Diaphragm and preparation method thereof, composite diaphragm, battery and electric equipment

Abstract

The invention relates to the technical field of battery diaphragms, in particular to a diaphragm and a preparation method thereof, a composite diaphragm, a battery and electric equipment. The diaphragm provided by the invention comprises a thermoplastic elastomer and an ionic conductive polymer. The battery diaphragm has relatively good elasticity, ionic conductivity and the like, and is excellent in comprehensive performance.

Description

Technical Field

[0001] The present invention relates to the technical field of battery diaphragms, and in particular to a diaphragm and a preparation method thereof, a composite diaphragm, a battery, and electrical equipment. Background Art

[0002] During the battery cell cycle, due to the "breathing effect" of the electrode, the diaphragm will be affected by periodic internal stress in the thickness direction, undergoing "compression-recovery" type fatigue aging, and irreversible plastic deformation in the thickness direction. This leads to insufficient elasticity of the diaphragm and deterioration of its liquid absorption and retention capacity, thereby reducing the battery's cycle capacity and life. Currently, there are relatively few reports on the optimization of diaphragm elasticity and flexibility, and most existing methods for improving diaphragm elasticity are to improve them by adding coatings or matrix mixing. Although improvements have been made to the diaphragm to improve its elasticity to a certain extent, it is difficult to take into account other key properties of the diaphragm, such as ion conductivity. Summary of the Invention

[0003] The diaphragm provided by the present invention has better elasticity, ion conductivity and the like, and excellent comprehensive performance.

[0004] The present invention achieves the above technical objectives through the following technical solutions:

[0005] A separator includes a thermoplastic elastomer and an ion-conducting polymer.

[0006] The diaphragm directly uses thermoplastic elastomer as the matrix, and adds ion conductive polymer to improve its ion conductivity. It has better elasticity and better ion conductivity, and has excellent comprehensive performance.

[0007] According to the above-mentioned separator, the glass transition temperature of the thermoplastic elastomer is -50 to -30°C, and the melt index at 170 to 210°C is 5 to 15 g / 10 min.

[0008] According to the above-mentioned diaphragm, the thermoplastic elastomer is selected from one or more of styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer (SEBS), polyurethane thermoplastic elastomer (TPU), polyester thermoplastic elastomer (TPEE) or polyamide thermoplastic elastomer (TPAE).

[0009] According to the above-mentioned diaphragm, the thermoplastic elastomer is selected from two of styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer (SEBS), polyurethane thermoplastic elastomer (TPU), polyester thermoplastic elastomer (TPEE) or polyamide thermoplastic elastomer (TPAE), and the mass ratio of the two is 1:1~1:4.

[0010] According to the above-mentioned separator, the mass ratio of the thermoplastic elastomer to the ion conductive polymer is (8-12): (4-6).

[0011] According to the above-mentioned separator, the ionic conductivity of the ion conductive polymer at 20-40°C is not less than 1×10 - 4 S / cm.

[0012] According to the above-mentioned separator, the ion conductive polymer is a polyethylene oxide-lithium salt complex, and the molar ratio of polyethylene oxide to lithium salt is 5:1 to 30:1.

[0013] The above-mentioned separator further comprises nanofibers and / or functional additives.

[0014] According to the above-mentioned separator, the surface of the nanofiber contains amino groups, and the content of the amino groups is 0.5-1.5 mmol / g.

[0015] According to the above-mentioned separator, the diameter of the nanofiber is 50-150 nm.

[0016] According to the above-mentioned separator, the nanofibers are basalt nanofibers.

[0017] According to the above-mentioned separator, the functional auxiliary agent is an organic compound containing one or both of phosphorus and nitrogen elements.

[0018] In the above-mentioned diaphragm, the functional additive is one or more of trimethyl phosphate, triphenyl phosphate, vinylphosphonic acid, ethylenediamine, melamine, acrylamide, and phosphoric acid triamide.

[0019] In the above-mentioned diaphragm, the mass ratio of the thermoplastic elastomer, the ion conductive polymer, the nanofiber and the functional additive is (8~12):(4~6):(2~4):(1~2).

[0020] The above-mentioned diaphragm has a thickness of 3-30 μm, a pore size of 1 nm-10 μm, and an air permeability of 60-300 S / 100 cc.

[0021] The present invention also provides a method for preparing the aforementioned diaphragm, comprising at least the following steps: mixing raw materials to form a wet film, and drying the wet film to obtain the diaphragm, wherein the raw materials include a thermoplastic elastomer and an ion-conductive polymer. The method for preparing the diaphragm provided by the present invention is simple.

[0022] According to the above-mentioned preparation method, the wet film is dried, then subjected to hot pressing, stretching and annealing treatment to obtain the diaphragm.

[0023] According to the preparation method described above, during the hot pressing and stretching, the temperature is 120-140°C, the pressure is 3-5 MPa, the stretching ratio is 1.5-4, and the time is 10-20 minutes.

[0024] According to the preparation method described above, the annealing temperature is 100~110℃ and the annealing time is 2~4h.

[0025] The preparation method of the diaphragm provided by the present invention is simple.

[0026] The present invention also provides a composite membrane comprising a base membrane and a coating located on at least one side of the base membrane, wherein the base membrane is the above-mentioned membrane or a membrane prepared by the above-mentioned preparation method. The composite membrane has excellent deformation recovery ability and excellent ion conductivity.

[0027] The present invention also provides a battery comprising the above-mentioned diaphragm or the diaphragm prepared by the above-mentioned preparation method or the above-mentioned composite diaphragm. The battery has good cycle performance and lifespan.

[0028] The present invention also provides an electrical device comprising the battery. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0030] To address the challenges of existing elastic membranes in balancing ionic conductivity and other key properties, the present invention provides a membrane comprising a thermoplastic elastomer and an ion-conductive polymer. This membrane, instead of relying on traditional polyolefin membranes for improvement, utilizes a thermoplastic elastomer as its matrix while adding an ion-conductive polymer to improve its ionic conductivity, resulting in both superior elasticity and ion conductivity.

[0031] There are no specific restrictions on the choice of thermoplastic elastomer. However, studies have shown that when the glass transition temperature of the thermoplastic elastomer is between -50°C and -30°C and the melt index at 170°C to 210°C is between 5 and 15 g / 10 min, the performance of the highly elastic battery separator is better. For example, the melt index at 170°C to 210°C can be 5 g / 10 min, 8 g / 10 min, 10 g / 10 min, 12 g / 10 min, 15 g / 10 min, or a range between any two of the above values.

[0032] When the thermoplastic elastomer can be selected from one or more of styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer (SEBS), polyurethane thermoplastic elastomer (TPU), polyester thermoplastic elastomer (TPEE) or polyamide thermoplastic elastomer (TPAE), it is more conducive to improving the elasticity and other properties of the diaphragm.

[0033] Further research also shows that when the thermoplastic elastomer is selected from any two of styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer (SEBS), polyurethane thermoplastic elastomer (TPU), polyester thermoplastic elastomer (TPEE) or polyamide thermoplastic elastomer (TPAE) and the mass ratio of the two is 1:1~1:4, the performance of the diaphragm is better.

[0034] When the mass ratio of thermoplastic elastomer to ion conductive polymer is (8~12):(4~6), it is more conducive to taking into account both elasticity and ion conductivity.

[0035] There is no specific restriction on the choice of ion-conducting polymer. However, studies have shown that when the ion-conducting polymer is selected, the ion conductivity at 20-40°C is not less than 1×10⁻ 4 When the polymer is used, the overall performance of the diaphragm is better.

[0036] Furthermore, when the ion conductive polymer is a polyethylene oxide-lithium salt complex and the molar ratio of polyethylene oxide to lithium salt is 5:1 to 30:1, the performance of the separator can be further improved.

[0037] The choice of lithium salt is not particularly limited. For example, the lithium salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluorophosphate (LiPF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalatoborate (LiDFOB) or lithium bis(oxalatoborate) (LiBOB).

[0038] In some embodiments of the present invention, the separator further comprises nanofibers. By adding a certain amount of nanofibers, the mechanical strength of the separator can be improved.

[0039] In other embodiments, the separator further includes a functional additive. The addition of the functional additive can further improve separator performance, enhance overall battery performance, or meet specific application requirements. The choice and amount of the functional additive are determined based on the separator material, battery system, and other factors.

[0040] Further studies have shown that when the surface of the nanofibers contains amino groups and the amino group content is 0.5-1.5 mmol / g, the performance of the separator can be further improved. This is because: the amino group can improve the fiber dispersion by chemical anchoring and polarity matching, and the amino group can enhance the wettability of the electrolyte and improve the overall ionic conductivity. For example, the amino group content can be 0.5 mmol / g, 0.8 mmol / g, 1.0 mmol / g, 1.2 mmol / g, 1.5 mmol / g, and the range between any two of the above values.

[0041] When the nanofiber diameter is 50-150 nm, the fibers within this diameter range can form a uniformly dispersed three-dimensional network skeleton within the elastomer matrix, providing rigid support and thereby improving the tensile strength and puncture resistance of the separator. For example, the nanofiber diameter can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, or ranges between any two of the aforementioned values.

[0042] The choice of nanofiber is not particularly limited. Exemplary examples include polypropylene fiber, polyethylene fiber, polyacrylonitrile fiber, polyester fiber, carbon nanofiber, ceramic fiber, and glass fiber. Basalt nanofiber is preferably used because it has high strength and high modulus properties, which can further enhance the tensile strength, puncture resistance, and thermal shrinkage resistance of the separator.

[0043] When the functional additive is an organic compound containing one or both of phosphorus and nitrogen elements, it can ensure that the thermal stability of the diaphragm is improved while also having a certain flame retardant effect.

[0044] For example, the above functional additives include but are not limited to trimethyl phosphate (C3H9O4P), triphenyl phosphate (C 18 H 15 O4P), vinylphosphonic acid (C2H3O3P), ethylenediamine (C2H8N2), melamine (C3H6N6), acrylamide (C3H5NO), phosphoric acid triamide (C3H 12 N3O4P) in one or more.

[0045] Studies have shown that when the mass ratio of thermoplastic elastomer, ion conductive polymer, nanofiber and functional additive is (8~12):(4~6):(2~4):(1~2), the comprehensive performance of the diaphragm is better.

[0046] Further tests show that the diaphragm prepared by the present invention can still maintain a high elastic recovery rate after undergoing long cycles, and the degree of physical property degradation in the thickness direction of the diaphragm is low. The diaphragm can maintain good liquid absorption and retention capabilities, maintaining the system's excellent reversible cycle capability and life. For example, in some embodiments, the prepared diaphragm with a thickness of 3 to 30 μm can have a pore size of 1 nm to 10 μm and an air permeability of 60 to 300 S / 100 cc, which is comparable to the performance of existing commercially available polypropylene or polyethylene diaphragms. After 2000 cycles of battery charge and discharge, the elastic recovery rate can reach more than 78%, the thickness retention rate is more than 80%, and the rate of change in liquid absorption and retention capacity is less than 12%. That is, the diaphragm still maintains excellent stability in long cycles and complex environments. In other embodiments, after 2000 cycles of battery charge and discharge, the elastic recovery rate can reach more than 93%, the thickness retention rate is more than 92%, and the rate of change in liquid absorption and retention capacity is less than 4%. In other embodiments, after the battery has been charged and discharged for 2000 cycles, the elastic recovery rate can reach more than 95%, the thickness retention rate is more than 95%, and the change rate of liquid absorption and retention capacity is 2% or less.

[0047] The preparation method for the battery separator is not specifically limited. In some embodiments, the separator can be prepared by mixing raw materials to form a wet film, which is then dried to obtain the separator. The raw materials include a thermoplastic elastomer and an ion-conductive polymer. This preparation method is simple and amenable to industrial large-scale production.

[0048] The method for preparing the wet film is not limited. For example, the common film-casting method in the art can be used, that is, the raw materials are mixed and then cast into a wet film. Dipping, spin coating, etc. can also be used.

[0049] After being cast into a wet film, the wet film may be subjected to hot pressing, stretching, and annealing. In some embodiments, the hot pressing and stretching temperature is 120-140°C, the pressure is 3-5 MPa, the stretch ratio is 1.5-4, and the hot pressing time is 10-20 minutes.

[0050] In some specific embodiments, the annealing temperature is 100-110° C., and the annealing time is 2-4 hours.

[0051] In some specific embodiments of the present invention, the highly elastic diaphragm is prepared by the following method:

[0052] Preparation of elastomer solution: Add the thermoplastic elastomer to an organic solvent and stir at 40-60°C until completely dissolved, forming a uniform elastomer solution. The organic solvent is not limited and may include tetrahydrofuran, N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), acetone, ethanol / isopropanol, etc.

[0053] Material mixing: then add the ion conductive polymer, nanofibers and functional additives to the above elastomer solution, continue stirring for 2 to 4 hours to fully mix the components to obtain a mixed solution.

[0054] It should be noted that there is no specific restriction on the order in which the materials are added, as long as the materials are uniformly dispersed in the final mixed solution. In actual production applications, the preparation is usually carried out in the order of first dissolving the thermoplastic elastomer, then adding the ion-conductive polymer, nanofibers, and functional additives, which is efficient and has a good mixing effect.

[0055] Tape casting: The mixed solution is evenly cast onto a smooth plate (such as a polytetrafluoroethylene plate) through a tape casting machine, and the casting thickness is controlled at 10~30μm to form a wet film.

[0056] Drying and desolvation: Place the plate with the wet film in a vacuum drying oven and dry it at 60-80°C for 8-12 hours to completely evaporate the organic solvent and obtain a solid diaphragm precursor.

[0057] Hot pressing orientation: The solid membrane precursor is hot pressed at 120~140℃ and pressure 3~5MPa for 10~20 minutes. At the same time, tensile force is applied along the TD (width direction) and MD (length direction) directions during the hot pressing process. The stretching ratio is 1.5~4, so that the molecular chains and nanofibers inside the membrane are oriented along the stretching direction, thereby enhancing the elasticity and mechanical properties of the membrane.

[0058] Annealing treatment: Anneal the hot-pressed diaphragm at 100~110℃ for 2~4 hours to eliminate internal stress and further stabilize the structure and performance of the diaphragm.

[0059] The present invention also provides a composite diaphragm, comprising a base membrane and a coating located on at least one side of the base membrane, wherein the base membrane is the above-mentioned high-elasticity battery diaphragm or the high-elasticity battery diaphragm prepared by the above-mentioned preparation method.

[0060] Specifically, the coating can be formed on only one side of the base film or on both sides of the base film. It is easy to understand that the above-mentioned one side or both sides of the base film refer to the side of the base film facing or away from the positive electrode active layer or the negative electrode active layer in the battery.

[0061] The material and thickness of the coating are not specifically limited. For example, the coating can be an organic coating or an inorganic coating, or an organic-inorganic hybrid coating can be selected at the same time. The organic coating can be selected from one or more of polyvinylidene fluoride, polyimide, aramid, aromatic sulfone, and polyacrylonitrile, and the inorganic coating can be selected from one or more of aluminum oxide, boehmite, magnesium hydroxide, aluminum hydroxide, zirconium oxide, or titanium dioxide. The thickness of the coating can be selected according to the conventional techniques in the art, usually 1-4 μm. The coating coating method can be prepared by conventional operations in the art, which will not be described in detail here.

[0062] The present invention also provides a battery comprising the aforementioned high-elasticity battery separator, the high-elasticity battery separator produced by the aforementioned preparation method, or the aforementioned composite separator. The battery type is not specifically limited and may include, for example, a lithium battery, a sodium battery, or a potassium battery. Furthermore, the battery may be a liquid battery, an all-solid-state battery, or a quasi-solid-state battery.

[0063] The batteries of the present invention may be in the form of battery cells, battery modules, and battery packs. In some embodiments, battery cells may be assembled into a battery module, which may contain one or more battery cells, with the specific number selected by those skilled in the art based on the application and capacity of the battery module. In some embodiments, battery modules may also be assembled into a battery pack, which may contain one or more battery modules, with the specific number selected by those skilled in the art based on the application and capacity of the battery pack.

[0064] The specific type of battery of the present invention is not particularly limited. For example, from the perspective of shape, the battery includes but is not limited to square-shell batteries, soft-pack batteries, and cylindrical batteries, etc., and the present invention does not impose any particular restrictions. From the perspective of the electrode core structure, the electrode core of the battery can be a wound electrode core (i.e., the positive electrode sheet, the negative electrode sheet, and the separator are stacked and then wound to form the electrode core) or a laminated electrode core (i.e., multiple positive electrode sheets, negative electrode sheets, and separators are stacked to form the electrode core). The outer shell can be a hard shell (such as a steel shell, a hard plastic shell, etc.) or a soft shell (such as an aluminum-plastic film, a bag-type soft shell, etc.). This application does not impose any particular restrictions.

[0065] The present invention also provides an electrical device comprising the aforementioned battery. The electrical device may be conventional electrical devices in the art, including consumer electronics (mobile communication devices, laptop computers, tablet computers, wearable devices, etc.), drones, power tools, energy storage devices, electric bicycles, electric vehicles, and the like.

[0066] The present invention is described in detail below with reference to specific embodiments.

[0067] Raw material information:

[0068] Styrene-butadiene-styrene block copolymer (SBS): styrene segment polymerization degree 120, butadiene segment polymerization degree 600, glass transition temperature of -35°C, melt index of 5.6g / 10min (190°C, 2.16kg);

[0069] Hydrogenated styrene-butadiene-styrene block copolymer (SEBS): styrene segment polymerization degree 100, ethylene-butylene segment polymerization degree 800, glass transition temperature of -40°C, melt index of 6.8g / 10min (190°C, 2.16kg);

[0070] Polyurethane thermoplastic elastomer (TPU): degree of polymerization 40, glass transition temperature -40°C, melt index 8.6g / 10min (190°C, 2.16kg);

[0071] Polyester thermoplastic elastomer (TPEE): degree of polymerization 35, glass transition temperature of -42°C, melt index of 5.0g / 10min (190°C, 2.16kg).

[0072] Basalt nanofibers: Surface treatment was performed by soaking in silane coupling agent KH-550. The amino content on the surface of the treated fibers was detected by X-ray photoelectron spectroscopy (XPS).

[0073] Example 1

[0074] Raw materials and mass proportions: SBS 20 parts, SEBS 20 parts, polyethylene oxide-LiTFSI complex (molar ratio 10:1, ionic conductivity at 30 ° C is 2.2×10 -4 S / cm) 20 parts, basalt nanofiber treated with KH-550 (diameter 120nm, surface amino content of 1.0mmol / g) 10 parts, functional additive trimethyl phosphate (C3H9O4P) 5 parts.

[0075] The preparation method is as follows:

[0076] Premixing treatment: Add SBS and SEBS into tetrahydrofuran and stir and dissolve at 50°C to form a uniform elastomer solution.

[0077] Adding and mixing: adding polyethylene oxide-LiTFSI complex, basalt nanofibers treated with KH-550, and functional additives to the elastomer solution, and continuing stirring for 3 hours to fully mix the components to obtain a mixed solution;

[0078] Tape casting: The mixed solution is evenly cast onto a smooth polytetrafluoroethylene plate through a tape casting machine, and the casting thickness is controlled to be 12 μm to form a wet film.

[0079] Drying and desolvation: Place the polytetrafluoroethylene plate with the wet film in a vacuum drying oven and dry it at 70°C for 10 hours to completely evaporate the organic solvent and obtain a solid diaphragm precursor;

[0080] Hot pressing orientation: The solid diaphragm precursor was hot pressed at 130°C and a pressure of 4 MPa for 15 minutes with a stretching ratio of 2.0, and finally annealed at 105°C for 3 hours to obtain the finished diaphragm.

[0081] Example 2

[0082] Raw materials: SBS 30 parts, TPU 20 parts, polyethylene oxide-LiTFSI complex (molar ratio 8:1, ionic conductivity at 30°C is 3×10 -4 S / cm) 25 parts, basalt nanofibers treated with KH-550 (diameter 89nm, surface amino content of 1.2mmol / g) 15 parts, functional additive melamine (C3H6N6) 8 parts.

[0083] Premixing treatment: Add SBS and TPU into tetrahydrofuran, stir and dissolve at 50°C to form a uniform elastomer solution.

[0084] Adding and mixing: adding polyethylene oxide-LiTFSI complex, basalt nanofibers treated with KH-550, and functional additives to the elastomer solution in sequence, and continuing stirring for 3 hours to fully mix the components to obtain a mixed solution;

[0085] Tape casting: The mixed solution is evenly cast onto a smooth polytetrafluoroethylene plate through a tape casting machine, and the casting thickness is controlled to be 12 μm to form a wet film.

[0086] Drying and desolvation: Place the polytetrafluoroethylene plate with the wet film in a vacuum drying oven and dry it at 75°C for 10 hours to completely evaporate the organic solvent and obtain a solid diaphragm precursor;

[0087] Hot pressing orientation: The solid diaphragm precursor was hot pressed at 140°C and a pressure of 4 MPa for 10 minutes with a stretching ratio of 3.0, and finally annealed at 110°C for 4 hours to obtain the finished diaphragm.

[0088] Example 3

[0089] Raw materials: SEBS 30 parts, TPEE 30 parts, polyethylene oxide-LiPF6 complex (molar ratio 10:1, ionic conductivity at 30°C is 3.4×10 -4 S / cm), 20 parts of basalt nanofibers treated with KH-550 (diameter 130nm, surface amino content 0.8mmol / g), and 10 parts of functional additive ethylenediamine (C2H8N2). The preparation method is as follows:

[0090] Premixing treatment: Add SEBS and TPEE into tetrahydrofuran and stir and dissolve at 60°C to form a uniform elastomer solution.

[0091] Adding and mixing: adding polyethylene oxide-LiPF6 complex, basalt nanofiber treated with KH-550, and functional additives to the elastomer solution in sequence, and continuing stirring for 4 hours to fully mix the components to obtain a mixed solution;

[0092] Tape casting: The mixed solution is evenly cast onto a smooth polytetrafluoroethylene plate through a tape casting machine, and the casting thickness is controlled to be 16 μm to form a wet film.

[0093] Drying and desolvation: Place the polytetrafluoroethylene plate with the wet film in a vacuum drying oven and dry it at 80°C for 10 hours to completely evaporate the organic solvent and obtain a solid diaphragm precursor;

[0094] Hot pressing orientation: The solid membrane precursor was hot pressed at 125°C and a pressure of 5 MPa for 20 minutes with a stretching ratio of 2.5, and finally annealed at 110°C for 4 hours to obtain the finished membrane.

[0095] Example 4

[0096] This example differs from Example 1 in that the thermoplastic elastomer used is SBS alone. Specifically, the raw material composition is: 40 parts SBS, 20 parts polyethylene oxide-LiTFSI complex (molar ratio 10:1), 10 parts KH-550-treated basalt nanofibers, and 5 parts trimethyl phosphate (C3H9O4P), a functional additive.

[0097] Example 5

[0098] This example differs from Example 1 in that the functional additive is ethyl acetate (C4H8O2). Specifically, the raw material composition is: 20 parts SBS, 20 parts SEBS, 20 parts polyethylene oxide-LiTFSI complex (molar ratio 10:1), 10 parts KH-550-treated basalt nanofibers, and 5 parts ethyl acetate (C4H8O2), the functional additive.

[0099] Example 6

[0100] This example differs from Example 1 in that no functional additives are included. Specifically, the raw material composition is: 20 parts SBS, 20 parts SEBS, 20 parts polyethylene oxide-LiTFSI complex (molar ratio 10:1), and 10 parts KH-550 treated basalt nanofibers.

[0101] Example 7

[0102] This embodiment differs from Example 1 in that equal parts by weight of polymethyl methacrylate (PMMA) are used in place of the ion-conductive polymer. Specifically, the raw material composition is: 20 parts SBS, 20 parts SEBS, 20 parts polymethyl methacrylate (PMMA), 10 parts KH-550-treated basalt nanofibers, and 5 parts trimethyl phosphate (C3H9O4P), a functional additive.

[0103] Example 8

[0104] This example differs from Example 1 in that equal parts by weight of polyisoprene (DP 5294, glass transition temperature -60°C, melt index 4.3 g / 10 min (190°C, 2.16 kg)) are used to replace the SBS and SEBS rings. Specifically, the raw material composition is: 40 parts polyisoprene, 20 parts polyethylene oxide-LiTFSI complex (molar ratio 10:1), 10 parts KH-550-treated basalt nanofibers, and 5 parts trimethyl phosphate (C3H9O4P), a functional additive.

[0105] Example 9

[0106] This embodiment differs from embodiment 1 in that it does not contain functional additives and nanofibers. Specifically, its raw material composition is: 25 parts of SBS, 25 parts of SEBS, and 25 parts of polyethylene oxide-LiTFSI complex (molar ratio 10:1).

[0107] Comparative Example 1

[0108] The difference between this comparative example and Example 1 is that it only contains thermoplastic elastomer, specifically: the raw material composition is 50 parts of SBS and 50 parts of SEBS.

[0109] Comparative Example 2

[0110] The thickness of the existing commercial polyethylene diaphragm is 12μm.

[0111] Comparative Example 3

[0112] The existing commercial polypropylene separator has a thickness of 16 μm.

[0113] Performance testing:

[0114] (1) Basic physical property testing

[0115] The membranes prepared in the above examples and comparative examples were tested for basic physical properties such as thickness, air permeability, and liquid retention, as well as physical properties such as ionic conductivity, puncture strength, and thermal shrinkage. The specific test methods and test results are as follows:

[0116] Thickness: Use a Mahr thickness gauge to evenly select 5 points along the transverse direction (MD) of the film for testing, record the values and calculate the average value D1.

[0117] Air permeability: Use Wang Yan's air permeability tester, select the measurement mode (MEASURE) as "JIS", select the measurement value as "500", and the test time (TIMER) as "5s" and lock it; place the membrane to be tested between the platform and the air nozzle, and evenly select 5 points along the transverse direction (MD) of the membrane for testing, and record the values.

[0118] Liquid absorption and retention rate: Take a certain area (100mm×100mm) of the separator and weigh it, the weight is recorded as m0; soak the separator in a standard electrolyte 1M LiPF6 / EC-DEC (volume ratio 1:1) for 10 minutes, then take it out and weigh it, the weight is recorded as m1; place the liquid-absorbing separator in air for 20 minutes and weigh it again, the weight is recorded as m2. The liquid absorption rate, liquid retention rate and liquid absorption and retention rate are calculated using the following formulas:

[0119] Liquid absorption rate = (m1-m0) / m0×100%;

[0120] Liquid retention rate = (m2-m0) / m0×100%;

[0121] Liquid absorption and retention rate = (liquid absorption rate + liquid retention rate) / 2×100%.

[0122] Ionic conductivity: The diaphragm was cut into 20 mm diameter discs and immersed in 1M LiPF6 / EC-DEC (volume ratio 1:1) electrolyte for 24 h to ensure that the pores were fully adsorbed by the electrolyte. A symmetrical structure of "stainless steel sheet / diaphragm / stainless steel sheet" was used and placed in a button cell battery shell (CR2032). A pressure of 10 kPa was applied to fix the structure. An electrochemical workstation (such as Autolab, CHI660E) was used with a frequency range of 10 -2 ~10 6 Hz, AC amplitude 5mV, and impedance spectra were collected at room temperature (25±2°C). The bulk resistance R of the diaphragm (the intersection of the semicircle arc in the high-frequency region and the real axis) was obtained by fitting the impedance spectrum. Combined with the diaphragm thickness and electrode area, the conductivity was calculated according to the following formula:

[0123]

[0124] in:

[0125] σ: ionic conductivity (mS / cm);

[0126] L: diaphragm thickness (cm);

[0127] R: diaphragm resistance (Ω, obtained by impedance spectrum fitting);

[0128] S: electrode effective area (cm²).

[0129] Puncture strength: Cut 50 mm × 50 mm diaphragm specimens and test five replicates per group. Remove moisture in a drying oven (60°C, 2 h) before testing. Use an electronic universal testing machine (such as the Instron 5967) equipped with a 1 mm diameter steel puncture needle (0.1 mm tip radius of curvature). Fix the specimen edge with a fixture. The effective testing area is a 30 mm diameter circular area. Use a puncture speed of 100 mm / min and a force resolution of 0.1 N. Record the force-displacement curve, and take the peak force as the puncture strength.

[0130] Thermal Shrinkage: Cut a 100mm x 100mm diaphragm specimen and mark two 80mm reference lines in the longitudinal and transverse directions with a marker (avoiding 5mm from the edges). Place the specimen flat on a glass plate, clamp it on both sides, and place it in a forced air drying oven. Heat it to the target temperature (120°C) and hold it there for 2 hours. Cool it to room temperature in the oven. Use a vernier caliper with an accuracy of 0.02mm to measure the length L0 of the reference lines after cooling. Calculate the longitudinal and transverse shrinkage using the following formula:

[0131]

[0132] Table 1

[0133]

[0134] As shown in Table 1, at the same thickness, the separators of Examples 1-9 of the present invention all exhibited superior air permeability, liquid absorption and retention, ionic conductivity, puncture strength, longitudinal thermal shrinkage, and transverse thermal shrinkage compared to Comparative Example 1, with no significant differences compared to existing commercial polyolefin separators. This demonstrates that the separators provided by the present invention not only maintain flexibility but also possess other properties such as excellent ionic conductivity, thermal stability, and mechanical strength.

[0135] It can also be seen from Table 1 above that compared with Examples 6 and 9, the comprehensive performance of Examples 1, 2, 4, 5, 7, and 8, such as the transverse heat shrinkage rate and the longitudinal heat shrinkage rate, is relatively excellent, indicating that the addition of functional additives and nanofibers can further improve the comprehensive performance of the diaphragm.

[0136] It can also be seen from Table 1 that compared with Example 4, the performance of Examples 1 and 2 is relatively excellent, indicating that the mixed thermoplastic elastomer is beneficial to improving the comprehensive performance of the diaphragm.

[0137] It can also be seen from Table 1 that compared with Examples 5, 7, and 8, Examples 1 and 2 have excellent comprehensive performance, indicating that the use of a thermoplastic elastomer with a glass transition temperature of -50 to -30°C, a melt index of 170-210°C of 5 to 15 g / 10 min, a polyethylene oxide-lithium salt complex as an ion conductive polymer, and an organic compound containing one or both of phosphorus and nitrogen elements as a functional additive is beneficial to improving the comprehensive performance of the diaphragm.

[0138] (2) Physical property test of diaphragm after cycling

[0139] Preparation of soft-pack batteries: The separators in the above examples and comparative examples were combined with lithium iron phosphate positive electrode sheets, graphite negative electrode sheets and standard lithium hexafluorophosphate (LiPF6, 1 mol / L) electrolyte to prepare soft-pack batteries.

[0140] After the above-mentioned soft-pack battery was cycled for 2000 cycles at a rate of 1C at 25°C, the capacity retention rate of the system was recorded, and the battery was disassembled to characterize the thickness of the diaphragm and the liquid absorption and retention rate after the cycle. The characterization methods of each indicator are as follows, and the characterization results are shown in Table 2 below.

[0141] Capacity retention rate: The above-mentioned battery was subjected to a cycle performance test at room temperature of 25°C. The test process is as follows: first, 1C constant current charging to 4.25V, and then 1C constant current discharging to 2.5V. After 2000 cycles, the 2000-cycle discharge capacity was divided by the discharge capacity of the first cycle to obtain the 2000-cycle cycle retention rate.

[0142] Elastic Recovery Rate: After cleaning the diaphragm after cycling, measure its thickness at five different locations (center + four edge points) using a Mahr thickness gauge. The average value is taken as the initial thickness, T0. Using a universal testing machine equipped with a compression fixture, compress the diaphragm at a rate of 1 mm / min to 0.5 T0 and hold for 5 minutes. Unload the pressure at the same rate as the loading, and let it rest for 5 minutes after release (to allow for full recovery of the elastic deformation). Immediately measure the thickness at the same five locations, and take the average value, T1. Calculate the elastic recovery rate using the following formula:

[0143]

[0144] Thickness retention: Use a Mahr thickness gauge to test five points evenly around the perimeter and center of the film. Record the values and calculate the average value as D2. Thickness retention = 1 - (D2 - D1) / D1.

[0145] The rate of change in liquid absorption and retention capacity is tested using the same test method as in the above-mentioned basic physical property test, and is calculated using the same method as the above-mentioned thickness retention rate.

[0146] Table 2

[0147]

[0148] From the results in Table 2, it can be seen that the battery prepared using the diaphragm of the present invention has a better system capacity retention rate after 2000 cycles than the batteries prepared using the diaphragms in Comparative Examples 1-3 (wherein Example 3 is compared with Comparative Example 3, and the other examples are compared with Comparative Examples 1 and 2).

[0149] It can also be seen from the results in Table 2 that compared with Examples 6, 8, and 9, the elastic recovery rate, thickness retention rate, and liquid absorption and retention capacity change rate of the diaphragm in Examples 1, 2, 4, 5, and 7 after 2000 cycles are all better, indicating that the use of a thermoplastic elastomer with a glass transition temperature of -50 to -30°C, a melt index of 170-210°C and a melt index of 5 to 15 g / 10 min, and the addition of functional additives and nanofibers are beneficial to further improve the comprehensive performance of the diaphragm, thereby extending the life of the battery.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A diaphragm, characterized in that: These include thermoplastic elastomers and ion-conducting polymers.

2. The diaphragm according to claim 1, characterized in that The thermoplastic elastomer has a glass transition temperature of -50 to -30°C and a melt index of 5 to 15 g / 10 min at 170 to 210°C.

3. The diaphragm according to claim 1 or 2, characterized in that The thermoplastic elastomer is selected from one or more of styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, polyurethane thermoplastic elastomer, polyester thermoplastic elastomer or polyamide thermoplastic elastomer.

4. The diaphragm according to claim 3, characterized in that The thermoplastic elastomer is selected from two of styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, polyurethane thermoplastic elastomer, polyester thermoplastic elastomer or polyamide thermoplastic elastomer, and the mass ratio of the two is 1:1 to 1:

4.

5. The diaphragm according to any one of claims 1 to 4, characterized in that: The mass ratio of the thermoplastic elastomer to the ion conductive polymer is (8-12): (4-6).

6. The diaphragm according to any one of claims 1 to 5, characterized in that: The ionic conductivity of the ion conductive polymer at 20-40°C is not less than 1×10 -4 S / cm.

7. The diaphragm according to any one of claims 1 to 6, characterized in that: The ion conductive polymer is a polyethylene oxide-lithium salt complex, and the molar ratio of polyethylene oxide to lithium salt is 5:1 to 30:

1.

8. The diaphragm according to any one of claims 1 to 7, characterized in that: Nanofibers and / or functional additives are also included.

9. The diaphragm according to claim 8, characterized in that The surface of the nanofiber contains amino groups, and the content of the amino groups is 0.5-1.5 mmol / g; and / or The diameter of the nanofiber is 50-150 nm; and / or The nanofibers are basalt nanofibers; and / or The functional auxiliary agent is an organic compound containing one or both of phosphorus and nitrogen elements.

10. The diaphragm according to claim 9, characterized in that The functional additive is one or more of trimethyl phosphate, triphenyl phosphate, vinylphosphonic acid, ethylenediamine, melamine, acrylamide, and phosphoric acid triamide.

11. The diaphragm according to any one of claims 8 to 10, characterized in that: The mass ratio of the thermoplastic elastomer, the ion conductive polymer, the nanofiber and the functional additive is (8-12): (4-6): (2-4): (1-2).

12. The diaphragm according to any one of claims 1 to 11, characterized in that: The thickness of the diaphragm is 3-30 μm, the pore size is 1 nm-10 μm, and the air permeability is 60-300 S / 100 cc.

13. A method for preparing a diaphragm according to any one of claims 1 to 12, characterized in that: At least the following steps are included: The raw materials are mixed to prepare a wet film, and the wet film is dried to obtain the separator. The raw materials include a thermoplastic elastomer and an ion conductive polymer.

14. The method for preparing a diaphragm according to claim 13, wherein: The wet film is dried, stretched, and annealed to obtain the diaphragm.

15. The method for preparing a diaphragm according to claim 14, characterized in that: During hot pressing and stretching, the temperature is 120-140°C, the pressure is 3-5 MPa, the stretching ratio is 1.5-4, and the time is 10-20 min; and / or The annealing temperature is 100~110℃ and the annealing time is 2~4h.

16. A composite diaphragm, characterized in that: The invention comprises a base film and a coating located on at least one side of the base film, wherein the base film is the diaphragm according to any one of claims 1 to 12 or the diaphragm prepared by the preparation method according to any one of claims 13 to 15.

17. A battery, characterized in that: The invention comprises the diaphragm according to any one of claims 1 to 12, the diaphragm prepared by the preparation method according to any one of claims 13 to 15, or the composite diaphragm according to claim 16.

18. An electrical device, characterized in that: Including the battery according to claim 17.

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