Lithium ion battery and preparation method thereof

Abstract

The invention provides a lithium ion battery and a preparation method thereof. The lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, the positive electrode comprises a first current collector and a positive electrode active layer arranged on the surface of the first current collector, and the negative electrode comprises a second current collector and a negative electrode active layer arranged on the surface of the second current collector; the diaphragm comprises a base membrane, a first microcapsule filled with a repairing agent and a second microcapsule filled with a curing agent, wherein the first microcapsule and the second microcapsule are arranged on at least one side surface of the base membrane; the repairing agent comprises epoxy resin; the electrolyte comprises a self-repairing additive, wherein the self-repairing additive is a sulfydryl-containing compound; the positive electrode active layer and the negative electrode active layer respectively and independently comprise a nano metal oxide and an organic polymer; the organic polymer is selected from any one or more of polyurethane, polycaprolactone and polylactic acid. According to the lithium ion battery, a self-repairing mechanism is established from the three dimensions of the diaphragm, the electrolyte and the electrode coating, the safety of the battery is improved comprehensively, and the cycle life of the battery is prolonged comprehensively.

Description

Technical Field

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

[0002] Lithium-ion batteries, as an important energy storage device, are widely used in electric vehicles, portable electronic devices, and energy storage power stations. However, some problems still exist in the use of lithium-ion batteries, limiting further improvements in their performance and safety.

[0003] Currently, the main safety issue with lithium batteries stems from internal short circuits. During charging and discharging, the expansion and contraction of electrode materials and the presence of impurities can damage the separator, leading to direct contact between the positive and negative electrodes and causing an internal short circuit. In severe cases, this can even result in battery fires and explosions. For example, traditional liquid electrolyte lithium batteries typically use organic solvents as their electrolytes, which are flammable. An internal short circuit triggering high temperatures can easily ignite a fire. Furthermore, over long-term use, the electrode materials undergo gradual structural changes and performance degradation, leading to capacity reduction and shortened cycle life. For instance, during charging and discharging, the insertion and extraction of lithium ions alters the graphite interlayer structure, potentially causing graphite particles to detach after multiple cycles, thus affecting battery performance. To address these issues, several solutions have been proposed. For instance, improving the battery separator material can enhance its mechanical strength and thermal stability, reducing the risk of separator damage. However, this method only reduces the likelihood of separator damage to a certain extent and does not fundamentally solve the internal short circuit problem caused by separator damage. In addition, some approaches aim to improve electrode stability and cycle life by developing novel electrode materials, but these often face challenges such as high cost and complex manufacturing processes, hindering large-scale application. Therefore, there is an urgent need to develop a lithium-ion battery with high safety. Summary of the Invention

[0004] The main objective of this invention is to provide a lithium-ion battery and its preparation method, so as to solve the problems of easy damage to the separator leading to internal short circuits and easy degradation of electrode materials leading to decreased battery performance in existing lithium-ion batteries.

[0005] To achieve the above objectives, according to one aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode comprises a first current collector and a positive electrode active layer disposed on the surface of the first current collector. The negative electrode comprises a second current collector and a negative electrode active layer disposed on the surface of the second current collector. The separator comprises a base film and a first microcapsule and a second microcapsule disposed on at least one side surface of the base film. The first microcapsule comprises a first capsule shell, and the second microcapsule comprises a second capsule shell. The first capsule shell and the second capsule shell each independently form a closed cavity. The cavity of the first microcapsule is filled with a repair agent, and the cavity of the second microcapsule is filled with a curing agent. The repair agent comprises epoxy resin. The electrolyte comprises a self-healing additive, which is a compound containing thiol groups. The positive electrode active layer and the negative electrode active layer each independently comprise nano-metal oxides and organic polymers. The metal element in the nano-metal oxide is selected from any one or more of Ti, Zn, and Al. The organic polymer is selected from any one or more of polyurethane, polycaprolactone, and polylactic acid.

[0006] Furthermore, the first capsule shell and the second capsule shell each independently include, from the inside out, a capsule shell inner layer and a capsule shell outer layer arranged sequentially; the material of the capsule shell inner layer includes polyurea; the material of the capsule shell outer layer is urea-formaldehyde resin and / or phenolic resin; and / or, the ratio of the total mass of the first microcapsule and the second microcapsule to the mass of the base film is 5~20:80~95; and / or, the base film is a polyethylene base film and / or a polyacrylonitrile base film; and / or, the mass ratio of the repair agent to the first capsule shell is 3~7:1~3; and / or, the mass ratio of the capsule shell inner layer to the capsule shell outer layer in the first capsule shell is 1:4~5; and / or, the repair agent is selected from epoxy resin E-44, epoxy resin E-51 and epoxy resin E-54. The membrane comprises any one or more of the following: the molecular weight of the repair agent is 400-1000; and / or the mass ratio of the curing agent to the second capsule shell is 3-7:1-3; the curing agent is an organic amine curing agent selected from any one or more of isophorone diamine, 4,4'-diaminodicyclohexylmethane, and methylcyclohexanediamine; the mass ratio of the inner layer to the outer layer of the capsule shell in the second capsule shell is 1:0.5-0.6; and / or the mass ratio of the curing agent to the repair agent is 1-5:8-15; and / or the diaphragm further comprises an adhesive, which is polyvinylidene fluoride; the mass ratio of the total mass of the first microcapsule and the second microcapsule, the mass of the base membrane, and the mass of the adhesive is 5-20:80-95:1-2.

[0007] Furthermore, the self-healing additive in the electrolyte accounts for 1-5% by mass; the self-healing additive is selected from any one or more of mercaptoacetic acid, mercaptopropionic acid, and mercaptosuccinic acid; and / or, the electrolyte also includes a lithium salt and a first organic solvent; wherein the lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium tetrafluoroborate, and the molar concentration of the lithium salt in the electrolyte is 1-1.5 mol / L; the first organic solvent is selected from any one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0008] Furthermore, the nano-metal oxide in the positive electrode active layer is defined as the first nano-metal oxide, the organic polymer is defined as the first organic polymer, and the mass ratio of the first nano-metal oxide to the first organic polymer is 1~4:2~5; the first nano-metal oxide is selected from any one or more of nano-titanium oxide, nano-zinc oxide and nano-alumina; the first organic polymer is polyurethane and / or polycaprolactone.

[0009] Furthermore, the positive electrode active layer also includes a positive electrode active material and a first conductive agent; the mass ratio of the positive electrode active material to the first conductive agent is 80~95:2~8; the total mass ratio of the first nano-metal oxide and the first organic polymer to the mass of the positive electrode active material is 1~5:10~20; the positive electrode active material is selected from any one or more of lithium iron phosphate materials, lithium manganese iron phosphate materials, and lithium nickel cobalt manganese oxide ternary materials; the first conductive agent is selected from any one or more of conductive carbon black, graphene, and carbon nanotubes.

[0010] Furthermore, the nano-metal oxide in the negative electrode active layer is defined as the second nano-metal oxide, the organic polymer is defined as the second organic polymer, and the mass ratio of the second nano-metal oxide to the second organic polymer is 1~3:3~6; the second nano-metal oxide is selected from any one or more of nano-titanium oxide, nano-zinc oxide and nano-alumina, and the second organic polymer is polyurethane and / or polylactic acid.

[0011] Furthermore, the negative electrode active layer also includes a negative electrode active material and a second conductive agent; the mass ratio of the negative electrode active material and the second conductive agent is 85~98:1~5; the total mass ratio of the second nano-metal oxide and the second organic polymer to the mass of the negative electrode active material is 1~4:15~25; the negative electrode active material is graphite material and / or silicon-carbon composite material; the second conductive agent is selected from any one or more of conductive carbon black, graphene and carbon nanotubes.

[0012] According to another aspect of the present invention, a method for preparing the above-mentioned lithium-ion battery is provided, the method comprising: step S1, mixing raw materials including a first microcapsule, a second microcapsule, and a second organic solvent, and coating the mixture onto at least one side surface of a base film to obtain a separator; step S2, mixing raw materials including a lithium salt, a self-healing additive, and a first organic solvent to obtain an electrolyte; step S3, mixing raw materials including a positive electrode active material, a first conductive agent, a first nano-metal oxide, a first organic polymer, and a third organic solvent to obtain a positive electrode slurry, and coating the positive electrode slurry onto the surface of a first current collector to form a positive electrode active layer to obtain a positive electrode; step S4, mixing raw materials including a negative electrode active material, a second conductive agent, a second nano-metal oxide, a second organic polymer, and a fourth solvent to obtain a negative electrode slurry, and coating the negative electrode slurry onto the surface of a second current collector to form a negative electrode active layer to obtain a negative electrode; and step S5, assembling the positive electrode, the negative electrode, the separator, and the electrolyte to obtain a lithium-ion battery.

[0013] Further, in step S1 above, the raw materials including the binder and the second organic solvent are mixed to obtain a first mixture; the raw materials including the first microcapsule, the second microcapsule and the first mixture are mixed and coated on at least one side of the base film to obtain a diaphragm; wherein, the mass concentration of the binder in the first mixture is 1~5%; and the second organic solvent is N-methylpyrrolidone.

[0014] Further, in step S3 above, the raw materials comprising the first nano-metal oxide, the first organic polymer, and the third organic solvent are mixed to obtain a second mixture; the raw materials comprising the positive electrode active material, the first conductive agent, and the second mixture are mixed to obtain a positive electrode slurry; wherein the third organic solvent is selected from any one or more of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide; and / or, in step S4 above, the raw materials comprising the second nano-metal oxide, the second organic polymer, and the fourth solvent are mixed to obtain a third mixture; the raw materials comprising the negative electrode active material, the second conductive agent, and the third mixture are mixed to obtain a negative electrode slurry; wherein the fourth solvent is selected from any one or more of N-methylpyrrolidone, ethanol, and water.

[0015] Applying the technical solution of this invention, most current lithium-ion batteries only address a single problem, while this application innovatively constructs a self-healing system from three key dimensions: separator, electrolyte, and electrode coating, which can significantly improve battery safety and cycle performance. Specifically, 1) the separator composed of the above has a self-healing function, which can solve the hidden danger of internal short circuits in the battery caused by mechanical damage. The capsule shell has good chemical stability and mechanical strength, can exist stably in the electrolyte, and can effectively rupture and release the internal repair agent when the separator is subjected to external impact. At the same time, the three-dimensional network structure of the capsule shell gives the microcapsules a certain compressive strength, ensuring that they do not rupture prematurely under normal battery operating conditions, preventing premature release of the repair agent. The above-mentioned repair agents have excellent adhesion and polymerization properties. When the damaged part of the separator is exposed, the repair agent can quickly polymerize to form a high-strength repair layer, thereby restoring the separator's isolation function. 2) The self-healing additives mentioned above in the electrolyte contain the active reactive group thiol. During battery charging and discharging, when micro-cracks or defects appear on the electrode surface, a local electric field change occurs on the electrode surface. Driven by the electric field, the self-healing additive molecules migrate towards the defect. Upon reaching the defect, the thiol groups react chemically with the metal atoms on the electrode surface, forming a metal-sulfur bond, thereby constructing a new protective film on the electrode surface and repairing the damage. 3) The positive electrode active layer and the negative electrode active layer have self-healing properties, ensuring the integrity of the electrode structure during long-term charge-discharge cycles. Organic polymers, as self-healing components, contain soft and hard segments in their molecular structure. Soft segments provide good elasticity, while hard segments provide a certain strength. When micro-cracks appear in the positive and negative electrode active layers, under the action of intermolecular van der Waals forces and elastic restoring forces, the organic polymer molecular chains rearrange and flow, filling the cracks and thus improving electrode protection. Furthermore, the self-healing components (separator, electrolyte, and positive and negative electrode active layers) of this application possess intelligent response characteristics. When the separator ruptures due to physical stress changes, the microcapsules in the separator release the repair agent within. The self-healing additives in the electrolyte, under the influence of an electric field, can precisely migrate to the damaged electrode site for repair. The nano-metal oxides in the positive and negative electrode active layers possess high electronic conductivity, and the organic polymers provide self-healing elasticity. The combination of these two components enhances the conductivity of the electrodes and endows the positive and negative electrode active layers with self-repair capabilities. Simultaneously, it achieves a significant leap in battery performance without significantly increasing costs. Therefore, this intelligent response mechanism differs from traditional passive protection methods, not only greatly improving repair accuracy and efficiency but also enabling the battery to self-repair promptly under complex operating conditions, thereby maintaining stable battery performance. In summary, the lithium-ion battery of this application establishes a self-healing mechanism from three dimensions: separator, electrolyte, and electrode coating, comprehensively improving the safety and cycle life of lithium-ion batteries. Detailed Implementation

[0016] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0017] As analyzed in the background section of this application, existing lithium-ion batteries suffer from problems such as easy breakage of the separator leading to internal short circuits and easy degradation of electrode materials leading to decreased battery performance. In order to solve the above problems, this application provides a lithium-ion battery and its preparation method.

[0018] In a typical embodiment of this application, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a first current collector and a positive electrode active layer disposed on the surface of the first current collector. The negative electrode includes a second current collector and a negative electrode active layer disposed on the surface of the second current collector. The separator includes a base film and a first microcapsule and a second microcapsule disposed on at least one side of the base film. The first microcapsule includes a first capsule shell, and the second microcapsule includes a second capsule shell. The first capsule shell and the second capsule shell each independently form a closed cavity. The cavity of the first microcapsule is filled with a repair agent, and the cavity of the second microcapsule is filled with a curing agent. The repair agent includes epoxy resin. The electrolyte includes a self-healing additive. The self-healing additive is a compound containing thiol groups. The positive electrode active layer and the negative electrode active layer each independently include nano-metal oxides and organic polymers. The metal element in the nano-metal oxide is selected from any one or more of Ti, Zn, and Al. The organic polymer is selected from any one or more of polyurethane, polycaprolactone, and polylactic acid.

[0019] Currently, most lithium-ion batteries only address a single problem, while this application innovatively constructs a self-healing system from three key dimensions: separator, electrolyte, and electrode coating, which can significantly improve battery safety and cycle performance. Specifically, 1) the separator composed of the above components has a self-healing function, which can solve the hidden danger of internal short circuits caused by mechanical damage. The capsule shell has good chemical stability and mechanical strength, can exist stably in the electrolyte, and can effectively rupture and release the internal repair agent when the separator is subjected to external impact. At the same time, the three-dimensional network structure of the capsule shell gives the microcapsules a certain compressive strength, ensuring that they do not rupture prematurely under normal battery operating conditions, preventing premature release of the repair agent. The above-mentioned repair agents have excellent adhesion and polymerization properties. When the separator is exposed at the damaged area, the repair agent can rapidly polymerize under the action of the curing agent to form a high-strength repair layer, thereby restoring the separator's isolation function. 2) The self-healing additives mentioned above in the electrolyte contain the active reactive group thiol. During battery charging and discharging, when micro-cracks or defects appear on the electrode surface, a local electric field change occurs on the electrode surface. Driven by the electric field, the self-healing additive molecules migrate towards the defect. Upon reaching the defect, the thiol groups react chemically with the metal atoms on the electrode surface, forming a metal-sulfur bond, thereby constructing a new protective film on the electrode surface and repairing the damage. 3) The positive electrode active layer and the negative electrode active layer have self-healing properties, ensuring the integrity of the electrode structure during long-term charge-discharge cycles. Organic polymers, as self-healing components, contain soft and hard segments in their molecular structure. Soft segments provide good elasticity, while hard segments provide a certain strength. When micro-cracks appear in the positive and negative electrode active layers, under the action of intermolecular van der Waals forces and elastic restoring forces, the organic polymer molecular chains rearrange and flow, filling the cracks and thus improving electrode protection. Furthermore, the self-healing components (separator, electrolyte, and positive and negative electrode active layers) of this application possess intelligent response characteristics. When the separator ruptures due to physical stress changes, the microcapsules in the separator release the repair agent within. The self-healing additives in the electrolyte, under the influence of an electric field, can precisely migrate to the damaged electrode site for repair. The nano-metal oxides in the positive and negative electrode active layers possess high electronic conductivity, and the organic polymers provide self-healing elasticity. The combination of these two components enhances the conductivity of the electrodes and endows the positive and negative electrode active layers with self-repair capabilities. Simultaneously, it achieves a significant leap in battery performance without significantly increasing costs. Therefore, this intelligent response mechanism differs from traditional passive protection methods, not only greatly improving repair accuracy and efficiency but also enabling the battery to self-repair promptly under complex operating conditions, thereby maintaining stable battery performance. In summary, the lithium-ion battery of this application establishes a self-healing mechanism from three dimensions: separator, electrolyte, and electrode coating, comprehensively improving the safety and cycle life of lithium-ion batteries.

[0020] Epoxy resin, as a repair agent, possesses excellent adhesion and polymerization properties. When the diaphragm is exposed due to damage, the epoxy resin rapidly polymerizes under the action of a curing agent, forming a high-strength repair layer. The polymerization process is a ring-opening polymerization reaction; the epoxy groups open under the action of the curing agent and undergo cross-linking reactions with surrounding epoxy resin molecules, forming a tight three-dimensional cross-linked network structure. This effectively fills the diaphragm damage, thereby restoring the diaphragm's isolation function. Preferably, the molecular weights of the materials corresponding to the inner and outer layers of the capsule shell are each independently between 5000 and 20000.

[0021] Taking thioglycolic acid as an example, the thiol group in its molecule is the active reactive group. During battery charging and discharging, when micro-cracks or defects appear on the electrode surface, a local electric field change occurs on the electrode surface. Driven by the electric field, thioglycolic acid molecules migrate towards the defect. Upon reaching the defect, the thiol group reacts chemically with the metal atoms on the electrode surface to form a metal-sulfur chemical bond. For example, on the surface of a lithium metal electrode, the reaction can be represented as: 2RSH + 2Li → (RS)2Li2 + H2. This constructs a new protective film on the electrode surface, thus repairing the damage to the electrode surface.

[0022] Polyurethane, an organic polymer molecule, serves as a self-healing component, containing both soft and hard segments in its molecular structure. The soft segments provide good elasticity, while the hard segments offer a certain level of strength. When micro-cracks appear in the positive and negative electrode active layers, the polyurethane molecular chains rearrange and flow under the influence of intermolecular van der Waals forces and elastic restoring forces, filling the cracks. Simultaneously, the isocyanate groups in polyurethane can chemically react with active hydrogen groups (such as hydroxyl and amino groups) in the surrounding environment, further cross-linking and curing, thereby enhancing the strength of the repaired area and maintaining the protective function of the positive and negative electrode active layers.

[0023] In one embodiment of this application, the first capsule shell and the second capsule shell each independently include, from the inside out, a capsule shell inner layer and a capsule shell outer layer disposed sequentially; the material of the capsule shell inner layer includes polyurea; the material of the capsule shell outer layer is urea-formaldehyde resin and / or phenolic resin; and / or, the ratio of the total mass of the first microcapsule and the second microcapsule to the mass of the base film is 5~20:80~95; and / or, the base film is a polyethylene base film and / or a polyacrylonitrile base film; and / or, the mass ratio of the repair agent to the first capsule shell is 3~7:1~3; and / or, the mass ratio of the capsule shell inner layer to the capsule shell outer layer in the first capsule shell is 1:4~5; and / or, the repair agent is selected from epoxy resin E-44, epoxy resin E-51 and epoxy resin E The repair agent has a molecular weight of 400-1000; and / or, the mass ratio of the curing agent to the second capsule shell is 3-7:1-3; the curing agent is an organic amine curing agent selected from isophorone diamine, 4,4'-diaminodicyclohexylmethane, and methylcyclohexanediamine; the mass ratio of the inner layer to the outer layer of the capsule shell in the second capsule shell is 1:0.5-0.6; and / or, the mass ratio of the curing agent to the repair agent is 1-5:8-15; and / or, the diaphragm also includes an adhesive, which is polyvinylidene fluoride; the mass ratio of the total mass of the first microcapsule and the second microcapsule, the mass of the base membrane, and the mass of the adhesive is 5-20:80-95:1-2.

[0024] Preferably, the first and second capsule shells are double-layered structures. Controlling the materials of the inner and outer layers of the capsule shells within the aforementioned range helps improve the stability of the microcapsules, preventing premature rupture under normal battery operating conditions. When the separator is subjected to external impact, the microcapsules effectively rupture, releasing the internal repair and curing agents, thereby improving the separator's self-repair efficiency and response speed. Preferably, controlling the mass ratio of the total mass of the first and second microcapsules to the mass of the base membrane within the aforementioned range helps improve the separator's self-repair efficiency and response speed. The mass ratio of the total mass of the first and second microcapsules to the mass of the base membrane can be 5:95, 7:93, 10:90, 12:88, 15:85, 17:83, or 20:80, etc.

[0025] Preferring a base membrane type within the aforementioned range helps provide the separator with good mechanical strength and stability. Preferring to control the mass ratio of the repair agent to the first capsule shell, as well as the type and molecular weight of the repair agent, within the aforementioned range, helps improve the separator's self-healing efficiency. This ensures sufficient repair agent within the microcapsules, allowing for full release and effective coverage of the damaged area when the separator is damaged, forming a high-strength repair layer. This restores the separator's isolation function and reduces the risk of internal short circuits in the battery.

[0026] Preferably controlling the mass ratio of the inner to outer layer of the first capsule shell and the mass ratio of the inner to outer layer of the second capsule shell within the aforementioned range helps to further enhance the stability of the microcapsules, thereby preventing premature rupture under normal battery operating conditions. Furthermore, the mass ratio of the repair agent to the first capsule shell can be 3:1, 4:1.5, 5:2, 6:2.5, or 7:3, etc. The mass ratio of the inner to outer layer of the first capsule shell can be 1:4, 1:4.2, 1:4.5, 1:4.7, or 1:5, etc.

[0027] Preferably controlling the mass ratio of the curing agent to the second capsule shell, the mass ratio of the inner layer to the outer layer of the second capsule shell, and the type of curing agent within the aforementioned ranges helps ensure rapid release of the curing agent when the diaphragm is exposed due to damage. This allows the repair agent to rapidly polymerize under the action of the curing agent, forming a high-strength repair layer that effectively fills the diaphragm damage and restores the diaphragm's isolation function. Furthermore, the mass ratio of the curing agent to the second capsule shell can be 3:1, 4:1.5, 5:2, 6:2.5, or 7:3, etc. The mass ratio of the inner layer to the outer layer of the second capsule shell can be 1:0.5, 1:0.52, 1:0.55, 1:0.58, or 0.6, etc. The mass ratio of the curing agent to the repair agent can be 1:8, 2:9, 3:10, 4:13, or 5:15, etc.

[0028] The preferred diaphragm also includes the aforementioned type of binder. Controlling the ratio of the total mass of the first and second microcapsules, the mass of the base membrane, and the mass of the binder within the aforementioned range helps the microcapsules adhere better to the surface of the base membrane, thereby improving the structural stability of the diaphragm. Furthermore, the ratio of the total mass of the first and second microcapsules, the mass of the base membrane, and the mass of the binder can be 5:93:2, 10:88:2, 15:84:1, 18:80:2, or 20:79:1, etc.

[0029] In one embodiment of this application, the self-healing additive in the electrolyte accounts for 1-5% by mass; the self-healing additive is selected from any one or more of mercaptoacetic acid, mercaptopropionic acid, and mercaptosuccinic acid; and / or, the electrolyte further includes a lithium salt and a first organic solvent; wherein the lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium tetrafluoroborate, and the molar concentration of the lithium salt in the electrolyte is 1-1.5 mol / L; the first organic solvent is selected from any one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0030] Preferably controlling the mass percentage and type of self-healing additives in the electrolyte within the aforementioned range helps the self-healing additives to rapidly migrate to the defect sites, react with the electrode surface, and form a protective film, thereby improving the repair efficiency of electrode surface damage. Preferably, the electrolyte also includes lithium salt and a first organic solvent. Controlling the types of lithium salt and the first organic solvent, as well as the molar concentration of lithium salt in the electrolyte, within the aforementioned range not only helps improve the ionic conductivity of the electrolyte, thereby increasing ion transport efficiency, but also helps form a solid electrolyte interphase (SEI) film, thereby improving battery stability and cycle life. Furthermore, the mass percentage of self-healing additives in the electrolyte can be 1%, 2%, 3%, 4%, or 5%, etc.

[0031] In one embodiment of this application, the nano-metal oxide in the positive electrode active layer is defined as the first nano-metal oxide, the organic polymer is defined as the first organic polymer, and the mass ratio of the first nano-metal oxide to the first organic polymer in the positive electrode active layer is 1~4:2~5; the first nano-metal oxide is selected from any one or more of nano-titanium oxide, nano-zinc oxide and nano-alumina; the first organic polymer is polyurethane and / or polycaprolactone.

[0032] Preferably, the types and mass ratio of the first nano-metal oxide and the first organic polymer in the positive electrode active layer are within the aforementioned range, which helps to improve their synergistic effect, thereby further enhancing the conductivity and self-repair capability of the positive electrode. A preferred thickness of 20-80 μm for the positive electrode active layer helps to improve the battery's energy density, optimize internal resistance, and improve the battery's cycle stability and safety. The first current collector includes, but is not limited to, aluminum foil. Furthermore, the mass ratio of the first nano-metal oxide to the first organic polymer in the positive electrode active layer can be 1:5, 2:3, 3:4, or 4:2, etc.

[0033] To further improve the cycle performance of the positive electrode, in one embodiment of this application, the positive electrode active layer further includes a positive electrode active material and a first conductive agent; the mass ratio of the positive electrode active material to the first conductive agent is 80~95:2~8; the total mass ratio of the first nano-metal oxide and the first organic polymer to the mass ratio of the positive electrode active material is 1~5:10~20; the positive electrode active material is selected from any one or more of lithium iron phosphate, lithium manganese iron phosphate, and lithium nickel cobalt manganese oxide ternary materials; the first conductive agent is selected from any one or more of conductive carbon black, graphene, and carbon nanotubes.

[0034] In addition, the ratio of the total mass of the first nano-metal oxide and the first organic polymer to the mass of the positive electrode active material can be 1:10, 1.5:11, 2:12, 2.5:14, 3:15, 3.5:16, 4:17, 4.5:18 or 5:20, etc.

[0035] In one embodiment of this application, the nano-metal oxide in the negative electrode active layer is defined as the second nano-metal oxide, the organic polymer is defined as the second organic polymer, and the mass ratio of the second nano-metal oxide and the second organic polymer in the negative electrode active layer is 1~3:3~6; the second nano-metal oxide is selected from any one or more of nano-titanium oxide, nano-zinc oxide and nano-alumina, and the second organic polymer is polyurethane and / or polylactic acid.

[0036] Preferably, the types and mass ratios of the second nano-metal oxide and the second organic polymer in the negative electrode active layer are within the aforementioned ranges, which helps to improve their synergistic effect, thereby further enhancing the conductivity and self-healing ability of the negative electrode. Preferably, the thickness of the negative electrode active layer is 30~100μm, which helps to improve the energy density, cycle stability, and safety of the battery. Preferably, the second current collector includes, but is not limited to, copper foil. Furthermore, the mass ratio of the second nano-metal oxide and the second organic polymer in the negative electrode active layer is 1:3, 2:3.5, 3:4, 3:5, or 2.5:6, etc.

[0037] To further improve the energy density of the negative electrode, in one embodiment of this application, the negative electrode active layer further includes a negative electrode active material and a second conductive agent; the mass ratio of the negative electrode active material and the second conductive agent is 85~98:1~5; the total mass ratio of the second nano-metal oxide and the second organic polymer to the mass of the negative electrode active material is 1~4:15~25; the negative electrode active material is a graphite material and / or a silicon-carbon composite material; the second conductive agent is selected from any one or more of conductive carbon black, graphene, and carbon nanotubes.

[0038] Furthermore, the mass ratio of the second nano-metal oxide and the second organic polymer to the negative electrode active material can be 1:15, 1.5:16, 2:17, 2.5:18, 3:20, 3.5:12, or 4:25, etc.

[0039] The aforementioned nano-metal oxides and organic polymers form a nano-composite coating layer on the positive or negative electrode active material, and also play a binding role. Therefore, the positive and negative electrode active coatings of this application do not require the addition of binders.

[0040] In another typical embodiment of this application, a method for preparing the above-mentioned lithium-ion battery is provided. The method includes: step S1, mixing raw materials including a first microcapsule, a second microcapsule, and a second organic solvent, and coating them onto at least one side surface of a base film to obtain a separator; step S2, mixing raw materials including a lithium salt, a self-healing additive, and a first organic solvent to obtain an electrolyte; step S3, mixing raw materials including a positive electrode active material, a first conductive agent, a first nano-metal oxide, a first organic polymer, and a third organic solvent to obtain a positive electrode slurry, and coating the positive electrode slurry onto the surface of a first current collector to form a positive electrode active layer to obtain a positive electrode; step S4, mixing raw materials including a negative electrode active material, a second conductive agent, a second nano-metal oxide, a second organic polymer, and a fourth solvent to obtain a negative electrode slurry, and coating the negative electrode slurry onto the surface of a second current collector to form a negative electrode active layer to obtain a negative electrode; and step S5, assembling the positive electrode, the negative electrode, the separator, and the electrolyte to obtain a lithium-ion battery.

[0041] The lithium-ion battery prepared by the above method exhibits excellent self-healing capabilities, thereby improving battery safety and cycle stability. The separator obtained in step S1 possesses excellent self-healing properties, effectively mitigating the risk of internal short circuits caused by mechanical damage. The electrolyte obtained in step S2 contains self-healing additives, which can chemically react with the electrode surface to form a protective film when micro-cracks or defects appear, thus repairing surface damage. The positive and negative electrodes obtained in steps S3 and S4 also possess self-healing properties, ensuring the integrity of the electrode structure during long-term charge-discharge cycles. In summary, the lithium-ion battery of this application establishes a self-healing mechanism from three dimensions: separator, electrolyte, and electrode coating, comprehensively improving the safety and cycle life of the lithium-ion battery. Furthermore, the preparation process of the lithium-ion battery of this application is relatively simple, requiring no additional complex equipment or processes, and is easily achievable for large-scale production.

[0042] In one embodiment of this application, in step S1 above, raw materials including an adhesive and a second organic solvent are mixed to obtain a first mixture; raw materials including a first microcapsule, a second microcapsule and the first mixture are mixed and coated on at least one side of a base film to obtain a diaphragm; wherein, the mass concentration of the adhesive in the first mixture is 1~5%; and the second organic solvent is N-methylpyrrolidone.

[0043] By applying a coating layer containing the first and second microcapsules to the surface of the diaphragm through step S1, the self-healing function of the diaphragm can be improved. Preferably, the mixing method is stirring to form a slurry, and the coating method is spraying or scraping.

[0044] Microcapsules containing repair agents or curing agents are prepared by interfacial polymerization, as exemplarily as follows:

[0045] Preparation of the first microcapsule (containing a repair agent):

[0046] Step 1: Preparation of the inner layer of capsule shell polyurea (PU) (interfacial polymerization method):

[0047] Oil phase preparation: Mix epoxy resin with isocyanate (monomer of capsule shell inner layer material, accounting for 10~20% of the mass of the repair agent), add emulsifier Span 80 (emulsifier, accounting for 1~3% of the mass of the oil phase), stir evenly (200~500 rpm, 5~15 min) to obtain the oil phase.

[0048] Aqueous phase preparation: Dissolve dispersant PVA1788 in deionized water, heat to 55~65℃ and stir until completely dissolved, cool to room temperature and add catalyst triethylamine (EDA) (mass ratio of catalyst to dispersant is 1~5:10), adjust pH to 8~9 to obtain aqueous phase.

[0049] Emulsification and polymerization: The oil phase is slowly added dropwise to the aqueous phase (the mass ratio of oil phase to aqueous phase is 1:3~6), and high-speed shear emulsification (3000~5000 rpm, 10~15 min) is performed to form an O / W emulsion (the droplet size is controlled at 50~100 μm); then the temperature is raised to 50~55℃, and an aqueous solution of chain extender EDA (the molar ratio of chain extender to isocyanate is 1:1~5) is added dropwise. The reaction is kept at this temperature for 2~3 h, and isocyanate and ethylenediamine polymerize at the oil-water interface to form polyurea in the inner layer of the capsule shell, thus obtaining a PU microcapsule dispersion.

[0050] Step 2: Coating the outer layer of the capsule shell with urea-formaldehyde (MF) resin (in-situ polymerization method)

[0051] Preparation of urea-formaldehyde prepolymer: Melamine is mixed with a 35-40% formaldehyde aqueous solution (mass ratio of the two is 1:3-5), the pH is adjusted to 8-9 with sodium hydroxide, and the mixture is heated at 55-65℃ for 1-2 hours to form a transparent urea-formaldehyde prepolymer (solid content is 25-35%).

[0052] Secondary coating: The PU microcapsule dispersion obtained in step 1 is heated to 55~65℃, urea-formaldehyde prepolymer is added, and the pH is adjusted to 4~5 with formic acid (acidic conditions promote urea-formaldehyde polymerization). The reaction is kept at this temperature for 3~4 hours, and the prepolymer is polymerized in situ on the outer surface of the PU shell to form the outer layer of the urea-formaldehyde capsule shell.

[0053] Post-processing: After the reaction, adjust the pH to 7 with sodium hydroxide, cool to room temperature, centrifuge (3000~5000 rpm, 10~15 min), wash with deionized water 3~5 times (to remove free monomers), and vacuum dry at 55~65℃ for 6~10 h to obtain white powdery microcapsules, which are the core-shell materials coated with the repair agent.

[0054] Preparation of the second microcapsule (containing a curing agent):

[0055] Step 1: Preparation of inner polyurea (PU) microcapsules

[0056] Oil phase preparation: Mix the curing agent with isocyanate (monomer of capsule shell inner layer material, accounting for 10~15% of the mass of the repair agent) (the curing agent is an amine, so the amount of isocyanate needs to be reduced to avoid premature reaction), add Span 80, and stir evenly.

[0057] Aqueous phase preparation: Dissolve dispersant PVA1788 in deionized water, heat to 55-65℃ and stir until completely dissolved, then cool to room temperature to obtain the aqueous phase. (No catalyst is added to avoid accelerating the reaction between the curing agent and isocyanate).

[0058] Emulsification and polymerization: The oil phase is dropped into the aqueous phase (the mass ratio of oil phase to aqueous phase is 1:3~6), and high-speed shearing (3000~5000 rpm, 10~15 min) is performed to form an O / W emulsion (the droplet size is controlled at 30~80 μm); the temperature is raised to 40℃ (low temperature slows down the reaction between the curing agent and isocyanate), and an aqueous solution of chain extender EDA (the molar ratio of chain extender to isocyanate is 1:1~5) is added dropwise. The reaction is kept at this temperature for 1~3 h to form the inner layer of the capsule shell, polyurea, and PU microcapsule dispersion is obtained.

[0059] Step 2: Outer urea-formaldehyde (MF) coating: Refer to the preparation method in Step 2 of the first microcapsule. The amount of urea-formaldehyde prepolymer used is 70-80% of the mass of the PU microcapsule (the curing agent has a small molecular weight, so the outer layer thickness needs to be reduced to avoid over-coating and difficulty in release). The reaction temperature in the secondary coating is 55-65℃, and the time is 2-3 hours, finally obtaining a second microcapsule containing the curing agent.

[0060] In one embodiment of this application, in step S3 above, raw materials comprising a first nano-metal oxide, a first organic polymer, and a third organic solvent are mixed to obtain a second mixture; raw materials comprising a positive electrode active material, a first conductive agent, and the second mixture are mixed to obtain a positive electrode slurry; wherein the third organic solvent is selected from any one or more of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide; and / or, in step S4 above, raw materials comprising a second nano-metal oxide, a second organic polymer, and a fourth solvent are mixed to obtain a third mixture; raw materials comprising a negative electrode active material, a second conductive agent, and the third mixture are mixed to obtain a negative electrode slurry; wherein the fourth solvent is selected from any one or more of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide.

[0061] In step S3, the raw materials comprising the first nano-metal oxide, the first organic polymer, and the third organic solvent are mixed, which helps the first nano-metal oxide and the first organic polymer to be fully dispersed in the third organic solvent, forming a uniform suspension. Immersing the positive electrode active material and the first conductive agent in the second mixture helps to form a nanocomposite coating layer on the surface of the positive electrode active material, thereby improving the self-healing ability of the positive electrode.

[0062] In step S4, the raw materials comprising the second nano-metal oxide, the second organic polymer, and the fourth solvent are mixed, which helps the second nano-metal oxide and the second organic polymer to be fully dispersed in the fourth solvent, forming a uniform suspension. Immersing the negative electrode active material and the second conductive agent in the third mixture helps to form a nanocomposite coating layer on the surface of the negative electrode active material, thereby improving the self-healing ability of the negative electrode.

[0063] The positive or negative electrode slurry is preferably coated on the surface of the current collector by spraying.

[0064] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0065] Example 1

[0066] Preparation of the diaphragm:

[0067] 1) Preparation of the first microcapsule (containing the repair agent):

[0068] Step 1: Preparation of polyurea (PU) microcapsules for the inner layer of the capsule shell (interfacial polymerization method)

[0069] Oil phase preparation: Mix 100g of repair agent epoxy resin E-51 (molecular weight 500) with 15g of isocyanate, add 2g of emulsifier Span 80, and stir at 300rpm for 5min to obtain the oil phase.

[0070] Aqueous phase preparation: Dissolve 5g of dispersant PVA1788 in 500mL of deionized water, heat to 60℃ and stir until completely dissolved, cool to room temperature (25℃) and add 0.5g of catalyst triethylamine, adjust the pH to 8 to obtain the aqueous phase.

[0071] Emulsification and polymerization: The oil phase was slowly added dropwise to the aqueous phase (the mass ratio of oil phase to aqueous phase was 1:5), and high-speed shear emulsification (3000 rpm, 10 min) was performed to form an O / W emulsion (the droplet size was controlled at 50~100 μm); then the temperature was raised to 50℃, and 5 g of chain extender EDA aqueous solution was added dropwise. The reaction was kept at this temperature for 2 h, and isocyanate and ethylenediamine were polymerized at the oil-water interface to form the inner layer of the polyurea capsule shell, thus obtaining a PU microcapsule dispersion.

[0072] Step 2: Coating the outer layer of the capsule shell with urea-formaldehyde (MF) resin (in-situ polymerization method)

[0073] Preparation of urea-formaldehyde prepolymer: 30g of melamine was mixed with 90g of a 37% formaldehyde aqueous solution, the pH was adjusted to 8 with sodium hydroxide, and the mixture was heated at 60℃ for 1 hour to form a transparent urea-formaldehyde prepolymer (solid content of 30%).

[0074] Secondary coating: The PU microcapsule dispersion obtained in step 1 (100g of PU microcapsules) was heated to 60℃, and 100g of urea-formaldehyde prepolymer was added. The pH was adjusted to 4 using formic acid, and the reaction was maintained at this temperature for 3 hours. The urea-formaldehyde prepolymer polymerized in situ on the outer surface of the inner layer of the capsule shell to form the outer layer of the urea-formaldehyde capsule shell, thus obtaining the first microcapsule. The first microcapsule includes a first capsule shell, which forms a closed cavity. The cavity of the first microcapsule is filled with a repair agent. The first capsule shell consists of an inner capsule shell and an outer capsule shell arranged sequentially from the inside out. The mass ratio of the repair agent to the first capsule shell is 5:2; the mass ratio of the inner capsule shell to the outer capsule shell is 1:4.

[0075] 2) Preparation of the second microcapsule (containing a curing agent):

[0076] Step 1: Preparation of inner polyurea (PU) microcapsules

[0077] Oil phase preparation: Mix 100g of curing agent 4,4'-diaminodicyclohexylmethane with 12g of isocyanate, add 1.5g of emulsifier Span 80, and stir at 300rpm for 5min to obtain the oil phase.

[0078] Aqueous phase preparation: Dissolve 5g of dispersant PVA1788 in 500mL of deionized water, heat to 60℃ and stir until completely dissolved, then cool to room temperature (25℃) to obtain the aqueous phase.

[0079] Emulsification and polymerization: The oil phase is dropped into the aqueous phase (the mass ratio of oil phase to aqueous phase is 1:6), and high-speed shearing (4000 rpm, 15 min) is performed to form an O / W emulsion (the droplet size is controlled at 30~80 μm); the temperature is raised to 40℃, 4 g of EDA aqueous solution is added dropwise, and the reaction is kept at this temperature for 1.5 h to form a polyurea inner layer, thus obtaining a PU microcapsule dispersion.

[0080] Step 2: Outer urea-formaldehyde (MF) coating: Similar to the preparation method in Step 2 of the first microcapsule, 80g of urea-formaldehyde prepolymer is used to obtain the second microcapsule. The second microcapsule includes a second capsule shell, which forms a closed cavity filled with a curing agent. The second capsule shell comprises an inner shell layer and an outer shell layer arranged sequentially from the inside out. The mass ratio of the curing agent to the second capsule shell is 4:1, and the mass ratio of the inner shell layer to the outer shell layer in the second capsule shell is 1:0.5. The binder PVDF and the second organic solvent N-methylpyrrolidone (NMP) are mixed to obtain a first mixture, with a binder concentration of 3%. 10g of the first microcapsule, 1g of the second microcapsule, and the first mixture are mixed to obtain a liquid mixture, which is then sprayed onto both sides of a polyethylene film to obtain a diaphragm. The ratio of the total mass of the first microcapsule and the second microcapsule, the mass of the base film, and the mass of the binder is 11:88:1, and the ratio of the total mass of the repair agent in 10g of the first microcapsule to the total mass of the curing agent in 1g of the second microcapsule is 8:1.

[0081] Electrolyte preparation:

[0082] Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1:1 to obtain the first organic solvent. Lithium hexafluorophosphate (LiPF6) was dissolved in the first solvent at a molar concentration of 1 mol / L. Then, the self-healing additive mercaptoacetic acid was added and stirred until homogeneous to obtain the electrolyte. The mass percentage of mercaptoacetic acid in the electrolyte was 3%.

[0083] Preparation of the positive electrode:

[0084] A first nano-metal oxide, nano-titanium dioxide (D50 particle size of 50 nm), and a first organic polymer, polyurethane (molecular weight of 80 kDa), are mixed at a mass ratio of 1:3 and dispersed in a third organic solvent, N-methylpyrrolidone, to obtain a second mixture. A positive electrode active material, lithium nickel cobalt manganese oxide (NCM811), a first conductive agent, conductive carbon black, and the second mixture are mixed to obtain a positive electrode slurry. The mass ratio of the positive electrode active material to the first conductive agent is 90:5, and the mass ratio of the total mass of the first nano-metal oxide and the first organic polymer to the mass of the positive electrode active material is 3:15. The positive electrode slurry is sprayed onto the surface of a first current collector aluminum foil to form a positive electrode active layer with a thickness of 50 μm, thus obtaining the positive electrode.

[0085] Preparation of the negative electrode:

[0086] A second nano-metal oxide, nano-titanium dioxide (D50 particle size of 50 nm), and a second organic polymer, polyurethane (molecular weight of 80 kDa), are mixed at a mass ratio of 1:3 and dispersed in a fourth solvent, deionized water, to obtain a third mixture. The negative electrode active material, graphite, the second conductive agent, conductive carbon black, and the third mixture are then mixed to obtain a negative electrode slurry. The mass ratio of the negative electrode active material to the second conductive agent is 95:3, and the total mass ratio of the second nano-metal oxide and the second organic polymer to the negative electrode active material is 2:20. The negative electrode slurry is sprayed onto the surface of a second current collector copper foil to form a 70 μm thick negative electrode active layer, thus obtaining the negative electrode.

[0087] A lithium-ion battery is obtained by assembling the positive electrode, negative electrode, separator, and electrolyte.

[0088] Example 2

[0089] The difference from Example 1 is in the preparation of the diaphragm: the binder in the first mixture is 1%, and the ratio of the total mass of the first microcapsule and the second microcapsule, the mass of the base membrane and the mass of the binder is 15:84:1, thus obtaining the diaphragm.

[0090] Preparation of electrolyte: The electrolyte contains 1.5 mol / L lithium salt and 5% mercaptoacetic acid by mass, thus obtaining the final electrolyte.

[0091] Preparation of the positive electrode: The thickness of the positive electrode active layer is 60 μm, the mass ratio of the positive electrode active material to the first conductive agent is 88:6, the mass ratio of the first nano-metal oxide nano-zinc oxide to the first organic polymer polycaprolactone is 2:5, and the total mass ratio of the first nano-metal oxide nano-zinc oxide and the first organic polymer polycaprolactone to the mass ratio of the positive electrode active material is 5:20, thus obtaining the positive electrode.

[0092] Preparation of the negative electrode: The thickness of the negative electrode active layer is 80 μm, the mass ratio of the negative electrode active material and the second conductive agent is 93:4, the mass ratio of the second nano-metal oxide nano-zinc oxide and the second organic polymer polylactic acid is 1:6, and the total mass ratio of the second nano-metal oxide nano-zinc oxide and the second organic polymer polylactic acid to the mass of the negative electrode active material is 4:25, thus obtaining the negative electrode and the lithium-ion battery.

[0093] Example 3

[0094] The difference from Example 1 is that the mass ratio of the repair agent to the first capsule shell is 6:2.5, the mass ratio of the inner layer to the outer layer of the first capsule shell is 1:5, the mass ratio of the curing agent to the first capsule shell is 6:2.5, the mass ratio of the inner layer to the outer layer of the second capsule shell is 1:0.6, and the mass ratio of the curing agent to the repair agent is 4:15, ultimately yielding a lithium-ion battery.

[0095] Example 4

[0096] The difference from Example 1 is that the mass ratio of the repair agent to the first capsule shell is 2:1, the mass ratio of the inner layer to the outer layer of the capsule shell in the first microcapsule is 1:3, the mass ratio of the curing agent to the second capsule shell is 2:1, the mass ratio of the inner layer to the outer layer of the capsule shell in the second microcapsule is 1:0.8, and the mass ratio of the curing agent to the repair agent is 1:5, ultimately yielding a lithium-ion battery.

[0097] Example 5

[0098] The difference from Example 1 is that the ratio of the total mass of the first microcapsule and the second microcapsule, the mass of the base film and the mass of the binder is 19:80:1, and a lithium-ion battery is finally obtained.

[0099] Example 6

[0100] The difference from Example 1 is that the ratio of the total mass of the first microcapsule and the second microcapsule, the mass of the base film and the mass of the binder is 4:95:1, and a lithium-ion battery is finally obtained.

[0101] Example 7

[0102] The difference from Example 1 is that the mass percentage of mercaptoacetic acid in the electrolyte is 1%, and a lithium-ion battery is finally obtained.

[0103] Example 8

[0104] The difference from Example 1 is that the mass percentage of mercaptoacetic acid in the electrolyte is 0.5%, and a lithium-ion battery is finally obtained.

[0105] Example 9

[0106] The difference from Example 1 is that the mass ratio of the first nano-metal oxide to the first organic polymer in the positive electrode active layer is 1:2, and the ratio of the total mass of the first nano-metal oxide and the first organic polymer to the mass of the positive electrode active material is 1:10, thus obtaining a lithium-ion battery.

[0107] Example 10

[0108] The difference from Example 1 is that the mass ratio of the first nano-metal oxide to the first organic polymer in the positive electrode active layer is 1:1, and the ratio of the total mass of the first nano-metal oxide and the first organic polymer to the mass of the positive electrode active material is 1:20, thus obtaining a lithium-ion battery.

[0109] Example 11

[0110] The difference from Example 1 is that the mass ratio of the second nano-metal oxide and the second organic polymer in the negative electrode active layer is 3:6, and the ratio of the total mass of the second nano-metal oxide and the second organic polymer to the mass of the negative electrode active material is 1:15, thus obtaining a lithium-ion battery.

[0111] Example 12

[0112] The difference from Example 1 is that the mass ratio of the second nano-metal oxide and the second organic polymer in the negative electrode active layer is 1:7, and the total mass ratio of the second nano-metal oxide and the second organic polymer to the mass ratio of the negative electrode active material is 4:30, thus obtaining a lithium-ion battery.

[0113] Comparative Example 1

[0114] The difference from Example 1 is that the diaphragm is a polyethylene-based membrane. No self-healing additives are added to the electrolyte.

[0115] Preparation of the positive electrode: The positive electrode active material lithium nickel cobalt manganese oxide (NCM811), the first conductive agent conductive carbon black, the first binder polyvinylidene fluoride and the third organic solvent are mixed to obtain the positive electrode slurry; wherein, the mass ratio of the positive electrode active material, the first conductive agent and the first binder is 97:1:2, and the positive electrode is finally obtained.

[0116] Preparation of the negative electrode: The raw materials of graphite (negative electrode active material), conductive carbon black (second conductive agent), and styrene-butadiene rubber emulsion (second binder) are mixed to obtain a negative electrode slurry; wherein, the mass ratio of graphite (negative electrode active material), conductive carbon black (second conductive agent), sodium carboxymethyl cellulose and styrene-butadiene rubber emulsion is 96:1:1.2:1.8, and finally a negative electrode is obtained, and finally a lithium-ion battery is obtained.

[0117] Comparative Example 2

[0118] The difference from Example 1 is that the separator is a polyethylene-based membrane, and a lithium-ion battery is finally obtained.

[0119] Comparative Example 3

[0120] The difference from Example 1 is that no self-healing additives are added to the electrolyte, resulting in a lithium-ion battery.

[0121] Comparative Example 4

[0122] The difference from Example 1 lies in the preparation of the positive electrode: the positive electrode active material lithium nickel cobalt manganese oxide (NCM811), the first conductive agent conductive carbon black, the first binder polyvinylidene fluoride and the third organic solvent are mixed to obtain a positive electrode slurry; wherein, the mass ratio of the positive electrode active material, the first conductive agent and the first binder is 97:1:2, and the positive electrode is finally obtained.

[0123] Preparation of the negative electrode: The raw materials of graphite (negative electrode active material), conductive carbon black (second conductive agent), and styrene-butadiene rubber emulsion (second binder) are mixed to obtain a negative electrode slurry; wherein, the mass ratio of graphite (negative electrode active material), conductive carbon black (second conductive agent), sodium carboxymethyl cellulose and styrene-butadiene rubber emulsion is 96:1:1.2:1.8, and finally a negative electrode is obtained, and finally a lithium-ion battery is obtained.

[0124] Test method:

[0125] Electrochemical testing: charging voltage is 4.2V, discharge cutoff voltage is 2.5V, and charge / discharge current is 0.5C.

[0126] Needle penetration test: Use a 3mm diameter steel needle to puncture the battery at a speed of 10mm / s and observe whether it catches fire.

[0127] The test results are shown in Table 1.

[0128] Table 1

[0129]

[0130] As shown in Table 1, compared with Comparative Example 1, the lithium-ion battery of the present application exhibits excellent cycle performance. For the nail penetration test, simulating an internal short circuit, the conventional lithium-ion battery of Comparative Example 1 rapidly ignited and burned after nail penetration. However, in the lithium-ion battery prepared in this application, the self-healing separator and self-healing additives in the electrolyte quickly took effect after nail penetration, preventing further development of the internal short circuit. The battery did not ignite and burned, only exhibiting slight heating, demonstrating the high safety of the lithium-ion battery of this application.

[0131] As can be seen, the safety of the lithium-ion battery of this application is significantly improved: the novel intelligent self-healing separator and the self-healing additives in the electrolyte can quickly and automatically repair themselves when internal short circuits occur, such as separator damage or electrode surface damage, effectively preventing internal short circuits and reducing the safety risks of battery fires and explosions. At the same time, the battery's cycle life is extended: the nano-metal oxides and organic polymers in the positive and negative electrode active layers, as well as the self-healing additives in the electrolyte, can repair damage to the electrodes during charging and discharging, improve electrode stability, and reduce electrode material degradation, thereby significantly extending the battery's cycle life and reducing usage costs.

[0132] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0133] Currently, most lithium-ion batteries only address a single problem, while this application innovatively constructs a self-healing system from three key dimensions: separator, electrolyte, and electrode coating, which can significantly improve battery safety and cycle performance. Specifically, 1) the separator composed of the above components has a self-healing function, which can solve the hidden danger of internal short circuits caused by mechanical damage. The capsule shell has good chemical stability and mechanical strength, can exist stably in the electrolyte, and can effectively rupture and release the internal repair agent when the separator is subjected to external impact. At the same time, the three-dimensional network structure of the capsule shell gives the microcapsules a certain compressive strength, ensuring that they do not rupture prematurely under normal battery operating conditions, preventing premature release of the repair agent. The above-mentioned repair agents have excellent adhesion and polymerization properties. When the separator is exposed at the damaged area, the repair agent can rapidly polymerize to form a high-strength repair layer, thereby restoring the separator's isolation function. 2) The self-healing additives mentioned above in the electrolyte contain the active reactive group thiol. During battery charging and discharging, when micro-cracks or defects appear on the electrode surface, a local electric field change occurs on the electrode surface. Driven by the electric field, the self-healing additive molecules migrate towards the defect. Upon reaching the defect, the thiol groups react chemically with the metal atoms on the electrode surface, forming a metal-sulfur bond, thereby constructing a new protective film on the electrode surface and repairing the damage. 3) The positive electrode active layer and the negative electrode active layer have self-healing properties, ensuring the integrity of the electrode structure during long-term charge-discharge cycles. Organic polymers, as self-healing components, contain soft and hard segments in their molecular structure. Soft segments provide good elasticity, while hard segments provide a certain strength. When micro-cracks appear in the positive and negative electrode active layers, under the action of intermolecular van der Waals forces and elastic restoring forces, the organic polymer molecular chains rearrange and flow, filling the cracks and thus improving electrode protection. Furthermore, the self-healing components (separator, electrolyte, and positive and negative electrode active layers) of this application possess intelligent response characteristics. When the separator ruptures due to physical stress changes, the microcapsules in the separator release the repair agent within. The self-healing additives in the electrolyte, under the influence of an electric field, can precisely migrate to the damaged electrode site for repair. The nano-metal oxides in the positive and negative electrode active layers possess high electronic conductivity, and the organic polymers provide self-healing elasticity. The combination of these two components enhances the conductivity of the electrodes and endows the positive and negative electrode active layers with self-repair capabilities. Simultaneously, it achieves a significant leap in battery performance without significantly increasing costs. Therefore, this intelligent response mechanism differs from traditional passive protection methods, not only greatly improving repair accuracy and efficiency but also enabling the battery to self-repair promptly under complex operating conditions, thereby maintaining stable battery performance. In summary, the lithium-ion battery of this application establishes a self-healing mechanism from three dimensions: separator, electrolyte, and electrode coating, comprehensively improving the safety and cycle life of lithium-ion batteries.

[0134] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises a first current collector and a positive electrode active layer disposed on the surface of the first current collector, and the negative electrode comprises a second current collector and a negative electrode active layer disposed on the surface of the second current collector, characterized in that, The diaphragm includes a base membrane and a first microcapsule and a second microcapsule disposed on at least one side surface of the base membrane. The first microcapsule includes a first capsule shell, and the second microcapsule includes a second capsule shell. The first capsule shell and the second capsule shell each independently form a closed cavity. The cavity of the first microcapsule is filled with a repair agent, and the cavity of the second microcapsule is filled with a curing agent. The repair agent includes epoxy resin. The electrolyte includes a self-healing additive, which is a compound containing a thiol group; The positive electrode active layer and the negative electrode active layer each independently include nano-metal oxides and organic polymers; the metal element in the nano-metal oxide is selected from any one or more of Ti, Zn and Al; the organic polymer is selected from any one or more of polyurethane, polycaprolactone and polylactic acid.

2. The lithium-ion battery according to claim 1, characterized in that, The first capsule shell and the second capsule shell each independently include, from the inside out, a capsule shell inner layer and a capsule shell outer layer arranged sequentially; the material of the capsule shell inner layer includes polyurea; the material of the capsule shell outer layer is urea-formaldehyde resin and / or phenolic resin. And / or, the ratio of the total mass of the first microcapsule and the second microcapsule to the mass of the base film is 5~20:80~95; and / or, the base film is a polyethylene base film and / or a polyacrylonitrile base film; And / or, the mass ratio of the repair agent to the first capsule shell is 3~7:1~3; and / or, the mass ratio of the inner layer of the capsule shell to the outer layer of the capsule shell in the first capsule shell is 1:4~5; and / or, the repair agent is selected from any one or more of epoxy resin E-44, epoxy resin E-51 and epoxy resin E-54, and the molecular weight of the repair agent is 400~1000; And / or, the mass ratio of the curing agent to the second capsule shell is 3~7:1~3; the curing agent is an organic amine curing agent, selected from any one or more of isophorone diamine, 4,4'-diaminodicyclohexylmethane and methylcyclohexane diamine; the mass ratio of the inner layer of the capsule shell to the outer layer of the capsule shell in the second capsule shell is 1:0.5~0.6; And / or, the mass ratio of the curing agent to the repair agent is 1~5:8~15; And / or, the diaphragm further includes an adhesive, the adhesive being polyvinylidene fluoride; the ratio of the total mass of the first microcapsule and the second microcapsule, the mass of the base membrane, and the mass of the adhesive is 5~20:80~95:1~2.

3. The lithium-ion battery according to claim 1, characterized in that, The self-healing additive in the electrolyte accounts for 1-5% of the mass; the self-healing additive is selected from any one or more of mercaptoacetic acid, mercaptopropionic acid and mercaptosuccinic acid. And / or, the electrolyte further includes a lithium salt and a first organic solvent; wherein the lithium salt is selected from any one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium tetrafluoroborate, and the molar concentration of the lithium salt in the electrolyte is 1~1.5 mol / L; the first organic solvent is selected from any one or more of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

4. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The nano-metal oxide in the positive electrode active layer is defined as the first nano-metal oxide, and the organic polymer is defined as the first organic polymer. The mass ratio of the first nano-metal oxide to the first organic polymer is 1~4:2~5. The first nano-metal oxide is selected from any one or more of nano-titanium oxide, nano-zinc oxide, and nano-alumina. The first organic polymer is polyurethane and / or polycaprolactone.

5. The lithium-ion battery according to claim 4, characterized in that, The positive electrode active layer further includes a positive electrode active material and a first conductive agent; the mass ratio of the positive electrode active material to the first conductive agent is 80~95:2~8; the mass ratio of the total mass of the first nano metal oxide and the first organic polymer to the mass of the positive electrode active material is 1~5:10~20; The positive electrode active material is selected from any one or more of lithium iron phosphate materials, lithium manganese iron phosphate materials, and lithium nickel cobalt manganese oxide ternary materials; The first conductive agent is selected from any one or more of conductive carbon black, graphene, and carbon nanotubes.

6. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The nano-metal oxide in the negative electrode active layer is defined as the second nano-metal oxide, and the organic polymer is defined as the second organic polymer. The mass ratio of the second nano-metal oxide to the second organic polymer is 1~3:3~6. The second nano-metal oxide is selected from any one or more of nano-titanium oxide, nano-zinc oxide, and nano-alumina, and the second organic polymer is polyurethane and / or polylactic acid.

7. The lithium-ion battery according to claim 6, characterized in that, The negative electrode active layer further includes a negative electrode active material and a second conductive agent; the mass ratio of the negative electrode active material to the second conductive agent is 85~98:1~5; the total mass ratio of the second nano-metal oxide and the second organic polymer to the mass of the negative electrode active material is 1~4:15~25; The negative electrode active material is a graphite material and / or a silicon-carbon composite material; The second conductive agent is selected from any one or more of conductive carbon black, graphene, and carbon nanotubes.

8. A method for preparing a lithium-ion battery according to any one of claims 1 to 7, characterized in that, The preparation method includes: Step S1: After mixing the raw materials including the first microcapsule, the second microcapsule, and the second organic solvent, the mixture is coated on at least one side of the base membrane to obtain a diaphragm. Step S2: Mix the raw materials including lithium salt, self-healing additive and first organic solvent to obtain electrolyte; Step S3: Mix raw materials including positive electrode active material, first conductive agent, first nano metal oxide, first organic polymer and third organic solvent to obtain positive electrode slurry, and coat the positive electrode slurry on the surface of the first current collector to form positive electrode active layer, thereby obtaining positive electrode; Step S4: Mix raw materials including a negative electrode active material, a second conductive agent, a second nano-metal oxide, a second organic polymer, and a fourth solvent to obtain a negative electrode slurry; coat the negative electrode slurry onto the surface of a second current collector to form a negative electrode active layer, thereby obtaining a negative electrode; and Step S5: Assemble the positive electrode, the negative electrode, the separator, and the electrolyte to obtain the lithium-ion battery.

9. The preparation method according to claim 8, characterized in that, In step S1, raw materials including an adhesive and the second organic solvent are mixed to obtain a first mixture; raw materials including the first microcapsule, the second microcapsule and the first mixture are mixed and coated on at least one side of the base membrane to obtain the diaphragm; wherein, the mass concentration of the adhesive in the first mixture is 1~5%; and the second organic solvent is N-methylpyrrolidone.

10. The preparation method according to claim 8, characterized in that, In step S3, the raw materials comprising the first nano-metal oxide, the first organic polymer, and the third organic solvent are mixed to obtain a second mixture; the raw materials comprising the positive electrode active material, the first conductive agent, and the second mixture are mixed to obtain the positive electrode slurry; wherein the third organic solvent is selected from any one or more of N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide; And / or, in step S4, the raw materials comprising the second nano-metal oxide, the second organic polymer and the fourth solvent are mixed to obtain a third mixture; the raw materials comprising the negative electrode active material, the second conductive agent and the third mixture are mixed to obtain the negative electrode slurry; wherein the fourth solvent is selected from any one or more of N-methylpyrrolidone, ethanol and water.

Images