A solid-state electrolyte membrane, a secondary battery including the same, and an electric device

Abstract

This application discloses a solid electrolyte membrane, a secondary battery containing the membrane, and an electrical device thereof, belonging to the field of battery technology. The solid electrolyte membrane provided in this application improves the ionic conductivity and tensile strength of the solid electrolyte simultaneously through the combined use of polymers with -CF2- groups, thiocyanate, polymers formed by the polymerization of alkenyl functionalized ionic liquid monomers, and lithium salts, thereby improving the cycle performance of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a solid electrolyte membrane and a secondary battery and power device comprising the same. Background Technology

[0002] Improving the ionic conductivity of solid-state electrolytes (SSEs) is beneficial to improving the cycle performance of secondary batteries. To improve the ionic conductivity of SSEs, succinate (SN) and ionic liquid (IL) can be added to the solid-state electrolyte. However, the addition of SN and IL will lead to a decrease in the mechanical properties (especially tensile strength) of the solid-state electrolyte. When the mechanical properties (especially tensile strength) of the solid-state electrolyte decrease, the ability of the solid-state electrolyte to suppress dendrite growth will be weakened, which will lead to a decrease in the cycle performance of the secondary battery.

[0003] Therefore, it is necessary to develop a solid electrolyte membrane that can simultaneously improve ionic conductivity and tensile strength to enhance the cycle performance of secondary batteries. Summary of the Invention

[0004] The purpose of this application is to solve the technical problem that solid electrolyte membranes cannot simultaneously improve ionic conductivity and tensile strength, and to provide a solid electrolyte membrane, a secondary battery containing the membrane, and an electrical device.

[0005] To achieve the above objectives, a first aspect of this application provides a solid electrolyte membrane comprising a polymer containing -CF2- groups, a thiocyanate, a polymer formed by polymerization of an alkenyl-functionalized ionic liquid monomer, and a lithium salt.

[0006] In some embodiments, the mass ratio of the polymer containing the -CF2- group to the polymer formed by polymerizing the alkenyl functionalized ionic liquid monomer is (1-7):1.

[0007] In some embodiments, the mass ratio of the thiocyanate to the lithium salt is (0.3-3):1.

[0008] In some embodiments, the ratio of the total mass of the polymer formed by polymerizing the -CF2- group-containing polymer and the alkenyl functionalized ionic liquid monomer to the total mass of the thiocyanate and lithium salt is (0.6-5):1.

[0009] In some embodiments, the polymer containing the -CF2- group includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, and polychlorotrifluoroethylene.

[0010] In some embodiments, the alkenyl-functionalized ionic liquid monomer includes at least one of 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-vinyl-3-ethylimidazolium tetrafluoroborate, 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide, and 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide.

[0011] In some embodiments, the lithium salt includes a fluorinated lithium salt.

[0012] In some embodiments, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalateborate, and lithium hexafluorophosphate.

[0013] In some embodiments, the thiocyanate includes at least one of lithium thiocyanate, potassium thiocyanate, and sodium thiocyanate.

[0014] In some embodiments, the thickness of the solid electrolyte membrane is 10 μm-30 μm.

[0015] In some embodiments, the density of the solid electrolyte membrane is ≥1.50 g / cm³. 3 .

[0016] A second aspect of this application provides a secondary battery including the solid electrolyte membrane described in this application.

[0017] A third aspect of this application provides an electrical device including the secondary battery described in this application.

[0018] Compared with the prior art, the beneficial effects of this application are: The solid electrolyte membrane provided in this application improves the ionic conductivity and tensile strength of the solid electrolyte simultaneously by using polymers with -CF2- groups, thiocyanate, polymers formed by the polymerization of alkenyl functionalized ionic liquid monomers, and lithium salts, thereby improving the cycle performance of secondary batteries. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0021] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0022] According to a first aspect of this application, a solid electrolyte membrane is provided, comprising a polymer containing -CF2- groups, a thiocyanate, a polymer formed by polymerization of an alkenyl-functionalized ionic liquid monomer, and a lithium salt.

[0023] The solid electrolyte membrane provided in this application improves the ionic conductivity and tensile strength of the solid electrolyte simultaneously by using polymers containing -CF2- groups, thiocyanate, polymers formed by the polymerization of alkenyl functionalized ionic liquid monomers, and lithium salts, thereby improving the cycle performance of secondary batteries.

[0024] In this application, the polymers containing -CF2- groups and the polymers formed by polymerizing alkenyl functionalized ionic liquid monomers form a stable interpenetrating network through physical entanglement and hydrogen bonding. This is beneficial for improving the tensile strength of the solid electrolyte, thereby inhibiting dendrite growth and improving the cycle performance of the secondary battery. Furthermore, the thiocyanate provides thiocyanate ions (SCN). - SCN forms coordinate bonds with -CF2- groups in the interpenetrating network. - The inclusion of these elements in the interpenetrating electrolyte network not only promotes the dissociation of thiocyanate but also facilitates the rapid transport of lithium ions within the network, thereby increasing the ionic conductivity of the solid electrolyte and improving the cycle performance of the secondary battery.

[0025] In some embodiments, the mass ratio of the polymer containing the -CF2- group to the polymer formed by polymerizing the alkenyl functionalized ionic liquid monomer is (1-7):1.

[0026] For example, the mass ratio of the polymer containing the -CF2- group and the polymer formed by polymerizing the alkenyl functionalized ionic liquid monomer can be any point value between (1-7):1 or a range between any two points, such as one of 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1 or a range between any two.

[0027] In some embodiments, the mass ratio of the polymer containing -CF2- groups to the polymer formed by the polymerization of alkenyl functionalized ionic liquid monomers is (3-5):1. When the mass ratio of the polymer containing -CF2- groups to the polymer formed by the polymerization of alkenyl functionalized ionic liquid monomers is within the above range, the interpenetrating network formed by the polymerization of the polymer containing -CF2- groups and the polymer formed by the polymerization of alkenyl functionalized ionic liquid monomers through physical entanglement and hydrogen bonding is more stable. At the same time, it can better promote the dissociation of thiocyanate and the rapid transport of lithium ions in the interpenetrating network, which is beneficial to further improve the ionic conductivity and tensile strength of the solid electrolyte, thereby better improving the cycle performance of the secondary battery.

[0028] It should be noted that the method for testing the mass ratio of the polymer containing -CF2- groups and the polymer formed by the polymerization of alkenyl functionalized ionic liquid monomers described in this application is as follows: Thermogravimetric analysis (TGA) is used to treat the solid electrolyte membrane at a heating rate of 10℃ / min. The solid electrolyte membrane will experience mass loss as the temperature increases. The polymer containing -CF2- groups (such as PVDF-HFP) in the solid electrolyte membrane will experience mass loss and form a plateau at 420-500℃, while the polymer formed by the polymerization of alkenyl functionalized ionic liquid monomers will experience mass loss and form a plateau at 250-380℃. The weight loss rate of the first mass loss step at 250-380℃ is denoted as ΔW1, and the weight loss rate of the second mass loss step at 420-500℃ is denoted as ΔW2. Therefore, the mass ratio of the polymer containing -CF2- groups and the polymer formed by the polymerization of alkenyl functionalized ionic liquid monomers = ΔW1:ΔW2. The vertical axis of the thermogravimetric analysis (TGA) curve represents the mass percentage (%). Compared to the initial mass percentage, the percentage of mass lost for each mass loss step (i.e., the difference in the vertical axis) is its weight loss rate.

[0029] In some embodiments, the mass ratio of the thiocyanate to the lithium salt is (0.3-3):1.

[0030] For example, the mass ratio of thiocyanate to lithium salt can be any point value between (0.3-3):1 or a range between any two points, such as one of 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.2:1, 1.3:1, 1.5:1, 1.7:1, 1.8:1, 2:1, 2.2:1, 2.3:1, 2.5:1, 2.7:1, 2.8:1, 3:1 or a range between any two.

[0031] In some embodiments, the mass ratio of the thiocyanate to the lithium salt is (1-2):1. When the mass ratio of the thiocyanate to the lithium salt is within the above range, it is possible not only to increase the thiocyanate (SCN) content... - The formation of coordinate bonds allows for more uniform distribution within the interpenetrating network, and better promotes the dissociation of thiocyanate and the rapid transport of lithium ions within the interpenetrating network. This is beneficial for further improving the ionic conductivity of the solid electrolyte, thereby enhancing the cycle performance of the secondary battery.

[0032] It should be noted that the test method for the mass ratio of thiocyanate and lithium salt described in this application is as follows: a solid electrolyte membrane is placed in a microwave digestion vessel and digested under high temperature and high pressure to obtain the test solution. The mass percentage of F element in the lithium salt is obtained by analyzing the test solution with ion chromatography, and the mass percentage of N element in the thiocyanate is obtained by analyzing the test solution with an elemental analyzer. The mass ratio of thiocyanate and lithium salt can be obtained by conversion.

[0033] In some embodiments, the ratio of the total mass of the polymer formed by polymerizing the -CF2- group-containing polymer and the alkenyl functionalized ionic liquid monomer to the total mass of the thiocyanate and lithium salt is (0.6-5):1.

[0034] For example, the ratio of the total mass of the polymer formed by polymerizing the polymer containing the -CF2- group and the alkenyl functionalized ionic liquid monomer to the total mass of the thiocyanate and lithium salt can be any point value or a range between any two points between (0.6-5):1. For example, it can be one of or a range between any two of the following: 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.2:1, 1.3:1, 1.5:1, 1.7:1, 1.8:1, 2:1, 2.2:1, 2.3:1, 2.5:1, 2.7:1, 2.8:1, 3:1, 3.2:1, 3.3:1, 3.5:1, 3.7:1, 3.8:1, 4:1, 4.2:1, 4.3:1, 4.5:1, 4.7:1, 4.8:1, 5:1.

[0035] In some embodiments, the ratio of the total mass of the polymer formed by the polymerization of the -CF2- group-containing polymer and the alkenyl functionalized ionic liquid monomer to the total mass of the thiocyanate and lithium salt is (1.5-3.5):1. When the ratio of the total mass of the polymer formed by the polymerization of the -CF2- group-containing polymer and the alkenyl functionalized ionic liquid monomer to the total mass of the thiocyanate and lithium salt is within the above range, the respective roles of the -CF2- group-containing polymer, thiocyanate, alkenyl functionalized ionic liquid monomer, and lithium salt can be more fully utilized, which is beneficial to further improve the ionic conductivity and tensile strength of the solid electrolyte, thereby better improving the cycle performance of the secondary battery.

[0036] It should be noted that the test method for the ratio of the total mass of the polymer formed by the polymerization of the polymer containing -CF2- groups and the alkenyl functionalized ionic liquid monomer to the total mass of the thiocyanate and lithium salt is as follows: Thermogravimetric analysis (TGA) is used, and the solid electrolyte membrane is treated with a heating rate of 10℃ / min. The solid electrolyte membrane will experience mass loss as the temperature increases. The polymer formed by the polymerization of the polymer containing -CF2- groups and the alkenyl functionalized ionic liquid monomer is denoted as the polymer phase, and the thiocyanate and lithium salt are denoted as the lithium salt phase. When the temperature reaches 500℃, the polymer phase has completely decomposed, while the lithium salt phase has not yet undergone significant decomposition. Combined with the TGA curve, the masses of the polymer phase and the lithium salt phase can be determined separately, thus obtaining the ratio of the total mass of the polymer formed by the polymerization of the polymer containing -CF2- groups and the alkenyl functionalized ionic liquid monomer to the total mass of the thiocyanate and lithium salt.

[0037] In some embodiments, the polymer containing -CF2- groups includes at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polychlorotrifluoroethylene (PCTFE).

[0038] In some embodiments, the alkenyl-functionalized ionic liquid monomer comprises at least one of 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide (CAS No.: 204854-22-8), 1-vinyl-3-ethylimidazolium tetrafluoroborate (CAS No.: 936030-51-2), 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide (CAS No.: 652134-11-7), and 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (CAS No.: 174899-81-1).

[0039] In some embodiments, the lithium salt includes a fluorinated lithium salt.

[0040] In some embodiments, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI, CAS No.: 171611-11-3), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, CAS No.: 90076-65-6), lithium difluorooxalate borate (LDFOB, CAS No.: 409071-16-5), and lithium hexafluorophosphate (LiPF6).

[0041] In some embodiments, the thiocyanate includes at least one of lithium thiocyanate, potassium thiocyanate, and sodium thiocyanate.

[0042] In some embodiments, the thickness of the solid electrolyte membrane is 10 μm-30 μm.

[0043] For example, the thickness of the solid electrolyte membrane can be any point value or a range between any two points between 10μm and 30μm, such as one of 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm or a range between any two.

[0044] When the thickness of the solid electrolyte membrane is within the above range, it is beneficial to further improve the cycle performance of the secondary battery.

[0045] It should be noted that the thickness testing method for the solid electrolyte membrane described in this application is as follows: the thickness of any five regions of the solid electrolyte membrane is measured using a thickness gauge, and the average value is recorded as the thickness of the solid electrolyte membrane.

[0046] In some embodiments, the density of the solid electrolyte membrane is ≥1.50 g / cm³. 3 .

[0047] For example, the density of the solid electrolyte membrane can be ≥1.50 g / cm³. 3 The value at any point or the range between any two points, for example, 1.50 g / cm³. 3 1.51g / cm 3 1.52g / cm 3 1.53g / cm 3 1.54g / cm 3 1.55g / cm 3 1.56g / cm 3 1.57g / cm 3 1.58g / cm 3 1.59g / cm 3 1.60g / cm 3 1.61 g / cm 3 1.62g / cm 3 1.63g / cm 3 1.64 g / cm 3 1.65g / cm 3 1.66 g / cm 3 1.67 g / cm 3 1.68g / cm 3 1.69 g / cm 3 1.70g / cm 3 1.71g / cm 3 1.72g / cm 31.73g / cm 3 1.74 g / cm 3 1.75g / cm 3 1.76 g / cm 3 1.77g / cm 3 1.78g / cm 3 1.79g / cm 3 1.80g / cm 3 The range of values ​​between one or any two of them.

[0048] When the density of the solid electrolyte membrane is within the above range, it is beneficial to further improve the cycle performance of the secondary battery.

[0049] It should be noted that the density test method for the solid electrolyte membrane described in this application is as follows: the mass m1 (in grams) of the solid electrolyte membrane is obtained by weighing the solid electrolyte membrane, and then the area S1 of the orthographic projection of the same solid electrolyte membrane (i.e., the product of the length and width of the solid electrolyte membrane, in cm) is measured. 2 The solid electrolyte membrane's thickness h1 (in cm) and density ρ1 (in g / cm³) are calculated using the following formula. 3 ): ρ1=m1 / (S1×h1); The test method for the thickness h1 of the solid electrolyte membrane is as follows: the thickness of any five regions of the solid electrolyte membrane is measured using a thickness gauge, and the average value is recorded as the thickness h1 of the solid electrolyte membrane.

[0050] In some embodiments, the solid electrolyte membrane also includes an initiator.

[0051] In some embodiments, the initiator includes at least one of azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), and 1-hydroxycyclohexylphenyl ketone (Irgacure-184, CAS No.: 947-19-3).

[0052] In some embodiments, the initiator accounts for 0.1%-1.0% of the mass of the solid electrolyte membrane.

[0053] For example, based on the mass of the solid electrolyte membrane, the mass percentage of the initiator can be any point value or a range between any two points between 0.1% and 1.0%, such as one of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or a range between any two.

[0054] It should be noted that, based on the mass of the solid electrolyte membrane, the method for testing the mass ratio of the initiator in this application is as follows: the solid electrolyte membrane is dissolved in a solvent (such as acetone, tetrahydrofuran, etc.) to form a sample to be tested, and the sample is analyzed by high performance liquid chromatography. The initiator and the polymer (including polymers containing -CF2- groups and polymers formed by the polymerization of alkenyl functionalized ionic liquid monomers) are separated by the difference in retention time in the chromatographic column, and quantification is performed by an ultraviolet detector to obtain the mass ratio data of the initiator in the solid electrolyte membrane.

[0055] In some embodiments, the method for preparing the solid electrolyte membrane includes the following steps: A solid electrolyte slurry is obtained by mixing a polymer containing -CF2- groups, thiocyanate, alkenyl functionalized ionic liquid monomer, lithium salt and initiator into an organic solvent. The solid electrolyte slurry is then coated onto a plate and polymerized by thermal initiation or ultraviolet initiation to obtain a solid electrolyte membrane.

[0056] In some embodiments, the organic solvent includes at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), and dichloromethane (DCM).

[0057] In some embodiments, the mixing temperature is 50°C-60°C.

[0058] For example, the mixing temperature can be any point value between 50℃ and 60℃ or a range value between any two points, such as one of 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃, 60℃ or a range value between any two.

[0059] In some embodiments, the thermal initiation is achieved by heating at 70°C-90°C.

[0060] For example, the heat initiation can be achieved by heating at any point value between 70℃ and 90℃ or within a range of any two points. For instance, it can be one of 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃, and 90℃ or within a range of any two.

[0061] In some embodiments, the ultraviolet initiation is achieved by ultraviolet irradiation.

[0062] In some embodiments, the ultraviolet light initiation is followed by drying.

[0063] According to a second aspect of this application, a secondary battery is provided, including the solid electrolyte membrane described in this application.

[0064] In some embodiments, the secondary battery further includes a positive electrode and a negative electrode.

[0065] In some embodiments, the positive electrode sheet includes a positive current collector and a layer of positive active material disposed on at least a portion of the surface of the positive current collector.

[0066] In some embodiments, the positive electrode active material layer includes at least one of a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder.

[0067] This application does not impose any particular restrictions on the selection of the positive electrode active material; conventional positive electrode active materials in the art can be used. For example, the positive electrode active material may be lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, etc.

[0068] This application does not impose any particular restrictions on the selection of the positive electrode conductive agent; conventional positive electrode conductive agents in the art can be used. For example, the positive electrode conductive agent includes at least one of conductive carbon black, acetylene black, SuperP, graphene, and carbon nanotubes (CNTs).

[0069] This application does not impose any particular restrictions on the selection of the positive electrode binder; conventional positive electrode binders in the art can be used. Exemplarily, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium polyacrylate (PAANa), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0070] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a layer of negative electrode active material disposed on at least a portion of the surface of the negative electrode current collector.

[0071] In some embodiments, the negative electrode active material layer includes at least one of a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0072] This application does not impose any particular restrictions on the selection of the negative electrode active material; conventional negative electrode active materials in the art can be used. For example, the negative electrode active material may be artificial graphite, natural graphite, silicon carbide, silicon oxide, etc.

[0073] This application does not impose any particular restrictions on the selection of the negative electrode conductive agent; conventional negative electrode conductive agents in the art can be used. For example, the negative electrode conductive agent includes at least one of conductive carbon black, acetylene black, graphene, and carbon nanotubes (CNTs).

[0074] This application does not impose any particular restrictions on the selection of the negative electrode binder; conventional negative electrode binders in the art can be used. Exemplarily, the negative electrode binder includes at least one of polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR).

[0075] In some embodiments, the method for preparing the secondary battery includes the following steps: (1) Preparation of negative electrode sheet: The negative electrode active material, negative electrode conductive agent and negative electrode binder are mixed and added to water to obtain negative electrode slurry. The negative electrode slurry is coated on at least one surface of the negative electrode current collector, and then dried, rolled, slit and cut to obtain negative electrode sheet. (2) Preparation of positive electrode sheet: The positive electrode active material, positive electrode conductive agent and positive electrode binder are mixed and then added to N-methylpyrrolidone to obtain positive electrode slurry. The positive electrode slurry is coated on at least one surface of the positive electrode current collector, and then dried, rolled, slit and cut into sheets to obtain positive electrode sheet. (3) Preparation of secondary battery: The positive electrode, negative electrode, solid electrolyte membrane and other components are assembled and then subjected to processes such as winding, hot pressing, super welding, core assembly, casing, baking, formation, aging, sealing and capacity testing to obtain secondary battery.

[0076] A third aspect of this application provides an electrical device including the secondary battery described in this application.

[0077] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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., but are not limited thereto.

[0078] Example 1 This application provides a solid electrolyte membrane comprising a polymer containing -CF2- groups (polyvinylidene fluoride-hexafluoropropylene copolymer, PVDF-HFP), thiocyanate (lithium thiocyanate), an alkenyl functionalized ionic liquid monomer (1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt, CAS No.: 204854-22-8) polymerized with lithium salt (LiFSI, CAS No.: 171611-11-3), and an initiator (azobisisobutyronitrile, AIBN); The polymer formed by polymerizing the -CF2- group-containing polymer (PVDF-HFP) and the alkenyl functionalized ionic liquid monomer (1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide) has a mass ratio of 4:1; the mass ratio of the thiocyanate (lithium thiocyanate) and the lithium salt (LiFSI) is 1.5:1; the ratio of the total mass of the polymer formed by polymerizing the -CF2- group-containing polymer and the alkenyl functionalized ionic liquid monomer to the total mass of the thiocyanate and the lithium salt is 2.5:1; based on the mass of the solid electrolyte membrane, the initiator (azobisisobutyronitrile, AIBN) accounts for 0.5% of the mass; the thickness of the solid electrolyte membrane is 20 μm.

[0079] The preparation method of the above-mentioned solid electrolyte membrane includes the following steps: S1. Add a polymer containing -CF2- groups (polyvinylidene fluoride-hexafluoropropylene copolymer, PVDF-HFP) to an organic solvent (N,N-dimethylacetamide, DMAC), stir at 60°C for 12 h to mix, add thiocyanate (lithium thiocyanate), continue stirring at 60°C for 12 h, then add alkenyl functionalized ionic liquid monomer (1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt, CAS No.: 204854-22-8) and lithium salt (lithium bis(trifluoromethanesulfonyl)imide salt, LiFSI), continue stirring at 60°C for 12 h, then add initiator (azobisisobutyronitrile, AIBN), stir and mix at 60°C for 1 h to obtain a solid electrolyte slurry; S2. Apply the solid electrolyte slurry onto a PET sheet using a doctor blade, and polymerize it by thermal initiation (drying at 80°C for 12 hours) to obtain a solid electrolyte membrane; The solid-liquid ratio of the polymer containing -CF2- groups (PVDF-HFP) to the organic solvent (DMAC) is 3g:20mL.

[0080] This embodiment also provides a secondary battery, the preparation method of which includes the following steps: (1) Preparation of negative electrode: The negative electrode active material (artificial graphite), negative electrode conductive agent (conductive carbon black), and negative electrode binder (polyvinylidene fluoride, PVDF) were mixed in a mass ratio of 95:2.5:2.5, and then thoroughly mixed in water to obtain a negative electrode slurry with a solid content of 50%. The negative electrode slurry was coated on both surfaces of a 4.5 μm thick negative electrode current collector (copper foil) at a flow rate of 1 m / min. The electrode sheet was then dried, rolled, slit, and cut to obtain the negative electrode sheet. The drying temperature was 100℃, and the rolling pressure was 40t during the rolling process. (2) Preparation of the positive electrode: The positive electrode active material (lithium cobalt oxide), positive electrode conductive agent (conductive carbon black), and positive electrode binder (polyvinylidene fluoride, PVDF) were mixed in a mass ratio of 85:7.5:7.5, and then thoroughly mixed in N-methylpyrrolidone to obtain a positive electrode slurry with a solid content of 68%. The positive electrode slurry was coated on both surfaces of a 13μm thick positive electrode current collector (aluminum foil) at a flow rate of 2m / min. The electrode sheet was then dried, rolled, slit, and cut to obtain the positive electrode sheet. The drying temperature was 100℃, and the rolling pressure was 40t during the rolling process. (3) Preparation of secondary battery: The solid electrolyte membrane was left to stand for 60 minutes at 25°C with water content <0.1 ppm and oxygen content <0.1 ppm. Then the positive electrode, negative electrode, solid electrolyte membrane and other components were assembled. After winding, hot pressing, super welding, core assembly, casing, baking, formation, aging, sealing and capacity testing, the secondary battery was obtained.

[0081] Examples 2-5 and Comparative Examples 1-2 Examples 2-5 and Comparative Examples 1-2 provide different solid-state electrolyte membranes and secondary batteries. The difference between them and Example 1 lies in the mass ratio of the polymer containing -CF2- groups (PVDF-HFP) and the alkenyl functionalized ionic liquid monomer (1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt) formed by polymerization. By adjusting the amount of the polymer containing -CF2- groups (polyvinylidene fluoride-hexafluoropropylene copolymer, PVDF-HFP) and the alkenyl functionalized ionic liquid monomer (1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt, CAS No.: 204854-22-8) in the preparation method of the solid-state electrolyte membrane, the mass ratio of the polymer formed by polymerization of the polymer containing -CF2- groups and the alkenyl functionalized ionic liquid monomer is shown in Table 1. The rest are the same as in Example 1.

[0082] Table 1 Examples 6-9 and Comparative Example 3 Examples 6-9 and Comparative Example 3 provide different solid electrolyte membranes and secondary batteries. The difference between them and Example 1 is that the mass ratio of thiocyanate (lithium thiocyanate) and lithium salt (LiFSI) is different. By adjusting the amount of thiocyanate (lithium thiocyanate) and lithium salt (LiFSI) in the preparation method of the solid electrolyte membrane, the mass ratio of thiocyanate and lithium salt is as shown in Table 2. All other aspects are the same as in Example 1.

[0083] Table 2 Examples 10-13 Examples 10-13 provide different solid-state electrolyte membranes and secondary batteries. The difference between them and Example 1 is that the ratio of the total mass of the polymer formed by the polymerization of the polymer containing -CF2- groups and the alkenyl functionalized ionic liquid monomer to the total mass of the thiocyanate and lithium salt is different. By adjusting the total amount of the polymer containing -CF2- groups (PVDF-HFP) and the alkenyl functionalized ionic liquid monomer (1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt) and the total amount of the thiocyanate (lithium thiocyanate) and lithium salt (LiFSI) in the preparation method of the solid-state electrolyte membrane, the ratio of the total mass of the polymer formed by the polymerization of the polymer containing -CF2- groups and the alkenyl functionalized ionic liquid monomer to the total mass of the thiocyanate and lithium salt is shown in Table 3. The rest is the same as Example 1.

[0084] Table 3 Examples 14-15 Examples 14-15 provide different solid electrolyte membranes and secondary batteries, which differ from Example 1 in that the types of polymers containing -CF2- groups are different, as shown in Table 4. All other aspects are the same as in Example 1.

[0085] Table 4 Examples 16-18 Examples 16-18 provide different solid electrolyte membranes and secondary batteries. The difference between them and Example 1 is that the types of alkenyl functionalized ionic liquid monomers are different, as shown in Table 5. All other aspects are the same as in Example 1.

[0086] Table 5 Examples 19-20 Examples 19-20 provide different solid electrolyte membranes and secondary batteries. The difference between them and Example 1 is that the thickness of the solid electrolyte membrane is different. The thickness of the solid electrolyte membrane is adjusted by adjusting the coating amount of the solid electrolyte slurry as shown in Table 6. All other aspects are the same as in Example 1.

[0087] Table 6 Example 21 Example 21 provides a different solid electrolyte membrane and secondary battery, which differs from Example 1 in that: (1) The lithium salt is replaced by lithium hexafluorophosphate (LiPF6) instead of lithium difluorosulfonylimide (LiFSI) in Example 1; (2) The thiocyanate is replaced with potassium thiocyanate instead of lithium thiocyanate in Example 1; (3) The initiator was replaced by 1-hydroxycyclohexylphenyl ketone (Irgacure 184, CAS No.: 947-19-3) instead of azobisisobutyronitrile (AIBN) in Example 1; (4) The organic solvent is replaced by N,N-dimethylformamide (DMF) instead of N,N-dimethylacetamide (DMAC) in Example 1; (5) In the method for preparing the solid electrolyte membrane, step S2 specifically includes: S2. The solid electrolyte slurry is coated onto a PET sheet using a scraper, and polymerization is initiated by ultraviolet light (UV lamp irradiation for 2.5 h). Then, it is dried in an oven at 80°C for 12 h to obtain a solid electrolyte membrane. Everything else is the same as in Example 1.

[0088] Performance testing The solid electrolyte membranes and secondary batteries prepared in the examples and comparative examples were subjected to performance tests, including the following aspects: 1. Density test of solid electrolyte membranes The mass m1 (in grams) of the solid electrolyte membrane is obtained by weighing it. Then, the area S1 (i.e., the product of the length and width of the solid electrolyte membrane, in cm) of the orthographic projection of the same solid electrolyte membrane is measured. 2 The solid electrolyte membrane's thickness h1 (in cm) and density ρ1 (in g / cm³) are calculated using the following formula. 3 ): ρ1=m1 / (S1×h1); The test method for the thickness h1 of the solid electrolyte membrane is as follows: the thickness of any five regions of the solid electrolyte membrane is measured using a thickness gauge, and the average value is recorded as the thickness h1 of the solid electrolyte membrane.

[0089] 2. Ionic conductivity testing of solid electrolyte membranes The secondary battery was discharged at a current of 0.1C to the lower voltage limit of 2.0V. After disassembly, a solid electrolyte membrane was obtained, cleaned with acetone, dried at 60℃, and then left to stand for 60 minutes at 25℃ with a water content <0.1 ppm and an oxygen content <0.1 ppm. The solid electrolyte membrane was then cut into 10mm diameter circular samples, and carbon-coated aluminum foil (current collectors) was attached to both sides of the circular samples, ensuring a tight fit between the carbon-coated surface and the sample surface. The samples were then placed in a PEEK sleeve of a molded battery. Two stainless steel pillars (blocking electrodes) were inserted from both ends of the PEEK sleeve, pressing the ends of the stainless steel pillars against the carbon-coated aluminum foil, forming a symmetrical blocking electrode structure of "stainless steel pillar - carbon-coated aluminum foil - circular sample - carbon-coated aluminum foil - stainless steel pillar". The assembled symmetrical blocking electrode structure was placed in a pressure device, and a pressure of 360 MPa was applied and maintained. AC impedance was tested using a 1260A impedance / gain-phase analyzer from TransPower, with a frequency range of 1MHz-0.1Hz. In the obtained Nyquist electrochemical impedance spectroscopy, the intercept of the semicircular arc in the high-frequency region with the real axis is the bulk impedance Re (in Ω) of the solid electrolyte membrane. The thickness L (in cm) and area A (in cm²) of the circular sample were measured. 2 The ionic conductivity d (mS / cm) of a solid electrolyte membrane is calculated using the following formula: d = 1000 × L / (Re × A); The acceptable standard for the ionic conductivity of solid electrolyte membranes is ≥1.0 mS / cm, and the excellent standard is ≥1.4 mS / cm.

[0090] 3. Tensile strength test of solid electrolyte membrane The solid electrolyte membrane was cut into samples of 8cm×8cm×0.2mm. The tensile strength (unit MPa) of the samples was tested using a ZWICK Z020 universal tensile testing machine at a speed of 10mm / min. The pass standard for tensile strength of solid electrolyte membranes is ≥30.0MPa, and the excellent standard is ≥40.0MPa.

[0091] 4. Cycle performance test of secondary batteries In a 25℃ environment, the secondary battery is charged to 4.25V at a constant current and constant voltage of 0.33C, and then discharged to 2.5V at a constant current of 0.33C. This constitutes one charge-discharge cycle. This charge-discharge cycle is repeated multiple times until the capacity retention rate of the secondary battery drops to 80%. The number of charge-discharge cycles at this point is recorded as the number of cycles with 80% capacity retention rate (unit: cycles). The higher the number of cycles with 80% capacity retention, the stronger the cycle performance of the secondary battery.

[0092] The experimental results are shown in Table 7: Table 7 As shown in Table 7, when the technical solution provided in this application is adopted, the obtained solid electrolyte membrane has high ionic conductivity and tensile strength, and the obtained secondary battery has high cycle performance; wherein, the density of the solid electrolyte membrane is ≥1.50 g / cm³. 3 The solid electrolyte membrane has an ionic conductivity ≥1.0 mS / cm, a tensile strength ≥30.0 ​​MPa, and a cycle count ≥500 cycles to maintain 80% capacity of the secondary battery.

[0093] As can be seen from Examples 1-21 and Comparative Examples 1-3, the solid electrolyte membrane provided in this application improves the ionic conductivity and tensile strength of the solid electrolyte simultaneously by using polymers with -CF2- groups, thiocyanate, polymers formed by the polymerization of alkenyl functionalized ionic liquid monomers, and lithium salts, thereby achieving the purpose of improving the cycle performance of secondary batteries.

[0094] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A solid electrolyte membrane, characterized in that, This includes polymers containing -CF2- groups, thiocyanates, polymers formed by the polymerization of alkenyl-functionalized ionic liquid monomers, and lithium salts.

2. The solid electrolyte membrane as described in claim 1, characterized in that, The mass ratio of the polymer containing -CF2- groups to the polymer formed by polymerization of the alkenyl functionalized ionic liquid monomer is (1-7):1; And / or, the mass ratio of the thiocyanate to the lithium salt is (0.3-3):1; And / or, the ratio of the total mass of the polymer formed by the polymerization of the polymer containing the -CF2- group and the alkenyl functionalized ionic liquid monomer to the total mass of the thiocyanate and lithium salt is (0.6-5):

1.

3. The solid electrolyte membrane as described in claim 1, characterized in that, The polymer containing -CF2- groups includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, and polychlorotrifluoroethylene.

4. The solid electrolyte membrane as described in claim 1, characterized in that, The alkenyl-functionalized ionic liquid monomer includes at least one of 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-vinyl-3-ethylimidazolium tetrafluoroborate, 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide, and 1,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide.

5. The solid electrolyte membrane as described in claim 1, characterized in that, The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalateborate, and lithium hexafluorophosphate.

6. The solid electrolyte membrane as described in claim 1, characterized in that, The thiocyanate includes at least one of lithium thiocyanate, potassium thiocyanate, and sodium thiocyanate.

7. The solid electrolyte membrane as described in claim 1, characterized in that, The thickness of the solid electrolyte membrane is 10μm-30μm.

8. The solid electrolyte membrane as described in claim 1, characterized in that, The density of the solid electrolyte membrane is ≥1.50 g / cm³. 3 .

9. A secondary battery, characterized in that, The secondary battery includes the solid electrolyte membrane according to any one of claims 1-8.

10. An electrical appliance, characterized in that, The electrical device includes the secondary battery as described in claim 9.

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