Lithium battery diaphragm and preparation method thereof

Abstract

The invention discloses a lithium battery diaphragm and a preparation method thereof, and relates to the technical field of lithium ion battery diaphragms. The preparation method comprises the following steps: carrying out graft polymerization modification on PVDF (Polyvinylidene Fluoride) compounded with a photoinitiator by using an organic monomer containing a hydrophilic ionic group under the action of ultraviolet radiation, coating a high-thermal-conductivity material aluminum nitride by using the obtained modified PVDF, and taking the obtained modified PVDF coated aluminum nitride powder as a raw material of a lithium battery diaphragm coating layer. The obtained lithium battery diaphragm has excellent heat conduction performance, can reduce the possibility of battery thermal runaway, improve the safety and stability of battery operation, can improve the charge-discharge efficiency, cycle stability and overall performance of the battery, and has the advantages of high production efficiency, low cost and very good application prospect.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery separator technology, and in particular to a lithium battery separator and its preparation method. Background Technology

[0002] Lithium-ion batteries, as core energy storage components in modern electronic devices and electric vehicles, are favored by users for their high efficiency and long lifespan. However, with the development and use of high-energy-density lithium-ion batteries, internal heat accumulation has become a significant safety hazard. During charge-discharge cycles, the electrochemical reactions in lithium-ion batteries not only release energy but also generate a large amount of heat. If this heat cannot be dissipated effectively and in a timely manner, it will accumulate inside the battery, triggering a series of chain reactions that seriously threaten the battery's performance, safety, and lifespan. First, internal heat accumulation directly leads to an increase in battery temperature, which has a significant negative impact on battery performance. Under high temperatures, the electrolyte may decompose more rapidly, producing gas, which not only reduces the number of usable lithium ions but may also cause rapid capacity decay and shorten the battery's cycle life. In addition, high temperatures can exacerbate side reactions inside the battery, such as the precipitation of metallic lithium, further deteriorating battery performance. More worryingly, excessively high temperatures can trigger thermal runaway, which is the most serious safety hazard of lithium-ion batteries. When the temperature in a localized area of ​​the battery rises sharply, it can cause rapid evaporation or even combustion of the electrolyte, while simultaneously accelerating the internal reaction rate of the battery, creating a vicious cycle. This uncontrolled thermal feedback can not only cause the battery to fail rapidly, but may also cause fires or even explosions, posing a direct threat to user safety.

[0003] Therefore, effective heat dissipation measures are crucial for ensuring the stable operation of lithium-ion batteries. As a key component inside the battery, the separator not only isolates the positive and negative electrodes to prevent short circuits, but its material properties and structure directly affect the battery's thermal management capabilities. Therefore, developing novel separator materials and structures to improve their thermal stability, ionic conductivity, and thermal conductivity is of great value. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a lithium battery separator and its preparation method.

[0005] The present invention proposes a lithium battery separator, comprising a base film and coating layers on two surfaces of the base film; the coating layers are made of a coating slurry, the raw materials of which include modified PVDF-coated aluminum nitride powder, wetting agent, dispersant and deionized water;

[0006] The preparation method of the modified PVDF-coated aluminum nitride powder includes the following steps:

[0007] (1) Add PVDF powder to a methanol solution of photoinitiator, let it stand to precipitate, filter, and dry the resulting solid at room temperature to obtain photoinitiator-PVDF composite material;

[0008] (2) The photoinitiator-PVDF composite material is first subjected to ultraviolet pre-irradiation treatment, and then an aqueous solution of organic monomers containing hydrophilic ionic groups is added, mixed evenly, and then subjected to graft polymerization reaction by ultraviolet irradiation. After filtration, washing, and drying, modified PVDF powder is obtained.

[0009] (3) Add the modified PVDF powder to the solvent and stir to dissolve it to obtain a modified PVDF solution; add aluminum nitride powder and dispersant to the modified PVDF solution, stir to disperse evenly, then remove the solvent, wash with water and dry to obtain modified PVDF coated aluminum nitride powder.

[0010] This invention first involves adding PVDF (polyvinylidene fluoride) powder to a methanol solution of a photoinitiator and allowing it to settle, thus adsorbing the photoinitiator onto the surface of the PVDF powder to obtain a photoinitiator-PVDF composite. Then, the photoinitiator-PVDF composite is modified by graft polymerization using an organic monomer containing hydrophilic ionic groups under ultraviolet irradiation. Finally, the modified PVDF is used to coat aluminum nitride, a material with high thermal conductivity. The resulting modified PVDF-coated aluminum nitride powder exhibits high thermal conductivity, hydrolysis resistance, and high ionic conductivity. Aluminum nitride possesses a thermal diffusivity several times that of aluminum oxide, enabling rapid heat dissipation from the battery, reducing the likelihood of thermal runaway, and improving the safety and stability of battery operation. Simultaneously, the modified PVDF coating on the aluminum nitride powder provides excellent coating and support, preventing severe water erosion caused by direct contact between aluminum nitride and water. The reaction process can support the mixing of aqueous slurry for the separator, effectively reducing costs and improving separator production efficiency. Furthermore, the coating formed by modified PVDF and aluminum nitride exhibits excellent electrolyte wettability, effectively improving electrolyte absorption and retention efficiency in the separator, reducing electrolyte usage in the battery cell, and lowering costs. The ionic groups grafted onto the modified PVDF can also assist lithium-ion transport, improving the lithium-ion conductivity of the separator and reducing internal resistance, thereby improving battery charge / discharge efficiency and rate performance, meeting the requirements for fast charging and discharging. The modified PVDF coating on the surface of aluminum nitride powder also plays a triple role in bonding aluminum nitride powder particles, bonding aluminum nitride powder to the base film, and bonding the separator to the electrode, reducing the coating thickness. This enhances both the energy density of the battery and the integrity of the separator and the battery, effectively reducing the side effects of interfacial interactions, improving overall battery performance, and demonstrating promising application prospects.

[0011] Preferably, in step (1), the settling time is 1–3 h, and the drying time at room temperature is 0.5–5 h. By controlling the settling and drying times, the photoinitiator can be more fully combined with PVDF, thereby making the polymerization reaction more complete, further improving lithium-ion transport performance, and increasing the charge and discharge efficiency of the battery.

[0012] Preferably, the mass ratio of the PVDF powder to the photoinitiator is 1:1 to 2.

[0013] This invention does not limit the specific photoinitiator used; any photoinitiator commonly used in the art is acceptable. Preferably, the photoinitiator is at least one selected from benzophenone, benzaldehyde-formaldehyde trimer, and ketamine photoinitiator.

[0014] Preferably, the methanol solution of the photoinitiator has a mass fraction of 15-30%.

[0015] Preferably, in step (2), the ultraviolet light intensity of the ultraviolet pre-irradiation treatment is 200–1000 mW / cm². 2 The time is 3–10 minutes, and the ultraviolet light intensity for graft polymerization is 200–1000 mW / cm². 2 The treatment time is 20–60 minutes. By controlling the intensity and duration of ultraviolet light during pre-irradiation and graft polymerization, the polymerization reaction can be made more complete, further improving lithium-ion transport performance and increasing the battery's charge and discharge efficiency.

[0016] In this invention, the purpose of ultraviolet pre-irradiation treatment is to initiate the hydrogen abstraction reaction of the photoinitiator, which facilitates the subsequent ultraviolet irradiation graft polymerization reaction.

[0017] Preferably, the mass ratio of the photoinitiator-PVDF composite material to the organic monomer with hydrophilic ionic groups is 20:5-10. By controlling the amount of organic monomer with hydrophilic ionic groups, the polymerization reaction can be made more complete, further improving lithium-ion transport performance and increasing the charge-discharge efficiency of the battery.

[0018] In this invention, the hydrophilic ionic group in the organic monomer containing the hydrophilic ionic group is preferably at least one of carboxyl, amino, hydroxyl, and sulfonic acid groups.

[0019] Preferably, the organic monomer containing the hydrophilic ionic group is at least one of acrylic acid (AA), 2-hydroxyethyl methacrylate (HEMA), 2-(methacryloyloxy)ethyl-dimethyl(3-flavopropyl)ammonium hydroxide (MEDSAH), and 3-[NN-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO).

[0020] Preferably, in step (3), the mass ratio of modified PVDF powder to aluminum nitride powder is 1:1 to 10, and the mass ratio of modified PVDF powder to dispersant is 10:0.1 to 0.5.

[0021] Preferably, the modified PVDF solution has a mass fraction of 10% to 50%.

[0022] Preferably, the particle size D50 of the aluminum nitride powder is 0.01 μm to 10 μm; more preferably, the particle size D50 of the aluminum nitride powder is 0.3 to 3 μm. By controlling the particle size of the aluminum nitride powder, the air permeability of the separator and the wettability of the electrolyte can be optimized, the ionic conductivity and the battery's electrolyte retention capacity can be improved, and the battery's cycle performance and high-temperature resistance can be further enhanced.

[0023] Preferably, in step (3), the solvent is selected from any one of NMP, DMAc, DMF, DMSO, and TEP.

[0024] Preferably, the mass ratio of the modified PVDF-coated aluminum nitride powder, wetting agent, and dispersant is 20:0.1-0.5:0.1-0.5.

[0025] Preferably, the base film is a PP (polypropylene) base film, a PE (polyethylene) base film, or a PP / PE composite base film.

[0026] Preferably, the thickness of the coating layer on a single surface of the base film is 1–5 μm.

[0027] The present invention also proposes a method for preparing the lithium battery separator, comprising the following steps: mixing modified PVDF-coated aluminum nitride powder, wetting agent, dispersant and deionized water evenly to obtain a coating slurry; coating the coating slurry onto two surfaces of a base film respectively, and drying to obtain a lithium battery separator.

[0028] Preferably, the solid content of the coating slurry is 15% to 40%.

[0029] The beneficial effects of the present invention are as follows:

[0030] This invention uses organic monomers containing hydrophilic ionic groups to graft polymerize and modify PVDF (polydimethylformamide) combined with a photoinitiator under ultraviolet irradiation. The resulting modified PVDF is then used to coat aluminum nitride (Anitride), a material with high thermal conductivity. The resulting PVDF-coated Anitride powder is used as the raw material for the coating layer of a lithium-ion battery separator. Aluminum nitride has a thermal diffusivity several times that of aluminum oxide, enabling rapid heat dissipation from the battery, reducing the possibility of thermal runaway, and improving the safety and stability of battery operation. Simultaneously, the modified PVDF coating on the surface of the Anitride powder provides excellent coating and support, preventing the violent hydrolysis reaction caused by direct contact between Anitride and water. This supports the mixing of aqueous separator slurries, effectively reducing costs and improving separator production efficiency. Furthermore, the coating formed by the modified PVDF-coated Anitride exhibits good electrolyte wettability, effectively improving electrolyte penetration within the separator. The PVDF-modified grafted ionic groups can improve the liquid absorption and retention efficiency, reduce the amount of electrolyte used in the battery cell, and lower costs. Furthermore, the PVDF-modified grafted ionic groups can assist in lithium-ion transport, improve the lithium-ion conductivity of the separator, reduce internal resistance, and meet the requirements for fast charging and discharging performance. The modified PVDF coated on the surface of aluminum nitride powder can also play a triple role in bonding aluminum nitride powder particles, bonding aluminum nitride powder to the base film, and bonding the separator to the electrode, reducing the thickness of the coating layer. This enhances both the energy density of the battery and the integrity of the separator and the battery, effectively reducing the side effects of interfacial interactions and improving the overall battery performance. In summary, the lithium battery separator of this invention has excellent thermal conductivity, which can reduce the possibility of battery thermal runaway and further improve the safety and stability of battery operation. It has high production efficiency, low cost, and the resulting battery has excellent charge-discharge efficiency, cycle stability, and other electrochemical properties, showing great application prospects. Attached Figure Description

[0031] Figure 1 The image shows the surface morphology of the diaphragm prepared in Example 1 under an optical microscope.

[0032] Figure 2 SEM image of the surface morphology of the diaphragm prepared in Example 1.

[0033] Figure 3 The results are the test results of the diaphragm liquid absorption and retention capacity of Examples 1-3 and Comparative Example 1.

[0034] Figure 4 The results of the cycle stability test for the diaphragm prepared in Example 1 are shown. Detailed Implementation

[0035] The technical solution of the present invention will now be described in detail through specific embodiments.

[0036] In the following embodiments and comparative examples:

[0037] The PVDF powder is of the Arkema LBG type, with a particle size D50 ≤ 200 nm;

[0038] The particle size D50 of the aluminum nitride powder is 0.92 μm.

[0039] The polyacrylate ammonium salt dispersant is designated as Sidmar DP03.

[0040] The polyether wetting agent is designated as BKY20990.

[0041] Example 1

[0042] The specific steps for preparing modified PVDF-coated aluminum nitride powder are as follows:

[0043] (1) Add 50g of PVDF powder to 500g of a methanol solution of photoinitiator BP with a mass fraction of 20%, let it stand to precipitate for 1h, filter, and dry the obtained solid at room temperature for 2h to obtain photoinitiator-PVDF composite material;

[0044] (2) Place 20g of photoinitiator-PVDF composite material in a quartz reaction tube, spread it evenly, and then use a light intensity of 800mW / cm². 2 Pre-irradiate with ultraviolet light for 5 minutes, then add 50g of 15% AA aqueous solution, mix well, and continue using light at an intensity of 800mW / cm². 2 The sample was irradiated with ultraviolet light for 30 minutes, then filtered, washed first with methanol aqueous solution, then washed with pure water, and naturally dried to obtain modified PVDF powder.

[0045] (3) Add 10g of modified PVDF powder to 200g of N-methylpyrrolidone (NMP) and stir to dissolve to obtain a modified PVDF solution; add 40g of aluminum nitride powder and 0.25g of ammonium polyacrylate dispersant to the modified PVDF solution, stir to disperse evenly, then place in a forced-air drying oven to evaporate and remove solvent, add 200g of deionized water to wash, and air dry to obtain modified PVDF coated aluminum nitride powder.

[0046] The specific steps for preparing a lithium battery separator are as follows:

[0047] 20g of modified PVDF-coated aluminum nitride powder was added to 100g of deionized water and stirred for 30min. Then, 0.24g of dispersant (sodium carboxymethyl cellulose) and 0.24g of polyether wetting agent were added and stirred for 30min to obtain the coating slurry. The coating slurry was then coated onto two surfaces of a polyethylene film, with a coating amount of 2.5g / m² on each surface. 2 The lithium battery separator was dried in an 80°C oven for 10 minutes.

[0048] Example 2

[0049] The specific steps for preparing modified PVDF-coated aluminum nitride powder are as follows:

[0050] (1) Add 50g of PVDF powder to 1000g of a methanol solution of photoinitiator BP with a mass fraction of 10%, let it stand for 1h to precipitate, filter, and dry the obtained solid at room temperature for 2h to obtain photoinitiator-PVDF composite material;

[0051] (2) Place 20g of photoinitiator-PVDF composite material in a quartz reaction tube, spread it evenly, and then use a light intensity of 800mW / cm². 2 Pre-irradiate with ultraviolet light for 5 minutes, then add 50g of a 20% HEMA aqueous solution, mix thoroughly, and continue using light at an intensity of 800mW / cm². 2 The sample was irradiated with ultraviolet light for 45 minutes, then filtered, washed first with methanol aqueous solution, then washed with pure water, and naturally dried to obtain modified PVDF powder.

[0052] (3) Add 10g of modified PVDF powder to 100g of N-methylpyrrolidone (NMP) and stir to dissolve to obtain a modified PVDF solution; add 40g of aluminum nitride powder and 0.25g of ammonium polyacrylate dispersant to the modified PVDF solution, stir to disperse evenly, then place in a forced-air drying oven to evaporate and remove solvent, add 200g of deionized water to wash, and air dry to obtain modified PVDF coated aluminum nitride powder.

[0053] The specific steps for preparing a lithium battery separator are as follows:

[0054] 20g of modified PVDF-coated aluminum nitride powder was added to 100g of deionized water and stirred for 30min. Then, 0.24g of sodium carboxymethyl cellulose and 0.24g of polyether wetting agent were added and stirred for 30min to obtain the coating slurry. The coating slurry was then coated onto two surfaces of a polyethylene film, with a coating amount of 2.5g / m² on each surface. 2 The lithium battery separator was dried in an 80°C oven for 10 minutes.

[0055] Example 3

[0056] The specific steps for preparing modified PVDF-coated aluminum nitride powder are as follows:

[0057] (1) Add 50g of PVDF powder to 500g of methanol solution of photoinitiator BPB with a mass fraction of 20%, let it stand for 1h to precipitate, filter, and dry the obtained solid at room temperature for 2h to obtain photoinitiator-PVDF composite material;

[0058] (2) Place 20g of photoinitiator-PVDF composite material in a quartz reaction tube, spread it evenly, and then use a light intensity of 800mW / cm². 2 Pre-irradiate with ultraviolet light for 5 minutes, then add 50g of 15% MEDSAH aqueous solution, mix well, and continue using light at an intensity of 800mW / cm². 2 The material was irradiated with ultraviolet light for 60 minutes, then filtered, washed first with methanol aqueous solution, then washed with pure water, and naturally dried to obtain modified PVDF powder.

[0059] (3) Add 10g of modified PVDF powder to 200g of N-methylpyrrolidone (NMP) and stir to dissolve to obtain a modified PVDF solution; add 40g of aluminum nitride powder and 0.25g of ammonium polyacrylate dispersant to the modified PVDF solution, stir to disperse evenly, then place in a forced-air drying oven to evaporate and remove solvent, add 200g of deionized water to wash, and air dry to obtain modified PVDF coated aluminum nitride powder.

[0060] The specific steps for preparing a lithium battery separator are as follows:

[0061] 20g of modified PVDF-coated aluminum nitride powder was added to 100g of deionized water and stirred for 30min. Then, 0.24g of sodium carboxymethyl cellulose and 0.24g of polyether wetting agent were added and stirred for 30min to obtain the coating slurry. The coating slurry was then coated onto two surfaces of a polyethylene film, with a coating amount of 2.5g / m² on each surface. 2 The lithium battery separator was dried in an 80°C oven for 10 minutes.

[0062] Example 4

[0063] The specific steps for preparing modified PVDF-coated aluminum nitride powder are as follows:

[0064] (1) Add 50g of PVDF powder to 500g of a methanol solution of photoinitiator KAP with a mass fraction of 20%, let it stand to precipitate for 1h, filter, and dry the obtained solid at room temperature for 2h to obtain photoinitiator-PVDF composite material;

[0065] (2) Place 20g of photoinitiator-PVDF composite material in a quartz reaction tube, spread it evenly, and then use a light intensity of 800mW / cm². 2 Pre-irradiate with ultraviolet light for 5 minutes, then add 50g of a 15% DIPSO aqueous solution, mix thoroughly, and continue using light at an intensity of 800mW / cm². 2 The material was irradiated with ultraviolet light for 60 minutes, then filtered, washed first with methanol aqueous solution, then washed with pure water, and naturally dried to obtain modified PVDF powder.

[0066] (3) Add 10g of modified PVDF powder to 500g of N-methylpyrrolidone (NMP) and stir to dissolve to obtain a modified PVDF solution; add 80g of aluminum nitride powder and 0.25g of ammonium polyacrylate dispersant to the modified PVDF solution, stir to disperse evenly, then place in a forced-air drying oven to evaporate and remove solvent, add 200g of deionized water to wash, and air dry to obtain modified PVDF coated aluminum nitride powder.

[0067] The specific steps for preparing a lithium battery separator are as follows:

[0068] 20g of modified PVDF-coated aluminum nitride powder was added to 100g of deionized water and stirred for 30min. Then, 0.24g of sodium carboxymethyl cellulose and 0.24g of polyether wetting agent were added and stirred for 30min to obtain the coating slurry. The coating slurry was then coated onto two surfaces of a polyethylene film, with a coating amount of 2.5g / m² on each surface. 2 The lithium battery separator was dried in an 80°C oven for 10 minutes.

[0069] Comparative Example 1

[0070] 20g of alumina powder (particle size D50 of 0.8μm) was added to 100g of deionized water and stirred for 30min. Then, 0.24g of dispersant (sodium carboxymethyl cellulose) and 0.24g of polyether wetting agent were added and stirred for 30min to obtain a coating slurry. The coating slurry was then coated onto two surfaces of a polyethylene film, with a coating amount of 2.5g / m² on each surface. 2 The lithium battery separator was dried in an 80°C oven for 10 minutes.

[0071] Comparative Example 2

[0072] The specific steps for preparing PVDF-coated aluminum nitride powder are as follows:

[0073] 10g of PVDF powder was added to 200g of N-methylpyrrolidone (NMP) and stirred to dissolve, thus obtaining a PVDF solution. 40g of aluminum nitride powder and 0.25g of ammonium polyacrylate dispersant were added to the PVDF solution and stirred to disperse evenly. The solution was then placed in a forced-air drying oven to evaporate and remove the solvent. 200g of deionized water was added for washing, and the solution was naturally dried to obtain PVDF-coated aluminum nitride powder.

[0074] The specific steps for preparing a lithium battery separator are as follows:

[0075] 20g of PVDF-coated aluminum nitride powder was added to 100g of deionized water and stirred for 30min. Then, 0.24g of sodium carboxymethyl cellulose and 0.24g of polyether wetting agent were added and stirred for 30min to obtain the coating slurry. The coating slurry was then coated onto two surfaces of a polyethylene film, with a coating amount of 2.5g / m² on each surface. 2 The lithium battery separator was dried in an 80°C oven for 10 minutes.

[0076] Test example

[0077] The membranes prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to performance tests. The test indicators and methods are as follows:

[0078] (1) Increase in air permeability: The air permeability value A of the diaphragm in Examples 1-4 and the air permeability value B of the polyethylene base membrane in Comparative Examples 1-2 were tested using a Wang Yan-type air permeability meter. The increase in air permeability = AB. The test results are shown in Table 1. As can be seen from the data in Table 1, the air permeability of the diaphragm of the present invention is significantly improved compared with the base membrane, and no obvious pore blockage occurs.

[0079] (2) Internal resistance test: The internal resistance of the batteries assembled with separators and polyethylene-based membranes in Examples 1-4 and Comparative Examples 1-2 was tested using an electrochemical workstation. Test conditions: AC disturbance voltage 10mV, frequency range: 1MHz-10000Hz. The test results are shown in Table 1. As can be seen from the data in Table 1, Comparative Example 2, which uses ungrafted PVDF-coated aluminum nitride powder as the main component of the separator coating, showed a significant increase in battery internal resistance compared to the polyethylene-based membrane and the alumina separator in Comparative Example 1, thus reducing battery performance. In contrast, the present invention uses PVDF-coated aluminum nitride powder grafted with organic monomers containing hydrophilic ionic groups, which significantly reduces battery internal resistance. This is because the grafting of ion transport groups improves the ion transport performance of the separator.

[0080] (3) Heat resistance test: The diaphragms and polyethylene films from Examples 1-4 and Comparative Examples 1-2 were cut into 100mm*100mm samples, and their longitudinal (MD) dimension a1 and transverse (TD) dimension b1 were measured. The marked samples were then placed in an oven at 130°C for 1 hour and the longitudinal dimension a2 and transverse dimension b2 were measured. The longitudinal shrinkage rate and transverse shrinkage rate of the diaphragm were then calculated using the following formula to evaluate its heat resistance.

[0081] TD shrinkage rate (%) = (b1-b2) / b1*100%;

[0082] TD shrinkage rate (%) = (b1-b2) / b1*100%.

[0083] The test results are shown in Table 1. As can be seen from the data in Table 1, the heat resistance of the diaphragm of the present invention is consistent with that of the alumina diaphragm in Comparative Example 1, and it has high high temperature resistance and heat shrinkage performance.

[0084] (4) Surface morphology test: The diaphragm from Example 1 was placed under an optical microscope, and its surface morphology was photographed. Test conditions: eyepiece magnification: 10×, objective lens magnification: 20×. Test results are as follows: Figure 1 As shown. SEM testing was performed on the diaphragm in Example 1, and the test results are as follows. Figure 2 As shown, where Figure 2 The left image is a SEM image magnified at 5kx, and the right image is a SEM image magnified at 50kx. (Source: [Insert Source Here]) Figure 1 , Figure 2 The results show that the coating on the diaphragm surface is uniformly distributed and has a clear porous structure, which ensures ion transport and improves the electrolyte wetting ability.

[0085] (5) Thermal diffusivity test: The permeable thermal diffusivity of the separators and polyethylene-based membranes in Examples 1-4 and Comparative Examples 1-2 was tested using a laser thermal conductivity meter (Netzsch LFA467, Germany). Test conditions: 80℃. The test results are shown in Table 1. As can be seen from the data in Table 1, the thermal diffusivity of the separator of the present invention is significantly improved compared with the alumina-coated separator in Comparative Example 1. This indicates that the separator of the present invention can provide faster and more efficient heat conduction performance compared with the alumina-coated separator, thereby effectively avoiding problems such as heat accumulation in the separator and further improving battery safety performance.

[0086] (6) Liquid absorption and retention capacity test: The diaphragm and polyethylene film in Examples 1-4 and Comparative Examples 1-2 were cut into 100mm*500mm samples, and the mass was recorded as m1. They were soaked in 150mL electrolyte for 1h, the surface electrolyte was wiped dry and weighed, and the mass was recorded as m2. The wiped diaphragm was placed in a fume hood and left to stand for 1h, and the mass was recorded as m3.

[0087] Liquid absorption rate = (m2-m1) / m1*100%;

[0088] Liquid retention rate = (m3-m1) / m1*100%;

[0089] Liquid retention efficiency = (m3-m1) / (m2-m1)*100%.

[0090] The test results of the diaphragm liquid absorption and retention capacity of Examples 1-3 and Comparative Examples 1-2 are as follows: Figure 3 As shown. Figure 3 As can be seen, thanks to the porous morphology of the coating, the separator of the present invention exhibits electrolyte wetting performance similar to that of an alumina separator, which can effectively reduce the amount of battery electrolyte added and improve energy density and safety performance.

[0091] (7) Battery Testing: Batteries (using ternary lithium battery electrolyte) were fabricated by winding the separators and polyethylene films from Examples 1-4 and Comparative Examples 1-2 with positive electrode sheets (lithium iron phosphate) and negative electrode sheets (graphite). The batteries were then subjected to 1000 charge-discharge cycles at 25±2℃ and 1C rate, and the change in battery capacity retention was recorded to evaluate the cycle stability of the modified separator. The test results for the separator in Example 1 are as follows: Figure 4 As shown. Figure 4 It is evident that the capacity retention rate of the diaphragm after 1000 cycles at room temperature reaches over 90%. Furthermore, the capacity retention rates of the diaphragms in Examples 2-4 after 1000 cycles at room temperature are close to those of Comparative Examples 1-2 and the polyethylene-based membrane, all exceeding 85%, meeting the requirements of the national standard GB / T31484-2015. This demonstrates that the diaphragm of the present invention possesses excellent electrochemical performance.

[0092] Table 1

[0093]

[0094] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A lithium battery separator, characterized in that, The lithium battery separator includes a base film and coating layers on two surfaces of the base film; the coating layers are made of a coating slurry, and the raw materials of the coating slurry include modified PVDF-coated aluminum nitride powder, wetting agent, dispersant and deionized water; The preparation method of the modified PVDF-coated aluminum nitride powder includes the following steps: (1) Add PVDF powder to a methanol solution of photoinitiator, let it stand to precipitate, filter, and dry the resulting solid at room temperature to obtain photoinitiator-PVDF composite material; (2) The photoinitiator-PVDF composite material is first subjected to ultraviolet pre-irradiation treatment, and then an aqueous solution of organic monomers containing hydrophilic ionic groups is added, mixed evenly, and then subjected to graft polymerization reaction by ultraviolet irradiation. After filtration, washing, and drying, modified PVDF powder is obtained. (3) Add the modified PVDF powder to the solvent and stir to dissolve it to obtain a modified PVDF solution; add aluminum nitride powder and dispersant to the modified PVDF solution, stir to disperse evenly, then remove the solvent, wash with water and dry to obtain modified PVDF coated aluminum nitride powder.

2. The lithium battery separator according to claim 1, characterized in that, In step (1), the settling time is 1 to 3 hours, and the drying time at room temperature is 0.5 to 5 hours.

3. The lithium battery separator according to claim 1, characterized in that, The mass ratio of PVDF powder to photoinitiator is 1:1 to 2; the photoinitiator is at least one of benzophenone, benzaldehyde-formaldehyde trimer, and ketamine photoinitiator.

4. The lithium battery separator according to claim 1, characterized in that, In step (2), the ultraviolet light intensity of the ultraviolet pre-irradiation treatment is 200–1000 mW / cm². 2 The time is 3–10 minutes, and the ultraviolet light intensity for graft polymerization is 200–1000 mW / cm². 2 The time is 20 to 60 minutes.

5. The lithium battery separator according to claim 1, characterized in that, The mass ratio of the photoinitiator-PVDF composite material to the organic monomer with hydrophilic ionic groups is 20:5 to 10.

6. The lithium battery separator according to claim 1, characterized in that, The organic monomer containing the hydrophilic ionic group is at least one of acrylic acid, 2-hydroxyethyl methacrylate, 2-(methacryloyloxy)ethyl-dimethyl(3-flavopropyl)ammonium hydroxide, and 3-[NN-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid.

7. The lithium battery separator according to claim 1, characterized in that, In step (3), the mass ratio of modified PVDF powder to aluminum nitride powder is 1:1 to 10, and the mass ratio of modified PVDF powder to dispersant is 10:0.1 to 0.

5.

8. The lithium battery separator according to claim 1, characterized in that, The modified PVDF solution has a mass fraction of 10% to 50%.

9. The lithium battery separator according to claim 1, characterized in that, The particle size D50 of the aluminum nitride powder is 0.01 μm to 10 μm.

10. A method for preparing a lithium battery separator as described in any one of claims 1 to 9, characterized in that, The process includes the following steps: mixing modified PVDF-coated aluminum nitride powder, wetting agent, dispersant and deionized water evenly to obtain a coating slurry; coating the coating slurry onto the two surfaces of the base film and drying it to obtain a lithium battery separator.

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