Preparation method for dual-enhanced interface solid polymer electrolyte by means of step-by-step polymerization

Abstract

A preparation method for a dual-enhanced interface solid polymer electrolyte by means of step-by-step polymerization, the preparation method comprising: mixing a matrix monomer and a first photoinitiator to obtain a mixed slurry, and illuminating same to obtain a pre-polymerized slurry; adding a lithium salt and a second photoinitiator to the pre-polymerized slurry, mixing same 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; and pouring the polymer slurry A on a first face of a base membrane, performing a treatment on same, pouring the polymer slurry B on a second face of the base membrane, and performing a treatment on same, so as to obtain a stepwise-polymerized dual-enhanced interface solid polymer electrolyte. The solid polymer electrolyte is prepared by means of using a step-by-step polymerization method, thereby optimizing a positive electrode side interface and a negative electrode side interface, and realizing continuous large-scale production of a solid polymer electrolyte.

Description

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

[0001] The present application relates to the technical field of new energy battery, more particularly, to a preparation method of step-by-step polymerization double-enhanced interface solid-state polymer electrolyte. BACKGROUND

[0002] The rapid development of electric vehicles, electric aircraft, energy storage systems and other fields puts higher and higher requirements on the energy density and safety performance of secondary batteries. At present, commercial liquid lithium-ion batteries have reached the performance upper limit and are facing a bottleneck. Therefore, solid-state lithium metal batteries are considered as the next generation of energy storage devices with great potential.

[0003] A solid-state lithium metal battery is composed of a positive current collector, a positive active material, a solid-state electrolyte, a negative active material and a negative current collector. The solid-state electrolyte includes a polymer electrolyte, which has good processability, flexibility and compatibility and plays an important role in the research of solid-state electrolyte. However, the interface problem in the solid-state lithium metal battery cannot be ignored, which limits its popularization in practical application.

[0004] Due to the high activity of lithium metal, the growth of a large amount of lithium dendrites and the generation of dead lithium during battery cycling challenge the mechanical stability of the polymer electrolyte. Meanwhile, the contact problem of solid / solid interface leads to high interface impedance, which affects the efficiency of ion transmission and limits the performance of battery capacity. The mechanical properties and high-pressure stability of conventional solid-state polymer electrolyte are poor, which will limit the long-term operation of high-nickel ternary lithium metal batteries. In addition, the existing interface optimization strategy can only optimize the negative electrode or the positive electrode on one side, or cause the increase of interface impedance when constructing a stable SEI (Solid-Electrolyte Interphase) / CEI (Chemical-Electrochemical Interface) layer, which affects the ion transmission effect. There is a lack of comprehensive interface improvement. In addition, the conventional ultraviolet polymer electrolyte process is one-step polymerization, and the precursor has low viscosity and is not easy to hang liquid on the substrate. Therefore, it is often only small-scale in-situ pouring or non-in-situ pouring to form a mold, which cannot realize continuous production. SUMMARY

[0005] Therefore, the present application provides a preparation method of step-by-step polymerization double-enhanced interface solid-state polymer electrolyte. The method uses step-by-step polymerization to prepare the solid-state polymer electrolyte, optimizes the positive electrode side interface and the negative electrode side interface, and realizes continuous large-scale production of the solid-state polymer electrolyte.

[0006] The present application provides a preparation method of step-by-step polymerization double-enhanced interface solid-state polymer electrolyte, which comprises the following steps:

[0007] The base monomer and the first photoinitiator are provided, and the base monomer and the first photoinitiator are uniformly mixed to obtain a mixed slurry; the mixed slurry is irradiated with ultraviolet light to obtain a prepolymer slurry;

[0008] Lithium salt and a second photoinitiator are added to the prepolymer slurry, and after uniform mixing, a polymer slurry is obtained; the polymer slurry is evenly divided into a first polymer slurry and a second polymer slurry, a nitrogen-containing functional monomer is added to the first polymer slurry to obtain a polymer slurry A, and a fluorine-containing functional monomer is added to the second polymer slurry to obtain a polymer slurry B;

[0009] A base film is provided, the base film includes a first surface and a second surface arranged opposite to each other, the polymer slurry A is poured onto the first surface, the polymer slurry A is subjected to continuous roll-to-roll doctor blade coating and ultraviolet light curing forming treatment, the polymer slurry B is poured onto the second surface, and the polymer slurry B is subjected to continuous roll-to-roll doctor blade coating and ultraviolet light curing forming treatment to obtain a step-by-step polymerization double-enhanced interfacial solid-state polymer electrolyte.

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

[0011] Optionally, the mass ratio of the first polymer slurry and the nitrogen-containing functional monomer ranges from 5:1 to 20:1; the mass ratio of the second polymer slurry and the fluorine-containing functional monomer ranges from 5:1 to 20:1.

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

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

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

[0015] Optionally, the base 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, 4-dimethylaminoethyl benzoate, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methylpropyl phenyl ketone, and methyl benzoylformate.

[0017] 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, 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(oxalate)borate, lithium difluoro(oxalate)borate.

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

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

[0021] Compared with the prior art, the preparation method of the step-by-step polymerization double-reinforced interface solid-state polymer electrolyte provided by the application at least achieves the following beneficial effects:

[0022] In the first aspect, the solid-state polymer electrolyte is prepared by the step-by-step polymerization method. The first polymerization of part of the base monomer is used as a pre-polymerization slurry. The molecular weight structure of the base polymer can be adjusted. The viscosity of the subsequent polymerization slurry is suitable and controllable, and the slurry can be uniformly coated on the base film to maintain sufficient liquid hanging. Continuous coating can be performed to ensure that the subsequently formed solid-state polymer electrolyte is in good contact with the electrode. The process difficulty of manufacturing the solid-state polymer electrolyte is reduced, which is conducive to large-scale industrialized production. The functional monomer and the lithium salt are added in the pre-polymerization slurry, and then cross-linking polymerization is performed. This is conducive to the uniform mixing of the components and the control of the structure of the generated polymer. In the polymerization process, the base monomer and the functional monomer can form a stable cross-linking structure, which is conducive to enhancing the structural stability and ion transmission performance, promoting the improvement of the high-voltage stability of the solid-state polymer electrolyte. The battery prepared from the solid-state polymer electrolyte has good mechanical stability and can overcome the problems of life decay caused by lithium dendrite growth.

[0023] In the second aspect, by coating the polymer electrolyte with different properties on the first and second surfaces (the first and second surfaces can also be understood as the positive electrode side and the negative electrode side) of the base film respectively, the solid-state polymer electrolyte containing nitrogen elements can construct a CEI layer (Cathode Electrolyte Interface) rich in high-strength oxidation-stable nitro groups on the positive electrode side, and the polymer electrolyte containing fluorine elements can construct a stable SEI layer (Solid Electrolyte Interphase) rich in lithium fluoride (chemical formula: LiF) on the negative electrode side. The synergistic effect of fluorine elements and nitrogen elements modified realizes the effect of double enhancement of the positive electrode side interface and the negative electrode side interface.

[0024] In the third aspect, the solid-state polymer electrolyte prepared by the preparation method of the step-by-step polymerization double-enhanced interface solid-state polymer electrolyte has high ionic conductivity and high mechanical stability, and the solid-state lithium metal battery prepared from the solid-state polymer electrolyte has improved interface performance compared with the existing solid-state lithium metal battery.

[0025] Of course, it is not necessary to achieve all the technical effects described above at the same time in order to implement any product of the present application.

[0026] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments thereof, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings incorporated in and forming a part of the specification, illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application.

[0028] FIG. 1 is a flowchart of the preparation method of the step-by-step polymerization double-enhanced interface solid-state polymer electrolyte provided by the present application. DETAILED DESCRIPTION

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

[0030] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way limiting to the scope of the application or its applications or uses.

[0031] Techniques, methods, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail herein, but should be considered as part of the specification, where appropriate.

[0032] In all of the examples shown and discussed herein, any specific values should be interpreted as merely exemplary, and not as a limitation. Thus, other examples of the exemplary embodiments can have different values.

[0033] It should be noted that like numerals and letters refer to like items throughout the several views, as such, once an item is defined in one view, it need not be discussed further in subsequent views.

[0034] Referring to FIG. 1, FIG. 1 is a flow chart of a preparation method of a step-by-step polymerization double-enhanced interface solid-state polymer electrolyte provided by the present application. The present embodiment provides a preparation method of a step-by-step polymerization double-enhanced interface solid-state 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, irradiating the mixed slurry with ultraviolet light to obtain a pre-polymerization slurry.

[0036] Specifically, referring to FIG. 1, the polymer is formed by polymerization, copolymerization, or polycondensation reaction of one or more simple low-molecular compounds (monomers), is repeatedly connected by many monomers, and has a relative molecular mass of up to 10 4 The above compounds, the base monomer is the basic unit of the polymer, is a small molecule for synthesizing the polymer, and can be regarded as a basic component constituting the polymer compound; the first photoinitiator belongs to the photoinitiator, the photoinitiator (photoinitiator) is also called a photosensitizer (photosensitizer) or a photocuring agent (photocuring agent), which is a kind of compound that can absorb energy of a certain wavelength in the ultraviolet light region (wavelength range of 250 nm to 420 nm) or the visible light region (wavelength range of 400 nm to 800 nm), generate free radicals, cations, etc., thereby initiating polymerization and crosslinking of the base monomer. The base monomer and the first photoinitiator are uniformly mixed to ensure sufficient reaction between the two. The mixed slurry is irradiated with ultraviolet light, the first photoinitiator can absorb the energy of the ultraviolet light and initiate the polymerization between the base monomers, thereby obtaining a pre-polymerization slurry. The viscosity of the pre-polymerization slurry is suitable and controllable, can be uniformly coated on the support film to maintain sufficient liquid hanging, can be continuously coated, ensures good contact between the solid-state electrolyte and the electrode, reduces the process difficulty of manufacturing the solid-state polymer electrolyte, and is conducive to large-scale industrialized production.

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

[0038] Specifically, the nitrogen is an inert gas, which can be used as a protective gas to avoid the reaction of the matrix monomer and the first photoinitiator during the mixing process; the uniform mixing method includes but is not limited to magnetic stirring or ultrasonic stirring, and the method for uniformly mixing the matrix monomer and the first photoinitiator is the prior art in the field, which 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, the 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 No.: 27813-02-1), and vinyl acetate (also known as vinyl acetate, molecular formula: C4H6O2, CAS No.: 108-05-4); wherein, the CAS No. (CAS Registry Number or CAS Number, CAS Rn, CAS#) is also known as the CAS number, CAS login number or CAS registration number, which is the unique digital identification number of a certain substance (compound, polymer material, biological sequence, mixture or alloy); the material of the matrix monomer and the number of types of the matrix monomer in the prepolymer slurry can be adjusted as needed, which is not specifically limited here.

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

[0042] Specifically, the 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), ethyl 4-dimethylaminobenzoate (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 No. 7473-98-5), methyl benzoylformate (molecular formula: C9H8O3, CAS No. 15206-55-0); the number of types of the first photoinitiator that can be selected and the first photoinitiator in the prepolymer slurry can be adjusted as appropriate according to actual conditions, and are not specifically limited here.

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

[0044] The embodiment explains that the base monomer and the first photoinitiator have a certain mass ratio to obtain the prepolymer slurry, and the mass ratio of the base monomer and the first photoinitiator can range from 100:1 to 5000:1, such as 100:1, 200:1, 300:1, 500:1, 1000:1, 2000:1, 3000:1, or 5000:1, so as to avoid that the mass ratio of the base monomer and the first photoinitiator is too small to form a prepolymer slurry with sufficient viscosity, and also avoid that the mass ratio of the base monomer and the first photoinitiator is too large to cause the base monomers to not react. Therefore, the embodiment sets the mass ratio of the base monomer and the first photoinitiator to range from 100:1 to 5000:1, which can ensure that the base monomers react while avoiding the formation of a prepolymer slurry with insufficient viscosity.

[0045] Optionally, the wavelength of the ultraviolet light ranges from 220 nm to 400 nm, and the irradiation time ranges from 0.2 min to 2 min.

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

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

[0048] Optionally, the viscosity of the prepolymer slurry is 500 cP to 3500 cP.

[0049] The embodiment explains that the prepolymer slurry has a certain viscosity to generate a step-by-step polymerization double-reinforced interface solid-state polymer electrolyte, and the viscosity of the prepolymer slurry can be 500 cP to 3500 cP, such as 500 cP, 800 cP, 1000 cP, 1500 cP, 2000 cP, 2500 cP, 3000 cP or 3500 cP, so as to avoid that the prepolymer slurry cannot form a solid-state polymer when the viscosity is too low, and also avoid that the prepolymer slurry cannot be doped with other monomers subsequently when the viscosity is too high. Therefore, the viscosity range of the prepolymer slurry is set to 500 cP to 3500 cP in the embodiment, which can avoid that the solid-state polymer cannot be formed and ensure that the prepolymer slurry can be doped with other monomers subsequently.

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

[0051] Specifically, continuing to refer to FIG. 1, the lithium salt refers to a salt containing lithium element. Since the base 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 functional groups such as ester groups and hydroxyl groups can form a complex structure with lithium ions in the lithium salt, realizing the transmission of lithium ions in the polymer main chain, thereby improving the electrochemical performance of the electrolyte, and further improving the performance of the battery prepared subsequently. At the same time, after the base monomer and the lithium salt are completely polymerized, the surface of the solid-state polymer electrolyte film formed subsequently can be wrapped by an elastic polymer, which can reduce the interface resistance between the solid-state 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 uniform mixing method is the prior art in the field, which is not specifically limited here.

[0052] Continuing to refer to FIG. 1, the nitrogen-containing functional monomer contains nitrogen (element symbol: N) element, which can be used as an additive for modification of the positive electrode interface, and is beneficial to form a nitrogen-containing enhanced stable interface during the battery cycle process, 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 modification of the negative electrode interface, and is beneficial to form a fluorine-containing enhanced stable interface during the battery cycle process, and improve the negative electrode side interface; by dividing the polymer slurry into the first polymer slurry and the second polymer slurry, the nitrogen-containing functional monomer is added to the first polymer slurry to obtain the polymer slurry A, and the fluorine-containing functional monomer is added to the second polymer slurry to obtain the polymer slurry B, and then the polymer slurry A and the polymer slurry B are respectively cast on both sides of the base film, so as to obtain a step-by-step polymerization double-enhanced interface solid-state polymer electrolyte film, thereby forming a double-enhanced stable interface, and playing a role of simultaneously improving the positive electrode side interface and the negative electrode side interface.

[0053] In this embodiment, by polymerizing the base monomer and the functional monomer under the condition of ultraviolet light, a stable polymer network composed of crosslinking of the two kinds of monomers is realized, which is beneficial to enhance the structural stability and ion transmission, and promote the improvement of the high-voltage stability of the solid-state polymer electrolyte, so that the battery prepared from the solid-state polymer electrolyte has good mechanical stability, and can overcome the life attenuation caused by lithium dendrite growth. At the same time, since the preparation method of the step-by-step polymerization double-enhanced interface solid-state polymer electrolyte adds a prepolymerization process before the functional monomer, the prepolymerization process can achieve higher monomer conversion rate and more favorable long-chain polymer structure regulation, which is beneficial to improve 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 bisfluorosulfonylimide, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate.

[0055] Specifically, lithium hexafluorophosphate (molecular formula: F6LiP, CAS number: 21324-40-3), lithium perchlorate (molecular formula: LiClO4, CAS number: 7791-03-9), lithium bistrifluoromethylsulfonylimide (molecular formula: CF3SO2NLiSO2CF3, CAS number: 90076-65-6), lithium bisfluorosulfonylimide (molecular formula: F2LiNO4S2, CAS number: 171611-11-3), lithium tetrafluoroborate (molecular formula: BF4Li, CAS number: 14283-07-9), lithium bis(oxalato)borate (molecular formula: LiB(C2O4)2, CAS number: 244761-29-3), lithium difluoro(oxalato)borate (molecular formula: C2BF2LiO4, CAS number: 409071-16-5); the material that can be selected for the lithium salt and the number of types of lithium salt in the polymer slurry can be adjusted as appropriate according to the actual situation, and no specific limitation is made here.

[0056] Optionally, 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. The material of the second photoinitiator can be the same as or different from that of the first photoinitiator, which is not introduced here. The number of types of the second photoinitiator in the polymer slurry can be adjusted as appropriate according to the actual situation, and no specific limitation is made here.

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

[0058] The embodiment explains that the prepolymerization slurry and the second photoinitiator have a certain mass ratio to obtain the polymer slurry, and the mass ratio of the prepolymerization slurry to the second photoinitiator can range from 20:1 to 500:1, such as 20:1, 50:1, 100:1, 200:1, or 500:1, so that the polymer slurry can be successfully coated when the mass ratio of the prepolymerization slurry to the second photoinitiator is too small, and the crosslinked structure of the base monomer and the functional monomer can be successfully formed when the mass ratio of the prepolymerization slurry to the second photoinitiator is too large. Therefore, the embodiment sets the mass ratio of the prepolymerization slurry to the second photoinitiator to range from 20:1 to 500:1, which can ensure the formation of the solid polymer slurry with appropriate viscosity while avoiding the failure of the base monomer and the functional monomer to form the crosslinked structure.

[0059] Optionally, the nitrogen-containing functional monomer includes at least one of N,N'-methylenebisacrylamide, N-phenylmethylacrylamide, 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-phenylmethacrylamide (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-vinylcaprolactam (molecular formula: C8H 13 NO, CAS No.: 2235-00-9); the material that can be selected for the nitrogen-containing functional monomer and the number of types of nitrogen-containing functional monomers in the polymer slurry A can be adjusted as appropriate according to the actual situation, and are not specifically limited here.

[0061] Optionally, the mass ratio of the first polymer slurry and the nitrogen-containing functional monomer ranges from 5:1 to 20:1.

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

[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 material that can be selected for the fluorine-containing functional monomer and the number of types of fluorine-containing functional monomers in the polymer slurry B can be adjusted as appropriate according to the actual situation, and are not specifically limited here.

[0065] Optionally, the mass ratio of the second polymer slurry and the fluorine-containing functional monomer ranges from 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 the 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 5:1, 6.25:1, 10:1, 12.5:1, 15:1, or 20:1, so that 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 can be avoided to be not stable enough, and 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 can also be avoided. Therefore, this embodiment sets the mass ratio of the second polymer slurry and the fluorine-containing functional monomer to range from 5:1 to 20:1, which can avoid the problems of the interface of the fluorine-containing element not being stable enough and the interface of the fluorine-containing element not being formed.

[0067] S3: providing a base film including a first surface and a second surface arranged oppositely, pouring the polymer slurry A on the first surface, performing continuous roll-to-roll doctor blade coating and ultraviolet light curing forming treatment on the polymer slurry A, pouring the polymer slurry B on the second surface, and performing continuous roll-to-roll doctor blade coating and ultraviolet light curing forming treatment on the polymer slurry B to obtain a step-by-step polymerization double-enhanced interface solid-state polymer electrolyte.

[0068] Specifically, continuing to refer to FIG. 1, 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 resistance processing performance; the base film is a film structure, including oppositely arranged first and second surfaces, in this embodiment, the first surface can correspond to the polymer slurry A, and the second surface can correspond to the polymer slurry B, in other embodiments, the first surface can correspond to the polymer slurry B, and the second surface can correspond to the polymer slurry A, which is not limited here; the polymer slurry A is poured onto the first surface, and the polymer slurry A is subjected to continuous roll-to-roll knife coating and ultraviolet curing forming treatment, the polymer slurry B is poured onto the second surface, and the polymer slurry B is subjected to continuous roll-to-roll knife coating and ultraviolet curing forming treatment, to obtain a step-by-step polymerization double-enhanced interface solid-state polymer electrolyte, roll-to-roll knife coating can ensure that the polymer slurry A is evenly coated on the first surface of the base film, and the polymer slurry B is evenly coated on the second surface of the base film, and ultraviolet curing forming treatment ensures that the polymer slurry A and the polymer slurry B are both converted from liquid to solid, thereby obtaining a solid-state polymer electrolyte; wherein, continuous roll-to-roll knife coating and ultraviolet curing forming treatment are both prior art in the art, which will not be described here.

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

[0070] Optionally, in the ultraviolet curing forming treatment, the wavelength of the ultraviolet light ranges from 220 nm to 400 nm, and the irradiation time is 1 min to 10 min.

[0071] The embodiment explains that the ultraviolet light has a certain wavelength to convert the polymer slurry A and the polymer slurry B from a liquid state to a solid state, the wavelength range of the ultraviolet light can be 220 nm to 400 nm, for example, the wavelength of the ultraviolet light can be 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 345 nm, 365 nm, 380 nm or 400 nm, etc., so as to avoid that the liquid polymer slurry A and the polymer slurry B cannot be converted into a solid state when the wavelength of the ultraviolet light is too short, and the structure of the formed solid electrolyte can also be destroyed when the wavelength of the ultraviolet light is too long. Therefore, the wavelength range of the ultraviolet light is set to 220 nm to 400 nm in the embodiment, which can avoid that the liquid polymer slurry A and the polymer slurry B cannot be converted into a solid state, and the structure of the solid electrolyte is also avoided to be destroyed.

[0072] The embodiment explains that the ultraviolet light has a certain irradiation time to convert the polymer slurry A and the polymer slurry B from a liquid state to a solid state, the irradiation time of the ultraviolet light can be 1 min to 10 min, for example, the irradiation time of the ultraviolet light can be 1 min, 2 min, 3 min, 5 min, 8 min or 10 min, etc., so as to avoid that the liquid polymer slurry A and the polymer slurry B cannot be converted into a solid state when the irradiation time of the ultraviolet light is too short, and the structure of the formed solid electrolyte can also be destroyed when the irradiation time of the ultraviolet light is too long. Therefore, the irradiation time of the ultraviolet light is set to 1 min to 10 min in the embodiment, which can avoid that the liquid polymer slurry A and the polymer slurry B cannot be converted into a solid state, and the structure of the solid electrolyte is also avoided to be destroyed.

[0073] Embodiment 1:

[0074] First step: provide 100 g of polyethylene glycol diacrylate (matrix monomer) and 0.03 g of 2-hydroxy-2-methylpropiophenone (first photoinitiator), the polyethylene glycol diacrylate and the 2-hydroxy-2-methylpropiophenone are added to a reaction kettle, stirred in a nitrogen atmosphere, and uniformly mixed to obtain a mixed slurry of embodiment 1. The mixed slurry is irradiated with ultraviolet light with a wavelength of 365 nm to obtain a pre-polymerization slurry of embodiment 1 with a viscosity of about 2000 cP;

[0075] Second step: 20g of lithium bis-trifluoromethanesulfonimide (lithium salt) and 1g of 2-hydroxy-2-methylpropiophenone (second photoinitiator) are added to the prepolymer slurry of Example 1, and after uniform mixing, the polymer slurry of Example 1 is obtained. The polymer slurry of Example 1 is evenly divided into the first polymer slurry of Example 1 and the second polymer slurry of Example 1, which are placed in two reaction kettles respectively. 5g of N,N'-methylenebisacrylamide (nitrogen-containing functional monomer) is added to the first polymer slurry of Example 1 to obtain the polymer slurry A of Example 1, and 5g of hexafluoroisopropyl acrylate (fluorine-containing functional monomer) is added to the second polymer slurry of Example 1 to obtain the polymer slurry B of Example 1.

[0076] Third step: A PP base film is provided, which includes a first face and a second face arranged oppositely. First, the polymer slurry A of Example 1 is cast on the first face, and the continuous roll-to-roll knife coating process is performed on the polymer slurry A of Example 1, with the film layer thickness of the polymer slurry A of Example 1 controlled at 25μm. Then, the first face is subjected to ultraviolet light curing and forming treatment by using ultraviolet light with a wavelength of 365nm. Next, the polymer slurry B of Example 1 is cast on the second face, and the continuous roll-to-roll knife coating process is performed on the polymer slurry B of Example 1, with the film layer thickness of the polymer slurry B of Example 1 controlled at 25μm. Then, the second face is subjected to ultraviolet light curing and forming treatment by using ultraviolet light with a wavelength of 365nm. Thus, the polymer electrolyte film of Example 1 is obtained, and the substances on the first face and the second face of the polymer electrolyte film are the step-by-step polymerized double-enhanced interface solid-state polymer electrolyte.

[0077] Example 2:

[0078] First step: 100g of polyethylene glycol diacrylate (base monomer) and 0.03g of 2-hydroxy-2-methylpropiophenone (first photoinitiator) are added to a reaction kettle, stirred in a nitrogen atmosphere, and uniformly mixed to obtain the mixed slurry of Example 2. The mixed slurry is irradiated with ultraviolet light with a wavelength of 365nm to obtain the prepolymer slurry of Example 2 with a viscosity of about 2000cP.

[0079] Second step: 20g of lithium bis-trifluoromethanesulfonimide (lithium salt) and 1g of 1-hydroxycyclohexyl phenyl ketone (second photoinitiator) are added to the prepolymer slurry of Example 2, and after uniform mixing, the polymer slurry of Example 2 is obtained. The polymer slurry of Example 2 is evenly divided into the first polymer slurry of Example 2 and the second polymer slurry of Example 2, which are placed in two reaction kettles respectively. 10g of N,N'-methylenebisacrylamide (nitrogen-containing functional monomer) is added to the first polymer slurry of Example 2 to obtain the polymer slurry A of Example 2, and 10g of hexafluoroisopropyl acrylate (fluorine-containing functional monomer) is added to the second polymer slurry of Example 2 to obtain the polymer slurry B of Example 2.

[0080] Third step: provide a PP base film, the PP base film includes a first face and a second face arranged oppositely, first, pour the polymer slurry A of Example 2 on the first face, and perform continuous roll-to-roll doctor blade coating treatment on the polymer slurry A of Example 2, and control the film layer thickness of the polymer slurry A of Example 2 to be 25 μm, second, perform ultraviolet light curing forming treatment on the first face by using ultraviolet light with a wavelength of 365 nm, then, pour the polymer slurry B of Example 2 on the second face, and perform continuous roll-to-roll doctor blade coating treatment on the polymer slurry B of Example 2 first, and control the film layer thickness of the polymer slurry B of Example 2 to be 25 μm, and then, perform ultraviolet light curing forming treatment on the second face by using ultraviolet light with a wavelength of 365 nm, to obtain a polymer electrolyte film, and the substances on the first face and the second face of the polymer electrolyte film are step-by-step polymerized double-enhanced interface solid-state polymer electrolyte.

[0081] Compared with Example 1, the mass of the nitrogen-containing functional monomer and the fluorine-containing functional monomer is increased in Example 2.

[0082] Example 3:

[0083] First step: provide 100 g of polyethylene glycol diacrylate (base monomer) and 0.03 g of 1-hydroxycyclohexyl phenone (first photoinitiator), and add the polyethylene glycol diacrylate and the 1-hydroxycyclohexyl phenone into a reaction kettle, stir in a nitrogen atmosphere, and after uniform mixing, obtain a mixed slurry of Example 3, and irradiate the mixed slurry by using ultraviolet light with a wavelength of 365 nm, to obtain a pre-polymerized slurry of Example 3 with a viscosity of about 2000 cP;

[0084] Second step: add 20 g of lithium bis-trifluoromethanesulfonimide (lithium salt) and 1 g of 1-hydroxycyclohexyl phenone (second photoinitiator) into the pre-polymerized slurry of Example 3, and after uniform mixing, obtain a polymer slurry of Example 3, and divide the polymer slurry of Example 3 into a first polymer slurry of Example 3 and a second polymer slurry of Example 3, and respectively place them in two reaction kettles, add 5 g of N,N'-methylenebisacrylamide (nitrogen-containing functional monomer) into the first polymer slurry of Example 3, to obtain a polymer slurry A of Example 3, and add 5 g of hexafluoroisopropyl acrylate (fluorine-containing functional monomer) into the second polymer slurry of Example 3, to obtain a polymer slurry B of Example 3;

[0085] Third step: provide a PP base film, the PP base film includes a first face and a second face arranged oppositely, first, pour the polymer slurry A of Example 3 on the first face, and perform continuous roll-to-roll doctor blade coating treatment on the polymer slurry A of Example 3, and control the film layer thickness of the polymer slurry A of Example 3 to be 25 μm, second, perform ultraviolet light curing forming treatment on the first face by using ultraviolet light with a wavelength of 365 nm, then, pour the polymer slurry B of Example 3 on the second face, and perform continuous roll-to-roll doctor blade coating treatment on the polymer slurry B of Example 3 first, and control the film layer thickness of the polymer slurry B of Example 3 to be 25 μm, and then, perform ultraviolet light curing forming treatment on the second face by using ultraviolet light with a wavelength of 365 nm, to obtain the polymer electrolyte film of Example 3, and the substances on the first face and the second face of the polymer electrolyte film are the step-by-step polymerized double-enhanced interface solid-state polymer electrolyte.

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

[0087] Example 4:

[0088] First step: provide 100 g of polyethylene glycol diacrylate (base monomer) and 0.03 g of 2-hydroxy-2-methylpropiophenone (first photoinitiator), and add the polyethylene glycol diacrylate and the 2-hydroxy-2-methylpropiophenone into a reaction kettle, stir in a nitrogen atmosphere, and after uniform mixing, obtain the mixed slurry of Example 4, and irradiate the mixed slurry by using ultraviolet light with a wavelength of 365 nm, to obtain the pre-polymerized slurry of Example 4 with a viscosity of about 2000 cP;

[0089] Second step: add 20 g of bis-trifluoromethanesulfonimide lithium (lithium salt) and 2 g of 2-hydroxy-2-methylpropiophenone (second photoinitiator) into the pre-polymerized slurry of Example 4, and after uniform mixing, obtain the polymer slurry of Example 4, and divide the polymer slurry of Example 4 into the first polymer slurry of Example 4 and the second polymer slurry of Example 4, and place them in two reaction kettles respectively, add 5 g of N,N'-methylenebisacrylamide (nitrogen-containing functional monomer) into the first polymer slurry of Example 4, to obtain the polymer slurry A of Example 4, and add 5 g of hexafluoroisopropyl acrylate (fluorine-containing functional monomer) into the second polymer slurry of Example 4, to obtain the polymer slurry B of Example 4;

[0090] Third step: provide a PP base film, the PP base film includes a first face and a second face arranged oppositely, first, pour the polymer slurry A of Example 4 on the first face, and perform continuous roll-to-roll doctor blade coating treatment on the polymer slurry A of Example 4, and control the film layer thickness of the polymer slurry A of Example 4 to be 25 μm, second, perform ultraviolet light curing forming treatment on the first face by using ultraviolet light with a wavelength of 365 nm, then, pour the polymer slurry B of Example 4 on the second face, and perform continuous roll-to-roll doctor blade coating treatment on the polymer slurry B of Example 4 first, and control the film layer thickness of the polymer slurry B of Example 4 to be 25 μm, and then, perform ultraviolet light curing forming treatment on the second face by using ultraviolet light with a wavelength of 365 nm, to obtain the polymer electrolyte film of Example 4, and the substances on the first face and the second face of the polymer electrolyte film are the step-by-step polymerized double-enhanced interface solid-state polymer electrolyte.

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

[0092] Example 5:

[0093] First step: provide 100 g of polyethylene glycol diacrylate (base monomer) and 0.03 g of 2-hydroxy-2-methylpropiophenone (first photoinitiator), and add the polyethylene glycol diacrylate and the 2-hydroxy-2-methylpropiophenone into a reaction kettle, stir in a nitrogen atmosphere, and after uniform mixing, obtain the mixed slurry of Example 5, and irradiate the mixed slurry by using ultraviolet light with a wavelength of 365 nm, to obtain the pre-polymerized slurry of Example 5 with a viscosity of about 2000 cP;

[0094] Second step: add 20 g of bis-trifluoromethanesulfonimide lithium (lithium salt) and 2 g of 2-hydroxy-2-methylpropiophenone (second photoinitiator) into the pre-polymerized slurry of Example 5, and after uniform mixing, obtain the polymer slurry of Example 5, and divide the polymer slurry of Example 5 into the first polymer slurry of Example 5 and the second polymer slurry of Example 5, and respectively place them in two reaction kettles, add 5 g of N,N'-methylenebisacrylamide (nitrogen-containing functional monomer) into the first polymer slurry of Example 5, to obtain the polymer slurry A of Example 5, and add 5 g of dodecafluoroheptyl methacrylate (fluorine-containing functional monomer) into the second polymer slurry of Example 5, to obtain the polymer slurry B of Example 5;

[0095] Third step: provide a PP base film, the PP base film includes a first face and a second face arranged oppositely, first, pour the polymer slurry A of Example 5 on the first face, and perform continuous roll-to-roll doctor blade coating treatment on the polymer slurry A of Example 5, and control the film layer thickness of the polymer slurry A of Example 5 to be 25 μm, second, perform ultraviolet light curing forming treatment on the first face by using ultraviolet light with a wavelength of 365 nm, then, pour the polymer slurry B of Example 5 on the second face, and perform continuous roll-to-roll doctor blade coating treatment on the polymer slurry B of Example 5 first, and control the film layer thickness of the polymer slurry B of Example 5 to be 25 μm, and then, perform ultraviolet light curing forming treatment on the second face by using ultraviolet light with a wavelength of 365 nm, to obtain a polymer electrolyte film, and the substances on the first face and the second face of the polymer electrolyte film are step-by-step polymerized double-enhanced interface solid-state polymer electrolyte.

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

[0097] Example 6:

[0098] First step: provide 100 g of vinyl acetate (base monomer) and 0.03 g of 2-hydroxy-2-methylpropiophenone (first photoinitiator), and add the vinyl acetate and 2-hydroxy-2-methylpropiophenone into a reaction kettle, stir in a nitrogen atmosphere, and after uniform mixing, obtain a mixed slurry of Example 6, and irradiate the mixed slurry by using ultraviolet light with a wavelength of 365 nm, to obtain a pre-polymerized slurry of Example 6 with a viscosity of about 2000 cP;

[0099] Second step: add 20 g of lithium bis-trifluoromethanesulfonimide (lithium salt) and 2 g of 2-hydroxy-2-methylpropiophenone (second photoinitiator) into the pre-polymerized slurry of Example 6, and after uniform mixing, obtain a polymer slurry of Example 6, and divide the polymer slurry of Example 6 into a first polymer slurry of Example 6 and a 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) into the first polymer slurry of Example 6, to obtain a polymer slurry A of Example 6, and add 5 g of dodecafluoroheptyl methacrylate (fluorine-containing functional monomer) into the second polymer slurry of Example 6, to obtain a polymer slurry B of Example 6;

[0100] Third step: provide a PP base film, the PP base film includes oppositely arranged first and second surfaces, first, pour the polymer slurry A of Example 6 on the first surface, and perform continuous roll-to-roll knife coating treatment on the polymer slurry A of Example 6, control the film layer thickness of the polymer slurry A of Example 6 to be 25 μm, second, perform ultraviolet light curing forming treatment on the first surface by using ultraviolet light with a wavelength of 365 nm, then pour the polymer slurry B of Example 6 on the second surface, first perform continuous roll-to-roll knife coating treatment on the polymer slurry B of Example 6, control the film layer thickness of the polymer slurry B of Example 6 to be 25 μm, then perform ultraviolet light curing forming treatment on the second surface by using ultraviolet light with a wavelength of 365 nm, to obtain the polymer electrolyte film of Example 6, the substances on the first and second surfaces of the polymer electrolyte film are step-by-step polymerized double-enhanced interface solid-state polymer electrolyte.

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

[0102] Comparative Example 1:

[0103] First step: provide 100 g of polyethylene glycol diacrylate (base monomer) and 0.03 g of 2-hydroxy-2-methylpropiophenone (first photoinitiator), add the polyethylene glycol diacrylate and 2-hydroxy-2-methylpropiophenone into a reaction kettle, stir in a nitrogen atmosphere, and after uniform mixing, obtain the mixed slurry of Comparative Example 1, irradiate the mixed slurry by using ultraviolet light with a wavelength of 365 nm, to obtain the pre-polymerized slurry of Comparative Example 1 with a viscosity of about 2000 cP;

[0104] Second step: add 20 g of lithium bis-trifluoromethanesulfonimide (lithium salt) and 1 g of 2-hydroxy-2-methylpropiophenone (second photoinitiator) into the pre-polymerized slurry of Comparative Example 1, uniformly mix to obtain the polymer slurry of Comparative Example 1;

[0105] Third step: provide a PP base film, the PP base film includes oppositely arranged first and second surfaces, pour the polymer slurry of Comparative Example 1 directly on the first and second surfaces, perform continuous roll-to-roll knife coating treatment on the polymer slurry of Comparative Example 1, control the film layer thickness of the polymer slurry of Comparative Example 1 to be 25 μm, perform ultraviolet light curing forming treatment on the first and second surfaces by using ultraviolet light with a wavelength of 365 nm at the same time, to obtain the polymer electrolyte film of Comparative Example 1, the substances on the first and second surfaces of the polymer electrolyte film are step-by-step polymerized solid-state polymer electrolyte without functional monomers.

[0106] Comparative Example 1 does not use the step-by-step method to prepare the solid-state polymer electrolyte compared with Example 1, and does not add nitrogen-containing functional monomers and fluorine-containing functional monomers into the base monomer.

[0107] Comparative Example 2:

[0108] First step: provide 100 g of polyethylene glycol diacrylate (base monomer) and 0.03 g of 2-hydroxy-2-methylpropiophenone (first photoinitiator), and add the polyethylene glycol diacrylate and 2-hydroxy-2-methylpropiophenone into a reaction kettle, stir under a nitrogen atmosphere, and after uniform mixing, obtain the mixed slurry of Comparative Example 2. The mixed slurry is irradiated with ultraviolet light of wavelength 365 nm to obtain the pre-polymerized slurry of Comparative Example 2 with a viscosity of about 2000 cP.

[0109] Second step: add 20 g of lithium bis(trifluoromethanesulfonyl)imide (lithium salt) and 1 g of 2-hydroxy-2-methylpropiophenone (second photoinitiator) to the pre-polymerized slurry of Comparative Example 2, and after uniform mixing, add 10 g of hexafluoroisopropyl acrylate (fluorine-containing functional monomer), and after uniform mixing, obtain the polymer slurry of Comparative Example 2.

[0110] Third step: provide a PP base film including oppositely arranged first and second faces, and directly cast the polymer slurry of Comparative Example 2 on the first and second faces. The polymer slurry of Comparative Example 2 is subjected to continuous roll-to-roll doctor blade coating treatment, and the film layer thickness of the polymer slurry of Comparative Example 2 is controlled to be 25 μm. The first and second faces are simultaneously subjected to ultraviolet light curing and forming treatment using ultraviolet light of wavelength 365 nm, and the polymer electrolyte film of Comparative Example 2 is obtained. The substances on the first and second faces of the polymer electrolyte film are single-enhanced polymer solid-state polymer electrolytes.

[0111] Comparative Example 2 has an increased mass of fluorine-containing functional monomer, does not use a step-by-step method to prepare a solid-state polymer electrolyte, and does not add a nitrogen-containing functional monomer to the base monomer.

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

[0113] First step: disperse the positive electrode material, binder, and conductive agent in a solvent, and after uniform mixing, obtain a positive electrode slurry. The positive electrode slurry is coated on both sides of the current collector, vacuum dried, and then die cut to obtain positive electrode sheets with a certain size.

[0114] It should be noted that the positive electrode material can be selected as lithium nickel cobalt manganese oxide, abbreviated as NCM811, which is a high-nickel ternary material. The lithium metal battery prepared from the material is a high-nickel ternary system lithium metal battery. NCM811 is a single crystal structure, which has the advantages of high capacity, high first efficiency, high energy density, stable structure, good high-temperature and cycle performance, etc. The binder can be selected as polyvinylidene fluoride, abbreviated as PVDF, which is a highly non-reactive thermoplastic fluorine-containing polymer, and has the advantages of anti-aging, chemical resistance, weather resistance, and ultraviolet radiation resistance. The conductive agent can be selected as carbon black, which is abbreviated as SP, and has the advantages of small particle size, large specific surface area, high structure, and clean surface. The solvent can be selected as N-methyl pyrrolidone (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: The lithium-copper composite tape is die-cut to obtain lithium metal negative electrode sheets with a certain size.

[0116] Step 3: According to the requirements of the test items, the positive electrode sheet, the polymer electrolyte film, and the negative electrode sheet are assembled into 2032 type button cells or aluminum-plastic film packaged soft package batteries, respectively. The polymer electrolyte film is the polymer electrolyte film in Example 1 to Example 6 and Comparative Example 1 to Comparative Example 2.

[0117] The batteries assembled from the polymer electrolyte films of Example 1 to Example 6 and Comparative Example 1 to Comparative Example 2 are tested for various performance tests. The 2032 type button cell assembled with a stainless steel sheet as a blocking electrode is tested for ionic conductivity. This test is a prior art in the field, and will not be described here. The test results are shown in Table 1.

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

[0119] As can be seen from the comparison results in Table 1, the ionic conductivity of Example 1 to Example 6 is greatly improved compared to Comparative Example 1 to Comparative Example 2. At the same time, Example 1 has the highest ionic conductivity. In Example 1 to Example 6, the functional monomer is added, and the functional monomer and the base monomer are crosslinked with each other to form a three-dimensional network structure that can promote the rapid transmission of lithium ions. The amide group in the polymer and the anion in the electrolyte component have a bonding effect, which can fix the anion and promote the dissociation of lithium salt, thereby improving the efficiency of lithium ion transmission. Therefore, the step-by-step polymerization double-enhanced interface solid-state polymer electrolyte in Example 1 to Example 6 can exhibit higher ionic conductivity than the step-by-step polymerization solid-state polymer electrolyte without functional monomer (Example 1) and the single-enhanced solid-state polymer electrolyte (Comparative Example 2).

[0120] Then, the 2 Ah soft package batteries assembled from the polymer electrolyte films of the above-mentioned Examples 1-6 and Comparative Examples 1-2 were subjected to electrochemical cycle testing (0.5C) at 25°C, which is a prior art in the field, and the test results are shown in Table 2.

[0121] Table 2: Cycle performance comparison of solid-state lithium metal soft package batteries

[0122] It should be noted that:

[0123] (1) The first cycle coulombic 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 coulombic efficiency, the better the battery performance.

[0124] (2) The capacity retention rate is the ability of the battery to retain capacity after multiple charge and discharge cycles relative to the initial capacity; the cycle 100 capacity retention rate can be understood as the ability of the battery to retain capacity after 100 charge and discharge cycles relative to the initial capacity; the higher the capacity retention rate, the better the battery performance.

[0125] (3) The cycle performance of the battery is mainly measured by three indicators: cycle number, first discharge capacity and retained capacity; cycle number refers to the number of complete charge and discharge cycles that the battery can perform; first discharge capacity is the maximum amount of electricity that the battery can release during the first charge-discharge test; retained capacity refers to the discharge capacity that the battery can still maintain after a certain number of charge-discharge cycles; the larger the first cycle coulombic efficiency and the cycle 100 capacity retention rate, the better the cycle performance of the battery.

[0126] 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 coulombic efficiency and the cycle 100 capacity retention rate in Examples 1-6 and Comparative Examples 1-2, it is shown that the nitrogen element and the fluorine element in the step-by-step polymerization double-enhanced interfacial solid-state polymer electrolyte can respectively construct stable CEI layers (positive electrode-electrolyte interface layers) / SEI layers (electrolyte intermediate interface layers) at the positive electrode and the negative electrode. The nitration group at the positive electrode side can effectively improve the oxidation resistance of the electrode and reduce the tendency of high-pressure decomposition of the polymer electrolyte. The fluorine-containing polymer provides abundant lithium fluoride (chemical formula: LiF) at the negative electrode interface, which can form a dense and stable SEI layer to inhibit the growth of lithium dendrites. The double enhancement of the positive electrode interface and the negative electrode interface enables the battery to exhibit longer and more stable electrochemical cycles.

[0127] From the above examples, it can be seen that the preparation method of the step-by-step polymerization double-enhanced interfacial solid-state polymer electrolyte provided by the present application at least achieves the following beneficial effects:

[0128] In the first aspect, the solid-state polymer electrolyte is prepared by a step-by-step polymerization method. First, a part of the base monomer is polymerized as a pre-polymer slurry to adjust the molecular weight structure of the long chain of the base polymer. The viscosity of the subsequent polymerization slurry is suitable and controllable, which can be uniformly coated on the base film to maintain sufficient liquid hanging and continuous coating. The solid-state polymer electrolyte formed subsequently can be in good contact with the electrode, which reduces the process difficulty of manufacturing the solid-state polymer electrolyte, is conducive to large-scale industrialized production, and adds a functional monomer and lithium salt in the pre-polymer slurry, and then cross-linking polymerization is performed. This is conducive to the uniform mixing of the components, and the structure of the generated polymer can be controlled. In the polymerization process, the base monomer and the functional monomer can form a stable cross-linking structure, which is conducive to enhancing the structural stability and ion transmission performance, promoting the high-voltage stability of the solid-state polymer electrolyte, so that the battery prepared from the solid-state polymer electrolyte has good mechanical stability and can overcome the problem of life attenuation caused by lithium dendrite growth.

[0129] In the second aspect, the polymer electrolyte with different properties is coated on the first and second surfaces (the first and second surfaces can also be understood as the positive and negative sides) of the base film. The solid-state polymer electrolyte containing nitrogen elements can construct a CEI layer (positive electrode-electrolyte interface layer) rich in high-strength oxidatively stable nitration groups on the positive side, and the polymer electrolyte containing fluorine elements can construct a stable SEI layer (electrolyte intermediate interface layer) rich in lithium fluoride (chemical formula: LiF) on the negative side. The synergistic effect of fluorine elements and nitrogen elements realizes the double-enhanced effect of the positive side interface and the negative side interface.

[0130] In the third aspect, the solid-state polymer electrolyte prepared by the preparation method of the step-by-step polymerization double-enhanced interface solid-state polymer electrolyte has high ionic conductivity and high mechanical stability. The solid-state lithium metal battery prepared from the solid-state polymer electrolyte has improved interface performance compared with the existing solid-state lithium metal battery.

[0131] Although some specific embodiments of the present application have been described in detail through examples, those skilled in the art should understand that the above examples are only for illustration, but not for limiting the scope of the present application. Those skilled in the art should understand that the above embodiments can be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A method for the preparation of a step-growth, dual-reinforced interfacial solid-state polymer electrolyte, characterized in that, The method comprises the following steps: providing a base monomer and a first photoinitiator, uniformly mixing the base monomer and the first photoinitiator to obtain a mixed slurry, irradiating the mixed slurry with ultraviolet light to obtain a prepolymerized slurry; adding a lithium salt and a second photoinitiator to the prepolymerized 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; providing a base film comprising a first surface and a second surface arranged opposite to each other, pouring the polymer slurry A on the first surface, performing continuous roll-to-roll doctor blade coating and ultraviolet light curing molding treatment on the polymer slurry A, pouring the polymer slurry B on the second surface, and performing continuous roll-to-roll doctor blade coating and ultraviolet light curing molding treatment on the polymer slurry B to obtain a step-by-step polymerization double-enhanced interfacial solid-state polymer electrolyte.

2. The method for preparing a stepwise polymerized dual-reinforced interface solid polymer electrolyte according to claim 1, characterized in that, The mass ratio of the base monomer to the first photoinitiator ranges from 100:1 to 5000:1, and the mass ratio of the prepolymerized slurry to the second photoinitiator ranges from 20:1 to 500:

1.

3. The method for preparing a stepwise polymerized dual-reinforced interface solid polymer electrolyte according to claim 1, characterized in that, The mass ratio of the first polymer slurry to the nitrogen-containing functional monomer ranges from 5:1 to 20:1, and the mass ratio of the second polymer slurry to the fluorine-containing functional monomer ranges from 5:1 to 20:

1.

4. The method for preparing a stepwise polymerized dual-reinforced interface solid polymer electrolyte according to claim 1, characterized in that, In the irradiation of the mixed slurry with ultraviolet light, the wavelength of the ultraviolet light ranges from 220 nm to 400 nm, and the irradiation time ranges from 0.2 min to 2 min; in the ultraviolet light curing molding treatment, the wavelength of the ultraviolet light ranges from 220 nm to 400 nm, and the irradiation time ranges from 1 min to 10 min.

5. The method for preparing a stepwise polymerized dual-reinforced 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 stepwise polymerized dual-reinforced interface solid polymer electrolyte according to claim 1, characterized in that, The viscosity of the prepolymerized slurry ranges from 500 cP to 3500 cP.

7. The method for preparing a stepwise polymerized dual-reinforced interface solid polymer electrolyte according to claim 1, characterized in that, The base monomer comprises 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, 4-dimethylaminoethyl benzoate, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methylpropiophenone, and methyl benzoylformate; The second photoinitiator is at least one of benzophenone, 2,2-dimethoxy-2-phenylacetophenone, 4-dimethylaminoethyl benzoate, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methylpropiophenone, and methyl benzoylformate.

8. The method for preparing a stepwise polymerized dual-reinforced interface solid polymer electrolyte according to claim 1, characterized in that, The lithium salt comprises at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate.

9. The method for preparing a stepwise polymerized dual-reinforced 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-phenylmethylacrylamide, N,N'-bis(acryloyl)cystamine, acrylamide, N-isopropylacrylamide, N-vinylcaprolactam.

10. The method of claim 1-9, wherein the method is characterized by, The fluorine-containing functional monomer includes at least one of hexafluoroisopropyl acrylate, hexafluorobutyl acrylate, hexafluorobutyl methacrylate, trifluoroethyl methacrylate, dodecafluoroheptyl methacrylate.

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