A composite polymer solid electrolyte membrane, and a preparation method and application thereof

Abstract

The application provides a composite polymer solid electrolyte membrane and a preparation method and application thereof, wherein lithium salt, a cyclic ether compound and a non-ether polymer soluble in or insoluble in the cyclic ether compound are mixed, a polymerizable system is uniformly coated on one side or both sides of a porous membrane through a method such as drop coating, blade coating, spray coating, gravure coating and the like, the non-ether polymer soluble in or insoluble in the cyclic ether compound in the mixture is intercepted on one side of the porous membrane, part of the lithium salt and the cyclic ether compound penetrate into the inside of the porous membrane and the other side under the action of gravity and capillary force, and a polymer electrolyte layer different from the inside of the porous membrane is formed on both sides of the porous membrane through ring-opening polymerization, so that the composite polymer solid electrolyte membrane is obtained.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to a composite polymer solid electrolyte membrane, its preparation method, and its application. Background Technology

[0002] Due to the high theoretical specific capacity of lithium metal (3860 mAh g⁻¹) -1 The low redox potential (-3.040V compared to the standard hydrogen electrode) and high capacity of nickel-manganese electrode have made it a highly sought-after anode material for high-energy-density batteries. Matching a high-voltage cathode and a high-capacity anode with a suitable electrolyte is one way to achieve high energy density. However, several issues hinder the development of lithium metal batteries in liquid electrolytes. This is mainly because nickel-manganese electrode materials often require high operating voltages, which traditional liquid electrolytes often cannot meet, potentially leading to electrolyte decomposition. Furthermore, during cycling, liquid electrolytes can cause non-uniform lithium deposition / stripping on the lithium metal anode, resulting in uncontrolled lithium dendrite growth, severe battery capacity decay, and a series of safety issues.

[0003] To address this issue, researchers have employed various methods, including using electrolyte additives, 3D current collector designs, and advanced separators. While these strategies can improve the performance of lithium metal batteries to some extent, the problem of reaction between the liquid electrolyte and lithium metal remains.

[0004] Replacing liquid electrolytes with solid electrolytes is an effective strategy to address the aforementioned safety issues. Solid electrolytes can be broadly classified into inorganic solid electrolytes and polymer electrolytes. Inorganic solid electrolytes have higher mechanical strength and can withstand higher operating voltages, effectively suppressing lithium dendrite punctures generated during cycling. However, insufficient contact between inorganic solid electrolytes and the cathode material leads to significant interfacial resistance, resulting in battery capacity decay and reduced lifespan. Ether polymer electrolytes are the most widely studied type of polymer electrolyte. Their molecular chains possess a certain degree of flexibility, solving the problem of high interfacial resistance between the electrolyte and the electrode, and exhibiting good stability against metallic lithium. CN112002941 mentions in-situ copolymerization of 1,3-dioxolane and tetrahydrofuran into a polypropylene separator to prepare an ether gel polymer electrolyte. However, when this ether gel polymer electrolyte is used in high-voltage battery systems, capacity decay is rapid because ether polymers are prone to degradation in the presence of transition metals such as cobalt and nickel. To improve the cycle stability of ether polymer electrolytes in high-voltage battery systems, CN112018427 proposes using an ether gel polymer electrolyte layer on the negative electrode side and introducing an ester gel polymer electrolyte layer on the positive electrode side, enabling its application in high-voltage battery systems. This asymmetric gel polymer electrolyte structure is easily implemented in coin cell assembly, but cannot be achieved through simple electrolyte injection in wound or stacked batteries. Therefore, improving the performance of ether polymer electrolytes and enhancing their interfacial compatibility with high-voltage positive electrode materials containing transition metals such as cobalt and nickel remains a pressing market need. Summary of the Invention

[0005] To address the shortcomings of existing technologies, researchers have discovered that introducing other non-ether polymers with high decomposition voltages into ether polymer electrolytes to form composite electrolytes helps to increase the decomposition voltage and improve the stability of the interface with high-voltage cathode materials. Based on this, the present invention provides a composite polymer solid electrolyte membrane, its preparation method, and its applications. This composite polymer solid electrolyte membrane can solve the problems of battery capacity decay and reduced lifespan caused by the degradation of ether polymer electrolytes on the surface of high-voltage cathode materials.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A solid electrolyte membrane, the solid electrolyte membrane comprising a porous membrane, a first polymer electrolyte layer inside the porous membrane and on a first surface, and a second polymer electrolyte layer on a second surface of the porous membrane opposite to the first surface;

[0008] The first polymer electrolyte in the first polymer electrolyte layer includes lithium salt and ether polymer;

[0009] The second polymer electrolyte in the second polymer electrolyte layer includes lithium salts, ether polymers, and non-ether polymers;

[0010] The ether polymers are obtained by ring-opening polymerization of cyclic ether compounds;

[0011] The non-ether polymer is either a polymer soluble in cyclic ether compounds or a polymer insoluble in cyclic ether compounds.

[0012] According to the present invention, the porous membrane contains the first polymer electrolyte.

[0013] According to the present invention, the thickness of the first polymer electrolyte layer is 2 μm to 20 μm.

[0014] According to the present invention, the thickness of the second polymer electrolyte layer is 0.5 μm to 20 μm.

[0015] According to the present invention, in the first polymer electrolyte, the mass percentage of the lithium salt is greater than or equal to 5 wt% and less than or equal to 60 wt%; the mass percentage of the ether polymer is greater than or equal to 40 wt% and less than or equal to 95 wt%.

[0016] Preferably, in the first polymer electrolyte, the lithium salt has a mass percentage content of 10 wt% or more and 40 wt% or less; and the ether polymer has a mass percentage content of 40 wt% or more and 60 wt% or less.

[0017] According to the present invention, in the second polymer electrolyte, the mass percentage of the lithium salt is greater than 5 wt% and less than or equal to 60 wt%; the mass percentage of the ether polymer is greater than or equal to 40 wt% and less than or equal to 95 wt%; and the mass percentage of the non-ether polymer is greater than 0 and less than or equal to 30 wt%.

[0018] Preferably, in the second polymer electrolyte, the lithium salt has a mass percentage content of 10 wt% or more and 40 wt% or less; the polymer-like substance has a mass percentage content of 40 wt% or more and 60 wt% or less; and the non-ether polymer has a mass percentage content of 0 wt% or less and 50 wt%.

[0019] According to the present invention, the porous membrane is selected from one or more of the following: polyolefin separators (dry-stretched uniaxial polypropylene separators, dry-stretched biaxial polypropylene separators, wet-stretched biaxial polyethylene separators), polyolefin separators coated with alumina on one or both sides, polyolefin separators coated with polyvinylidene fluoride on one or both sides, polyolefin separators coated with alumina / polyvinylidene fluoride composite coating on one or both sides, and polyolefin separators coated with inorganic solid electrolyte coating on one or both sides.

[0020] In this invention, the porous membrane can serve as a carrier for a solid electrolyte membrane. Because polyolefin membranes or coated polyolefin membranes have a thickness of less than 30 μm and very high strength (longitudinal tensile strength greater than 100 MPa), solid electrolyte membranes using these porous membranes as carriers possess the characteristics of being ultra-thin and high-strength.

[0021] According to the present invention, the thickness of the porous membrane is 5 μm to 20 μm, the pore size is 100 nm to 200 nm, and the porosity is 30% to 70%.

[0022] According to the present invention, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium dioxalate borate, lithium difluorooxalate borate, lithium perchlorate, lithium trifluoromethanesulfonate, lithium perfluorobutyl sulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium aluminate, lithium chloroaluminate, lithium fluorosulfonylimide, lithium chloride, and lithium iodide; preferably, the lithium salt is selected from one or two of lithium difluorooxalate borate, lithium perchlorate, lithium hexafluorophosphate, and lithium tetrafluoroborate.

[0023] According to the present invention, the cyclic ether compound is selected from one or more cyclic ether compounds containing one oxygen, two oxygens, three oxygens or more oxygens.

[0024] According to the present invention, the non-ether polymers soluble in cyclic ether compounds are selected from one or more polymers and their derivatives, such as polyvinylpyrrolidone, polycarbonate, polymethyl methacrylate, polymethyl acrylate, polyvinyl chloride, polyvinyl butyral, and polyvinyl acetate.

[0025] According to the present invention, the non-ether polymer that is insoluble in cyclic ether compounds is selected from one or more of polyacrylonitrile, polyvinyl alcohol, cellulose, polyacrylic acid, and their derivatives.

[0026] According to the present invention, the decomposition voltage of the solid electrolyte membrane is 4.2V to 6V, preferably 4.2V to 4.7V.

[0027] According to the present invention, the conductivity of the solid electrolyte membrane is 1×10⁻⁶. -6 ~1×10 -1 S / cm, preferably 1×10-5 ~9×10 -2 S / cm.

[0028] According to the present invention, the thickness of the solid electrolyte membrane is 4 μm to 40 μm, preferably 5 μm to 20 μm.

[0029] The present invention also provides a method for preparing the above-mentioned solid electrolyte membrane, the method comprising the following steps:

[0030] (1) Prepare a polymerizable system, wherein the polymerizable system includes lithium salts, cyclic ether compounds and non-ether polymers, wherein the non-ether polymers are polymers that can be dissolved in cyclic ether compounds;

[0031] Alternatively, (1') prepare a polymerizable system comprising lithium salts, cyclic ether compounds, and non-ether polymers, wherein the non-ether polymers are polymers insoluble in the cyclic ether compounds and are dispersed in the cyclic ether compounds in particulate or other forms;

[0032] (2) The polymerizable system is coated onto one side of the porous membrane and left to stand. The cyclic ether compounds in the polymerizable system undergo a polymerization reaction to prepare the solid electrolyte membrane.

[0033] According to the present invention, the lithium salt, cyclic ether compounds, porous membranes and non-ether polymers need to be pre-treated for dehydration; preferably, the lithium salt, ether compounds, optional porous membranes and polymers are pre-treated for dehydration by molecular sieves and high-temperature drying or vacuum drying.

[0034] According to the present invention, in step (2), the first polymerizable system is coated onto the second surface of the porous membrane and left to stand. During the standing process, the polymer in the first polymerizable system that is soluble in the cyclic ether compound is trapped on the second surface of the porous membrane, while the lithium salt and the cyclic ether compound permeate into the first surface of the porous membrane under the action of gravity. The polymer is then polymerized and dried to form the solid electrolyte membrane.

[0035] The present invention also provides a secondary battery, the secondary battery comprising the above-described solid electrolyte membrane.

[0036] According to the present invention, the secondary battery is at least one of a button battery, a stacked battery, and a wound battery. Preferably, the outer packaging of the secondary battery is a soft plastic package or a steel shell package.

[0037] The present invention also provides the application of the above-mentioned solid electrolyte membrane, which can be used to prepare secondary batteries.

[0038] According to the present invention, the secondary battery includes at least one of lithium-ion batteries, lithium-sulfur batteries, lithium-air batteries, and sodium-ion batteries.

[0039] The beneficial effects of this invention are:

[0040] The inventors of this application discovered in their research that by mixing lithium salt, cyclic ether compounds, and polymers soluble in the cyclic ether compounds, and then uniformly coating the mixture onto one side of a porous membrane using methods such as drop coating, blade coating, spray coating, or gravure coating, the polymers soluble in the cyclic ether compounds in the mixture are trapped on one side of the porous membrane. Most of the lithium salt and cyclic ether compounds permeate to the other side of the porous membrane under the influence of gravity and capillary forces. Through ring-opening polymerization or self-assembly, two electrolyte layers with different compositions are formed on the two sides of the porous membrane, resulting in a composite polymer solid electrolyte membrane.

[0041] The inventors of this application also discovered in their research that by mixing lithium salts, cyclic ether compounds, and polymers insoluble in the cyclic ether compounds, and then uniformly coating the mixture onto one side of a porous membrane using methods such as drop coating, blade coating, spray coating, or gravure coating, the polymers insoluble in the cyclic ether compounds, a portion of the lithium salt, and the ring-opening polymerized cyclic ether compounds in the mixture form a composite polymer electrolyte layer on one side of the porous membrane. The remaining lithium salts and ring-opening polymerized cyclic ether compounds penetrate into the interior of the porous membrane and the other side surface under the influence of gravity and capillary forces, forming an ether polymer electrolyte layer, thus obtaining a composite polymer solid electrolyte membrane. Alternatively, by mixing lithium salts and cyclic ether compounds, and then uniformly coating the mixture onto the other side of the porous membrane using methods such as drop coating, blade coating, spray coating, or gravure coating, the lithium salts and cyclic ether compounds in the mixture form an ether polymer electrolyte layer on the other side surface of the porous membrane through ring-opening polymerization. In other words, two electrolyte layers with different compositions are formed on both sides of the porous membrane, resulting in a composite polymer solid electrolyte membrane.

[0042] This invention provides a composite polymer solid electrolyte membrane, its preparation method, and its applications. The composite polymer solid electrolyte membrane exhibits a significantly improved decomposition voltage, which can enhance the performance of lithium metal batteries using high-voltage cathode materials. Furthermore, the thickness of the solid electrolyte membrane is comparable to that of the porous membrane serving as the substrate, and due to the porous membrane's support, the solid electrolyte membrane of this invention possesses excellent strength, meeting the requirements for long-term use. Further, the mechanical strength of the composite polymer solid electrolyte membrane can be controlled by adjusting the content of the polymer and lithium salt, and the thermomechanical properties of the composite polymer solid electrolyte can be controlled by changing the type of porous membrane. Batteries assembled using the solid electrolyte membrane of this invention can simultaneously meet the requirements of both positive and negative electrodes, significantly improving the cycle performance of secondary batteries. Attached Figure Description

[0043] Figure 1The cycle performance of the lithium-ion battery assembled using the composite polymer solid electrolyte membrane in Example 1 is shown.

[0044] Figure 2 This is a scanning electron microscope image of the surface of the composite polymer solid electrolyte membrane in Example 1.

[0045] Figure 3 This is a cross-sectional scanning electron microscope image of the composite polymer solid electrolyte membrane in Example 1. Detailed Implementation

[0046] [Cyclic ether compounds]

[0047] The solid electrolyte membrane of the present invention includes polymerized cyclic ether compounds selected from C2 to C3 groups containing at least one oxygen atom. 20 Cycloalkanes (i.e., those with 2-20 carbon atoms in a cyclic structure) or C3-C4 hydrocarbons containing at least one oxygen atom 20 Cyclic alkenes (i.e., cyclic structures with 3-20 carbon atoms) contain at least one carbon-carbon double bond.

[0048] In this invention, the cycloalkane or cycloalkene is a monocyclic, fused (e.g., bicyclic), spirocyclic, or bridged ring; when the cycloalkane or cycloalkene is a spirocyclic or bridged ring and contains two or more oxygen atoms, the oxygen atoms may be on one ring or on multiple rings.

[0049] In this invention, the cyclic ether compounds are selected from C2 to C3 compounds containing at least one oxygen atom. 20 Monocyclic alkanes, preferably selected from C3 to C4 groups containing at least one oxygen atom. 20 Monocyclic alkanes, for example, one of the following Class I compounds:

[0050]

[0051] In this invention, the cyclic ether compounds are selected from C4 to C5 groups containing at least one oxygen atom. 20 Fused cycloalkanes, for example, one of the following Class II compounds:

[0052]

[0053]

[0054] In this invention, the cyclic ether compounds are selected from C4 to C5 groups containing at least one oxygen atom. 20 Bridged cycloalkanes, for example, are one of the following third-class compounds:

[0055]

[0056] In this invention, the cyclic ether compounds are selected from C4 to C5 groups containing at least one oxygen atom. 20 Spirocycloalkanes, for example, one of the following Class IV compounds:

[0057]

[0058]

[0059] In this invention, compounds in which at least one C=C bond in the ring structure of the above four types of compounds is replaced by C=C and is stable are those containing at least one oxygen atom in the C3-C series. 20 Cyclic olefins are a preferred type of cyclic ether compound in this invention.

[0060] In this invention, when the cycloalkane or cycloalkene is a monocyclic or fused ring, one or more R1 groups may be substituted on the carbon atoms of the ring; when the cycloalkane or cycloalkene is a bridged ring, one or more R1 groups may be substituted on the non-bridged ring carbon atoms; when the cycloalkane or cycloalkene is a spirocyclic ring, one or more R1 groups may be substituted on the carbon atoms of the ring; the R1 group is selected from one of the following groups: alkyl, alkenyl, alkynyl, alkoxy, alkylthio, haloalkyl, cycloalkyl, cycloalkyloxy, cycloalkylthio, heterocyclic, heterocyclic oxy, heterocyclic thio, aryl, aryloxy, heteroaryl, heteroaryloxy, hydroxyl, mercapto, nitro, carboxyl, amino, ester, halogen, acyl, aldehyde.

[0061] In this invention, the cyclic ether compound containing one oxygen atom is selected from substituted or unsubstituted oxetanes, substituted or unsubstituted tetrahydrofurans, and substituted or unsubstituted tetrahydropyrans; the number of substituents may be one or more; the substituents are the R1 groups mentioned above.

[0062] In this invention, the cyclic ether compound containing one oxygen atom is selected from 3,3-dichloromethyloxetane, 2-chloromethyloxetane, 2-chloromethylepoxypropane, 1,3-epoxycyclohexane, 1,4-epoxycyclohexane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, tetrahydropyran, 2-methyltetrahydropyran, oxetane, oxetane, oxetane, nonane, or oxetane.

[0063] In this invention, the cyclic ether compound containing two oxygen atoms is selected from substituted or unsubstituted 1,3-dioxolane (DOL) and substituted or unsubstituted 1,4-dioxane; the number of substituents may be one or more; the substituents are the R1 groups mentioned above.

[0064] In this invention, the cyclic ether compound containing three oxygen atoms is selected from substituted or unsubstituted paraformaldehyde; the number of substituents can be one or more; the substituents are the R1 groups mentioned above.

[0065] In this invention, the ether compound containing more oxygen is selected from substituted or unsubstituted 18-crown-6, substituted or unsubstituted 12-crown-4, and substituted or unsubstituted 24-crown-8; the number of substituents may be one or more; the substituents are the R1 groups mentioned above.

[0066] [Terms and Definitions]

[0067] Unless otherwise stated, the definitions of functional groups and terms described in this application, including definitions as examples, exemplary definitions, preferred definitions, definitions listed in tables, and definitions of specific compounds in the examples, can be arbitrarily combined and combined with each other. Such combinations and combinations of functional group definitions and compound structures shall fall within the scope of protection of this application.

[0068] The numerical range described in this application specification, when defined as "integer," should be understood as including the two endpoints of the range and every integer within the range. For example, "integers from 0 to 10" should be understood as including every integer of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. When the numerical range is defined as "number," it should be understood as including the two endpoints of the range, every integer within the range, and every decimal within the range. For example, "numbers from 0 to 10" should be understood as including not only every integer of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10, but also at least the sum of each of these integers with 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9.

[0069] The term "halogen" as used in this invention refers to fluorine, chlorine, bromine, and iodine.

[0070] The term "alkyl" as used alone or as a suffix or prefix in this invention is intended to include branched and straight-chain saturated aliphatic hydrocarbon groups having 1 to 20, preferably 1 to 6, carbon atoms (or, if a specific number of carbon atoms is provided, that specific number). For example, "C 1-6 "Alkyl" means a straight-chain or branched alkyl group having 1, 2, 3, 4, 5, or 6 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, and hexyl.

[0071] The use of "halogenated alkyl" or "alkyl halide" alone or as a suffix or prefix in this invention is intended to include branched and straight-chain saturated aliphatic hydrocarbon groups having at least one halogen substituent and having 1 to 20, preferably 1 to 6, carbon atoms (or, if a specific number of carbon atoms is provided, that specific number). For example, "C 1-10 "Halogenated alkyl" refers to an alkyl halogroup having 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 carbon atoms. Examples of alkyl halogroups include, but are not limited to, fluoromethyl, difluoromethyl, trifluoromethyl, chlorofluoromethyl, 1-fluoroethyl, 3-fluoropropyl, 2-chloropropyl, and 3,4-difluorobutyl.

[0072] The term "alkenyl" as used alone or as a suffix or prefix in this invention is intended to include branched and straight-chain aliphatic hydrocarbon groups comprising alkenyl or olefin having 2 to 20, preferably 2 to 6, carbon atoms (or, if a specific number of carbon atoms is provided, that specific number). For example, "C 2-6 "Alkenyl" refers to an alkenyl group having 2, 3, 4, 5, or 6 carbon atoms. Examples of alkenyl groups include, but are not limited to, vinyl, allyl, 1-propenyl, 1-butenyl, 2-butenyl, 3-butenyl, 2-methylbut-2-enyl, 3-methylbut-1-enyl, 1-pentenyl, 3-pentenyl, and 4-hexenyl.

[0073] The term "alkynyl" as used alone or as a suffix or prefix in this invention is intended to include branched and straight-chain aliphatic hydrocarbon groups comprising an alkynyl group or alkyne having 2 to 20, preferably 2 to 6, carbon atoms (or, if a specific number of carbon atoms is provided, that specific number). Examples include ethynyl, propynyl (e.g., 1-propynyl, 2-propynyl), 3-butynyl, pentyynyl, hexynyl, and 1-methylpentan-2-ynyl.

[0074] As used in this invention, the term "aryl" refers to an aromatic ring structure consisting of 5 to 20 carbon atoms. For example, an aromatic ring structure containing 5, 6, 7, and 8 carbon atoms can be a monocyclic aromatic group such as phenyl; a ring structure containing 8, 9, 10, 11, 12, 13, or 14 carbon atoms can be a polycyclic group such as naphthyl. The aromatic ring may be substituted with one or more of the aforementioned substituents at one or more ring positions. The term "aryl" also includes polycyclic systems having two or more rings, wherein two or more carbons are shared by two adjacent rings (the rings are "fused rings"), wherein at least one ring is aromatic and the other rings may be, for example, cycloalkyl, cycloalkenyl, cycloalkynyl, aryl, and / or heterocyclic groups. Examples of polycyclics include, but are not limited to, 2,3-dihydro-1,4-benzodioxanediene and 2,3-dihydro-1-benzofuran.

[0075] The term "cycloalkyl" as used in this invention is intended to include saturated cyclic groups having a specified number of carbon atoms. These terms may include fused or bridged polycyclic systems. Cycloalkyl groups have 3 to 40 carbon atoms in their ring structure. In one embodiment, a cycloalkyl group has 3, 4, 5, or 6 carbon atoms in its ring structure. For example, "C 3-6 "Cycloalkyl" refers to groups such as cyclopropyl, cyclobutyl, cyclopentyl, or cyclohexyl.

[0076] As used in this invention, "heteroaryl" refers to a heterocyclic aromatic ring having at least one cyclic heteroatom (e.g., sulfur, oxygen, or nitrogen). Heteroaryl includes monocyclic and polycyclic systems (e.g., having 2, 3, or 4 fused rings). Examples of heteroaryl include, but are not limited to, pyridinyl, pyrazinyl, pyridazinyl, triazinyl, furanyl, quinolinyl, isoquinolinyl, thiopheneyl, imidazolyl, thiazolyl, indolyl, pyrroleyl, oxazolyl, benzofuranyl, benzothiopheneyl, benzothiazolyl, isoxazolyl, pyrazolyl, triazolyl, tetrazolyl, inzolyl, 1,2,4-thiadiazolyl, isothiazolyl, benzothiopheneyl, purinyl, carbazoleyl, benzoimidazolyl, benzoxazolyl, azabenzoxazolyl, imidazothiazolyl, benzo[1,4]dioxacyclohexenyl, benzo[1,3]dioxacyclopentenyl, etc. In some embodiments, the heteroaryl group has 3 to 40 carbon atoms, and in other embodiments, it has 3 to 20 carbon atoms. In some embodiments, the heteroaryl group comprises 3 to 14, 4 to 14, 3 to 7, or 5 to 6 cyclic atoms. In some embodiments, the heteroaryl group has 1 to 4, 1 to 3, or 1 to 2 heteroatoms. In some embodiments, the heteroaryl group has 1 heteroatom.

[0077] Unless otherwise stated, the term "heterocyclic group" as used in this invention refers to a saturated, unsaturated, or partially saturated monocyclic, bicyclic, or tricyclic ring comprising 3 to 20 atoms, wherein 1, 2, 3, 4, or 5 ring atoms are selected from nitrogen, sulfur, or oxygen, and unless otherwise stated, it may be linked by carbon or nitrogen, wherein the -CH2- group is optionally replaced by -C(O)-; and wherein, unless otherwise stated to the contrary, the cyclic nitrogen atom or cyclic sulfur atom is optionally oxidized to form an N-oxide or S-oxide, or the cyclic nitrogen atom is optionally quaternized; wherein the -NH in the ring is optionally replaced by an acetyl, formyl, methyl, or methanesulfonyl group; and the ring is optionally replaced by one or more halogens. It should be understood that when the total number of S and O atoms in the heterocyclic group exceeds 1, these heteroatoms are not adjacent to each other. If the heterocyclic group is bicyclic or tricyclic, at least one ring may optionally be a heteroaromatic ring or an aromatic ring, provided that at least one ring is non-heteroaromatic. If the heterocyclic group is monocyclic, it is necessarily not aromatic. Examples of heterocyclic groups include, but are not limited to, piperidinyl, N-acetylpiperidinyl, N-methylpiperidinyl, N-formylpiperazinyl, N-methanesulfonylpiperazinyl, homopiperazinyl, piperazinyl, azacyclic butyl, oxacyclic butyl, morpholinyl, tetrahydroisoquinolinyl, tetrahydroquinolinyl, dihydroindolyl, tetrahydropyranyl, dihydro-2H-pyranyl, tetrahydrofuranyl, tetrahydrothiaranyl, tetrahydrothiaran-1-oxide, tetrahydrothiaran-1,1-dioxide, 1H-pyridin-2-one, and 2,5-dioxoimidazolyl.

[0078] The preparation method of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0079] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0080] In the description of this invention, it should be noted that the terms "first," "second," etc., are used for descriptive purposes only and are not intended to indicate or imply relative importance.

[0081] Test method:

[0082] The conductivity described in this embodiment was obtained using an Interface 1000 electrochemical workstation from Gamry Corporation, with a test scan frequency of 1.0 Hz to 100 kHz.

[0083] In this embodiment, the lithium salt is pre-dehydrated by vacuum drying at 50°C for more than 24 hours before use.

[0084] In this embodiment, the cyclic ether compound is dehydrated by molecular sieve before use.

[0085] In this embodiment, the porous membrane is pre-treated by vacuum drying at 40°C for more than 12 hours before use to remove water.

[0086] In this embodiment, the decomposition voltage of the solid electrolyte membrane is tested using a lithium-stainless steel battery via linear sweep voltammetry. During the test, the first polymer electrolyte layer is in contact with the lithium sheet, and the second polymer electrolyte layer is in contact with the stainless steel.

[0087] In this embodiment, the lithium-ion battery is subjected to charge-discharge cycle testing at 0.5C.

[0088] Preparation of positive electrode sheet for lithium-ion battery: 85 parts by mass of positive electrode active material nickel cobalt manganese (NCM532), 5 parts by mass of acetylene black, 5 parts by mass of conductive graphite, and 5 parts by mass of PVDF are thoroughly mixed with N-methylpyrrolidone (NMP) to obtain positive electrode slurry, which is uniformly coated on the surface of aluminum foil current collector and dried in a vacuum oven at 120℃ for later use.

[0089] Negative electrode: Lithium metal sheet.

[0090] Example 1

[0091] (1) Preparation of composite polymer solid electrolyte membrane

[0092] Weigh 0.5g of polymethyl methacrylate, 1.46g of LiTFSI, and 0.75g of LiPF6 into a reagent bottle, add 8.9g of tetrahydrofuran, and stir magnetically for 2 hours to dissolve and mix the polymethyl methacrylate and lithium salt evenly, obtaining a polymerizable system. Drop-coat this polymerizable system onto one side of a PP porous membrane, leaving the polymethyl methacrylate on the upper side of the porous membrane, while some of the LiTFSI, LiPF6, and tetrahydrofuran solvent permeates to the other side of the PP porous membrane. After standing for a period of time to allow the tetrahydrofuran to polymerize, dry the membrane in a vacuum oven for 12 hours to obtain an asymmetric solid electrolyte membrane.

[0093] The asymmetric solid electrolyte membrane includes a porous membrane, a first polymer electrolyte layer inside the porous membrane and on a first surface, and a second polymer electrolyte layer on a second surface of the porous membrane opposite to the first surface; wherein, the first polymer electrolyte in the first polymer electrolyte layer includes 32 wt% lithium salt and 68 wt% cyclic ether polymer; the second polymer electrolyte in the second polymer electrolyte layer includes 30 wt% lithium salt, 63 wt% ether polymer and 7 wt% non-ether polymer, wherein the non-ether polymer is polymethyl methacrylate.

[0094] The decomposition voltage of the solid electrolyte membrane is 4.5V.

[0095] (2) Battery manufacturing

[0096] The asymmetric solid electrolyte membrane prepared above was used as an electrolyte in a button cell, and the cycle performance of the battery was tested using a Blue Battery charge-discharge tester (the test results are listed in Table 1). The button cell was prepared by contacting the second polymer electrolyte layer of the asymmetric solid electrolyte membrane prepared above with the positive electrode, and the first polymer electrolyte layer with the negative electrode. After encapsulation and compaction, the cells were assembled into a CR-2032 type button cell.

[0097] Example 2

[0098] (1) Preparation of composite polymer solid electrolyte membrane

[0099] 0.5 g of granular polyacrylonitrile and 0.94 g of LiBF4 were added to a reagent bottle, and 10 mL of 1,3-dioxolane was added. The mixture was magnetically stirred for 2 h to dissolve and mix the lithium salt evenly and to disperse the polyacrylonitrile evenly, thus obtaining a polymerizable system. This polymerizable system was drop-coated onto one side of a PP porous membrane, with the polyacrylonitrile remaining on the upper side of the PP porous membrane. After standing for a period of time to allow the 1,3-dioxolane to polymerize, the membrane was dried in a vacuum oven for 12 h to obtain a composite polymer solid electrolyte membrane.

[0100] The solid electrolyte membrane includes a porous membrane, a first polymer electrolyte layer inside the porous membrane and on a first surface, and a second polymer electrolyte layer on a second surface of the porous membrane opposite to the first surface; wherein the first polymer electrolyte in the first polymer electrolyte layer includes 16 wt% lithium salt and 84 wt% ether polymer; the second polymer electrolyte in the second polymer electrolyte layer includes 15 wt% lithium salt, 77 wt% polymerized cyclic ether compound and 8 wt% non-ether polymer, wherein the non-ether polymer is polyacrylonitrile.

[0101] The decomposition voltage of the solid electrolyte membrane is 4.5V.

[0102] (2) Battery manufacturing

[0103] The preparation method is the same as in Example 1.

[0104] Example 3

[0105] (1) Preparation of composite polymer solid electrolyte membrane

[0106] Weigh 0.5g of polyvinylidene fluoride, 0.73g of LiTFSI, and 0.75g of LiPF6 and add them to a reagent bottle. Add 10mL of 1,3-dioxolane and stir magnetically for 2 hours to obtain a homogeneous mixed solution, thus obtaining a polymerizable system. Drop-coat this polymerizable system onto one side of a PP porous membrane. After standing for a period of time to allow the 1,3-dioxolane to polymerize, place the membrane in a vacuum oven and dry for 12 hours to obtain a composite polymer solid electrolyte membrane.

[0107] The solid electrolyte membrane includes a porous membrane, a first polymer electrolyte layer inside the porous membrane and on a first surface, and a second polymer electrolyte layer on a second surface of the porous membrane opposite to the first surface; wherein the first polymer electrolyte in the first polymer electrolyte layer includes 23 wt% lithium salt and 77 wt% ether polymer; the second polymer electrolyte in the second polymer electrolyte layer includes 21 wt% lithium salt, 72 wt% ether polymer and 7 wt% non-ether polymer, wherein the non-ether polymer is polyvinylidene fluoride.

[0108] The test method for the decomposition voltage of the solid electrolyte membrane is the same as in Example 1, and its decomposition voltage is 4.5V.

[0109] (2) Battery manufacturing

[0110] The preparation method is the same as in Example 1.

[0111] Example 4

[0112] (1) Preparation of composite polymer solid electrolyte membrane

[0113] Weigh 0.73g LiTFSI and 0.75g LiPF6 together and add them to a reagent bottle. Add 10mL of 1,3-dioxolane and stir magnetically for 2h to obtain a homogeneous polymerizable system. Drop-coat the polymerizable system onto one side of a PVDF / PE / PVDF porous membrane. After standing for a period of time to allow the 1,3-dioxolane to polymerize, dry the membrane in a vacuum oven for 12h to obtain a composite polymer solid electrolyte membrane.

[0114] The solid electrolyte membrane comprises a porous membrane, a first polymer electrolyte layer inside the porous membrane, and a second polymer electrolyte layer on two surfaces of the porous membrane; wherein the first polymer electrolyte layer comprises 23 wt% lithium salt and 77 wt% ether polymer; the second polymer electrolyte layer comprises 12 wt% lithium salt, 38 wt% ether polymer, and 50 wt% non-ether polymer, wherein the non-ether polymer is polyvinylidene fluoride.

[0115] The solid electrolyte membrane has a decomposition voltage of 4.5V.

[0116] (2) Battery manufacturing

[0117] The preparation method is as follows: the two surfaces of the composite polymer solid electrolyte membrane are respectively brought into contact with the positive and negative electrodes, and after encapsulation and compaction, they are assembled into a CR-2032 button cell.

[0118] Comparative Example 1

[0119] (1) Dissolve 0.25g of lithium fluorosulfonylimide and 0.25g of lithium hexafluorophosphate in 4.5g of 1,4-epoxycyclohexane / 1,3-dioxolane (mass ratio 1:1) to obtain a mixed system. Then, drop the mixed system onto one side of the PP porous membrane so that the PP porous membrane is uniformly permeated by the mixed solution. After standing at room temperature for 12h, vacuum dry for 12h to obtain a homogeneous solid electrolyte membrane.

[0120] The homogeneous solid electrolyte membrane was tested and found to have a decomposition voltage of 4.1V.

[0121] (2) Battery manufacturing

[0122] The homogeneous solid electrolyte membrane prepared by the above method is brought into contact with the NCM532 positive electrode and lithium sheet, and after being packaged and compacted, it is assembled into a CR-2032 button battery.

[0123] Comparative Example 2

[0124] (1) Preparation of homogeneous solid electrolyte membranes

[0125] Weigh 1.46g LiBF4 into a reagent bottle, add 8.9g tetrahydrofuran, stir magnetically for 12h, mix evenly, and then drop the solution onto a PE porous membrane so that the PE porous membrane is evenly permeated by the mixed solution. After standing at room temperature for 12h, vacuum dry for 12h to obtain a homogeneous solid electrolyte membrane.

[0126] The homogeneous solid electrolyte membrane was tested and found to have a decomposition voltage of 4.1V.

[0127] (2) Battery manufacturing

[0128] The preparation method is the same as that of Comparative Example 1.

[0129] Table 1. Performance parameters of the batteries prepared in Examples 1-4 and Comparative Examples 1-2.

[0130]

[0131] As shown in Table 1, the NCM532 lithium metal battery using a composite polymer solid electrolyte membrane exhibits more stable cycle capacity and slower capacity decay. This is because non-ether polymers with high decomposition voltage at the cathode material interface enhance the interfacial stability of the solid electrolyte membrane.

[0132] Figure 1 This is a cycle performance diagram of a lithium-ion battery assembled from the composite polymer solid electrolyte membrane in Example 1. Figure 1 It can be seen that the battery exhibits stable cycle performance, and its specific capacity remains basically unchanged.

[0133] Figure 2 This is a scanning electron microscope (SEM) image of the surface of the composite polymer solid electrolyte membrane in Example 1. Figure 2 It can be seen that the surface of the porous membrane is completely coated with polymer.

[0134] Figure 3 This is a cross-sectional scanning electron microscope (SEM) image of the composite polymer solid electrolyte membrane obtained in Example 1. Figure 3 It can be seen that the porous membrane is coated with polymer on both the top and bottom sides, and the interior of the porous membrane is also completely wetted by polymer.

[0135] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A solid-state electrolyte membrane, characterized by, The solid electrolyte membrane includes a porous membrane, a first polymer electrolyte layer on a first surface of the porous membrane, and a second polymer electrolyte layer on a second surface of the porous membrane opposite to the first surface; the first polymer electrolyte in the first polymer electrolyte layer includes lithium salt and ether polymer; the second polymer electrolyte in the second polymer electrolyte layer includes lithium salt, ether polymer, and non-ether polymer. The first polymer electrolyte layer and the second polymer electrolyte layer formed on both sides of the porous membrane have different compositions; the first polymer electrolyte layer does not include non-ether polymers. The interior of the porous membrane includes a first polymer electrolyte; the first polymer electrolyte includes lithium salts and ether polymers, but does not include non-ether polymers; The ether polymers are obtained by ring-opening polymerization of cyclic ether compounds; the non-ether polymers are polymers soluble in cyclic ether compounds or polymers insoluble in cyclic ether compounds. The pore size of the porous membrane is 100nm-200nm.

2. The solid-state electrolyte film of claim 1, wherein, The thickness of the first polymer electrolyte layer is 2μm to 20μm; the thickness of the second polymer electrolyte layer is 0.5μm to 20μm.

3. The solid-state electrolyte film of claim 1 or 2, wherein, In the first polymer electrolyte, the lithium salt has a mass percentage content of 5 wt% or more and 60 wt% or less; the ether polymer has a mass percentage content of 40 wt% or more and 95 wt% or less.

4. The solid-state electrolyte film of claim 3, wherein, In the polymer electrolyte, the lithium salt has a mass percentage content of ≥10wt% and ≤40wt%; the ether polymer has a mass percentage content of ≥40wt% and ≤60wt%.

5. The solid-state electrolyte film of claim 1 or 2, wherein, In the second polymer electrolyte, the lithium salt has a mass percentage content greater than 5 wt% and less than or equal to 60 wt%; the ether polymer has a mass percentage content greater than or equal to 40 wt% and less than or equal to 95 wt%; and the non-ether polymer has a mass percentage content greater than 0 and less than or equal to 70 wt%.

6. The solid-state electrolyte film of claim 5, wherein, In the second polymer electrolyte, the lithium salt has a mass percentage content of ≥10wt% and ≤40wt%; the ether polymer has a mass percentage content of ≥40wt% and ≤60wt%; and the non-ether polymer has a mass percentage content of ≥0wt% and ≤50wt%.

7. The solid-state electrolyte film of claim 1 or 2, wherein, The polymer soluble in cyclic ether compounds is selected from one or more of polyvinylpyrrolidone, polycarbonate, polymethyl methacrylate, polymethyl methacrylate, polyvinyl chloride, polyvinyl butyral, polyvinyl acetate and their derivatives. The polymer that is insoluble in cyclic ether compounds is selected from one or more of polyacrylonitrile, polyvinyl alcohol, cellulose powder, polyacrylic acid and its derivatives.

8. The solid-state electrolyte film of claim 1 or 2, wherein, The decomposition voltage of the solid electrolyte membrane is 4.2V~6V; and / or the solid-state electrolyte film has an electrical conductivity of 10 -6 S / cm -1 S / cm And / or, the thickness of the solid electrolyte membrane is 4μm~40μm.

9. A method for preparing a solid electrolyte membrane according to any one of claims 1-8, the method comprising the following steps: (1) Prepare a polymerizable system, wherein the polymerizable system includes lithium salts, cyclic ether compounds and non-ether polymers, wherein the non-ether polymers are polymers soluble in cyclic ether compounds; Alternatively, (1') prepare a polymerizable system comprising lithium salts, cyclic ether compounds, and non-ether polymers, wherein the non-ether polymers are polymers insoluble in the cyclic ether compounds and are dispersed in the cyclic ether compounds in particulate form; (2) The polymerizable system is coated onto one side of the porous membrane and left to stand. The cyclic ether compounds in the polymerizable system undergo a polymerization reaction to prepare the solid electrolyte membrane.

10. The production method according to claim 9, wherein In step (2), the polymerizable system is coated onto one side of the porous membrane and left to stand. During the standing process, the non-ether polymers in the polymerizable system that are soluble and / or insoluble in the cyclic ether compounds are trapped on the surface of the porous membrane. The lithium salt and cyclic ether compounds permeate into the interior of the porous membrane and the other side of the membrane under the action of gravity, polymerize, and dry to form the solid electrolyte membrane.

11. A secondary battery comprising the solid electrolyte membrane according to any one of claims 1-8.

Images