Lithium battery separator with self-repairing function and preparation method thereof

Abstract

The application discloses a lithium battery diaphragm with self-repairing function and a preparation method thereof, and belongs to the field of lithium battery diaphragms. The lithium battery diaphragm comprises a polymer base film and a ceramic coating; the ceramic coating is coated on one side surface of the polymer base film facing the negative electrode or the double side surfaces of the polymer base film; the ceramic coating comprises the following raw materials in mass fractions: modified ceramic particles 40-50 parts, self-repairing microcapsules 4-8 parts, a dispersing agent 0.5-3 parts and water 50-60 parts; the surface of the modified ceramic particles is grafted with amino-phenylboric acid bifunctional silane; the self-repairing microcapsules take chitosan / polyurethane as wall material and take polyisocyanate as core material. When the lithium ion diaphragm is subjected to stress or is punctured by dendrites, the polyisocyanate is released, cross-linked by reaction, seals the generated cracks and reconstructs the ion channel. Through the physical barrier of the ceramic coating and the self-repairing effect of the self-repairing microcapsules, the mechanical strength and ion transmission performance of the lithium battery diaphragm can be effectively maintained.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separators, and particularly to a lithium battery separator with self-healing function and its preparation method. Background Technology

[0002] As one of the key materials for lithium-ion batteries, the main function of the battery separator is to separate the positive and negative electrodes of the battery, preventing short circuits caused by contact between the two electrodes. It can also act as an electrolyte ion channel. The performance of the separator determines the battery's interface structure, internal resistance, etc., and directly affects the battery's safety, capacity, and cycle life.

[0003] Common materials used for lithium-ion battery separators include polyethylene and polypropylene. Improving separator performance requires further modification, and coating the separator surface with a ceramic coating is one such modification method used in battery production. By coating the separator with a ceramic layer, the uniformity of current distribution within the battery during charging and discharging can be significantly improved, enhancing the separator's stability and breakdown resistance. This prevents the positive and negative electrodes from contacting due to significant shrinkage or puncture, thereby reducing the risk of thermal runaway or even fire and explosion in lithium-ion batteries.

[0004] However, the inorganic powder in the ceramic coating will aggregate in the slurry due to the presence of a large number of unsaturated bonds, affecting the stability of the slurry. After being coated on the battery separator, it will affect the bonding force between the coating and the separator, causing the inorganic powder to detach from the coating during battery charging and discharging, forming gaps between the separator and the motor. This leads to increased internal impedance of the battery, uneven current density distribution, and uneven lithium deposition, which further accelerates the growth of lithium dendrites, affecting the battery's electrical performance and lifespan.

[0005] Lithium dendrites formed during charging and discharging can pierce the battery separator, causing a short circuit between the positive and negative electrodes. Alternatively, the separator structure may be damaged when subjected to pressure, puncture, or impact from foreign objects, triggering a chain reaction. The aforementioned modification method of coating with ceramic coating can improve the separator's resistance to damage to a certain extent because it establishes a physical barrier. However, the ceramic coating only passively resists initial damage. It will gradually lose its protective effect against lithium dendrites that continue to grow during charging and discharging or large microcracks caused by cyclic stress, which is detrimental to the safety and lifespan of lithium batteries. Summary of the Invention

[0006] This invention provides a self-healing lithium battery separator and its preparation method, which can solve the problem that existing lithium battery separators are unable to withstand dendrite or other external force damage for a long time, resulting in a decline in lithium battery performance and a reduction in service life.

[0007] In a first aspect, the present invention provides a lithium battery separator with self-healing function, the lithium battery separator comprising a polymer base film and a ceramic coating; the ceramic coating is coated on the side surface of the polymer base film facing the negative electrode or on both sides of the polymer base film;

[0008] The ceramic coating comprises the following raw materials in parts by weight:

[0009] 40-50 parts of modified ceramic particles;

[0010] 4-8 portions of self-repairing microcapsules;

[0011] Dispersant 0.5–3 parts;

[0012] 50-60 parts water;

[0013] The surface of the modified ceramic particles is grafted with amino-phenylboronic acid bifunctional silane;

[0014] The self-healing microcapsules use chitosan / polyurethane as the wall material and polyisocyanate as the core material.

[0015] Preferably, the polymer-based membrane includes any one of polyethylene membrane, polypropylene membrane, polyethylene / polypropylene double-layer co-extruded membrane, and polypropylene / polyethylene / polypropylene triple-layer co-extruded membrane.

[0016] Preferably, the dispersant includes one or more combinations of sodium carboxymethyl cellulose, polyethylene oxide, hydroxyethyl cellulose, ammonium polyacrylate, lithium polyacrylate, sodium polyacrylate, polyvinyl alcohol, and polyvinylpyrrolidone.

[0017] By adopting the above technical solution, self-healing microcapsules are introduced into the ceramic coating. When the lithium-ion separator is subjected to external stress or lithium dendrite puncture, the cracks in the ceramic coating will cause the self-healing microcapsules to rupture during the propagation process. The polyisocyanate, which is the core material of the self-healing microcapsule, will be released. The polyisocyanate contains multiple isocyanate groups, which can react with water or substances containing active hydrogen such as hydroxyl groups in the system and gradually branch and crosslink, sealing the generated cracks and rebuilding ion channels, blocking short-circuit paths, and enabling rapid self-repair of the lithium battery separator after the material is damaged.

[0018] Because lithium dendrites are easily generated and grown at the negative electrode of a battery due to lithium deposition, the lithium-ion battery separator of this invention always has one side of the ceramic coating facing the negative electrode of the lithium battery. It can achieve active immunity through the passive defense of the physical barrier of the ceramic coating and the self-healing ability of the self-healing microcapsules, repairing the microscopic damage caused by dendrite growth, restoring the integrity of the ion channels, maintaining not only the good mechanical strength of the lithium battery separator, but also maintaining the electrochemical performance of the lithium battery and extending the service life of the lithium battery.

[0019] Furthermore, the ceramic particles in the ceramic coating of this invention have undergone modification treatment, with amino-phenylboronic acid bifunctional silanes grafted onto their surfaces. On the one hand, this improves the dispersibility of the ceramic particles in the ceramic coating and reduces agglomeration. On the other hand, the alkyl chains in the silane compounds provide a hydrophobic interface that matches the non-polar polymer base film, enhancing the interfacial bonding and stability between the two. This significantly reduces problems such as increased impedance, delamination, and rapid lithium dendrite growth caused by accelerated lithium deposition due to ceramic particle shedding during charging and discharging. It can ensure the stability of the lithium battery's cycle performance and improve battery safety.

[0020] Furthermore, the self-healing microcapsules of the present invention use chitosan / polyurethane as the wall material of the microcapsules. The polar groups contained in chitosan can directly combine with the amino-phenylboronic acid bifunctional silane grafted onto the modified ceramic particles to form a hydrogen bond network, which can improve the dispersibility of the self-healing microcapsules among the ceramic particles, uniformly distribute them in the ceramic coating, and also enhance the bonding force between the two, avoiding the loss of the self-healing function of the diaphragm due to the detachment of the self-healing microcapsules.

[0021] Furthermore, in the self-healing microcapsules of the present invention, the chitosan wall material contains amino groups, with hydroxyl groups at the ortho position of the free amino groups. These hydroxyl groups react with the phenylboronic acid groups on the surface of the modified ceramic particles to form amino-boronic acid bonds. These amino-boronic acid bonds have a reversible breaking effect, allowing them to absorb mechanical energy through breakage when subjected to external forces, and then quickly recombine to prevent crack propagation. By introducing a dynamically constructed repair interface, the microcapsules resist some minor stresses that are difficult to cause them to rupture, and improve overall stability through hydrogen bonding between hydroxyl groups. This enhances the self-healing effect of the lithium battery separator and effectively improves the mechanical strength and capacity retention of the lithium battery separator.

[0022] Preferably, the raw materials for the modified ceramic particles include ceramic particles, aminophenylboronic acid, and silane compounds in a mass ratio of 1:(3-5):(5.5-6.5).

[0023] Preferably, the ceramic particles comprise one or more of alumina, silicon oxide, barium sulfate, and magnesium oxide.

[0024] Preferably, aminophenylboronic acid includes one or more combinations of 3-aminophenylboronic acid, 4-aminomethylphenylboronic acid, and 3-amino-4-methylphenylboronic acid.

[0025] Preferably, the silane compound includes one or a combination of two of 3-isocyanopropyltriethoxysilane and α-isocyanomethyltriethoxysilane.

[0026] Preferably, the modified ceramic particles are prepared according to the following method:

[0027] Aminophenylboronic acid was dissolved in a solvent, and a silane compound was added. The mixture was stirred and reacted at room temperature for 20–24 h to obtain an amino-phenylboronic acid bifunctional silane. The amino-phenylboronic acid bifunctional silane was added to a buffer solution, stirred and dispersed, and then ceramic particles were added. The mixture was stirred and reacted at room temperature for 10–15 h. Finally, the modified ceramic particles were obtained by filtration, washing and drying.

[0028] More preferably, the solvent includes any one of tetrahydrofuran, methanol, and ethanol.

[0029] More preferably, the buffer solution includes any one of an acetate-sodium acetate buffer solution, a phosphate buffer solution, and a Tris-HCl buffer solution.

[0030] By adopting the above technical solution, the amino group in aminophenylboronic acid will undergo an addition reaction with the isocyanate group in the silane compound to obtain an amino-phenylboronic acid bifunctional silane. Boric acid bonds are introduced into the silane compound, and then covalent bonds are formed between the silanol groups in the silane and the hydroxyl groups on the surface of the ceramic particles to graft the amino-phenylboronic acid bifunctional silane onto the surface of the ceramic particles.

[0031] The bonding force between the silane-modified ceramic particles and the polymer base film is improved, and the dispersion between particles is enhanced. This results in improved adhesion between the ceramic coating and the polymer base film, significantly reducing the adverse effects of delamination on the diaphragm. The introduced boric acid bonds can form dynamic coordination bonds in the coating system, absorbing impact energy, dispersing local stress, and inhibiting crack propagation. Even without rupture of the self-healing microcapsules, the ceramic coating can possess a certain degree of stress crack resistance and responsive repair capability.

[0032] Meanwhile, after modification, the introduction of amino groups can reduce the resistance to lithium ion transport, improve the lithium ion transport efficiency, thereby improving the ion transport efficiency of the separator, enhancing electrical performance, delaying the growth and penetration of lithium dendrites, and thus extending the service life of lithium batteries.

[0033] Preferably, the raw materials for the self-healing microcapsules include chitosan, emulsifier, polyurethane prepolymer, polyisocyanate and chain extender in a mass ratio of 1:(0.4-0.5):(0.8-0.9):(3-4):(0.6-0.8).

[0034] Preferably, the polyisocyanate includes one or more combinations of hexamethylene diisocyanate and isophorone diisocyanate.

[0035] More preferably, the emulsifier includes one or more combinations of polysorbate-20, Span 20, and fatty alcohol polyoxyethylene ether.

[0036] More preferably, the chain extender includes one or more combinations of 1,4-butanediol, ethylene glycol, butanediol and ethylenediamine.

[0037] More preferably, the self-healing microcapsules are prepared according to the following method:

[0038] Chitosan and emulsifier were added to an acidic solution to adjust the pH to 4.5–5. The solution was stirred and dissolved at 50–60°C to obtain an aqueous phase. Polyurethane prepolymer and polyisocyanate were added to ethyl acetate and stirred to obtain an oil phase. The oil phase was added dropwise to the aqueous phase, and then a chain extender was added. After stirring and mixing, the mixture was stirred and reacted at 50–55°C for 1–2 hours. Finally, the self-healing microcapsules were obtained after washing, filtration and drying.

[0039] More preferably, the acidic solution includes any one of aqueous acetic acid solution, aqueous formic acid solution, aqueous lactic acid solution, and aqueous citric acid solution.

[0040] By adopting the above technical solution, the present invention uses the emulsion method to prepare self-healing microcapsules. Under the action of the chain extender, the polyurethane prepolymer can undergo a cross-linking reaction with the amino and hydroxyl groups contained in chitosan, extend the molecular chain, form a wall material, enhance the compactness of the wall material, and encapsulate the core material inside to obtain self-healing microcapsules.

[0041] Self-healing microcapsules are dispersed in a ceramic coating. When the coating is subjected to external forces, such as charging and discharging stress or lithium dendrite puncture, cracks are generated. The self-healing microcapsules rupture and release a polyisocyanate core material. The core material reacts with water molecules in the environment to form a polyurea network, which fills and seals the cracks. Moreover, no catalyst is required. The resulting polyurea repair film has high density, which can further improve the ceramic coating's resistance to stress and effectively improve the coating's corrosion resistance. By combining the coating's physical barrier and active immunity, the integrity of ion transport channels is restored while eliminating cracks, thereby improving the cycle performance of lithium batteries.

[0042] Furthermore, this invention selects chitosan as the main material of the wall material. The composite wall material formed by chitosan through emulsification and cross-linking with polyurethane prepolymer can effectively encapsulate and protect the internal core material. The polar groups contained in chitosan can improve the dispersibility of self-healing microcapsules in the ceramic coating and the binding force between them and the modified ceramic particles, thereby achieving uniform dispersion of the self-healing microcapsules and reducing their detachment.

[0043] On the other hand, the active amino groups contained in chitosan can react with the borate groups on the surface of modified ceramic particles to form dynamic bonds, repairing cracks between the base film and the coating, and inhibiting secondary cracking. This can further enhance the self-healing effect of the self-healing microcapsules in the coating, resulting in a high-performance lithium battery composite separator.

[0044] Secondly, the present invention provides a method for preparing a lithium battery separator with self-healing function, comprising the following process steps:

[0045] S1. Add dispersant, modified ceramic particles and self-healing microcapsules to water in sequence, and stir to disperse to obtain ceramic slurry;

[0046] S2. The ceramic slurry is uniformly coated on the surface of the polymer base film and dried to form a ceramic coating with a thickness of 1-3 μm, thus obtaining a lithium battery separator with self-healing function.

[0047] The beneficial effects of this invention are:

[0048] 1. The ceramic coating of this invention incorporates self-healing microcapsules. When the lithium-ion separator is subjected to external stress or lithium dendrite puncture, the microcapsules rupture, releasing the polyisocyanate from the core material. This reaction cross-links, sealing the cracks and rebuilding ion channels, thus achieving self-repair of the separator. Through the passive defense of the ceramic coating's physical barrier and the active immunity achieved by the self-healing microcapsules, microscopic damage caused by dendrite growth is repaired, and the integrity of ion channels is restored. This not only maintains the good mechanical strength of the lithium battery separator but also effectively preserves the electrochemical performance of the lithium battery, extending its lifespan.

[0049] 2. In the ceramic coating of the present invention, the ceramic particles are also modified by grafting amino-phenylboronic acid bifunctional silane onto the surface of the ceramic particles. On the one hand, this can improve the bonding force between the particles and the polymer base film and reduce a series of adverse effects caused by particle shedding. On the other hand, the phenylboronic acid contained therein can also form dynamic bonds with the amino groups in the self-healing microcapsule wall material chitosan, resisting some minor stresses that are difficult to cause microcapsule rupture, thereby enhancing the self-healing effect of the lithium battery separator and effectively improving the mechanical strength and cycle performance of the lithium battery separator. Detailed Implementation

[0050] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0051] Preparation Example 1

[0052] Preparation Example 1-1: A modified ceramic particle was prepared according to the following method:

[0053] 40g of 3-aminophenylboronic acid was dissolved in 250mL, and 60g of 3-isocyanate-propyltriethoxysilane was added. The mixture was stirred at room temperature for 24h to obtain amino-phenylboronic acid bifunctional silane.

[0054] The amino-phenylboronic acid bifunctional silane obtained above was added to 500 mL of 0.1 mol / L acetate-sodium acetate buffer solution, stirred and dispersed, and then 10 g of alumina (average particle size of 75 μm) was added. The mixture was stirred and reacted at room temperature for 12 h. Finally, the modified ceramic particles were obtained by filtration, washing and drying.

[0055] Preparation Example 1-2, a modified ceramic particle, differs from Preparation Example 1-1 only in that the amount of 3-aminophenylboronic acid added is 30g and the amount of 3-isocyanate-propyltriethoxysilane added is 55g.

[0056] Preparation Examples 1-3, a modified ceramic particle, differs from Preparation Example 1-1 only in that the amount of 3-aminophenylboronic acid added is 50g and the amount of 3-isocyanate-propyltriethoxysilane added is 65g.

[0057] Preparation Examples 1-4: A modified ceramic particle, differing from Preparation Example 1-1 only in that the amount of 3-aminophenylboronic acid added is 20g.

[0058] Preparation Examples 1-5: A modified ceramic particle, differing from Preparation Example 1-1 only in that the amount of 3-aminophenylboronic acid added is 60g.

[0059] Preparation Examples 1-6: A modified ceramic particle was prepared according to the following method:

[0060] 60g of 3-isocyanate-propyltriethoxysilane was added to 500mL of 0.1mol / L acetate-sodium acetate buffer solution. After stirring and dispersing, 10g of alumina (average particle size of 75μm) was added. The mixture was stirred and reacted at room temperature for 12h. Finally, the modified ceramic particles were obtained by filtration, washing and drying.

[0061] Preparation Example 2

[0062] Preparation Example 2-1: A self-healing microcapsule was prepared according to the following method:

[0063] Add 10g of chitosan and 4g of polysorbate-20 to 100mL of 1% acetic acid solution, adjust the pH of the solution to 4.7, and stir at 60℃ to dissolve and obtain the aqueous phase.

[0064] 8g of polyurethane prepolymer and 30g of isophorone diisocyanate were added to 8g of ethyl acetate and stirred to obtain an oil phase. The oil phase was then added dropwise to the aqueous phase, followed by the addition of 6g of 1,4-butanediol. After stirring and mixing, the mixture was stirred at 50°C for 1 hour. Finally, the self-healing microcapsules were obtained after washing, filtration and drying.

[0065] Preparation Example 2-1: A self-healing microcapsule was prepared according to the following method:

[0066] Add 10g of chitosan and 5g of polysorbate-20 to 100mL of 1% acetic acid solution, adjust the pH of the solution to 4.7, and stir at 60℃ to dissolve and obtain the aqueous phase.

[0067] Add 9g of polyurethane prepolymer and 40g of isophorone diisocyanate to 10g of ethyl acetate, stir and mix to obtain an oil phase, add the oil phase dropwise to the aqueous phase, then add 8g of 1,4-butanediol, stir and mix, and then stir and react at 50℃ for 1h. Finally, after washing, filtering and drying, self-healing microcapsules are obtained.

[0068] Preparation Examples 2-3: A self-healing microcapsule was prepared according to the following method:

[0069] Add 10g of gum arabic to 400mL of water and stir at 50℃ to dissolve and obtain the aqueous phase;

[0070] 6.8 g of diphenylmethane diisocyanate and 30 g of isophorone diisocyanate were mixed to obtain an oil phase. The oil phase was then added dropwise to the aqueous phase. After stirring and mixing, 1.6 g of triethylenetetramine was added. Finally, the reaction was continued at 50 °C for 2 h. After filtration, washing and drying, self-healing microcapsules were obtained.

[0071] Example

[0072] Example 1: A self-healing lithium battery separator was prepared according to the following process steps:

[0073] S1. Add 2 parts of sodium polyacrylate, 45 parts of modified ceramic particles prepared in Preparation Example 1-1 and 6 parts of self-healing microcapsules prepared in Preparation Example 2-1 to 55 parts of water in sequence, and stir to disperse to obtain ceramic slurry;

[0074] S2. The ceramic slurry is uniformly coated on the surface of a polyethylene film (12 μm thick), and after drying, a ceramic coating is formed with a thickness of 2 μm, thus obtaining a lithium battery separator with self-healing function.

[0075] Examples 2 and 3 describe a self-healing lithium battery separator, differing from Example 1 only in the adjustment of the raw material ratio for the ceramic coating, as shown in Table 1.

[0076] Table 1. Raw material formulations for ceramic coatings in Examples 1-3

[0077] Modified ceramic particles / part 45 40 50 Self-repairing microcapsules / serving 6 4 8 Sodium polyacrylate / part 2 0.5 3 Water / part 55 50 60

[0078] In both Examples 2 and 3, the modified ceramic particles prepared in Example 1-1 and the self-healing microcapsules prepared in Example 2-1 were used.

[0079] Example 4: A lithium battery separator with self-healing function, which differs from Example 1 only in that the modified ceramic particles prepared in Preparation Example 1-1 are replaced with an equal amount of the modified ceramic particles prepared in Preparation Example 1-2.

[0080] Example 5: A lithium battery separator with self-healing function, which differs from Example 1 only in that the modified ceramic particles prepared in Preparation Example 1-1 are replaced with an equal amount of the modified ceramic particles prepared in Preparation Examples 1-3.

[0081] Example 6: A lithium battery separator with self-healing function, which differs from Example 1 only in that the self-healing microcapsules prepared in Example 2-1 are replaced with an equal amount of the self-healing microcapsules prepared in Example 2-2.

[0082] Example 7: A lithium battery separator with self-healing function, which differs from Example 1 only in that the modified ceramic particles prepared in Preparation Example 1-1 are replaced with an equal amount of the modified ceramic particles prepared in Preparation Examples 1-3.

[0083] Example 8: A lithium battery separator with self-healing function, which differs from Example 1 only in that the modified ceramic particles prepared in Preparation Example 1-1 are replaced with an equal amount of the modified ceramic particles prepared in Preparation Examples 1-4.

[0084] Comparative Example

[0085] Comparative Example 1, a lithium battery separator with self-healing function, differs from Example 1 only in that the amount of self-healing microcapsules added in Preparation Example 2-1 is 2 parts.

[0086] Comparative Example 2, a lithium battery separator with self-healing function, differs from Example 1 only in that the amount of self-healing microcapsules added in Preparation Example 2-1 is 10 parts.

[0087] Comparative Example 3 is a lithium battery separator with self-healing function. The only difference from Example 1 is that the modified ceramic particles prepared in Preparation Example 1-1 are replaced with an equal amount of the modified ceramic particles prepared in Preparation Examples 1-6.

[0088] Comparative Example 4, a lithium battery separator with self-healing function, differs from Example 1 only in that the modified ceramic particles prepared in Preparation Example 1-1 are replaced with an equal amount of alumina.

[0089] Comparative Example 5 is a lithium battery separator with self-healing function. The only difference from Example 1 is that the self-healing microcapsules prepared in Example 2-1 are replaced with an equal amount of the self-healing microcapsules prepared in Example 2-3.

[0090] Comparative Example 6 is a lithium battery separator with self-healing function, which differs from Example 1 only in that the self-healing microcapsules prepared in Preparation Example 2-1 are not added.

[0091] Performance testing

[0092] 1. Peel strength test: The peel strength of the lithium battery separators obtained in the examples and comparative examples was tested according to the relevant description in Method 3 of GB / T 2792-2014 "Test method for peel strength of adhesive tape".

[0093] 2. Cyclic performance test: The separators obtained in the examples and comparative examples were used as lithium battery separators. LiNiCoMnO2 electrodes were used as positive electrodes, graphite electrodes as negative electrodes, and lithium hexafluorophosphorus (LiPF6) based on ethylene carbonate / ethyl methyl carbonate / diethyl carbonate (EC / EMC / DEC = 3:2:5) was used as electrolyte to prepare lithium-ion battery samples.

[0094] The obtained lithium-ion battery samples were charged and discharged at 25°C using a 1C rate for 200 cycles to test the rate of capacity decay before and after the cycles.

[0095] The results of the above experiments are shown in Table 2:

[0096] Table 2 Performance Test Results

[0097]

[0098] According to Table 2, and in conjunction with Examples 1, 1, 2, and 6, it can be seen that the peel strength of Comparative Examples 1, 2, and 6 decreased and the capacity decay rate increased compared to Example 1. This indicates that the interfacial adhesion and self-healing effect of the ceramic coatings in Comparative Examples 1, 2, and 6 decreased. The reason for this is that the amount of self-healing microcapsules added in Comparative Example 1 was reduced. Consequently, the barrier and self-healing capabilities of the diaphragm decreased in resisting cyclic stress and dendrite puncture during the charging and discharging process, resulting in a corresponding performance decline. In Comparative Example 6, no self-healing microcapsules were added, and the performance decline was even more pronounced. In Comparative Example 2, the amount of self-healing microcapsules was increased because the surface of the self-healing microcapsules contains a large number of polar groups, which can combine with the modified ceramic particles and improve the dispersibility and binding force of the self-healing microcapsules in the ceramic coating. However, when the content of self-healing microcapsules increases, on the one hand, the binding force between them and the non-polar polymer membrane is poor, and on the other hand, excessive addition will cause the self-healing microcapsules to spontaneously aggregate. After being subjected to stress, the released polyisocyanates aggregate and trigger cross-linking, which will lead to excessive local rigidity. This is not conducive to maintaining the strength of the ceramic coating and resisting cracks, resulting in a decline in performance.

[0099] Based on Examples 1, 3, and 4, it can be seen that the peel strength of Comparative Examples 3 and 4 decreased and the capacity decay rate increased compared to Example 1. This is because the modified ceramic particles in Comparative Example 3 were only grafted with silane compounds and did not have composite phenylboronic acid groups. The lack of dynamic bond formation between phenylboronic acid and self-healing microcapsule chitosan further affected the stress resistance of the ceramic membrane, leading to a decrease in performance. In Comparative Example 4, no modification treatment was performed, which not only lacked dynamic repair but also affected the bonding force between the ceramic particles and the polymer base membrane. During cycling, the detachment of ceramic particles not only affected the strength of the membrane itself but also caused uneven lithium-ion transport, leading to rapid lithium dendrite growth, which was detrimental to improving cycle performance.

[0100] Combining Example 1 and Comparative Example 5, it can be seen that the performance of Comparative Example 5 is lower than that of Example 1. The reason is that in Comparative Example 5, conventional isocyanate microcapsules were used to replace the self-healing microcapsules of this application, and the wall material was polyurea obtained by reacting gum arabic and isocyanate. This not only led to a decrease in compatibility and dispersibility, but also lacked synergistic effect with the modified ceramic particles, thus resulting in a decrease in performance.

[0101] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A lithium battery separator with self-healing function, characterized in that, The lithium battery separator includes a polymer base film and a ceramic coating; the ceramic coating is applied to the side of the polymer base film facing the negative electrode or to both sides of the polymer base film. The ceramic coating comprises the following raw materials in parts by weight: 40-50 parts of modified ceramic particles; 4-8 portions of self-repairing microcapsules; Dispersant 0.5–3 parts; 50-60 parts water; The modified ceramic particles are grafted with amino-phenylboronic acid bifunctional silanes on their surface. The raw materials for the modified ceramic particles include ceramic particles, aminophenylboronic acid, and silane compounds in a mass ratio of 1:(3-5):(5.5-6.5). The aminophenylboronic acid includes one or more combinations of 3-aminophenylboronic acid, 4-aminomethylphenylboronic acid and 3-amino-4-methylphenylboronic acid; The silane compound includes one or a combination of two of 3-isocyanopropyltriethoxysilane and α-isocyanomethyltriethoxysilane; The amino-phenylboronic acid bifunctional silane was prepared by the following method: aminophenylboronic acid was dissolved in a solvent, a silane compound was added, and the mixture was stirred at room temperature for 20-24 h to obtain the amino-phenylboronic acid bifunctional silane. The self-healing microcapsules use chitosan / polyurethane as the wall material and polyisocyanate as the core material; the raw materials of the self-healing microcapsules include chitosan, emulsifier, polyurethane prepolymer, polyisocyanate and chain extender in a mass ratio of 1:(0.4-0.5):(0.8-0.9):(3-4):(0.6-0.8).

2. The lithium battery separator with self-healing function according to claim 1, characterized in that, The ceramic particles include one or more of alumina, silicon oxide, barium sulfate, and magnesium oxide.

3. The lithium battery separator with self-healing function according to claim 1, characterized in that, The modified ceramic particles were prepared according to the following method: Aminophenylboronic acid was dissolved in a solvent, and a silane compound was added. The mixture was stirred and reacted at room temperature for 20–24 h to obtain an amino-phenylboronic acid bifunctional silane. The amino-phenylboronic acid bifunctional silane was added to a buffer solution, stirred and dispersed, and then ceramic particles were added. The mixture was stirred and reacted at room temperature for 10–15 h. Finally, the modified ceramic particles were obtained by filtration, washing and drying.

4. The lithium battery separator with self-healing function according to claim 1, characterized in that, The polyisocyanate includes one or more combinations of hexamethylene diisocyanate and isophorone diisocyanate.

5. The lithium battery separator with self-healing function according to claim 1, characterized in that, The polymer-based membrane includes any one of polyethylene membrane, polypropylene membrane, polyethylene / polypropylene double-layer co-extruded membrane, and polypropylene / polyethylene / polypropylene triple-layer co-extruded membrane.

6. A method for preparing a lithium battery separator with self-healing function according to any one of claims 1 to 5, characterized in that, The process includes the following steps: S1. Add dispersant, modified ceramic particles and self-healing microcapsules to water in sequence, and stir to disperse to obtain ceramic slurry; S2. The ceramic slurry is uniformly coated on the surface of the polymer base film and dried to form a ceramic coating with a thickness of 1-3 μm, thus obtaining a lithium battery separator with self-healing function.

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