A double-layer polymer solid-state electrolyte, a preparation method thereof and a lithium ion battery

Abstract

The application provides a double-layer polymer solid electrolyte and a preparation method thereof and a lithium ion battery, and belongs to the technical field of solid electrolyte manufacturing. The raw materials of a first polymer solid electrolyte layer include 4-30 parts of a first reaction monomer A, 5-25 parts of a first reaction monomer B, a first crosslinking agent, a first photoinitiator, a first lithium salt, 1-20 parts of a carbonate plasticizer, and 20-45 parts of a nitrile plasticizer; the raw materials of a second polymer solid electrolyte layer include 4-30 parts of a second reaction monomer A, 5-25 parts of a second reaction monomer B, a second crosslinking agent, a second photoinitiator, a second lithium salt, 1-35 parts of a carbonate plasticizer, and 10-35 parts of a fluorine-containing plasticizer. The double-layer polymer solid electrolyte has the advantages of high ionic conductivity and compatibility with high-voltage battery anodes and low-voltage lithium metal cathodes, so that the corresponding battery has excellent cycle performance and high capacity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid electrolyte manufacturing, in particular to a double-layer polymer solid electrolyte, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries are selected as a green energy storage device due to their high energy density, long service life and environmental friendliness, and have successfully dominated the energy storage and power equipment market. At present, graphite is often used as the negative electrode of lithium ion batteries, which is prone to damage during charging and discharging, reducing its capacity and limiting the development of higher energy density. The high specific capacity (3860 mAh / g) of lithium metal can easily break through this barrier. However, the main use of organic solvents as electrolytes in current commercial lithium ion batteries has problems such as high toxicity, easy leakage, flammability and explosion. More importantly, it has poor compatibility with lithium metal, and a large amount of dendrites will be generated when it comes into contact with lithium metal. The growth of lithium dendrites is easy to pierce the separator and cause short circuit of the battery, which will bring serious safety problems. At the same time, the active substances in the positive electrode material will also dissolve and shuttle to the negative electrode, causing capacity decline. Therefore, using non-flammable solid electrolyte to replace liquid electrolyte is one of the important ways to solve the safety performance of lithium ion batteries, and it has become one of the important technical development directions of the next generation of batteries.

[0003] In the prior art, the research on solid electrolyte mainly includes inorganic ceramic electrolyte and organic polymer electrolyte. Both of these two kinds of solid electrolytes have relatively high low-voltage stability, and are expected to match metal lithium negative electrode. Among them, the polymer solid electrolyte has the advantages of good flexibility, good interface contact between the electrode and the interface, low interface impedance, easy processing and molding, and easy industrialization. However, the existing polymer solid electrolyte has the problems of low ionic conductivity and difficulty in matching high-voltage battery anodes and low-voltage lithium metal negative electrodes due to unreasonable design, which further affects the cycle performance and capacity of the corresponding battery. SUMMARY

[0004] The purpose of the present application is to provide a double-layer polymer solid electrolyte, a preparation method thereof and a lithium ion battery. The double-layer polymer solid electrolyte has the advantages of high ionic conductivity and compatibility with high-voltage battery anodes and low-voltage lithium metal negative electrodes, so that the corresponding battery has excellent cycle performance and high capacity.

[0005] The embodiments of the present application are implemented as follows:

[0006] In a first aspect, the embodiments of the present application provide a double-layer polymer solid-state electrolyte, comprising a first polymer solid-state electrolyte layer for contacting a positive electrode and a second polymer solid-state electrolyte layer for contacting a negative electrode, which are stacked; the raw materials of the first polymer solid-state electrolyte layer include, in terms of mass fraction, 4-30 parts of a first reaction monomer A, 5-25 parts of a first reaction monomer B, 2-10 parts of a first crosslinking agent, 0.1-1.1 parts of a first photoinitiator, 5-15 parts of a first lithium salt, 1-20 parts of a first carbonate-based plasticizer, and 20-45 parts of a nitrile-based plasticizer; the raw materials of the second polymer solid-state electrolyte layer include, in terms of mass fraction, 4-30 parts of a second reaction monomer A, 5-25 parts of a second reaction monomer B, 2-10 parts of a second crosslinking agent, 0.1-1.1 parts of a second photoinitiator, 5-15 parts of a second lithium salt, 1-35 parts of a second carbonate-based plasticizer, and 10-35 parts of a fluorine-containing plasticizer; wherein the first reaction monomer A and the second reaction monomer A are both ethoxyl-containing acrylate monomers, and the first reaction monomer B and the second reaction monomer B are both fluorinated group-containing acrylate monomers.

[0007] In the above technical solution, the polymer solid-state electrolyte has a double-layer structure, specifically, the first polymer solid-state electrolyte layer is used for contacting the positive electrode, and the raw materials for preparing the first polymer solid-state electrolyte layer are composed of specific components in specific mass fractions. On the one hand, the plasticizer is composed of a carbonate-based plasticizer and a nitrile-based plasticizer. This compound plasticizer makes the first polymer solid-state electrolyte layer have a higher electrochemical window, so that the first polymer solid-state electrolyte layer can better adapt to the high-voltage positive electrode. In addition, this compound plasticizer makes the first polymer solid-state electrolyte layer also have a higher ionic conductivity. On the other hand, the reaction monomer is composed of an ethoxyl-containing acrylate monomer and a fluorinated group-containing acrylate monomer. This compound reaction monomer also makes the first polymer solid-state electrolyte layer have a higher ionic conductivity. The second polymer solid-state electrolyte layer is used for contacting the negative electrode, and the raw materials for preparing the second polymer solid-state electrolyte layer are composed of specific components in specific mass fractions. On the one hand, the plasticizer is composed of a carbonate-based plasticizer and a fluorine-containing plasticizer. This compound plasticizer makes the second polymer solid-state electrolyte layer better adapt to the low-voltage negative electrode, and also helps the formation of the SEI film on the negative electrode side. In addition, this compound plasticizer makes the second polymer solid-state electrolyte layer also have a higher ionic conductivity. On the other hand, the reaction monomer is composed of an ethoxyl-containing acrylate monomer and a fluorinated group-containing acrylate monomer. This compound reaction monomer also makes the second polymer solid-state electrolyte layer have a higher ionic conductivity. The double-layer polymer solid-state electrolyte provided by the embodiments of the present application has the advantages of higher ionic conductivity and compatibility with the high-voltage battery positive electrode and the low-voltage lithium metal negative electrode, so that the corresponding battery has more excellent cycle performance and higher capacity.

[0008] In some optional embodiments, the nitrile plasticizer is selected from at least one of succinonitrile, adiponitrile, tetracyanoethylene, ethylene glycol bispropiononitrile ether, thio bispropiononitrile, 1,3,6-hexanetricarbonitrile, and 1,2,5-pentanetricarbonitrile.

[0009] In the above technical solution, the nitrile plasticizer applicable to the embodiments of the present application has a large variety, which can provide more implementable embodiments, thereby facilitating the popularization and application of the technical solution provided by the embodiments of the present application; in addition, the specific variety of the nitrile plasticizer can be better compounded with the carbonate plasticizer, so that the first polymer solid electrolyte layer has higher ionic conductivity and can better adapt to the positive electrode.

[0010] In some optional embodiments, the fluorine-containing plasticizer is selected from at least one of fluoroethylene carbonate, ethyl trifluoroacetate, trifluoroethyl trifluoroacetate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, fluorinated methanesulfonylimide, difluoroethane, and fluorinated malonate.

[0011] In the above technical solution, the fluorine-containing plasticizer applicable to the embodiments of the present application has a large variety, which can provide more implementable embodiments, thereby facilitating the popularization and application of the technical solution provided by the embodiments of the present application; in addition, the specific variety of the fluorine-containing plasticizer can be better compounded with the carbonate plasticizer, so that the second polymer solid electrolyte layer has higher ionic conductivity and can better adapt to the negative electrode.

[0012] In some optional embodiments, the first carbonate plasticizer and the second carbonate plasticizer are each independently selected from at least one of ethylene carbonate, vinylene carbonate, dimethyl carbonate, dipropyl carbonate, ethylene carbonate, butylene carbonate, methyl ethyl carbonate, and propylene carbonate.

[0013] In the above technical solution, the fluorine-containing plasticizer applicable to the embodiments of the present application has a large variety, which can provide more implementable embodiments, thereby facilitating the popularization and application of the technical solution provided by the embodiments of the present application.

[0014] In some optional embodiments, the first reaction monomer A and the second reaction monomer A are each independently selected from at least one of ethoxyethyl acrylate, ethoxylated tetrahydrofuran acrylate, ethoxylated trimethylol triacrylate, 3-ethoxyethyl acrylate, 2-phenoxyethyl acrylate, and 2-vinyloxyethoxy acrylate.

[0015] In the above technical solution, the reaction monomer A applicable to the embodiments of the present application has a large variety, which can provide more implementable embodiments, thereby facilitating the popularization and application of the technical solution provided by the embodiments of the present application; in addition, the specific variety of the reaction monomer A forms a polymer skeleton with higher ionic conductivity.

[0016] In some optional embodiments, the first reaction monomer B and the second reaction monomer B are each independently selected from at least one of hexafluorobutyl acrylate, tetrafluoropropyl acrylate, trifluoroethyl acrylate, dodecafluoroheptyl methacrylate, perfluoroalkyl ethyl acrylate, and N-methyl perfluorohexyl sulfonamide ester acrylate ethyl ester.

[0017] In the above technical solution, the reaction monomer B applicable to the embodiments of the present application has a large variety, which can provide more implementable embodiments, thereby facilitating the popularization and application of the technical solution provided by the embodiments of the present application; in addition, the polymer skeleton formed by the specific type of reaction monomer B has higher ionic conductivity.

[0018] In some optional embodiments, the double-layer polymer solid-state electrolyte satisfies at least one of the following conditions (1) to (3):

[0019] (1) The first crosslinking agent and the second crosslinking agent are each independently selected from at least one of diethylene glycol diacrylate, polyethylene glycol diacrylate, dipropylene glycol diacrylate, 1,6-hexanediol diacrylate, and ethoxylated bisphenol diacrylate.

[0020] (2) The first photoinitiator and the second photoinitiator are each independently selected from at least one of 2,2-dimethoxy-phenyl phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2,4,6-trimethylbenzoyl chloride-diphenyl phosphine oxide, 2,2-dimethoxy-phenyl phenylacetophenone, and 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0021] (3) The first lithium salt and the second lithium salt are each independently selected from at least one of lithium bistrifluoromethylsulfonylimide, lithium trifluoromethylsulfonate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorobisoxalate borate, and lithium bisdifluorosulfonylimide.

[0022] In the above technical solution, the crosslinking agent, the photoinitiator, and the lithium salt applicable to the embodiments of the present application each have a large variety, which can provide more implementable embodiments, thereby facilitating the popularization and application of the technical solution provided by the embodiments of the present application.

[0023] In a second aspect, the embodiments of the present application provide a preparation method of the double-layer polymer solid-state electrolyte provided in the first aspect, including the following steps:

[0024] The first reaction monomer A, the first reaction monomer B, the first lithium salt and a part of the first photoinitiator are mixed to obtain a first mixed solution; the first mixed solution is placed under ultraviolet light for reaction to obtain a first polymer matrix; the first polymer matrix, the first crosslinking agent, another part of the first photoinitiator, the first carbonate plasticizer and the nitrile plasticizer are mixed to obtain a first polymer solid electrolyte slurry; the first polymer solid electrolyte slurry is placed under violet light for curing to obtain a first polymer solid electrolyte layer. The second reaction monomer A, the second reaction monomer B, the second lithium salt and a part of the second photoinitiator are mixed to obtain a second mixed solution; the second mixed solution is placed under ultraviolet light for reaction to obtain a second polymer matrix; the second polymer matrix, the second crosslinking agent, another part of the second photoinitiator, the second carbonate plasticizer and the fluorine-containing plasticizer are mixed to obtain a second polymer solid electrolyte slurry; the second polymer solid electrolyte slurry is applied to the surface of the first polymer solid electrolyte layer and placed under violet light for curing to obtain a double-layer polymer solid electrolyte layer.

[0025] Alternatively, the second reaction monomer A, the second reaction monomer B, the second lithium salt and a part of the second photoinitiator are mixed to obtain a second mixed solution; the second mixed solution is placed under ultraviolet light for reaction to obtain a second polymer matrix; the second polymer matrix, the second crosslinking agent, another part of the second photoinitiator, the second carbonate plasticizer and the fluorine-containing plasticizer are mixed to obtain a second polymer solid electrolyte slurry; the second polymer solid electrolyte slurry is placed under violet light for curing to obtain a second polymer solid electrolyte layer. The first reaction monomer A, the first reaction monomer B, the first lithium salt and a part of the first photoinitiator are mixed to obtain a first mixed solution; the first mixed solution is placed under ultraviolet light for reaction to obtain a first polymer matrix; the first polymer matrix, the first crosslinking agent, another part of the first photoinitiator, the first carbonate plasticizer and the nitrile plasticizer are mixed to obtain a first polymer solid electrolyte slurry; the first polymer solid electrolyte slurry is applied to the surface of the second polymer solid electrolyte layer and placed under violet light for curing to obtain a double-layer polymer solid electrolyte layer.

[0026] In the above technical solution, the double-layer polymer solid electrolyte is prepared by the ultraviolet light curing method, which does not use volatile solvents, has the advantages of safety and environmental protection, and also has the advantages of low preparation cost and high preparation efficiency; in addition, there are many specific process forms (the first polymer solid electrolyte layer can be prepared first, or the second polymer solid electrolyte layer can be prepared first), which can provide more implementable ways.

[0027] In some alternative embodiments, the step of placing the first mixed solution under ultraviolet light for reaction is performed until the viscosity of the first mixed solution is 10000-15000 mPa.s; and / or, the step of placing the second mixed solution under ultraviolet light for reaction is performed until the viscosity of the second mixed solution is 10000-15000 mPa.s.

[0028] In the above technical solution, the mixed solution is cured and reacted under ultraviolet light until the viscosity of the mixed solution reaches the set range, so that the prepared corresponding polymer solid electrolyte layer has a relatively ideal ionic conductivity.

[0029] In a third aspect, the embodiments of the present application provide a lithium ion battery comprising the double-layer polymer solid electrolyte provided in the first aspect, wherein the first polymer solid electrolyte layer is in contact with the positive electrode of the battery, and the second polymer solid electrolyte layer is in contact with the negative electrode of the battery.

[0030] In the above technical solution, the lithium ion battery comprises the double-layer polymer solid electrolyte provided in the first aspect, wherein the double-layer polymer solid electrolyte has a relatively high ionic conductivity and can be compatible with the high-voltage battery positive electrode and the low-voltage lithium metal negative electrode, so that the battery has a relatively excellent cycle performance and a relatively high capacity. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0032] Figure 1 A structural schematic diagram of a double-layer polymer solid electrolyte provided in the embodiments of the present application.

[0033] Figure legend: 10-double-layer polymer solid electrolyte; 100-first polymer solid electrolyte layer; 200-second polymer solid electrolyte layer. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely. In the embodiments, the specific conditions not noted are performed according to the conventional conditions or the conditions suggested by the manufacturers. The reagents or instruments not noted by the manufacturers are all conventional products that can be obtained by market purchase.

[0035] It should be noted that "and / or" in the present application, such as "feature 1 and / or feature 2", means that it can be "feature 1" alone, "feature 2" alone, or "feature 1" plus "feature 2".

[0036] In addition, in the description of the present application, unless otherwise specified, the meaning of "multiple" in "one or more" is two or more; The range of "value a ~ value b" includes both end values "a" and "b", and "unit of measurement" in "value a ~ value b + unit of measurement" represents the "unit of measurement" of both "value a" and "value b".

[0037] The following will specifically describe a double-layer polymer solid electrolyte and a preparation method thereof according to an embodiment of the present application.

[0038] In a first aspect, the embodiment of the present application provides a double-layer polymer solid electrolyte, which comprises a first polymer solid electrolyte layer for contacting a positive electrode and a second polymer solid electrolyte layer for contacting a negative electrode in a stacked distribution; according to mass fraction, raw materials of the first polymer solid electrolyte layer include: 4-30 parts of a first reaction monomer A, 5-25 parts of a first reaction monomer B, 2-10 parts of a first crosslinking agent, 0.1-1.1 parts of a first photoinitiator, 5-15 parts of a first lithium salt, 1-20 parts of a first carbonate plasticizer, and 20-45 parts of a nitrile plasticizer; according to mass fraction, raw materials of the second polymer solid electrolyte layer include: 4-30 parts of a second reaction monomer A, 5-25 parts of a second reaction monomer B, 2-10 parts of a second crosslinking agent, 0.1-1.1 parts of a second photoinitiator, 5-15 parts of a second lithium salt, 1-35 parts of a second carbonate plasticizer, and 10-35 parts of a fluorine-containing plasticizer; wherein the first reaction monomer A and the second reaction monomer A are both ethoxy-containing acrylate monomers, and the first reaction monomer B and the second reaction monomer B are both fluorinated group-containing acrylate monomers.

[0039] In the present application, the polymer solid-state electrolyte has a double-layer structure. Specifically, the first polymer solid-state electrolyte layer is used to contact the positive electrode, and the raw materials for preparing the first polymer solid-state electrolyte layer are composed of specific components in specific mass fractions. On the one hand, the plasticizer is composed of a carbonate plasticizer and a nitrile plasticizer. Such a plasticizer makes the first polymer solid-state electrolyte layer have a higher electrochemical window, so that the first polymer solid-state electrolyte layer can better adapt to the high-voltage positive electrode. In addition, such a plasticizer makes the first polymer solid-state electrolyte layer also have a higher ionic conductivity. On the other hand, the reaction monomer is composed of an ethoxy-containing acrylate monomer and a fluorinated acrylate monomer. Such a reaction monomer also makes the first polymer solid-state electrolyte layer have a higher ionic conductivity. The second polymer solid-state electrolyte layer is used to contact the negative electrode, and the raw materials for preparing the second polymer solid-state electrolyte layer are composed of specific components in specific mass fractions. On the one hand, the plasticizer is composed of a carbonate plasticizer and a fluorine-containing plasticizer. Such a plasticizer makes the second polymer solid-state electrolyte layer better adapt to the low-voltage negative electrode, and also helps the formation of the SEI film on the negative electrode side. In addition, such a plasticizer makes the second polymer solid-state electrolyte layer also have a higher ionic conductivity. On the other hand, the reaction monomer is composed of an ethoxy-containing acrylate monomer and a fluorinated acrylate monomer. Such a reaction monomer also makes the second polymer solid-state electrolyte layer have a higher ionic conductivity. The double-layer polymer solid-state electrolyte provided in the present application has the advantages of higher ionic conductivity and compatibility with the high-voltage battery positive electrode and the low-voltage lithium metal negative electrode, so that the corresponding battery has excellent cycle performance and higher capacity.

[0040] It should be emphasized that there are few related researches on the double-layer polymer solid-state electrolyte, and in the part of the related information that has been disclosed, the conventional optimization method mainly uses different types of polymers for the high-voltage positive electrode and the low-voltage negative electrode to be compatible with the high-voltage positive electrode and the low-voltage negative electrode. There is no related report on optimizing the plasticizer to be compatible with the high-voltage positive electrode and the low-voltage negative electrode. Further, it is more difficult to know how to use the specific plasticizer to be compatible with the high-voltage positive electrode and the low-voltage negative electrode.

[0041] It should be noted that the types of the raw materials in the polymer solid-state electrolyte layer are not limited.

[0042] As an example, the nitrile plasticizer is selected from at least one of butanedinitrile, hexanedinitrile, tetracyanoethylene, ethylene glycol bispropionitrile ether, sulfuryl dinitrile, 1,3,6-hexanetristrile, and 1,2,5-pentanetristrile.

[0043] In this embodiment, the nitrile plasticizer applicable to the embodiments of the present application is of a large variety, which can provide more implementable schemes, thereby facilitating the popularization and application of the technical solutions provided by the embodiments of the present application; in addition, the specific variety of the nitrile plasticizer can be better compounded with the carbonate plasticizer, so that the first polymer solid electrolyte layer has a higher ionic conductivity and can be better adapted to the positive electrode.

[0044] As an example, the fluorine-containing plasticizer is selected from at least one of fluoroethylene carbonate, ethyl trifluoroacetate, trifluoroethyl trifluoroacetate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, fluorinated methanesulfonylimide, difluoroethane and fluorinated malonate.

[0045] In this embodiment, the fluorine-containing plasticizer applicable to the embodiments of the present application is of a large variety, which can provide more implementable schemes, thereby facilitating the popularization and application of the technical solutions provided by the embodiments of the present application; in addition, the specific variety of the fluorine-containing plasticizer can be better compounded with the carbonate plasticizer, so that the second polymer solid electrolyte layer has a higher ionic conductivity and can be better adapted to the negative electrode.

[0046] As an example, the first carbonate plasticizer and the second carbonate plasticizer are each independently selected from at least one of ethylene carbonate, vinylene carbonate, dimethyl carbonate, dipropyl carbonate, ethylene carbonate, butylene carbonate, methyl ethyl carbonate and propylene carbonate.

[0047] In this embodiment, the fluorine-containing plasticizer applicable to the embodiments of the present application is of a large variety, which can provide more implementable schemes, thereby facilitating the popularization and application of the technical solutions provided by the embodiments of the present application.

[0048] As an example, the first reaction monomer A and the second reaction monomer A are each independently selected from at least one of ethoxyethyl acrylate, ethoxylated tetrahydrofuran acrylate, ethoxylated trimethylol triacrylate, 3-ethoxyethyl acrylate, 2-phenoxyethyl acrylate and 2-vinyloxyethoxy acrylate.

[0049] In this embodiment, the reaction monomer A applicable to the embodiments of the present application is of a large variety, which can provide more implementable schemes, thereby facilitating the popularization and application of the technical solutions provided by the embodiments of the present application; in addition, the specific variety of the reaction monomer A forms a polymer skeleton with a higher ionic conductivity.

[0050] As an example, the first reaction monomer B and the second reaction monomer B are each independently selected from at least one of butyl hexafluoroacrylate, propyl tetrafluoroacrylate, ethyl trifluoroacrylate, dodecylfluoroheptyl methacrylate, perfluoroalkyl ethyl acrylate and N-methyl perfluoro hexyl sulfonamide ester acrylate.

[0051] In this embodiment, the reaction monomer B applicable to the embodiments of the present application has a large variety, which can provide more implementable schemes, thereby facilitating the popularization and application of the technical solutions provided by the embodiments of the present application; in addition, the polymer skeleton formed by the specific type of reaction monomer B has higher ionic conductivity.

[0052] As an example, the double-layer polymer solid electrolyte satisfies at least one of the following conditions (1) to (3):

[0053] (1) The first crosslinking agent and the second crosslinking agent are each independently selected from at least one of diethylene glycol diacrylate, polyethylene glycol diacrylate, dipropylene glycol diacrylate, 1,6-hexanediol diacrylate, and ethoxylated bisphenol diacrylate.

[0054] (2) The first photoinitiator and the second photoinitiator are each independently selected from at least one of 2,2-dimethoxy-phenylphenylmethanone, 1-hydroxycyclohexyl phenyl ketone, 2,4,6-trimethylbenzoyl chloride-diphenyl phosphine oxide, 2,2-dimethoxy-phenylphenylmethanone, and 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0055] (3) The first lithium salt and the second lithium salt are each independently selected from at least one of lithium bistrifluoromethylsulfonylimide, lithium trifluoromethylsulfonate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate oxalate borate, and lithium bisdifluorosulfonylimide.

[0056] In this embodiment, the crosslinking agent, the photoinitiator, and the lithium salt applicable to the embodiments of the present application have a large variety, which can provide more implementable schemes, thereby facilitating the popularization and application of the technical solutions provided by the embodiments of the present application.

[0057] As an example, the thickness ratio of the first polymer solid electrolyte layer and the second polymer solid electrolyte layer is 1:(0.9-1.1), for example, but not limited to, the thickness ratio of the two is any one point value or a range value between any two of 1:0.9, 1:1, and 1:1.

[0058] In this embodiment, the thickness of the two polymer solid electrolyte layers is set to be substantially the same, which can better adapt to the high-voltage positive electrode and the low-voltage negative electrode.

[0059] It should be noted that the components and their mass fraction ratios in the double-layer polymer solid electrolyte which are not specifically mentioned or limited can be set according to conventional selection in the art.

[0060] Referring to Figure 1 As an example, the double-layer polymer solid electrolyte 10 includes a first polymer solid electrolyte layer 100 and a second polymer solid electrolyte layer 200 which are stacked and distributed.

[0061] In a second aspect, the embodiments of the present application provide a preparation method of the double-layer polymer solid electrolyte provided in the first aspect, comprising the following steps:

[0062] mixing the first reaction monomer A, the first reaction monomer B, the first lithium salt and a part of the first photoinitiator to obtain a first mixed solution; placing the first mixed solution under ultraviolet light to react, to obtain a first polymer matrix; mixing the first polymer matrix, the first crosslinking agent, another part of the first photoinitiator, the first carbonate-based plasticizer and the nitrile-based plasticizer to obtain a first polymer solid electrolyte slurry; placing the first polymer solid electrolyte slurry under ultraviolet light to solidify, to obtain the first polymer solid electrolyte layer.

[0063] It should be noted that the sum of the masses of the two parts of the first photoinitiator is equal to the mass of the first photoinitiator in the raw material of the first polymer solid electrolyte layer.

[0064] mixing the second reaction monomer A, the second reaction monomer B, the second lithium salt and a part of the second photoinitiator to obtain a second mixed solution; placing the second mixed solution under ultraviolet light to react, to obtain a second polymer matrix; mixing the second polymer matrix, the second crosslinking agent, another part of the second photoinitiator, the second carbonate-based plasticizer and the fluorine-containing plasticizer to obtain a second polymer solid electrolyte slurry; applying the second polymer solid electrolyte slurry to the surface of the first polymer solid electrolyte layer and placing it under ultraviolet light to solidify, to obtain the double-layer polymer solid electrolyte layer.

[0065] It should be noted that the sum of the masses of the two parts of the second photoinitiator is equal to the mass of the first photoinitiator in the raw material of the second polymer solid electrolyte layer.

[0066] In other possible embodiments, the preparation method can further comprise the following steps:

[0067] mixing the second reaction monomer A, the second reaction monomer B, the second lithium salt and a part of the second photoinitiator to obtain a second mixed solution; placing the second mixed solution under ultraviolet light to react, to obtain a second polymer matrix; mixing the second polymer matrix, the second crosslinking agent, another part of the second photoinitiator, the second carbonate-based plasticizer and the fluorine-containing plasticizer to obtain a second polymer solid electrolyte slurry; placing the second polymer solid electrolyte slurry under ultraviolet light to solidify, to obtain the second polymer solid electrolyte layer.

[0068] The first reaction monomer A, the first reaction monomer B, the first lithium salt and a part of the first photoinitiator are mixed to obtain a first mixed solution; the first mixed solution is placed under ultraviolet light for reaction to obtain a first polymer matrix; the first polymer matrix, the first crosslinking agent, another part of the first photoinitiator, the first carbonate plasticizer and the nitrile plasticizer are mixed to obtain a first polymer solid electrolyte slurry; the first polymer solid electrolyte slurry is applied to the surface of the second polymer solid electrolyte layer and is placed under ultraviolet light for curing to obtain a double-layer polymer solid electrolyte layer.

[0069] In the present application, the double-layer polymer solid electrolyte is prepared by the ultraviolet curing method, which does not use volatile solvents, has the advantages of safety and environmental protection, and also has the advantages of low preparation cost and high preparation efficiency; in addition, there are many specific process forms (i.e., the first polymer solid electrolyte layer can be prepared first, or the second polymer solid electrolyte layer can be prepared first), which can provide more implementable ways (the present application embodiment is described by taking the first polymer solid electrolyte layer as an example).

[0070] It should be noted that when the raw materials of the first polymer solid electrolyte layer and the raw materials of the second polymer solid electrolyte layer are different only in the plasticizer, the first polymer matrix and the second polymer matrix formed are completely the same, then the polymer matrix can be prepared by one-step method, and then the polymer matrix is divided into two parts, i.e., the first polymer matrix and the second polymer matrix are prepared synchronously by one-step method; when the raw materials of the first polymer solid electrolyte layer and the raw materials of the second polymer solid electrolyte layer are different in multiple aspects, the first polymer matrix and the second polymer matrix are prepared separately, and the specific preparation method can be adjusted according to actual needs.

[0071] It should be noted that when the first polymer matrix and the second polymer matrix are prepared by a step-by-step method, the first polymer matrix can be prepared first, the second polymer matrix can be prepared first, or the first polymer matrix and the second polymer matrix can be prepared synchronously.

[0072] It should be noted that the method of "applying the first polymer solid electrolyte slurry to the surface of the second polymer solid electrolyte layer and placing it under ultraviolet light for curing to obtain the first polymer solid electrolyte layer" is not limited, for example, the first polymer solid electrolyte slurry can be transferred to a mold, and then cured under ultraviolet light to obtain the first polymer solid electrolyte layer; or the first polymer solid electrolyte slurry can be coated on a substrate, and then cured under ultraviolet light to obtain the first polymer solid electrolyte layer, and then the substrate is removed.

[0073] As an example, in the step of placing the first mixed solution under ultraviolet light for reaction, the viscosity of the first mixed solution is 10000-15000 mPa.s, for example but not limited to any one of the point values of 10000 mPa.s, 11000 mPa.s, 12000 mPa.s, 13000 mPa.s, 14000 mPa.s and 15000 mPa.s or a range value between any two of them; and / or, in the step of placing the second mixed solution under ultraviolet light for reaction, the viscosity of the second mixed solution is 10000-15000 mPa.s, for example but not limited to any one of the point values of 10000 mPa.s, 11000 mPa.s, 12000 mPa.s, 13000 mPa.s, 14000 mPa.s and 15000 mPa.s or a range value between any two of them.

[0074] In this embodiment, during the process of curing reaction of the mixed solution under ultraviolet light, the viscosity of the mixed solution reaches a set range, so that the prepared corresponding polymer solid electrolyte layer has a relatively ideal ionic conductivity.

[0075] It should be noted that the steps not specially described in the process of preparing the double-layer polymer solid electrolyte by the ultraviolet curing method can be set according to the conventional selection in the art.

[0076] As an example, the wavelength of the ultraviolet light is 300-400 nm, for example but not limited to any one of the point values of 300 nm, 320 nm, 340 nm, 360 nm, 380 nm and 400 nm or a range value between any two of them.

[0077] In a third aspect, the embodiments of the present application provide a lithium ion battery comprising the double-layer polymer solid electrolyte provided in the first aspect, wherein the first polymer solid electrolyte layer is in contact with the positive electrode of the battery, and the second polymer solid electrolyte layer is in contact with the negative electrode of the battery.

[0078] In the present application, the lithium ion battery comprises the double-layer polymer solid electrolyte provided in the first aspect, wherein the double-layer polymer solid electrolyte has a relatively high ionic conductivity and can be compatible with the high-voltage battery positive electrode and the low-voltage lithium metal negative electrode, so that the battery has a relatively excellent cycle performance and a relatively high capacity.

[0079] The features and performances of the present application are further described in detail below in combination with embodiments, wherein the raw materials of the first polymer solid electrolyte layer and the raw materials of the second polymer solid electrolyte layer are only different in the type of plasticizer, the types and amounts of the remaining functional components are the same, and the first polymer matrix and the second polymer matrix are prepared synchronously by one-step method.

[0080] Example 1

[0081] The embodiment of the present application provides a preparation method of a double-layer polymer solid electrolyte, comprising the following steps:

[0082] S1, 37.5 parts of ethoxyethyl acrylate (reaction monomer A), 37.5 parts of hexafluorobutyl propiolate (reaction monomer B), 22.5 parts of lithium bistrifluoromethanesulfonimide (lithium salt), 2.25 parts of lithium difluoro(oxalato)borate (lithium salt) and 0.25 parts of 1-hydroxycyclohexyl phenyl ketone (photoinitiator) are uniformly mixed to form a uniform liquid, the prepared uniform liquid is placed under a 350nm ultraviolet light for reaction, the liquid viscosity is raised to 12000mPa.s, the ultraviolet light is turned off, and continuous stirring is carried out until the temperature is room temperature, so that a polymer matrix (i.e. a first polymer matrix and a second polymer matrix) is obtained.

[0083] S2, the first polymer solid electrolyte slurry is uniformly mixed by using half of the polymer matrix, 3 parts of polyethylene glycol diacrylate (crosslinking agent), 0.5 parts of 2,2-dimethoxy-phenyl phenylacetophenone (photoinitiator), 33.5 parts of butanedinitrile (nitrile plasticizer) and 8 parts of propylene carbonate (acid ester plasticizer), then the first polymer solid electrolyte slurry is coated on PET and cured under 350nm ultraviolet light, so that a first polymer solid electrolyte layer is obtained.

[0084] S3, the second polymer solid electrolyte slurry is uniformly mixed by using the other half of the polymer matrix, 2.9 parts of polyethylene glycol diacrylate (crosslinking agent), 0.4 parts of 2,2-dimethoxy-phenyl phenylacetophenone (photoinitiator), 16.3 parts of fluoroethylene carbonate (fluorine-containing plasticizer) and 24.4 parts of propylene carbonate (acid ester plasticizer), then the second polymer solid electrolyte slurry is coated on the first polymer solid electrolyte layer and cured under 350nm ultraviolet light, and then the PFT substrate is removed, so that a double-layer polymer solid electrolyte layer is obtained.

[0085] Example 2

[0086] The embodiment of the present application provides a preparation method of a double-layer polymer solid electrolyte, comprising the following steps:

[0087] S1, 46 parts of ethoxyethyl acrylate (reaction monomer A), 30.7 parts of hexafluorobutyl propiolate (reaction monomer B), 23.2 parts of lithium bistrifluoromethanesulfonimide (lithium salt) and 0.1 parts of 1-hydroxycyclohexyl phenyl ketone (photoinitiator) are uniformly mixed to form a uniform liquid, the prepared uniform liquid is placed under a 350nm ultraviolet light for reaction, the liquid viscosity is raised to 12000mPa.s, the ultraviolet light is turned off, and continuous stirring is carried out until the temperature is room temperature, so that a polymer matrix (i.e. a first polymer matrix and a second polymer matrix) is obtained.

[0088] S2mixing half of the polymer matrix, 3 parts of polyethylene glycol diacrylate (crosslinking agent), 0.5 parts of 2,2-dimethoxy-phenyl phenylacetophenone (photoinitiator), 25 parts of succinonitrile (nitrile plasticizer) and 16.5 parts of propylene carbonate (acid ester plasticizer) to obtain a first polymer solid electrolyte slurry, then coating on PET and curing under 350 nm ultraviolet light, to obtain a first polymer solid electrolyte layer.

[0089] S3mixing the other half of the polymer matrix, 3 parts of polyethylene glycol diacrylate (crosslinking agent), 0.5 parts of 2,2-dimethoxy-phenyl phenylacetophenone (photoinitiator), 12.5 parts of fluoroethylene carbonate (fluorine-containing plasticizer) and 29 parts of propylene carbonate (acid ester plasticizer) to obtain a second polymer solid electrolyte slurry, then coating on the first polymer solid electrolyte layer and curing under 350 nm ultraviolet light, and then removing the PFT substrate, to obtain a double-layer polymer solid electrolyte layer.

[0090] Example 3

[0091] The embodiment of the present application provides a preparation method of a double-layer polymer solid electrolyte, comprising the following steps:

[0092] S1mixing 37.5 parts of ethoxyethyl acrylate (reaction monomer A), 37.5 parts of hexafluorobutyl propiolate (reaction monomer B), 22.5 parts of lithium bis-trifluoromethanesulfonimide (lithium salt), 2.25 parts of lithium difluoro(oxalato)borate (lithium salt) and 0.25 parts of 1-hydroxycyclohexyl phenyl ketone (photoinitiator) to obtain a uniform liquid, and then placing the obtained uniform liquid under a 350 nm ultraviolet light to react, until the viscosity of the liquid rises to 12000 mPa.s, then turning off the ultraviolet light and continuously stirring until the temperature is room temperature, to obtain a polymer matrix (i.e. a first polymer matrix and a second polymer matrix).

[0093] S2mixing half of the polymer matrix, 2.6 parts of polyethylene glycol diacrylate (crosslinking agent), 0.4 parts of 2,2-dimethoxy-phenyl phenylacetophenone (photoinitiator), 40 parts of succinonitrile (nitrile plasticizer) and 4 parts of propylene carbonate (acid ester plasticizer) to obtain a first polymer solid electrolyte slurry, then coating on PET and curing under 350 nm ultraviolet light, to obtain a first polymer solid electrolyte layer.

[0094] S3 mixed the other half of the polymer matrix, 3 parts of polyethylene glycol diacrylate (crosslinking agent), 0.5 parts of 2,2-dimethoxy-phenyl phenylacetophenone (photoinitiator), 20.75 parts of fluoroethylene carbonate (fluorine-containing plasticizer) and 20.75 parts of propylene carbonate (acid ester plasticizer) uniformly to obtain a second polymer solid electrolyte slurry, which was then coated on the first polymer solid electrolyte layer and cured under 350 nm ultraviolet light, and then the PFT substrate was removed to obtain a double-layer polymer solid electrolyte layer.

[0095] Comparative Example 1

[0096] The present application provides a preparation method of a double-layer polymer solid electrolyte, which is only different from Example 1 in that the butanedinitrile (nitrile plasticizer) is completely replaced by propylene carbonate (acid ester plasticizer).

[0097] Comparative Example 2

[0098] The present application provides a preparation method of a double-layer polymer solid electrolyte, which is only different from Example 1 in that the butanedinitrile (nitrile plasticizer) is completely replaced by propylene carbonate (acid ester plasticizer).

[0099] Comparative Example 3

[0100] The present application provides a preparation method of a double-layer polymer solid electrolyte, which is only different from Example 1 in that the fluoroethylene carbonate (fluorine-containing plasticizer) is completely replaced by propylene carbonate (acid ester plasticizer).

[0101] Comparative Example 4

[0102] The present application provides a preparation method of a double-layer polymer solid electrolyte, which is only different from Example 1 in that the fluoroethylene carbonate (fluorine-containing plasticizer) is completely replaced by propylene carbonate (acid ester plasticizer).

[0103] Comparative Example 5

[0104] The present application provides a preparation method of a double-layer polymer solid electrolyte, which is only different from Example 1 in that the butanedinitrile (nitrile plasticizer) is completely replaced by propylene carbonate (acid ester plasticizer).

[0105] Comparative Example 6

[0106] The present application provides a preparation method of a double-layer polymer solid electrolyte, which is only different from Example 1 in that the butanedinitrile (nitrile plasticizer) is completely replaced by propylene carbonate (acid ester plasticizer).

[0107] Test Example

[0108] Material ion conductivity test

[0109] Test method:

[0110] The polymer electrolytes prepared in Examples 1-3 and Comparative Examples 1-6 were assembled into devices and tested for ionic conductivity. Specifically, the polymer electrolytes prepared in Examples 1-3 and Comparative Examples 1-6 were placed between two pieces of stainless steel in an argon-protected glove box, and then assembled into a test device in a coin cell shell, and the test conditions were: a test temperature of 25°C, a scan rate of 1 mV / s, and a frequency range of 1 Hz-1 MHz, and the test results are shown in Table 1.

[0111] Electrochemical window test of the material

[0112] Test method:

[0113] The polymer electrolytes prepared in Examples 1-3 and Comparative Examples 1-6 were assembled into devices and tested for electrochemical window. Specifically, the polymer electrolytes prepared in Examples 1-3 and Comparative Examples 1-6 were placed between stainless steel and lithium sheet in an argon-protected glove box, wherein the first polymer solid-state electrolyte layer was in contact with the stainless steel and the second polymer solid-state electrolyte layer was in contact with the lithium sheet, and then assembled into a test device in a coin cell shell, and the test conditions were: a scan rate of 1 mV / s, and a test voltage range of 2-6 V, and the test results are shown in Table 1.

[0114] Electrical performance test of the battery

[0115] Test method:

[0116] The polymer electrolytes prepared in Examples 1-3 and Comparative Examples 1-6 were assembled into devices and tested for discharge specific capacity and cycle performance. Specifically:

[0117] S1 LiFePO4 (positive active material), conductive carbon black (conductive agent), and polyvinylidene fluoride (binder) were mixed in a mass ratio of 80:10:10, dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry; then, the positive electrode slurry was uniformly coated on both sides of an aluminum foil; then, the material was sequentially subjected to drying, calendering, and vacuum drying, and the dried material was cut into a circular sheet with a diameter of 16 mm using a sheet cutter to obtain a positive electrode sheet.

[0118] S2 Graphite (negative active material), conductive carbon black (conductive agent), and carboxymethyl cellulose (binder) were mixed in a mass ratio of 90:5:5, dispersed in deionized water to obtain a negative electrode slurry; then, the negative electrode slurry was uniformly coated on one side of a carbon-coated copper foil; then, the material was sequentially subjected to drying, calendering, and vacuum drying, and the dried material was cut into a circular sheet with a diameter of 16 mm using a sheet cutter to obtain a negative electrode sheet.

[0119] S3 will be prepared to obtain the positive electrode sheet, negative electrode sheet and the polymer solid electrolyte layer prepared by the preparation process of examples 1-3 and comparative examples 1-6 are stacked in turn, wherein the first polymer solid electrolyte layer is in contact with the positive electrode of the battery, and the second polymer solid electrolyte layer is in contact with the negative electrode of the battery, then the stacked battery is assembled in the battery shell, and the capacity test is carried out, and the battery is obtained.

[0120] The test steps of related electrical properties are as follows:

[0121] (1) Discharge specific capacity test

[0122] At 60℃, the battery is charged to 3.8V at 2C constant current, then rested for 5 minutes, and then discharged to 2.5V at 2C constant current, which is one charge-discharge cycle. The discharge specific capacity of this time is recorded as the discharge specific capacity of the first cycle of the battery.

[0123] (2) Capacity retention rate test of battery after 200 cycles at 60℃:

[0124] At 60℃, the battery is first charged to 3.8V at 1C constant current, and then discharged to 2.5V at 1C constant current, which is one charge-discharge cycle. The discharge specific capacity of this time is the discharge specific capacity of the first cycle. The battery is tested by multiple cycles of charge-discharge in the above manner, and the discharge specific capacity of the 200th cycle is detected, and the capacity retention rate of the battery after cycling is calculated by the following formula. The capacity retention rate of the battery after 200 cycles (%) = [the discharge specific capacity of the 200th cycle / the discharge specific capacity of the first cycle] x 100%.

[0125] Table 1

[0126]

[0127] Referring to Table 1, according to the test results of examples 1-3 and comparative examples 1-6, the preparation of the polymer solid electrolyte layer is prepared according to the preparation process provided in the examples, and the polymer solid electrolyte layer prepared has high ion conductivity and high electrochemical window, so that the prepared battery has excellent discharge specific capacity and capacity retention rate.

[0128] According to the test results of examples 1 and comparative examples 1-2, when the complex system of nitrile plasticizer and carbonate plasticizer is used as the plasticizer in the first polymer solid electrolyte, compared with the plasticizer without nitrile plasticizer, the polymer solid electrolyte layer corresponding to the former has high ion conductivity and high electrochemical window, so that the prepared battery has excellent discharge specific capacity and capacity retention rate.

[0129] From the test results of Example 1 and Comparative Examples 3-4, when the compounding system of the fluorine-containing plasticizer and the carbonate plasticizer is used as the plasticizer in the second polymer solid electrolyte, the polymer solid electrolyte layer corresponding to the former has higher ionic conductivity and higher electrochemical window, so that the battery prepared has more excellent discharge specific capacity and capacity retention.

[0130] From the test results of Example 1 and Comparative Examples 5-6, when the compounding system of the ethoxyl-containing acrylate monomer and the fluorinated group-containing acrylate monomer is used as the reaction monomer, the polymer solid electrolyte layer corresponding to the former has higher ionic conductivity, so that the battery prepared has more excellent discharge specific capacity and capacity retention.

[0131] The above-described examples are part of the embodiments of the present application, rather than all the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present application.

Claims

1. A lithium-ion battery, characterized by, The double-layer polymer solid-state electrolyte includes a first polymer solid-state electrolyte layer for contact with a positive electrode and a second polymer solid-state electrolyte layer for contact with a negative electrode, which are stacked and distributed; The raw materials of the first polymer solid-state electrolyte layer include, in terms of mass fraction, 4-30 parts of a first reaction monomer A, 5-25 parts of a first reaction monomer B, 2-10 parts of a first crosslinking agent, 0.1-1.1 parts of a first photoinitiator, 5-15 parts of a first lithium salt, 1-20 parts of a first carbonate-based plasticizer, and 20-45 parts of a nitrile-based plasticizer; The raw materials of the second polymer solid-state electrolyte layer include, in terms of mass fraction, 4-30 parts of a second reaction monomer A, 5-25 parts of a second reaction monomer B, 2-10 parts of a second crosslinking agent, 0.1-1.1 parts of a second photoinitiator, 5-15 parts of a second lithium salt, 1-35 parts of a second carbonate-based plasticizer, and 10-35 parts of a fluorine-containing plasticizer; The first reaction monomer A and the second reaction monomer A are both ethoxyl-containing acrylate monomers, and the first reaction monomer B and the second reaction monomer B are both fluorinated group-containing acrylate monomers. The nitrile-based plasticizer is selected from at least one of butanedinitrile, hexanedinitrile, tetracyanoethylene, ethylene glycol bispropionitrile ether, sulfuryl dithiopropionitrile, 1,3,6-hexanetristitnitrile, and 1,2,5-pentanetristitnitrile. The fluorine-containing plasticizer is selected from at least one of fluoroethylene carbonate, ethyl trifluoroacetate, trifluoroethyl trifluoroacetate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, fluorinated methanesulfonylimide, difluoroethane, and fluorinated malonate. The first polymer solid-state electrolyte layer is in contact with a battery positive electrode, and the second polymer solid-state electrolyte layer is in contact with a battery negative electrode.

2. The lithium-ion battery of claim 1, wherein, The first carbonate-based plasticizer and the second carbonate-based plasticizer are both independently selected from at least one of ethylene carbonate, vinylene carbonate, dimethyl carbonate, dipropyl carbonate, ethylene carbonate, butylene carbonate, methyl ethyl carbonate, and propylene carbonate.

3. The lithium-ion battery of claim 1, wherein, The first reaction monomer A and the second reaction monomer A are both independently selected from at least one of ethoxyethyl acrylate, ethoxylated tetrahydrofuran acrylate, ethoxylated trimethylol triacrylate, 3-ethoxy acrylate, 2-phenoxyethyl acrylate, and 2-vinyloxy ethoxy acrylate.

4. The lithium-ion battery of claim 1, wherein, The first reaction monomer B and the second reaction monomer B are both independently selected from at least one of hexafluorobutyl acrylate, tetrafluoropropyl acrylate, trifluoroethyl acrylate, methyl dodecafluoroheptyl acrylate, perfluoroalkyl ethyl acrylate, and N-methyl perfluorohexyl sulfonamide ester acrylate.

5. The lithium-ion battery of claim 1, wherein, At least one of the following conditions (1)-(3) is satisfied: The first crosslinking agent and the second crosslinking agent are both independently selected from at least one of diethylene glycol diacrylate, polyethylene glycol diacrylate, dipropylene glycol diacrylate, 1,6-hexanediol diacrylate, and ethoxylated bisphenol diacrylate. (2) the first photoinitiator and the second photoinitiator are each independently selected from at least one of 2,2-dimethoxy-phenylphenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2,4,6-trimethylbenzoyl chloride-diphenyl phosphine oxide, 2,2-dimethoxy-phenylphenylacetophenone and 2-hydroxy-2-methyl-1-phenyl-1-propanone; (3) the first lithium salt and the second lithium salt are each independently selected from at least one of lithium bistrifluoromethylsulfonylimide, lithium triflate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate and lithium bishydrodifluorosulfonylimide.

6. The lithium-ion battery of any one of claims 1 to 5, characterized in that The preparation method of the double-layer polymer solid-state electrolyte comprises the following steps: mixing the first reaction monomer A, the first reaction monomer B, the first lithium salt and a part of the first photoinitiator to obtain a first mixed solution; placing the first mixed solution under ultraviolet light for reaction to obtain a first polymer matrix; mixing the first polymer matrix, the first crosslinking agent, another part of the first photoinitiator, the first carbonate-based plasticizer and the nitrile-based plasticizer to obtain a first polymer solid-state electrolyte slurry; placing the first polymer solid-state electrolyte slurry under ultraviolet light for solidification to obtain the first polymer solid-state electrolyte layer; mixing the second reaction monomer A, the second reaction monomer B, the second lithium salt and a part of the second photoinitiator to obtain a second mixed solution; placing the second mixed solution under ultraviolet light for reaction to obtain a second polymer matrix; mixing the second polymer matrix, the second crosslinking agent, another part of the second photoinitiator, the second carbonate-based plasticizer and the fluorine-containing plasticizer to obtain a second polymer solid-state electrolyte slurry; applying the second polymer solid-state electrolyte slurry to the surface of the first polymer solid-state electrolyte layer and placing it under ultraviolet light for solidification to obtain the double-layer polymer solid-state electrolyte layer; or, mixing the second reaction monomer A, the second reaction monomer B, the second lithium salt and a part of the second photoinitiator to obtain a second mixed solution; placing the second mixed solution under ultraviolet light for reaction to obtain a second polymer matrix; mixing the second polymer matrix, the second crosslinking agent, another part of the second photoinitiator, the second carbonate-based plasticizer and the fluorine-containing plasticizer to obtain a second polymer solid-state electrolyte slurry; placing the second polymer solid-state electrolyte slurry under ultraviolet light for solidification to obtain the second polymer solid-state electrolyte layer; The first reaction monomer A, the first reaction monomer B, the first lithium salt and a part of the first photoinitiator are mixed to obtain a first mixed solution; the first mixed solution is placed under ultraviolet light for reaction to obtain a first polymer matrix; the first polymer matrix, the first crosslinking agent, another part of the first photoinitiator, the first carbonate plasticizer and the nitrile plasticizer are mixed to obtain a first polymer solid-state electrolyte slurry; the first polymer solid-state electrolyte slurry is applied to the surface of the second polymer solid-state electrolyte layer and is placed under ultraviolet light for curing to obtain the double-layer polymer solid-state electrolyte layer.

7. The lithium-ion battery of claim 6, wherein, In the step of placing the first mixed solution under ultraviolet light for reaction, the viscosity of the first mixed solution is 10000-15000 mPa.s; and / or, in the step of placing the second mixed solution under ultraviolet light for reaction, the viscosity of the second mixed solution is 10000-15000 mPa.s.

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