Preparation method of step-by-step polymerization double-enhanced interface solid polymer electrolyte

Abstract

The invention discloses a preparation method of a step-by-step polymerization double-enhanced interface solid polymer electrolyte, which comprises the following steps: mixing a matrix monomer and a first photoinitiator to obtain mixed slurry, and illuminating to obtain prepolymerized slurry; adding a lithium salt and a second photoinitiator into the pre-polymerized slurry, mixing to obtain polymer slurry, dividing the polymer slurry into first polymer slurry and second polymer slurry, adding a nitrogen-containing functional monomer into the first polymer slurry to obtain polymer slurry A, and adding a fluorine-containing functional monomer into the second polymer slurry to obtain polymer slurry B; and pouring the polymer slurry A on the first surface of the base membrane, treating the first surface, pouring the polymer slurry B on the second surface of the base membrane, and treating the second surface of the base membrane to obtain the step-by-step polymerization double-enhanced interface solid polymer electrolyte. The solid polymer electrolyte is prepared by adopting a step-by-step polymerization method, a positive electrode side interface and a negative electrode side interface are optimized, and continuous large-scale production of the solid polymer electrolyte is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy batteries, and more specifically, to a method for preparing a step-by-step polymerization double-enhanced interface solid polymer electrolyte. Background Art

[0002] The rapid development of electric vehicles, electric aircraft, energy storage systems and other fields has put forward increasingly higher requirements on the energy density and safety performance of secondary batteries. Currently, commercial liquid lithium-ion batteries have already reached the bottleneck of their performance ceiling. Therefore, solid-state lithium metal batteries are regarded as the next generation of energy storage devices with great potential.

[0003] Solid-state lithium metal batteries are composed of positive electrode current collectors, positive electrode active materials, solid electrolytes, negative electrode active materials and negative electrode current collectors. Solid-state electrolytes include polymer electrolytes. Polymer electrolytes have good processability, flexibility and compatibility, and they play an important role in the research of solid-state electrolytes. However, the interface problems that cannot be ignored in solid-state lithium metal batteries limit their promotion in practical applications.

[0004] Due to the high activity of lithium metal, the growth of a large number of lithium dendrites and the generation of dead lithium during the battery cycle pose a challenge to the mechanical stability of the polymer electrolyte. At the same time, the contact problem of the solid / solid interface leads to high interface impedance, which affects the efficiency of ion transmission and limits the battery capacity. Conventional solid polymer electrolytes have poor mechanical properties and high-voltage stability, which will limit the long-term operation of high-nickel ternary lithium metal batteries. In addition, existing interface optimization strategies can often only optimize the negative electrode or positive electrode, or increase the interface impedance when constructing a stable SEI (full name: Solid-Electrolyte Interphase, electrolyte intermediate interface) / CEI (full name: Chemical-Electrochemical Interface, positive electrode-electrolyte interface) layer, which affects the ion transmission effect and lacks comprehensive interface improvement. At the same time, the conventional UV polymer electrolyte process is a one-step polymerization, and the precursor has low viscosity and is not easy to hang on the substrate. It can often only be cast in situ in a small range or cast in a mold by non-in-situ method, and continuous production cannot be achieved. Therefore, it is a technical problem that needs to be solved in this field. Summary of the invention

[0005] In view of this, the present invention provides a method for preparing a step-by-step polymerization dual-enhanced interface solid polymer electrolyte, which adopts a step-by-step polymerization method to prepare a solid polymer electrolyte, while optimizing the positive electrode side interface and the negative electrode side interface to achieve continuous large-scale production of the solid polymer electrolyte.

[0006] The present application provides a method for preparing a step-by-step polymerization double-enhanced interface solid polymer electrolyte, comprising the following steps:

[0007] Providing a matrix monomer and a first photoinitiator, uniformly mixing the matrix monomer and the first photoinitiator to obtain a mixed slurry, and irradiating the mixed slurry with ultraviolet light to obtain a prepolymerized slurry;

[0008] Adding lithium salt and a second photoinitiator into the prepolymer slurry, uniformly mixing to obtain a polymer slurry, dividing the polymer slurry into a first polymer slurry and a second polymer slurry, adding a nitrogen-containing functional monomer to the first polymer slurry to obtain a polymer slurry A, and adding a fluorine-containing functional monomer to the second polymer slurry to obtain a polymer slurry B;

[0009] A base film is provided, which includes a first surface and a second surface arranged opposite to each other. Polymer slurry A is poured on the first surface, and polymer slurry A is subjected to continuous roll-to-roll scraper coating and ultraviolet light curing molding treatment. Polymer slurry B is poured on the second surface, and polymer slurry B is subjected to continuous roll-to-roll scraper coating and ultraviolet light curing molding treatment to obtain a step-polymerized dual-reinforced interface solid polymer electrolyte.

[0010] Optionally, the mass ratio of the matrix monomer to the first photoinitiator ranges from 100:1 to 5000:1; the mass ratio of the prepolymer syrup to the second photoinitiator ranges from 20:1 to 500:1.

[0011] Optionally, the mass ratio of the first polymer syrup to the nitrogen-containing functional monomer is in the range of 5:1 to 20:1; the mass ratio of the second polymer syrup to the fluorine-containing functional monomer is in the range of 5:1 to 20:1.

[0012] Optionally, in the ultraviolet light irradiation mixed slurry, the wavelength range of the ultraviolet light is 220nm to 400nm, and the irradiation time is 0.2min to 2min; in the ultraviolet light curing molding process, the wavelength range of the ultraviolet light is 220nm to 400nm, and the irradiation time is 1 to 10min.

[0013] Optionally, the base monomer and the first photoinitiator are uniformly mixed in a nitrogen atmosphere.

[0014] Optionally, the viscosity of the prepolymerization slurry ranges from 500 cP to 3500 cP.

[0015] Optionally, the matrix monomer includes at least one of polyethylene glycol diacrylate, polyethylene glycol methyl ether methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl acrylate, hydroxypropyl methacrylate, and vinyl acetate;

[0016] The first photoinitiator is at least one of benzophenone, 2,2-dimethoxy-2-phenylacetophenone, ethyl 4-dimethylaminobenzoate, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methylpropiophenone, and methyl benzoylformate;

[0017] The second photoinitiator is at least one of benzophenone, 2,2-dimethoxy-2-phenylacetophenone, ethyl 4-dimethylaminobenzoate, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methylpropiophenone, and methyl benzoylformate.

[0018] Optionally, the lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalatoborate), and lithium difluorooxalatoborate.

[0019] Optionally, the nitrogen-containing functional monomer includes at least one of: N,N'-methylenebisacrylamide, N-phenylmethacrylamide, N,N'-bis(acryloyl)cystamine, acrylamide, N-isopropylacrylamide, and N-vinylcaprolactam.

[0020] Optionally, the fluorine-containing functional monomer includes at least one of hexafluoroisopropyl acrylate, hexafluorobutyl acrylate, hexafluorobutyl methacrylate, trifluoroethyl methacrylate, and dodecafluoroheptyl methacrylate.

[0021] Compared with the prior art, the method for preparing a step-by-step polymerization double-enhanced interface solid polymer electrolyte provided by the present invention achieves at least the following beneficial effects:

[0022] First, a solid polymer electrolyte is prepared by a step-by-step polymerization method. First, a part of the matrix monomer is polymerized as a prepolymer slurry, and the long-chain molecular weight structure of the matrix polymer can be adjusted. The viscosity of the subsequent polymerization slurry is suitable and controllable, and it can be evenly coated on the base film to maintain sufficient liquid hanging, and can be continuously coated to ensure that the subsequently formed solid polymer electrolyte has good contact with the electrode, which reduces the process difficulty of manufacturing the solid polymer electrolyte and is conducive to large-scale industrial promotion and production. Functional monomers and lithium salts are added to the prepolymer slurry, and then cross-linking polymerization is carried out, which is conducive to sufficient and uniform mixing between the components and the structure of the generated polymer can be controlled. During the polymerization process, the matrix monomer and the functional monomer can form a stable cross-linked structure, which is conducive to enhancing the structural stability and ion transport performance, and promoting the improvement of the high-voltage stability of the solid polymer electrolyte, so that the battery prepared by the solid polymer electrolyte has good mechanical stability and can overcome the problems of life attenuation caused by the growth of lithium dendrites.

[0023] Secondly, by coating polymer electrolytes of different properties on the first and second surfaces of the base film respectively (the first and second surfaces can also be understood as the positive electrode side and the negative electrode side), the solid polymer electrolyte containing nitrogen elements can construct a CEI (positive electrode-electrolyte interface) layer rich in high-strength oxidation-stable nitration groups on the positive electrode side, and the polymer electrolyte containing fluorine elements can construct a stable SEI (electrolyte intermediate interface) layer rich in lithium fluoride (chemical formula: LiF) beneficial inorganic components on the negative electrode side. The synergistic effect of fluorine and nitrogen element modifications achieves the effect of dual enhancement of the positive electrode side interface and the negative electrode side interface at the same time.

[0024] Thirdly, the solid polymer electrolyte prepared by the step-by-step polymerization double-enhanced interface solid polymer electrolyte preparation method has high ionic conductivity and high mechanical stability. The solid-state lithium metal battery prepared by the solid polymer electrolyte has improved interface performance compared with the solid-state lithium metal battery in the prior art.

[0025] Of course, any product implementing the present invention does not necessarily need to achieve all of the technical effects described above at the same time.

[0026] Further features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0028] Figure 1 The present invention provides a flow chart of a method for preparing a step-by-step polymerization double-enhanced interface solid polymer electrolyte. DETAILED DESCRIPTION

[0029] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless otherwise specifically stated.

[0030] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0031] Technologies, methods, and devices known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and devices should be considered as part of the specification.

[0032] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0033] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0034] Reference Figure 1 As shown, Figure 1 This embodiment provides a method for preparing a step-by-step polymerization dual-enhanced interface solid polymer electrolyte, comprising the following steps:

[0035] S1: providing a base monomer and a first photoinitiator, uniformly mixing the base monomer and the first photoinitiator to obtain a mixed slurry, and irradiating the mixed slurry with ultraviolet light to obtain a prepolymerized slurry.

[0036] Specifically, refer to Figure 1 As shown in the figure, polymers are formed by polymerization, copolymerization, and polycondensation of one or more simple low molecular weight compounds (monomers), and are composed of many monomers repeatedly connected and have a relative molecular mass of up to 10 4 In the above compounds, the matrix monomer is the basic unit of the polymer, which is a small molecule for synthesizing polymers and can be regarded as the basic component of the polymer compound; the first photoinitiator belongs to the photoinitiator, which is also called photosensitizer or photocuring agent, and is a type of compound that can absorb energy of a certain wavelength in the ultraviolet region (wavelength range of 250 to 420nm) or the visible region (wavelength range of 400 to 800nm), generate free radicals, cations, etc., thereby initiating the polymerization, cross-linking and curing of the matrix monomer. The matrix monomer and the first photoinitiator are uniformly mixed to ensure sufficient reaction between the two. The mixed slurry is irradiated with ultraviolet light, and the first photoinitiator can absorb the energy of ultraviolet light and initiate polymerization between the matrix monomers, thereby obtaining a prepolymer slurry. The viscosity of the prepolymer slurry is suitable and controllable, and it can be evenly coated on the support film to maintain sufficient liquid hanging, and can be continuously coated to ensure that the solid electrolyte is in good contact with the electrode, which reduces the process difficulty of manufacturing solid polymer electrolytes and is conducive to large-scale industrial promotion and production.

[0037] Optionally, the base monomer and the first photoinitiator are uniformly mixed in a nitrogen atmosphere.

[0038] Specifically, nitrogen is an inert gas and can be used as a protective gas to prevent the matrix monomer and the first photoinitiator from reacting during the mixing process; the method of uniform mixing includes but is not limited to magnetic stirring or ultrasonic stirring. The method of uniformly mixing the matrix monomer and the first photoinitiator is the prior art in the art and is not specifically limited here.

[0039] Optionally, the matrix monomer includes at least one of polyethylene glycol diacrylate, polyethylene glycol methyl ether methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl acrylate, hydroxypropyl methacrylate, and vinyl acetate.

[0040] Specifically, polyethylene glycol diacrylate (molecular formula: (C2H4O) n C6H6O3, CAS No.: 26570-48-9), polyethylene glycol methyl ether methacrylate (molecular formula: (C2H4O) n C5H8O2, CAS No.: 26915-72-0), ethyl methacrylate (molecular formula: C6H 10 O2, CAS No.: 97-63-2), butyl methacrylate (molecular formula: C8H 14 O2, CAS No.: 97-88-1), 2-ethylhexyl acrylate (also known as: 2-octyl acrylate, molecular formula: C 11 H 20 O2, CAS No.: 42928-85-8), Hydroxypropyl Methacrylate (Molecular Formula: C7H 12 O3, CAS number: 27813-02-1), vinyl acetate (also known as: vinyl acetate, molecular formula: C4H6O2, CAS number: 108-05-4); wherein, CAS number (CAS Registry Number or CAS Number, CAS Rn, CAS#), also known as CAS number, CAS accession number or CAS registration number, is a unique digital identification number for a substance (compound, polymer material, biological sequence (Biological sequences), mixture or alloy); the materials that can be selected for the matrix monomer and the types and quantities of the matrix monomers in the prepolymer slurry can be adaptively adjusted according to actual conditions, and are not specifically limited here.

[0041] Optionally, the first photoinitiator is at least one of benzophenone, 2,2-dimethoxy-2-phenylacetophenone, ethyl 4-dimethylaminobenzoate, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methylpropiophenone, and methyl benzoylformate.

[0042] Specifically, benzophenone (molecular formula: C 13 H 10O, CAS No.: 119-61-9), 2,2-dimethoxy-2-phenylacetophenone (also known as: benzoin dimethyl ether, molecular formula: C 16 H 16 O3, CAS No.: 24650-42-8), 4-dimethylaminobenzoic acid ethyl ester (molecular formula: C 11 H 15 NO2, CAS No.: 10287-53-3), 1-hydroxycyclohexyl phenyl ketone (molecular formula: C 13 H 16 O2, CAS No.: 947-19-3), 2-hydroxy-2-methylpropiophenone (molecular formula: C 10 H 12 O2, CAS number: 7473-98-5), methyl benzoylformate (molecular formula: C9H8O3, CAS number: 15206-55-0); the material that can be selected for the first photoinitiator and the type and quantity of the first photoinitiator in the pre-polymerization slurry can be adaptively adjusted according to actual conditions and are not specifically limited here.

[0043] Optionally, the mass ratio of the base monomer to the first photoinitiator ranges from 100:1 to 5000:1.

[0044] This embodiment explains that the matrix monomer and the first photoinitiator have a certain mass ratio to obtain a prepolymer slurry, and the mass ratio of the matrix monomer and the first photoinitiator can range from 100:1 to 5000:1, such as the mass ratio of the matrix monomer and the first photoinitiator can be 100:1, 200:1, 300:1, 500:1, 1000:1, 2000:1, 3000:1 or 5000:1, etc., so as to avoid the mass ratio of the matrix monomer and the first photoinitiator being too small to form a prepolymer slurry with sufficient suitable viscosity, and to avoid the inability to polymerize between the matrix monomers when the mass ratio of the matrix monomer and the first photoinitiator is too large. Therefore, this embodiment sets the mass ratio of the matrix monomer and the first photoinitiator to range from 100:1 to 5000:1, which can avoid the inability to form a prepolymer slurry with sufficient suitable viscosity while ensuring the polymerization reaction between the matrix monomers.

[0045] Optionally, the mixed slurry is irradiated with ultraviolet light, the wavelength range of the ultraviolet light is 220nm to 400nm, and the irradiation time is 0.2min to 2min.

[0046] This embodiment explains that the ultraviolet light has a certain wavelength to provide reaction conditions for the polymerization reaction, and the wavelength range of the ultraviolet light can be 220nm to 400nm, such as the wavelength of the ultraviolet light can be 220nm, 250nm, 300nm, 320nm, 345nm, 365nm, 380nm or 400nm, so as to avoid the polymerization reaction being insufficient when the wavelength of the ultraviolet light is too short, and to avoid the polymerization reaction being excessive when the wavelength of the ultraviolet light is too long. Therefore, this embodiment sets the wavelength range of the ultraviolet light to 220nm to 400nm, which can avoid the polymerization reaction being insufficient and the polymerization reaction being excessive.

[0047] This embodiment explains that the ultraviolet light has a certain irradiation time to provide reaction conditions for the polymerization reaction. The irradiation time of the ultraviolet light can be 0.2min to 2min, such as the irradiation time of the ultraviolet light can be 0.2min, 0.5min, 1min, 1.2min, 1.5min or 2min, etc., so as to avoid the polymerization reaction being insufficient when the irradiation time of the ultraviolet light is too short, and to avoid the polymerization reaction being excessive when the irradiation time of the ultraviolet light is too long. Therefore, this embodiment sets the irradiation time of the ultraviolet light to 0.2min to 2min, which can avoid the polymerization reaction being insufficient and the polymerization reaction being excessive.

[0048] Optionally, the viscosity of the prepolymerization slurry ranges from 500 cP to 3500 cP.

[0049] This embodiment explains that the prepolymer slurry has a certain viscosity to generate a step-polymerized dual-enhanced interface solid polymer electrolyte. The viscosity of the prepolymer slurry can range from 500cP to 3500cP, such as the viscosity of the prepolymer slurry can be 500cP, 800cP, 1000cP, 1500cP, 2000cP, 2500cP, 3000cP or 3500cP, etc., so as to avoid the inability to form a solid polymer when the viscosity of the prepolymer slurry is too small, and to avoid the inability to subsequently dope other monomers when the viscosity of the prepolymer slurry is too large. Therefore, this embodiment sets the viscosity range of the prepolymer slurry to 500cP to 3500cP, which can avoid the inability to form a solid polymer while ensuring that the prepolymer slurry can be doped with other monomers later.

[0050] S2: adding lithium salt and a second photoinitiator into the prepolymer slurry, uniformly mixing to obtain a polymer slurry, dividing the polymer slurry into a first polymer slurry and a second polymer slurry, adding a nitrogen-containing functional monomer to the first polymer slurry to obtain a polymer slurry A, and adding a fluorine-containing functional monomer to the second polymer slurry to obtain a polymer slurry B.

[0051] Specifically, continue to refer to Figure 1As shown, lithium salt refers to salts containing lithium elements. Since the matrix monomer in the prepolymer slurry contains functional groups such as ester groups and hydroxyl groups, after the lithium salt is added to the prepolymer slurry, the ester groups, hydroxyl groups and other functional groups can form a complex structure with the lithium ions in the lithium salt, thereby realizing the transmission of lithium ions in the polymer main chain, thereby improving the electrochemical properties of the electrolyte, and then improving the performance of the battery prepared subsequently. At the same time, after the matrix monomer and the lithium salt are completely polymerized, the surface of the solid polymer electrolyte membrane formed subsequently can be wrapped by the elastic polymer, which can reduce the interface resistance between the solid electrolyte and the electrode and make it have excellent flexibility; the second photoinitiator can initiate polymerization between the lithium salt and the prepolymer slurry; the method of uniform mixing is the existing technology in the field and is not specifically limited here.

[0052] Continue to refer to Figure 1 As shown, the nitrogen-containing functional monomer contains nitrogen (element symbol: N) element, which can be used as an additive for positive electrode interface modification, which is beneficial to form an enhanced and stable interface containing nitrogen elements during the battery cycle and improve the positive electrode side interface; the fluorine-containing functional monomer contains fluorine (element symbol: F) element, which can be used as an additive for negative electrode interface modification, which is beneficial to form an enhanced and stable interface containing fluorine elements during the battery cycle and improve the negative electrode side interface; by dividing the polymer slurry equally into a first polymer slurry and a second polymer slurry, adding the nitrogen-containing functional monomer to the first polymer slurry to obtain polymer slurry A, adding the fluorine-containing functional monomer to the second polymer slurry to obtain polymer slurry B, and subsequently pouring the polymer slurry A and the polymer slurry B on both sides of the base film respectively, a step-polymerized dual-enhanced interface solid polymer electrolyte membrane can be obtained, thereby forming a dual-enhanced stable interface, which plays a role in simultaneously improving the positive electrode side interface and the negative electrode side interface.

[0053] This embodiment realizes a stable polymer network composed of two cross-linked monomers by polymerizing the matrix monomer and the functional monomer under ultraviolet light, which is beneficial to enhancing the structural stability and ion transport, promoting the improvement of the high-voltage stability of the solid polymer electrolyte, and making the battery prepared by the solid polymer electrolyte have good mechanical stability and can overcome the life attenuation caused by the growth of lithium dendrites. At the same time, since the preparation method of the step-by-step polymerization double-enhanced interface solid polymer electrolyte adds a prepolymerization process before the functional monomer, the prepolymerization process can achieve a higher monomer conversion rate and more favorable long-chain polymer structure regulation, which is beneficial to improving the high-voltage stability of the polymer electrolyte.

[0054] Optionally, the lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalatoborate), and lithium difluorooxalatoborate.

[0055] Specifically, lithium hexafluorophosphate (molecular formula: F6LiP, CAS number: 21324-40-3), lithium perchlorate (molecular formula: LiClO4, CAS number: 7791-03-9), lithium bis(trifluoromethanesulfonyl imide) (molecular formula: CF3SO2NLiSO2CF3, CAS number: 90076-65-6), lithium bis(fluorosulfonyl imide) (molecular formula: F2LiNO4S2, CAS number: 171611-11-3), tetrafluoroboric acid Lithium (molecular formula: BF4Li, CAS number: 14283-07-9), lithium bis(oxalatoborate) (molecular formula: LiB(C2O4)2, CAS number: 244761-29-3), lithium difluorooxalatoborate (molecular formula: C2BF2LiO4, CAS number: 409071-16-5); The materials that can be selected for lithium salts and the types and quantities of lithium salts in the polymer slurry can be adaptively adjusted according to actual conditions, and no specific restrictions are made here.

[0056] Optionally, the second photoinitiator is at least one of benzophenone, 2,2-dimethoxy-2-phenylacetophenone, ethyl 4-dimethylaminobenzoate, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methylpropiophenone, and methyl benzoylformate. The material of the second photoinitiator may be the same as or different from that of the first photoinitiator, which will not be described here; the type and quantity of the second photoinitiator in the polymer slurry may be adaptively adjusted according to actual conditions, and will not be specifically limited here.

[0057] Optionally, the mass ratio of the prepolymerized syrup to the second photoinitiator ranges from 20:1 to 500:1.

[0058] This embodiment explains that the prepolymer slurry and the second photoinitiator have a certain mass ratio to obtain the polymer slurry, and the mass ratio of the prepolymer slurry and the second photoinitiator can range from 20:1 to 500:1, such as the mass ratio of the prepolymer slurry and the second photoinitiator can be 20:1, 50:1, 100:1, 200:1 or 500:1, etc., so as to avoid the situation that the viscosity of the polymer slurry is too high and cannot be smoothly coated when the mass ratio of the prepolymer slurry and the second photoinitiator is too small, and the matrix monomer and the functional monomer cannot smoothly form a cross-linked structure when the mass ratio of the prepolymer slurry and the second photoinitiator is too large. Therefore, this embodiment sets the mass ratio of the prepolymer slurry and the second photoinitiator to a range of 20:1 to 500:1, which can avoid the situation that the matrix monomer and the functional monomer cannot smoothly form a cross-linked structure while ensuring the formation of a solid polymer slurry with a suitable viscosity.

[0059] Optionally, the nitrogen-containing functional monomer includes at least one of N,N'-methylenebisacrylamide, N-phenylmethacrylamide, N,N'-bis(acryloyl)cystamine, acrylamide, N-isopropylacrylamide, and N-vinylcaprolactam.

[0060] Specifically, N,N'-methylenebisacrylamide (molecular formula: C7H 10 N2O2, CAS No.: 110-26-9), N-phenylmethyl acrylamide (molecular formula: C 10 H 11 NO, CAS No.: 1611-83-2), N, N'-bis (acryloyl) cystamine (molecular formula: C 10 H 16 N2O2S2, CAS No.: 60984-57-8), acrylamide (molecular formula: C3H5NO, CAS No.: 79-06-1), N-isopropylacrylamide (molecular formula: C6H 11 NO, CAS No.: 2210-25-5), N-vinyl caprolactam (molecular formula: C8H 13 NO, CAS No.: 2235-00-9); the materials that can be selected for the nitrogen-containing functional monomers and the types and quantities of the nitrogen-containing functional monomers in the polymer slurry A can be adaptively adjusted according to actual conditions and are not specifically limited here.

[0061] Optionally, the mass ratio of the first polymer syrup to the nitrogen-containing functional monomer is in the range of 5:1 to 20:1.

[0062] This embodiment explains that the first polymer slurry and the nitrogen-containing functional monomer have a certain mass ratio to obtain polymer slurry A. The mass ratio of the first polymer slurry and the nitrogen-containing functional monomer can range from 5:1 to 20:1, such as the mass ratio of the first polymer slurry and the nitrogen-containing functional monomer can be 5:1, 6.25:1, 10:1, 12.5:1, 15:1 or 20:1, etc., so as to avoid the nitrogen-containing element interface formed when the mass ratio of the first polymer slurry and the nitrogen-containing functional monomer is too small and is not stable enough, and can also avoid the nitrogen-containing element interface cannot be formed when the mass ratio of the first polymer slurry and the nitrogen-containing functional monomer is too large. Therefore, this embodiment sets the mass ratio of the first polymer slurry and the nitrogen-containing functional monomer to a range of 5:1 to 20:1, which can avoid the nitrogen-containing element interface formed is not stable enough and avoid the problem of not being able to form the nitrogen-containing element interface.

[0063] Optionally, the fluorine-containing functional monomer includes at least one of hexafluoroisopropyl acrylate, hexafluorobutyl acrylate, hexafluorobutyl methacrylate, trifluoroethyl methacrylate, and dodecafluoroheptyl methacrylate.

[0064] Specifically, hexafluoroisopropyl acrylate (molecular formula: C6H3F7O2, CAS number: 74359-06-1), hexafluorobutyl acrylate (molecular formula: C7H6F6O2, CAS number: 54052-90-3), hexafluorobutyl methacrylate (molecular formula: C8H8F6O2, CAS number: 36405-47-7), trifluoroethyl methacrylate (molecular formula: C6H7F3O2, CAS number: 352-87-4), dodecafluoroheptyl methacrylate (molecular formula: C 11 H8F 12 O2, CAS number: 2261-99-6); the materials that can be selected for the fluorine-containing functional monomers and the types and quantities of the fluorine-containing functional monomers in the polymer slurry B can be adaptively adjusted according to actual conditions and are not specifically limited here.

[0065] Optionally, the mass ratio of the second polymer syrup to the fluorine-containing functional monomer is in the range of 5:1 to 20:1.

[0066] This embodiment explains that the second polymer slurry and the fluorine-containing functional monomer have a certain mass ratio to obtain polymer slurry B, and the mass ratio of the second polymer slurry and the fluorine-containing functional monomer can range from 5:1 to 20:1, such as the mass ratio of the second polymer slurry and the fluorine-containing functional monomer can be 5:1, 6.25:1, 10:1, 12.5:1, 15:1 or 20:1, etc., so as to avoid the interface of the fluorine-containing element formed when the mass ratio of the second polymer slurry and the fluorine-containing functional monomer is too small and is not stable enough, and can also avoid the interface of the fluorine-containing element cannot be formed when the mass ratio of the second polymer slurry and the fluorine-containing functional monomer is too large. Therefore, this embodiment sets the mass ratio of the second polymer slurry and the fluorine-containing functional monomer to a range of 5:1 to 20:1, which can avoid the problem that the interface of the fluorine-containing element formed is not stable enough and cannot form the interface of the fluorine-containing element.

[0067] S3: Provide a base film, the base film comprising a first surface and a second surface arranged opposite to each other, pour polymer slurry A on the first surface, and perform continuous roll-to-roll scraper coating and UV-curing molding treatment on polymer slurry A, pour polymer slurry B on the second surface, and perform continuous roll-to-roll scraper coating and UV-curing molding treatment on polymer slurry B to obtain a step-polymerized dual-reinforced interfacial solid polymer electrolyte.

[0068] Specifically, continue to refer to Figure 1As shown, the base film can be selected from polypropylene, which is commonly known as PP plastic, and has good chemical resistance, heat resistance, electrical insulation, high-strength mechanical properties and high wear-resistant processing properties; the base film is a thin film structure, including a first surface and a second surface that are relatively arranged. In this embodiment, the first surface can correspond to polymer slurry A, and the second surface can correspond to polymer slurry B. In other embodiments, the first surface can correspond to polymer slurry B, and the second surface can correspond to polymer slurry A, which is not limited here; by pouring polymer slurry A on the first surface, the polymer slurry A is continuously roll-to-roll scraper coated and UV-cured. Molding treatment, pouring polymer slurry B on the second surface, performing continuous roll-to-roll blade coating and UV-curing molding treatment on polymer slurry B, to obtain a step-polymerized dual-reinforced interface solid polymer electrolyte, roll-to-roll blade coating can ensure that polymer slurry A is evenly applied to the first surface of the base film, and at the same time ensure that polymer slurry B is evenly applied to the second surface of the base film, and UV-curing molding treatment ensures that both polymer slurry A and polymer slurry B are converted from liquid to solid, thereby obtaining a solid polymer electrolyte; wherein, continuous roll-to-roll blade coating and UV-curing molding treatment are both existing technologies in the field and will not be repeated here.

[0069] It should also be noted that, in this embodiment, by coating polymer electrolytes of different properties on the first and second surfaces of the base film respectively (the first and second surfaces can also be understood as the positive electrode side and the negative electrode side), the solid polymer electrolyte containing nitrogen elements can construct a CEI (positive electrode-electrolyte interface) layer rich in high-strength oxidation-stable nitration groups on the positive electrode side, and the polymer electrolyte containing fluorine elements can construct a stable SEI (electrolyte intermediate interface) layer rich in lithium fluoride (chemical formula: LiF) beneficial inorganic components on the negative electrode side. The synergistic effect of fluorine and nitrogen element modifications achieves a double enhancement effect on the positive electrode side interface and the negative electrode side interface.

[0070] Optionally, in the UV curing molding process, the wavelength range of the UV light is 220 nm to 400 nm, and the irradiation time is 1 min to 10 min.

[0071] This embodiment explains that the ultraviolet light has a certain wavelength to convert the polymer slurry A and the polymer slurry B from liquid to solid, and the wavelength range of the ultraviolet light can be 220nm to 400nm, such as the wavelength of the ultraviolet light can be 220nm, 250nm, 280nm, 300nm, 320nm, 345nm, 365nm, 380nm or 400nm, etc., so as to avoid the inability to convert the liquid polymer slurry A and the polymer slurry B into a solid state when the wavelength of the ultraviolet light is too short, and to avoid the destruction of the structure of the formed solid electrolyte when the wavelength of the ultraviolet light is too long. Therefore, this embodiment sets the wavelength range of the ultraviolet light to 220nm to 400nm, which can avoid the inability to convert the liquid polymer slurry A and the polymer slurry B into a solid state while avoiding the destruction of the structure of the solid electrolyte.

[0072] This embodiment explains that the ultraviolet light has a certain irradiation time to convert the polymer slurry A and the polymer slurry B from liquid to solid, and the irradiation time of the ultraviolet light can be 1min to 10min, such as the irradiation time of the ultraviolet light can be 1min, 2min, 3min, 5min, 8min or 10min, so as to avoid the inability to convert the liquid polymer slurry A and the polymer slurry B into a solid state when the irradiation time of the ultraviolet light is too short, and it can also avoid the destruction of the structure of the formed solid electrolyte when the irradiation time of the ultraviolet light is too long. Therefore, this embodiment sets the irradiation time of the ultraviolet light to 1min to 10min, which can avoid the inability to convert the liquid polymer slurry A and the polymer slurry B into a solid state while avoiding the destruction of the structure of the solid electrolyte.

[0073] Embodiment 1:

[0074] The first step: providing 100 g of polyethylene glycol diacrylate (matrix monomer) and 0.03 g of 2-hydroxy-2-methylpropiophenone (first photoinitiator), adding polyethylene glycol diacrylate and 2-hydroxy-2-methylpropiophenone into a reaction kettle, stirring in a nitrogen atmosphere, and mixing evenly to obtain a mixed slurry of Example 1, irradiating the mixed slurry with ultraviolet light having a wavelength of 365 nm to obtain a pre-polymerized slurry of Example 1 having a viscosity of about 2000 cP;

[0075] Step 2: Add 20g of lithium bis(trifluoromethanesulfonyl)imide (lithium salt) and 1g of 2-hydroxy-2-methylpropiophenone (second photoinitiator) into the prepolymer slurry of Example 1, mix them evenly to obtain the polymer slurry of Example 1, divide the polymer slurry of Example 1 into the first polymer slurry of Example 1 and the second polymer slurry of Example 1, place them in two reaction kettles respectively, add 5g of N,N'-methylenebisacrylamide (nitrogen-containing functional monomer) to the first polymer slurry of Example 1 to obtain polymer slurry A of Example 1, add 5g of hexafluoroisopropyl acrylate (fluorine-containing functional monomer) to the second polymer slurry of Example 1 to obtain polymer slurry B of Example 1;

[0076] The third step: providing a PP base film, the PP base film comprising a first surface and a second surface arranged opposite to each other, firstly, pouring the polymer slurry A of Example 1 on the first surface, and subjecting the polymer slurry A of Example 1 to continuous roll-to-roll blade coating, and controlling the film thickness of the polymer slurry A of Example 1 to 25 μm, and secondly, subjecting the first surface to ultraviolet light curing molding treatment with ultraviolet light having a wavelength of 365 nm, and then pouring the polymer slurry B of Example 1 on the second surface, and subjecting the polymer slurry B of Example 1 to continuous roll-to-roll blade coating treatment, and controlling the film thickness of the polymer slurry B of Example 1 to 25 μm, and then subjecting the second surface to ultraviolet light curing molding treatment with ultraviolet light having a wavelength of 365 nm, to obtain the polymer electrolyte membrane of Example 1, wherein the substances on the first and second surfaces of the polymer electrolyte membrane are step-polymerized dual-reinforced interfacial solid polymer electrolytes.

[0077] Embodiment 2:

[0078] The first step: providing 100 g of polyethylene glycol diacrylate (matrix monomer) and 0.03 g of 2-hydroxy-2-methylpropiophenone (first photoinitiator), adding polyethylene glycol diacrylate and 2-hydroxy-2-methylpropiophenone into a reaction kettle, stirring in a nitrogen atmosphere, mixing evenly to obtain a mixed slurry of Example 2, irradiating the mixed slurry with ultraviolet light having a wavelength of 365 nm, and obtaining a pre-polymerized slurry of Example 2 having a viscosity of about 2000 cP;

[0079] Step 2: Add 20g of lithium bis(trifluoromethanesulfonyl)imide (lithium salt) and 1g of 1-hydroxycyclohexyl phenone (second photoinitiator) into the prepolymer slurry of Example 2, mix them evenly to obtain the polymer slurry of Example 2, divide the polymer slurry of Example 2 into the first polymer slurry of Example 2 and the second polymer slurry of Example 2, place them in two reaction kettles respectively, add 10g of N,N'-methylenebisacrylamide (nitrogen-containing functional monomer) to the first polymer slurry of Example 2 to obtain polymer slurry A of Example 2, add 10g of hexafluoroisopropyl acrylate (fluorine-containing functional monomer) to the second polymer slurry of Example 2 to obtain polymer slurry B of Example 2;

[0080] The third step: providing a PP base film, the PP base film comprising a first surface and a second surface arranged opposite to each other, firstly, pouring the polymer slurry A of Example 2 on the first surface, and subjecting the polymer slurry A of Example 2 to continuous roll-to-roll blade coating, and controlling the film thickness of the polymer slurry A of Example 2 to 25 μm, and secondly, subjecting the first surface to ultraviolet light curing molding treatment with ultraviolet light having a wavelength of 365 nm, and then pouring the polymer slurry B of Example 2 on the second surface, and subjecting the polymer slurry B of Example 2 to continuous roll-to-roll blade coating treatment, and controlling the film thickness of the polymer slurry B of Example 2 to 25 μm, and then subjecting the second surface to ultraviolet light curing molding treatment with ultraviolet light having a wavelength of 365 nm, to obtain the polymer electrolyte membrane of Example 2, wherein the substances on the first and second surfaces of the polymer electrolyte membrane are step-polymerized dual-reinforced interfacial solid polymer electrolytes.

[0081] Compared with Example 1, Example 2 increases the mass of nitrogen-containing functional monomers and fluorine-containing functional monomers.

[0082] Embodiment 3:

[0083] The first step: providing 100 g of polyethylene glycol diacrylate (matrix monomer) and 0.03 g of 1-hydroxycyclohexyl phenone (first photoinitiator), adding polyethylene glycol diacrylate and 1-hydroxycyclohexyl phenone into a reaction kettle, stirring in a nitrogen atmosphere, and mixing evenly to obtain a mixed slurry of Example 3, irradiating the mixed slurry with ultraviolet light having a wavelength of 365 nm to obtain a pre-polymerized slurry of Example 3 having a viscosity of about 2000 cP;

[0084] Step 2: Add 20g of lithium bis(trifluoromethanesulfonyl)imide (lithium salt) and 1g of 1-hydroxycyclohexyl phenone (second photoinitiator) into the prepolymer slurry of Example 3, mix them evenly to obtain the polymer slurry of Example 3, divide the polymer slurry of Example 3 into the first polymer slurry of Example 3 and the second polymer slurry of Example 3, place them in two reaction kettles respectively, add 5g of N,N'-methylenebisacrylamide (nitrogen-containing functional monomer) to the first polymer slurry of Example 3 to obtain polymer slurry A of Example 3, add 5g of hexafluoroisopropyl acrylate (fluorine-containing functional monomer) to the second polymer slurry of Example 3 to obtain polymer slurry B of Example 3;

[0085] The third step: providing a PP base film, the PP base film comprising a first surface and a second surface arranged opposite to each other, firstly, pouring the polymer slurry A of Example 3 on the first surface, and performing continuous roll-to-roll blade coating on the polymer slurry A of Example 3 to control the film thickness of the polymer slurry A of Example 3 to be 25 μm, secondly, performing UV curing molding treatment on the first surface with UV light having a wavelength of 365 nm, then pouring the polymer slurry B of Example 3 on the second surface, and performing continuous roll-to-roll blade coating treatment on the polymer slurry B of Example 3 to control the film thickness of the polymer slurry B of Example 3 to be 25 μm, and then performing UV curing molding treatment on the second surface with UV light having a wavelength of 365 nm to obtain the polymer electrolyte membrane of Example 3, wherein the substances on the first and second surfaces of the polymer electrolyte membrane are step-polymerized dual-reinforced interfacial solid polymer electrolytes.

[0086] Compared with Example 1, Example 3 changes the materials of the first photoinitiator and the second photoinitiator.

[0087] Embodiment 4:

[0088] The first step: providing 100 g of polyethylene glycol diacrylate (matrix monomer) and 0.03 g of 2-hydroxy-2-methylpropiophenone (first photoinitiator), adding polyethylene glycol diacrylate and 2-hydroxy-2-methylpropiophenone into a reaction kettle, stirring in a nitrogen atmosphere, and mixing evenly to obtain a mixed slurry of Example 4, irradiating the mixed slurry with ultraviolet light having a wavelength of 365 nm to obtain a pre-polymerized slurry of Example 4 having a viscosity of about 2000 cP;

[0089] Step 2: Add 20 g of lithium bis(trifluoromethanesulfonyl)imide (lithium salt) and 2 g of 2-hydroxy-2-methylpropiophenone (second photoinitiator) into the prepolymer slurry of Example 4, mix them evenly to obtain the polymer slurry of Example 4, divide the polymer slurry of Example 4 into the first polymer slurry of Example 4 and the second polymer slurry of Example 4, place them in two reaction kettles respectively, add 5 g of N,N'-methylenebisacrylamide (nitrogen-containing functional monomer) to the first polymer slurry of Example 4 to obtain polymer slurry A of Example 4, add 5 g of hexafluoroisopropyl acrylate (fluorine-containing functional monomer) to the second polymer slurry of Example 4 to obtain polymer slurry B of Example 4;

[0090] The third step: providing a PP base film, the PP base film comprising a first surface and a second surface arranged opposite to each other, firstly, pouring the polymer slurry A of Example 4 on the first surface, and performing continuous roll-to-roll blade coating on the polymer slurry A of Example 4 to control the film thickness of the polymer slurry A of Example 4 to be 25 μm, secondly, performing UV curing molding treatment on the first surface with UV light having a wavelength of 365 nm, then pouring the polymer slurry B of Example 4 on the second surface, and performing continuous roll-to-roll blade coating treatment on the polymer slurry B of Example 4 to control the film thickness of the polymer slurry B of Example 4 to be 25 μm, and then performing UV curing molding treatment on the second surface with UV light having a wavelength of 365 nm to obtain the polymer electrolyte membrane of Example 4, wherein the substances on the first and second surfaces of the polymer electrolyte membrane are step-polymerized dual-reinforced interfacial solid polymer electrolytes.

[0091] Compared with Example 1, Example 4 increases the mass of the second photoinitiator.

[0092] Embodiment 5:

[0093] The first step: providing 100 g of polyethylene glycol diacrylate (matrix monomer) and 0.03 g of 2-hydroxy-2-methylpropiophenone (first photoinitiator), adding polyethylene glycol diacrylate and 2-hydroxy-2-methylpropiophenone into a reaction kettle, stirring in a nitrogen atmosphere, and mixing evenly to obtain a mixed slurry of Example 5, irradiating the mixed slurry with ultraviolet light having a wavelength of 365 nm to obtain a pre-polymerized slurry of Example 5 having a viscosity of about 2000 cP;

[0094] Step 2: Add 20 g of lithium bis(trifluoromethanesulfonyl)imide (lithium salt) and 2 g of 2-hydroxy-2-methylpropiophenone (second photoinitiator) into the prepolymer slurry of Example 5, mix them evenly to obtain the polymer slurry of Example 5, divide the polymer slurry of Example 5 into the first polymer slurry of Example 5 and the second polymer slurry of Example 5, place them in two reaction kettles respectively, add 5 g of N,N'-methylenebisacrylamide (nitrogen-containing functional monomer) to the first polymer slurry of Example 5 to obtain polymer slurry A of Example 5, add 5 g of dodecafluoroheptyl methacrylate (fluorine-containing functional monomer) to the second polymer slurry of Example 5 to obtain polymer slurry B of Example 5;

[0095] The third step: providing a PP base film, the PP base film comprising a first surface and a second surface arranged opposite to each other, firstly, pouring the polymer slurry A of Example 5 on the first surface, and subjecting the polymer slurry A of Example 5 to continuous roll-to-roll blade coating, and controlling the film thickness of the polymer slurry A of Example 5 to 25 μm, and secondly, subjecting the first surface to ultraviolet light curing molding treatment with ultraviolet light having a wavelength of 365 nm, and then pouring the polymer slurry B of Example 5 on the second surface, and subjecting the polymer slurry B of Example 5 to continuous roll-to-roll blade coating treatment, and controlling the film thickness of the polymer slurry B of Example 5 to 25 μm, and then subjecting the second surface to ultraviolet light curing molding treatment with ultraviolet light having a wavelength of 365 nm, to obtain the polymer electrolyte membrane of Example 5, wherein the substances on the first and second surfaces of the polymer electrolyte membrane are step-polymerized dual-reinforced interfacial solid polymer electrolytes.

[0096] Compared with Example 1, Example 5 increases the mass of the second photoinitiator and changes the material of the fluorine-containing functional monomer.

[0097] Embodiment 6:

[0098] The first step: providing 100 g of vinyl acetate (matrix monomer) and 0.03 g of 2-hydroxy-2-methylpropiophenone (first photoinitiator), adding vinyl acetate and 2-hydroxy-2-methylpropiophenone into a reaction kettle, stirring in a nitrogen atmosphere, and mixing evenly to obtain a mixed slurry of Example 6, and irradiating the mixed slurry with ultraviolet light having a wavelength of 365 nm to obtain a prepolymerized slurry of Example 6 having a viscosity of about 2000 cP;

[0099] Step 2: Add 20 g of lithium bistrifluoromethanesulfonyl imide (lithium salt) and 2 g of 2-hydroxy-2-methylpropiophenone (second photoinitiator) to the prepolymer slurry of Example 6, mix them evenly to obtain the polymer slurry of Example 6, divide the polymer slurry of Example 6 into the first polymer slurry of Example 6 and the second polymer slurry of Example 6, and place them in two reaction kettles respectively, add 5 g of N, N'-methylenebisacrylamide (nitrogen-containing functional monomer) to the first polymer slurry of Example 6 to obtain polymer slurry A of Example 6, and add 5 g of dodecafluoroheptyl methacrylate (fluorine-containing functional monomer) to the second polymer slurry of Example 6 to obtain polymer slurry B of Example 6;

[0100] The third step: providing a PP base film, the PP base film comprising a first surface and a second surface arranged opposite to each other, firstly, pouring the polymer slurry A of Example 6 on the first surface, and subjecting the polymer slurry A of Example 6 to continuous roll-to-roll blade coating, and controlling the film thickness of the polymer slurry A of Example 6 to 25 μm, and secondly, subjecting the first surface to ultraviolet light curing molding treatment with ultraviolet light having a wavelength of 365 nm, and then pouring the polymer slurry B of Example 6 on the second surface, and subjecting the polymer slurry B of Example 6 to continuous roll-to-roll blade coating treatment, and controlling the film thickness of the polymer slurry B of Example 6 to 25 μm, and then subjecting the second surface to ultraviolet light curing molding treatment with ultraviolet light having a wavelength of 365 nm, to obtain the polymer electrolyte membrane of Example 6, wherein the substances on the first and second surfaces of the polymer electrolyte membrane are step-polymerized dual-reinforced interfacial solid polymer electrolytes.

[0101] Compared with Example 1, Example 6 changes the materials of the base monomer and the fluorine-containing functional monomer, and increases the mass of the second photoinitiator.

[0102] Comparative Example 1:

[0103] The first step: providing 100 g of polyethylene glycol diacrylate (matrix monomer) and 0.03 g of 2-hydroxy-2-methylpropiophenone (first photoinitiator), adding polyethylene glycol diacrylate and 2-hydroxy-2-methylpropiophenone into a reaction kettle, stirring in a nitrogen atmosphere, mixing evenly to obtain a mixed slurry of Comparative Example 1, irradiating the mixed slurry with ultraviolet light having a wavelength of 365 nm, and obtaining a pre-polymerized slurry of Comparative Example 1 having a viscosity of about 2000 cP;

[0104] Step 2: Add 20 g of lithium bis(trifluoromethanesulfonyl)imide (lithium salt) and 1 g of 2-hydroxy-2-methylpropiophenone (second photoinitiator) into the prepolymer slurry of Comparative Example 1, and mix them evenly to obtain the polymer slurry of Comparative Example 1;

[0105] The third step: providing a PP base film, the PP base film includes a first surface and a second surface arranged opposite to each other, directly pouring the polymer slurry of comparative example 1 on the first surface and the second surface, performing continuous roll-to-roll doctor blade coating treatment on the polymer slurry of comparative example 1, controlling the film thickness of the polymer slurry of comparative example 1 to be 25 μm, and performing UV curing molding treatment on the first surface and the second surface simultaneously with UV light having a wavelength of 365 nm to obtain a polymer electrolyte membrane of comparative example 1, wherein the material on the first surface and the second surface of the polymer electrolyte membrane is a step-polymerized solid polymer electrolyte without functional monomers.

[0106] Compared with Example 1, Comparative Example 1 does not adopt a step-by-step method to prepare the solid polymer electrolyte, and does not add nitrogen-containing functional monomers and fluorine-containing functional monomers to the matrix monomer.

[0107] Comparative Example 2:

[0108] The first step: providing 100 g of polyethylene glycol diacrylate (matrix monomer) and 0.03 g of 2-hydroxy-2-methylpropiophenone (first photoinitiator), adding polyethylene glycol diacrylate and 2-hydroxy-2-methylpropiophenone into a reaction kettle, stirring in a nitrogen atmosphere, mixing evenly to obtain a mixed slurry of comparative example 2, irradiating the mixed slurry with ultraviolet light having a wavelength of 365 nm, and obtaining a pre-polymerized slurry of comparative example 2 having a viscosity of about 2000 cP;

[0109] Step 2: Add 20g of lithium bis(trifluoromethanesulfonyl)imide (lithium salt) and 1g of 2-hydroxy-2-methylpropiophenone (second photoinitiator) to the prepolymer slurry of Comparative Example 2, mix them evenly, then add 10g of hexafluoroisopropyl acrylate (fluorine-containing functional monomer), mix them evenly to obtain the polymer slurry of Comparative Example 2;

[0110] The third step: providing a PP base film, the PP base film includes a first surface and a second surface arranged opposite to each other, directly pouring the polymer slurry of comparative example 2 on the first surface and the second surface, performing continuous roll-to-roll scraper coating treatment on the polymer slurry of comparative example 2, controlling the film thickness of the polymer slurry of comparative example 2 to be 25 μm, and performing UV curing molding treatment on the first surface and the second surface simultaneously with UV light having a wavelength of 365 nm to obtain a polymer electrolyte membrane of comparative example 2, wherein the material on the first surface and the second surface of the polymer electrolyte membrane is a single-reinforced polymer solid polymer electrolyte.

[0111] Compared with Example 1, Comparative Example 2 increases the mass of fluorine-containing functional monomers, does not adopt a step-by-step method to prepare the solid polymer electrolyte, and does not add nitrogen-containing functional monomers to the matrix monomers.

[0112] After obtaining the polymer electrolyte membranes of Examples 1 to 6 and Comparative Examples 1 to 2, respectively, the polymer electrolyte membranes, the positive electrode sheets, and the negative electrode sheets are assembled into a solid-state lithium metal battery. The assembly process of the solid-state lithium metal battery is as follows:

[0113] Step 1: Disperse the positive electrode material, binder and conductive agent in a solvent, mix them evenly to obtain positive electrode slurry, apply the positive electrode slurry on both sides of the current collector, vacuum dry it and then die-cut it to obtain positive electrode sheets of a certain size.

[0114] It should be noted that the positive electrode material can be selected from lithium nickel cobalt manganese oxide, referred to as NCM811, which is a high-nickel ternary material. The lithium metal battery prepared from this material is a high-nickel ternary system lithium metal battery. NCM811 is a single crystal structure with the advantages of high gram capacity, high initial efficiency, high energy density, stable structure, high temperature and good cycle performance; the binder can be selected from polyvinylidene fluoride, referred to as PVDF, which is a highly non-reactive thermoplastic fluoropolymer with the advantages of anti-aging, chemical resistance, weather resistance, and ultraviolet radiation resistance; the conductive agent can be selected from carbon black, referred to as SP, which has the advantages of small particle size, large specific surface area and roughness, high structure, and clean surface; the solvent can be selected from N-methylpyrrolidone (chemical formula: C5H9NO), which has the advantages of being able to dissolve most organic and inorganic compounds, polar gases, natural and synthetic polymer compounds, and being miscible with water.

[0115] Step 2: Die-cut the lithium-copper composite tape to obtain a lithium metal negative electrode sheet of a certain size.

[0116] Step 3: According to the requirements of the test items, the positive electrode plate, the polymer electrolyte membrane, and the negative electrode plate are respectively assembled into 2032-type button batteries or soft-pack batteries encapsulated with aluminum-plastic film, wherein the polymer electrolyte membrane is the polymer electrolyte membrane in Examples 1 to 6 and Comparative Examples 1 to 2.

[0117] Various performance tests were performed on the batteries assembled from the polymer electrolyte membranes of the above-mentioned Examples 1 to 6 and Comparative Examples 1 to 2. The ion conductivity of the 2032-type button batteries assembled using stainless steel sheets as blocking electrodes was tested. This test is a prior art in the field and will not be described in detail here. The test results are shown in Table 1.

[0118] Table 1: Comparison of ionic conductivity of different polymer electrolytes

[0119] <![CDATA[Ionic conductivity (mScm -1 , 25 °C)]]> <![CDATA[Ionic conductivity (mScm -1 , 25 °C)]]> Example 1 1.76 Example 5 0.93 Example 2 0.78 Example 6 0.89 Example 3 1.03 Comparative Example 1 0.21 Example 4 1.21 Comparative Example 2 0.57

[0120] From the comparison results in Table 1, it can be seen that the ionic conductivity in Examples 1 to 6 is significantly improved compared to that in Comparative Examples 1 to 2, and Example 1 has the highest ionic conductivity. Functional monomers are added in Examples 1 to 6, and the functional monomers are cross-linked with the matrix monomers to form a three-dimensional network structure that can promote rapid lithium ion transmission. The amide groups in the polymer and the anions in the electrolyte component have a bonding effect, which can fix the anions and promote the dissociation of lithium salts, thereby improving the lithium ion transmission efficiency. Therefore, the step-by-step polymerization double-enhanced interface solid polymer electrolytes in Examples 1 to 6 can exhibit higher ionic conductivity than the step-by-step polymerization solid polymer electrolytes without functional monomers (Example 1) and the single-enhanced solid polymer electrolytes (Comparative Example 2).

[0121] Next, an electrochemical cycle test (0.5C) was performed on the 2Ah soft-pack battery assembled from the polymer electrolyte membranes of Examples 1 to 6 and Comparative Examples 1 to 2 at 25°C. This test is a prior art in the art and will not be described in detail here. The test results are shown in Table 2.

[0122] Table 2: Comparison of cycle performance of solid-state lithium metal soft-pack batteries

[0123] First-cycle Coulomb efficiency Capacity retention rate after 100 cycles Example 1 89.76％ 95.86％ Example 2 88.25％ 85.71％ Example 3 89.36％ 90.56％ Example 4 90.77％ 91.44％ Example 5 87.54％ 88.04％ Example 6 85.12％ 83.28％ Comparative Example 1 84.89％ 52.62％ Comparative Example 2 87.67％ 78.34％

[0124] It should be noted that:

[0125] (1) The first-cycle coulomb efficiency refers to the ratio of the discharge capacity to the charge capacity during the first charge and discharge process of the battery. The higher the first-cycle coulomb efficiency, the better the battery performance.

[0126] (2) Capacity retention rate refers to the ability of a battery to maintain its capacity relative to its initial capacity after multiple charge and discharge cycles. The 100-cycle capacity retention rate can be understood as the ability of a battery to maintain its capacity relative to its initial capacity after 100 charge and discharge cycles. The higher the capacity retention rate, the better the battery performance.

[0127] (3) The cycling performance of a battery is measured mainly by three indicators: number of cycles, first discharge capacity and retention capacity; the number of cycles refers to the number of complete cycles that a battery can undergo for charging and discharging; the first discharge capacity is the maximum amount of electricity that a battery can release in the first charge-discharge test; the retention capacity refers to the discharge capacity that a battery can maintain after completing a certain number of charge-discharge cycles; the greater the first-cycle coulomb efficiency and the capacity retention rate after 100 cycles, the better the cycling performance of the battery.

[0128] From the comparison results in Table 2, it can be seen that Example 1 has the most ideal long cycle performance. By comparing the first cycle coulomb efficiency and the capacity retention rate after 100 cycles in Example 1-Example 6 and Comparative Example 1-Comparative Example 2, it is explained that the nitrogen element and the fluorine element in the step-by-step polymerization dual-enhanced interface solid polymer electrolyte can construct a stable CEI (positive electrode-electrolyte interface) / SEI (electrolyte intermediate interface) layer at the positive electrode and the negative electrode, respectively. The nitration group on the positive electrode side can effectively improve the oxidation resistance of the electrode and reduce the tendency of the polymer electrolyte to decompose under high pressure. The fluorine-containing polymer provides rich lithium fluoride (chemical formula: LiF) for the negative electrode interface, which can form a dense and stable SEI layer and inhibit the growth of lithium dendrites. The dual enhancement of the positive electrode interface and the negative electrode interface enables the battery to exert a longer and more stable electrochemical cycle.

[0129] It can be seen from the above embodiments that the method for preparing the step-by-step polymerization dual-reinforced interface solid polymer electrolyte provided by the present invention achieves at least the following beneficial effects:

[0130] First, a solid polymer electrolyte is prepared by a step-by-step polymerization method. First, a part of the matrix monomer is polymerized as a prepolymer slurry, and the long-chain molecular weight structure of the matrix polymer can be adjusted. The viscosity of the subsequent polymerization slurry is suitable and controllable, and it can be evenly coated on the base film to maintain sufficient liquid hanging, and can be continuously coated to ensure that the subsequently formed solid polymer electrolyte has good contact with the electrode, which reduces the process difficulty of manufacturing the solid polymer electrolyte and is conducive to large-scale industrial promotion and production. Functional monomers and lithium salts are added to the prepolymer slurry, and then cross-linking polymerization is carried out, which is conducive to sufficient and uniform mixing between the components and the structure of the generated polymer can be controlled. During the polymerization process, the matrix monomer and the functional monomer can form a stable cross-linked structure, which is conducive to enhancing the structural stability and ion transport performance, and promoting the improvement of the high-voltage stability of the solid polymer electrolyte, so that the battery prepared by the solid polymer electrolyte has good mechanical stability and can overcome the problems of life attenuation caused by the growth of lithium dendrites.

[0131] Secondly, by coating polymer electrolytes of different properties on the first and second surfaces of the base film respectively (the first and second surfaces can also be understood as the positive electrode side and the negative electrode side), the solid polymer electrolyte containing nitrogen elements can construct a CEI (positive electrode-electrolyte interface) layer rich in high-strength oxidation-stable nitration groups on the positive electrode side, and the polymer electrolyte containing fluorine elements can construct a stable SEI (electrolyte intermediate interface) layer rich in lithium fluoride (chemical formula: LiF) beneficial inorganic components on the negative electrode side. The synergistic effect of fluorine and nitrogen element modifications achieves the effect of dual enhancement of the positive electrode side interface and the negative electrode side interface at the same time.

[0132] Thirdly, the solid polymer electrolyte prepared by the step-by-step polymerization double-enhanced interface solid polymer electrolyte preparation method has high ionic conductivity and high mechanical stability. The solid-state lithium metal battery prepared by the solid polymer electrolyte has improved interface performance compared with the solid-state lithium metal battery in the prior art.

[0133] Although some specific embodiments of the present invention have been described in detail by way of example, it will be appreciated by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present invention. It will be appreciated by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A method for preparing a step-by-step polymerization double-enhanced interface solid polymer electrolyte, characterized in that: The following steps are involved: Providing a matrix monomer and a first photoinitiator, uniformly mixing the matrix monomer and the first photoinitiator to obtain a mixed slurry, and irradiating the mixed slurry with ultraviolet light to obtain a prepolymerized slurry; Adding lithium salt and a second photoinitiator into the prepolymer slurry, uniformly mixing to obtain a polymer slurry, dividing the polymer slurry into a first polymer slurry and a second polymer slurry, adding a nitrogen-containing functional monomer to the first polymer slurry to obtain a polymer slurry A, and adding a fluorine-containing functional monomer to the second polymer slurry to obtain a polymer slurry B; A base film is provided, wherein the base film comprises a first surface and a second surface arranged opposite to each other, the polymer slurry A is poured on the first surface, and the polymer slurry A is subjected to continuous roll-to-roll blade coating and ultraviolet light curing molding treatment, the polymer slurry B is poured on the second surface, and the polymer slurry B is subjected to continuous roll-to-roll blade coating and ultraviolet light curing molding treatment, so as to obtain a step-polymerized dual-reinforced interfacial solid polymer electrolyte.

2. The method for preparing a step-by-step polymerization double-enhanced interface solid polymer electrolyte according to claim 1, characterized in that: The mass ratio of the matrix monomer to the first photoinitiator ranges from 100:1 to 5000:1; the mass ratio of the prepolymer syrup to the second photoinitiator ranges from 20:1 to 500:

1.

3. The method for preparing a step-by-step polymerization double-enhanced interface solid polymer electrolyte according to claim 1, characterized in that: The mass ratio of the first polymer syrup to the nitrogen-containing functional monomer is in the range of 5:1 to 20:1; the mass ratio of the second polymer syrup to the fluorine-containing functional monomer is in the range of 5:1 to 20:

1.

4. The method for preparing a step-by-step polymerization double-enhanced interface solid polymer electrolyte according to claim 1, characterized in that: When the ultraviolet light is irradiated on the mixed slurry, the wavelength range of the ultraviolet light is 220nm to 400nm, and the irradiation time is 0.2min to 2min; in the ultraviolet light curing molding process, the wavelength range of the ultraviolet light is 220nm to 400nm, and the irradiation time is 1 to 10min.

5. The method for preparing a step-by-step polymerization double-enhanced interface solid polymer electrolyte according to claim 1, characterized in that: The base monomer and the first photoinitiator are uniformly mixed in a nitrogen atmosphere.

6. The method for preparing a step-by-step polymerization double-enhanced interface solid polymer electrolyte according to claim 1, characterized in that: The viscosity of the prepolymerization slurry ranges from 500 cP to 3500 cP.

7. The method for preparing a step-by-step polymerization double-enhanced interface solid polymer electrolyte according to claim 1, characterized in that: The matrix monomer includes at least one of polyethylene glycol diacrylate, polyethylene glycol methyl ether methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl acrylate, hydroxypropyl methacrylate, and vinyl acetate; The first photoinitiator is at least one of benzophenone, 2,2-dimethoxy-2-phenylacetophenone, ethyl 4-dimethylaminobenzoate, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methylpropiophenone, and methyl benzoylformate; The second photoinitiator is at least one of benzophenone, 2,2-dimethoxy-2-phenylacetophenone, ethyl 4-dimethylaminobenzoate, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methylpropiophenone, and methyl benzoylformate.

8. The method for preparing a step-by-step polymerization double-enhanced interface solid polymer electrolyte according to claim 1, characterized in that: The lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalatoborate), and lithium difluorooxalatoborate.

9. The method for preparing a step-by-step polymerization double-enhanced interface solid polymer electrolyte according to claim 1, characterized in that: The nitrogen-containing functional monomer includes at least one of N,N'-methylenebisacrylamide, N-phenylmethacrylamide, N,N'-bis(acryloyl)cystamine, acrylamide, N-isopropylacrylamide and N-vinylcaprolactam.

10. The method for preparing a step-by-step polymerization double-reinforced interface solid polymer electrolyte according to any one of claims 1 to 9, characterized in that: The fluorine-containing functional monomer includes at least one of hexafluoroisopropyl acrylate, hexafluorobutyl acrylate, hexafluorobutyl methacrylate, trifluoroethyl methacrylate, and dodecafluoroheptyl methacrylate.

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