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

Abstract

The invention discloses a lithium battery diaphragm with a 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 membrane and a ceramic coating, the ceramic coating is coated on one side surface, facing the negative electrode, of the polymer base membrane or two side surfaces of the polymer base membrane; the ceramic coating comprises the following raw materials in parts by mass: 40-50 parts of modified ceramic particles, 4-8 parts of self-repairing microcapsules, 0.5-3 parts of a dispersing agent and 50-60 parts of water; the surfaces of the modified ceramic particles are grafted with amino-phenylboronic acid difunctional silane; chitosan / polyurethane is used as a wall material of the self-repairing microcapsule, and polyisocyanate is used as a core material of the self-repairing microcapsule. When the lithium ion diaphragm is stressed or punctured by dendritic crystals, the polyisocyanate can be released to react and crosslink, the generated cracks are closed, and an ion channel is reconstructed. Through the physical barrier of the ceramic coating and the self-repairing effect of the self-repairing microcapsule, the mechanical strength and the ion transmission performance of the lithium battery diaphragm can be effectively maintained.

Description

Technical Field

[0001] The present invention relates to the field of lithium battery separators, and in particular to a lithium battery separator with a self-repairing function and a preparation method thereof. Background Art

[0002] As one of the key materials of lithium-ion batteries, the main function of the battery separator is to separate the positive and negative electrodes of the battery to prevent the two electrodes from contacting and causing a short circuit. It can also act as an electrolyte ion channel. The performance of the separator determines the interface structure and internal resistance of the battery, and directly affects the battery's safety, capacity and cycle life.

[0003] Common materials for lithium battery separators include polyethylene and polypropylene. Improving separator performance requires further modification, and applying a ceramic coating to the separator surface is one of the current modification methods used in battery production. Applying a ceramic coating to the separator surface significantly improves the uniformity of current distribution within the lithium-ion battery during charge and discharge, enhancing the separator's stability and resistance to penetration. This prevents significant contraction or puncture of the separator, which could lead to contact between the positive and negative electrodes, thereby reducing the risk of thermal runaway and even fire and explosion in lithium batteries.

[0004] However, the inorganic powder in the ceramic coating will precipitate 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 strength between the coating and the separator, causing the inorganic powder to detach from the coating during the battery charging and discharging process, forming a gap between the separator and the motor, resulting in increased impedance inside the battery, uneven current density distribution, and uneven lithium deposition, thereby further accelerating the growth of lithium dendrites and affecting the battery's electrical performance and service life.

[0005] The lithium dendrites formed during the charge and discharge process will pierce the battery separator, causing a short circuit between the positive and negative electrodes, or the separator structure will be damaged when squeezed, punctured or impacted by foreign objects, triggering a chain reaction. The above-mentioned modification method of applying ceramic coating can improve the damage resistance of the separator 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 the charge and discharge process or large microcracks caused by cyclic stress, which is not conducive to improving the safety and service life of lithium batteries. Summary of the Invention

[0006] The present invention provides a lithium battery separator with self-repairing function and a preparation method thereof, which can solve the problem in the prior art that the battery separator is difficult to resist dendrites or other external force damage for a long time, resulting in decreased lithium battery performance and shortened service life.

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

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

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

[0010] 4 to 8 parts of self-repairing microcapsules;

[0011] 0.5-3 parts of dispersant;

[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 film includes any one of a polyethylene membrane, a polypropylene membrane, a polyethylene / polypropylene double-layer co-extruded membrane, and a polypropylene / polyethylene / polypropylene three-layer co-extruded membrane.

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

[0017] By adopting the above technical solution, self-healing microcapsules are introduced into the ceramic coating. When the lithium-ion membrane is affected by external stress or punctured by lithium dendrites, the cracks will cause the self-healing microcapsules to rupture during the expansion of the ceramic coating, and the polyisocyanate serving as the core material of the self-healing microcapsules 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 cross-link, sealing the cracks and rebuilding the ion channels, blocking the short-circuit path, and can quickly achieve self-repair of the lithium battery membrane after the material is damaged.

[0018] Because lithium is easily deposited at the negative electrode of the battery, causing lithium dendrites to be generated and grow at the negative electrode, the lithium-ion battery separator of the present invention always faces one side of the ceramic coating to the negative electrode of the lithium battery. Active immunity can be achieved through the passive defense of the physical barrier of the ceramic coating and the self-repairing ability of the self-repairing microcapsules, repairing the microscopic damage caused by dendrite growth and restoring the integrity of the ion channel. It can not only maintain the good mechanical strength of the lithium battery separator, but also well maintain the electrochemical properties of the lithium battery and extend the service life of the lithium battery.

[0019] In addition, the ceramic particles in the ceramic coating of the present invention have been modified and have amino-phenylboronic acid bifunctional silane grafted on the surface. On the one hand, this can improve the dispersibility of the ceramic particles in the ceramic coating and reduce agglomeration. On the other hand, the alkyl chain in the silane compound can provide a hydrophobic interface that matches the ceramic particles with the non-polar polymer base film, thereby enhancing the interfacial bonding and stability between the two, thereby greatly reducing problems such as increased impedance, stratification, and rapid growth of lithium dendrites caused by the shedding of ceramic particles during the charge and discharge process, thereby ensuring the stability of the lithium battery cycle performance and improving the safety of the battery.

[0020] Moreover, the self-repairing 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 on the modified ceramic particles to form a hydrogen bond network, which can improve the dispersibility of the self-repairing microcapsules between the ceramic particles and evenly distribute them in the ceramic coating. It can also enhance the bonding force between the two and avoid the loss of the self-repairing effect of the diaphragm caused by the shedding of the self-repairing microcapsules.

[0021] Furthermore, in the self-healing microcapsules of the present invention, because the chitosan of the wall material contains amino groups, the ortho position of the free amino group is a hydroxyl group, which reacts with the phenylboronic acid group on the surface of the modified ceramic particles to form an amino-boric acid bond. The amino-boric acid bond has a reversible breaking effect and can absorb mechanical energy by breaking when subjected to external effects, and then quickly reorganize to avoid crack expansion. By introducing a repair interface through dynamic construction, it can resist some tiny stress effects that are difficult to cause microcapsule rupture, and improve the overall stability through the hydrogen bonding effect between the hydroxyl groups, thereby enhancing the self-healing effect of the lithium battery separator and effectively improving the mechanical strength and capacity retention rate of the lithium battery separator.

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

[0023] Preferably, the ceramic particles include a combination of one or more of aluminum oxide, silicon oxide, barium sulfate and magnesium oxide.

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

[0025] Preferably, the silane compound includes one or a combination of 3-isocyanatepropyltriethoxysilane and α-isocyanatemethyltriethoxysilane.

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

[0027] The aminophenylboronic acid is dissolved in a solvent, a silane compound is added, and the mixture is stirred and reacted at room temperature for 20 to 24 hours to obtain amino-phenylboronic acid bifunctional silane; the amino-phenylboronic acid bifunctional silane is added to a buffer solution, stirred and dispersed, and then ceramic particles are added, and the mixture is stirred and reacted at room temperature for 10 to 15 hours. Finally, the modified ceramic particles are obtained by filtering, 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 acetic acid-sodium acetate buffer solution, phosphate buffer solution and 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 amino-phenylboronic acid bifunctional silane, a boronic acid bond is introduced into the silane compound, and then a covalent bond is formed between the silanol group in the silane and the hydroxyl group on the surface of the ceramic particle to graft the amino-phenylboronic acid bifunctional silane onto the surface of the ceramic particle.

[0031] Silane modification enhances the bonding strength between the ceramic particles and the polymer-based membrane, improving the dispersion of the particles. This, in turn, enhances the adhesion between the resulting ceramic coating and the polymer-based membrane, significantly reducing adverse effects on the separator, such as delamination. The introduced boric acid bonds form dynamic coordination bonds within the coating system, absorbing impact energy, dispersing localized stress, and inhibiting crack propagation. This, when the self-healing microcapsules are intact, allows the ceramic coating to possess a certain degree of resistance to stress cracking and responsive repair capabilities.

[0032] At the same time, after modification, the introduction of amino groups can reduce the transmission resistance of lithium ions and improve the transmission efficiency of lithium ions, thereby improving the ion transmission efficiency of the diaphragm, improving electrical performance, delaying the growth and penetration of lithium dendrites, and thus extending the service life of lithium batteries.

[0033] Preferably, the raw materials of the self-repairing 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 a combination of one or more of hexamethylene diisocyanate and isophorone diisocyanate.

[0035] More preferably, the emulsifier includes a combination of one or more 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-repairing microcapsules are prepared according to the following method:

[0038] Chitosan and an emulsifier are added to an acidic solution, the pH value of the solution is adjusted to 4.5-5, and the solution is stirred and dissolved at 50-60°C to obtain an aqueous phase; a polyurethane prepolymer and polyisocyanate are added to ethyl acetate, and the mixture is stirred to obtain an oil phase, which is added dropwise to the aqueous phase, and then a chain extender is added, and the mixture is stirred and reacted at 50-55°C for 1-2 hours. Finally, the self-healing microcapsules are obtained through washing, filtering and drying.

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

[0040] By adopting the above technical solution, the present invention adopts an emulsion method to prepare self-repairing microcapsules. Under the action of a chain extender, the polyurethane prepolymer can undergo a cross-linking reaction with the amino and hydroxyl groups contained in chitosan, extending the molecular chain to form a wall material, enhancing the density of the wall material, and wrapping the core material inside to obtain a self-repairing microcapsule.

[0041] Self-healing microcapsules are dispersed in the ceramic coating. When the coating is subjected to external forces, such as charge and discharge stress, puncture of lithium dendrites, etc., and cracks are generated, the self-healing microcapsules rupture and release the polyisocyanate core material. The core material reacts with water molecules in the environment to form a polyurea network, filling and sealing the cracks. Moreover, no catalyst is required. The obtained polyurea repair film has high density, which can further improve the stress resistance of the ceramic coating and effectively improve the corrosion resistance of the coating. The physical barrier and active immunity of the coating are combined to eliminate cracks while restoring the integrity of the ion transmission channel, thereby improving the cycle performance of the lithium battery.

[0042] Furthermore, the present invention uses chitosan as the primary wall material. The composite wall material formed by emulsification and crosslinking of chitosan with a polyurethane prepolymer effectively coats and protects the internal core material. The polar groups contained in chitosan enhance the dispersibility of the self-healing microcapsules in the ceramic coating and their binding strength with the modified ceramic particles, achieving uniform dispersion of the self-healing microcapsules and reducing their shedding.

[0043] On the other hand, the active amino groups contained in chitosan can react with the boric acid groups on the surface of the modified ceramic particles to form dynamic bonds, repair the cracks between the base film and the coating, and inhibit secondary cracking, thereby further improving the self-healing effect of the self-healing microcapsules in the coating and obtaining a lithium battery composite separator with excellent performance.

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

[0045] S1. Sequentially adding a dispersant, modified ceramic particles, and self-healing microcapsules to water and stirring and dispersing the resulting ceramic slurry;

[0046] S2. The ceramic slurry is evenly coated on the surface of the polymer base film, and after drying, a ceramic coating is formed. The thickness of the ceramic coating is 1 to 3 μm, thereby obtaining a lithium battery separator with self-repairing function.

[0047] Beneficial effects of the present invention:

[0048] 1. The ceramic coating of the present invention incorporates newly added self-healing microcapsules. When the lithium-ion separator is subjected to external stress or punctured by lithium dendrites, the microcapsules rupture. The polyisocyanate in the core material is released, reacting and cross-linking to seal the resulting cracks and rebuild the ion channels, enabling the separator to self-repair. Through the passive defense of the ceramic coating's physical barrier and the active immunity achieved by the self-healing ability of the self-healing microcapsules, the microscopic damage caused by dendrite growth is repaired and the integrity of the ion channels is restored. This not only maintains the good mechanical strength of the lithium battery separator, but also effectively protects the electrochemical performance of the lithium battery, extending its service life.

[0049] 2. In the ceramic coating of the present invention, the ceramic particles are also modified, and amino-phenylboronic acid bifunctional silane is grafted on the surface of the ceramic particles. On the one hand, it can improve the bonding force between the particles and the polymer base membrane and reduce a series of adverse effects caused by particle shedding. On the other hand, the phenylboric acid contained in it can also form dynamic bonds with the amino groups in the self-repairing microcapsule wall material chitosan, resisting some tiny stress effects that are difficult to cause microcapsule rupture, thereby enhancing the self-repairing effect of the lithium battery separator and effectively improving the mechanical strength and cycle performance of the lithium battery separator. DETAILED DESCRIPTION

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

[0051] Preparation Example 1

[0052] Preparation Example 1-1, a modified ceramic particle is prepared according to the following method:

[0053] Dissolve 40 g of 3-aminophenylboronic acid in 250 mL of water, add 60 g of 3-isocyanatepropyltriethoxysilane, and stir at room temperature for 24 h 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 acetic acid-sodium acetate buffer solution, stirred and dispersed, and then 10 g of aluminum oxide (average particle size of 75 μm) was added. The reaction was stirred at room temperature for 12 hours, and 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 added amount of 3-aminophenylboronic acid is 30 g, and the added amount of 3-isocyanatepropyltriethoxysilane is 55 g.

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

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

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

[0059] Preparation Example 1-6, a modified ceramic particle was prepared according to the following method:

[0060] Take 60g of 3-isocyanatepropyltriethoxysilane and add it to 500mL of 0.1mol / L acetic acid-sodium acetate buffer solution. After stirring and dispersing, add 10g of aluminum oxide (average particle size of 75μm) and stir the reaction at room temperature for 12h. Finally, filter, wash and dry to obtain modified ceramic particles.

[0061] Preparation Example 2

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

[0063] 10 g of chitosan and 4 g of polysorbate 20 were added to 100 mL of 1% acetic acid solution, the pH value of the solution was adjusted to 4.7, and the mixture was stirred and dissolved at 60°C to obtain an aqueous phase;

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

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

[0066] 10 g of chitosan and 5 g of polysorbate 20 were added to 100 mL of 1% acetic acid solution, the pH value of the solution was adjusted to 4.7, and the mixture was stirred and dissolved at 60°C to obtain an aqueous phase;

[0067] 9 g of polyurethane prepolymer and 40 g of isophorone diisocyanate were added to 10 g of ethyl acetate, and the mixture was stirred to obtain an oil phase. The oil phase was added dropwise to the aqueous phase, and then 8 g of 1,4-butanediol was added. After stirring and mixing, the mixture was stirred at 50 ° C for 1 hour. Finally, the self-healing microcapsules were obtained after washing, filtering and drying.

[0068] Preparation Example 2-3, a self-repairing microcapsule, was prepared according to the following method:

[0069] 10 g of gum arabic was added to 400 mL of water and dissolved by stirring at 50 °C to obtain an aqueous phase;

[0070] 6.8 g of diphenylmethane diisocyanate and 30 g of isophorone diisocyanate were mixed to obtain an oil phase, which was 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 hours, and then the self-healing microcapsules were obtained by filtration, washing and drying.

[0071] Example

[0072] Example 1: A lithium battery separator with self-repairing function is prepared according to the following process steps:

[0073] S1. 2 parts of sodium polyacrylate, 45 parts of the modified ceramic particles prepared in Preparation Example 1-1 and 6 parts of the self-repairing microcapsules prepared in Preparation Example 2-1 were sequentially added to 55 parts of water and stirred to obtain a ceramic slurry;

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

[0075] Example 2 and Example 3 are lithium battery separators with self-repairing function. The only difference from Example 1 is that the raw material ratio of the ceramic coating is adjusted, as shown in Table 1:

[0076] Table 1 Raw material formula of ceramic coating of Example 1 to Example 3

[0077] Example 1 Example 2 Example 3 Modified ceramic particles / part 45 40 50 Self-repairing microcapsules / unit 6 4 8 Sodium polyacrylate / part 2 0.5 3 Water / part 55 50 60

[0078] Among them, Example 2 and Example 3 both use the modified ceramic particles prepared in Preparation Example 1-1 and the self-repairing microcapsules prepared in Preparation Example 2-1.

[0079] Example 4, a lithium battery separator with self-repairing function, is different from Example 1 only in that the modified ceramic particles prepared in Preparation Example 1-1 are replaced by an equal amount of modified ceramic particles prepared in Preparation Example 1-2.

[0080] Example 5, a lithium battery separator with self-repairing function, is different from Example 1 only in that the modified ceramic particles prepared in Preparation Example 1-1 are replaced by an equal amount of modified ceramic particles prepared in Preparation Example 1-3.

[0081] Example 6, a lithium battery separator with self-repairing function, is different from Example 1 only in that the self-repairing microcapsules prepared in Preparation Example 2-1 are replaced by an equal amount of self-repairing microcapsules prepared in Preparation Example 2-2.

[0082] Example 7, a lithium battery separator with self-repairing function, is different from Example 1 only in that the modified ceramic particles prepared in Preparation Example 1-1 are replaced by an equal amount of modified ceramic particles prepared in Preparation Example 1-3.

[0083] Example 8, a lithium battery separator with self-repairing function, is different from Example 1 only in that the modified ceramic particles prepared in Preparation Example 1-1 are replaced by an equal amount of modified ceramic particles prepared in Preparation Example 1-4.

[0084] Comparative Example

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

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

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

[0088] Comparative Example 4, a lithium battery separator with self-repairing function, is different from Example 1 only in that the modified ceramic particles prepared in Preparation Example 1-1 are replaced by an equal amount of aluminum oxide.

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

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

[0091] Performance testing

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

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

[0094] The obtained lithium-ion battery sample was charged and discharged at a rate of 1C at 25°C for 200 cycles, and the attenuation rate of the battery specific capacity before and after the cycle was tested.

[0095] The above test results are shown in Table 2:

[0096] Table 2 Performance test results

[0097]

[0098] According to Table 2, in combination with Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 6, it can be seen that the peel strength of Comparative Example 1, Comparative Example 2 and Comparative Example 6 is decreased and the capacity attenuation rate is increased compared with that of Example 1, indicating that the interfacial adhesion and self-repairing effect of the ceramic coating of Comparative Example 1, Comparative Example 2 and Comparative Example 6 are decreased. The reason is that the amount of self-repairing microcapsules added in Comparative Example 1 is reduced. Accordingly, the barrier and self-repairing capabilities of the diaphragm are decreased in resisting cyclic stress and dendrite puncture during charge and discharge, and the corresponding performance is decreased. No self-repairing microcapsules are added in Comparative Example 6, and the performance decreases more significantly. In Comparative Example 2, the amount of self-repairing microcapsules added was increased because the surface of the self-repairing microcapsules contained a large number of polar groups, which could combine with the modified ceramic particles, thereby improving the dispersibility and binding force of the self-repairing microcapsules in the ceramic coating. However, when the content of self-repairing microcapsules increased, on the one hand, the binding force with the non-polar polymer membrane was poor, and on the other hand, excessive addition would cause the self-repairing microcapsules to spontaneously aggregate. After being subjected to stress, the released polyisocyanates aggregated and initiated cross-linking, resulting in excessive local rigidity, which is not conducive to maintaining the strength of the ceramic coating and its resistance to cracks, resulting in performance degradation.

[0099] In combination with Example 1, Comparative Example 3 and Comparative Example 4, it can be seen that the peel strength of Comparative Example 3 and Comparative Example 4 is lower than that of Example 1, and the capacity attenuation rate is increased. The reason is that the modified ceramic particles in Comparative Example 3 are only grafted with silane compounds, and there is no composite phenylboronic acid group. The lack of the formation of dynamic bonds between phenylboric acid and self-healing microcapsule chitosan will further affect the stress resistance of the ceramic diaphragm and lead to performance degradation; Comparative Example 4 has not undergone modification treatment, not only lacks the dynamic repair effect, but also affects the bonding force between the ceramic particles and the polymer base film. The falling of ceramic particles during the cycle will not only affect the strength of the diaphragm itself, but also cause uneven lithium ion transmission, resulting in rapid growth of lithium dendrites, which is not conducive to the improvement of cycle performance.

[0100] Combining Example 1 and Comparative Example 5, it can be seen that the various performances of Comparative Example 5 are lower than those of Example 1. The reason is that conventional isocyanate microcapsules are used to replace the self-healing microcapsules of the present application in Comparative Example 5, and its wall material is polyurea obtained by the reaction of gum arabic and isocyanate, which not only leads to a decrease in compatibility and dispersibility, but also lacks synergistic effect with the modified ceramic particles, resulting in a decrease in performance.

[0101] The above disclosures are only a few specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. A lithium battery separator with self-repairing function, characterized in that: The lithium battery separator comprises a polymer base film and a ceramic coating; the ceramic coating is coated on one side of the polymer base film facing the negative electrode or on both sides of the polymer base film; The ceramic coating comprises the following raw materials in parts by mass: 40-50 parts of modified ceramic particles; 4 to 8 parts of self-repairing microcapsules; 0.5-3 parts of dispersant; 50-60 parts water; The surface of the modified ceramic particles is grafted with amino-phenylboronic acid bifunctional silane; The self-repairing microcapsules use chitosan / polyurethane as wall material and polyisocyanate as core material.

2. The lithium battery separator with self-repairing function according to claim 1, characterized in that The raw materials of the modified ceramic particles include ceramic particles, aminophenylboronic acid and silane compounds in a mass ratio of 1:(3-5):(5.5-6.5).

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

4. The lithium battery separator with self-repairing function according to claim 2, characterized in that The aminophenylboronic acid includes one or more of 3-aminophenylboronic acid, 4-aminomethylphenylboronic acid and 3-amino-4-methylphenylboronic acid.

5. The lithium battery separator with self-repairing function according to claim 2, characterized in that: The silane compound includes one or a combination of 3-isocyanatepropyltriethoxysilane and α-isocyanatemethyltriethoxysilane.

6. The lithium battery separator with self-repairing function according to claim 2, characterized in that: The modified ceramic particles are prepared according to the following method: The aminophenylboronic acid is dissolved in a solvent, a silane compound is added, and the mixture is stirred and reacted at room temperature for 20 to 24 hours to obtain amino-phenylboronic acid bifunctional silane; the amino-phenylboronic acid bifunctional silane is added to a buffer solution, stirred and dispersed, and then ceramic particles are added, and the mixture is stirred and reacted at room temperature for 10 to 15 hours. Finally, the modified ceramic particles are obtained by filtering, washing and drying.

7. The lithium battery separator with self-repairing function according to claim 1, characterized in that The raw materials of the self-repairing 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).

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

9. The lithium battery separator with self-repairing function according to claim 1, characterized in that: The polymer-based film includes any one of a polyethylene diaphragm, a polypropylene diaphragm, a polyethylene / polypropylene double-layer co-extruded diaphragm, and a polypropylene / polyethylene / polypropylene three-layer co-extruded diaphragm.

10. A method for preparing a lithium battery separator with self-repairing function according to any one of claims 1 to 9, characterized in that: The process steps include: S1. Sequentially adding a dispersant, modified ceramic particles, and self-healing microcapsules to water and stirring and dispersing the resulting ceramic slurry; S2. The ceramic slurry is evenly coated on the surface of the polymer base film, and after drying, a ceramic coating is formed. The thickness of the ceramic coating is 1 to 3 μm, thereby obtaining a lithium battery separator with self-repairing function.

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