Diaphragm for non-aqueous secondary battery and preparation method thereof

Abstract

The invention discloses a diaphragm for a non-aqueous secondary battery and a preparation method of the diaphragm. The diaphragm comprises a porous base material, the surfaces of the two sides of the porous base material are coated with first polymer porous layers, the surfaces of the first polymer porous layers are coated with second polymer porous layers, and the surfaces of the second polymer porous layers are coated with inorganic ceramic layers; wherein the first polymer porous layer contains dynamic covalent bonds, the second polymer porous layer has a porous structure, the porous structure is filled with carbon nanotubes and microcapsules, the microcapsules are internally provided with organic phase change materials, and the inorganic ceramic layer comprises inorganic ceramic nanowires and solid electrolyte nanosheets; through the mode, the strength and the lithium dendrite resistance of the battery diaphragm can be improved, and meanwhile, the high lithium ion conduction rate can be kept.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and in particular to a separator for a non-aqueous secondary battery and a preparation method thereof. Background Art

[0002] As global energy is gradually consumed, available non-renewable energy will become less and less, and the continuous use of non-renewable energy will bring challenges to the environment. Sustainable energy has the advantages of sustainable use, environmental friendliness, safety and convenience, and lithium-ion batteries have attracted much attention among sustainable energy.

[0003] Lithium-ion batteries are currently the most convenient energy storage devices with high energy density. They dominate the power supply market from electronic products to electric vehicles and are the most widely used commercial energy storage system. Traditional liquid LiBs have good ionic conductivity, high specific energy, and long life. However, due to the flammability of liquid organic electrolytes, uncontrollable chemical side reactions, and the growth of lithium dendrites that easily cause internal short circuits, LiBs therefore have huge safety hazards. Moreover, as the lithium-ion battery market continues to expand, the demand for battery capacity and energy density is also increasing. In this case, the capacity of LiBs has long failed to meet the requirements, so lithium metal anodes have attracted much attention due to their high theoretical capacity and low redox potential, but this anode has not yet been put into practical use. Because during the charging process, lithium dendrites are very easy to form on the metal surface. After the dendrites grow to a certain extent, they may pierce the diaphragm, causing thermal runaway and short circuits, reducing battery safety.

[0004] Semi-solid batteries have the advantages of both liquid and solid batteries, with high energy density and good safety, so they have the potential to become the next generation of batteries. In semi-solid batteries, the quality of the separator is directly related to the performance and life of the battery.

[0005] Semi-solid batteries can effectively reduce the amount of liquid electrolyte in lithium-ion batteries, reduce the potential safety hazards caused by liquid electrolytes, and will not easily explode when encountering abnormal usage conditions such as overcharge, over-discharge, impact, crushing and puncture. However, the inhibitory effect of semi-solid battery separators on lithium dendrites is still limited, and the heat resistance of the separator is far inferior to that of solid electrolyte separators. At the same time, the effect of improving ion conductivity is not good. Therefore, it is necessary to further improve the ability of semi-solid battery separators to inhibit lithium dendrites and heat resistance to improve battery safety performance, reduce battery impedance, and increase battery life. A non-porous aramid diaphragm and lithium battery reported in the Chinese patent with publication number CN119231091A prevents the growth of lithium dendrites by removing the pores of the diaphragm and introduces sulfonic acid groups as ion transition sites to increase the number of lithium ion migration, but it will greatly reduce the lithium ion permeability and affect the charge and discharge rate; Patent CN110171833A introduces a gel electrolyte with lithium salt into the battery, which can effectively improve the ion conductivity. The porous silica nanofibers therein are also beneficial to increase the heat resistance, but they are only attached to the silica by impregnation. The amount of lithium salt on the surface is limited, and the improvement of ionic conductivity is not obvious. The loose gel structure and a small amount of nanofibers have limited effect on improving the heat resistance of the diaphragm, and the resistance to lithium dendrites is poor. Patent CN117996347A constructs dynamic hydrogen bonds on the porous layer of the diaphragm polymer to achieve self-repair of the micro-short-circuit area of ​​the diaphragm caused by lithium dendrites and self-extinguishing of the diaphragm under thermal runaway, effectively improving the safety of lithium-ion batteries. However, the strength of the diaphragm is low, the resistance to lithium dendrites is poor, the proportion of flame retardants is low, and the heat resistance effect is insufficient.

[0006] For semi-solid batteries with higher energy density, the separator design must be able to inhibit the growth of lithium dendrites, maintain high ionic conductivity, and have high heat resistance and certain self-healing ability. Therefore, the existing lithium battery separators still need to be improved. Summary of the invention

[0007] In view of the deficiencies in the prior art, the present invention provides a non-aqueous secondary battery separator and a preparation method thereof, which improves the strength and lithium dendrite resistance of the battery separator while maintaining a high lithium ion conductivity.

[0008] To achieve the above purpose, the present invention adopts the following technical solutions: A non-aqueous secondary battery separator comprises a porous substrate, wherein both sides of the porous substrate are coated with a first polymer porous layer, the first polymer porous layer is coated with a second polymer porous layer, and the second polymer porous layer is coated with an inorganic ceramic layer; wherein the first polymer porous layer contains dynamic covalent bonds, the second polymer porous layer has a porous structure, the porous structure is filled with carbon nanotubes and microcapsules, the microcapsules have organic phase change materials inside, the inorganic ceramic layer comprises inorganic ceramic nanowires and solid electrolyte nanosheets; by adding solid Solid electrolyte nanosheets can not only improve the ionic conductivity of the porous substrate, but also partially replenish the lithium ions lost during the formation process, thereby improving the battery cycle life. In addition, inorganic ceramic nanowires with extremely high rigidity are used in the inorganic ceramic layer to form a strong lithium dendrite-resistant layer with the solid electrolyte nanosheets, thereby improving the lithium dendrite resistance of the diaphragm. By adding carbon nanotubes to the second polymer layer, the ionic conductivity of the coating can be effectively improved. Since the microcapsules are filled with phase change materials, the microcapsules can absorb heat by dissolving when the battery temperature is out of control, thereby delaying the thermal runaway of the battery. The first polymer porous layer forms a thermal response at high temperature, and recovers by cooling, thereby preventing diaphragm defects caused by coating damage.

[0009] As a preferred embodiment, the porous substrate is a composite porous material formed by stacking one or more of a porous membrane, a porous aromatic skeleton, a non-woven fabric, a molecular sieve and a mesoporous material; the first polymer porous layer is formed by coating a first polymer slurry on the surface of the porous substrate, the first polymer slurry includes a first polymer containing a dynamic covalent bond and a first solvent, the first polymer is one of aramid, polyvinylidene fluoride, polymethacrylate, polyacrylonitrile, and vinylidene fluoride-co-hexafluoropropylene resin; the second polymer porous layer is formed by coating a second polymer slurry on the surface of the first polymer porous layer, the second polymer slurry includes a second polymer, a foaming agent, carbon nanotubes, microcapsules and a catalyst, the second polymer is aramid, polyvinylidene fluoride, polymethacrylate, polyacrylonitrile, and vinylidene fluoride-co-hexafluoropropylene resin. The second polymer porous layer is composed of one or a mixture of two or more of polyvinylidene fluoride-co-hexafluoropropylene; the microcapsule is one of SiO2@trimethylolethane capsule, polyurea@paraffin capsule, and Al2O3@maltitol capsule; the inorganic ceramic layer is formed by coating an inorganic ceramic slurry on the surface of the second polymer porous layer, the inorganic ceramic slurry includes inorganic ceramic nanowires, solid electrolyte nanosheets, glue and a second solvent, the inorganic ceramic nanowires are one of hydroxyapatite nanowires, Al2O3 nanowires, SiO2 nanowires, and hydroxyaluminum oxide nanowires; the solid electrolyte nanosheets are one of LATP nanosheets, LLZO nanosheets, LAGP nanosheets, and LLTO nanosheets; the glue is one of polyimide, polyacrylic acid, and polyacrylate.

[0010] As a preferred solution, the thickness of the porous substrate is 3-20 μm; the thickness of the first polymer porous layer is 0.5-3 μm; the thickness of the second polymer porous layer is 2-8 μm; and the thickness of the inorganic ceramic layer is 3-7 μm.

[0011] As a preferred embodiment, in the first polymer slurry, the mass percentage of the first polymer containing dynamic covalent bonds is 1-20%; and the mass percentage of the first solvent is 80%-99%.

[0012] As a preferred embodiment, the mass percentage of the second polymer in the second polymer slurry is 1-20%, the mass percentage of the foaming agent is 0.1-2%, the mass percentage of the carbon nanotubes is 2-5%, the mass percentage of the microcapsules is 6.0-12.0%, the mass percentage of the catalyst is 0.01-0.2%, the sum of the proportions of each component is 100%, and the total mass percentage of solid matter in the second polymer slurry is 5-40%.

[0013] As a preferred embodiment, the organic phase change material is composed of a mixture or derivatives of one or more of mannitol, maltitol, trimethylolethane, pentaerythritol, paraffin, fatty acid, and polyethylene glycol.

[0014] As a preferred embodiment, the mass percentage of inorganic ceramic nanowires in the inorganic ceramic layer is 12-25.5%, the mass percentage of solid electrolyte nanosheets is 4.5-18%, the mass percentage of glue is 0.6-3%, the mass percentage of the second solvent is 50-85%, and the sum of the proportions of each component is 100%; the total mass percentage of solid matter in the inorganic ceramic layer is 15-50%.

[0015] A method for preparing a separator for a non-aqueous secondary battery comprises the following steps: Step 1, first coating: dissolving a first polymer in a first solvent to form a slurry, then coating the first polymer slurry on a porous substrate, curing it in a first coagulation bath, then curing it in a second coagulation bath, and then drying the water to obtain a diaphragm coated with a first polymer porous layer on the surface; Step 2, second coating: a second polymer, a foaming agent, carbon nanotubes, microcapsules, and a catalyst are mixed and stirred to form a second polymer slurry, and the diaphragm prepared in step 1 is preheated at 80°C-100°C for 20-30min, and then the second polymer slurry is coated on the surface of the first polymer porous layer, and placed at 100°C-180°C for 15-30min for foaming, and then dried at 25°C-140°C for 2-3h to obtain a diaphragm coated with the first polymer porous layer and the second polymer porous layer; Step three, the third coating: the inorganic ceramic nanowires, solid electrolyte nanosheets, glue, and the second solvent are mixed and stirred to form an inorganic ceramic slurry, and then the inorganic ceramic slurry is coated on the diaphragm prepared in step two, and dried in an oven at 60°C-100°C for 5-30 minutes to obtain a finished diaphragm.

[0016] As a preferred embodiment, the coagulation bath in step one is composed of a good solvent and a phase separation agent, the mass percentage of the good solvent in the coagulation bath is greater than or equal to 20%, and the mass percentage of the phase separation agent is less than or equal to 80%, the good solvent is dimethylacetamide, N-methylpyrrolidone, dimethylformamide, and the phase separation agent is one of deionized water, ethanol, isopropanol, and glycerol.

[0017] As a preferred embodiment, in step 1, the mass percentage of the good solvent in the first coagulation bath is 60%, and the mass percentage of the phase separation agent is 40%; the mass percentage of the good solvent in the second coagulation bath is 20%, and the mass percentage of the phase separation agent is 80%.

[0018] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, by adding solid electrolyte nanosheets to the inorganic ceramic layer, not only can the ionic conductivity of the porous substrate be improved, but also the lithium ions lost in the formation process can be partially supplemented, thereby improving the battery cycle life. In addition, inorganic ceramic nanowires with excellent rigidity are used in the inorganic ceramic layer, which can form a strong lithium dendrite-resistant layer with the solid electrolyte nanosheets, thereby improving the lithium dendrite resistance of the diaphragm. By adding carbon nanotubes to the second polymer layer, the ionic conductivity of the coating can be effectively improved. Since the microcapsules are filled with phase change materials, the microcapsules can reduce the heating rate by dissolving and absorbing heat when the battery temperature is out of control, thereby playing the role of delaying the thermal runaway of the battery. The first polymer porous layer forms a thermal response at high temperature, and recovers by cooling, thereby preventing diaphragm defects caused by coating damage.

[0019] In order to more clearly explain the structural features, technical means and specific purposes and functions achieved by the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments: BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic structural diagram of an embodiment of the present invention.

[0021] Description of the accompanying drawings: 10 - porous substrate; 20 - first polymer porous layer; 30 - second polymer porous layer; 40 - inorganic ceramic layer. DETAILED DESCRIPTION

[0022] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside" and "outside" etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the positions or elements referred to must have specific directions, be constructed and operated in specific directions. Therefore, they should not be understood as limitations on the present invention.

[0023] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0024] like Figure 1 As shown, the present invention discloses a separator for a non-aqueous secondary battery, comprising a porous substrate 10, wherein the surfaces of both sides of the porous substrate 10 are coated with a first polymer porous layer 20, the surface of the first polymer porous layer 20 is coated with a second polymer porous layer 30, and the surface of the second polymer porous layer 30 is coated with an inorganic ceramic layer 40; wherein the first polymer porous layer 20 contains dynamic covalent bonds, the second polymer porous layer 30 has a porous structure, the porous structure is filled with carbon nanotubes and microcapsules, the microcapsules have organic phase change materials inside, and the inorganic ceramic layer 40 contains inorganic ceramic nanowires and solid electrolyte nanosheets; By adding solid electrolyte nanosheets to the inorganic ceramic layer 40, not only can the ionic conductivity of the porous substrate 10 be improved, but also the lithium ions lost during the formation process can be partially supplemented, thereby improving the battery cycle life. In addition, inorganic ceramic nanowires with excellent rigidity are used in the inorganic ceramic layer 40 to form a strong lithium dendrite-resistant layer with the solid electrolyte nanosheets, thereby improving the lithium dendrite resistance of the diaphragm. By adding carbon nanotubes to the second polymer layer, the ionic conductivity of the coating can be effectively improved. Since the microcapsules are filled with phase change materials, the microcapsules can reduce the heating rate by dissolving and absorbing heat when the battery temperature is out of control, thereby playing a role in delaying the thermal runaway of the battery. The first polymer porous layer 20 forms a thermal response at high temperature, and recovers by cooling to prevent diaphragm defects caused by coating damage.

[0025] The porous substrate 10 is a composite porous material formed by stacking one or more of a porous membrane, a porous aromatic skeleton, a non-woven fabric, a molecular sieve and a mesoporous material; the first polymer porous layer 20 is formed by coating a first polymer slurry on the surface of the porous substrate 10, the first polymer slurry includes a first polymer containing a dynamic covalent bond and a first solvent, the first polymer is one of aramid, polyvinylidene fluoride, polymethacrylate, polyacrylonitrile, and vinylidene fluoride-co-hexafluoropropylene resin; the second polymer porous layer 30 is formed by coating a second polymer slurry on the surface of the first polymer porous layer 20, the second polymer slurry includes a second polymer, a foaming agent, carbon nanotubes, microcapsules and a catalyst, the second polymer is aramid, polyvinylidene fluoride, polymethacrylate The second polymer porous layer is composed of one or a mixture of two or more of ester, polyvinylidene fluoride-co-hexafluoropropylene; the microcapsule is one of SiO2@trimethylolethane capsule, polyurea@paraffin capsule, Al2O3@maltitol capsule; the inorganic ceramic layer 40 is formed by coating an inorganic ceramic slurry on the surface of the second polymer porous layer, the inorganic ceramic slurry includes inorganic ceramic nanowires, solid electrolyte nanosheets, glue and a second solvent, the inorganic ceramic nanowires are one of hydroxyapatite nanowires, Al2O3 nanowires, SiO2 nanowires, hydroxyaluminum oxide nanowires; the solid electrolyte nanosheets are one of LATP nanosheets, LLZO nanosheets, LAGP nanosheets, and LLTO nanosheets; the glue is one of polyimide, polyacrylic acid, and polyacrylate.

[0026] The thickness of the porous substrate 10 is 3-20 μm; the thickness of the first polymer porous layer 20 is 0.5-3 μm; the thickness of the second polymer porous layer 30 is 2-8 μm; and the thickness of the inorganic ceramic layer 40 is 3-7 μm.

[0027] In the first polymer slurry, the mass percentage of the first polymer containing dynamic covalent bonds is 1-20%; the mass percentage of the first solvent is 80%-99%.

[0028] The mass percentage of the second polymer in the second polymer slurry is 1-20%, the mass percentage of the foaming agent is 0.1-2%, the mass percentage of the carbon nanotubes is 2-5%, the mass percentage of the microcapsules is 6.0-12.0%, the mass percentage of the catalyst is 0.01-0.2%, the sum of the proportions of each component is 100%, and the total mass percentage of solid matter in the second polymer slurry is 5-40%.

[0029] The organic phase change material is composed of a mixture or derivatives of one or more of mannitol, maltitol, trimethylolethane, pentaerythritol, paraffin, fatty acid, and polyethylene glycol.

[0030] The mass percentage of inorganic ceramic nanowires in the inorganic ceramic layer 40 is 12-25.5%, the mass percentage of solid electrolyte nanosheets is 4.5-18%, the mass percentage of glue is 0.6-3%, the mass percentage of the second solvent is 50-85%, and the sum of the proportions of each component is 100%; the total mass percentage of solid matter in the inorganic ceramic layer 40 is 15-50%.

[0031] A method for preparing a separator for a non-aqueous secondary battery comprises the following steps: Step 1, first coating: dissolving the first polymer in the first solvent to form a slurry, and then coating the first polymer slurry on the porous substrate 10, curing it in the first coagulation bath, and then curing it in the second coagulation bath, and then drying the water to obtain a diaphragm coated with the first polymer porous layer 20 on the surface; Step 2, second coating: a second polymer, a foaming agent, carbon nanotubes, microcapsules, and a catalyst are mixed and stirred to form a second polymer slurry, and the diaphragm prepared in step 1 is preheated at 80°C-100°C for 20-30min, and then the second polymer slurry is coated on the surface of the first polymer porous layer 20, and placed at 100°C-180°C for 15-30min for foaming, and then dried at 25°C-140°C for 2-3h to obtain a diaphragm coated with the first polymer porous layer 20 and the second polymer porous layer 30; Step three, the third coating: the inorganic ceramic nanowires, solid electrolyte nanosheets, glue, and the second solvent are mixed and stirred to form an inorganic ceramic slurry, and then the inorganic ceramic slurry is coated on the diaphragm prepared in step two, and dried in an oven at 60°C-100°C for 5-30 minutes to obtain a finished diaphragm.

[0032] The coagulation bath in step 1 is composed of a good solvent and a phase separation agent, the mass percentage of the good solvent in the coagulation bath is greater than or equal to 20%, and the mass percentage of the phase separation agent is less than or equal to 80%, the good solvent is dimethylacetamide, N-methylpyrrolidone, dimethylformamide, and the phase separation agent is one of deionized water, ethanol, isopropanol, and glycerol.

[0033] In step 1, the mass percentage of the good solvent in the first coagulation bath is 60%, and the mass percentage of the phase separation agent is 40%; the mass percentage of the good solvent in the second coagulation bath is 20%, and the mass percentage of the phase separation agent is 80%.

[0034] The following examples and comparative examples are given to further illustrate the technical solution of the present application, but the present application is not limited to these examples.

[0035] Example 1

[0036] Diaphragm production: Preparation of the first polymer porous layer 20: Dissolve the modified aramid containing dynamic covalent bonds (first polymer) in dimethylacetamide (first solvent) to form a first polymer slurry, and the solid content of the slurry is 10%.

[0037] The first polymer slurry is coated in equal amounts on the surface of a polyethylene porous membrane (thickness 9 μm, air permeability 120 s / 100 cc, porosity 50%), and immersed in a first coagulation bath (water: dimethylformamide: N-methylpyrrolidone = 40:50:10 (mass percentage)) to solidify it, and then immersed in a second coagulation bath (water: dimethylformamide = 80:20 (mass percentage)) to solidify it, and then washed and dried to obtain a polyethylene porous membrane coated with a first polymer porous layer 20 on the surface. The thickness of the first polymer porous layer 20 is 1.5 μm. Regarding the preparation process of SiO2@trimethylolethane capsules: porous SiO2 and deionized water are ultrasonically formed into a dispersion liquid 1, polypropylene imine and deionized water are mixed to form a solution 1, the dispersion liquid 1 is mixed with the solution 1, and heated to 90°C, maintained for 2 hours, and the mixed liquid is centrifuged, ultrasonically washed, and dried to obtain a hollow porous SiO2. Trimethylolethane and hollow porous SiO2 were mixed, stirred and heated to 200°C, and the mixture was transferred to a vacuum oven at 200°C and stored for 30 minutes, then centrifuged, washed, and dried at room temperature to obtain microcapsules.

[0038] Aramid fiber accounting for 10% of the total mass percentage of the slurry is dispersed into a nanofiber (ANF) aqueous solution, and then 1% of NaHCO3, 1% of oxalic acid, 5% of carbon nanotubes, 10% of microcapsules, 0.1% of triethylenediamine, and 72.9% of deionized water are added and stirred to form a second polymer slurry with a solid content of 27.1%.

[0039] The polyethylene porous membrane coated with the first polymer porous layer 20 was placed in a 100°C oven for preheating for 30 minutes, and then the second polymer slurry was evenly coated on the surface of the first polymer porous layer 20, and then placed for 30 minutes for foaming, and the expansion height was monitored in real time, and finally dried at 100°C for 2 hours for curing. The thickness of the second polymer porous layer 30 was 4.0 μm.

[0040] 18% of hydroxyapatite nanowires, 10.5% of LATP nanosheets, 1.5% of polyimide and 70% of deionized water are mixed and stirred to form an inorganic ceramic slurry with a solid content of 30%.

[0041] The inorganic ceramic slurry was coated on the surface of the second polymer porous layer 30 in equal amounts and dried in an oven at 60° C. for 5 minutes to obtain a composite separator having an inorganic ceramic layer 40 formed of hydroxyapatite nanowires and LATP nanosheets on the surface of the second polymer porous layer 30. The inorganic ceramic layer 40 had a thickness of 5.0 μm.

[0042] The separator was placed in a vacuum oven and dried at 60° C. for 10 h to ensure that the separator was completely dry before assembling the battery to obtain the battery to be tested.

[0043] Example 2

[0044] Diaphragm production: Preparation of the first polymer porous layer 20: Dissolve modified polymethyl methacrylate containing dynamic covalent bonds (first polymer) in dimethylacetamide (first solvent) to form a first polymer slurry, and the solid content of the slurry is 10%.

[0045] The first polymer slurry is coated in equal amounts on the surface of a polyethylene porous membrane (membrane thickness 20 μm, air permeability 160 s / 100 cc, porosity 50%), and immersed in a first coagulation bath (ethanol: dimethylformamide: N-methylpyrrolidone = 40:50:10 (mass percentage)) to solidify it, and then immersed in a second coagulation bath (ethanol: dimethylformamide = 80:20 (mass percentage)) to solidify it, and then washed with water and dried to obtain a polyethylene porous membrane with a first polymer porous layer 20 coated on the surface. The first polymer porous layer 20 has a thickness of 0.5 μm.

[0046] Regarding the preparation process of polyurea@paraffin capsules: paraffin accounting for 4.22% of the total mass percentage of the emulsion is dissolved in toluene (total mass percentage 8.43%, 60°C water bath), HDI (total mass percentage 1.55%, molar ratio of NCO:NH2=1:1) is added to form an oil phase, and an emulsifier (SDS, total mass percentage 0.85%) is added to deionized water accounting for 84.32% of the total mass percentage of the emulsion. After stirring and dissolving, amines (DETA, total mass percentage 0.63%) are added to form an aqueous phase. The oil phase is slowly poured into the aqueous phase, and high-speed homogenization (10000 rpm, 5min) is used to form an O / W emulsion. The reaction is carried out at 60°C for 2h, microcapsules are collected by centrifugation, and microcapsules are obtained by vacuum drying.

[0047] Polymethyl methacrylate (second polymer) accounting for 10% of the total mass percentage of the slurry, azodicarbonamide accounting for 1% of the total mass percentage, carbon nanotubes accounting for 5% of the total mass percentage, microcapsules accounting for 10% of the total mass percentage, triethylenediamine accounting for 0.1% of the total mass percentage, and deionized water accounting for 73.9% of the total mass percentage are stirred to form a second polymer slurry, and the solid content of the slurry is 26.1%.

[0048] The polyethylene porous membrane coated with the first polymer porous layer 20 was placed in an oven at 80°C for preheating for 20 minutes, and then the second polymer slurry was evenly coated on the surface of the first polymer porous layer 20, placed at 160°C for 15 minutes for foaming, and the expansion height was monitored in real time, and finally naturally cooled to room temperature (25°C) for curing, which took 3 hours. The thickness of the second polymer porous layer 30 was 8.0 μm.

[0049] SiO2 nanowires accounting for 18% of the total mass percentage of the slurry, LLZO nanosheets accounting for 10.5% of the total mass percentage, polyacrylic acid accounting for 1.5% of the total mass percentage, and deionized water accounting for 70% of the total mass percentage are mixed and stirred to form an inorganic ceramic slurry with a solid content of 30%.

[0050] The inorganic ceramic slurry was coated on the surface of the second polymer porous layer 30 in equal amounts and dried in an oven at 80° C. for 15 minutes to obtain a composite separator having an inorganic ceramic layer 40 formed of SiO2 nanowires and LLZO nanosheets on the surface of the second polymer porous layer 30. The inorganic ceramic layer 40 had a thickness of 3.0 μm.

[0051] In the same manner as in Example 1, a test battery of Example 2 was produced.

[0052] Example 3

[0053] Diaphragm production: Preparation of the first polymer porous layer 20: Dissolve the modified polyvinylidene fluoride containing dynamic covalent bonds (first polymer) in dimethylacetamide (first solvent) to form a first polymer slurry, and the solid content of the slurry is 10%.

[0054] The first polymer slurry is coated in equal amounts on the surface of a polyethylene porous membrane (membrane thickness 3 μm, air permeability 100 s / 100 cc, porosity 50%), and immersed in a first coagulation bath (isopropanol: dimethylformamide: N-methylpyrrolidone = 40:50:10 (mass percentage)) to solidify it, and then immersed in a second coagulation bath (isopropanol: dimethylformamide = 80:20 (mass percentage)) to solidify it, and then washed with water and dried to obtain a first polymer porous layer 20 on both sides of the polyethylene porous membrane. The thickness of the first polymer porous layer 20 is 3.0 μm.

[0055] About Al2O3@maltitol capsule process: Porous Al2O3 and deionized water are ultrasonically formed into dispersion liquid 2, polypropylene imine and deionized water are mixed to form solution 2, dispersion liquid 2 is mixed with solution 2, and heated to 90°C for 2 hours, the mixed liquid is centrifuged, ultrasonically washed, and dried to obtain hollow porous Al2O3. Maltitol and hollow porous Al2O3 are mixed, stirred and heated to 150°C, the mixture is transferred to a vacuum oven at 150°C, stored for 30 minutes, and then centrifuged, washed, and dried at room temperature to obtain microcapsules.

[0056] 10% of polyvinylidene fluoride (second polymer) accounting for the total mass percentage of the slurry, 1% of NaHCO3, 1% of oxalic acid, 5% of carbon nanotubes, 10% of microcapsules, 0.1% of triethylenediamine, and 72.9% of deionized water are stirred to form a second polymer slurry with a solid content of 27.1%.

[0057] The polyethylene porous membrane coated with the first polymer porous layer 20 was placed in a 100°C oven for preheating for 30 minutes, and then the second polymer slurry was evenly coated on the surface of the first polymer porous layer 20, placed at 180°C for 20 minutes for foaming, and the expansion height was monitored in real time, and finally dried at 140°C for 2 hours for curing. The second polymer porous layer 30 has a thickness of 2.0 μm.

[0058] 18% of Al2O3 nanowires, 10.5% of LAGP nanosheets, 1.5% of polyacrylate and 70% of deionized water are mixed and stirred to form an inorganic ceramic slurry with a solid content of 30%.

[0059] The inorganic ceramic slurry was coated on the surface of the second polymer porous layer 30 in equal amounts and dried in an oven at 100° C. for 30 minutes to obtain a composite membrane having an inorganic ceramic layer 40 formed of Al2O3 nanowires and LAGP nanosheets on the surface of the second polymer porous layer 30. The inorganic ceramic layer 40 had a thickness of 7.0 μm.

[0060] In the same manner as in Example 1, a test battery of Example 3 was produced.

[0061] Comparative Example 1 The preparation process of the first polymer was changed, and no dynamic covalent bond was introduced. The synthetic product was aramid (first polymer). Otherwise, the membrane of Comparative Example 1 was produced in the same manner as in Example 1.

[0062] Consistent with Example 1, a test battery of Comparative Example 1 was produced.

[0063] Comparative Example 2 The membrane of Comparative Example 2 was produced in the same manner as in Example 2 except that the composition of the second polymer slurry was changed and microcapsules were not introduced.

[0064] Consistent with Example 2, a test battery of Comparative Example 2 was produced.

[0065] Comparative Example 3 A diaphragm of Comparative Example 3 was produced in the same manner as in Example 2 except that the composition of the second polymer slurry was changed and carbon nanotubes were not introduced.

[0066] Consistent with Example 2, a test battery of Comparative Example 3 was produced.

[0067] Comparative Example 4 The diaphragm of Comparative Example 4 was produced in the same manner as in Example 3 except that the composition of the inorganic ceramic slurry was changed and Al2O3 nanowires were not introduced.

[0068] Consistent with Example 3, a test battery of Comparative Example 4 was produced.

[0069] Comparative Example 5 The diaphragm of Comparative Example 5 was produced in the same manner as in Example 3 except that the composition of the inorganic ceramic slurry was changed and LAGP nanosheets were not introduced.

[0070] Consistent with Example 3, a test battery of Comparative Example 5 was produced.

[0071] Test Method: 1. Coating thickness The thickness of the first polymer porous layer is the thickness of the separator coated with the first polymer porous layer minus the thickness of the porous substrate. If the first polymer porous layer is double-sided, the thickness is calculated by dividing by 2.

[0072] The thickness of the second polymer porous layer is obtained by subtracting the thickness of the separator coated with the first polymer porous layer from the thickness of the separator coated with the second polymer porous layer. If the second polymer porous layer is double-sided, the thickness is further divided by 2.

[0073] The thickness of the inorganic ceramic layer is the thickness of the inorganic ceramic layer separator minus the thickness of the separator coated with the second polymer porous layer. If the inorganic ceramic layer is double-sided, the thickness is calculated by dividing by 2.

[0074] The thickness of the porous substrate, the first polymer porous layer, the second polymer porous layer, the inorganic ceramic layer, and the separator as a whole was measured by overlapping 8 layers of porous substrates or separators, and using a Mahr thickness gauge, 10 points were randomly selected on an area of ​​10 cm x 10 cm, and the average was divided by 8 to obtain the thickness.

[0075] 2. Particle size distribution of inorganic particles The inorganic particles were dispersed in pure water, stirred, and then ultrasonically dispersed. The particle size was measured using a laser particle size distribution instrument (Beettersize 2000).

[0076] In the volume-based particle size distribution, the particle size at which the volume accumulation from the smaller particle size side reaches 50% is called the median particle size (D50), which is the volume average particle size of the inorganic particles.

[0077] 3. Tensile strength Tensile strength refers to the maximum stress value reached by a material from the beginning of loading to the occurrence of fracture when it is subjected to axial tensile load. In simple terms, it is the maximum ability of a material to resist tensile damage. When a gradually increasing tensile force is applied to a material, a corresponding stress will be generated inside the material. As the tensile force continues to increase, the stress continues to increase until the material can no longer withstand it and breaks. At this time, the corresponding stress value is the tensile strength of the material.

[0078] The diaphragm was cut into 2.0 cm x 8 cm strips and the maximum tensile stress of the diaphragm was tested using a HY~0350 universal tensile testing machine.

[0079] 4. Acupuncture intensity Needle penetration strength refers to the maximum force that a material can withstand when a needle of a specific specification is inserted vertically into the material at a certain speed under specified test conditions. This indicator reflects the comprehensive properties of the material, such as the tightness of the internal structure, the intermolecular force, and the overall toughness and rigidity of the material.

[0080] The diaphragm was cut into 8 cm x 8 cm pieces and the maximum needle penetration force of the diaphragm was tested using a HY~0350 universal tensile testing machine.

[0081] 5. Battery ion conductivity The test method of conductivity is as follows: at room temperature 25°C, button cell, frequency 0-100000Hz, disturbance voltage 5 mV, ion conductivity unit σ / mS cm-1. Metrohm Autolab PGSTAT302N electrochemical workstation is used to measure ion conductivity.

[0082] 6. Battery first effect After the non-aqueous secondary battery is manufactured, it is charged to 4.2V at a constant current of 0.2C, then charged to 0.02A at a constant voltage of 4.2V, left for 5 hours, and then discharged to 2.5V at 0.2C. The discharge capacity / charge capacity is the first efficiency.

[0083] 7. Battery furnace temperature test The furnace temperature test is also called the hot box test, which is mainly used to test the safety performance of power batteries under high temperature conditions. This experiment requires that the power battery be heated to 120°C (Example 2), 140°C (Example 3), and 200°C (Example 1) by continuous heating, and the temperature is maintained for 30 minutes. During this period, the power battery cannot catch fire or explode.

[0084] 8. Self-repair thermal cycle test Thermal cycling test is a key experiment to evaluate its long-term stability and repair efficiency, which needs to be completed by combining temperature cycling with performance recovery test. The tensile strength, elongation at break, and modulus of the original sample were tested, the initial surface morphology was recorded by optical microscopy, and blade scratches (length 10 mm, depth 0.5-1.5 μm) were introduced. The temperature was raised to 135°C in a temperature-controlled box at a rate of 5°C / min, maintained at the temperature for 30 minutes, and finally the temperature was lowered to 75°C at a rate of 2°C / min, and the above steps were repeated 10 times. Repeat the mechanical test after every 10 cycles to calculate the strength recovery ratio of the material.

[0085] According to the above test method, Examples 1-3 and Comparative Examples 1-5 were tested, and the test results are shown in Table 1.

[0086]

[0087] As shown in Table 1, the strength recovery ratio of the diaphragm after thermal cycling of Example 1 is significantly better than that of Comparative Example 1. This is because the dynamic covalent bonds introduced into the diaphragm coating of Example 1 have self-repairing ability, and can self-repair after the diaphragm coating is damaged due to abnormalities inside the battery, and can bridge the damaged parts. After thermal cycling, the diaphragm strength recovers well, while without dynamic covalent bonds, the strength irreversibly decreases after thermal cycling.

[0088] As shown in Table 1, the battery furnace temperature test result of Example 2 is better than that of Comparative Example 2, indicating that the phase change material in the microcapsule in the separator of Example 2 can reduce the battery temperature rise rate by dissolving and absorbing heat, and plays a role in delaying the battery thermal runaway when the battery temperature is out of control, so the battery furnace temperature test is passed. The ionic conductivity of the separator of Example 2 is higher than that of Comparative Example 3, because the addition of carbon nanotubes in the second polymer layer can form a conductive network, which effectively improves the ionic conductivity of the coating.

[0089] As shown in Table 1, the tensile strength and needle puncture strength of the diaphragm of Example 3 are better than those of Comparative Example 4. This is because the inorganic ceramic layer 40 uses Al2O3 nanowires with extremely high rigidity, which can form a strong lithium dendrite-resistant layer and improve the puncture resistance of the diaphragm. The first efficiency of the battery in Example 3 is higher than that of Comparative Example 5 because there are a large number of active lithium ions in the LAGP nanosheets in the inorganic ceramic layer 40, which can replenish a large number of lithium ions during the first charge and discharge process, reduce the loss of lithium ions in the SEI film formation process, and can form ion-conducting channels with carbon nanotubes to improve ionic conductivity.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Therefore, any modification, equivalent replacement, improvement, etc. made to the above embodiment based on the technical practice of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A separator for a non-aqueous secondary battery, characterized in that: It comprises a porous substrate, wherein both sides of the porous substrate are coated with a first polymer porous layer, the first polymer porous layer is coated with a second polymer porous layer, and the second polymer porous layer is coated with an inorganic ceramic layer; The first polymer porous layer contains dynamic covalent bonds, the second polymer porous layer has a porous structure, the porous structure is filled with carbon nanotubes and microcapsules, the microcapsules have organic phase change materials inside, and the inorganic ceramic layer contains inorganic ceramic nanowires and solid electrolyte nanosheets.

2. A non-aqueous secondary battery separator according to claim 1, characterized in that: The porous substrate is a composite porous material formed by stacking one or more of a porous membrane, a porous aromatic skeleton, a non-woven fabric, a molecular sieve and a mesoporous material; The first polymer porous layer is formed by coating a first polymer slurry on the surface of a porous substrate, wherein the first polymer slurry comprises a first polymer containing a dynamic covalent bond and a first solvent, and the first polymer is one of aramid, polyvinylidene fluoride, polymethacrylate, polyacrylonitrile, and vinylidene fluoride-co-hexafluoropropylene resin; The second polymer porous layer is formed by coating the second polymer slurry on the surface of the first polymer porous layer, the second polymer slurry includes a second polymer, a foaming agent, carbon nanotubes, microcapsules and a catalyst, the second polymer is one of aramid, polyvinylidene fluoride, polymethacrylate, polyvinylidene fluoride-co-hexafluoropropylene, or a mixture of two or more thereof; the microcapsules are one of SiO2@trimethylolethane capsules, polyurea@paraffin capsules and Al2O3@maltitol capsules; The inorganic ceramic layer is formed by coating an inorganic ceramic slurry on the surface of the second polymer porous layer. The inorganic ceramic slurry includes inorganic ceramic nanowires, solid electrolyte nanosheets, glue and a second solvent. The inorganic ceramic nanowires are one of hydroxyapatite nanowires, Al2O3 nanowires, SiO2 nanowires, and hydroxyaluminum oxide nanowires; the solid electrolyte nanosheets are one of LATP nanosheets, LLZO nanosheets, LAGP nanosheets, and LLTO nanosheets; and the glue is one of polyimide, polyacrylic acid, and polyacrylate.

3. A non-aqueous secondary battery separator according to claim 1, characterized in that: The thickness of the porous substrate is 3-20 μm; the thickness of the first polymer porous layer is 0.5-3 μm; the thickness of the second polymer porous layer is 2-8 μm; and the thickness of the inorganic ceramic layer is 3-7 μm.

4. A non-aqueous secondary battery separator according to claim 2, characterized in that: In the first polymer slurry, the mass percentage of the first polymer containing dynamic covalent bonds is 1-20%; the mass percentage of the first solvent is 80%-99%.

5. The non-aqueous secondary battery separator according to claim 2, characterized in that: The mass percentage of the second polymer in the second polymer slurry is 1-20%, the mass percentage of the foaming agent is 0.1-2%, the mass percentage of the carbon nanotubes is 2-5%, the mass percentage of the microcapsules is 6.0-12.0%, the mass percentage of the catalyst is 0.01-0.2%, the sum of the proportions of each component is 100%, and the total mass percentage of solid matter in the second polymer slurry is 5-40%.

6. The non-aqueous secondary battery separator according to claim 1, characterized in that: The organic phase change material is composed of a mixture or derivatives of one or more of mannitol, maltitol, trimethylolethane, pentaerythritol, paraffin, fatty acid, and polyethylene glycol.

7. The non-aqueous secondary battery separator according to claim 2, characterized in that: The mass percentage of inorganic ceramic nanowires in the inorganic ceramic layer is 12-25.5%, the mass percentage of solid electrolyte nanosheets is 4.5-18%, the mass percentage of glue is 0.6-3%, the mass percentage of the second solvent is 50-85%, and the sum of the proportions of each component is 100%; the total mass percentage of solid matter in the inorganic ceramic layer is 15-50%.

8. A method for preparing a separator for a non-aqueous secondary battery, characterized in that: The following steps are involved: Step 1, first coating: dissolving a first polymer in a first solvent to form a slurry, then coating the first polymer slurry on a porous substrate, curing it in a first coagulation bath, then curing it in a second coagulation bath, and then drying the water to obtain a diaphragm coated with a first polymer porous layer on the surface; Step 2, second coating: a second polymer, a foaming agent, carbon nanotubes, microcapsules, and a catalyst are mixed and stirred to form a second polymer slurry, and the diaphragm prepared in step 1 is preheated at 80°C-100°C for 20-30min, and then the second polymer slurry is coated on the surface of the first polymer porous layer, and placed at 100°C-180°C for 15-30min for foaming, and then dried at 25°C-140°C for 2-3h to obtain a diaphragm coated with the first polymer porous layer and the second polymer porous layer; Step three, the third coating: the inorganic ceramic nanowires, solid electrolyte nanosheets, glue, and the second solvent are mixed and stirred to form an inorganic ceramic slurry, and then the inorganic ceramic slurry is coated on the diaphragm prepared in step two, and dried in an oven at 60°C-100°C for 5-30 minutes to obtain a finished diaphragm.

9. The method for preparing a non-aqueous secondary battery separator according to claim 8, characterized in that: The coagulation bath in step 1 is composed of a good solvent and a phase separation agent, the mass percentage of the good solvent in the coagulation bath is greater than or equal to 20%, and the mass percentage of the phase separation agent is less than or equal to 80%, the good solvent is dimethylacetamide, N-methylpyrrolidone, dimethylformamide, and the phase separation agent is one of deionized water, ethanol, isopropanol, and glycerol.

10. The method for preparing a separator for a non-aqueous secondary battery according to claim 9, characterized in that: In step 1, the mass percentage of the good solvent in the first coagulation bath is 60%, and the mass percentage of the phase separation agent is 40%; the mass percentage of the good solvent in the second coagulation bath is 20%, and the mass percentage of the phase separation agent is 80%.

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