Diaphragm, preparation method thereof and battery

Abstract

The invention provides a diaphragm, a preparation method thereof and a battery. The preparation method comprises the following steps: S1, carrying out first mixing on a chitosan solution and a polyvinyl alcohol solution to obtain a mixed solution; s2, carrying out second mixing on the mixed solution and nano-hydroxyapatite to obtain a gel product; s3, pouring the gel product into a gel sheet material, and dipping the gel sheet material in a polyethyleneimine solution for cross-linking treatment to obtain a cross-linked sheet material; and S4, curing, washing and freeze-drying the cross-linked sheet in sequence to obtain the diaphragm. The diaphragm prepared by adopting the preparation method disclosed by the invention has good thermal stability, and is beneficial to effectively inhibiting electrochemical polarization, reducing ion transmission impedance and improving the safety performance of the battery. In addition, the preparation cost is low, and the diaphragm is biodegradable.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a diaphragm, a preparation method thereof, and a battery. Background Art

[0002] With the rapid development of the global economy, the demand for energy continues to increase. As the pillar of national economic development, energy plays a vital role in global sustainable development. However, the uneven distribution of energy resources and the difficulty of development have led to a severe shortage of per capita oil and natural gas resources. Furthermore, over-reliance on traditional fossil resources has a significant impact on the environment. Therefore, it is imperative to replace some fossil fuels with clean, renewable energy to address the energy shortage and environmental pollution crises.

[0003] Lithium-ion batteries, with their high energy density, long cycle life, pollution-free operation, and rapid charge and discharge, have become a new clean energy source that can replace traditional fossil fuels. Currently, lithium-ion batteries are widely used in the energy storage industry and have become a promising energy storage system.

[0004] Currently, commercial lithium-ion battery separators primarily utilize polyolefin materials. However, these materials suffer from poor wettability and thermal stability. When the temperature rises above a certain level, polyolefin separators experience significant dimensional shrinkage, which can cause short circuits within the lithium-ion battery and trigger thermal runaway, severely impacting the battery's safety.

[0005] Chitosan is a natural polymer material that is biodegradable, renewable, non-toxic, pollution-free, easily modifiable, and biocompatible. Due to its abundant source, low cost, high heat resistance, and good liquid absorption and wettability, chitosan and its composite materials are ideal alternatives to polyolefin separators.

[0006] However, the process of preparing diaphragms using chitosan in the prior art is complex and costly, and the wettability of the prepared diaphragms to electrolytes and their thermal stability still need to be improved. Summary of the Invention

[0007] The main purpose of the present application is to provide a diaphragm and a preparation method thereof and a battery, so as to solve the problems of low wettability of the diaphragm to the electrolyte and poor thermal stability in the prior art.

[0008] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a method for preparing a diaphragm is provided, which comprises the following steps: step S1, first mixing a chitosan solution and a polyvinyl alcohol solution to obtain a mixed solution; step S2, second mixing the mixed solution and nanohydroxyapatite to obtain a gel product; step S3, casting the gel product into a gel sheet, immersing the gel sheet in a polyethyleneimine solution for cross-linking treatment, and obtaining a cross-linked sheet; step S4, curing, washing and freeze-drying the cross-linked sheet in sequence to obtain a diaphragm.

[0009] Furthermore, in the above step S3, the cross-linking treatment temperature is 35-55°C; and / or the cross-linking treatment time is 12-72h; and / or the ratio of the mass of the gel sheet to the volume of the polyethyleneimine solution is (2-10g):(100-5000mL).

[0010] Furthermore, the mass concentration of the polyethyleneimine solution is 10-50%; further, the weight average molecular weight of the polyethyleneimine in the polyethyleneimine solution is 600-2000 g / mol.

[0011] Furthermore, in the above step S2, the ratio of the mass of the nano-hydroxyapatite to the volume of the mixed solution is (1-3 g):(100-500 mL); further, the D50 of the nano-hydroxyapatite is 40-80 nm.

[0012] Furthermore, in the above step S2, the temperature of the second mixing is 25-45°C; and / or the time of the second mixing is 8-24 hours; further, the second mixing is carried out in a stirring state, and the stirring speed of the second mixing is 500-1000 rpm.

[0013] Furthermore, in the above step S1, the mass ratio of the chitosan solution to the polyvinyl alcohol solution is (2-5):(1-2); further, the concentration of the chitosan solution is 0.03-0.1 g / mL; and / or, the concentration of the polyvinyl alcohol solution is 0.03-0.1 g / mL; further, the weight-average molecular weight of the polyvinyl alcohol in the polyvinyl alcohol solution is 25,000-35,000 g / mol; and / or, the degree of deacetylation of the chitosan in the chitosan solution is 75-95%.

[0014] Furthermore, in the above step S1, the temperature of the first mixing is 30-45° C.; and / or the time of the first mixing is 8-24 hours; further, the first mixing is carried out in a stirring state, and the stirring speed of the first mixing is 500-800 rpm.

[0015] Furthermore, in the above step S4, the cross-linked sheet is immersed in an aqueous HCl solution for curing; further, the curing temperature is 20-25° C.; and / or the curing time is 2-5 hours; and / or the mass concentration of the aqueous HCl solution is 2-4%.

[0016] According to another aspect of the present application, a diaphragm is provided, which is prepared by the aforementioned preparation method.

[0017] According to another aspect of the present application, a battery is provided, comprising a positive electrode sheet, a separator, an electrolyte and a negative electrode sheet, wherein the separator is the aforementioned separator.

[0018] Applying the technical solution of the present application, in step S1, a chitosan solution and a polyvinyl alcohol solution are first mixed, and non-covalent cross-linking through multiple hydrogen bonds between the molecules helps to ultimately form a diaphragm with high thermal stability. In step S2, the introduction of nano-hydroxyapatite helps to further improve the mechanical strength and thermal stability of the diaphragm, which helps maintain the integrity and structural stability of the diaphragm during battery operation, reduces the occurrence of thermal runaway events, and thus helps to improve the safety performance of the battery. In step S3, the gel sheet is immersed in a polyethyleneimine solution for cross-linking treatment, which helps to enhance the wet strength of the diaphragm in the battery. In the presence of electrolyte, it is more conducive to the shuttle of ions between the positive and negative electrodes, reducing the impedance of ion transfer, thereby helping to improve the cycle stability of the battery. In step S4, the cross-linked sheet is sequentially cured, washed, and freeze-dried to further help improve the structural stability of the diaphragm. Therefore, the diaphragm prepared using the preparation method of the present application has good thermal stability, helps to effectively suppress electrochemical polarization, reduce ion transfer impedance, and improve the safety performance of the battery. In addition, the preparation method of the present application is low-cost and the diaphragm is biodegradable. DETAILED DESCRIPTION

[0019] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the embodiments.

[0020] As analyzed in the background technology of this application, the diaphragm in the prior art has the problems of low wettability to the electrolyte and poor thermal stability. In order to solve this problem, this application provides a diaphragm, a preparation method thereof, and a battery.

[0021] In a typical embodiment of the present application, a method for preparing a diaphragm is provided, which comprises the following steps: step S1, first mixing a chitosan solution and a polyvinyl alcohol solution to obtain a mixed solution; step S2, second mixing the mixed solution and nanohydroxyapatite to obtain a gel product; step S3, casting the gel product into a gel sheet, immersing the gel sheet in a polyethyleneimine solution for cross-linking treatment, and obtaining a cross-linked sheet; step S4, sequentially curing, washing, and freeze-drying the cross-linked sheet to obtain a diaphragm.

[0022] In step S1, the chitosan solution and the polyvinyl alcohol solution are first mixed, and the non-covalent cross-linking through multiple hydrogen bonds between the molecules helps to finally form a diaphragm with higher thermal stability. In step S2, by introducing nano-hydroxyapatite, it helps to further improve the mechanical strength and thermal stability of the diaphragm, which helps to maintain the integrity and structural stability of the diaphragm when the battery is working, reduce the occurrence of thermal runaway events, and thus help to improve the safety performance of the battery. In step S3, the gel sheet is immersed in a polyethyleneimine solution for cross-linking treatment, which helps to enhance the wet strength of the diaphragm in the battery. In the presence of an electrolyte, it is more conducive to the shuttle of ions between the positive and negative electrodes, reducing the impedance of ion transfer, thereby helping to improve the cycle stability of the battery. In step S4, the cross-linked sheet is sequentially cured, washed and freeze-dried, which helps to further improve the structural stability of the diaphragm. Therefore, the diaphragm prepared by the preparation method of the present application has good thermal stability, helps to effectively inhibit electrochemical polarization, reduce ion transfer impedance, and improve the safety performance of the battery. In addition, the preparation of the present application is low-cost and the diaphragm is biodegradable.

[0023] In one embodiment of the present application, in the above-mentioned step S3, the temperature of the cross-linking treatment is 35-55°C; and / or, the time of the cross-linking treatment is 12-72h; and / or, the ratio of the mass of the gel sheet to the volume of the polyethyleneimine solution is (2-10g):(100-5000mL); in one embodiment of the present application, the ratio of the mass of the gel sheet to the volume of the polyethyleneimine solution is 5g:(500-1000mL), specifically 5g:500mL, 5g:600mL, 5g:700mL, 5g:800mL, 5g:900mL, 5g:1000mL and a range value between any two ratios.

[0024] Controlling the cross-linking temperature and time within the aforementioned ranges helps promote effective cross-linking between the polyethyleneimine and the gel sheet, thereby forming a more stable separator structure and improving the separator's wettability to the electrolyte. Controlling the gel sheet mass to polyethyleneimine solution volume ratio within the aforementioned range helps optimize the cross-linking reaction and achieve an appropriate cross-linking density. This appropriate cross-linking density balances the separator's mechanical strength and lithium ion conductivity, allowing the separator to maintain good structural stability without excessively hindering ion transport, thereby improving safety without sacrificing the battery's electrochemical performance.

[0025] In one embodiment of the present application, the mass concentration of the above-mentioned polyethyleneimine solution is 10-50%; in one embodiment of the present application, the weight-average molecular weight of polyethyleneimine in the polyethyleneimine solution is 600-2000 g / mol, specifically 600 g / mol, 800 g / mol, 1000 g / mol, 1200 g / mol, 1400 g / mol, 1600 g / mol, 1800 g / mol, 2000 g / mol and a range value between any two values; and / or, the solvent in the polyethyleneimine solution is water.

[0026] Controlling the concentration of the polyethyleneimine solution within the above range helps control the degree of crosslinking, effectively enhancing the separator's wet strength and electrolyte wettability while preventing excessive hardening or embrittlement, which could affect its flexibility and ion transport performance in the battery. Controlling the weight-average molecular weight of the polyethyleneimine in the polyethyleneimine solution within the above range helps balance the separator's strength, stability, and ion transport capacity.

[0027] In one embodiment of the present application, the thickness of the gel sheet is 25-60 μm.

[0028] Controlling the thickness of the gel sheet within the above range, on the one hand, helps to improve the uniformity of cross-linking the gel sheet with polyethyleneimine, thereby helping to further improve the wet strength of the separator in the battery; on the other hand, it helps to control the thickness of the final separator, thereby helping to optimize the ion transmission path between the positive and negative electrodes of the battery.

[0029] In one embodiment of the present application, in the above step S2, the ratio of the mass of nanohydroxyapatite to the volume of the mixed solution is (1-3 g):(100-500 mL); in one embodiment of the present application, the D50 of the nanohydroxyapatite is 40-80 nm.

[0030] The addition of an appropriate amount of nanohydroxyapatite helps enhance the mechanical strength of the separator and improve its thermal stability and flame retardancy. This is because the presence of nanohydroxyapatite can fill the tiny pores in the chitosan matrix, forming a denser structure. At the same time, nanohydroxyapatite can form effective interfacial interactions with chitosan and polyvinyl alcohol, improving the overall performance of the separator. Controlling the D50 of nanohydroxyapatite within the above range helps improve its dispersibility in the mixed solution, thereby further contributing to the improvement of the mechanical strength and thermal stability of the separator.

[0031] In order to further improve the mechanical strength and thermal stability of the diaphragm, in one embodiment of the present application, the preparation method of the above-mentioned nano-hydroxyapatite includes: mixing CaCl2, (NH4)2HPO4 and water to obtain a mixed solution, adjusting the pH value of the mixed solution to 9.5-10.5, stirring for 1-3 hours, and standing for 7-9 hours to obtain a precipitate, and calcining the precipitate at a temperature of 500-800°C for 11-13 hours to obtain nano-hydroxyapatite.

[0032] In order to improve the dispersibility of nanohydroxyapatite in the mixed solution, in one embodiment of the present application, in the above step S2, the temperature of the second mixing is 25 to 45°C; and / or, the time of the second mixing is 8 to 24 hours; in one embodiment of the present application, the second mixing is carried out under stirring, and the stirring speed of the second mixing is 500 to 1000 rpm.

[0033] In one embodiment of the present application, in the above step S1, the mass ratio of the chitosan solution to the polyvinyl alcohol solution is (2-5):(1-2); in one embodiment of the present application, the concentration of the chitosan solution is 0.03-0.1 g / mL; and / or, the concentration of the polyvinyl alcohol solution is 0.03-0.1 g / mL.

[0034] Chitosan, due to its biocompatibility, degradability and rich hydroxyl groups, can form a hydrogen bond network with polyvinyl alcohol, which helps to improve the film-forming property and thermal stability of the diaphragm. A higher chitosan ratio may increase the flexibility of the diaphragm and the wettability of the electrolyte, while a higher polyvinyl alcohol ratio may enhance the mechanical strength and dimensional stability of the diaphragm. Controlling the mass ratio of the chitosan solution to the polyvinyl alcohol solution within the above range helps to balance the mechanical properties, thermal stability and electrolyte wettability of the diaphragm, so that the diaphragm has sufficient strength and stability in the battery, and can effectively promote the penetration of the electrolyte and reduce the impedance of lithium ion transmission. Controlling the concentration of the chitosan solution and the concentration of the polyvinyl alcohol solution within the above range helps to control the viscosity of the solution within an appropriate range while improving the interaction between chitosan and polyvinyl alcohol, facilitating the subsequent processing and film formation of the material.

[0035] In one embodiment of the present application, the weight-average molecular weight of the polyvinyl alcohol in the polyvinyl alcohol solution is 25,000 to 35,000 g / mol; and / or the degree of deacetylation of chitosan in the chitosan solution is 75 to 95%. Controlling the weight-average molecular weight of the polyvinyl alcohol within the above range helps balance the production efficiency, mechanical strength, and thermal stability of the diaphragm. Controlling the degree of deacetylation of chitosan in the chitosan solution within the above range helps optimize the film-forming and reactivity of the diaphragm, improve its thermal stability and electrolyte wettability, while maintaining good mechanical properties.

[0036] In one embodiment of the present application, the method for preparing the chitosan solution includes: mixing phosphoric acid, chitosan and water to obtain the chitosan solution.

[0037] The purpose of adding phosphoric acid is to promote the dispersibility of chitosan in water, thereby helping to form a uniform chitosan solution, thereby helping chitosan and polyvinyl alcohol to fully contact and interact, and thus helping to form a diaphragm with a more stable structure.

[0038] In one embodiment of the present application, the method for preparing the polyvinyl alcohol solution comprises: mixing polyvinyl alcohol and water at 45-50° C. to obtain the polyvinyl alcohol solution.

[0039] Controlling the mixing temperature within the above range helps to improve the dispersibility of polyvinyl alcohol in water, thereby helping to form a uniform polyvinyl alcohol solution.

[0040] In order to further improve the uniformity of dispersion and interaction between the chitosan solution and the polyvinyl alcohol solution, in one embodiment of the present application, in the above step S1, the temperature of the first mixing is 30 to 45°C; and / or the time of the first mixing is 8 to 24 hours; in one embodiment of the present application, the first mixing is carried out under stirring, and the stirring speed of the first mixing is 500 to 800 rpm.

[0041] In one embodiment of the present application, in the above step S4, the cross-linked sheet is immersed in an aqueous HCl solution for curing; in one embodiment of the present application, the curing temperature is 20-25° C.; and / or, the curing time is 2-5 hours; and / or, the mass concentration of the aqueous HCl solution is 2-4%.

[0042] Controlling the curing temperature and time within the above ranges helps improve the structural stability of the separator. Lower HCl concentrations may not provide a sufficiently acidic environment to activate the curing reaction, while excessively high concentrations may cause excessive reaction or corrosion of the material, reducing separator performance. Controlling the mass concentration of the HCl aqueous solution within the above range helps balance the reaction activity and material stability, promoting the curing reaction while improving the structural integrity and electrochemical performance of the separator.

[0043] In another typical embodiment of the present application, a diaphragm is provided. The diaphragm is prepared by the aforementioned preparation method.

[0044] Since the above-mentioned diaphragm is prepared using the preparation method of the present application, the diaphragm has good thermal stability, which can effectively inhibit electrochemical polarization, reduce ion transfer impedance, and improve the safety performance of the battery.

[0045] In another typical embodiment of the present application, a battery is provided, including a positive electrode sheet, a separator, an electrolyte and a negative electrode sheet, wherein the separator is the aforementioned separator.

[0046] Since the battery contains the separator prepared by the preparation method of the present application, the battery has high cycle stability and safety.

[0047] The beneficial effects of the present application will be further illustrated below with reference to examples.

[0048] Example 1

[0049] Stage 1: Use a pipette to add 0.5 mL of phosphoric acid to a beaker containing 300 mL of deionized water. Under mechanical stirring, add 9.0 g of chitosan (Sinopharm Group, deacetylation degree 95%) in small amounts and multiple times to the beaker, and then maintain mechanical stirring for 6 hours to obtain a chitosan solution; in a 45°C water bath environment, add 3.0 g of polyvinyl alcohol (weight-average molecular weight 30,000 g / mol) to 100 mL of deionized water and stir for 2 hours to fully dissolve to obtain a polyvinyl alcohol solution.

[0050] The second stage: the chitosan solution and the polyvinyl alcohol solution were first mixed at a mass ratio of 2:1 at 30° C. and stirred for 8 h at a stirring speed of 500 rpm to obtain 200 mL of a mixed solution.

[0051] The third stage: add 14.0g of anhydrous CaCl2 to 500mL of deionized water and stir for 1h to fully dissolve; add 10g of (NH4)2HPO4 while stirring, and adjust the pH value of the solution to 10 with 1.0mol / L NH3·H2O solution. Stir for 2h and let it stand for 8h to obtain a precipitated product; wash the product with deionized water several times and filter it until the filtrate is neutral; calcinate the filter cake at 700℃ in a muffle furnace for 12h to obtain nanohydroxyapatite with a D50 of 60nm.

[0052] The fourth stage: 1.0 g of nano-hydroxyapatite was added to the mixed solution obtained in the second stage, and the mixture was mixed for the second time at 25° C. and stirred for 8 h at a stirring speed of 500 rpm to obtain a mixed product, which was centrifugally filtered using a centrifuge to obtain a gel product.

[0053] The fifth stage: Use a glass rod to cast the gel product on a smooth glass plate to obtain a gel-like sheet with a thickness of 30 μm; at the same time, in a water bath environment at 35°C, prepare a polyethyleneimine aqueous solution with a mass concentration of 10% (the weight-average molecular weight of polyethyleneimine is 1000 g / mol); then place 5 g of the gel sheet in 500 mL of the above polyethyleneimine aqueous solution and keep it in a water bath for reaction and cross-linking treatment for 12 hours to obtain a cross-linked sheet.

[0054] Finally, the cross-linked sheet was placed in a 2% aqueous HCl solution and cured at 25°C for 2 hours to produce a wet membrane. The wet membrane was then washed with deionized water until neutral. The cleaned wet membrane was pre-frozen in liquid nitrogen for 5 minutes and then freeze-dried to produce a diaphragm.

[0055] Example 2

[0056] The difference from Example 1 is that the temperature of the cross-linking treatment is 55° C., the time of the cross-linking treatment is 72 h, and a separator is finally obtained.

[0057] Example 3

[0058] The difference from Example 1 is that the temperature of the cross-linking treatment is 25° C., the time of the cross-linking treatment is 5 h, and a separator is finally obtained.

[0059] Example 4

[0060] The difference from Example 1 is that the weight average molecular weight of polyethyleneimine is 600 g / mol, and a separator is finally obtained.

[0061] Example 5

[0062] The difference from Example 1 is that the weight average molecular weight of polyethyleneimine is 3000 g / mol, and a separator is finally obtained.

[0063] Example 6

[0064] The difference from Example 1 is that the mass of the nano-hydroxyapatite is 6 g, and a diaphragm is finally obtained.

[0065] Example 7

[0066] The difference from Example 1 is that the mass of the nano-hydroxyapatite is 7 g, and a diaphragm is finally obtained.

[0067] Example 8

[0068] The difference from Example 1 is that the temperature of the second mixing is 45° C., the time of the second mixing is 24 h, and the stirring speed of the second mixing is 1000 rpm, and finally a diaphragm is obtained.

[0069] Example 9

[0070] The difference from Example 1 is that the temperature of the second mixing is 50° C., the time of the second mixing is 30 h, and the stirring speed of the second mixing is 400 rpm, and finally a diaphragm is obtained.

[0071] Example 10

[0072] The difference from Example 1 is that the mass ratio of the chitosan solution to the polyvinyl alcohol solution is 1:1, and a diaphragm is finally obtained.

[0073] Example 11

[0074] The difference from Example 1 is that the mass ratio of the chitosan solution to the polyvinyl alcohol solution is 6:1, and a diaphragm is finally obtained.

[0075] Example 12

[0076] The difference from Example 1 is that the weight average molecular weight of polyvinyl alcohol is 35000 g / mol, the deacetylation degree of chitosan in the chitosan solution is 75%, and finally a diaphragm is obtained.

[0077] Example 13

[0078] The difference from Example 1 is that the weight average molecular weight of polyvinyl alcohol is 40,000 g / mol, the deacetylation degree of chitosan in the chitosan solution is 70%, and finally a diaphragm is obtained.

[0079] Example 14

[0080] The difference from Example 1 is that, in the first stage: 0.5 mL of phosphoric acid was added to a beaker containing 300 mL of deionized water using a pipette, and 10 g of chitosan (Sinopharm Group, with a degree of deacetylation of 90%) was added to the beaker in small amounts and multiple times under mechanical stirring, and then mechanical stirring was maintained for 6 hours to obtain a chitosan solution; in a 45°C water bath environment, 10 g of polyvinyl alcohol (weight-average molecular weight of 25,000 g / mol) was added to 100 mL of deionized water and stirred for 2 hours to fully dissolve to obtain a polyvinyl alcohol solution.

[0081] The second stage: the chitosan solution and the polyvinyl alcohol solution were first mixed at a mass ratio of 2:1 at 45° C. and stirred for 24 h at a stirring speed of 800 rpm to obtain 500 mL of a mixed solution.

[0082] The third stage: 14.0g of anhydrous CaCl2 was added to 500mL of deionized water and stirred for 1h to fully dissolve; 10g of (NH4)2HPO4 was added while stirring, and the pH value of the solution was adjusted to 10 with 1.0mol / L NH3·H2O solution. The solution was stirred for 2h and allowed to stand for 8h to obtain a precipitated product; the product was washed with deionized water several times and filtered until the filtrate was neutral; the filter cake was calcined at 800℃ in a muffle furnace for 12h to obtain nanohydroxyapatite.

[0083] The fourth stage: 1.0 g of nano-hydroxyapatite was added to the mixed solution obtained in the second stage, and the mixture was mixed for the second time at 25° C. and stirred for 8 h at a stirring speed of 500 rpm to obtain a mixed product, which was centrifugally filtered using a centrifuge to obtain a gel product.

[0084] The fifth stage: Use a glass rod to cast the gel product on a smooth glass plate to obtain a gel-like sheet with a thickness of 60 μm; at the same time, in a water bath environment at 35°C, prepare a polyethyleneimine aqueous solution with a mass concentration of 50% (the weight-average molecular weight of polyethyleneimine is 2000 g / mol); then place 5 g of the gel sheet in 1000 mL of the above polyethyleneimine aqueous solution and keep the water bath reaction cross-linking treatment for 12 hours to obtain a cross-linked sheet.

[0085] Finally, the cross-linked sheet was placed in a 4% aqueous HCl solution and cured at 20°C for 5 hours to produce a wet membrane. The wet membrane was then washed with deionized water until neutral. The cleaned wet membrane was pre-frozen in liquid nitrogen for 5 minutes and then freeze-dried to produce a diaphragm.

[0086] Comparative Example 1

[0087] A polypropylene diaphragm (manufacturer: ZTE New Materials, thickness: 20 μm) was used as the diaphragm.

[0088] Comparative Example 2

[0089] The difference from Example 1 is that the gel sheet is not placed in a polyethyleneimine aqueous solution for cross-linking treatment, and the gel sheet is directly placed in a 2% HCl aqueous solution for curing treatment to finally obtain a diaphragm.

[0090] Comparative Example 3

[0091] The difference from Example 1 is that the addition of nano-hydroxyapatite is eliminated, and a diaphragm is finally obtained.

[0092] Performance Testing

[0093] Liquid absorption rate test: Soak a sample of mass m1 in EL-1 electrolyte. After 30 minutes, remove the sample and wipe the surface of the electrolyte with a non-woven cloth. Weigh and record m2; the liquid absorption rate L = (m2-m1) / m1×100%.

[0094] High temperature resistance test: Cut the diaphragm into samples with a size of 10 cm in length and 10 cm in width, heat them in an oven at a test temperature of 200°C for 1 hour, and calculate their thermal shrinkage.

[0095] Electrical performance test: The separator was assembled into a battery with the positive electrode sheet, negative electrode sheet and electrolyte. The battery was tested at 25°C on an electrochemical workstation battery test system with a current density of 0.2C and a charge and discharge voltage window of 2.5-3.65V. The initial discharge capacity and capacity retention after 1000 cycles were tested.

[0096] The membranes prepared in the examples and comparative examples were subjected to liquid absorption test, high temperature resistance test and electrical performance test in sequence. The test results are shown in Table 1.

[0097] Table 1

[0098]

[0099] From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects:

[0100] In step S1, the chitosan solution and the polyvinyl alcohol solution are first mixed, and the non-covalent cross-linking through multiple hydrogen bonds between the molecules helps to finally form a diaphragm with higher thermal stability. In step S2, by introducing nano-hydroxyapatite, it helps to further improve the mechanical strength and thermal stability of the diaphragm, which helps to maintain the integrity and structural stability of the diaphragm when the battery is working, reduce the occurrence of thermal runaway events, and thus help to improve the safety performance of the battery. In step S3, the gel sheet is immersed in a polyethyleneimine solution for cross-linking treatment, which helps to enhance the wet strength of the diaphragm in the battery. In the presence of an electrolyte, it is more conducive to the shuttle of ions between the positive and negative electrodes, reducing the impedance of ion transfer, thereby helping to improve the cycle stability of the battery. In step S4, the cross-linked sheet is sequentially cured, washed and freeze-dried, which helps to further improve the structural stability of the diaphragm. Therefore, the diaphragm prepared by the preparation method of the present application has good thermal stability, helps to effectively inhibit electrochemical polarization, reduce ion transfer impedance, and improve the safety performance of the battery. In addition, the preparation of the present application is low-cost and the diaphragm is biodegradable.

[0101] The above are merely preferred embodiments of the present application and are not intended to limit the present application. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for preparing a diaphragm, characterized in that: The preparation method comprises the following steps: Step S1, mixing the chitosan solution and the polyvinyl alcohol solution to obtain a mixed solution; Step S2, performing a second mixing of the mixed solution and nano-hydroxyapatite to obtain a gel product; Step S3, casting the gel product into a gel sheet, and immersing the gel sheet in a polyethyleneimine solution for cross-linking treatment to obtain a cross-linked sheet; Step S4, curing, washing and freeze-drying the cross-linked sheet in sequence to obtain the diaphragm.

2. The preparation method according to claim 1, characterized in that In step S3, the cross-linking treatment temperature is 35 to 55° C.; and / or the cross-linking treatment time is 12 to 72 hours; And / or, the ratio of the mass of the gel sheet to the volume of the polyethyleneimine solution is (2-10 g): (100~5000mL).

3. The preparation method according to claim 1 or 2, characterized in that The mass concentration of the polyethyleneimine solution is 10-50%; Preferably, the weight average molecular weight of the polyethyleneimine in the polyethyleneimine solution is 600 to 2000 g / mol.

4. The preparation method according to any one of claims 1 to 3, characterized in that In step S2, the ratio of the mass of the nano-hydroxyapatite to the volume of the mixed solution is (1-3 g):(100-500 mL); preferably, the D50 of the nano-hydroxyapatite is 40-80 nm.

5. The preparation method according to any one of claims 1 to 4, characterized in that In step S2, the temperature of the second mixing is 25 to 45° C.; and / or the time of the second mixing is 8 to 24 hours; Preferably, the second mixing is performed in a stirring state, and the stirring speed of the second mixing is 500-1000 rpm.

6. The preparation method according to any one of claims 1 to 5, characterized in that In the step S1, the mass ratio of the chitosan solution to the polyvinyl alcohol solution is (2-5):(1-2); Preferably, the concentration of the chitosan solution is 0.03 to 0.1 g / mL; and / or the concentration of the polyvinyl alcohol solution is 0.03 to 0.1 g / mL; Further preferably, the weight average molecular weight of the polyvinyl alcohol in the polyvinyl alcohol solution is 25,000 to 35,000 g / mol; and / or the degree of deacetylation of the chitosan in the chitosan solution is 75 to 95%.

7. The preparation method according to any one of claims 1 to 6, characterized in that In step S1, the temperature of the first mixing is 30 to 45° C.; and / or the time of the first mixing is 8 to 24 hours; Preferably, the first mixing is performed in a stirring state, and the stirring speed of the first mixing is 500-800 rpm.

8. The preparation method according to any one of claims 1 to 7, characterized in that In the step S4, the cross-linked sheet is immersed in an aqueous HCl solution for curing; preferably, the curing temperature is 20-25° C.; and / or the curing time is 2-5 hours; and / or the mass concentration of the aqueous HCl solution is 2-4%.

9. A diaphragm, characterized in that: The diaphragm is prepared by the preparation method according to any one of claims 1 to 8.

10. A battery comprising a positive electrode, a separator, an electrolyte and a negative electrode, characterized in that: The diaphragm is the diaphragm according to claim 9.

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