Diaphragm and preparation method and application thereof

Abstract

The invention provides a diaphragm as well as a preparation method and an application thereof. The diaphragm at least comprises a base membrane, the super-crosslinked polymer coating is arranged on at least one surface of the base membrane, the super-crosslinked polymer coating is provided with a micropore structure, the pore diameter of the micropore structure is smaller than 2 nm, and the porosity of the super-crosslinked polymer coating is 30%-70%. According to the diaphragm as well as the preparation method and the application thereof provided by the invention, the dissolution of transition metal ions can be blocked on the premise of not influencing the safety of the diaphragm, so that the cycle life of a battery under high-voltage and high-temperature conditions is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of power batteries, and in particular to a diaphragm and a preparation method and application thereof. Background Art

[0002] During the long cycle of lithium-ion batteries, transition metal ions in the positive electrode material will gradually diffuse to the negative electrode side, thereby destroying the solid electrolyte interface (SEI) membrane and increasing the negative electrode interface impedance, thereby reducing the cycle life of the battery under high voltage and high temperature conditions. Summary of the Invention

[0003] The present invention proposes a diaphragm and its preparation method and application. The diaphragm and its preparation method and application provided by the present invention can block the dissolution of transition metal ions without affecting the safety of the diaphragm, thereby improving the cycle life of the battery under high voltage and high temperature conditions.

[0004] In order to solve the above technical problems, the present invention provides a diaphragm, comprising at least: basement membrane; and The hypercrosslinked polymer coating is arranged on at least one surface of the base film, and the hypercrosslinked polymer coating has a microporous structure, the pore size of the microporous structure is less than 2nm, and the porosity of the hypercrosslinked polymer coating is 30%-70%.

[0005] In one embodiment of the present invention, among all the micropores in the microporous structure, the number of micropores with a pore diameter of less than 0.7 nm accounts for 0-10%, the number of micropores with a pore diameter of 0.7 nm ≤ ≤ 1 nm accounts for 80%-90%, and the number of micropores with a pore diameter of 1 nm < 2 nm accounts for 0-10%.

[0006] In one embodiment of the present invention, the porosity of the hyper-crosslinked polymer coating is 40%-60%.

[0007] In one embodiment of the present invention, the monomers of the hyper-crosslinked polymer include at least one of benzyl diamine, triphenyl, 1,3-adamantanediol diacrylate, 1-adamantyl acrylate, 2-ethyl-2-adamantyl methacrylate, 4,4''-diamino-p-terphenyl, or 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl.

[0008] In one embodiment of the present invention, the thickness of the hyper-crosslinked polymer coating is 0.5 μm-3 μm; And / or, the crosslinking density of the hypercrosslinked polymer is ≥5×10 - ³mol / cm³; and / or, the Young's modulus of the hyper-crosslinked polymer is ≥2 GPa; And / or, the specific surface area of the hypercrosslinked polymer is 1000m 2 / g-1400m 2 / g.

[0009] In one embodiment of the present invention, the thickness of the base film is 3 μm-9 μm; And / or, the base membrane has a porous structure, and the pore size of the porous structure is 20nm-100nm; And / or, the material of the base film includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyimide, polyamide, polyacrylonitrile, polyethylene glycol, polyphenylene ether, polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene or polyvinylidene fluoride-chlorotrifluoroethylene.

[0010] The present invention also provides a method for preparing a diaphragm, which comprises at least the following steps: After dissolving the monomer of the hyper-crosslinked polymer in a good solvent, a crosslinking agent is added and mixed uniformly to obtain a dispersion; coating the dispersion on at least one surface of the base film and then immersing the dispersion in a first mixed solution for a first preset time and then taking it out, wherein the first mixed solution contains the good solvent and the poor solvent; The base film is taken out and immersed in the second mixed solution for a second preset time, and then taken out again for drying and heating annealing to form a hypercrosslinked polymer coating on at least one surface of the base film, thereby obtaining a diaphragm, wherein the second mixed solution contains the poor solvent.

[0011] In one embodiment of the present invention, the good solvent comprises at least one of N-methylpyrrolidone or N,N-dimethylformamide; and / or, the content of the monomer in the good solvent is 10 wt % to 20 wt %; and / or, in the dispersion, the amount of the cross-linking agent is 8%-12% by mass of the monomer; and / or, the poor solvent comprises water; and / or, the content of the good solvent in the first mixed solution is 2 wt%-4 wt%; And / or, the first mixed solution and the second mixed solution further contain an acid, and the pH value of the first mixed solution and the second mixed solution are each independently selected from 2-3; And / or, the heating annealing temperature is 120° C.-140° C.; And / or, the heating annealing time is 2h-4h.

[0012] The present invention also provides a lithium ion battery, comprising at least: Positive electrode; negative electrode; A diaphragm, disposed between the positive electrode sheet and the negative electrode sheet, the diaphragm being selected from the above-mentioned diaphragms or the diaphragms obtained according to the above-mentioned preparation method; and The electrolyte is filled between the positive electrode sheet, the negative electrode sheet and the separator.

[0013] The present invention also provides an electronic device comprising the above-mentioned lithium-ion battery.

[0014] In summary, the present invention proposes a diaphragm, its preparation method, and application. By providing a hypercrosslinked polymer coating on the base membrane, it is possible to block the dissolution of transition metal ions, prevent transition metal ions from damaging the SEI membrane, avoid increasing the negative electrode interface impedance, and improve the cycle life of the battery under high voltage and high temperature conditions without affecting the safety of the diaphragm. It can ensure the permeability of the diaphragm to the electrolyte, while avoiding the formation of a rapid migration path for transition metal ions, and ensure the diaphragm's barrier efficiency for transition metal ions. It can also ensure the mechanical strength of the hypercrosslinked polymer coating, further improving the cycle life of the battery under high voltage and high temperature conditions. DETAILED DESCRIPTION

[0015] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0016] It should be understood that the present invention can be implemented in different forms and should not be interpreted as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0017] The technical solutions of the present invention are further described in detail below with reference to the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] The present invention provides a separator comprising at least a base membrane and a hypercrosslinked polymer coating. The hypercrosslinked polymer coating is disposed on at least one surface of the base membrane and has a microporous structure, with pore sizes, for example, less than 2 nm, and a porosity, for example, of 30% to 70%. By controlling the porosity and pore size of the hypercrosslinked polymer coating, the separator provided by the present invention can prevent transition metal ions dissolved from the positive electrode from diffusing to the negative electrode, thereby improving the cycle life of the battery under high voltage and high temperature conditions while ensuring the safety of the separator.

[0019] In one embodiment of the present invention, the thickness of the base film is, for example, 3 μm to 9 μm, and the base film has a porous structure with a pore size of, for example, 20 nm to 100 nm, so that lithium ions can migrate back and forth between the positive and negative electrodes. However, the pore size of the porous structure is too large to block transition metal ions dissolved from the positive electrode. Furthermore, the material of the base film includes, for example, at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyimide, polyamide, polyacrylonitrile, polyethylene glycol, polyphenylene ether, polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene, or polyvinylidene fluoride-chlorotrifluoroethylene, so that the base film has insulating properties and can produce a circuit breaker effect.

[0020] In one embodiment of the present invention, a hypercrosslinked polymer coating is disposed on at least one surface of the base film. The thickness of the hypercrosslinked polymer coating is, for example, 0.5 μm to 3 μm. If the hypercrosslinked polymer coating is too thin, it will not improve the wettability of the separator to the electrolyte. Conversely, if the hypercrosslinked polymer coating is too thick, it will increase the overall thickness of the separator and reduce the energy density of the battery cell.

[0021] In one embodiment of the present invention, the hyper-cross-linked polymer coating has a microporous structure. Wherein, the hyper-cross-linked polymer is an amorphous permanent microporous material, which presents a continuous cross-linked network as a whole. The microporous structure is generated from the three-dimensional network gaps formed by covalent cross-linking of polymer molecular chains. The size and distribution of the micropores are jointly determined by the monomer rigidity, cross-linking density and synthesis process. Specifically, the pore size of the microporous structure is, for example, less than 2nm, and the porosity of the hyper-cross-linked polymer coating is, for example, 30%-70%, which can block the transition metal ions dissolved from the positive electrode, and at the same time can avoid defects in the hyper-cross-linked polymer coating structure caused by excessive pore size or excessive distribution, thereby affecting the safety performance of the diaphragm. Wherein, the pore size is defined, for example, by the equivalent diameter assuming that the micropores in the microporous structure are regular geometric shapes, such as spheres or cylinders, and the porosity is defined by the ratio of the volume of the microporous structure in the hyper-cross-linked polymer coating to the total volume of the hyper-cross-linked polymer coating. In further research, the inventors found that when using the above-mentioned diaphragm, although it can effectively block the transition metal ions dissolved from the positive electrode and control the interface impedance of the negative electrode, the balanced performance of the diaphragm, such as the permeability to the electrolyte, mechanical properties, and lithium ion passage rate, will be unstable or limited. Therefore, in order to further improve it, in one embodiment of the present invention, the number of all micropores in the microporous structure is limited, and the number of micropores with a pore size of less than 0.7nm accounts for, for example, 0-10%, which can avoid the problem that the proportion of small-diameter micropores is too large, resulting in lithium ions being unable to pass through the diaphragm; the number of micropores with a pore size of 0.7nm≤≤1nm is less than 0.7nm. The mesh ratio is, for example, 80%-90%, which can ensure that lithium ions pass through the hyper-cross-linked polymer coating smoothly. At the same time, size screening can block the transition metal ions dissolved from the positive electrode from diffusing to the surface of the negative electrode, thereby avoiding the formation of metal particles or dendrites on the surface of the negative electrode, and reducing the risk of internal short circuit and thermal runaway of the battery; the number of micropores with a pore size of 1nm < 2nm accounts for, for example, 0-10%. Controlling the proportion of micropores in this range can improve the permeability of the diaphragm to the electrolyte, while avoiding the formation of a rapid migration path for transition metal ions dissolved from the positive electrode, thereby improving the barrier efficiency of transition metal ions.

[0022] In one embodiment of the present invention, the pore size of the microporous structure is, for example, less than 2 nm, and the porosity of the hyper-crosslinked polymer coating is, for example, 30%-70%, which can block the transition metal ions dissolved from the positive electrode, while avoiding defects in the hyper-crosslinked polymer coating structure caused by excessive pore size or excessive distribution, affecting the safety performance of the diaphragm. Although the micropores in the hyper-crosslinked polymer coating can block the transition metal ions dissolved from the positive electrode, the blocking efficiency and mechanical strength are limited. Further, in one embodiment of the present invention, the porosity of the hyper-crosslinked polymer coating is limited to, for example, 40%-60%, which can improve the blocking efficiency of the micropores in the hyper-crosslinked polymer coating for the transition metal ions dissolved from the positive electrode, while maintaining the high mechanical strength of the hyper-crosslinked polymer coating.

[0023] In one embodiment of the present invention, in the hyper-crosslinked polymer coating, the monomers of the hyper-crosslinked polymer include at least one of a rigid monomer such as benzyldiamine, triphenyl, 1,3-adamantanediol diacrylate, 1-adamantyl acrylate, 2-ethyl-2-adamantyl methacrylate, 4,4''-diamino-p-terphenyl or 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, and the crosslinking density of the hyper-crosslinked polymer is, for example, ≥5×10 - ³mol / cm³, a high cross-linking density can enhance the network rigidity of the hyper-cross-linked polymer and inhibit the swelling of the polymer, thereby maintaining the stability of the microporous structure in the polymer, and further improving the stability of the coating in blocking transition metal ions. Among them, the cross-linking density is defined, for example, by the density of the molecular chains in the hyper-cross-linked polymer connected by chemical bonds to form a three-dimensional network structure. Moreover, the Young's modulus of the hyper-cross-linked polymer is, for example, ≥2GPa. The Young's modulus is positively correlated with the cross-linking density. A high Young's modulus can ensure that the coating can maintain the integrity of the microporous structure in the polymer when immersed in electrolyte or squeezed by external force, thereby further improving the stability of the coating in blocking transition metal ions. Among them, the Young's modulus is defined, for example, by the ratio of stress to strain during uniaxial tension or compression of the hyper-cross-linked polymer in the elastic deformation stage. Therefore, by jointly controlling the pore size distribution and porosity of the microporous structure in the hyper-cross-linked polymer coating, as well as the cross-linking density and Young's modulus of the hyper-cross-linked polymer, the synergistic effect can improve the barrier efficiency of the membrane to transition metal ions while ensuring the stability of the microporous structure in the polymer and the overall performance of the membrane in terms of electrolyte permeability, mechanical properties, and lithium ion passage rate, thereby greatly improving the cycle life of the battery under high voltage and high temperature conditions.

[0024] In one embodiment of the present invention, in the hyper-cross-linked polymer coating, the specific surface area of the hyper-cross-linked polymer is, for example, 1000 m 2 / g-1400m 2 / g, thereby increasing the electrolyte retention rate and improving the dynamic performance of the battery. The specific surface area is defined, for example, by the total surface area per unit mass of the hyper-crosslinked polymer.

[0025] Based on the above-mentioned diaphragm, the present invention further proposes a method for preparing the diaphragm, which at least includes steps S11 to S13.

[0026] Step S11: dissolving the monomers of the hyper-crosslinked polymer in a good solvent, adding a crosslinking agent and mixing uniformly to obtain a dispersion.

[0027] Step S12: coating the dispersion on at least one surface of the base film and then immersing the dispersion in a first mixed solution for a first preset time and then taking it out, wherein the first mixed solution contains a good solvent and a poor solvent.

[0028] Step S13: take out the base film and continue to immerse it in the second mixed solution for a second preset time, then take it out again, dry it, and heat it for annealing to form a hyper-crosslinked polymer coating on at least one surface of the base film, thereby obtaining a diaphragm. The second mixed solution includes a poor solvent.

[0029] In one embodiment of the present invention, in step S11, a monomer is added to a good solvent and stirred until the monomer is completely dissolved, and then a crosslinker is added and stirred for a set time to obtain a dispersion with a uniform composition. The good solvent may include, for example, at least one of N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF), the monomer content in the good solvent may be, for example, 10 wt% to 20 wt%, the crosslinker may include, for example, at least one of hexamethylenetetramine, glutaraldehyde, or glyoxal, and the amount of the crosslinker in the dispersion may be, for example, 8% to 12% of the monomer mass, and the set time may be, for example, 20 min to 120 min.

[0030] In one embodiment of the present invention, after obtaining the dispersion, in step S12, the dispersion is coated on at least one surface of the base film, and after the base film is loaded with the monomer, cross-linking agent and good solvent, the base film is immersed in the first mixed solution for a first preset time. Among them, the method of coating the dispersion includes, for example, coating method, spraying method or dipping method, etc., the coating method includes, for example, blade coating, comma coating or slit die coating, etc., the spraying method includes, for example, air spraying or electrostatic spraying, etc., and the dipping method includes, for example, direct dipping or vacuum dipping, etc. The first mixed solution includes a good solvent, a poor solvent and an acid, etc. The type of good solvent is the same as the type of good solvent for dissolving the monomer in step S11, and will not be elaborated here. The content of the good solvent in the first mixed solution is, for example, 2wt%-4wt%, the poor solvent includes, for example, water, and the acid includes, for example, at least one of acetic acid, formic acid and citric acid, etc. The pH value of the first mixed solution is, for example, 2-3, the temperature of the first mixed solution is, for example, 0℃-2℃, the immersion speed of the base film in the first mixed solution is, for example, 0.5mm / s-2mm / s, and the first preset time is, for example, 2min-20min. Specifically, the base membrane is immersed in the first mixed solution, the poor solvent in the first mixed solution preliminarily replaces the good solvent loaded on the base membrane, and simultaneously the monomer and the cross-linking agent are polymerized on the base membrane to form a super cross-linked polymer with a microporous structure.

[0031] In one embodiment of the present invention, after removing the base membrane from the first mixed solution, in step S13, the base membrane is further immersed in a second mixed solution and stirred for a second preset time. The second mixed solution contains a poor solvent and an acid, the type of poor solvent being the same as that in the mixed solution in step S12, and the acid comprising at least one of acetic acid, formic acid, and citric acid. The pH of the second mixed solution is, for example, 2-3, the temperature of the second mixed solution is, for example, 0°C-2°C, and the second preset time is, for example, 1 hour-5 hours. Specifically, the base membrane is immersed in the second mixed solution, and the poor solvent in the second mixed solution again displaces the good solvent remaining on the base membrane. Simultaneously, the monomers and crosslinking agents remaining on the base membrane continue to polymerize to form a hyper-crosslinked polymer having a microporous structure. By immersing the base membrane twice in mixed solutions with decreasing good solvent content and controlling the temperature and pH of the mixed solution, the pore size distribution in the microporous structure of the hyper-crosslinked polymer can be adjusted, thereby adjusting the barrier efficiency of the hyper-crosslinked polymer coating against transition metal ions dissolved from the positive electrode.

[0032] In one embodiment of the present invention, after the base film is removed from the second mixed solution, in step S13, the base film is dried, for example, by supercritical drying, and the good solvent and the poor solvent remaining in the base film are replaced with CO2. Specifically, the base film is placed in an autoclave, and then liquid CO2 is introduced into the autoclave until the pressure in the autoclave reaches, for example, 6MPa-12MPa, and the temperature reaches, for example, 35°C-45°C. The temperature is maintained for, for example, 1h-3h, and the CO2 changes from liquid to supercritical state, replacing the solvent in the microporous structure of the hyper-cross-linked polymer on the base film. The pressure in the autoclave is then reduced to normal pressure, for example, at a rate of 0.2MPa / min-0.5MPa / min, and the CO2 changes from the supercritical state to the gaseous state, detaching from the microporous structure, completing the drying. By controlling the pressure and temperature in the autoclave during the supercritical drying process, as well as the pressure reduction rate, the porosity in the hyper-cross-linked polymer coating can be adjusted, thereby improving the barrier efficiency of the coating to transition metal ions.

[0033] In one embodiment of the present invention, after drying the base film, in step S13, the dried base film is heated and annealed in a stabilizing gas atmosphere to activate the residual cross-linking sites, forming a hyper-cross-linked polymer coating on the base film to obtain a diaphragm. The stabilizing gas, for example, includes at least one of nitrogen and an inert gas, which can prevent the hyper-cross-linked polymer from being oxidized. The heating annealing temperature is, for example, 120°C to 140°C, and the heating annealing time is, for example, 2h to 4h. By controlling the temperature and time of the heating annealing, the cross-linking density of the hyper-cross-linked polymer coating can be adjusted, the network rigidity of the hyper-cross-linked polymer can be enhanced, and the swelling of the hyper-cross-linked polymer can be suppressed, thereby maintaining the stability of the microporous structure in the polymer, thereby improving the stability of the coating in blocking transition metal ions.

[0034] Based on the above-mentioned separator and its preparation method, the present invention further provides a lithium-ion battery, which can be, for example, a primary battery or a secondary battery. The secondary battery can be, for example, a soft-pack battery, a hard-shell battery, or a cylindrical battery. The present invention does not specifically limit the type or type of lithium-ion battery. The lithium-ion battery includes a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte.

[0035] In one embodiment of the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer coated on at least one surface of the positive electrode current collector. The positive electrode current collector is, for example, a surface-treated foil of nickel, titanium, aluminum, silver, stainless steel, or carbon. In addition to foil, the positive electrode current collector may also be in the form of a film, mesh, porous material, foam, or non-woven fabric, among other forms, or any combination thereof.

[0036] In one embodiment of the present invention, the positive electrode active layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder can be selected based on actual needs. In this embodiment, the positive electrode active material includes, for example, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese-rich oxide, or lithium nickel manganese oxide (LNMO).

[0037] In one embodiment of the present invention, the positive electrode conductive agent is, for example, selected from at least one of conductive carbon black (Super P), acetylene black, carbon nanotubes, or graphene, and the positive electrode binder is, for example, selected from at least one of polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene, or styrene-butadiene rubber (SBR).

[0038] In one embodiment of the present invention, the positive electrode current collector is, for example, aluminum foil, the positive electrode conductive agent is, for example, Super P, the positive electrode binder is, for example, PVDF, and the chemical formula of the positive electrode active material is, for example, LiNi 0.8 Co 0.1 Mn 0.1O2. Specifically, LiNi 0.8 Co 0.1 Mn 0.1 The O2 positive electrode active material, PVDF, and Super P are mixed in a mass ratio of, for example, 98:1:1, dissolved in an organic solvent, and stirred in a vacuum mixer until the system becomes uniform to obtain a positive electrode slurry. The positive electrode slurry is then evenly coated on aluminum foil, dried at room temperature, and then transferred to an oven for drying. The positive electrode sheets are obtained through cold pressing and slitting. The organic solvent is, for example, NMP.

[0039] In one embodiment of the present invention, the negative electrode plate is, for example, an indium plate, a lithium plate, an aluminum plate, or an alloy plate composed of at least two of the above metals. In other embodiments of the present invention, the negative electrode plate further comprises, for example, a negative electrode current collector and a negative electrode active layer coated on at least one surface of the negative electrode current collector. The negative electrode current collector may be, for example, a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foam copper current collector, or a stainless steel current collector, and the negative electrode active layer may comprise, for example, a negative electrode active material, a negative electrode conductive agent, a negative electrode thickener, and a negative electrode binder. The ratio of the negative electrode active material, the negative electrode conductive agent, the negative electrode thickener, and the negative electrode binder may be selected according to actual needs. In this embodiment, the negative electrode active material is selected from at least one of graphite, silicon or carbon dioxide, the negative electrode conductive agent is selected from at least one of Super P, acetylene black, Ketjen black, carbon nanotubes or graphene, the negative electrode thickener includes, for example, sodium carboxymethyl cellulose (CMC-Na), and the negative electrode binder is selected from at least one of polypropylene, polyacrylate, polyethylene ether, PMMA, polyhexafluoropropylene or SBR.

[0040] In one embodiment of the present invention, the negative electrode current collector is, for example, copper foil, the negative electrode active material is, for example, graphite, the negative electrode conductive agent is, for example, Super P, the negative electrode thickener is, for example, CMC-Na, and the negative electrode binder is, for example, SBR. Specifically, the negative electrode active material, the negative electrode conductive agent, the negative electrode thickener, and the negative electrode binder are mixed in a mass ratio of 96:1:1:2, and deionized water is added as a solvent. The mixture is then thoroughly stirred and mixed in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is then coated on copper foil, dried at room temperature, and then transferred to an oven for drying. After cold pressing and slitting, the negative electrode sheet is obtained.

[0041] In one embodiment of the present invention, a separator is positioned between the positive electrode and the negative electrode to prevent a short circuit between the positive and negative electrodes, allowing lithium ions to pass through. The separator may be, for example, the separator described above or obtained by the preparation method described above, which will not be elaborated upon here. When only one surface of the separator has a hypercrosslinked polymer coating, the hypercrosslinked polymer coating may be positioned toward either the positive electrode or the negative electrode.

[0042] In one embodiment of the present invention, an electrolyte is filled between the positive electrode plate, the separator, and the negative electrode plate to conduct ions. The electrolyte includes at least a solvent and a lithium salt. The solvent may include, for example, at least one of diethyl carbonate, fluoroethylene carbonate, difluoroethyl acetate, dimethyl carbonate, ethylene carbonate, propylene carbonate, or ethyl methyl carbonate. The lithium salt may include at least one of lithium fluorosulfonyl imide or lithium hexafluorophosphate (LiPF6). The lithium salt content in the electrolyte may be, for example, 10-18 wt%. Furthermore, the electrolyte may also include at least one of a film-forming additive, such as vinylene carbonate, or a flame retardant additive, such as trimethyl phosphate or triethyl phosphate.

[0043] In one embodiment of the present invention, the electrolyte includes a solvent such as diethyl carbonate, fluoroethylene carbonate, difluoroethyl acetate, and dimethyl carbonate, and the lithium salt is, for example, LiPF6. Specifically, diethyl carbonate, fluoroethylene carbonate, difluoroethyl acetate, dimethyl carbonate, and LiPF6 are uniformly mixed in a mass ratio of 60:10:10:6:14 to obtain the electrolyte.

[0044] In one embodiment of the present invention, the above-mentioned positive electrode sheet, separator and negative electrode sheet are placed in sequence, so that the separator is located between the positive electrode sheet and the negative electrode sheet to play an isolating role, and are placed in an aluminum-plastic film. After being transferred to an environment with a dew point of -60°C and a vacuum degree of -98kPa, 3.4g of electrolyte is injected and sealed. After being allowed to stand at room temperature for 48 hours, a soft-pack lithium-ion battery is obtained after electrolyte formation, exhaust and aging.

[0045] Hereinafter, the present invention will be explained in more detail by citing examples, which should not be construed as limiting. Appropriate modifications may be made within the scope consistent with the gist of the present invention, all of which fall within the technical scope of the present invention.

[0046] Example 1 Preparation of the diaphragm: dissolve benzyl diamine in NMP, heat to 60°C and stir for 2 hours until completely dissolved, then add hexamethylenetetramine and continue stirring for 30 minutes to obtain a dispersion. The content of benzyl diamine in NMP is 15wt%, and the mass of hexamethylenetetramine is 10% of the mass of benzyl diamine. After the dispersion is evenly coated on one surface of the polyethylene polymer layer through a slit coater, the polyethylene polymer layer is immersed in the first mixed solution at a speed of 1mm / s, allowed to stand for 5 minutes, and then immersed in the second mixed solution and slowly stirred for 2 hours. The thickness of the polyethylene polymer layer is 7μm, the pore size is 40nm-80nm, the first mixed solution contains, for example, NMP, water and glacial acetic acid, the content of NMP in the first mixed solution is 4wt%, the pH of the first mixed solution is 3, and the temperature of the first mixed solution is 1°C. The second mixed solution contains water and acetic acid, the pH of the second mixed solution is 3, and the temperature of the second mixed solution is 1°C. The polyethylene polymer layer was then removed from the second mixed solution and placed in an autoclave. Liquid CO₂ was introduced until the pressure within the autoclave reached 8 MPa and the temperature reached 40°C. This pressure was then maintained for 2 hours. The pressure within the autoclave was then reduced to atmospheric pressure at a rate of 0.3 MPa / min, completing supercritical drying. The polyethylene polymer layer was then heated to 120°C under a nitrogen atmosphere and annealed for 2 hours, resulting in a hypercrosslinked polymer coating on one surface of the polyethylene polymer layer. The hypercrosslinked polymer coating had a thickness of 2 μm. This process was repeated on the other surface of the polyethylene polymer layer to obtain a hypercrosslinked polymer coating on the other surface, thus completing the separator.

[0047] Preparation of positive electrode: LiNi 0.8 Co 0.1 Mn 0.1 O2 positive electrode active material, PVDF and Super P are mixed in a mass ratio of 98:1:1, dissolved in NMP, and stirred under a vacuum mixer until the system is uniform to obtain positive electrode slurry. Then the positive electrode slurry is evenly coated on aluminum foil, and then transferred to an oven for drying after drying at room temperature. After cold pressing and slitting, the positive electrode sheet is obtained. 0.8 Co 0.1 Mn 0.1 O2 comes from Xiamen Tungsten Co., Ltd., model M821A.

[0048] Preparation of negative electrode sheet: Lithium metal sheet is selected as the negative electrode sheet.

[0049] Preparation of the electrolyte: 60 g of diethyl carbonate, 10 g of fluoroethylene carbonate, 10 g of difluoroethyl acetate, 6 g of dimethyl carbonate, and 14 g of LiPF6 were mixed to obtain an electrolyte. Diethyl carbonate, fluoroethylene carbonate, difluoroethyl acetate, dimethyl carbonate, and LiPF6 were all obtained from Guangzhou Tianci High-Tech Materials Co., Ltd.

[0050] Battery preparation: The positive electrode, separator, and negative electrode are placed in sequence and enclosed in aluminum-plastic film to obtain a dry cell. This is then transferred to an environment with a dew point of -60°C and a vacuum of -98kPa. 3.4g of electrolyte is injected into the dry cell and sealed. After standing at room temperature for 48 hours, the cell undergoes electrolyte formation, degassing, and aging to obtain a soft-pack lithium-ion battery. Specifically, the cell is charged to 4.3V at a 0.1C charge rate, with a degassing time of 20s, a degassing vacuum of -98kPa, an aging temperature of 45°C, and an aging time of 24 hours.

[0051] Characterization of the pore size distribution, specific surface area and porosity of the hyper-cross-linked polymer coating: for example, by Brunauer-Emmett-Teller (BET) analyzer. Specifically, the membrane is placed in an N,N-dimethylformamide solution and stirred at room temperature for 24 hours to dissolve the hyper-cross-linked polymer component. After dissolution, a portion of the liquid is centrifuged, and the supernatant is dried to obtain a hyper-cross-linked polymer powder. The pore size distribution, specific surface area and porosity of the hyper-cross-linked polymer coating are then determined according to the mercury intrusion method or the gas adsorption method. The characterization results are shown in Table 1, wherein, among all the micropores in the microporous structure, the number of micropores with a pore size of <0.7nm accounts for 10%, the number of micropores with a pore size of 0.7nm≤pore size≤1nm accounts for 80%, the number of micropores with a pore size of 1nm<pore size<2nm accounts for 10%, the porosity of the hyper-cross-linked polymer coating is 50%, and the specific surface area of the hyper-cross-linked polymer is 1000m 2 / g.

[0052] Characterization of the cross-linking density of the hyper-cross-linked polymer coating: Place the membrane in N,N-dimethylformamide solution and stir at room temperature for 24 hours to dissolve the hyper-cross-linked polymer components. After dissolution, take part of the liquid and centrifuge it. The supernatant is dried to obtain the hyper-cross-linked polymer powder. The powder is then immersed in tetrahydrofuran for 24 hours to allow the powder to swell. The powder is filtered out and the residual solvent on the surface of the powder is gently wiped with filter paper or gauze. The weight of the swollen powder is weighed. s Then the powder is dried and the weight of the dried powder is measured. d , and according to the formula (W s -W d ) / W dCalculate the swelling ratio SR. After obtaining the swelling ratio SR, the crosslink density is calculated according to the Flory-Rehner equation. The characterization results are shown in Table 1, where the crosslink density of the hypercrosslinked polymer is 4×10 - ³mol / cm³.

[0053] The Young's modulus of the hyper-cross-linked polymer coating can be characterized, for example, by nanoindentation. Specifically, a load is applied to the coating surface using an indenter while the load-displacement curve is recorded. The contact stiffness and release depth are then extracted from the curve, and the Young's modulus is calculated using the elastic contact mechanics formula. The characterization results are shown in Table 1, where the Young's modulus of the hyper-cross-linked polymer is 2 GPa.

[0054] Example 2 The content of NMP in the first mixed solution was adjusted to 3 wt %, the pH of the first mixed solution was adjusted to 2.5, and the temperature of the first mixed solution was adjusted to 0° C. to adjust the pore size distribution of the hyper-cross-linked polymer coating to: among all the micropores in the microporous structure, the number of micropores with a pore size of less than 0.7 nm accounted for 15%, the number of micropores with a pore size of 0.7 nm ≤ ≤ 1 nm accounted for 70%, and the number of micropores with a pore size of 1 nm < 2 nm accounted for 15%. The other steps were the same as in Example 1.

[0055] Example 3 The content of NMP in the first mixed solution was adjusted to 2 wt %, the pH of the first mixed solution was 2, and the temperature of the first mixed solution was 0° C., so as to adjust the pore size distribution of the hyper-cross-linked polymer coating to: among all the micropores in the microporous structure, the number of micropores with a pore diameter of less than 0.7 nm accounted for 5%, the number of micropores with a pore diameter of 0.7 nm ≤ ≤ 1 nm accounted for 90%, and the number of micropores with a pore diameter of 1 nm < 2 nm accounted for 5%. The other steps were the same as in Example 1.

[0056] Example 4 During supercritical drying, the pressure in the autoclave was adjusted to 12 MPa, the temperature was adjusted to 45° C., and the pressure reduction rate was adjusted to 0.2 MPa / min to adjust the porosity of the hyper-crosslinked polymer coating to 70%. The other steps were the same as in Example 1.

[0057] Example 5 During supercritical drying, the pressure in the autoclave was adjusted to 6 MPa, the temperature was adjusted to 35° C., and the pressure reduction rate was adjusted to 0.5 MPa / min to adjust the porosity of the hyper-crosslinked polymer coating to 30%. The other steps were the same as in Example 1.

[0058] Example 6 During supercritical drying, the pressure in the autoclave was adjusted to 10 MPa, the temperature was adjusted to 45° C., and the pressure reduction rate was adjusted to 0.2 MPa / min to adjust the porosity of the hyper-crosslinked polymer coating to 60%. The other steps were the same as in Example 1.

[0059] Example 7 The content of NMP in the first mixed solution was adjusted to 2 wt %, the pH of the first mixed solution was 2, and the temperature of the first mixed solution was 0° C., so as to adjust the pore size distribution of the hyper-crosslinked polymer coating to: among all the micropores in the microporous structure, the number of micropores with a pore size of less than 0.7 nm accounted for 5%, the number of micropores with a pore size of 0.7 nm ≤ ≤ 1 nm accounted for 90%, and the number of micropores with a pore size of 1 nm < 2 nm accounted for 5%. During supercritical drying, the pressure in the autoclave was adjusted to 10 MPa, the temperature was 45° C., and the pressure reduction rate was 0.2 MPa / min to adjust the porosity of the hyper-crosslinked polymer coating to 60%. The other steps were the same as in Example 1.

[0060] Example 8 During the heating annealing process, the heating temperature was adjusted to 130 °C and the annealing time was adjusted to 3 h to adjust the crosslinking density of the hypercrosslinked polymer to 5 × 10 - ³mol / cm³, and the Young's modulus of the hyper-crosslinked polymer was adjusted to 3 GPa. The other steps were the same as in Example 1.

[0061] Example 9 During the heating annealing process, the heating temperature was adjusted to 140 °C and the annealing time was adjusted to 4 h to adjust the crosslinking density of the hypercrosslinked polymer to 6 × 10 - ³mol / cm³, and the Young's modulus of the hyper-crosslinked polymer was adjusted to 4 GPa. The other steps were the same as in Example 1.

[0062] Example 10 The content of NMP in the first mixed solution was adjusted to 2 wt %, the pH of the first mixed solution was adjusted to 2, and the temperature of the first mixed solution was adjusted to 0° C., so as to adjust the pore size distribution of the hyper-crosslinked polymer coating to: among all the micropores in the microporous structure, the number of micropores with a pore size of less than 0.7 nm accounted for 5%, the number of micropores with a pore size of 0.7 nm ≤ ≤ 1 nm accounted for 90%, and the number of micropores with a pore size of 1 nm < 2 nm accounted for 5%. During supercritical drying, the pressure in the autoclave was adjusted to 10 MPa, the temperature was adjusted to 45° C., and the depressurization rate was adjusted to 0.2 MPa / min to adjust the porosity of the hyper-crosslinked polymer coating to 60%. During the heating annealing process, the heating temperature was adjusted to 130° C. and the annealing time was adjusted to 3 h to adjust the crosslinking density of the hyper-crosslinked polymer to 5×10 -³mol / cm³, and the Young's modulus of the hyper-crosslinked polymer was adjusted to 3 GPa. The other steps were the same as in Example 1.

[0063] Example 11 The content of benzyl diamine in NMP was adjusted to 20 wt % to adjust the specific surface area of the hyper-crosslinked polymer to 1400 m 2 / g, and the other steps are the same as in Example 1.

[0064] Example 12 The content of benzyl diamine in NMP was adjusted to 10 wt % to adjust the specific surface area of the hypercrosslinked polymer to 600 m 2 / g, and the other steps are the same as in Example 1.

[0065] Example 13 The content of benzyl diamine in NMP was adjusted to 17 wt % to adjust the specific surface area of the hypercrosslinked polymer to 1200 m 2 / g, and the other steps are the same as in Example 1.

[0066] Example 14 The content of NMP in the first mixed solution was adjusted to 2 wt %, the pH of the first mixed solution was adjusted to 2, and the temperature of the first mixed solution was adjusted to 0° C., so as to adjust the pore size distribution of the hyper-crosslinked polymer coating to: among all the micropores in the microporous structure, the number of micropores with a pore size of less than 0.7 nm accounted for 5%, the number of micropores with a pore size of 0.7 nm ≤ ≤ 1 nm accounted for 90%, and the number of micropores with a pore size of 1 nm < 2 nm accounted for 5%. During supercritical drying, the pressure in the autoclave was adjusted to 10 MPa, the temperature was adjusted to 45° C., and the depressurization rate was adjusted to 0.2 MPa / min to adjust the porosity of the hyper-crosslinked polymer coating to 60%. During the heating annealing process, the heating temperature was adjusted to 130° C. and the annealing time was adjusted to 3 h to adjust the crosslinking density of the hyper-crosslinked polymer to 5×10 - ³mol / cm³, the Young's modulus of the hyper-crosslinked polymer was adjusted to 3GPa, and the content of benzyl diamine in NMP was adjusted to 20wt%, so as to adjust the specific surface area of the hyper-crosslinked polymer to 1400m 2 / g, and the other steps are the same as in Example 1.

[0067] Example 15 The diaphragm is provided with a hyper-crosslinked polymer coating on only one surface, and the hyper-crosslinked polymer coating is provided toward the positive electrode plate. The other steps are the same as those in Example 1.

[0068] Example 16 The diaphragm is provided with a hyper-crosslinked polymer coating on only one surface, and the hyper-crosslinked polymer coating is provided toward the negative electrode plate. The other steps are the same as those in Example 1.

[0069] Example 17 Using LNMO to replace LiNi 0.8 Co 0.1 Mn 0.1 O2, and the other steps are the same as those in Example 1. Wherein, LNMO is specifically a single crystal LiNi coated with Li2ZrO3 0.5 Mn 1.5 O4, from Xiamen Tungsten Co., Ltd., model number is XW46.

[0070] Comparative Example 1 The coating material on both surfaces of the separator was ceramic, and the ceramic material was aluminum oxide. The other steps were the same as in Example 1. Specifically, when forming the aluminum oxide coating on one surface of the polyethylene polymer layer, aluminum oxide and PVDF were dissolved in N-methylpyrrolidone at a mass ratio of 95:5 to form a uniform solution with a concentration of 10 wt%. This solution was then quickly applied to the surface of the polyethylene polymer layer. After vacuum drying at 80°C for 24 hours, the aluminum oxide coating was obtained on one surface of the polymer layer.

[0071] Comparative Example 2 The coating material on both surfaces of the separator was PVDF, and the other steps were the same as in Example 1. Specifically, when forming the PVDF coating on one surface of the polyethylene polymer layer, PVDF was dissolved in N-methylpyrrolidone to form a uniform solution with a concentration of 10 wt%. The solution was then quickly applied to the surface of the polyethylene polymer layer. After vacuum drying at 80°C for 24 hours, a PVDF coating was obtained on one surface of the polymer layer.

[0072] Comparative Example 3 The coating material on both surfaces of the separator was a polymer of intrinsic microporosity-1 (PIM-1). All other steps were the same as in Example 1. Specifically, to form the PIM-1 coating on one surface of the polyethylene polymer layer, PIM-1 was dissolved in N-methylpyrrolidone to form a uniform solution with a concentration of 10 wt%. This solution was then rapidly coated on the surface of the polyethylene polymer layer. After vacuum drying at 80°C for 24 hours, a PIM-1 coating was obtained on one surface of the polymer layer.

[0073] Comparative Example 4 The content of NMP in the first mixed solution was adjusted to 1 wt % and the pH of the first mixed solution was adjusted to 1.5 to adjust the pore size of the hyper-crosslinked polymer coating to > 2 nm. The other steps were the same as those in Example 1.

[0074] Comparative Example 5 During supercritical drying, the pressure in the autoclave was adjusted to 4 MPa, the temperature was adjusted to 25° C., and the pressure reduction rate was adjusted to 1 MPa / min to adjust the porosity of the hyper-crosslinked polymer coating to 20%. The other steps were the same as in Example 1.

[0075] Comparative Example 6 During supercritical drying, the pressure in the autoclave was adjusted to 20 MPa, the temperature was adjusted to 45° C., and the pressure reduction rate was adjusted to 0.1 MPa / min to adjust the porosity of the hyper-crosslinked polymer coating to 90%. The other steps were the same as in Example 1.

[0076] In the present invention, performance tests were performed on the separators and lithium-ion batteries in Examples 1-17 and Comparative Examples 1-6. The test results are shown in Table 1.

[0077] In one embodiment of the present invention, the puncture strength of the entire diaphragm is tested, for example, through a puncture test. Specifically, a steel needle with a diameter of 1.0 mm and a tip radius of 0.5 mm is used to puncture the diaphragm sample at a speed of 50 ± 5 mm / min. The average value of five samples is taken as the puncture strength. The diaphragm puncture strength test specification is primarily based on GB / T 36363-2018.

[0078] In one embodiment of the present invention, for example, a high-temperature cycle stability test is performed on a lithium-ion battery. Specifically, at 45°C, the battery is subjected to long-cycle charge and discharge within the charge and discharge cut-off voltage at a constant current charge and discharge rate of 1C / 1C, and the battery capacity is measured. The test is terminated when the battery capacity reaches 80% of the first cycle capacity (State of Health (SOH), and the number of 45°C cycles of the battery is recorded. Among them, for the batteries in Examples 1-16 and Comparative Examples 1-6, the charge and discharge cut-off voltage is 2.8V-4.3V, and for the battery in Example 17, the charge and discharge cut-off voltage is 2V-4.85V.

[0079] In one embodiment of the present invention, for example, a high-temperature storage performance test is performed on a lithium-ion battery. Specifically, the initial DC resistance (DCR) of the battery is first tested. The battery is then placed in a 60°C environment for 90 days, and the DCR of the battery is tested. The DCR increase is calculated according to the following formula: DCR increase = (DCR of the battery after 90 days - initial DCR) / initial DCR × 100%.

[0080] Table 1. Performance test results of Examples 1-17 and Comparative Examples 1-6

[0081] As shown in Table 1, by comparing Example 1 and Comparative Examples 1-3, it can be seen that, compared with the ceramic coating, PVDF coating and PIM-1 coating, after the hyper-crosslinked polymer coating is provided on the base membrane, the number of cycles at 45°C of the battery is significantly increased and the DCR increase is significantly reduced, indicating that by providing a hyper-crosslinked polymer coating on the base membrane, the high-temperature cycle stability and high-temperature storage stability of the battery can be improved.

[0082] As shown in Table 1, by comparing Examples 1-3 and Comparative Example 4, it can be seen that when the pore size in the microporous structure of the hyper-cross-linked polymer is less than 2 nm, the puncture strength of the diaphragm is significantly increased, the number of cycles at 45°C of the battery is significantly increased, and the DCR increase is significantly reduced, indicating that by controlling the pore size in the hyper-cross-linked polymer coating to be less than 2 nm, the mechanical strength of the diaphragm can be improved, and the transition metal ions dissolved from the positive electrode can be blocked, thereby jointly improving the high-temperature cycle stability and high-temperature storage stability of the battery.

[0083] As shown in Table 1, by comparing Examples 1-3 and Comparative Example 4, it can be seen that when the concentration of the good solvent in the first mixed solution is reduced from 4wt% to 2wt%, the pH of the first mixed solution is reduced from 3 to 2, and the temperature of the first mixed solution is reduced from 1°C to 0°C, the proportion of macropores with a pore size of 1nm < pore size < 2nm in the microporous structure of the hypercrosslinked polymer coating gradually increases, indicating that maintaining a low temperature and low concentration of the first mixed solution can accelerate phase separation, and maintaining strong acidity can inhibit molecular chain relaxation, thereby forming subnanometer-scale pores in the hypercrosslinked polymer. However, when the concentration of the good solvent in the first mixed solution continues to decrease from 2wt% to 1wt%, and the pH of the first mixed solution continues to decrease from 2 to 1.5, insufficient good solvent in the first mixed solution will lead to rapid phase separation, thereby forming macropores with a pore size of > 2nm in the hypercrosslinked polymer. Therefore, by controlling the change in the content of the good solvent in the first mixed solution, the change in the pH of the first mixed solution, and the change in the temperature of the first mixed solution, the pore size distribution in the microporous structure of the hypercrosslinked polymer coating can be changed.

[0084] As shown in Table 1, by comparing Example 2 with Example 1 and Example 3, it can be seen that in the microporous structure of the hyper-cross-linked polymer, when the proportion of the number of micropores with a pore diameter of less than 0.7 nm and the proportion of the number of micropores with a pore diameter of 1 nm < 2 nm exceeds 10%, and the proportion of the number of micropores with a pore diameter of 0.7 nm ≤ ≤ 1 nm is less than 80%, the puncture strength of the diaphragm is small, the number of 45°C cycles of the battery is small, and the DCR increase is large, indicating that by reducing the proportion of micropores with a pore diameter of less than 0.7 nm to 0-10%, the proportion of micropores with a pore diameter of 0.7 nm ≤ ≤ 1 nm to 80%-90%, and the proportion of micropores with a pore diameter of 1 nm < 2 nm to 0-10%, the mechanical strength of the diaphragm can be improved, and the high temperature cycle stability and high temperature storage stability of the battery can be improved.

[0085] As shown in Table 1, by comparing Example 1, Examples 4-6, and Comparative Examples 5-6, it can be seen that during the supercritical drying process, the porosity of the hyper-cross-linked polymer coating changes with the changes in pressure, temperature, and depressurization rate in the autoclave. This indicates that during the supercritical drying process, pressure can control the contraction and expansion of the pores, temperature affects the solvent volatilization rate, and depressurization rate affects the pore retention rate. These three parameters jointly affect the porosity of the coating.

[0086] As shown in Table 1, by comparing Example 1, Examples 4-6 and Comparative Examples 5-6, it can be seen that when the porosity of the hyper-cross-linked polymer coating is less than 30%, although the puncture strength of the diaphragm is large, the number of cycles at 45°C of the battery is small, and the DCR increase is large. When the porosity increases from 30% to 90%, the puncture strength of the diaphragm decreases significantly, the number of cycles at 45°C of the battery is still low, and the DCR increase is high. That is, when the mechanical strength of the diaphragm is the largest, the high-temperature cycle stability and high-temperature storage stability of the battery are not the best. As the porosity changes, although the mechanical strength of the diaphragm is affected, the barrier efficiency of the diaphragm to the transition metal ions dissolved from the positive electrode shows a trend of first increasing and then decreasing. Therefore, by controlling the porosity at 30%-70%, the diaphragm can maintain a high mechanical strength and the high-temperature cycle stability and high-temperature storage stability of the battery can still be improved. It can be seen from Examples 1 and 6 that by further limiting the porosity of the hyper-cross-linked polymer coating to 40%-60%, the barrier efficiency of the micropores in the hyper-cross-linked polymer coating to transition metal ions dissolved from the positive electrode can be improved, while taking into account the mechanical strength of the diaphragm, thereby jointly improving the high-temperature cycle stability and high-temperature storage stability of the battery.

[0087] As shown in Table 1, by comparing Example 1 with Examples 8-9, it can be seen that when the temperature and time of the heating annealing increase, the crosslinking density and Young's modulus of the hyper-crosslinked polymer coating increase, indicating that by increasing the temperature of the heating annealing process and extending the heating annealing time, the crosslinking network between benzyl diamine and hexamethylenetetramine can be densified, thereby increasing the crosslinking density and Young's modulus of the hyper-crosslinked polymer coating, and thus improving the mechanical strength of the coating.

[0088] As shown in Table 1, by comparing Example 1 with Examples 8-9, it can be seen that when the cross-linking density of the hyper-cross-linked polymer coating is increased from 4×10 - ³mol / cm³ increased to 5×10 - ³mol / cm³, and the Young's modulus increased from 2GPa to 3GPa, the number of cycles at 45℃ increased, the DCR increase decreased, and the puncture strength of the separator increased; when the cross-linking density of the hyper-cross-linked polymer coating continued to increase from 5×10 - ³mol / cm³ increased to 6×10 -³mol / cm³, and the Young's modulus continues to increase from 3GPa to 4GPa, the puncture strength of the separator increases, but the number of cycles at 45°C of the battery decreases, and the DCR increase increases, which shows that by controlling the cross-linking density and Young's modulus of the hyper-cross-linked polymer, the high-temperature cycle stability, high-temperature storage stability of the battery and the mechanical strength of the separator can be taken into account.

[0089] As shown in Table 1, by comparing Example 1 with Examples 11-13, it can be seen that as the content of benzyl diamine in NMP increases, the specific surface area of the hyper-crosslinked polymer increases accordingly, indicating that changes in the monomer content in a good solvent can change the density of rigid aromatic rings, expand the gaps between the molecular skeletons, and thus change the specific surface area of the hyper-crosslinked polymer.

[0090] Please refer to Table 1. Comparison between Example 1 and Examples 11-13 shows that when the specific surface area of the hypercrosslinked polymer increases from 600 m 2 / g increased to 1400m 2 / g, although the puncture strength of the separator is slightly reduced, the number of cycles at 45°C of the battery increases and the DCR increase decreases, which shows that by controlling the specific surface area of the hyper-cross-linked polymer, the high-temperature cycle stability and high-temperature storage stability of the battery can be improved.

[0091] As shown in Table 1, by comparing Example 1, Example 7, Example 10 and Example 14, it can be seen that when the pore size distribution, porosity, specific surface area and Young's modulus of the hyper-cross-linked polymer are kept within the control range, the battery has the largest number of cycles at 45°C and the smallest increase in DCR, which indicates that by synergistically controlling the pore size distribution, porosity, specific surface area and Young's modulus of the hyper-cross-linked polymer, the high-temperature cycling stability and high-temperature storage stability of the battery can be maximized.

[0092] As shown in Table 1, by comparing Example 1, Example 15 and Example 16, it can be seen that when the hyper-cross-linked polymer coating is provided on both sides of the diaphragm, the battery has the largest number of cycles at 45°C, the smallest increase in DCR, and the largest puncture strength of the diaphragm. This indicates that, compared with providing a hyper-cross-linked polymer coating on one side of the diaphragm, providing a coating on both sides of the diaphragm can improve the high-temperature cycle stability, high-temperature storage stability of the battery and the mechanical strength of the diaphragm.

[0093] Please refer to Table 1. Comparing Example 1 and Example 17, it can be seen that no matter whether the positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 Whether it is O2 or LNMO, the number of cycles at 45°C of the battery is relatively large, and the increase in DCR is relatively small, which shows that regardless of the type of positive electrode active material, the hyper-cross-linked polymer coating set on the diaphragm will improve the high-temperature cycle stability and high-temperature storage stability of the battery.

[0094] The present invention also provides an electronic device, which includes at least one of the above-mentioned lithium-ion batteries, and the lithium-ion battery is used to provide electrical energy. The electronic device may be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, and an electric tool, etc. In one embodiment of the present invention, the vehicle is, for example, a new energy vehicle, which may be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, etc. The spacecraft includes airplanes, rockets, space shuttles, and spacecraft, etc. The electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. The electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools, and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The electronic device includes the above-mentioned lithium-ion battery, and therefore includes the advantages of the above-mentioned lithium-ion battery, which will not be elaborated on here.

[0095] In summary, the present invention proposes a diaphragm and its preparation method and application. By providing a hyper-crosslinked polymer coating on the base membrane, it is possible to block the diffusion of transition metal ions dissolved from the positive electrode to the negative electrode without affecting the safety of the diaphragm and destroying the permeability of the diaphragm to the electrolyte, thereby improving the cycle life of the battery under high voltage and high temperature conditions. By jointly controlling the pore size distribution and porosity of the microporous structure in the hyper-crosslinked polymer coating, as well as the crosslinking density and Young's modulus of the hyper-crosslinked polymer, the synergistic effect can improve the barrier efficiency of the diaphragm to transition metal ions while ensuring the stability of the microporous structure in the polymer and the comprehensive performance of the diaphragm as a whole in terms of electrolyte permeability, mechanical properties, and lithium ion passage rate, thereby greatly improving the cycle life of the battery under high voltage and high temperature conditions.

[0096] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by the specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept, such as the technical solutions formed by replacing the above features with (but not limited to) technical features with similar functions disclosed in this application. In addition to the technical features described in the specification, the remaining technical features are known technologies to those skilled in the art. In order to highlight the innovative features of the present invention, the remaining technical features will not be repeated here.

Claims

1. A diaphragm, characterized in that: At least: basement membrane; and The hypercrosslinked polymer coating is arranged on at least one surface of the base film, and the hypercrosslinked polymer coating has a microporous structure, the pore size of the microporous structure is less than 2nm, and the porosity of the hypercrosslinked polymer coating is 30%-70%.

2. The diaphragm according to claim 1, characterized in that Among all the micropores in the microporous structure, the number of micropores with a pore diameter of less than 0.7 nm accounts for 0-10%, the number of micropores with a pore diameter of 0.7 nm ≤ ≤ 1 nm accounts for 80%-90%, and the number of micropores with a pore diameter of 1 nm < < 2 nm accounts for 0-10%.

3. The diaphragm according to claim 1, characterized in that The porosity of the hyper-crosslinked polymer coating is 40%-60%.

4. The diaphragm according to claim 1, characterized in that The monomers of the hyper-crosslinked polymer include at least one of benzyldiamine, triphenyl, 1,3-adamantanediol diacrylate, 1-adamantyl acrylate, 2-ethyl-2-adamantyl methacrylate, 4,4''-diamino-p-terphenyl, or 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl.

5. The diaphragm according to claim 1, characterized in that The thickness of the hyper-crosslinked polymer coating is 0.5 μm-3 μm; And / or, the crosslinking density of the hypercrosslinked polymer is ≥5×10 - ³mol / cm³; and / or, the Young's modulus of the hyper-crosslinked polymer is ≥2 GPa; And / or, the specific surface area of the hypercrosslinked polymer is 1000m 2 / g-1400m 2 / g.

6. The diaphragm according to claim 1, characterized in that The thickness of the base film is 3 μm-9 μm; And / or, the base membrane has a porous structure, and the pore size of the porous structure is 20nm-100nm; And / or, the material of the base film includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyimide, polyamide, polyacrylonitrile, polyethylene glycol, polyphenylene ether, polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene or polyvinylidene fluoride-chlorotrifluoroethylene.

7. A method for preparing a diaphragm according to any one of claims 1 to 6, characterized in that: At least the following steps are included: After dissolving the monomer of the hyper-crosslinked polymer in a good solvent, a crosslinking agent is added and mixed uniformly to obtain a dispersion; coating the dispersion on at least one surface of the base film and then immersing the dispersion in a first mixed solution for a first preset time and then taking it out, wherein the first mixed solution contains the good solvent and the poor solvent; The base film is taken out and immersed in the second mixed solution for a second preset time, and then taken out again for drying and heating annealing to form a hypercrosslinked polymer coating on at least one surface of the base film, thereby obtaining a diaphragm, wherein the second mixed solution contains the poor solvent.

8. The method for preparing a diaphragm according to claim 7, characterized in that: The good solvent comprises at least one of N-methylpyrrolidone or N,N-dimethylformamide; and / or, the content of the monomer in the good solvent is 10 wt % to 20 wt %; and / or, in the dispersion, the amount of the cross-linking agent is 8%-12% by mass of the monomer; and / or, the poor solvent comprises water; and / or, the content of the good solvent in the first mixed solution is 2 wt%-4 wt%; And / or, the first mixed solution and the second mixed solution further contain an acid, and the pH value of the first mixed solution and the second mixed solution are each independently selected from 2-3; And / or, the heating annealing temperature is 120° C.-140° C.; And / or, the heating annealing time is 2h-4h.

9. A lithium-ion battery, characterized in that: At least: Positive electrode; negative electrode; A separator, disposed between the positive electrode sheet and the negative electrode sheet, wherein the separator is selected from the separator according to any one of claims 1 to 6, or the separator obtained by the preparation method according to any one of claims 7 to 8; as well as The electrolyte is filled between the positive electrode sheet, the negative electrode sheet and the separator.

10. An electronic device, characterized in that: Including the lithium ion battery according to claim 9.

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