A ceramic-coated lithium-ion battery separator with high conductivity and high peel strength and a method of making the same

Abstract

The application provides a ceramic-coated lithium ion battery diaphragm with high conductivity and high peeling strength and a preparation method thereof. A 9-micron base film with high porosity (41%±5) is prepared by using a wet process and is combined with a low-Na (<100 ppm) boehmite coating developed by research and development. Since the peeling strength of the boehmite slurry coated diaphragm is low, the low-sodium boehmite and a two-component adhesive (A glue is an acrylic resin emulsion and B glue is a silane coupling agent) and a PVA adhesion aid are used in combination, the baking process is adjusted, the diaphragm resistance is effectively reduced, the adhesion between the ceramic coating and the base film is increased, the peeling strength is improved, the problem of the coating layer falling off of the lithium battery diaphragm is solved, the safety hazards such as battery short circuit caused by the problem are reduced, and the safety of the film and the cycle capacity of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery separators, specifically to a ceramic-coated lithium-ion battery separator with high conductivity and high peel strength, and its preparation method. Background Technology

[0002] To alleviate energy shortages and environmental pollution, high-energy-density lithium-ion batteries have been vigorously developed. The separator is an essential component of lithium-ion batteries, directly or indirectly affecting their electrical and safety performance. With the increasing demands on lithium-ion battery performance for energy storage applications, the requirements for separator performance have also intensified, including dimensional stability, liquid retention capacity, and electrode interface compatibility. Its primary function is to separate the positive and negative electrodes to prevent short circuits, while its unique microporous structure allows lithium ions to migrate, thus influencing the battery's electrochemical performance to some extent.

[0003] Although the separator does not participate in the electrochemical reactions within the battery, its structure and performance significantly impact the battery's capacity, internal resistance, cycle life, and safety. Most lithium-ion battery separators suffer from low conductivity, high interfacial resistance at room temperature, and poor adhesion to the battery electrodes. In particular, water-based boehmite-coated films generally exhibit low conductivity and peel strength, limiting the battery to only a few hundred effective cycles at low current densities, resulting in a short lifespan. To reduce separator internal resistance and improve lithium-ion transport efficiency, a common approach is to increase the porosity and permeability of the base film. Uniform nanoscale pore sizes ensure high-speed charging and discharging and extend battery life. Higher separator porosity allows for more efficient lithium-ion passage, enabling the cell to maintain stable cycling during prolonged charging and discharging, thus extending its lifespan. There are currently no reports of improving the peel strength, conductivity, and transmission efficiency of a membrane by simply modifying the coating material and coating method without changing the porosity and permeability of the base membrane. This method has lower requirements for the base membrane and a wider range of applications. Summary of the Invention

[0004] To address the aforementioned technical problems in the prior art, this invention provides a method for preparing a ceramic-coated lithium-ion battery separator. Without altering the base membrane itself, the method improves the formulation and coating process to enhance the separator's peel strength, conductivity, and transport efficiency, thereby enabling long-cycle use of lithium iron phosphate batteries.

[0005] To achieve the objective of this invention, the technical solution is as follows:

[0006] The first objective of this invention is to provide a ceramic-coated lithium-ion battery separator with high electrical conductivity and high peel strength, the ceramic-coated lithium-ion battery separator comprising a base film and a mixed coating coated on at least one side of the base film;

[0007] The hybrid coating comprises a two-component adhesive, which includes an acrylic resin emulsion and a silane coupling agent; the sodium content of the hybrid coating is less than 1000 ppm and does not contain sodium carboxymethyl cellulose (CMC);

[0008] The peel strength between the hybrid coating and the polymer base film is 140-160 N / m; preferably, the peel strength between the hybrid coating and the polymer base film is 140-200 N / m; preferably, the peel strength between the hybrid coating and the polymer base film is 140-160 N / m.

[0009] The ceramic-coated lithium-ion battery separator has an ionic conductivity of 1.5 mS / cm or higher.

[0010] The mass ratio of the acrylic resin emulsion to the silane coupling agent is 50:1 to 100:1.

[0011] The hybrid coating comprises the following components:

[0012] Dispersant: 2-4 parts;

[0013] Low-sodium boehmite powder: 290-310 parts;

[0014] Two-component adhesive: 20-50 parts;

[0015] Wetting agent: 1-5 parts;

[0016] Adhesive promoter: 1-5 parts

[0017] The low-sodium boehmite powder has a sodium content of ≤100ppm.

[0018] A second objective of this invention is to provide a method for preparing a ceramic-coated lithium-ion battery separator with high electrical conductivity and high peel strength, the method comprising the following steps:

[0019] (1) Preparation of slurry:

[0020] An adhesive aid is stirred in water to prepare an aqueous solution of the adhesive aid, wherein the adhesive aid is polyvinyl alcohol;

[0021] Low-sodium boehmite powder was added to the stirred pure water to obtain a low-sodium boehmite dispersion.

[0022] A two-component adhesive, an aqueous solution of a tackifier, a wetting agent, and a dispersant are added to a low-sodium boehmite dispersion and mixed evenly to prepare a slurry. The two-component adhesive includes an acrylic resin emulsion and a silane coupling agent.

[0023] The low-sodium boehmite is defined as having a sodium content of <100ppm;

[0024] (2) The slurry prepared in step (1) is coated onto at least one side of the base film by gravure coating to obtain a coated film;

[0025] (3) The coated film is baked to obtain the high conductivity ceramic coated lithium-ion battery separator.

[0026] Furthermore, the dispersant in step (1) is an ammonium hydroxide dispersant; the mass percentage of the dispersant in the slurry is 0.2%-0.4%.

[0027] Furthermore, the adhesive used in step (1) is selected from LSE-16AD12A and LSE-16AD12A-IX;

[0028] The mass ratio of the acrylic resin emulsion to the silane coupling agent is 50:1 to 100:1, preferably 60:1 to 75:1.

[0029] The binder constitutes 2%-5% of the slurry by mass.

[0030] Furthermore, the adhesive aid in step (1) is selected from polyvinyl alcohol (PVA); the mass percentage of the adhesive aid in the slurry is 0.5%-1.5%.

[0031] Furthermore, the wetting agent in step (1) is selected from polyoxyalkylene wetting agents, and the mass percentage of the wetting agent in the slurry is 0.1%-0.5%.

[0032] Furthermore, the low-sodium boehmite BGG-611D described in step (1) has a mass percentage of 29%-31% in the slurry.

[0033] Furthermore, the porosity of the base membrane in step (2) is 41% ± 5%.

[0034] Furthermore, the baking conditions in step (3) are 110℃±20℃, 8H±2H.

[0035] The beneficial effects of this invention are as follows:

[0036] This invention combines a 9μm base membrane with high porosity (41% ± 5%) fabricated using a wet process with a low-Na (<100ppm) boehmite coating developed through research. Since the peel strength of the boehmite slurry-coated separator is relatively low, a combination of low-sodium boehmite, a two-component binder (A is an acrylic resin emulsion, B is a silane coupling agent), and a PVA adhesion promoter is used. The two-component binder is obtained by mixing the acrylic resin emulsion and silane coupling agent in a specific ratio. The PVA is diluted with water to a specific concentration to obtain an adhesion promoter to optimize the slurry formulation. The coated separator is baked at 110℃ for 8 hours. This baking process effectively reduces separator resistance, increases the adhesion between the ceramic coating and the base membrane, improves peel strength, solves the problem of lithium battery separator coating peeling, reduces safety hazards such as battery short circuits, and improves the safety of the membrane and the cycle life of the battery. Detailed Implementation

[0037] The present invention will be further explained below with reference to the embodiments, but the embodiments do not limit the present invention in any way.

[0038] Example 1:

[0039] (1) Preparation of slurry:

[0040] (1-1) First, take 1.5 kg of the adhesive agent polyvinyl alcohol SR-180 and 1.5 kg of deionized water, stir and dilute evenly to obtain a PVA aqueous solution;

[0041] (1-2) Add 60 kg of low-sodium boehmite BG-611D (Anhui Yishitong) to 115 kg of deionized water, stir, disperse, grind and filter thoroughly to obtain low-sodium boehmite dispersion.

[0042] (1-3) Take 9 kg of binder A acrylic resin emulsion LSE-16AD12A and 0.15 kg of binder B silane coupling agent LSE-16AD12A-IX and mix them evenly. Add the previously prepared PVA aqueous solution, low sodium boehmite dispersion, 0.222 kg of polyepoxide wetting agent 202E and 0.522 kg of ammonium hydroxide dispersant D-3019 and disperse evenly to obtain 200 kg of slurry, which is labeled as slurry 1.

[0043] (2) The slurry 1 is coated onto one side of a 3μm to 9μm base film by gravure coating to obtain a 9+3 coated film.

[0044] (3) Then place the coated film in an oven and bake it at 110°C for 8 hours to obtain diaphragm A.

[0045] Example 2:

[0046] (1) Preparation of slurry:

[0047] (1-1) First, take 1.5 kg of the adhesive agent polyvinyl alcohol SR-180 and 1.5 kg of deionized water and stir them evenly to obtain a PVA aqueous solution;

[0048] (1-2) Add 60 kg of low-sodium boehmite BG-611D (Anhui Yishitong) to 120 kg of deionized water, stir, disperse, grind and filter thoroughly to obtain low-sodium boehmite dispersion.

[0049] (1-3) Take 5.77 kg of binder A acrylic resin emulsion LSE-16AD12A and 0.096 kg of binder B silane coupling agent LSE-16AD12A-IX and mix them evenly. Add the previously prepared PVA aqueous solution, low sodium boehmite dispersion, 0.222 kg of wetting agent 202E and 0.522 kg of ammonium hydroxide dispersant D-3019 and disperse evenly to obtain 197 kg of slurry, which is labeled as slurry 2.

[0050] (2) The slurry 2 is coated onto one side of a 3μm to 9μm base film by gravure coating to obtain a 9+3 coated film.

[0051] (3) Place the coated film in an oven and bake at 110°C for 8 hours to obtain diaphragm B.

[0052] Example 3:

[0053] (1) Preparation of slurry:

[0054] (1-1) First, take 1.5 kg of the adhesive agent polyvinyl alcohol SR-180 and 1.5 kg of deionized water and stir them evenly to obtain a PVA aqueous solution;

[0055] (1-2) Add 60 kg of low-sodium boehmite BG-611D to 121 kg of deionized water, stir, disperse, grind and filter thoroughly to obtain a low-sodium boehmite dispersion.

[0056] (1-3) Take 9 kg of binder A acrylic resin emulsion LSE-16AD12A and 0.15 kg of binder B silane coupling agent LSE-16AD12A-IX and mix them evenly. Add the previously prepared PVA aqueous solution, low sodium boehmite dispersion, 0.222 kg of wetting agent 202E and 0.522 kg of ammonium hydroxide dispersant D-3019 and disperse evenly to obtain 201 kg of slurry, which is numbered slurry 3.

[0057] (2) The slurry 3 is coated onto one side of the 3μm to 9μm base film by gravure coating to obtain a 9+3 coated film.

[0058] (3) Place the coated film in an oven and bake at 110°C for 8 hours to obtain diaphragm C.

[0059] Comparative Example 1:

[0060] (1) Preparation of slurry:

[0061] (1-1) First, take 1.5 kg of the adhesive agent polyvinyl alcohol SR-180 and 1.5 kg of deionized water and stir them evenly to obtain a PVA aqueous solution;

[0062] (1-2) Take 0.73 kg of sodium carboxymethyl cellulose and mix it with 17.58 kg of deionized water to obtain a CMC aqueous solution;

[0063] Then, add 18 kg of CMC aqueous solution and 60 kg of low-sodium boehmite BG-611D to 129 kg of deionized water, stir, disperse, grind and filter thoroughly to obtain a low-sodium boehmite dispersion.

[0064] (1-3) Take 9 kg of acrylic resin emulsion LSE-16AD12A and 0.15 kg of binder B silane coupling agent LSE-16AD12A-IX and mix them evenly. Add the previously prepared PVA aqueous solution, low sodium boehmite dispersion, 0.222 kg of wetting agent 202E and 0.522 kg of ammonium hydroxide dispersant D-3019 and disperse evenly to obtain 20 kg of slurry, which is numbered slurry 4.

[0065] (2) The slurry 4 is coated onto one side of the 3μm to 9μm base film by gravure coating to obtain a 9+3 coated film.

[0066] (3) Place the coated film in an oven and bake it at 110°C for 8 hours to obtain diaphragm D.

[0067] Comparative Example 2:

[0068] (1) Preparation of slurry:

[0069] Add 60 kg of low-sodium boehmite BG-611D and 0.52 kg of dispersant D-3019 to 120 kg of deionized water, stir, disperse, grind and filter thoroughly, then add 9.86 kg of binder 900B and 0.21 kg of wetting agent 202E and disperse evenly to obtain 200 kg of slurry, which is numbered slurry 5.

[0070] (2) The slurry 5 is coated onto one side of the 3μm to 9μm base film by gravure coating to obtain a 9+3 coated film, which is called diaphragm E.

[0071] The addition ratios of each raw material in the ceramic slurry formulations of the above embodiments and comparative examples are shown in Table 1 below:

[0072] Table 1. Summary of the addition ratio of each raw material in the ceramic slurry formulation in the examples and comparative examples.

[0073]

[0074]

[0075] The slurry was prepared using the above-mentioned dosage of additives, its properties were tested, and a base membrane was coated onto it to obtain sample diaphragms, which were then numbered. Subsequently, the physical properties of the sample diaphragms were tested, and comparative analysis was performed.

[0076] The slurry data is as follows:

[0077]

[0078] The diaphragm data is as follows:

[0079]

[0080] <Evaluation Methods>

[0081] (1) Peel strength between ceramic layer and base film

[0082] A 12mm wide and 15cm long adhesive tape (Scotch, model 550R-12) is adhered to the ceramic layer surface of one side of the diaphragm. The diaphragm is then cut to match the width and length of the adhesive tape to create a test sample. When applying the adhesive tape to the diaphragm, its length direction is aligned with the MD direction of the diaphragm. It should be noted that the adhesive tape is used as a support for peeling off one side of the ceramic layer.

[0083] The sample was placed in an atmosphere with a temperature of 23±1℃ and a relative humidity of 50±5% for more than 24 hours, and the following determinations were performed in the same atmosphere.

[0084] Peel the adhesive tape and the ceramic layer immediately below it together for about 10 cm, separating the laminate (1) of adhesive tape and ceramic layer from the laminate (2) of porous substrate and the other ceramic layer by about 10 cm. Fix the end of the laminate (1) to the upper clamp of TENSILON (Orientec RTC-1210A) and the end of the laminate (2) to the lower clamp of TENSILON. Suspend the test sample along the direction of gravity and make the stretching angle (the angle of the laminate (1) relative to the test sample) 180°. Stretch the laminate (1) at a stretching speed of 20 mm / min and measure the load when the laminate (1) is peeled from the porous substrate. Obtain the load from 10 mm to 40 mm after the start of the test at intervals of 0.4 mm, and take the average value as the peel strength.

[0085] (2) Membrane internal resistance and ionic conductivity

[0086] Electrochemical impedance spectroscopy (EIS) was used for measurement. The separator sample was assembled into a coin cell in the following order: positive electrode shell - separator - stainless steel gasket - spring gasket - negative electrode shell. Electrochemical impedance spectroscopy scanning was performed using an electrochemical workstation at a frequency of 0.01 Hz-10 Hz. 6 With a voltage amplitude of 5mV and a frequency of Hz, the internal resistance Rb of the diaphragm is obtained. The formula for calculating the ionic conductivity of the diaphragm is: K = d / (S * Rb), where K is the ionic conductivity of the diaphragm (mS / cm), d is the thickness of the diaphragm (cm), and S is the effective working area of ​​the diaphragm (cm²). 2 ).

[0087] The results above show that by using low-sodium boehmite, a two-component binder, and PVA as a binder in the slurry formulation, the gas permeability of the separator is reduced, and the internal resistance of the separator is significantly decreased, resulting in good performance of the separator. Furthermore, by adjusting the ceramic layer slurry formulation and adding a post-coating baking process, the decrease in the adhesion performance of the ceramic slurry caused by the removal of the CMC solution is compensated for. While maintaining the original low internal resistance level, the peel strength of the ceramic layer can be increased to over 140 N / m, extending the cycle life of the lithium battery and demonstrating promising application prospects.

[0088] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A ceramic-coated lithium-ion battery separator with high electrical conductivity and high peel strength, characterized in that, The ceramic-coated lithium-ion battery separator includes a base film and a mixed coating coated on at least one side of the base film; The base film is a polymer-based film; The hybrid coating comprises a two-component binder and an adhesion promoter. The two-component binder comprises an acrylic resin emulsion and a silane coupling agent, and the adhesion promoter is selected from polyvinyl alcohol. The sodium content of the hybrid coating is less than 1000 ppm and does not contain sodium carboxymethyl cellulose (CMC). The peel strength between the hybrid coating and the polymer base film is above 140 N / m; The ceramic-coated lithium-ion battery separator has an ionic conductivity of 1.5 mS / cm or higher. The mass ratio of the acrylic resin emulsion to the silane coupling agent is 50:1 to 100:1; The porosity of the base membrane is 41% ± 5%.

2. The ceramic-coated lithium-ion battery separator with high conductivity and high peel strength according to claim 1, characterized in that, The hybrid coating comprises the following components: Dispersant: 2-4 parts; Low-sodium boehmite powder: 290-310 parts; Two-component adhesive: 20-50 parts; Wetting agent: 1-5 parts; Adhesive promoter: 1-5 parts The low-sodium boehmite powder has a sodium content of ≤100ppm.

3. The ceramic-coated lithium-ion battery separator with high conductivity and high peel strength according to claim 1, characterized in that, The peel strength between the hybrid coating and the polymer base film is 140-200 N / m.

4. The ceramic-coated lithium-ion battery separator with high conductivity and high peel strength according to claim 3, characterized in that, The peel strength between the hybrid coating and the polymer base film is 140-160 N / m.

5. The method for preparing the ceramic-coated lithium-ion battery separator with high conductivity and high peel strength as described in claim 1, characterized in that, The method includes the following steps: (1) Preparation of slurry: An adhesive aid is stirred in water to prepare an aqueous solution of the adhesive aid, wherein the adhesive aid is polyvinyl alcohol; Low-sodium boehmite powder was added to the stirred pure water to obtain a low-sodium boehmite dispersion. A two-component binder, an aqueous solution of a tackifier, a wetting agent, and a dispersant are added to a low-sodium boehmite dispersion and mixed evenly to prepare a slurry. The two-component binder includes an acrylic resin emulsion and a silane coupling agent. The low-sodium boehmite has a sodium content of <100ppm; (2) The slurry prepared in step (1) is coated onto at least one side of the base film by gravure coating to obtain a coated film; (3) The coated film is baked to obtain the ceramic coated lithium-ion battery separator with high conductivity and high peel strength. The baking conditions in step (3) are 110℃±20℃, 8H±2H.

6. The preparation method according to claim 5, characterized in that, The dispersant in step (1) is ammonium hydroxide dispersant; the mass percentage of the dispersant in the slurry is 0.2%-0.4%.

7. The preparation method according to claim 5, characterized in that, The acrylic resin emulsion in step (1) is selected from LSE-16AD12A, and the silane coupling agent is selected from LSE-16AD12A-IX.

8. The preparation method according to claim 5, characterized in that, The mass ratio of the acrylic resin emulsion and the silane coupling agent in step (1) is 60:1-75:

1.

9. The preparation method according to claim 5, characterized in that, The mass percentage of the two-component binder in the slurry in step (1) is 2%-5%.

10. The preparation method according to claim 5, characterized in that, The mass percentage of the adhesive in step (1) is 0.5%-1.5%.

11. The preparation method according to claim 5, characterized in that, The wetting agent in step (1) is selected from polyoxyalkylene wetting agents or modified polyoxyalkylene wetting agents; the mass percentage of the wetting agent in the slurry is 0.1%-0.5%.

12. The preparation method according to claim 5, characterized in that, The low-sodium boehmite in step (1) has a mass percentage of 29%-31% in the slurry.

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