Polymer and preparation thereof, electrolyte membrane and preparation thereof

Abstract

This application provides a polymer synthesized from monomer 1, monomer 2, and monomer 3, wherein monomer 1 has the structure of formula 1, monomer 2 has the structure of formula 2, and monomer 3 has the structure of formula 3, wherein R1, R2, R3, R4, R5, Rf, x, and A + Q ‑ As defined in the specification. This application also provides a polymer electrolyte membrane comprising an interpenetrating network structure formed of a polymer and a carbonate polymer. The polymer electrolyte membrane provided in this application has excellent mechanical strength, improved ionic conductivity and ion mobility, and the batteries prepared from it exhibit high voltage resistance and excellent high-voltage cycling performance.

Description

Technical Field

[0001] This application relates to a polymer. Furthermore, this application also relates to an electrolyte membrane comprising the polymer, a secondary battery comprising the electrolyte membrane, a battery pack comprising the secondary battery, a battery module, and an electrical device. Background Technology

[0002] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Due to the significant advancements in lithium-ion battery technology, higher requirements have been placed on its electrolyte.

[0003] Most commercially available lithium batteries currently use organic liquid electrolytes, which have high ionic conductivity (10⁻⁶). -3 The advantages of lithium batteries include high specific capacity (e.g., 3860 mAh / g) and good electrode surface wettability. However, organic liquid electrolytes, due to their easy flow, volatility, and poor thermal stability, greatly limit the potential for improvement in the safety of lithium batteries. On the other hand, the rapid development of modern society has placed higher demands on the energy density and cycle life of batteries. Therefore, batteries with high specific capacity (e.g., 3860 mAh / g) and extremely low potential (e.g., -3.04 V vs. H2 / H) are preferred. + The lithium metal anode has once again attracted the attention of researchers. However, the high reactivity of lithium and the problem of lithium dendrite short circuits are insurmountable obstacles to the development of lithium metal batteries. The emergence of solid-state electrolytes has broken this barrier. Replacing organic liquid electrolytes with solid-state electrolytes can not only fundamentally solve the safety problems of batteries, but also provide possibilities for the further development of lithium metal batteries.

[0004] Using aluminum-based polymers as solid polymer electrolyte membranes in lithium metal secondary batteries is currently a relatively effective approach. However, there is still room for improvement in the high-voltage resistance and safety performance of these solid polymer electrolyte membranes. Therefore, there is still a need to provide a solid electrolyte membrane that possesses high mechanical strength, good high-voltage resistance, and excellent flame-retardant properties. Summary of the Invention

[0005] This application addresses the aforementioned issues and aims to provide a polymer with good flame retardant properties, resistance to oxidation under high voltage, and the ability to improve ionic conductivity and lithium-ion transference number when used as an electrolyte membrane material, making it suitable for high-voltage battery systems, as well as a method for preparing the same. Furthermore, this application also provides a solid electrolyte membrane comprising the polymer, exhibiting good interfacial contact with the electrode, high ionic conductivity, good high-temperature stability, and good mechanical properties, as well as a method for preparing the same. Additionally, this application provides a secondary battery including the aforementioned electrolyte membrane.

[0006] Therefore, the first aspect of this application provides a polymer polymerized from monomer 1, monomer 2, and monomer 3, wherein monomer 1 has a structure of formula 1, monomer 2 has a structure of formula 2, and monomer 3 has a structure of formula 3.

[0007]

[0008] in,

[0009] R1 and R3 are each independently selected from hydrogen or C. 1-10 alkyl;

[0010] R4 is selected from C 1-10 A hydrocarbon group or a C group containing one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus. 1-10 hydrocarbon group;

[0011] R2 and R5 are each independently selected from hydrogen and C. 1-10 Hydrocarbon group or hydrocarbon group containing one or more of the elements fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus with a carbon number of less than or equal to 10, containing C=C or C≡C;

[0012] Rf is selected from hydrogen, or an ethoxy chain segment containing one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus with a carbon number of less than or equal to 16.

[0013] x is the number of repeating units of the methylene group, 0 ≤ x ≤ 20;

[0014] A + It is selected from one of the functional groups with nitrogen, sulfur, or phosphorus as the cation center;

[0015] Q - It is one, two or more anions selected from halide ions, haloborate ions, halooxaloborate ions, perhalate ions, halophosphate ions, and halosulfonylimide ions, optionally Q - It is one, two or more anions selected from chloride ion, tetrafluoroborate, difluorooxalateborate, perchlorate, hexafluorophosphate, and bis(fluorosulfonyl)imide.

[0016] E is selected from the structures (1) to (3).

[0017]

[0018] R6 is selected from hydrogen or C. 1-10 alkyl.

[0019] The polymer provided in this application is formed by the polymerization of three monomers (monomer 1, monomer 2, and monomer 3), with an ethyl group as the main chain. Its molecular structure contains functional groups such as ionic groups (from monomer 1), amides (from monomer 1), phosphate esters (from monomer 2), and fluorinated ethoxy groups (from monomer 3). These functional groups each provide different functions to the polymer. It is believed, for example, that the presence of the ionic groups and fluorine (mainly from monomer 3) is beneficial for improving the material's oxidation resistance or high-voltage stability (especially at voltages above 5V). When the polymer is used as an electrolyte membrane material in a secondary battery, the flexible ethoxy side chains in the polymer can drive lithium ion migration, and the cation centers in the ionic groups can interact with the anions in the lithium salt, thereby increasing the lithium ion migration number. The synergistic effect of the phosphate ester groups from monomer 2 and the fluorine element (mainly from monomer 3) makes the electrolyte containing the polymer exhibit excellent flame retardant properties, which can improve the safety of the battery when applied to lithium secondary batteries. The amide from monomer 1 gives the polymer molecules strong hydrogen bonding, and the presence of the strong hydrogen bonding and the construction of the cross-linked network centered on the phosphate ester (from monomer 2) are beneficial to enhancing the mechanical properties of the polymer material.

[0020] Optionally, the polymer has a triblock structure. The triblock structure of the polymer can block the contact between ethoxy side chains, reduce the crystallinity of the polymer material, and improve ionic conductivity when used in electrolyte membranes.

[0021] In any embodiment, the fluorine substitution rate in the Rf group is greater than 29.0%, and the fluorine substitution rate is the percentage of fluorine atoms based on the number of hydrogen atoms that can be substituted in the Rf group.

[0022] The term "number of substituted hydrogen atoms" should be understood as the number of substituted sites in the Rf group, that is, the maximum number of hydrogen atoms that can be bonded to carbon atoms, phosphorus atoms, nitrogen atoms, and sulfur atoms present in the group. If the hydrogen atoms have been replaced by other elements, such as halogen atoms, the number of substituted hydrogen atoms is the sum of the number of hydrogen atoms and the number of other atoms substituted.

[0023] A fluorine substitution rate of 29.0% or higher ensures the flame retardant properties of the polymer and improves the high-voltage stability and high-voltage cycle performance of batteries made from the polymer.

[0024] In any embodiment, in the polymer, cationic A + Choose one of the structural formulas (4) to (6):

[0025]

[0026] In any embodiment, in the polymer, the molar percentage of monomer 1 ranges from 3.7 to 92.6 mol%, the molar percentage of monomer 2 ranges from 2.0 to 33.3 mol%, and the molar percentage of monomer 3 ranges from 3.7 to 92.6 mol%, all based on the total molar number of monomers 1, 2, and 3.

[0027] Optionally, the molar ratio of monomer 1 to monomer 2 is in the range of 1:1 to 25:1;

[0028] Alternatively, the molar ratio of monomer 3 to monomer 2 is in the range of 1:1 to 25:1.

[0029] In any embodiment, the polymer has a thermal conductivity in the range of 0.06 to 0.35 W / m K and a flame retardant rating of 94V-0 or 94V-1.

[0030] The second aspect of this application provides a method for preparing the polymer described in the first aspect of this application, comprising the following steps: dissolving monomer 1, monomer 2, monomer 3, and an initiator in a solvent, reacting them under vacuum at 30–100°C for 0.2–24 h, optionally 6–24 h, and then drying. The polymer is prepared as a block copolymer. Optionally, the drying is carried out under vacuum at 25–140°C for 1–48 h. The main purpose of drying is to remove the solvent remaining after the reaction.

[0031] A third aspect of this application provides a polymer electrolyte membrane comprising the polymer described in the first aspect of this application or a polymer prepared by the method described in the second aspect of this application.

[0032] In any embodiment, the polymer electrolyte membrane further includes a second polymer dispersed in the polymer to form an interpenetrating network structure. The second polymer is formed from monomer 4, and the general formula of monomer 4 is as follows:

[0033]

[0034] in,

[0035] R7 is selected from hydrogen, or a hydrocarbon group with less than 7 carbon atoms that is unsubstituted or substituted by one or more elements selected from fluorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus.

[0036] As described above, "hydrocarbon groups with fewer than 7 carbon atoms" include, but are not limited to: alkyl groups with fewer than 7 carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, isopropyl, isobutyl, tert-butyl, isopentyl, tert-pentyl, neopentyl, 2-methylpentyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, etc.; alkenyl groups with fewer than 7 carbon atoms, such as ethylene, propylene, butene, butadiene, pentene, pentadiene, hexene, etc.; and alkynyl groups with fewer than 7 carbon atoms, such as acetylene, propyne, butyne, pentyne, hexyne, etc. Hydrocarbon groups with fewer than 7 carbon atoms can be unsubstituted or monosubstituted or polysubstituted by one or more elements selected from fluorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus.

[0037] In this application, the second polymer is used in contrast to the aforementioned polymer, and is intended to distinguish it from the aforementioned polymer.

[0038] The second polymer described in this application is an oligomer with carbonate as the main chain and a number average molecular weight M. n <2000 Da, viscosity less than 3000 cP, and possessing a certain degree of fluidity. The second polymer can also be called a carbonate polymer. This oligomer is uniformly dispersed in the network of the aforementioned polymers as a second polymer network. The presence of the carbonate backbone in the second polymer network ensures the high-voltage stability of the formed electrolyte membrane and contributes to the excellent high-voltage resistance of the secondary battery containing the electrolyte membrane. The second polymer in the interpenetrating network structure has a certain degree of fluidity and can wet the electrode, thereby improving the interfacial contact between the electrolyte membrane and the positive and negative electrodes. Therefore, in a solid electrolyte membrane comprising an interpenetrating network of a polymer network and a second polymer network, the introduction of a fluid second polymer network not only improves the wetting performance between the electrolyte membrane and the electrode and improves the interfacial contact between the electrolyte membrane and the positive and negative electrodes, but also ensures the high ionic conductivity of the electrolyte membrane because the chain movement of carbonate can drive the migration of lithium ions.

[0039] In some alternative embodiments, the electrolyte membrane containing the above-described interpenetrating network structure described in this application is suitable for high-voltage battery systems, such as 5V high-voltage battery systems. High-voltage battery cell series include, but are not limited to, LiNi... 0.8 Co 0.1 Mn 0.1 O2, LiCoO2, LiMn2O4, LiNiCoAlO2, LiNi 0.5 Mn 1.5 O4 and other battery systems.

[0040] Optionally, in the interpenetrating network structure, the mass ratio of the polymer to the second polymer is 20:1 to 2:1.

[0041] In any embodiment, the polymer electrolyte membrane further includes a lithium salt selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalateborate (LiDFOB), lithium perchlorate (LiClO4), and lithium dioxoborate (LiBOB).

[0042] The type of lithium salt affects the lithium-ion transference number of the prepared polymer electrolyte membrane. Different lithium salts exhibit varying degrees of dissociation between their cations and anions due to their different structures; lithium salts with higher degrees of dissociation can provide more charge carriers. + The concentration of [Li] affects the coordination-dissociation process between [Li] and the ether oxygen atoms and carbonyl groups in the polymer chain, thus affecting the charging and discharging process of Li. + And the migration ability of anions in the battery. Typically, PEO-based electrolytes have ether oxygen atoms that interact with Li... + The multidentate coordination chelation between them, and with TFSI - The relatively weak solvent effect of the anion results in a transfer number of less than 0.2.

[0043] In any embodiment, the mass percentage of lithium salt in the polymer electrolyte membrane is in the range of 6.8% to 30.0%, based on the total mass of the polymer electrolyte membrane.

[0044] In any embodiment, the fluorine content in the polymer electrolyte membrane is in the range of 12.5% ​​to 46.0% based on the total weight of the polymer electrolyte membrane.

[0045] To ensure the dual properties of high-pressure resistance and flame retardancy in the electrolyte membrane prepared using polymers, the substitution of fluorine in the Rf groups of the polymer should ideally be greater than or equal to 29.0%. Furthermore, controlling the fluorine content within this range in the polymer electrolyte membrane prepared using polymers is more conducive to achieving both high-pressure resistance and flame retardancy.

[0046] A third aspect of this application provides a method for preparing a polymer electrolyte membrane, comprising the following steps:

[0047] The monomers 1, 2, and 3 mentioned above, the monomer 4 mentioned above, the lithium salt mentioned above, the catalyst, and the initiator mentioned above are reacted at 30 to 100°C for 0.2 to 24 h to obtain product 1.

[0048] It is now believed that in this step, monomers 1, 2, and 3 undergo co-block polymerization in the presence of an initiator to form the polymer, and monomer 4 undergoes ionic copolymerization in the presence of a lithium salt and optionally a catalyst to form a fluid second polymer.

[0049] In any embodiment, the method for preparing a polymer electrolyte membrane further includes the step of anion exchange of the obtained product 1 with a lithium salt solution to obtain product 2.

[0050] After anion exchange, the anions Q inherent in the ionic groups of the polymer formed can be converted into anions. - For example, Cl, which can corrode aluminum foil - The target anion is replaced, optionally, with an anion of the same type as the anion in the lithium salt. This prevents some side reactions and also adjusts the binding affinity between the anion and the polymer and lithium ions.

[0051] In any embodiment, the method for preparing a polymer electrolyte membrane according to this application further includes drying the obtained product 2.

[0052] The purpose of drying is to remove residual solvent. Drying can be performed using any method conventionally used in the art, as long as it removes the solvent without degrading the electrolyte membrane. A vacuum drying oven can be used for drying.

[0053] In any embodiment, in the method for preparing a polymer electrolyte membrane according to this application, the ratio of the total mass of monomer 1, monomer 2, and monomer 3 to the mass of monomer 4 is 20:1 to 2:1.

[0054] In any embodiment, in the method for preparing a polymer electrolyte membrane according to this application, the mass ratio of the total mass of monomer 1, monomer 2, monomer 3, and monomer 4 to the mass of the lithium salt is in the range of 2.3 to 13.6.

[0055] In any embodiment, in the method for preparing a polymer electrolyte membrane according to this application, the weight ratio of the lithium salt to the initiator is 5:1 to 60:1; if a catalyst is used, the ratio between the sum of the weights of the lithium salt and the catalyst and the weight of the initiator is 7:1 to 80:1.

[0056] The initiator can be used to initiate the block copolymerization reaction of the polymer described in this application, and the lithium salt and catalyst can be used to initiate the ionic polymerization reaction of the second polymer. The ratio of the two can, to a certain extent, reflect the distribution of the two polymers and the structural composition of the interpenetrating network.

[0057] It is now believed that the polymer described in this application is prepared by block copolymerization initiated by an initiator. The second polymer is prepared by ionic polymerization catalyzed by a lithium salt and optionally a catalyst. Although the monomers of the two polymers are mixed together, they are prepared independently without interfering with each other. Furthermore, since the monomers, initiator, and optionally catalyst are uniformly mixed in solution before the polymerization reaction, the resulting product after complete polymerization is an interpenetrating network structure in which the polymer network and the second polymer network are uniformly interpenetrated, and the lithium salt is uniformly dispersed therein.

[0058] Optionally, in any embodiment, this application provides a solid electrolyte membrane prepared by the method described above for preparing a solid polymer electrolyte membrane.

[0059] This application provides a fifth aspect of a secondary battery, including a positive electrode and a negative electrode, wherein the battery further includes the polymer electrolyte membrane described in the third aspect of this application or a polymer electrolyte membrane prepared by the method described in the fourth aspect of this application. The secondary battery, battery module, battery pack, and power-consuming device of this application will be described below.

[0060] In any embodiment, the positive electrode includes a positive current collector and a positive electrode film layer, wherein the positive electrode film layer includes a positive electrode active material, the aforementioned second polymer, and the aforementioned lithium salt. Optionally, the second polymer accounts for 2-15% of the mass of the positive electrode film layer, and optionally, the lithium salt accounts for 0.5-10% of the mass of the positive electrode film layer.

[0061] Using a second polymer in the positive electrode membrane has the following advantages: the internal pores of the positive electrode membrane are filled with a fluid second polymer and lithium salt. The fluid second polymer not only wets the inside of the electrode, but the movement of its chain segments also provides a channel for lithium ions to transport inside the electrode, thereby enhancing ion transport inside the positive electrode membrane.

[0062] In any embodiment, in the secondary battery, the negative electrode includes a negative electrode current collector and a metal sheet formed of lithium metal or a lithium alloy.

[0063] The polymer electrolyte membrane described in this application is suitable for use with high specific capacity (3860 mAh / g) and extremely low potential (-3.04 V vs. H2 / H). + It can be used with lithium metal anode, lithium alloy anode, or a combination of both. Optionally, the thickness of the anode sheet is 9~50 μm.

[0064] The lithium alloys include, but are not limited to, lithium-aluminum alloys, lithium-magnesium alloys, and lithium-boron alloys.

[0065] In any embodiment, the thickness of the polymer electrolyte membrane in the secondary battery is 10~1000µm.

[0066] A sixth aspect of this application provides a battery module, which includes the secondary battery described in the fifth aspect of this application.

[0067] A seventh aspect of this application provides a battery pack, which includes the battery module described in the sixth aspect of this application.

[0068] An eighth aspect of this application provides an electrical device comprising at least one selected from the secondary battery described in the fifth aspect of this application, the battery module described in the sixth aspect of this application, or the battery pack described in the seventh aspect of this application. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of the interpenetrating network structure of the polymer and the second polymer described in this application, where the dots represent lithium salts and the two different random lines represent the polymer and the second polymer, respectively.

[0070] Figure 2 The charge-discharge curves of the cell (i.e., the battery obtained after matching the positive and negative electrodes) during high-voltage cycling performance testing of the solid electrolyte membrane prepared in Example 1 are shown.

[0071] Figure 3 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0072] Figure 4 yes Figure 3 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0073] Figure 5 This is a schematic diagram of a battery module according to one embodiment of this application.

[0074] Figure 6 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0075] Figure 7 yes Figure 6 An exploded view of a battery pack according to one embodiment of this application is shown.

[0076] Figure 8 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0077] Explanation of reference numerals in the attached figures:

[0078] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0079] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the polymer, polymer electrolyte membrane, lithium battery, and manufacturing method thereof. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0080] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-6. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when stating that a parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. In this article, when representing a range, "~" and "-" have the same meaning.

[0081] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0082] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0083] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0084] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0085] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0086] Solid-state batteries can be classified into four categories based on their solid electrolyte chemical systems: polymer, sulfide, oxide, and chloride. Among them, polymer solid electrolytes, represented by the polyethylene oxide (PEO) system, were the first to achieve commercial application in the 1990s due to their advantages such as good interfacial wetting, excellent processing performance, lightweight and low density, and low cost. However, most of these polymer electrolytes have a low voltage window (e.g., PEO ≥ 3.9V), making it difficult to match with high-voltage cathodes. This greatly limits the improvement of battery energy density. At the same time, the flammability of polymers cannot meet the high safety requirements of next-generation batteries.

[0087] One example of a high-voltage resistant solid electrolyte membrane is prepared using a modified aluminum-based polymer. This electrolyte membrane is made by uniformly mixing the modified aluminum-based polymer, branched polymer, and electrolyte, adding a photoinitiator, and then cross-linking under stirring conditions. Secondary batteries with this electrolyte membrane exhibit high conductivity and can achieve stable cycling at 4.2V. Furthermore, due to the cross-linked structure of the polymer, it provides high mechanical strength to the solid electrolyte membrane and reduces dendrite formation, thereby improving the safety of lithium metal secondary batteries. However, this modified aluminum-based polymer membrane has a polyester-based structure, which is inherently not resistant to high voltage, and the improvement in high-voltage stability after aluminum-based modification is limited. Secondly, this modified aluminum-based polymer membrane contains inorganic components and has a cross-linked structure; although mechanical properties are improved, this affects the interfacial contact between the solid electrolyte membrane and the positive and negative electrodes. Additionally, this solid electrolyte membrane only focuses on high-voltage resistance and does not address the material's inherent safety properties such as flame retardancy.

[0088] Unexpectedly, this application provides a new polymer that has good flame retardant properties and can form an interpenetrating network structure with other polymers. Using a polymer with this structure as an electrolyte membrane can provide better mechanical strength, and the secondary battery prepared using this electrolyte membrane has better safety performance, better high-voltage stability and better high-voltage cycle performance, and can achieve better interfacial contact between the electrolyte membrane and the positive and negative electrodes.

[0089] Therefore, the first aspect of this application provides a polymer polymerized from monomer 1, monomer 2, and monomer 3, wherein monomer 1 has a structure of formula 1, monomer 2 has a structure of formula 2, and monomer 3 has a structure of formula 3.

[0090]

[0091] in,

[0092] R1 and R3 are each independently selected from hydrogen or C. 1-10 alkyl;

[0093] R4 is selected from C 1-10 A hydrocarbon group or a C group containing one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus. 1-10 hydrocarbon group;

[0094] R2 and R5 are each independently selected from hydrogen and C. 1-10 Hydrocarbon group or hydrocarbon group containing one or more of the elements fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus with a carbon number of less than or equal to 10, containing C=C or C≡C;

[0095] Rf is selected from hydrogen, or an ethoxy chain segment containing one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus with a carbon number of less than or equal to 16.

[0096] x is the number of repeating units of the methylene group, 0 ≤ x ≤ 20;

[0097] A + It is selected from one of the functional groups with nitrogen, sulfur, or phosphorus as the cation center;

[0098] Q - It is one, two or more anions selected from halide ions, haloborate ions, halooxaloborate ions, perhalate ions, halophosphate ions, and halosulfonylimide ions, optionally Q - It is one, two or more anions selected from chloride ion, tetrafluoroborate, difluorooxalateborate, perchlorate, hexafluorophosphate, and bis(fluorosulfonyl)imide.

[0099] E is selected from the structures (1) to (3).

[0100]

[0101] R6 is selected from hydrogen or C. 1-10 alkyl.

[0102] In this application, C 1-10 The alkyl group is a straight-chain or branched alkyl group containing 1-10 carbon atoms, including, but not limited to, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, isopropyl, isobutyl, tert-butyl, isopentyl, tert-pentyl, neopentyl, 2-methylpentyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 2-methylhexyl, 3-methylhexyl, 2,2-dimethylpentyl, 3,3-dimethylpentyl, 2,3-dimethylpentyl, 2,4-dimethylpentyl, 3-ethylpentyl, 2,2,3-trimethylbutyl, 2-methylheptyl 2,2-dimethylhexyl, 3-methylheptyl, 4-methylheptyl, 2,2-dimethylhexyl, 3,3-dimethylhexyl, 2,3-dimethylhexyl, 2,4-dimethylhexyl, 2,5-dimethylhexyl, 3,4-dimethylhexyl, 3-ethylhexyl, 2,2,3-trimethylpentyl, 2,2,4-trimethylpentyl, 2,3,3-trimethylpentyl, 2,3,4-trimethylpentyl, 2-methyl-3-ethylpentyl, 3-methyl-3-ethylpentyl, 2,2,3,3-tetramethylbutyl, nonyl, decyl.

[0103] In this application, C 1-10 Hydrocarbon groups may include the above-mentioned C 1-10 Alkyl, C 6-10 Aromatic, straight-chain or branched C 2-10alkenyl, straight-chain or branched C 2-10 Alkyne groups, etc. C 6-10 The aromatic group can be, for example, phenyl, naphthyl, C 1-4 Alkyl-substituted phenyl. C 2-10 The alkenyl group can be, for example, vinyl, propenyl, allyl, butenyl, butadienyl, pentenyl, pentadienyl, hexenyl, etc. C 2-10 The alkynyl group can be, for example, ethynyl, propynyl, butynyl, butyynyl, pentynyl, pentynyl, hexynyl, etc.

[0104] In this application, the R4 group of monomer 2 is defined as "a C group containing one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus". 1-10 The "hydrocarbon group" can be straight-chain or branched, monosubstituted or polysubstituted, saturated or unsaturated. "Containing one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus" indicates that these elements are contained in a substituted form, such as, but not limited to, fluorine, chlorine, bromine, and iodine. These elements can also be contained in other forms, such as as components of a group or the main structure of a structural formula, such as, but not limited to, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus, as long as it is chemically feasible. For example, the R4 group can be phenyl, vinyl, propenyl, allyl, pyridyl, pyrimidinyl, etc.

[0105] In this application, the R2 and R5 groups of monomer 2 are defined as "hydrocarbon groups containing C=C or C≡C with one or more carbon atoms of one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus, and the number of carbon atoms is less than or equal to 10." This can also be expressed as C=C or C≡C groups containing one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus. 2-10 alkenyl or C 2-10 The alkynyl group can be straight-chain or branched, and monosubstituted or polysubstituted. As mentioned above, C 2-10 The alkenyl group can be, for example, vinyl, propenyl, butenyl, butadienyl, pentenyl, pentadienyl, hexenyl, etc.; C 2-10 The alkynyl group can be, for example, ethynyl, propynyl, butynyl, butyynyl, pentynyl, pentyynyl, hexynyl, etc. "Containing one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus" indicates that these elements are contained in a substituted form, such as, but not limited to, fluorine, chlorine, bromine, and iodine. These elements can also be contained in other forms, such as as a group or a component of the main structure of a structural formula, such as, but not limited to, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus, as long as it is chemically feasible. As examples, R2 and R5 can be hydrogen, vinyl, propenyl, allyl, etc.

[0106] In this application, the definition of the Rf group in monomer 3, "an ethoxy segment containing one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus with a carbon number of less than or equal to 16," indicates a segment having 1 to 8 ethoxy groups and containing one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus. "Containing one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus" indicates that these elements are contained in a substituted form, such as, but not limited to, fluorine, chlorine, bromine, and iodine, or in other forms, such as as components of a group or the main structure of a structural formula, such as, but not limited to, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus, as long as it is chemically feasible. The 1 to 8 ethoxy segments can also be branched or straight-chain C 1-10 Alkyl or haloalkyl substitution. As an example, an ethoxy segment containing one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus with 16 or fewer carbon atoms can be an ethoxy segment attached to cyclotriphosphazene, or an ethoxy segment substituted with one or more elements selected from fluorine, chlorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus.

[0107] In this application, A + In the definition, "functional groups with nitrogen, sulfur, or phosphorus as cation centers" means that the functional group contains nitrogen, sulfur, or phosphorus, and that nitrogen, sulfur, or phosphorus is the cation center. Optionally, A + The functional group is a nitrogen-containing cation, more preferably selected from ammonium cations, imidazolium cations, and pyridinium cations, and most preferably, A + -N(R')2 + -、

[0108] or R' is independently selected from hydrogen or C. 1-10 alkyl.

[0109] In this application, Q - Defined as one, two, or more anions selected from halide ions, haloborate ions, halooxaloborate ions, perhalate ions, halophosphate ions, and halosulfonamide ions, the number of anions depending on A. + The number of cations in, for example, in A + When the group carries two positive charges, Q - It can be two anions with a single charge. A + Q - The number of ions in the sample is not specifically limited, as long as it is chemically feasible.

[0110] In this application, the halide ion may be a fluoride ion, chloride ion, bromide ion, or iodide ion. The halogenation may be fluorinated, chlorinated, brominated, or iodinated, and may be fluorinated. The halogenation may be monosubstituted, disubstituted, or polysubstituted. The perhalate anion may be a perfluoride anion, perchlorate anion, perbromate anion, or periodate anion.

[0111] The polymer provided in this application is formed by the polymerization of three monomers (monomer 1, monomer 2, and monomer 3), with an ethyl group as the main chain. Its molecular structure contains functional groups such as ionic groups (from monomer 1), amides (from monomer 1), phosphate esters (from monomer 2), and fluorinated ethoxy groups (from monomer 3). These functional groups each provide different functions to the polymer. It is believed, for example, that the presence of the ionic groups and fluorine (mainly from monomer 3) is beneficial for improving the material's oxidation resistance or high-voltage stability (especially at voltages above 5V). When the polymer is used as an electrolyte membrane material in a secondary battery, the flexible ethoxy side chains in the polymer can drive lithium ion migration, and the cation centers in the ionic groups can interact with the anions in the lithium salt, thereby increasing the lithium ion migration number. The synergistic effect of the phosphate ester groups from monomer 2 and the fluorine element (mainly from monomer 3) makes the electrolyte containing the polymer exhibit excellent flame retardant properties, which can improve the safety of the battery when applied to lithium secondary batteries. The amide from monomer 1 gives the polymer molecules strong hydrogen bonding, and the presence of the strong hydrogen bonding and the construction of the cross-linked network centered on the phosphate ester (from monomer 2) are beneficial to enhancing the mechanical properties of the polymer material.

[0112] The polymer described in this application may be a random triblock polymer. In some embodiments, the polymer described in this application has the following structural formula:

[0113]

[0114] Among them, R1, R2, R3, R4, Rf, E, A + Q - x is defined above, and

[0115] n, m, and p are the number of repeating units, where 0 < n ≤ 5000, 0 < m ≤ 1000, 0 < p ≤ 5000, and

[0116] The ratio of n to m (n:m) is in the range of 1:1 to 25:1, and the ratio of p to m (p:m) is in the range of 1:1 to 25:1.

[0117] The tilde represents the crosslinking site between a polymer molecule of Formula 4 and another polymer molecule of Formula 4.

[0118] Optionally, the polymer has a triblock structure. The triblock structure of the polymer can block the contact between ethoxy side chains, reduce the crystallinity of the polymer material, and improve ionic conductivity when used in electrolyte membranes.

[0119] In some embodiments, the fluorine substitution rate in the Rf group is greater than 29.0%, and the fluorine substitution rate is the percentage of fluorine atoms based on the number of hydrogen atoms that can be substituted in the Rf group.

[0120] The term "number of substituted hydrogen atoms" should be understood as the number of substituted sites in the Rf group, that is, the maximum number of hydrogen atoms that can be bonded to carbon atoms, phosphorus atoms, nitrogen atoms, and sulfur atoms present in the group. If the hydrogen atoms have been replaced by other elements, such as halogen atoms, the number of substituted hydrogen atoms is the sum of the number of hydrogen atoms and the number of other atoms substituted.

[0121] A fluorine substitution rate of 29.0% or higher ensures the flame retardant properties of the polymer and improves the high-voltage stability and high-voltage cycle performance of batteries made from the polymer.

[0122] In some embodiments, in the polymer, cationic A + Choose one of the structural formulas (4) to (6):

[0123]

[0124] In some embodiments, in the polymer, the molar percentage of monomer 1 ranges from 3.7 to 92.6 mol%, the molar percentage of monomer 2 ranges from 2.0 to 33.3 mol%, and the molar percentage of monomer 3 ranges from 3.7 to 92.6 mol%, all based on the total molar number of monomers 1, 2, and 3.

[0125] Optionally, the molar ratio of monomer 1 to monomer 2 is in the range of 1:1 to 25:1;

[0126] Alternatively, the molar ratio of monomer 3 to monomer 2 is in the range of 1:1 to 25:1.

[0127] In some embodiments, the polymer has a thermal conductivity in the range of 0.06 to 0.35 W / m K and a flame retardant rating of 94V-0 or 94V-1.

[0128] The thermal conductivity of the polymer and the electrolyte membrane can be determined according to GB / T 10294-2008.

[0129] The flame retardancy rating of the polymer and the electrolyte membrane can be determined according to the UL94 vertical burning test of ASTM D3801.

[0130] The second aspect of this application provides a method for preparing the polymer described in the first aspect of this application, comprising the following steps: dissolving monomer 1, monomer 2, monomer 3, and an initiator in a solvent, reacting them under vacuum at 30–100°C for 0.2–24 h, optionally 6–24 h, and then drying. The polymer is in the form of a block copolymer. Optionally, the drying is carried out under vacuum at 25–140°C for 1–48 h. The main purpose of drying is to remove the solvent remaining after the reaction.

[0131] A third aspect of this application provides a polymer electrolyte membrane comprising the polymer described in the first aspect of this application or a polymer prepared by the method described in the second aspect of this application.

[0132] In some embodiments, the polymer electrolyte membrane further includes a second polymer dispersed within the polymer to form an interpenetrating network structure. The second polymer is formed from monomer 4, which has the following general formula:

[0133]

[0134] in,

[0135] R7 is selected from hydrogen, or a hydrocarbon group with less than 7 carbon atoms that is unsubstituted or substituted by one or more elements selected from fluorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus.

[0136] As described above, "hydrocarbon groups with fewer than 7 carbon atoms" include, but are not limited to: alkyl groups with fewer than 7 carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, isopropyl, isobutyl, tert-butyl, isopentyl, tert-pentyl, neopentyl, 2-methylpentyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, etc.; alkenyl groups with fewer than 7 carbon atoms, such as ethylene, propylene, butene, butadiene, pentene, pentadiene, hexene, etc.; and alkynyl groups with fewer than 7 carbon atoms, such as acetylene, propyne, butyne, pentyne, hexyne, etc. Hydrocarbon groups with fewer than 7 carbon atoms can be unsubstituted or monosubstituted or polysubstituted by one or more elements selected from fluorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus.

[0137] In this application, the second polymer is used in contrast to the aforementioned polymer, and is intended to distinguish it from the aforementioned polymer.

[0138] The polymer described in this application can form an interpenetrating network structure with other polymers, optionally with flowable polymers, to obtain a polymer with higher mechanical strength. Optionally, the second polymer is uniformly dispersed in the polymer to form an interpenetrating network structure. See the schematic diagram of the interpenetrating network of the polymer and the second polymer. Figure 1 .

[0139] The interpenetrating network structure is a special type of blend, also known as an interpenetrating polymer network (IPN).

[0140] In solid electrolyte membranes comprising an interpenetrating network structure formed by a polymer network and a second polymer network, the presence of ionic groups and fluorine in the polymer network effectively enhances the high-voltage stability of the electrolyte membrane and gives it a wide electrochemical window, making it suitable for high-voltage battery systems. For example, it exhibits excellent cycle stability in NCM811 / Li batteries. Furthermore, the synergistic effect of phosphate groups and fluorine in the polymer network gives the polymer electrolyte membrane excellent flame-retardant properties, improving the safety of lithium metal batteries. In addition, the flexible ethoxy segments in the polymer network can drive lithium-ion migration, and ionic groups with nitrogen, phosphorus, and sulfur as cation centers can restrict the movement of anions in lithium salts by interacting with them, thereby increasing the lithium-ion transference number. The strong hydrogen bonding between amide molecules in the polymer network and the construction of a cross-linked network centered on phosphate esters are beneficial to enhancing the mechanical properties of the material. At the same time, the triblock structure of the polymer can also form contacts with the ethoxy side chain base, reducing the crystallinity of the material and improving the ionic conductivity of the electrolyte membrane.

[0141] It should be understood that the foregoing description of polymers also applies to polymers in interpenetrating networks or electrolyte membranes.

[0142] The second polymer described in this application is an oligomer with carbonate as the main chain and a number average molecular weight M. n <2000 Da, viscosity less than 3000 cP, and possessing a certain degree of fluidity. The second polymer can also be called a carbonate polymer. This oligomer is uniformly dispersed in the polymer network as a second polymer network, i.e., in the above-mentioned random triblock polymer. The presence of the carbonate backbone in the second polymer network ensures the high-voltage stability of the formed electrolyte membrane and contributes to the excellent high-voltage resistance of the secondary battery containing the electrolyte membrane. The second polymer in the interpenetrating network structure has a certain degree of fluidity and can play a role in wetting the electrode, thereby improving the interfacial contact between the electrolyte membrane and the positive and negative electrodes. Therefore, in the solid electrolyte membrane including the interpenetrating network formed by the polymer network and the second polymer network, the introduction of the fluid second polymer network not only improves the wetting performance between the electrolyte membrane and the electrode and improves the interfacial contact between the electrolyte membrane and the positive and negative electrodes, but also ensures the high ionic conductivity of the electrolyte membrane because the chain movement of carbonate can drive the migration of lithium ions.

[0143] In some alternative embodiments, the electrolyte membrane containing the above-described interpenetrating network structure described in this application is suitable for high-voltage battery systems, such as 5V high-voltage battery systems. High-voltage battery cell series include, but are not limited to, LiNi... 0.8 Co 0.1 Mn 0.1 O2, LiCoO2, LiMn2O4, LiNiCoAlO2, LiNi 0.5 Mn 1.5 O4 and other battery systems.

[0144] Optionally, in the interpenetrating network structure, the mass ratio of the polymer to the second polymer is 20:1 to 2:1.

[0145] In some embodiments, the polymer electrolyte membrane further includes a lithium salt selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalate borate (LiDFOB), lithium perchlorate (LiClO4), and lithium dioxoborate (LiBOB).

[0146] The type of lithium salt affects the lithium-ion transference number of the prepared polymer electrolyte membrane. Different lithium salts exhibit varying degrees of dissociation between their cations and anions due to their different structures; lithium salts with higher degrees of dissociation can provide more charge carriers. + The concentration of [Li] affects the coordination-dissociation process between [Li] and the ether oxygen atoms and carbonyl groups in the polymer chain, thus affecting the charging and discharging process of Li. + And the migration ability of anions in the battery. Typically, PEO-based electrolytes have ether oxygen atoms that interact with Li... + The multidentate coordination chelation between them, and with TFSI – The relatively weak solvent effect of the anion results in a transfer number of less than 0.2.

[0147] In some embodiments, the lithium salt content in the polymer electrolyte membrane is in the range of 6.8% to 30.0% by mass, based on the total mass of the polymer electrolyte membrane.

[0148] Optionally, in the polymer electrolyte membrane, the mass ratio of the interpenetrating network structure to the lithium salt can also be expressed as the mass ratio of the total mass of the polymer and the second polymer to the lithium salt, or the mass ratio of the total mass of monomers 1 to 4 to the lithium salt, that is, 2.3 to 13.6.

[0149] In some embodiments, the fluorine content in the polymer electrolyte membrane is in the range of 12.5% ​​to 46.0% based on the total weight of the polymer electrolyte membrane.

[0150] To ensure the dual properties of high-pressure resistance and flame retardancy in the electrolyte membrane prepared using polymers, the substitution of fluorine in the Rf groups of the polymer should ideally be greater than or equal to 29.0%. Furthermore, controlling the fluorine content within this range in the polymer electrolyte membrane prepared using polymers is more conducive to achieving both high-pressure resistance and flame retardancy.

[0151] A third aspect of this application provides a method for preparing a polymer electrolyte membrane, comprising the following steps:

[0152] The monomers 1, 2, and 3 mentioned above, monomer 4 mentioned above, lithium salt mentioned above, optional catalyst, and initiator are reacted at 30-100°C for 0.2-24 h to obtain product 1. It is now believed that in this step, monomers 1, 2, and 3 undergo co-block polymerization in the presence of the initiator to form the polymer, and monomer 4 undergoes ionic copolymerization in the presence of lithium salt and optional catalyst to form a fluid second polymer.

[0153] An initiator is used to initiate a block copolymerization reaction between monomer 1, monomer 2, and monomer 3 to form the polymer described in this application. The initiator includes, but is not limited to, azo or peroxide molecules, such as 2,2'-azobis(2,4-dimethylpentanonitrile), 2,2'-azobis(isobutylnitrile), 2,2'-azobis(methylbutanonitrile), 1,1'-azobis(cyanocyclohexane), benzoyl peroxide, dodecyl peroxide, di-tert-butyl peroxide, diisopropyl peroxide, and dicyclohexyl peroxide.

[0154] Optionally, the mass of the initiator does not exceed 5% of the total mass of the two polymer monomers and the lithium salt (i.e., the sum of the masses of monomer 1, monomer 2, monomer 3, monomer 4 and lithium salt).

[0155] The lithium salt is as described above. The lithium salt can be used to catalyze the ionic polymerization of monomer 4 to form a fluid-like second polymer.

[0156] In some cases, using only lithium salts to catalyze the ionic polymerization of monomer 4 is insufficient, and a catalyst is also required. Suitable catalysts include, but are not limited to, stannous isooctanoate, aluminum trifluoromethanesulfonate, aluminum trichloride, trimethylsilyl trifluoromethanesulfonate, boron trifluoride diethyl ether, triethylamine, and 1,8-diazabicyclo[5.4.0]undec-7-ene. The catalyst catalyzes the polymerization of the second polymer. In this application, the second polymer is obtained through ionic polymerization.

[0157] Optionally, in the method for preparing the polymer electrolyte membrane, monomer 1, monomer 2, monomer 3, monomer 4, lithium salt, catalyst, and initiator are dissolved in a solvent, and a homogeneous solution is obtained by stirring or other means.

[0158] Optionally, the homogeneous solution is poured into a tool conventionally used in the art (e.g., a polytetrafluoroethylene mold), heated to 30-100°C, and reacted under vacuum for 0.2-24 h. Optionally, the reaction is carried out in a vacuum oven.

[0159] In some embodiments, the method for preparing a polymer electrolyte membrane further includes a step of anion exchange of the obtained product 1 with a lithium salt solution to obtain product 2.

[0160] As mentioned earlier, Q exists in monomer 1. - Anions, some of which (such as chloride ions) may be detrimental to the cell system, for example, they may cause corrosion. Therefore, anion exchange is necessary. After anion exchange, the anions Q-type ions inherent in the ionic groups of the resulting polymer can be released. - For example, Cl, which can corrode aluminum foil - The target anion is replaced, optionally, with an anion of the same type as the anion in the lithium salt. This prevents some side reactions and also adjusts the binding affinity between the anion and the polymer and lithium ions.

[0161] Generally, the concentration of anions in the lithium salt solution used for anion exchange needs to be much higher than that in the polymer. - The concentration of Q. - The concentration of [the substance] can be determined using conventional techniques in the field, for example, in Cl [the concentration of the substance]. - In the case of chloride ions, silver nitrate can be used for titration in a neutral solution with potassium chromate as an indicator. The chloride ion concentration can be calculated by measuring the volume of silver nitrate solution consumed.

[0162] The lithium salt solution is a separately prepared solution. The lithium salt in the lithium salt solution may be the same as or different from the lithium salt in the electrolyte membrane; it is more advantageous if they are the same. Optionally, anion exchange may be performed for 1 to 20 hours. This time is not limiting and can be adjusted according to the actual situation.

[0163] In anion exchange, the solvent in the lithium salt solution used can be, for example, but not limited to, acetone, acetonitrile, ethylene glycol dimethyl ether, dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate.

[0164] In some embodiments, the method for preparing a polymer electrolyte membrane according to this application further includes drying the obtained product 2.

[0165] The purpose of drying is to remove residual solvent. Drying can be performed using any method conventionally used in the art, as long as it removes the solvent without degrading the electrolyte membrane. A vacuum drying oven can be used for drying.

[0166] Optionally, the drying temperature does not exceed 140°C and the drying time at 140°C does not exceed 1 hour.

[0167] Optionally, the thermal shrinkage temperature of the electrolyte membrane is around 140~160°C.

[0168] In some embodiments, in the method for preparing a polymer electrolyte membrane according to this application, the mass ratio of the total mass of monomer 1, monomer 2, and monomer 3 to the mass of monomer 4 is 20:1 to 2:1.

[0169] In some embodiments, in the method for preparing a polymer electrolyte membrane according to this application, the mass ratio of the total mass of monomer 1, monomer 2, monomer 3, and monomer 4 to the mass of the lithium salt is in the range of 2.3 to 13.6.

[0170] In some embodiments, in the method for preparing a polymer electrolyte membrane according to this application, the weight ratio of the lithium salt to the initiator is 5:1 to 60:1; if a catalyst is used, the ratio between the sum of the weights of the lithium salt and the catalyst and the weight of the initiator is 7:1 to 80:1.

[0171] The initiator can be used to initiate the block copolymerization reaction of the polymer described in this application, and the lithium salt and catalyst can be used to initiate the ionic polymerization reaction of the second polymer. The ratio of the two can, to a certain extent, reflect the distribution of the two polymers and the structural composition of the interpenetrating network.

[0172] According to this application, in the preparation of the polymer and electrolyte membrane, the solvent used may be acetonitrile or other solvents conventionally used in the art, such as acetone, 1,4-dioxane, etc. N 1-Methylpyrrolidone, dimethyl sulfoxide, ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, dimethyl glycol ether, etc.

[0173] It is now believed that the polymer described in this application is prepared by block copolymerization initiated by an initiator. The second polymer is prepared by ionic polymerization catalyzed by a lithium salt and optionally a catalyst. Although the monomers of the two polymers are mixed together, they are prepared independently without interfering with each other. Furthermore, since the monomers, initiator, and optionally catalyst are uniformly mixed in solution before the polymerization reaction, the resulting product after complete polymerization is an interpenetrating network structure in which the polymer network and the second polymer network are uniformly interpenetrated, and the lithium salt is uniformly dispersed therein.

[0174] It should be understood that the descriptions of method parameters and conditions such as solvents and initiators in the preparation of electrolyte membranes here also apply to the aforementioned polymer preparation methods.

[0175] Optionally, in some embodiments, this application provides a solid electrolyte membrane prepared by the method described above for preparing a solid polymer electrolyte membrane.

[0176] This application provides a fifth aspect of a secondary battery, including a positive electrode and a negative electrode, wherein the battery further includes the polymer electrolyte membrane described in the third aspect of this application or a polymer electrolyte membrane prepared by the method described in the fourth aspect of this application. The secondary battery, battery module, battery pack, and power-consuming device of this application will be described below.

[0177] Secondary batteries

[0178] The secondary battery described in this application includes a positive electrode, a negative electrode, and the polymer electrolyte membrane described in this application. During the charging and discharging process, active ions move back and forth between the positive and negative electrode, inserting and extracting. The polymer electrolyte membrane acts as a conductor of ions between the positive and negative electrode.

[0179] [Positive electrode plate]

[0180] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0181] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0182] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0183] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0184] Optionally, the positive electrode active material includes lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMnO2, LiMn2O4, etc.), and lithium nickel cobalt manganese oxide (LiNi). 0.8 Co 0.1 Mn 0.1 O2 or LiNi 0.6 Co 0.2 Mn 0.2O2), etc.

[0185] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0186] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0187] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer, wherein the positive electrode film layer includes a positive electrode active material, the aforementioned second polymer, and the aforementioned lithium salt. Optionally, the second polymer accounts for 2-15% of the mass of the positive electrode film layer, and optionally, the lithium salt accounts for 0.5-10% of the mass of the positive electrode film layer.

[0188] The lithium salt in the positive electrode film can be the same as or different from the lithium salt in the electrolyte. The aforementioned description of the lithium salt in the electrolyte film also applies to the lithium salt in the positive electrode film.

[0189] In some alternative embodiments, the positive electrode sheet can be prepared by dispersing the positive electrode active material, conductive agent (e.g., Super-p), monomer 4 used to prepare the second polymer, and any other components in a solvent (e.g., N-methylpyrrolidone, NMP), then adding the lithium salt and optionally a catalyst, and mixing to form a uniform positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and obtaining the positive electrode sheet after drying and other processes. Optionally, the drying can be carried out in an oven at 30~100°C. Optionally, in this preparation, the positive electrode active material accounts for 80%~95%, the conductive agent accounts for 1~5%, the monomer 4 accounts for 2~15%, and the lithium salt accounts for 0.5~10%, all based on the total weight of the positive electrode active material, conductive agent, monomer 4, and any other components.

[0190] Optionally, the lithium salt in the positive electrode membrane, the lithium salt in the electrolyte membrane, and the lithium salt in the optional anion exchange operation are of the same type.

[0191] Using a second polymer in the positive electrode membrane has the following advantages: the internal pores of the positive electrode membrane are filled with a fluid second polymer and lithium salt. The fluid second polymer not only wets the inside of the electrode, but the movement of its chain segments also provides a channel for lithium ions to transport inside the electrode, thereby enhancing ion transport inside the positive electrode membrane.

[0192] [Negative electrode plate]

[0193] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0194] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0195] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0196] In some embodiments, the negative electrode in the secondary battery includes a negative electrode current collector and a metal sheet formed of lithium metal or a lithium alloy.

[0197] The negative electrode current collector can be copper foil, but is not limited to continuous copper foil. It can also be copper wire woven copper mesh, foamed copper, or three-dimensional nanoporous copper.

[0198] The polymer electrolyte membrane described in this application is suitable for use with high specific capacity (3860 mAh / g) and extremely low potential (-3.04 V vs. H2 / H). + It can be used with lithium metal anode, lithium alloy anode, or a combination of both. Optionally, the thickness of the anode sheet is 9~50 μm.

[0199] The lithium alloys mentioned include, but are not limited to, lithium-aluminum alloys, lithium-magnesium alloys, and lithium-boron alloys. It should be understood that the lithium alloys described in this application are not limited to these three types; other lithium alloys capable of achieving the above objectives are also acceptable.

[0200] In some embodiments, the negative electrode sheet is commercially available or can be directly coated onto the current collector by cold pressing lithium metal and / or lithium alloy.

[0201] [Polymer electrolyte membrane]

[0202] The electrolyte acts as a conductor of ions between the positive and negative electrodes. Specifically, the secondary battery uses the solid polymer electrolyte membrane described in this application, which effectively conducts lithium ions and exhibits high safety performance.

[0203] In some embodiments, the thickness of the polymer electrolyte membrane in the secondary battery is 10~1000µm.

[0204] The positive electrode, the solid polymer electrolyte membrane, and the negative electrode are stacked in sequence to assemble a battery.

[0205] [Outer Packaging]

[0206] In some embodiments, the secondary battery may include an outer packaging for encapsulating the positive electrode, negative electrode, and electrolyte. As an example, the positive electrode, solid polymer electrolyte membrane, and negative electrode may be stacked to form a stacked cell or wound to form a wound cell, with the cell encapsulated within the outer packaging. The number of cells in the secondary battery can be one or more, adjustable as needed.

[0207] In one embodiment, this application provides an electrode assembly. In some embodiments, the positive electrode, solid electrolyte membrane, and negative electrode are fabricated into the electrode assembly using a lamination process or a winding process. The outer packaging can be used to encapsulate the aforementioned electrode assembly and solid electrolyte membrane.

[0208] In some embodiments, the outer packaging of the secondary battery can be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS). In some embodiments, the outer packaging of the secondary battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell.

[0209] Methods for preparing secondary batteries

[0210] In one embodiment, this application provides a method for preparing a secondary battery, wherein the polymer electrolyte membrane described in this application or the polymer electrolyte membrane prepared according to the method described in this application is used.

[0211] The fabrication of a secondary battery may also include the step of assembling the negative electrode, positive electrode, and electrolyte of this application to form a secondary battery. In some embodiments, the positive electrode, polymer electrolyte membrane, and negative electrode may be stacked in sequence and cold-pressed to assemble a full battery.

[0212] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3This is an example of a square-structured secondary battery 5.

[0213] In some implementations, refer to Figure 4 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0214] A sixth aspect of this application provides a battery module, which includes the secondary battery described in the fifth aspect of this application.

[0215] A seventh aspect of this application provides a battery pack, which includes the battery module described in the sixth aspect of this application.

[0216] An eighth aspect of this application provides an electrical device comprising at least one selected from the secondary battery described in the fifth aspect of this application, the battery module described in the sixth aspect of this application, or the battery pack described in the seventh aspect of this application.

[0217] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0218] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0219] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0220] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0221] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0222] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0223] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0224] Figure 8 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0225] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0226] Example

[0227] The following are embodiments used to illustrate this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0228] In the examples below, N,N,N-trimethyl-3-(2-methylallylamino)-1-propanediamine chloride, triallyl phosphate, perfluoropolyether acrylate (PFPE-MAA-1000), and fluoroethylene carbonate were purchased from Aladdin Reagents, Monomer-Polymer & Dajac Labs, Suzhou Cangmu, and Aladdin Reagents, respectively.

[0229] I. Preparation of polymers, second polymers, electrolyte membranes, and secondary batteries

[0230] I-1. Polymer Preparation

[0231] At 25°C and under a nitrogen atmosphere, 1.103 g of N,N,N-trimethyl-3-(2-methylallylamino)-1-propanediamine chloride, 0.218 g of triallyl phosphate, 5.465 g of perfluoropolyether acrylate (PFPE-MAA-1000), and 0.063 g of azobisisobutyronitrile (AIBN) were added to 20 mL of acetonitrile. The mixture was stirred magnetically until homogeneous, heated to 65°C, and reacted for 10 h. Then, the mixture was dried in a vacuum oven at 45°C for 6 h to obtain the polymer.

[0232] I-2. Preparation of the second polymer

[0233] The second polymer is ion-polymerized using fluoroethylene carbonate, as follows:

[0234] At 65°C, 1.4 g of fluoroethylene carbonate, 0.014 g of stannous isooctanoate, and 1.871 g of lithium difluorosulfonyl imide were uniformly mixed and reacted for 10 h to obtain a flowable second polymer. The number-average molecular weight of the second polymer was 2000. The molecular weight determination method is as follows:

[0235] Dissolve the above polymer in N In NMP (N-methylpyrrolidone), dissolved molecules are separated according to their size by gel permeation chromatography (GPC), which passes them through a chromatographic column containing microporous packing material. Once the sample is separated and eluted from the column, it can be characterized using a series of detectors (universal calibration and triple detection).

[0236] Preparation of I-3 polymer electrolyte membrane

[0237] At 25°C, 1.103 g of N,N,N-trimethyl-3-(2-methylallylamino)-1-propanediamine chloride (monomer 1), 0.218 g of triallyl phosphate (monomer 2), 5.465 g of perfluoropolyether acrylate (PFPE-MAA-1000) (monomer 3), 0.063 g of azobisisobutyronitrile (AIBN) (initiator), 1.4 g of fluoroethylene carbonate (monomer 4), 0.014 g of stannous isooctanoate (catalyst), and 1.871 g of lithium difluorosulfonylimide (lithium salt) were added to 20 mL of acetonitrile and mixed thoroughly. The homogeneous solution was poured into a polytetrafluoroethylene mold with a fixed depth and kept in a vacuum oven at 65°C for 10 h. Then, the electrolyte membrane was immersed in 50 mL of acetone solution of 3 M LiFSI for anion exchange for 12 h, and then dried in a vacuum oven at 45°C for 6 h to obtain a polymer solid electrolyte membrane with a thickness of 15 µm.

[0238] The prepared electrolyte membrane has the following dimensions: 100 mm × 100 mm × 15 µm

[0239] I-4. Battery Preparation

[0240] Step 1: Preparation of the positive electrode sheet

[0241] 4.5 g of lithium cobalt oxide (LiCoO2) and 0.05 g of conductive agent Super p and 0.275 g of fluoroethylene carbonate were added to 2 ml of N-methylpyrrolidone (NMP) and mixed thoroughly. Then, 1.2 ml of lithium difluorooxalate borate (LiDFOB) and stannous isooctanoate NMP solutions (mass concentrations of 12.5% ​​and 2.1%, respectively) were added to the above slurry and mixed quickly and evenly to obtain a positive electrode slurry. The slurry was coated onto a 13 µm aluminum foil and dried in a forced-air oven at 50–80 °C to obtain the positive electrode sheet.

[0242] Step 2: Preparation of the negative electrode plate

[0243] Negative electrode sheet: Lithium metal (purchased from Shenzhen Kejing Zhida Technology Co., Ltd., 30 µm thick) is cold-pressed onto copper foil to obtain the negative electrode sheet.

[0244] Step 3: Preparation of polymer electrolyte membrane

[0245] For the preparation of electrolyte membranes, see I-3.

[0246] Step 4: Preparation of the full cell

[0247] The positive electrode containing the second polymer, the polymer solid electrolyte membrane, and the lithium metal or lithium alloy negative electrode are stacked in sequence, cold-pressed and assembled into a full battery, and then subjected to subsequent charge-discharge and cycle tests.

[0248] I-5. Comparison of polymer and solid electrolyte membranes

[0249] PEO with an average molecular weight of ~1,000,000 (purchased from Aladdin Reagents) was used as a control and was used to prepare an electrolyte membrane. The preparation method is as follows:

[0250] 2 g of PEO powder and 0.3 g of lithium bis(fluorosulfonyl)imide (LiFSI) were dissolved in 35 g of acetonitrile and stirred until completely dissolved. Then, 0.7 g of TiO2 powder (10-20 nm) was added, stirred for 30 min, and ultrasonically dispersed. The dispersed slurry was poured into a self-made mold and dried in a vacuum oven at 60 °C for 12 h. After drying, the PEO electrolyte membrane was obtained.

[0251] Electrolyte membrane dimensions: 100 mm × 100 mm × 15 µm

[0252] II. Performance Evaluation of Polymers, Electrolyte Membranes, and Batteries

[0253] II-1. Swelling Parameters

[0254] The swelling parameters of the polymer prepared in I-1, the second polymer prepared in I-2, and the polymer electrolyte membrane prepared in I-3 were tested using the following methods:

[0255] The polymers prepared in I-1, the second polymer prepared in I-2, and the electrolyte membrane prepared in I-3 were each cut into 30 mm × 30 mm square samples. Three parallel samples were prepared for each group in each case, and the mass of each sample was weighed. The samples were then immersed in a 1 M LiFSI solution of ethyl methyl carbonate (EMC) for 12 h to induce swelling. After swelling, excess solvent adhering to the surface of the swollen sample was gently blotted dry with filter paper, and the mass of the swollen sample was measured. The swelling parameter is the percentage increase in mass of the swollen sample relative to the original sample mass.

[0256] Table 1: Results of swelling parameter tests

[0257]

[0258] The results in the table above indicate that the swelling parameters of the electrolyte membrane are between those of the polymer and the second polymer, which to some extent suggests that the electrolyte membrane is a blend of the polymer and the second polymer.

[0259] II-2. Flame retardant properties

[0260] The flame retardant properties of polymers were examined using polyethylene oxide (PEO) as a comparison.

[0261] The thermal conductivity of the polymer prepared in I-1, the electrolyte membrane prepared in I-3, the comparative polymer PEO in I-5, and the comparative electrolyte membrane prepared using PEO were determined according to GB / T 10294-2008.

[0262] The flame retardant properties of the polymer prepared in I-1, the electrolyte membrane prepared in I-3, the comparative polymer PEO in I-5, and the comparative electrolyte membrane prepared using PEO were determined according to the UL94 vertical burning test of ASTM D3801.

[0263] The performance test results are shown in the table below.

[0264] Table 2: Flame retardant properties of polymers

[0265]

[0266] The results in the table above show that, compared with the comparative PEO and the comparative electrolyte membrane, the polymer provided in this application and the electrolyte membrane prepared using the polymer have excellent flame retardant properties.

[0267] II-3. Effects of Monomer 1 and Monomer 2 on Electrolyte Membrane and Battery Performance

[0268] Examples 1-9

[0269] Examples 1-9 were used to investigate the effects of monomer 1 and monomer 2 on the mechanical properties of the electrolyte membrane and on the high-voltage stability and high-voltage cycle performance of the battery. The specific procedures are as follows:

[0270] Example 1: Preparation of a full cell based on I-3 and I-4.

[0271] Examples 2-9: Similar to the preparation in Example 1, except that the molar ratio of monomers 1-3 is changed (based on the total molar amount of monomers 1-3). The specific amount of monomers used and the molar ratio are shown in the table below.

[0272] The performance of the electrolyte membranes and full cells prepared in Examples 1-9 was tested using the following methods:

[0273] (1) Tensile strength and elongation test of electrolyte membrane

[0274] The electrolyte membranes from Examples 1-9 were cut into rectangular electrolyte membrane specimens with dimensions of 150 mm × 20 mm and a thickness of 15 µm. Using a general-purpose testing machine in accordance with the standard ASTM D882-10, the specimens were stretched from a relaxed state to failure at a crosshead speed of 50 mm / min. The tensile strength and length L at the point of fracture under maximum tensile stress were recorded. The elongation at break was calculated based on (L-L0) / L0 × 100%.

[0275] (2) High-voltage stability test of the battery

[0276] The linear sweep voltammetry was used at 5.0 mV s. -1 Linear potential scans were performed on each full cell within the range of 2–6 V at a scanning rate of 1.0 mV / s, and the current changes were recorded. A coin cell was assembled by sandwiching an electrolyte membrane between a stainless steel sheet and a lithium metal sheet, with the stainless steel sheet serving as the working electrode and the lithium metal sheet as the reference electrode. Linear potential scans were performed on the coin cell within the range of 2–6 V using an electrochemical workstation, with the voltage ranging from open circuit to 6.0 V. The initial voltage at which the electrolyte membrane underwent oxidative decomposition was recorded; a higher voltage indicated better stability.

[0277] The graph obtained from testing the battery in Example 1 is shown below. Figure 2 .

[0278] (3) High-voltage cycle performance test of the battery

[0279] Constant current charge-discharge tests were performed on the full cells in the examples at a charge-discharge rate of 0.5C to 0.5C within a voltage range of 2.8 to 4.3 V. The number of cycles (cls) of each full cell when the remaining charge was 80% during the high voltage upper limit charging process was measured and the value of the number of cycles was recorded. The more cycles, the better the high voltage cycle stability.

[0280] The test results are shown in the table below.

[0281] Table 3

[0282]

[0283] The results in the table above indicate that:

[0284] Examples 1-9 exhibit good high-pressure stability;

[0285] When the molar ratio of monomer 1 is low, such as in Examples 4 and 2, the resulting electrolyte membrane has relatively low tensile strength but high elongation. When the molar ratio of monomer 1 is too low, such as in Example 4, the high-voltage cycling performance of the resulting battery decreases significantly. When the molar ratio of monomer 1 is too high, such as in Example 5, the elongation of the resulting electrolyte membrane decreases significantly, and the high-voltage cycling performance of the battery using such an electrolyte membrane also decreases significantly. Therefore, for monomer 1, a molar ratio of 10-85% is preferred.

[0286] When the molar ratio of monomer 2 is low, such as in Examples 8 and 6, the tensile strength of the obtained electrolyte membrane is significantly lower. When the molar ratio of monomer 2 is too low, such as in Example 8, the high-voltage cycling performance is significantly reduced. When the molar ratio of monomer 2 is high, such as in Examples 7 and 9, the elongation of the obtained electrolyte is poor. When the molar ratio of monomer 2 is too high, such as in Example 9, the battery made using its electrolyte membrane has poor high-voltage stability and significantly reduced high-voltage cycling performance. Therefore, for monomer 2, the molar ratio is preferably 2.0~33.3%, preferably 5%~25%.

[0287] In summary, it can be seen that the molar ratio of monomer 1 and the molar ratio of monomer 2 have a significant impact on the mechanical strength (tensile strength and elongation) of the corresponding electrolyte membranes, and also have a significant impact on the high-voltage stability and high-voltage cycle performance of the corresponding batteries.

[0288] II-4. Effects of cations and lithium salts in monomer 1 on the lithium-ion transference number of the electrolyte membrane.

[0289] Example 1, 10~11

[0290] Examples 1, 10, and 11 investigate the effects of the type of cation and lithium salt in monomer 1 on the lithium-ion transference number.

[0291] Example 1: As described above, a full cell was prepared according to I-3 and I-4.

[0292] Example 10: Similar to Example 1, an electrolyte membrane and a full cell were prepared, except that in the preparation of the electrolyte membrane in I-3, monomer 1 was prepared using the monomer in the table below instead of N,N,N-trimethyl-3-(2-methylallylamino)-1-propanediamine chloride, and the lithium salt was LiBOB instead of LiFSI.

[0293] Example 11: Similar to Example 1, an electrolyte membrane and a full cell were prepared, except that in the preparation of the electrolyte membrane in I-3, monomer 1 was prepared using the monomer in the table below instead of N,N,N-trimethyl-3-(2-methylallylamino)-1-propanediamine chloride, and lithium salt LiBF4 was used instead of LiFSI.

[0294] Comparative Example 1: Similar to Example 1, an electrolyte membrane and a full cell were prepared, except that in the preparation of the electrolyte membrane in I-3, monomer 1 was prepared using the monomer in the table below instead of N,N,N-trimethyl-3-(2-methylallylamino)-1-propanediamine chloride.

[0295] The lithium-ion transference number of the electrolyte membranes prepared in each embodiment and comparative example was tested using the following methods:

[0296] The lithium-ion transference number (t) in polymer solid electrolytes was determined by potentiostatic polarization. ＋ The testing method is as follows:

[0297] Assemble a Li / polymer solid electrolyte / Li symmetric cell. Apply a small and constant potential difference ΔV (approximately 10 mV) to the symmetric cell and record the current change over time. Initially, all migratable ions in the battery system affect charge transport, resulting in the maximum current, which is recorded as [value missing]. I 0 (Initial current). As polarization progresses, a stable ion concentration gradient gradually forms inside the battery. Anion migration is suppressed, and the current in the battery system is contributed by cations (i.e., lithium ions). Record the current at this point. I s (Steady-state current). The lithium-ion transport number t can be calculated using Equation 1. ＋ ,

[0298] Formula 1:

[0299] Where R 0 el and R s elThese are the interfacial impedances of the electrode and the polymer electrolyte membrane before and after polarization. The interfacial impedance can be obtained through electrochemical impedance spectroscopy (EIS, also known as AC impedance spectroscopy): When a small-amplitude sinusoidal voltage signal with frequency w1 is applied to the battery system, the system generates a sinusoidal AC response with frequency w2. The ratio of the applied voltage to the generated current is the impedance of the system. The complex plane plot of this value as a function of the sinusoidal frequency ω is the Nyquist plot. The semicircular part in the high-frequency region corresponds to the charge transfer process, and the diameter of the semicircle represents the interfacial impedance.

[0300]

[0301] The results in the table above show that, compared with Comparative Example 1 which does not contain cations, using monomer 1 containing cations is beneficial to increasing the lithium-ion transference number of the polymer solid electrolyte. Furthermore, the higher the charge density around the cation, the stronger the dissociation ability of the lithium salt and the greater the lithium-ion transference number.

[0302] II-5. Effects of Monomer 3 on Electrolyte Membrane and Battery Performance

[0303] Examples 12-23

[0304] The effects of the type of Rf, the fluorine substitution rate, the type of E group, and the amount of monomer 3 on the performance of the electrolyte membrane and the battery were investigated.

[0305] Examples 12-15: Similar to Example 1, electrolyte membranes and full cells were prepared, except that the molar ratio of monomer 3 was not changed (the amounts of monomers 1 and 2 were changed accordingly based on the molar ratio in Example 1 and the mass of monomer 3 in Table 3), only the Rf and E groups in monomer 3 were changed. See Table 5 below for details.

[0306] Example 16: The amounts of monomer 1, monomer 2 and monomer 3 were 0.221 g, 0.218 g and 9.836 g, respectively, with molar percentages of 9.10%, 9.10% and 81.80%.

[0307] Example 17: The amounts of monomer 1, monomer 2 and monomer 3 were 1.985 g, 0.218 g and 1.094 g, respectively, with molar percentages of 81.80%, 9.10% and 9.10%, respectively.

[0308] Example 18: The amounts of monomer 1, monomer 2 and monomer 3 were 0.049 g, 0.218 g and 10.690 g, respectively, with molar percentages of 2.0%, 9.10% and 88.90%, respectively.

[0309] Example 19: The amounts of monomer 1, monomer 2, and monomer 3 were 2.087 g, 0.218 g, and 0.589 g, respectively, with molar percentages of 86.0%, 9.10%, and 4.90%, respectively.

[0310] The electrolyte membranes and full cells prepared in each embodiment were subjected to the following tests:

[0311] (1) Testing of ionic conductivity:

[0312] Cut the electrolyte membrane into A 19mm diameter disc was used to assemble an R2032 coin cell with a stainless steel sheet and an electrolyte membrane. After standing for 12 hours, electrochemical impedance spectroscopy (EIS) was performed using an electrochemical workstation, ranging from 0.1 to 10. 5 A frequency scan is performed at Hz, with a voltage amplitude of 5mV; the intersection of the graph and the horizontal axis represents the impedance R of the polymer film, and the ionic conductivity σ can be obtained from the formula...

[0313] σ=d / RA

[0314] The calculation yields d, where d is the thickness of the electrolyte membrane, R is the impedance value, and A is the area of ​​the electrolyte membrane.

[0315] (2) Test of the proportion of fluorine in the electrolyte membrane:

[0316] The fluorine content in the electrolyte membrane was determined by X-ray photoelectron spectroscopy (XPS).

[0317] (3) Calculation of the fluorine substitution rate in the Rf group:

[0318] The fluorine substitution rate is based on the number of hydrogen atoms that can be substituted in the Rf group, i.e., number of fluorine atoms / (total number of halogen atoms + number of hydrogen atoms).

[0319] (4) Calculation of the molar percentage of monomer 3: The mass of monomer 3 / the molecular weight of monomer 3 is the number of moles of monomer 3, and the number of moles of monomer 3 / (the number of moles of monomer 1 + the number of moles of monomer 2 + the number of moles of monomer 3) is the molar percentage of monomer 3.

[0320] For testing of the lithium-ion transference number of the electrolyte membrane and the high-voltage stability and high-voltage cycling performance of the battery, please refer to the above.

[0321] Table 5

[0322]

[0323] The results in the table above indicate that:

[0324] Compared with Comparative Example 2, each embodiment achieved better electrolyte membrane performance and battery performance;

[0325] The molar percentage of monomer 3 in monomers 1 to 3 is in the range of 8% to 85%, and can be selected to be in the range of 8% to 80%, which can achieve better performance of electrolyte membrane and battery;

[0326] The high fluorine substitution rate in the Rf group (greater than 29.0%) is beneficial for achieving better high-voltage stability in batteries.

[0327] The higher the fluorine content in the electrolyte membrane, the better the ionic conductivity of the electrolyte membrane and the better the high-voltage stability of the battery. However, if the fluorine content in the electrolyte membrane is too high, it may be detrimental to the lithium-ion transference number of the electrolyte membrane and the high-voltage cycle performance of the battery. As shown in the table above, a fluorine content in the electrolyte membrane in the range of 12.5% ​​to 46% can achieve better electrolyte membrane performance and battery performance.

[0328] II-6. The Influence of Monomer and Lithium Salt Amounts in the Second Polymer on the Electrolyte Membrane and Battery

[0329] Example 1, 20-27

[0330] The effects of monomer 4, used to prepare the second polymer, on the performance of the electrolyte membrane and battery were investigated.

[0331] Example 1: As described above

[0332] Examples 24-27: Similar to the preparation in Example 1, except that the amounts of monomers 1-3 and the amount of lithium salt added are kept constant, and only the amount of monomer 4 is changed.

[0333] Examples 28-31: Similar to the preparation in Example 1, except that the amounts of monomers 1-4 are kept constant, and only the amount of lithium salt added is changed.

[0334] In the table, the mass percentage of lithium salt is calculated as the mass of lithium salt / (total mass of monomers 1~4 + initiator + lithium salt + catalyst) × 100%.

[0335] For tensile strength, elongation, high pressure stability and high pressure cycling performance tests, please refer to the above text. The test results are shown in the table below.

[0336] Table 6

[0337]

[0338] The results in the table above show that when the total mass ratio of monomers 1-3 to monomer 4 is 2-20, the mass ratio of monomers 1-4 to lithium salt is 2.3-13.6, and the mass percentage of lithium salt in the electrolyte membrane is 6.8-30.0%, the electrolyte membrane achieves better tensile strength and elongation, and the battery achieves better high-voltage stability and high-voltage cycling performance.

[0339] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A polymer formed by polymerizing monomer 1, monomer 2, and monomer 3, wherein monomer 1 has a structure of formula 1, monomer 2 has a structure of formula 2, and monomer 3 has a structure of formula 3. in, R1 and R3 are each independently selected from hydrogen or C. 1-10 alkyl; R4 is selected from C of either straight chain or branched chain. 2-10 alkenyl; R2 and R5 are each independently selected from either straight or branched C. 2-10 alkenyl; Rf is selected from ethoxy segments containing fluorine with 16 or fewer carbon atoms; x is the number of repeating units of the methylene group, 0 ≤ x ≤ 20; A + It is selected from one of the functional groups with nitrogen, sulfur, or phosphorus as the cation center; Q - It is one or more anions selected from halide ions, haloborate ions, halooxalateborate ions, perhalate ions, halophosphate ions, and halosulfonylimide ions. E is selected from the structures (1) to (3). R6 is selected from hydrogen or C. 1-10 alkyl.

2. The polymer according to claim 1, characterized in that, Q - It is one or more anions selected from chloride ions, tetrafluoroborate, difluorooxalateborate, perchlorate, hexafluorophosphate, and bis(fluorosulfonyl)imide.

3. The polymer according to claim 1 or 2, characterized in that, In the Rf group, the fluorine substitution rate is greater than 29.0%, and the fluorine substitution rate is the percentage of fluorine atoms in the Rf group, based on the number of hydrogen atoms that can be substituted.

4. The polymer according to claim 1 or 2, characterized in that, Cation A + Choose one of the structural formulas (4) to (6): 。 5. The polymer according to claim 1 or 2, characterized in that, The molar percentage of monomer 1 ranges from 3.7 to 92.6 mol%, the molar percentage of monomer 2 ranges from 2.0 to 33.3 mol%, and the molar percentage of monomer 3 ranges from 3.7 to 92.6 mol%, all based on the total molar number of monomer 1, monomer 2, and monomer 3.

6. The polymer according to claim 1 or 2, characterized in that, The molar ratio of monomer 1 to monomer 2 is in the range of 1:1 to 25:

1.

7. The polymer according to claim 1 or 2, characterized in that, The molar ratio of monomer 3 to monomer 2 is in the range of 1:1 to 25:

1.

8. The polymer according to claim 1 or 2, characterized in that, The polymer has a thermal conductivity in the range of 0.06~0.35W / m K and a flame retardant rating of 94V-0 or 94V-1. The thermal conductivity of the polymer is determined according to GB T 10294-2008, and the flame retardant rating of the polymer is determined according to the UL94 vertical burning test of ASTM D3801.

9. A method for preparing the polymer according to any one of claims 1 to 8, comprising the following steps: The monomer 1, monomer 2, monomer 3 and initiator are dissolved in a solvent and kept in a vacuum at 30~100℃ for 0.2~24 h, and then dried.

10. A polymeric electrolyte membrane comprising the polymer of any one of claims 1 to 8 or the polymer prepared by the method of claim 9.

11. The polymer electrolyte membrane according to claim 10, characterized in that, It also includes a second polymer dispersed within the polymer to form an interpenetrating network structure. The second polymer is formed from monomer 4, which has the following general formula: in, R7 is selected from hydrogen, or a hydrocarbon group with less than 7 carbon atoms that is unsubstituted or substituted by one or more elements selected from fluorine, bromine, iodine, nitrogen, oxygen, sulfur, silicon, boron, and phosphorus.

12. The polymer electrolyte membrane according to claim 10 or 11, characterized in that, It also includes lithium salts selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalate borate, lithium perchlorate, and lithium dioxoborate.

13. The polymer electrolyte membrane according to claim 12, characterized in that, The mass percentage of lithium salt ranges from 6.8% to 30.0%, based on the total mass of the polymer electrolyte membrane.

14. The polymer electrolyte membrane according to claim 10 or 11, characterized in that, The fluorine content ranges from 12.5% ​​to 46.0%, based on the total weight of the polymer electrolyte membrane.

15. A method for preparing a polymer electrolyte membrane, comprising: The monomer 1, monomer 2, monomer 3, monomer 4, lithium salt, catalyst, and initiator according to any one of claims 1 to 8 are mixed in a solvent and reacted under vacuum at 30-100°C for 0.2-24 h to obtain a polymer electrolyte membrane. The catalyst includes one or more of stannous isooctanoate, aluminum trifluoromethanesulfonate, aluminum trichloride, trimethylsilyl trifluoromethanesulfonate, boron trifluoride ether, triethylamine, and 1,8-diazabicyclo[5.4.0]undec-7-ene. The initiator includes one or more of 2,2'-azobis(2,4-dimethylpentanonitrile), 2,2'-azobis(isobutylnitrile), 2,2'-azobis(methylbutanonitrile), 1,1'-azobis(cyanocyclohexane), benzoyl peroxide, dodecyl peroxide, ditert-butyl peroxide, diisopropyl peroxide, and dicyclohexyl peroxide.

16. The method for preparing a polymer electrolyte membrane according to claim 15, characterized in that, It also includes anion exchange between the obtained polymer electrolyte membrane and a lithium salt solution to obtain product 2.

17. The method for preparing a polymer electrolyte membrane according to claim 16, characterized in that, It also includes product 2 obtained by drying.

18. The method for preparing a polymer electrolyte membrane according to any one of claims 15 to 17, characterized in that, The ratio of the total mass of monomer 1, monomer 2, and monomer 3 to the mass of monomer 4 is 20:1 to 2:

1.

19. The method for preparing a polymer electrolyte membrane according to any one of claims 15 to 17, characterized in that, The mass ratio of the total mass of monomer 1, monomer 2, monomer 3, and monomer 4 to the mass of the lithium salt is in the range of 2.3 to 13.

6.

20. The method for preparing a polymer electrolyte membrane according to any one of claims 15 to 17, characterized in that, The weight ratio of the lithium salt to the initiator is 5:1 to 60:1; if a catalyst is used, the ratio between the sum of the weights of the lithium salt and the catalyst and the weight of the initiator is 7:1 to 80:

1.

21. A secondary battery, comprising a positive electrode and a negative electrode, characterized in that, It also includes the polymer electrolyte membrane according to any one of claims 10 to 14 or the polymer electrolyte membrane prepared by the method according to any one of claims 15 to 20.

22. The secondary battery according to claim 21, characterized in that, The thickness of the polymer electrolyte membrane is 10~1000 µm.

23. The secondary battery according to claim 21 or 22, characterized in that, The negative electrode includes a negative electrode current collector and a metal sheet formed of lithium metal and / or lithium alloy.

24. The secondary battery according to claim 21 or 22, characterized in that, The positive electrode includes a positive current collector and a positive electrode film layer, wherein the positive electrode film layer includes a positive electrode active material, the second polymer according to claim 11, and the lithium salt according to claim 12.

25. A battery module, characterized in that, The secondary battery includes any one of claims 21 to 24.

26. A battery pack, characterized in that, Includes the battery module as described in claim 25.

27. An electrical appliance, characterized in that, It includes at least one selected from the secondary battery of any one of claims 21 to 24, the battery module of claim 25, or the battery pack of claim 26.

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