A diaphragm and a method for manufacturing and using the same

Abstract

The application provides a diaphragm and a preparation method and application thereof, and the diaphragm at least comprises: a base film; and an ultracross-linked polymer coating arranged on at least one surface of the base film, wherein the ultracross-linked polymer coating has a microporous structure, the microporous structure has a pore size less than 2 nm, and the ultracross-linked polymer coating has a porosity of 30%-70%. The diaphragm and the preparation method and application thereof can block transition metal ion elution without affecting the safety of the diaphragm, thereby improving the cycle life of a battery under high-voltage and high-temperature conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power batteries, in particular to a separator and a preparation method and application thereof. BACKGROUND

[0002] In the long cycle period of a lithium ion battery, transition metal ions in the positive electrode material gradually diffuse to the negative electrode side, thereby damaging the solid electrolyte interface (SEI) film and increasing the negative electrode interface impedance, and further reducing the cycle life of the battery under high voltage and high temperature conditions. SUMMARY

[0003] The present application provides a separator and a preparation method and application thereof, which can block the dissolution of transition metal ions without affecting the safety of the separator, thereby improving the cycle life of the battery under high voltage and high temperature conditions.

[0004] To solve the above technical problems, the present application provides a separator, which at least comprises:

[0005] a base film; and

[0006] an ultracrosslinked polymer coating layer arranged on at least one surface of the base film, and the ultracrosslinked polymer coating layer has a microporous structure, the pore size of the microporous structure is less than 2 nm, and the porosity of the ultracrosslinked polymer coating layer is 30%-70%.

[0007] In an embodiment of the present application, among the total number of micropores in the microporous structure, the number of micropores with a pore size <0.7 nm accounts for 0-10%, the number of micropores with a pore size of 0.7 nm≤pore size≤1 nm accounts for 80%-90%, and the number of micropores with a pore size of 1 nm

[0008] In an embodiment of the present application, the porosity of the ultracrosslinked polymer coating layer is 40%-60%.

[0009] In an embodiment of the present application, the monomer of the ultracrosslinked polymer includes at least one of biphenyl diamine, triphenyl, 1,3-adamantane diol diacrylate, 1-adamantyl acrylate, 2-ethyl-2-adamantyl methacrylate, 4,4''-diamino-p-triphenyl or 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl.

[0010] In an embodiment of the present application, the thickness of the ultracrosslinked polymer coating layer is 0.5-3

[0011] And / or, the crosslinking density of the ultracrosslinked polymer is ≥5×10 -≥ 2 GPa;

[0012] and / or, the Young's modulus of the super-crosslinked polymer is ≥ 2 GPa;

[0013] and / or, the specific surface area of the super-crosslinked polymer is 1000 m 2 / g-1400 m 2 / g.

[0014] In an embodiment of the present application, the thickness of the base film is 3-9 μm;

[0015] and / or, the base film has a porous structure, and the pore size of the porous structure is 20-100 nm;

[0016] and / or, the material of the base film comprises 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.

[0017] The present application also provides a preparation method of the separator, comprising at least the following steps:

[0018] After dissolving the monomer of the super-crosslinked polymer in a good solvent, adding a crosslinking agent and mixing uniformly to obtain a dispersion liquid;

[0019] Coating the dispersion liquid on at least one surface of the base film and then immersing in a first mixed solution for a first preset time, wherein the first mixed solution comprises the good solvent and a poor solvent;

[0020] After taking out the base film and continuing to immerse in a second mixed solution for a second preset time, taking out again, drying and heating annealing to form a super-crosslinked polymer coating on at least one surface of the base film, i.e. to obtain the separator, wherein the second mixed solution comprises the poor solvent.

[0021] In an embodiment of the present application, the good solvent comprises at least one of N-methylpyrrolidone or N,N-dimethylformamide;

[0022] and / or, the content of the monomer in the good solvent is 10wt%-20wt%;

[0023] and / or, in the dispersion liquid, the amount of the crosslinking agent is 8%-12% of the mass of the monomer;

[0024] and / or, the poor solvent comprises water;

[0025] and / or, the content of the good solvent in the first mixed solution is 2wt%-4wt%;

[0026] and / or, the first mixed solution and the second mixed solution further comprise an acid, and the pH value of the first mixed solution and the second mixed solution is independently selected from 2-3;

[0027] and / or, the temperature of the heating annealing is 120-140℃;

[0028] and / or, the time of the heating annealing is 2-4h.

[0029] The application further provides a lithium ion battery, comprising at least:

[0030] a positive electrode sheet;

[0031] a negative electrode sheet;

[0032] a separator arranged between the positive electrode sheet and the negative electrode sheet, the separator being selected from the separators described above, or obtained according to the preparation method described above; and

[0033] an electrolyte filled between the positive electrode sheet, the negative electrode sheet and the separator.

[0034] The application further provides an electronic device comprising the lithium ion battery described above.

[0035] In summary, the application provides a separator and its preparation method and application, by arranging a super-crosslinked polymer coating on the base film, the transition metal ion dissolution can be blocked without affecting the safety of the separator, the transition metal ions can be prevented from destroying the SEI film, the increase of the negative electrode interface impedance can be avoided, and the cycle life of the battery under high voltage and high temperature conditions can be improved. The permeability of the separator to the electrolyte can be ensured, and the formation of the fast migration path of the transition metal ions can be avoided, and the blocking efficiency of the separator to the transition metal ions can be ensured. The mechanical strength of the super-crosslinked polymer coating can be ensured, and the cycle life of the battery under high voltage and high temperature conditions can be further improved. DETAILED DESCRIPTION

[0036] The embodiments of the present application will be described in detail hereinafter with specific reference to the drawings. Other advantages and effects of the present application can be easily understood by those skilled in the art from the contents disclosed in the present specification. The present application can also be implemented or applied in other different embodiments, and the details in the present specification can be modified or changed in various ways based on different views and applications without departing from the spirit of the present application.

[0037] It should be understood that the present application can be implemented in different forms, and should not be interpreted as being limited to the embodiments presented herein. On the contrary, these embodiments are provided to make the disclosure complete and full, and to fully convey the scope of the present application to those skilled in the art.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] In an embodiment of the present application, the super-crosslinked polymer coating has a microporous structure. The super-crosslinked polymer is an amorphous permanent microporous material with a continuous crosslinked network, and the microporous structure is generated from the gap of the three-dimensional network formed by the covalent crosslinking of the polymer molecular chain. The size and distribution of the micropores are determined by the rigidity of the monomer, the crosslinking density and the synthesis process. Specifically, the microporous structure has a pore size of, for example, less than 2 nm, and the porosity of the super-crosslinked polymer coating is, for example, 30%-70%, which can block the transition metal ions dissolved out of the positive electrode, while avoiding the defects in the structure of the super-crosslinked polymer coating caused by excessively large pore size or excessive distribution, thereby affecting the safety performance of the separator. The pore size is defined by the equivalent diameter of the micropores in the microporous structure assuming that the micropores 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 super-crosslinked polymer coating to the total volume of the super-crosslinked polymer coating. In further research, the inventors found that when using the above-mentioned separator, although the transition metal ions dissolved out of the positive electrode can be effectively blocked and the negative electrode interface impedance can be controlled, the balance performance of the separator, such as the permeability to electrolyte, mechanical performance and lithium ion passing rate, is unstable or limited. Therefore, to further improve the performance, in an embodiment of the present application, the proportion of the number of micropores with a pore size of less than 0.7 nm in the total number of micropores in the microporous structure is, for example, 0-10%, which can avoid the problem that too many micropores with small pore sizes prevent lithium ions from passing through the separator; the proportion of the number of micropores with a pore size of 0.7 nm to 1 nm is, for example, 80%-90%, which can ensure the smooth passing of lithium ions through the super-crosslinked polymer coating, and at the same time, the size screening can block the diffusion of transition metal ions dissolved out of the positive electrode to the surface of the negative electrode, thereby avoiding the formation of metal particles or dendrites on the surface of the negative electrode, reducing the risk of internal short circuit and thermal runaway of the battery; the proportion of the number of micropores with a pore size of 1 nm to 2 nm is, for example, 0-10%, which can control the proportion of micropores in this range, improve the permeability of the separator to electrolyte, and at the same time avoid the formation of a fast migration path for transition metal ions dissolved out of the positive electrode, thereby improving the blocking efficiency of transition metal ions.

[0043] In an embodiment of the present application, the microporous structure has a pore size of, for example, less than 2 nm, and the porosity of the super-crosslinked polymer coating is, for example, 30%-70%, which can block the transition metal ions dissolved out of the positive electrode, while avoiding the defects in the structure of the super-crosslinked polymer coating caused by excessively large pore size or excessive distribution, thereby affecting the safety performance of the separator. Although the micropores in the super-crosslinked polymer coating can block the transition metal ions dissolved out of the positive electrode, the blocking efficiency and mechanical strength are limited. Further, in an embodiment of the present application, the porosity of the super-crosslinked polymer coating is, for example, 40%-60%, which can improve the blocking efficiency of the micropores in the super-crosslinked polymer coating for the transition metal ions dissolved out of the positive electrode, while maintaining the high mechanical strength of the super-crosslinked polymer coating.

[0044] In an embodiment of the present application, in the super-crosslinked polymer coating, the monomer of the super-crosslinked polymer comprises at least one of rigid monomers such as biphenyl diamine, triphenyl, 1,3-adamantane diol 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 super-crosslinked polymer is, for example, ≥5×10 - ³mol / cm³. A high crosslinking density can enhance the rigidity of the network of the super-crosslinked polymer, inhibit 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. The crosslinking density is defined by, for example, the density of the three-dimensional network structure formed by the chemical bonds between the molecular chains in the super-crosslinked polymer. Moreover, the Young's modulus of the super-crosslinked polymer is, for example, ≥2GPa, and the Young's modulus is positively correlated with the crosslinking density. A high Young's modulus can ensure that the microporous structure in the polymer remains intact under electrolyte immersion or external pressure, thereby further improving the stability of the coating in blocking transition metal ions. The Young's modulus is defined by, for example, the ratio of stress to strain when the super-crosslinked polymer is uniaxially stretched or compressed in the elastic deformation stage. Therefore, by jointly controlling the pore size distribution and porosity of the microporous structure in the super-crosslinked polymer coating, and the crosslinking density and Young's modulus of the super-crosslinked polymer, the blocking efficiency of the separator for transition metal ions can be improved, while the stability of the microporous structure in the polymer and the comprehensive performance of the separator in terms of electrolyte permeability, mechanical properties, and lithium ion passing rate are ensured, thereby greatly improving the cycle life of the battery under high voltage and high temperature conditions.

[0045] In an embodiment of the present application, in the super-crosslinked polymer coating, the specific surface area of the super-crosslinked polymer is, for example, 1000m 2 / g-1400m 2 / g, so as to improve the liquid retention rate of the electrolyte and improve the kinetic performance of the battery. The specific surface area is defined by, for example, the total surface area of the super-crosslinked polymer per unit mass.

[0046] Based on the above-mentioned separator, the present application further provides a preparation method of a separator, comprising at least steps S11-S13.

[0047] In step S11, the monomer of the super-crosslinked polymer is dissolved in a good solvent, a crosslinking agent is added and uniformly mixed to obtain a dispersion liquid.

[0048] In step S12, the dispersion liquid is coated on at least one surface of the base film, and then the base film is immersed in a first mixed solution for a first preset time and taken out. The first mixed solution comprises a good solvent and a poor solvent.

[0049] Step S13, after the base film is taken out and continues to be immersed in the second mixed solution for a second preset time, the base film is taken out again, dried and heated to be annealed, to form a super-crosslinked polymer coating on at least one surface of the base film, i.e. to obtain a diaphragm, and the second mixed solution comprises a poor solvent.

[0050] In an embodiment of the present application, in step S11, after the monomer is added to the good solvent and stirred until the monomer is completely dissolved, the crosslinking agent is added and stirring is continued for a set time, to obtain a dispersion liquid with uniform composition. The good solvent, for example, comprises at least one of N-methylpyrrolidone (NMP) or N,N-dimethylformamide (DMF), etc., the content of the monomer in the good solvent is, for example, 10wt%-20wt%, the crosslinking agent, for example, comprises at least one of hexamethylenetetramine, glutaraldehyde or glyoxal, etc., and in the dispersion liquid, the amount of the crosslinking agent is, for example, 8%-12% of the mass of the monomer, and the set time is, for example, 20min-120min.

[0051] In an embodiment of the present application, after the dispersion liquid is obtained, in step S12, the dispersion liquid is coated on at least one surface of the base film, and after the base film is loaded with the monomer, the crosslinking agent and the good solvent, the base film is immersed in a first mixed solution for a first preset time. The method of coating the dispersion liquid, for example, comprises coating, spraying or dipping, etc., the coating, for example, comprises doctor blade coating, comma coating or slot die coating, etc., the spraying, for example, comprises air spraying or electrostatic spraying, etc., and the dipping, for example, comprises direct dipping or vacuum dipping, etc. The first mixed solution comprises a good solvent, a poor solvent and an acid, etc. The type of the good solvent is the same as that of the good solvent used to dissolve the monomer in step S11, which will not be described here. The content of the good solvent in the first mixed solution is, for example, 2wt%-4wt%, the poor solvent, for example, comprises water, and the acid, for example, comprises 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, when the base film is immersed in the first mixed solution, the poor solvent in the first mixed solution initially replaces the good solvent loaded on the base film, and at the same time, the monomer and the crosslinking agent are polymerized on the base film to form a super-crosslinked polymer with a microporous structure.

[0052] In an embodiment of the present application, after the base membrane is taken out from the first mixed solution, the base membrane is continuously immersed in the second mixed solution and stirred for a second preset time in step S13. The second mixed solution contains poor solvents and acids, etc. The types of the poor solvents are the same as those in the mixed solution in step S12. The acids include at least one of acetic acid, formic acid, citric acid, etc. The pH value of the second mixed solution is, for example, 2-3. The temperature of the second mixed solution is, for example, 0-2°C. The second preset time is, for example, 1-5 hours. Specifically, the base membrane is immersed in the second mixed solution, and the poor solvents in the second mixed solution replace the remaining good solvents on the base membrane again, while the remaining monomers and cross-linking agents on the base membrane continue to polymerize to form an ultracross-linked polymer with a microporous structure. By immersing the base membrane twice in the mixed solution with a decreasing content of good solvents and controlling the temperature and pH value of the mixed solution, the pore size distribution in the microporous structure of the ultracross-linked polymer can be adjusted, and the barrier efficiency of the ultracross-linked polymer coating to the transition metal ions dissolved from the positive electrode can be adjusted.

[0053] In an embodiment of the present application, after the base membrane is taken out from the second mixed solution, the base membrane is dried, for example, by supercritical drying in step S13, and CO2 is used to replace the remaining good solvents and poor solvents in the base membrane. Specifically, the base membrane is placed in an autoclave, and then liquid CO2 is introduced into the autoclave. When the pressure in the autoclave reaches, for example, 6-12 MPa and the temperature reaches, for example, 35-45°C, the CO2 changes from a liquid state to a supercritical state, replacing the solvents in the microporous structure of the ultracross-linked polymer on the base membrane. Then, the pressure in the autoclave is reduced to normal pressure at a rate of, for example, 0.2-0.5 MPa / min, and the CO2 changes from a supercritical state to a gaseous state, escaping from the microporous structure, and the drying is completed. By controlling the pressure and temperature in the autoclave and the pressure reduction rate during the supercritical drying process, the porosity of the ultracross-linked polymer coating can be adjusted, and the barrier efficiency of the coating to the transition metal ions can be improved.

[0054] In an embodiment of the present application, after the base membrane is dried, the dried base membrane is heated and annealed in a stable gas atmosphere in step S13 to activate the remaining cross-linking sites, form an ultracross-linked polymer coating on the base membrane, and obtain a separator. The stable gas includes at least one of nitrogen and inert gas, etc., which can avoid oxidation of the ultracross-linked polymer. The heating and annealing temperature is, for example, 120-140°C. The heating and annealing time is, for example, 2-4 hours. By controlling the heating and annealing temperature and time, the cross-linking density of the ultracross-linked polymer coating can be adjusted, the network rigidity of the ultracross-linked polymer can be enhanced, and the swelling of the ultracross-linked polymer can be inhibited, thereby maintaining the stability of the microporous structure in the polymer and improving the stability of the coating to the transition metal ions.

[0055] Based on the above-mentioned separator and the preparation method thereof, the present application further provides a lithium ion battery, for example, a primary battery or a secondary battery, and the secondary battery is for example a soft pack battery, a hard shell battery or a cylindrical battery, etc. The present application does not specifically limit the type and category of the lithium ion battery. The lithium ion battery comprises a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte.

[0056] In an embodiment of the present application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer coated on at least one side surface of the positive electrode current collector. The positive electrode current collector is for example a foil formed after surface treatment of nickel, titanium, aluminum, silver, stainless steel or carbon, and the positive electrode current collector can also be in the form of a film, a net, a porous material, a foam or a non-woven fabric, etc.

[0057] In an embodiment of the present application, the positive electrode active layer comprises a positive electrode active material, a positive electrode conductive agent and a positive electrode binder, etc. The ratio of the positive electrode active material, the positive electrode conductive agent and the positive electrode binder can be selected according to actual needs. In this embodiment, the positive electrode active material comprises 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-rich manganese-based oxide or lithium nickel manganese oxide (LNMO), etc.

[0058] In an embodiment of the present application, the positive electrode conductive agent is for example selected from at least one of conductive carbon black (Super P), acetylene black, carbon nanotube or graphene, etc., and the positive electrode binder is for example selected from at least one of polyvinylidene fluoride (PVDF), poly(ethylene oxide) (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene or polymerized styrene butadiene rubber (SBR), etc.

[0059] In an embodiment of the present application, the positive electrode current collector is for example an 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 O2 positive active material, PVDF and Super P are mixed in a mass ratio of 98:1:1, dissolved in an organic solvent, and stirred in a vacuum stirrer until the system is uniform to obtain a positive electrode slurry. Then the positive electrode slurry is uniformly coated on an aluminum foil, and then transferred to an oven for drying after drying at room temperature, and then subjected to cold pressing and slitting processes to obtain a positive electrode sheet. The organic solvent is, for example, NMP.

[0060] In an embodiment of the present application, the negative electrode sheet is, for example, an indium sheet, a lithium sheet, an aluminum sheet, or an alloy sheet composed of at least two of the above metals. In other embodiments of the present application, the negative electrode sheet further includes a negative electrode current collector and a negative electrode active layer coated on at least one side surface of the negative electrode current collector. The negative electrode current collector is, for example, a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, or a stainless steel current collector, and the negative electrode active layer includes a negative electrode active material, a negative electrode conductive agent, a negative electrode thickening agent, and a negative electrode binder. The ratio of the negative electrode active material, the negative electrode conductive agent, the negative electrode thickening agent, and the negative electrode binder can 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, for example, selected from at least one of Super P, acetylene black, Ketjen black, carbon nanotubes, or graphene, the negative electrode thickening agent includes, for example, carboxymethyl cellulose sodium (CMC-Na), and the negative electrode binder is, for example, selected from at least one of polypropylene, polyacrylate, polyvinyl ether, PMMA, polyhexafluoropropylene, or SBR.

[0061] In an embodiment of the present application, the negative electrode current collector is, for example, a copper foil, the negative electrode active material is, for example, graphite, the negative electrode conductive agent is, for example, Super P, the negative electrode thickening agent 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 thickening agent, and the negative electrode binder are mixed in a mass ratio of 96:1:1:2, and then deionized water is added as a solvent. The mixture is then thoroughly stirred and mixed uniformly in a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry is then coated on a copper foil, and then transferred to an oven for drying after drying at room temperature. The negative electrode sheet is obtained after being subjected to cold pressing and slitting processes.

[0062] In an embodiment of the present application, the separator is arranged between the positive electrode sheet and the negative electrode sheet to prevent short circuit between the positive electrode sheet and the negative electrode sheet and allow lithium ions to pass through. The separator is, for example, the separator described above or the separator obtained by the preparation method described above, and will not be described herein again. When only one surface of the separator has the supercrosslinked polymer coating, the supercrosslinked polymer coating can be arranged towards the positive electrode sheet or the negative electrode sheet.

[0063] In an embodiment of the present application, the electrolyte is filled between the positive electrode sheet, the separator and the negative electrode sheet to play a role of conducting ions. The electrolyte at least includes a solvent and a lithium salt, for example, at least one of diethyl carbonate, fluoroethylene carbonate, difluoroethyl acetate, dimethyl carbonate, ethylene carbonate, propylene carbonate or methyl ethyl carbonate, and at least one of lithium fluorosulfonylimide or lithium hexafluorophosphate (LiPF6), and the content of the lithium salt in the electrolyte is, for example, 10wt%-18wt%. Further, the electrolyte can further include at least one of a film-forming additive or a flame-retardant additive, for example, at least one of vinylene carbonate or trimethyl phosphate or triethyl phosphate.

[0064] In an embodiment of the present application, in the electrolyte, the solvent includes, for example, 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.

[0065] In an embodiment of the present application, the positive electrode sheet, the separator and the negative electrode sheet described above are sequentially arranged, so that the separator is arranged between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then the positive electrode sheet, the separator and the negative electrode sheet are loaded into an aluminum plastic film, transferred to an environment with a dew point of -60°C and a vacuum degree of -98kPa, and then 3.4g of electrolyte is injected and sealed after sealing, and then soaked for 48h at room temperature, and then subjected to electrolytic liquefaction, degassing and aging to obtain a soft-pack lithium ion battery.

[0066] Hereinafter, the present application will be explained more specifically by reference to the examples, which should not be understood as limiting. Suitable modifications can be made within the scope consistent with the gist of the present application, and all fall within the technical scope of the present application.

[0067] Example 1

[0068] Preparation of the separator: Diphenyl diamine was dissolved in NMP and heated to 60°C for 2 hours to completely dissolve, then hexamethylenetetramine was added, and stirring was continued for 30 minutes to obtain a dispersion liquid, the content of diphenyl diamine in NMP was 15 wt%, and the mass of hexamethylenetetramine was 10% of the mass of diphenyl diamine. The dispersion liquid was uniformly coated on one surface of the polyethylene polymer layer by a slit coater, then the polyethylene polymer layer was immersed in the first mixed solution at a speed of 1 mm / s, and was left to stand for 5 minutes, then was immersed in the second mixed solution, and was slowly stirred for 2 hours. The thickness of the polyethylene polymer layer was 7 μm, the pore size was 40 nm-80 nm, the first mixed solution contained NMP, water and glacial acetic acid, the content of NMP in the first mixed solution was 4 wt%, the pH of the first mixed solution was 3, the temperature of the first mixed solution was 1°C, the second mixed solution contained water and acetic acid, the pH of the second mixed solution was 3, and the temperature of the second mixed solution was 1°C. Then the polyethylene polymer layer was taken out from the second mixed solution, was placed in an autoclave, and liquid CO2 was introduced until the pressure in the autoclave reached 8 MPa and the temperature reached 40°C, and then was kept for 2 hours, after which the pressure in the autoclave was reduced to normal pressure at a rate of 0.3 MPa / min to complete the supercritical drying. Then the polyethylene polymer layer was heated to 120°C under a nitrogen atmosphere, and was annealed for 2 hours to obtain a supercrosslinked polymer coating on one surface of the polyethylene polymer layer, and the thickness of the supercrosslinked polymer coating was 2 μm. The above operation was repeated on the other surface of the polyethylene polymer layer to obtain a supercrosslinked polymer coating on the other surface, thereby obtaining the separator.

[0069] Preparation of the positive electrode sheet: LiNi 0.8 Co 0.1 Mn 0.1 O2 positive active material, PVDF and Super P were mixed in a mass ratio of 98:1:1, were dissolved in NMP, and were stirred in a vacuum stirrer until the system was uniform to obtain a positive electrode slurry, then the positive electrode slurry was uniformly coated on an aluminum foil, and then was transferred to an oven for drying after being dried at room temperature, and was subjected to cold pressing and slitting to obtain the positive electrode sheet. The LiNi 0.8 Co 0.1 Mn 0.1 O2 was from Xiamen Tungsten Co., Ltd., and the model was M821A.

[0070] Preparation of the negative electrode sheet: A lithium metal sheet was selected as the negative electrode sheet.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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 dThe swelling degree SR was calculated. After obtaining the swelling degree SR, the crosslinking density was calculated according to the Flory-Rehner equation. The characterization results are shown in Table 1, wherein the crosslinking density of the hypercrosslinked polymer is 4 x 10 - ³mol / cm³.

[0075] The Young's modulus of the hypercrosslinked polymer coating was characterized, for example, by nanoindentation method. Specifically, a load was applied to the surface of the coating by a pressure head, and a load-displacement curve was recorded synchronously, and then the contact stiffness and unloading depth were extracted from the curve, and the Young's modulus was calculated according to the elastic contact mechanics formula. The characterization results are shown in Table 1, wherein the Young's modulus of the hypercrosslinked polymer is 2 GPa.

[0076] Example 2

[0077] The content of NMP in the first mixed solution was adjusted to 3wt%, the pH of the first mixed solution was 2.5, the temperature of the first mixed solution was 0°C, so as to adjust the pore size distribution of the hypercrosslinked polymer coating: the number of micropores with a pore size of <0.7nm accounted for 15% of the total number of micropores in the microporous structure, the number of micropores with a pore size of 0.7nm≤pore size≤1nm accounted for 70%, the number of micropores with a pore size of 1nm

[0078] Example 3

[0079] The content of NMP in the first mixed solution was adjusted to 2wt%, the pH of the first mixed solution was 2, the temperature of the first mixed solution was 0°C, so as to adjust the pore size distribution of the hypercrosslinked polymer coating: the number of micropores with a pore size of <0.7nm accounted for 5% of the total number of micropores in the microporous structure, the number of micropores with a pore size of 0.7nm≤pore size≤1nm accounted for 90%, the number of micropores with a pore size of 1nm

[0080] Example 4

[0081] During supercritical drying, the pressure in the autoclave was adjusted to 12MPa, the temperature was 45°C, and the pressure reduction rate was 0.2MPa / min, so as to adjust the porosity of the hypercrosslinked polymer coating to 70%, and the other steps were the same as those of Example 1.

[0082] Example 5

[0083] During supercritical drying, the pressure in the autoclave was adjusted to 6MPa, the temperature was 35°C, and the pressure reduction rate was 0.5MPa / min, so as to adjust the porosity of the hypercrosslinked polymer coating to 30%, and the other steps were the same as those of Example 1.

[0084] Example 6

[0085] In the supercritical drying, the pressure in the autoclave is adjusted to 10 MPa, the temperature is 45 °C, and the depressurization rate is 0.2 MPa / min to adjust the porosity of the supercrosslinked polymer coating to 60%, and the other steps are the same as in Example 1.

[0086] Example 7

[0087] The content of NMP in the first mixed solution is adjusted to 2 wt%, the pH of the first mixed solution is 2, the temperature of the first mixed solution is 0 °C, to adjust the pore size distribution of the supercrosslinked polymer coating: the number of micropores with a pore size < 0.7 nm accounts for 5% of the total number of micropores in the microporous structure, the number of micropores with a pore size of 0.7 nm ≤ pore size ≤ 1 nm accounts for 90%, the number of micropores with a pore size of 1 nm < pore size < 2 nm accounts for 5%, and in the supercritical drying, the pressure in the autoclave is adjusted to 10 MPa, the temperature is 45 °C, and the depressurization rate is 0.2 MPa / min to adjust the porosity of the supercrosslinked polymer coating to 60%, and the other steps are the same as in Example 1.

[0088] Example 8

[0089] In the heating annealing process, the heating temperature is adjusted to 130 °C, and the annealing time is 3 h to adjust the crosslinking density of the supercrosslinked polymer to 5 × 10 - ³mol / cm³, and the Young's modulus of the supercrosslinked polymer is adjusted to 3 GPa, and the other steps are the same as in Example 1.

[0090] Example 9

[0091] In the heating annealing process, the heating temperature is adjusted to 140 °C, and the annealing time is 4 h to adjust the crosslinking density of the supercrosslinked polymer to 6 × 10 - ³mol / cm³, and the Young's modulus of the supercrosslinked polymer is adjusted to 4 GPa, and the other steps are the same as in Example 1.

[0092] Example 10

[0093] adjusting the content of NMP in the first mixed solution to 2wt%, the pH of the first mixed solution to 2, the temperature of the first mixed solution to 0℃, to adjust the pore size distribution of the super-crosslinked polymer coating to: the number of micropores with a pore size <0.7nm accounts for 5% of the total number of micropores of the microporous structure, the number of micropores with a pore size of 0.7nm≤pore size≤1nm accounts for 90%, the number of micropores with a pore size of 1nm<pore size<2nm accounts for 5%, and during supercritical drying, adjusting the pressure in the autoclave to 10MPa, the temperature to 45℃, and the depressurization rate to 0.2MPa / min, to adjust the porosity of the super-crosslinked polymer coating to 60%, and during the heating annealing process, adjusting the heating temperature to 130℃ and the annealing time to 3h, to adjust the crosslinking density of the super-crosslinked polymer to 5×10 - ³mol / cm³, the Young's modulus of the super-crosslinked polymer to 3GPa, and the other steps being the same as in Example 1.

[0094] Example 11

[0095] adjusting the content of biphenyl diamine in NMP to 20wt% to adjust the specific surface area of the super-crosslinked polymer to 1400m 2 / g, and the other steps being the same as in Example 1.

[0096] Example 12

[0097] adjusting the content of biphenyl diamine in NMP to 10wt% to adjust the specific surface area of the super-crosslinked polymer to 600m 2 / g, and the other steps being the same as in Example 1.

[0098] Example 13

[0099] adjusting the content of biphenyl diamine in NMP to 17wt% to adjust the specific surface area of the super-crosslinked polymer to 1200m 2 / g, and the other steps being the same as in Example 1.

[0100] Example 14

[0101] The content of NMP in the first mixed solution is adjusted to 2wt%, the pH of the first mixed solution is 2, the temperature of the first mixed solution is 0℃, so as to adjust the pore size distribution of the super-crosslinked polymer coating to: the number of micropores with a pore size <0.7nm accounts for 5% of the total number of micropores of the microporous structure, the number of micropores with a pore size of 0.7nm≤pore size≤1nm accounts for 90%, the number of micropores with a pore size of 1nm<pore size<2nm accounts for 5%, and during supercritical drying, the pressure in the autoclave is adjusted to 10MPa, the temperature is 45℃, and the pressure reduction rate is 0.2MPa / min, so as to adjust the porosity of the super-crosslinked polymer coating to 60%, and during the heating annealing process, the heating temperature is adjusted to 130℃, and the annealing time is 3h, so as to adjust the crosslinking density of the super-crosslinked polymer to 5×10 - ³mol / cm³, the Young's modulus of the super-crosslinked polymer is adjusted to 3GPa, and the content of biphenyl diamine in NMP is adjusted to 20wt%, so as to adjust the specific surface area of the super-crosslinked polymer to 1400m 2 / g, and the other steps are the same as those in Example 1.

[0102] Example 15

[0103] The separator has a super-crosslinked polymer coating on only one surface, and the super-crosslinked polymer coating is arranged towards the positive electrode tab, and the other steps are the same as those in Example 1.

[0104] Example 16

[0105] The separator has a super-crosslinked polymer coating on only one surface, and the super-crosslinked polymer coating is arranged towards the negative electrode tab, and the other steps are the same as those in Example 1.

[0106] Example 17

[0107] LNMO is used to replace LiNi 0.8 Co 0.1 Mn 0.1 O2, and the other steps are the same as those in Example 1. Among them, the LNMO is specifically single-crystal LiNi 0.5 Mn 1.5 O4 coated with Li2ZrO3, which is from Xiamen Tungsten Co., Ltd. and the model number is XW46.

[0108] Comparative Example 1

[0109] The material of the coating on both surfaces of the separator is ceramic, the material of the ceramic is alumina, and the other steps are the same as those of Example 1. Specifically, when forming the alumina coating on one surface of the polyethylene polymer layer, alumina and PVDF are dissolved in N-methyl pyrrolidone at a mass ratio of 95:5 to form a uniform solution with a concentration of 10 wt%. The solution is then quickly coated on the surface of the polyethylene polymer layer, and after vacuum drying at 80°C for 24 hours, an alumina coating is obtained on one surface of the polymer layer.

[0110] Comparative Example 2

[0111] The material of the coating on both surfaces of the separator is PVDF, and the other steps are the same as those of Example 1. Specifically, when forming the PVDF coating on one surface of the polyethylene polymer layer, PVDF is dissolved in N-methyl pyrrolidone to form a uniform solution with a concentration of 10 wt%. The solution is then quickly coated on the surface of the polyethylene polymer layer, and after vacuum drying at 80°C for 24 hours, a PVDF coating is obtained on one surface of the polymer layer.

[0112] Comparative Example 3

[0113] The material of the coating on both surfaces of the separator is Polymer of Intrinsic Microporosity-1 (PIM-1), and the other steps are the same as those of Example 1. Specifically, when forming the PIM-1 coating on one surface of the polyethylene polymer layer, PIM-1 is dissolved in N-methyl pyrrolidone to form a uniform solution with a concentration of 10 wt%. The solution is then quickly coated on the surface of the polyethylene polymer layer, and after vacuum drying at 80°C for 24 hours, a PIM-1 coating is obtained on one surface of the polymer layer.

[0114] Comparative Example 4

[0115] The content of NMP in the first mixed solution is adjusted to 1 wt%, and the pH of the first mixed solution is adjusted to 1.5 to adjust the pore size of the super-crosslinked polymer coating to >2 nm, and the other steps are the same as those of Example 1.

[0116] Comparative Example 5

[0117] During supercritical drying, the pressure in the autoclave is adjusted to 4 MPa, the temperature is adjusted to 25°C, and the pressure reduction rate is adjusted to 1 MPa / min to adjust the porosity of the super-crosslinked polymer coating to 20%, and the other steps are the same as those of Example 1.

[0118] Comparative Example 6

[0119] In the supercritical drying, the pressure in the autoclave is adjusted to 20 MPa, the temperature is 45℃, and the pressure reduction rate is 0.1 MPa / min to adjust the porosity of the super-crosslinked polymer coating to 90%, and the other steps are the same as those in Example 1.

[0120] In the present application, the performance of the separators and lithium ion batteries in Examples 1-17 and Comparative Examples 1-6 is tested, and the test results are shown in Table 1.

[0121] In an embodiment of the present application, the puncture strength of the whole separator is tested, for example, by a puncture test. Specifically, a steel needle with a diameter of 1.0 mm and a needle tip radius of 0.5 mm is used to puncture the separator sample at a speed of 50±5 mm / min, and the average of 5 samples is taken as the puncture strength. Among them, the test specification of the puncture strength of the separator mainly refers to GB / T 36363-2018.

[0122] In an embodiment of the present application, for example, the high-temperature cycle stability of the lithium ion battery is tested. Specifically, at 45℃, the battery is subjected to long cycle charging and discharging within the charging and discharging cut-off voltage at a constant current charging and discharging rate of 1C / 1C, the capacity of the battery is measured, and when the battery capacity reaches 80% State of Health (SOH) of the first cycle capacity, the test is ended, and the 45℃ cycle number of the battery is recorded. Among them, for the batteries in Examples 1-16 and Comparative Examples 1-6, the charging and discharging cut-off voltage is 2.8V-4.3V, and for the battery in Example 17, the charging and discharging cut-off voltage is 2V-4.85V.

[0123] In an embodiment of the present application, for example, the high-temperature storage performance of the lithium ion battery is tested. Specifically, the initial direct current resistance (DCR) of the battery is first tested, then the battery is placed in an environment at 60℃ for 90 days, the DCR of the battery is tested, and the DCR increment is calculated according to the following formula:

[0124] DCR increment = (DCR of the battery after 90 days-initial DCR) / initial DCR×100%.

[0125] Table 1, performance test results of Examples 1-17 and Comparative Examples 1-6

[0126]

[0127] As shown in Table 1, compared with the ceramic coating, the PVDF coating and the PIM-1 coating, the 45℃ cycle number of the battery is significantly increased and the DCR increment is significantly reduced after the super-crosslinked polymer coating is arranged on the base film, which indicates that the high-temperature cycle stability and the high-temperature storage stability of the battery can be improved by arranging the super-crosslinked polymer coating on the base film.

[0128] As shown in Table 1, it can be seen from Comparative Examples 1-3 and Comparative Example 4 that when the pore size in the microporous structure of the hypercrosslinked polymer is less than 2 nm, the puncture strength of the separator is significantly increased, the 45°C cycle number of the battery is significantly increased, and the increase in DCR is significantly reduced, thereby indicating that by controlling the pore size in the hypercrosslinked polymer coating to be less than 2 nm, the mechanical strength of the separator can be improved, and the transition metal ions dissolved out of the positive electrode can be blocked, thereby jointly improving the high-temperature cycle stability and high-temperature storage stability of the battery.

[0129] As shown in Table 1, it can be seen from Comparative Examples 1-3 and Comparative Example 4 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 large pores with a pore size of 1nm

[0130] As shown in Table 1, it can be seen from Comparative Example 2 and Examples 1 and 3 that in the microporous structure of the hypercrosslinked polymer, when the proportion of micropores with a pore size of <0.7nm and the proportion of micropores with a pore size of 1nm

[0131] As shown in Table 1, it can be seen from Comparative Example 1, Examples 4-6 and Comparative Examples 5-6 that, in the supercritical drying process, the porosity of the supercrosslinked polymer coating changes with the changes in the pressure, temperature and pressure reduction rate in the autoclave, thereby indicating that, in the supercritical drying process, the pressure can control the shrinkage and expansion of the pores, the temperature affects the solvent evaporation rate, the pressure reduction rate affects the pore retention rate, and the three parameters jointly affect the porosity of the coating.

[0132] As shown in Table 1, it can be seen from Comparative Example 1, Examples 4-6 and Comparative Examples 5-6 that, when the porosity of the supercrosslinked polymer coating is less than 30%, although the puncture strength of the separator is large, the 45°C cycle number of the battery is small and the DCR increase is large, when the porosity increases from 30% to 90%, the puncture strength of the separator decreases significantly, the 45°C cycle number of the battery is still low and the DCR increase is high, that is, when the mechanical strength of the separator is the largest, the high-temperature cycle stability and high-temperature storage stability of the battery are not the best, with the change of the porosity, although the mechanical strength of the separator is affected, the barrier efficiency of the separator to the transition metal ions dissolved out of the positive electrode shows a trend of first increasing and then decreasing, therefore, by controlling the porosity to be 30%-70%, the separator 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 Example 1, Example 6 that, by further limiting the porosity of the supercrosslinked polymer coating to be 40%-60%, the barrier efficiency of the micropores in the supercrosslinked polymer coating to the transition metal ions dissolved out of the positive electrode can be improved, while the mechanical strength of the separator is taken into account, thereby jointly improving the high-temperature cycle stability and high-temperature storage stability of the battery.

[0133] As shown in Table 1, it can be seen from Comparative Example 1 and Examples 8-9 that, when the temperature and time of the heating annealing increase, the crosslinking density and Young's modulus of the supercrosslinked polymer coating increase, thereby indicating that, by increasing the temperature of the heating annealing process and prolonging the heating annealing time, the crosslinking network between the diphenyl diamine and the hexamethylenetetramine can be densified, thereby increasing the crosslinking density and Young's modulus of the supercrosslinked polymer coating, and further improving the mechanical strength of the coating.

[0134] As shown in Table 1, it can be seen from Comparative Example 1 and Examples 8-9 that, when the crosslinking density of the supercrosslinked polymer coating increases from 4×10 - ³mol / cm³ to 5×10 - ³mol / cm³ and the Young's modulus increases from 2 GPa to 3 GPa, the 45°C cycle number of the battery increases, the DCR increase decreases, and the puncture strength of the separator increases; when the crosslinking density of the supercrosslinked polymer coating continues to increase from 5×10 - ³mol / cm³ to 6×10 -When the crosslinking density of the supercrosslinked polymer is greater than or equal to 3 mol / cm3 and the Young's modulus continues to increase from 3 GPa to 4 GPa, the puncture strength of the separator increases, but the 45°C cycle number of the battery decreases and the DCR increment increases, thereby indicating that by controlling the crosslinking density and the Young's modulus of the supercrosslinked polymer, the high-temperature cycle stability, the high-temperature storage stability of the battery and the mechanical strength of the separator can be taken into account.

[0135] As shown in Table 1, it can be seen from Comparative Example 1 and Examples 11-13 that when the content of biphenyl diamine in NMP increases, the specific surface area of the supercrosslinked polymer increases, thereby indicating that the change in the content of the monomer in the good solvent can change the rigid aromatic ring density, expand the gap between the molecular skeletons, and thus change the specific surface area of the supercrosslinked polymer.

[0136] As shown in Table 1, it can be seen from Comparative Example 1 and Examples 11-13 that when the specific surface area of the supercrosslinked polymer increases from 600 m 2 / g to 1400 m 2 / g, although the puncture strength of the separator slightly decreases, the 45°C cycle number of the battery increases and the DCR increment decreases, thereby indicating that by controlling the specific surface area of the supercrosslinked polymer, the high-temperature cycle stability and the high-temperature storage stability of the battery can be improved.

[0137] As shown in Table 1, it can be seen from Comparative Example 1, Example 7, Example 10 and Example 14 that when the pore size distribution, porosity, specific surface area and Young's modulus of the supercrosslinked polymer are all kept within the control range, the 45°C cycle number of the battery is the largest and the DCR increment is the smallest, thereby indicating that by synergistically controlling the pore size distribution, porosity, specific surface area and Young's modulus of the supercrosslinked polymer, the high-temperature cycle stability and the high-temperature storage stability of the battery can be improved to the greatest extent.

[0138] As shown in Table 1, it can be seen from Comparative Example 1, Example 15 and Example 16 that when the supercrosslinked polymer coating layer is arranged on both sides of the separator, the 45°C cycle number of the battery is the largest, the DCR increment is the smallest, and the puncture strength of the separator is the largest, thereby indicating that compared to arranging the supercrosslinked polymer coating layer on one side of the separator, arranging the coating layer on both sides of the separator can improve the high-temperature cycle stability, the high-temperature storage stability of the battery and the mechanical strength of the separator.

[0139] As shown in Table 1, it can be seen from Comparative Example 1 and Example 17 that no matter whether the positive active material is LiNi 0.8 Co 0.1 Mn 0.1 O2 or LNMO, the 45°C cycle number of the battery is relatively large and the DCR increment is relatively small, thereby indicating that regardless of the type of the positive active material, the supercrosslinked polymer coating layer arranged on the separator can improve the high-temperature cycle stability and the high-temperature storage stability of the battery.

[0140] The electronic device can be a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy, an electric tool, or the like. In an embodiment of the present application, the vehicle is a new energy vehicle, which can be a pure electric vehicle, a hybrid electric vehicle, or a range extended electric vehicle. The spacecraft includes an airplane, a rocket, a space shuttle, a spacecraft, or the like. The electric toy includes a stationary or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, an electric airplane toy, or the like. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembling electric tool, and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact electric drill, a concrete vibrator, an electric planer, or the like. The electronic device includes the lithium ion battery, and thus has the advantages of the lithium ion battery.

[0141] In summary, the present application provides a separator, a preparation method and an application thereof. By arranging an ultracrosslinked polymer coating layer on the base film, the permeability of the separator to electrolyte can be destroyed without affecting the safety of the separator, so as to block the diffusion of transition metal ions dissolved from the positive electrode to the negative electrode, 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 ultracrosslinked polymer coating layer, and the crosslinking density and Young's modulus of the ultracrosslinked polymer, the barrier efficiency of the separator to transition metal ions can be improved while the stability of the microporous structure in the polymer and the overall performance of the separator in electrolyte permeability, mechanical properties, and lithium ion passing rate are ensured, thereby greatly improving the cycle life of the battery under high voltage and high temperature conditions.

[0142] The above description is merely the preferred embodiments of the present application and the explanation of the applied technical principles, and those skilled in the art should understand that the application scope involved in the present application is not limited to the technical solutions formed by the specific combinations of the above technical features, and should also cover other technical solutions formed by any combinations of the above technical features or their equivalent features without departing from the inventive concept, such as the technical solutions formed by the mutual replacement of the above features and the technical features disclosed in the present application (but not limited to) having similar functions. In addition to the technical features described in the specification, the remaining technical features are known to those skilled in the art, and in order to highlight the innovative features of the present application, the remaining technical features are not described here.

Claims

1. A diaphragm, characterized in that: At least: basement membrane; and A hypercrosslinked polymer coating is disposed 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 2 nm, the porosity of the hypercrosslinked polymer coating is 30%-70%, and among all the micropores in the microporous structure, the number of micropores with a pore size less than 0.7 nm accounts for 0-10%, the number of micropores with a pore size of 0.7 nm ≤ ≤ 1 nm accounts for 80%-90%, and the number of micropores with a pore size of 1 nm < 2 nm accounts for 0-10%; Wherein, the diaphragm is prepared by 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 base film 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 pH value of the first mixed solution is 2-3, and the temperature of the first mixed solution is 0° C.-2° C.; The base film is taken out and continued to be immersed in the second mixed solution for a second preset time, and then taken out again to be dried and heated for annealing to form a hyper-cross-linked polymer coating on at least one surface of the base film, that is, a diaphragm is obtained, the second mixed solution contains the poor solvent, the pH value of the second mixed solution is 2-3, and the temperature of the second mixed solution is 0°C-2°C.

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

3. 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.

4. 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 -3 mol / cm 3 ; 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.

5. 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.

6. The diaphragm according to claim 1, 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 acid; And / or, the heating annealing temperature is 120° C.-140° C.; And / or, the heating annealing time is 2h-4h.

7. 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, the separator being selected from the separator according to any one of claims 1 to 6; and The electrolyte is filled between the positive electrode sheet, the negative electrode sheet and the separator.

8. An electronic device, characterized in that: Including the lithium ion battery according to claim 7.

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