 0.2C, the first discharge specific capacity is up to more than 1300mAh/g, and the specific capacity of more than 821mAh/g can be still maintained after 500 cycles; after 500 cycles at a current density of 0.2C, the capacity fade was about 37%.
Drawings
Fig. 1 is a schematic structural view of a functional separator.
Fig. 2 is a schematic diagram of the mechanism of operation of a battery comprising a functional separator.
Fig. 3 is a 500 cycle diagram of a lithium sulfur battery assembled with a cyclodextrin/graphitic carbon-modified lithium sulfur battery separator prepared in example 1.
Fig. 4 is an assembly configuration diagram of a button-type lithium sulfur battery.
In the figure: 1. a positive electrode case; 2. an electrolyte; 3. a lithium sheet; 4. a stainless steel sheet; 5. a spring plate; 6. a negative electrode case; 7. a battery separator; 8. a sulfur cathode plate.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings and examples. It should be noted that these embodiments are not intended to limit the present invention, and those skilled in the art should be able to make functional, methodical, or structural equivalents or substitutions according to these embodiments without departing from the scope of the present invention.
Fig. 1 is a schematic structural view of a functional separator according to the present application. As can be seen from fig. 1, the cyclodextrin/graphitic carbon modified lithium sulfur battery separator prepared by the present application comprises a base separator and a modified functional layer; the base diaphragm is a nanofiber membrane; the modified functional layer comprises a cyclodextrin layer and a graphite carbon layer which are respectively arranged on two sides of the basic diaphragm.
Fig. 2 is a schematic diagram of the operation mechanism of a battery comprising the functional separator of the present application. As can be seen from fig. 2, in the lithium sulfur battery containing the functional separator, sulfur molecules are subjected to a reduction reaction to generate polysulfides at the sulfur cathode, and when the polysulfides pass through the functional separator, the shuttle effect of the polysulfides can be synergistically inhibited by the functional separator through a chemisorption method and a molecular sieve barrier method; at the lithium anode, lithium simple substances are subjected to oxidation reaction to generate lithium ions, and the lithium ions are mutually transferred in the cathode region and the anode region through the diaphragm, so that the charging and discharging processes of the lithium-sulfur battery are realized.
Example 1
A cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm is prepared by the following steps:
the first step is as follows: preparing a basic diaphragm by an electrostatic spinning technology:
weighing acetone and N, N-dimethylacetamide according to a mass ratio of 1:1 to obtain a mixed solution, weighing cellulose diacetate, dissolving the cellulose diacetate in the mixed solution of acetone and N, N-dimethylacetamide to obtain 15% cellulose diacetate, stirring at a rotating speed of 150r/min for 48 hours to obtain a transparent spinning solution, standing for 2 hours to remove bubbles, and then placing the spinning solution in an injector and loading the spinning solution on an injection pump for spinning for 30 hours. Setting spinning process parameters as spinning voltage 16KV, receiving distance 15cm, advancing speed 1.0mL/h, and continuously spinning for 30h to obtain the basic diaphragm with the fiber diameter of 180nm and the thickness of 20 μm.
The second step is that: preparing a base diaphragm with cyclodextrin modified on one side by an interfacial polymerization method:
preparing cyclodextrin with the mass concentration of 0.35% and sodium hydroxide with the mass concentration of 0.5% into cyclodextrin water solution by using deionized water. Placing a circular basic diaphragm with the diameter of 15cm in a culture dish container with the diameter of 10cm, adding the cyclodextrin aqueous solution, soaking the part of the basic diaphragm which is in contact with the container for 30 minutes, then discharging liquid, gently adding 8mL of trimesoyl chloride solution with the mass concentration of 0.2% on the surface of the basic diaphragm, carrying out interfacial polymerization on the cyclodextrin on one side of the basic diaphragm through connection of trimesoyl chloride to form a film, absorbing and removing redundant liquid after reacting for 5 minutes, washing with water to remove redundant trimesoyl chloride solution on the upper surface of the basic diaphragm and cyclodextrin solution on the lower surface of the basic diaphragm, taking out the basic diaphragm, naturally airing for 1 hour, and drying for 12 hours at 60 ℃ to prepare the basic diaphragm with the cyclodextrin modified on one side, wherein the aperture of a cyclodextrin layer is 0.6-0.9 nm.
The third step: preparing a cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm by a magnetron sputtering technology:
installing a base diaphragm with cyclodextrin modification on one side and a graphite carbon target material in a vacuum chamber of high-vacuum multifunctional magnetron sputtering equipment, wherein the installation is to make the surface of the base diaphragm which is not modified by cyclodextrin opposite to the graphite carbon target material so that the vacuum degree reaches 6.6 x 10 of the background vacuum degree-4At Pa, at a distance of 30cm3Introducing argon gas at a speed of/min, starting a magnetron sputtering device, sputtering for 30 minutes under the sputtering power of 80W and the working pressure of 0.8Pa, and depositing the graphite carbon with the thickness of 80nm to obtain the cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm with the thickness of 20.2 mu m.
Example 2
A cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm is prepared by the following steps:
the first step is as follows: preparing a basic diaphragm by an electrostatic spinning technology:
weighing acetone and N, N-dimethylacetamide according to a mass ratio of 1.5:1 to obtain a mixed solution, weighing cellulose monoacetate, dissolving the cellulose monoacetate in the mixed solution of the acetone and the N, N-dimethylacetamide to obtain 13% cellulose monoacetate, stirring at a rotating speed of 120r/min for 36 hours to obtain a transparent spinning solution, standing for defoaming for 1 hour, and then placing the spinning solution in an injector and loading the injection pump for spinning for 24 hours. Setting the spinning process parameters as spinning voltage 14KV, receiving distance 10cm, advancing speed 0.8mL/h, and continuously spinning for 24h to obtain the basic diaphragm with fiber diameter of 240nm and thickness of 18 μm.
The second step is that: preparing a base diaphragm with cyclodextrin modified on one side by an interfacial polymerization method:
preparing cyclodextrin with the mass concentration of 0.30% and sodium hydroxide with the mass concentration of 0.45% to form cyclodextrin water solution. Placing a circular base diaphragm with the diameter of 15cm in a culture dish container with the diameter of 10cm, adding the cyclodextrin aqueous solution, soaking the part of the base diaphragm which is in contact with the container for 20 minutes, then discharging liquid, gently adding 5mL of trimesoyl chloride solution with the mass concentration of 0.1% on the surface of the base diaphragm, carrying out interfacial polymerization on the cyclodextrin on one side of the base diaphragm through connection of trimesoyl chloride to form a film, absorbing and removing redundant liquid after reacting for 3 minutes, washing with water to remove redundant trimesoyl chloride solution on the upper surface of the base diaphragm and cyclodextrin solution on the lower surface of the base diaphragm, taking out the base diaphragm, naturally airing for 0.5h, and drying for 11h at 50 ℃ to prepare the base diaphragm with the cyclodextrin modified on one side, wherein the aperture of a cyclodextrin layer is 0.6-0.9 nm.
The third step: preparing a cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm by a magnetron sputtering technology:
installing a base diaphragm with cyclodextrin modification on one side and a graphite carbon target material in a vacuum chamber of high-vacuum multifunctional magnetron sputtering equipment, wherein the installation is to make the surface of the base diaphragm which is not modified by cyclodextrin opposite to the graphite carbon target material so that the vacuum degree reaches 6.0 x 10 of the background vacuum degree-4At Pa, at a distance of 25cm3Introducing argon gas at a speed of/min, starting a magnetron sputtering device, sputtering for 20 minutes under the sputtering power of 50W and the working pressure of 0.5Pa, and depositing graphite carbon with the thickness of 50nm to obtain the cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm with the thickness of 18.2 mu m.
Example 3
A cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm is prepared by the following steps:
the first step is as follows: preparing a basic diaphragm by an electrostatic spinning technology:
weighing acetone and N, N-dimethylacetamide according to a mass ratio of 2:1 to obtain a mixed solution, weighing cellulose triacetate, dissolving the cellulose triacetate in the mixed solution of acetone and N, N-dimethylacetamide to obtain 12% cellulose monoacetate, stirring at a rotating speed of 135r/min for 42 hours to obtain a transparent spinning solution, standing for defoaming for 1.5 hours, and then placing the spinning solution in an injector and loading the injection pump for spinning for 36 hours. Setting the spinning process parameters as spinning voltage 18KV, receiving distance 20cm, advancing speed 1.2mL/h, and continuously spinning for 36h to obtain the basic diaphragm with the fiber diameter of 200nm and the thickness of 22 μm.
The second step is that: preparing a base diaphragm with cyclodextrin modified on one side by an interfacial polymerization method:
preparing cyclodextrin with mass concentration of 0.40% and sodium hydroxide with mass concentration of 0.55% to form cyclodextrin water solution. Placing a circular base diaphragm with the diameter of 15cm in a culture dish container with the diameter of 10cm, adding the cyclodextrin aqueous solution, soaking the part of the base diaphragm which is in contact with the container for 40 minutes, then discharging liquid, gently adding 6.5mL of trimesoyl chloride solution with the mass concentration of 0.4% on the surface of the base diaphragm, carrying out interfacial polymerization on the cyclodextrin on one side of the base diaphragm through connection of the trimesoyl chloride to form a film, absorbing and removing redundant liquid after reacting for 10 minutes, washing with water to remove redundant trimesoyl chloride solution on the upper surface of the base diaphragm and cyclodextrin solution on the lower surface of the base diaphragm, taking out the base diaphragm, naturally airing for 0.8h, and drying for 10h at 70 ℃ to prepare the base diaphragm with the cyclodextrin modified on one side, wherein the aperture of a cyclodextrin layer is 0.6-0.9 nm.
The third step: preparing a cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm by a magnetron sputtering technology:
installing a base diaphragm with cyclodextrin modification on one side and a graphite carbon target material in a vacuum chamber of high-vacuum multifunctional magnetron sputtering equipment, wherein the installation is to make the surface of the base diaphragm which is not modified by cyclodextrin opposite to the graphite carbon target material so that the vacuum degree reaches 7.0 x 10 of the background vacuum degree-4At Pa, at a distance of 35cm3Introducing argon gas at a speed of/min, starting a magnetron sputtering device, sputtering for 40 minutes under the sputtering power of 100W and the working pressure of 1.0Pa, and depositing graphite carbon with the thickness of 100nm to obtain the cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm with the thickness of 22.2 mu m.
Comparative example 1
The lithium sulfur battery separator is a commercial polypropylene separator.
Comparative example 2
The lithium-sulfur battery diaphragm is a cellulose acetate diaphragm.
Weighing acetone and N, N-dimethylacetamide according to a mass ratio of 1:1 to obtain a mixed solution, weighing cellulose diacetate, dissolving the cellulose diacetate in the mixed solution of acetone and N, N-dimethylacetamide to obtain 15% cellulose diacetate, stirring at a rotating speed of 150r/min for 48 hours to obtain a transparent spinning solution, standing for 2 hours to remove bubbles, and then placing the spinning solution in an injector and loading the spinning solution on an injection pump for spinning for 30 hours. Setting spinning process parameters as spinning voltage 16KV, receiving distance 15cm, advancing speed 1.0mL/h, and continuously spinning for 30h to obtain the basic diaphragm with the fiber diameter of 180nm and the thickness of 20 μm.
Comparative example 3
The lithium-sulfur battery diaphragm is a cyclodextrin/cellulose acetate film.
The first step is as follows: preparing a basic diaphragm by an electrostatic spinning technology:
weighing acetone and N, N-dimethylacetamide according to a mass ratio of 1:1 to obtain a mixed solution, weighing cellulose diacetate, dissolving the cellulose diacetate in the mixed solution of acetone and N, N-dimethylacetamide to obtain 15% cellulose diacetate, stirring at a rotating speed of 150r/min for 48 hours to obtain a transparent spinning solution, standing for 2 hours to remove bubbles, and then placing the spinning solution in an injector and loading the spinning solution on an injection pump for spinning for 30 hours. Setting spinning process parameters as spinning voltage 16KV, receiving distance 15cm, advancing speed 1.0mL/h, and continuously spinning for 30h to obtain the basic diaphragm with the fiber diameter of 180nm and the thickness of 20 μm.
The second step is that: preparing a base diaphragm with cyclodextrin modified on one side by an interfacial polymerization method:
preparing cyclodextrin with the mass concentration of 0.35% and sodium hydroxide with the mass concentration of 0.5% into cyclodextrin water solution by using deionized water. Placing a circular basic diaphragm with the diameter of 15cm in a culture dish container with the diameter of 10cm, adding the cyclodextrin aqueous solution, soaking the part of the basic diaphragm which is in contact with the container for 30 minutes, then discharging liquid, gently adding 8mL of trimesoyl chloride solution with the mass concentration of 0.2% on the surface of the basic diaphragm, carrying out interfacial polymerization on the cyclodextrin on one side of the basic diaphragm through connection of trimesoyl chloride to form a film, absorbing and removing redundant liquid after reacting for 5 minutes, washing with water to remove redundant trimesoyl chloride solution on the upper surface of the basic diaphragm and cyclodextrin solution on the lower surface of the basic diaphragm, taking out the basic diaphragm, naturally airing for 1 hour, and drying for 12 hours at 60 ℃ to prepare the basic diaphragm with the cyclodextrin modified on one side, wherein the aperture of a cyclodextrin layer is 0.6-0.9 nm.
Test example:
the method for assembling the button type lithium-sulfur battery containing the battery diaphragm comprises the following steps:
as shown in fig. 4, the button cell is assembled by sequentially arranging the negative electrode case, the spring plate, the stainless steel gasket, the lithium sheet, the lithium-sulfur battery electrolyte, the battery diaphragm, the lithium-sulfur battery electrolyte, the sulfur cathode sheet and the positive electrode case.
The preparation of the sulfur cathode pole piece is that 0.08g of acetylene black and 0.24g of sulfur powder are mixed and ground for 0.5h, 2-3 drops of NMP (N, N-dimethyl pyrrolidone) are dripped, stirred into uniform slurry to be coated on aluminum foil paper, and the uniform slurry is dried in vacuum for 12h at the temperature of 60 ℃ to obtain the carbon-sulfur composite cathode material.
The lithium-sulfur battery separators prepared in examples 1 to 3 and the battery separators prepared in comparative examples 1 to 3 were assembled into a button-type lithium-sulfur battery according to the assembly method of the test example, and the ionic conductivity and the interfacial impedance were tested using an electrochemical workstation, where the test parameters of the electrochemical workstation were set as follows: high frequency 106Hz, low frequency 1Hz, the amplitude is set to 0.01V when the ionic conductivity is measured, and the amplitude is set to 0.02V when the interfacial impedance is measured; the battery test system is used for testing the cycle performance and the rate performance of the diaphragm for 500 times, wherein the initial voltage is 1.5V, the cut-off voltage is 3.0V, the current density is 0.2C, and the test results are shown in Table 1.
TABLE 1
As can be seen from Table 1: compared with comparative examples 1 to 3, the battery separators prepared in examples 1 to 3 have the advantages that the barrier to polysulfides is more effective, the ionic conductivity is improved, the interfacial impedance is reduced, the polysulfides are effectively captured, the loss of active substances is reduced, the battery cycle is more stable, the discharge capacity is further improved, and the electrochemical performances related to the rate capability and the like of the battery are remarkably enhanced.
Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. A cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm is characterized by comprising a basic diaphragm and a modified functional layer; the base diaphragm is a nanofiber membrane; the modified functional layer comprises a cyclodextrin layer and a graphite carbon layer which are respectively arranged on two sides of the basic diaphragm.
2. The cyclodextrin/graphite carbon modified lithium-sulfur battery separator according to claim 1, wherein the nanofiber membrane is prepared from cellulose acetate by electrospinning, has a three-dimensional network structure, and has a thickness of 18-22 μm; the cellulose acetate is one or more of cellulose monoacetate, cellulose diacetate and cellulose triacetate.
3. The cyclodextrin/graphite carbon-modified lithium-sulfur battery separator according to claim 1, wherein the cyclodextrin layer is a molecular sieve membrane formed by an interfacial polymerization method, and the pore diameter is 0.6 to 0.9 nm.
4. The cyclodextrin/graphitic carbon-modified lithium-sulfur battery separator according to claim 1, wherein the graphitic carbon layer is prepared by physical deposition and has a thickness of 50 to 100 nm.
5. A method of preparing a cyclodextrin/graphitic carbon-modified lithium-sulfur battery separator according to claim 1, comprising the steps of:
(1) weighing cellulose acetate, adding the cellulose acetate into a mixed solution of acetone and N, N-dimethylacetamide, stirring, standing and defoaming to obtain a cellulose acetate solution;
(2) placing the cellulose acetate solution prepared in the step (1) into an injector, installing the injector on an injection pump, setting spinning voltage to be 14-18 KV, receiving distance to be 10-20 cm and propelling speed to be 0.8-1.2 mL/h, and turning on the injection pump to carry out electrostatic spinning to obtain a basic diaphragm;
(3) weighing cyclodextrin and NaOH, and preparing a solution by using deionized water;
(4) placing the basic diaphragm prepared in the step (2) above a culture dish, slowly pouring the solution prepared in the step (3) onto the surface of the basic diaphragm, absorbing and removing the solution after impregnation, dropwise adding a trimesoyl chloride solution onto the upper surface of the basic diaphragm, absorbing and removing redundant solution after reaction, washing with water to remove the redundant trimesoyl chloride solution on the upper surface of the basic diaphragm and the cyclodextrin solution on the lower surface of the basic diaphragm, taking out the basic diaphragm, naturally airing, and drying to obtain the basic diaphragm with one cyclodextrin modified side;
(5) and (3) mounting the base diaphragm which is prepared in the step (4) and is modified by cyclodextrin and the graphite carbon target material on one side in a vacuum chamber of magnetron sputtering equipment, setting sputtering parameters, introducing argon, and opening the magnetron sputtering equipment for sputtering to obtain the cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm.
6. The preparation method according to claim 5, wherein in the step (1), the mass concentration of the cellulose acetate is 12-15%; the mass ratio of the acetone to the N, N-dimethylacetamide is (1-2): 1; the stirring speed is 120-150 r/min, and the stirring time is 36-48 h; the standing time is 1-2 h.
7. The preparation method according to claim 5, wherein in the step (2), the electrostatic spinning time is 24-36 h; the diameter of a single fiber of the electrostatic spinning is 180-240 nm; in the solution obtained in the step (3), the mass concentration of cyclodextrin is 0.3-0.4%, and the mass concentration of NaOH is 0.45-0.55%.
8. The method according to claim 5, wherein in the step (4), the size of the culture dish is smaller than that of the base membrane; the dipping time is 20-40 min; the mass concentration of the trimesoyl chloride solution is 0.1-0.4%; the reaction time is 3-10 min; the natural airing time is 0.5-1 h; the drying temperature is 50-70 ℃, and the drying time is 10-12 h.
9. The method according to claim 5, wherein in the step (5), the mounting is performed by facing a surface of the base separator which is not modified with cyclodextrin, with a graphite carbon target material; the sputtering parameters are as follows: sputtering power is 50-100 w, and working pressure is 0.5-1.0 Pa; the vacuum degree of the vacuum chamber is 7 x 10-4～6*10-4Pa, the introducing speed of the argon is 25-35 cm3Min; the sputtering time is 20-40 min; the thickness of the sputtered carbon layer is 50-100 nm; the thickness of the cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm is 18.2-22.2 microns.
10. A lithium sulfur battery prepared with the cyclodextrin/graphitic carbon-modified lithium sulfur battery separator of claim 1, wherein the lithium sulfur battery comprises: the lithium-sulfur battery comprises a positive electrode, a negative electrode, a cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm and electrolyte; the positive electrode comprises a carbon material and a sulfur active substance, wherein the carbon material is acetylene black; the sulfur active substance is sublimed sulfur; the negative electrode is a lithium sheet; the cyclodextrin layer of the cyclodextrin/graphite carbon modified lithium-sulfur battery diaphragm faces the cathode, and the graphite carbon layer faces the anode; the electrolyte consists of 1, 3-dioxolane, ethylene glycol dimethyl ether, lithium bistrifluoromethylenesulfonate imide and lithium nitrate.
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Application publication date: 20210817 |