Diaphragm and preparation method thereof, secondary battery and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a diaphragm and a preparation method thereof, a secondary battery and an electric device. The separator comprises: a fibrous membrane; and the gel body is arranged in the pores of the fiber membrane, and the gel body comprises a silica gel matrix and solid electrolyte particles dispersed in the silica gel matrix. According to the diaphragm provided by the invention, the pores of the fiber membrane are filled with the gel, the gel and the fiber membrane form an interpenetrating network structure, the number and efficiency of ion conduction channels are improved, the silica gel matrix is used as a carrier to fix the solid electrolyte particles, and a continuous ion conduction path is formed, so that the ion conductivity of the diaphragm is improved, and the service life of the diaphragm is prolonged. The internal resistance of the battery is reduced, so that the rate capability and the cycle life of the battery are improved; meanwhile, pores of the fiber membrane are filled with the gel, so that the thickness of the diaphragm is not additionally increased, the energy density of the battery is improved, and the problem that a coating structure is easy to fall off in the prior art is solved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a diaphragm and a preparation method thereof, a secondary battery, and an electrical device. Background Art

[0002] Secondary batteries are widely used in consumer electronics, energy storage devices, and electric vehicles due to their high energy density, long cycle life, and low self-discharge rate. As a core component of secondary batteries, the separator separates the positive and negative electrodes while providing an ion conduction path. Its performance directly impacts the battery's safety, cycle life, and rate capability.

[0003] Currently, the separators used in secondary batteries are primarily polyolefins, which offer low cost and moderate mechanical strength. However, polyolefin separators are susceptible to thermal shrinkage at high temperatures, increasing the risk of short circuits. Furthermore, their limited porosity and ionic conductivity make them difficult to meet the ultra-thin, high-ionic conductivity requirements of high-performance batteries.

[0004] In traditional technology, there are two technical solutions: (1) using polymer fiber membrane to replace polyolefin base membrane to improve the thermal stability of the diaphragm; (2) preparing inorganic particles or solid electrolyte particles into slurry and coating it on the surface of polyolefin base membrane to form a surface coating structure to improve the thermal stability or ionic conductivity of the diaphragm.

[0005] However, the pore structure of a single fiber membrane makes it difficult to simultaneously take into account high ionic conductivity and electrolyte retention capacity, resulting in limited improvement in battery performance; the surface coating structure has the problem of easy coating shedding, and the coating increases the thickness of the diaphragm, which is not conducive to improving the battery energy density. Summary of the Invention

[0006] Based on this, it is necessary to provide a diaphragm and its preparation method, a secondary battery, and an electrical device to reduce the thickness of the diaphragm while improving the thermal stability, ionic conductivity and mechanical properties of the diaphragm, thereby reducing the interfacial impedance and improving the safety performance, energy density, rate performance and cycle performance of the battery.

[0007] A first aspect of the present application provides a diaphragm, which includes: a fiber membrane; and a gel disposed in pores of the fiber membrane, wherein the gel includes a silicone gel matrix and solid electrolyte particles dispersed in the silicone gel matrix.

[0008] In some embodiments, the fiber membrane includes: a polyimide matrix; and inorganic modified particles dispersed in the polyimide matrix, wherein the surfaces of the inorganic modified particles have Si—O—Si bonds.

[0009] In some embodiments, the fiber membrane further comprises: graphene oxide dispersed in a polyimide matrix.

[0010] In some embodiments, the average particle size of the solid electrolyte particles is 50 nm to 150 nm.

[0011] In some embodiments, in the gel, the mass ratio of the silicone gel matrix to the solid electrolyte particles is (0.2-0.72):1.

[0012] In some embodiments, the thickness of the separator is 5 μm to 15 μm.

[0013] In some embodiments, the porosity of the separator is 60% to 70%.

[0014] In some embodiments, the separator has a tensile strength of 100 MPa to 200 MPa and an elongation at break of 50% to 150%.

[0015] In some embodiments, the ionic conductivity of the separator at 25°C is 2.0*10 -4 S / cm~1.8*10 -3 S / cm.

[0016] In some embodiments, the electrolyte absorption rate of the separator is 90% to 130%.

[0017] In some embodiments, the separator has a heat shrinkage of <1% at 150°C.

[0018] The second aspect of the present application provides a method for preparing a diaphragm, which comprises the following steps: dispersing solid electrolyte particles in silica sol to obtain a composite sol liquid; filling the composite sol liquid into the pores of a fiber membrane, performing a gelation treatment, and obtaining a diaphragm; wherein the diaphragm comprises a fiber membrane and a gel body, and the gel body comprises a silica gel matrix and solid electrolyte particles dispersed in the silica gel matrix.

[0019] In some embodiments, the step of filling the composite sol liquid into the pores of the fiber membrane and performing a gelation treatment to obtain a diaphragm specifically includes the following steps: placing the fiber membrane into the composite sol liquid for immersion treatment, so that the composite sol liquid fills the pores of the fiber membrane to obtain a sol-filled fiber membrane; and performing a gelation treatment on the sol-filled fiber membrane to obtain a diaphragm.

[0020] In some embodiments, before the step of gelling the sol-filled fiber membrane to obtain a separator, the following steps are included: taking out the sol-filled fiber membrane and hanging it vertically.

[0021] A third aspect of the present application provides a secondary battery, which includes the diaphragm provided by the first aspect, or the diaphragm prepared by the method for preparing the diaphragm provided by the second aspect.

[0022] A fourth aspect of the present application provides an electrical device, which includes the secondary battery provided by the third aspect.

[0023] Compared with traditional technologies, this application has at least the following beneficial effects:

[0024] The diaphragm provided by the present application, on the one hand, forms an interpenetrating network structure with the fiber membrane by filling the gel into the pores of the fiber membrane, thereby improving the number and efficiency of ion conduction channels. The silicone gel matrix acts as a carrier to fix the solid electrolyte particles, forming a continuous ion conduction path. The high porosity of the fiber membrane provides a three-dimensional permeation channel. The silicone groups and solid electrolyte particles of the silicone gel matrix have good wettability, which improves the liquid absorption and liquid retention properties of the diaphragm, thereby improving the ionic conductivity of the diaphragm, reducing the internal resistance of the battery, and further improving the rate performance and cycle life of the battery. At the same time, the gel is filled into the pores of the fiber membrane, which neither increases the thickness of the diaphragm nor improves the energy density of the battery, nor does it have the problem of easy detachment of the coating structure in traditional technologies.

[0025] On the other hand, the high thermal stability of the fiber membrane and the three-dimensional network structure of the gel jointly limit the thermal shrinkage behavior of the membrane at high temperatures, thereby improving the thermal stability of the membrane and improving the safety performance of the battery; at the same time, the flexible network of the fiber membrane and the gel forms an interpenetrating network structure, which disperses the stress and enhances the mechanical properties and puncture resistance of the membrane, ensuring the stability of the membrane during battery assembly and operation, and preventing battery failure due to mechanical damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the process for preparing a diaphragm in one embodiment of the present application. DETAILED DESCRIPTION

[0027] References to embodiments of the present application will now be provided in detail, one or more examples of which are described below. Each example is provided to illustrate, not to limit, the present application. Indeed, it will be apparent to those skilled in the art that various modifications and variations may be made to the present application without departing from the scope or spirit of the present application. For example, features illustrated or described as part of one embodiment may be used in another embodiment to produce further embodiments.

[0028] Therefore, it is intended that this application covers such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the present application are disclosed in or are apparent from the following detailed description. Those skilled in the art will appreciate that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the present application.

[0029] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0030] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0031] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0032] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, it is mentioned that the method may also include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0034] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0035] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0036] The first aspect of the present application provides a diaphragm, which includes a fiber membrane and a gel. The gel is arranged in the pores of the fiber membrane, and the gel includes a silicone gel matrix and solid electrolyte particles dispersed in the silicone gel matrix.

[0037] The diaphragm provided by the present application, on the one hand, forms an interpenetrating network structure with the fiber membrane by filling the gel into the pores of the fiber membrane, thereby improving the number and efficiency of ion conduction channels. The silicone gel matrix acts as a carrier to fix the solid electrolyte particles, forming a continuous ion conduction path. The high porosity of the fiber membrane provides a three-dimensional permeation channel. The silicone groups and solid electrolyte particles of the silicone gel matrix have good wettability, which improves the liquid absorption and liquid retention properties of the diaphragm, thereby improving the ionic conductivity of the diaphragm, reducing the internal resistance of the battery, and further improving the rate performance and cycle life of the battery. At the same time, the gel is filled into the pores of the fiber membrane, which neither increases the thickness of the diaphragm nor improves the energy density of the battery, nor does it have the problem of easy detachment of the coating structure in traditional technologies.

[0038] On the other hand, the high thermal stability of the fiber membrane and the three-dimensional network structure of the gel jointly limit the thermal shrinkage behavior of the membrane at high temperatures, thereby improving the thermal stability of the membrane and improving the safety performance of the battery; at the same time, the flexible network of the fiber membrane and the gel forms an interpenetrating network structure, which disperses the stress and enhances the mechanical properties and puncture resistance of the membrane, ensuring the stability of the membrane during battery assembly and operation, and preventing battery failure due to mechanical damage.

[0039] In some embodiments, the fiber membrane includes a polyimide matrix and inorganic modified particles. The inorganic modified particles are dispersed in the polyimide matrix, and the surface of the inorganic modified particles has Si-O-Si bonds. In this way, by using the polyimide matrix as the matrix material of the fiber membrane, the thermal stability and mechanical strength of the diaphragm are improved; by dispersing the inorganic modified particles in the polyimide matrix, the compatibility of the inorganic particles and the polyimide matrix is enhanced, and the thermal stability and mechanical strength of the diaphragm are further improved. At the same time, the Si-O-Si bonds on the surface of the inorganic modified particles can form new Si-O-Si chemical bonds or adsorb with the siloxy groups in the silicone gel matrix, thereby enhancing the interaction between the modified inorganic particles and the silicone gel matrix at the interface, forming a tighter and continuous composite network structure, reducing the risk of the gel falling off from the fiber membrane, improving the mechanical strength and ionic conductivity of the diaphragm, limiting the thermal shrinkage behavior of the diaphragm at high temperatures, and further improving the safety performance and electrochemical performance of the battery.

[0040] In some embodiments, the Si-O-Si bonds on the surface of the inorganic modified particles are obtained by modifying the inorganic particles with a silane coupling agent.

[0041] In some embodiments, the silane coupling agent is selected from at least one of γ-aminopropyltriethoxysilane (KH-550), γ-glycidoxypropyltrimethoxysilane (KH-560), and γ-methacryloxypropyltrimethoxysilane (KH-570).

[0042] In some embodiments, the inorganic particles are selected from at least one of silica, alumina, titania, boehmite, magnesium oxide, magnesium hydroxide, and zirconium oxide.

[0043] In some embodiments, the mass percentage of the silane coupling agent to the inorganic particles is 1% to 5%. For example, the mass percentage of the silane coupling agent to the inorganic particles can be 1%, 2%, 3%, 4%, or 5%.

[0044] In some embodiments, the fiber membrane also includes graphene oxide. The graphene oxide is dispersed in a polyimide matrix. By dispersing graphene oxide within the fiber membrane, the oxygen-containing functional groups (e.g., carboxyl and hydroxyl groups) on the graphene oxide surface can interact with the siloxy groups of the silica gel matrix through hydrogen bonding or van der Waals forces, enhancing interfacial bonding and further increasing the mechanical strength and thermal stability of the separator. Furthermore, the oxygen-containing functional groups in the graphene oxide also possess a certain degree of ionic conductivity and lyophilic properties, further improving the electrochemical performance of the battery.

[0045] In some embodiments, the average particle size of the solid electrolyte particles is 50 nm to 150 nm. For example, the average particle size of the solid electrolyte particles may be, but is not limited to, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, or 150 nm. Within the above particle size range, a smaller particle size increases the specific surface area of the solid electrolyte particles, increases the contact area with the silica gel matrix, and reduces interparticle gaps, thereby making the particles more evenly dispersed in the silica gel matrix, forming a more continuous ion conduction path, further improving the ionic conductivity of the separator, and improving the rate performance of the battery.

[0046] In some embodiments, the mass ratio of the silicone gel matrix to the solid electrolyte particles in the gel is (0.2-0.72):1. For example, the mass ratio of the silicone gel matrix to the solid electrolyte particles in the gel can be, but is not limited to, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, or 0.72:1. Within this mass ratio range, the solid electrolyte particles are uniformly dispersed in the silicone gel matrix and form an effective ion-conducting network, while maintaining the flexibility and stability of the gel. This ensures high ionic conductivity while maintaining good mechanical properties and thermal stability, further enhancing the safety and electrochemical performance of the separator.

[0047] In some embodiments, the thickness of the separator is 5 μm to 15 μm. For example, the thickness of the separator can be, but is not limited to, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, and 15 μm. Within the above thickness range, the thinner thickness reduces the internal resistance of the battery and increases the energy density while ensuring sufficient mechanical strength and safety, thereby further improving the energy density and cycle life of the battery while optimizing battery performance.

[0048] In some embodiments, the porosity of the separator is 60% to 70%. For example, the separator porosity may be, but is not limited to, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, or 70%. Within the above porosity range, high porosity provides more ion conduction channels while maintaining sufficient mechanical strength, thereby further improving the separator's ionic conductivity and the battery's rate capability while ensuring separator strength.

[0049] In some embodiments, the tensile strength of the separator is 100 MPa to 200 MPa, and the elongation at break is 50% to 150%. For example, the tensile strength of the separator may be, but is not limited to, 100 MPa, 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, 170 MPa, 180 MPa, 190 MPa, or 200 MPa, and the elongation at break may be, but is not limited to, 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, or 150%.

[0050] In some embodiments, the ionic conductivity of the separator at 25°C is 2.0*10 -4 S / cm~1.8*10 -3S / cm. For example, the ionic conductivity of the membrane at 25°C may be, but is not limited to, 2.0*10 -4 S / cm、2.5*10 -4 S / cm, 1.0*10 -3 S / cm、1.8*10 -3 S / cm.

[0051] In some embodiments, the electrolyte absorption rate of the separator is 90% to 130%. For example, the electrolyte absorption rate of the separator can be, but is not limited to, 90%, 100%, 110%, 120%, or 130%.

[0052] In some embodiments, the thermal shrinkage of the separator at 150° C. is less than 1%. For example, the thermal shrinkage of the separator at 150° C. may be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 0.95%.

[0053] The second aspect of the present application provides a method for preparing a diaphragm, such as Figure 1 As shown, the preparation method comprises the following steps:

[0054] S1. Dispersing solid electrolyte particles in silica sol to obtain a composite sol solution.

[0055] S2. Filling the composite sol solution into the pores of the fiber membrane and performing gelation treatment to obtain a diaphragm.

[0056] The diaphragm includes a fiber membrane and a gel, and the gel includes a silicone gel matrix and solid electrolyte particles dispersed in the silicone gel matrix.

[0057] The preparation method of the diaphragm provided in the present application is to fill the pores of the fiber membrane with a composite sol liquid and perform a gelation treatment. The solid electrolyte particles and silica sol in the composite sol liquid are gelated in the pores of the fiber membrane to form an interpenetrating network structure, so that the gel is evenly filled in the pores of the fiber membrane, thereby forming a continuous ion conduction path, improving the ionic conductivity and mechanical properties of the diaphragm, and enhancing the electrochemical performance and safety performance of the battery.

[0058] In some embodiments, before step S1, the preparation method further comprises the following steps:

[0059] S01 and alkoxysilane undergo hydrolysis and condensation reaction under acidic conditions to obtain silica sol.

[0060] In some embodiments, the alkoxysilane is selected from at least one of tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), dimethyldiethoxysilane (DEDMS), and ethyltriethoxysilane (ETES).

[0061] In some embodiments, step S1 specifically includes the following steps:

[0062] S11. Put the solid electrolyte particles into the silica sol and perform ultrasonic treatment to obtain a composite sol solution.

[0063] In some embodiments, the ultrasonic treatment time is 0.5 h to 2 h.

[0064] In some embodiments, step S2 specifically includes the following steps:

[0065] S21. Place the fiber membrane into the composite sol solution for immersion treatment, so that the composite sol solution fills the pores of the fiber membrane to obtain a sol-filled fiber membrane.

[0066] S23, performing gelation treatment on the sol-filled fiber membrane to obtain a separator.

[0067] In this way, by immersing the fiber membrane in the composite sol liquid, the immersion treatment allows the composite sol liquid to fully penetrate into the pores of the fiber membrane, ensuring the uniform distribution of the gel in the membrane and improving the performance consistency and stability of the membrane; by gelating the sol-filled fiber membrane, the silica sol is converted into a silica gel matrix and the solid electrolyte particles are fixed to form a three-dimensional network structure, thereby enhancing the mechanical strength and ion conduction efficiency of the membrane and further improving the overall performance of the membrane.

[0068] In some embodiments, the soaking time is 3 min to 10 min.

[0069] In some embodiments, the gelation treatment is performed at a temperature of 20° C. to 30° C. for a time of 8 h to 20 h.

[0070] In some embodiments, before step S23, the following steps are included:

[0071] S22. Take out the sol-filled fiber membrane and hang it vertically.

[0072] In this way, by taking out the sol-filled fiber membrane and hanging it vertically, the excess composite sol liquid flows out of the fiber membrane, controlling the filling amount of the gel, thereby ensuring the appropriate filling of the gel in the pores of the fiber membrane and reducing the thickness of the diaphragm.

[0073] In some embodiments, after step S23, the following steps are included:

[0074] S3. The diaphragm is dried and cured in sequence.

[0075] In this way, by sequentially drying and curing the separator, on the one hand, the residual solvent in the gel is removed, promoting the condensation reaction of the silicone gel matrix to form a stable Si-O-Si network, anchoring the solid electrolyte particles in the Si-O-Si network, and solidifying the gel structure, thereby improving the structural and thermal stability of the separator. At the same time, the drying process allows the gel to closely adhere to the pore walls of the fiber membrane, strengthening the interfacial bonding force of the interpenetrating network, thereby improving the mechanical strength of the separator. On the other hand, the drying and curing processes can regulate the pore structure of the silicone gel matrix, preserving its porosity and lyophilicity, enabling the separator to efficiently adsorb electrolyte and wet the solid electrolyte particles, optimizing the ion conduction path, thereby improving ionic conductivity and enhancing the battery's rate performance.

[0076] In some embodiments, the drying process is carried out at a temperature of 45° C. to 70° C. and for a time of 10 to 20 hours.

[0077] In some embodiments, the curing temperature is 100° C.-130° C., and the curing time is 0.5 h-3 h.

[0078] In some embodiments, after step S3, the following steps are included:

[0079] S4. Plasma treatment is performed on the surface of the diaphragm.

[0080] Specifically, the plasma treatment gas is oxygen. This introduces polar functional groups such as hydroxyl and carbonyl groups onto the surface of the diaphragm, further enhancing the wettability of the diaphragm to the electrolyte. At the same time, without the need for an additional coating, the diaphragm is made ultra-thin.

[0081] In some embodiments, the plasma treatment power is 80W-120W, and the treatment time is 3 min-5 min.

[0082] In some embodiments, after step S4, the following steps are included:

[0083] S5. Coating a polyvinylidene fluoride layer on the surface of the diaphragm.

[0084] In this way, coating the polyvinylidene fluoride layer on the surface of the diaphragm further improves the wettability of the diaphragm to the electrolyte.

[0085] A third aspect of the present application provides a secondary battery, which includes the separator provided by the second aspect.

[0086] In some embodiments, the secondary battery comprises a lithium ion battery or a sodium ion battery. The secondary battery of the present application includes a battery cell form, a battery module form and a battery pack form.

[0087] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the charge and discharge process, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0088] Positive electrode:

[0089] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer is provided on at least one side of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0090] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0091] In some embodiments, the positive electrode 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 material base layer and a metal layer formed on at least one surface of the polymer material base layer. 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 material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0092] In some embodiments, the positive electrode active material layer may further include a positive electrode active material. The positive electrode active material may be a positive electrode active material for batteries known in the art.

[0093] As an example, when the positive electrode plate is used in a lithium-ion battery, the positive electrode active material may be a positive electrode active material for lithium-ion batteries that is well known in the art. Furthermore, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries 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 may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) or at least one of its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0094] In some embodiments, the positive electrode active material layer may further include a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0095] In some embodiments, the positive electrode active material layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0096] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0097] Negative electrode:

[0098] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0099] As an example, the negative electrode current collector has two surfaces opposite to each other in its 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.

[0100] 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 base layer and a metal layer formed on at least one surface of the polymer base layer. 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 base layer (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0101] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0102] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0103] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0104] In some embodiments, the negative electrode film layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0105] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0106] Electrolyte:

[0107] In some embodiments, the electrolyte includes an electrolyte salt and a solvent.

[0108] In some embodiments, when the secondary battery is a lithium ion battery, the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0109] In some embodiments, the solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone, and diethyl sulfone.

[0110] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0111] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0112] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0113] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, or polybutylene succinate.

[0114] A fourth aspect of the present application provides an electrical device, which includes the secondary battery provided by the third aspect.

[0115] The secondary battery provided herein can be used as a power source for an electrical device or as an energy storage unit for an electrical device. Electrical devices may include, but are not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, and energy storage systems. Examples of mobile devices include, but are not limited to, mobile phones and laptops; and examples of electric vehicles include, but are not limited to, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks.

[0116] The present application will be further described below with reference to specific embodiments and comparative examples.

[0117] Example 1

[0118] Diaphragm:

[0119] (1) 10 g of nano-alumina (particle size 50 nm) and 10 g of nano-silica (particle size 20 nm) were added to 200 mL of anhydrous ethanol, and the two suspensions were ultrasonically dispersed for 30 min using an ultrasonic disperser with a power of 300 W and a frequency of 20 kHz. Then, 0.2 g of silane coupling agent KH-550 (2% of the mass of the inorganic particles) was slowly added to each of the two suspensions at a stirring speed of 300 rpm, and the stirring was continued for 1 h to allow the coupling agent to fully react with the surface of the nanoparticles. The pH value of the suspension was adjusted to 4.5 using 0.1 M hydrochloric acid. The above suspension was placed in a constant temperature water bath at 60°C and the stirring reaction was continued for 2 h. After the reaction was completed, the suspension was centrifuged at 8000 rpm for 10 min to collect the modified nanoparticles. Subsequently, the nanoparticles were washed three times with anhydrous ethanol, adding 100 mL of ethanol each time, stirring evenly and centrifuging to remove unreacted residues; finally, the washed nanoparticles were dried in a vacuum drying oven at 60°C for 12 h to obtain surface-modified nano-Al2O3 and SiO2.

[0120] (2) Add 15 g of polyamic acid (PAA) to 85 mL of N,N-dimethylformamide (DMF). At room temperature (25°C), a magnetic stirrer was used to stir at a speed of 500 rpm for 4 h until PAA was completely dissolved to form a transparent solution with a mass fraction of 15%; 0.75 g PVDF (molecular weight of about 530,000 g / mol, accounting for 5% of the mass of PAA) was added to the above PAA solution, and the stirring was continued at a speed of 500 rpm for 6 h to ensure that PVDF was uniformly dispersed in the solution to form a stable blend solution; 2.5 g each of the modified nano-Al2O3 and SiO2 obtained in step (1) was slowly added to the blend solution, and the stirring speed was increased to 600 rpm. Stirring was carried out while adding to prevent the agglomeration of nanoparticles; in order to further ensure the uniform dispersion of the nanomaterials in the solution, the mixed solution was placed in an ultrasonic disperser with a power of 200 W and intermittent ultrasonic treatment (working for 2 seconds and stopping for 2 seconds) was carried out for 1 h. During this process, the solution was placed in an ice bath to prevent the solution temperature from being too high due to ultrasound; 1 g of graphene oxide (GO) was added to 50 mL of DMF was ultrasonically dispersed for 1 h to form a 2 wt% GO dispersion; then, the GO dispersion was slowly poured into the spinning solution and stirred for 2 h to ensure that GO was evenly dispersed in the solution. The solution was placed in a vacuum degassing device and allowed to stand for 12 h to eliminate bubbles in the solution to obtain the spinning solution.

[0121] (3) A stainless steel needle with an inner diameter of 0.6 mm was selected as the nozzle and connected to the injection pump. The collector used a rotating drum with a diameter of 10 cm. The speed of the collector was set to 100 rpm, which was conducive to the orientation and uniformity of the fibers. The voltage was set to 18 kV, the distance between the nozzle and the collector was 15 cm, the solution flow rate was 0.5 mL / h, and the time was set to 4 h. Electrospinning was performed to prepare a fiber membrane precursor with a thickness of 12 μm. The fiber membrane precursor was subjected to an imidization reaction to convert polyamic acid (PAA) into polyimide (PI) to obtain a fiber membrane. The fiber membrane was placed in a vacuum drying oven with the temperature set to 80 °C and dried for 1 h to remove the residual solvent.

[0122] Among them, the imidization reaction includes a programmed temperature rising process and a cooling process; the programmed temperature rising process is divided into the following stages: stage 1, heating from 80°C to 150°C at a heating rate of 2°C / min, and keeping warm for 1 hour; stage 2, continuing to heat to 200°C, keeping warm for 1 hour, and further dehydration; stage 3: heating to 250°C, keeping warm for 1 hour; stage 4, finally heating to 350°C, keeping warm for 1 hour; during the entire heating process, nitrogen protection is maintained, and the nitrogen flow rate is 50mL / min; then the heating device is turned off, and the fiber membrane is allowed to cool naturally to room temperature in a nitrogen atmosphere. The fiber membrane is taken out and its color is observed to gradually change from light yellow to golden yellow, indicating that the imidization reaction is successfully completed.

[0123] (4) Add 10 mL of tetraethoxysilane to 40 mL of anhydrous ethanol and stir evenly. Add 2 mL of deionized water and 0.1 mL of 0.1 M hydrochloric acid as a catalyst to the mixed solution and continue stirring for 2 h to form a uniform silica sol.

[0124] (5) 5g of cubic phase Li7La3Zr2O 12 Nanoparticles (average particle size of 100 nm) were added to silica sol and ultrasonicated for 1 h using an ultrasonic disperser to obtain a composite sol solution.

[0125] (6) The fiber membrane is immersed in the composite sol solution for 5 minutes, so that the composite sol solution fills the pores of the fiber membrane to obtain a sol-filled fiber membrane; the fiber membrane is slowly taken out and hung vertically to allow excess sol to drip naturally to prevent the formation of an excessively thick coating; the sol-filled fiber membrane is placed at room temperature for 12 hours to allow the sol to gel in the fiber membrane to obtain a gel body, and the gel body and the fiber membrane form an interpenetrating network structure to obtain a diaphragm; the diaphragm is placed in a vacuum drying oven at 60°C and dried for 12 hours; the dried fiber membrane is then placed in an oven at 120°C and cured for 2 hours.

[0126] The gel comprises a silica gel matrix and Li7La3Zr2O dispersed in the silica gel matrix. 12Particles, silica gel matrix and Li7La3Zr2O 12 The mass ratio of the particles is 0.54:1.

[0127] (7) Use a plasma cleaning machine and set the parameters as follows: the gas type is oxygen, the flow rate is 100 cm 3 / min, power is 100W, and processing time is 5min; place the diaphragm flatly in the plasma reaction chamber, close the chamber door, and start the equipment for processing.

[0128] (8) Dissolve 1 g of polyvinylidene fluoride (PVDF) in 99 mL of DMF and stir for 6 h. Use a spin coater to evenly coat the PVDF solution on the surface of the diaphragm. The spin coating parameters are set to a speed of 3000 rpm and a time of 30 seconds. Place the coated diaphragm in an oven at 60°C and dry for 1 h to form a polyvinylidene fluoride layer on the surface of the diaphragm.

[0129] Secondary batteries:

[0130] The secondary battery is a lithium-ion battery, which includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator located between the two. The separator uses the above-mentioned separator. The positive electrode is prepared by coating a positive electrode slurry containing 96.8% lithium iron phosphate, 1.0% carbon black (SP), 0.4% carbon nanotubes (CNT), and 1.8% polyvinylidene fluoride (PVDF) on aluminum foil, based on a 100% solid content in the slurry. The negative electrode is prepared by coating a negative electrode slurry containing 95.5% graphite, 1.5% carbon black (SP), 1.2% carboxymethyl cellulose (CMC), and 1.8% styrene-butadiene rubber (SBR) on copper foil, based on a 100% solid content in the negative electrode slurry. The electrolyte is a 1.1 mol / L LiPF6 system, and the solvent is a carbonate system.

[0131] Example 2

[0132] The preparation method of the separator and the secondary battery in this embodiment is basically the same as that in Example 1, except that:

[0133] In step (6), the silica gel matrix and Li7La3Zr2O 12 The mass ratio of the particles is 0.72:1.

[0134] Example 3

[0135] The preparation method of the separator and the secondary battery in this embodiment is basically the same as that in Example 1, except that:

[0136] In step (6), the silica gel matrix and Li7La3Zr2O 12 The mass ratio of the particles is 0.2:1.

[0137] Example 4

[0138] The preparation method of the separator and the secondary battery in this embodiment is basically the same as that in Example 1, except that:

[0139] In step (5), Li7La3Zr2O 12 The average particle size of the nanoparticles is 50 nm.

[0140] Example 5

[0141] The preparation method of the separator and the secondary battery in this embodiment is basically the same as that in Example 1, except that:

[0142] In step (5), Li7La3Zr2O 12 The average particle size of the nanoparticles is 150 nm.

[0143] Example 6

[0144] The preparation method of the separator and the secondary battery in this embodiment is basically the same as that in Example 1, except that:

[0145] In step (6), the silica gel matrix and Li7La3Zr2O 12 The mass ratio of the particles is 0.1:1.

[0146] Example 7

[0147] The preparation method of the separator and the secondary battery in this embodiment is basically the same as that in Example 1, except that:

[0148] In step (6), the silica gel matrix and Li7La3Zr2O 12 The mass ratio of the particles is 0.8:1.

[0149] Example 8

[0150] The preparation method of the separator and the secondary battery in this embodiment is basically the same as that in Example 1, except that:

[0151] (2) Add 15 g of polypropylene (PP) to 85 mL of a mixed solvent of N,N-dimethylformamide (DMF) and cyclohexane (volume ratio 1:1), and stir magnetically at 500 rpm at 60°C for 4 h until PP is completely dissolved to form a solution with a mass fraction of about 15%; add 0.75 g of PVDF (molecular weight of about 530,000 g / mol, accounting for 5% of the mass of PP) to the above solution, and continue stirring at 500 rpm for 6 h to ensure that PVDF is evenly dispersed; slowly add 2.5 g each of modified nano-Al2O3 and SiO2 obtained in step (1) to the solution, place the mixed solution in an ultrasonic disperser with a power of 200 W, and intermittently ultrasonicate (work 2s, stop 2s) for 1 h. The solution is placed in an ice bath to prevent overheating; add 1 g of graphene oxide (GO) to 50 mL of DMF, ultrasonicate for 1 h to form a 2 wt% GO dispersion, and slowly pour it into the spinning solution and stir for 2 h. h to ensure that GO is evenly dispersed, and then placed in a vacuum degassing device for 12 h to remove bubbles to prepare the spinning solution.

[0152] (3) A stainless steel needle with an inner diameter of 0.6 mm was selected as the nozzle, connected to a syringe pump, and the collector was a rotating drum with a diameter of 10 cm. The speed was 100 rpm, the voltage was 18 kV, the distance between the nozzle and the collector was 15 cm, the solution flow rate was 0.5 mL / h, and the spinning time was 4 h. Electrospinning was performed to prepare a polypropylene-based fiber membrane with a thickness of about 12 μm. The fiber membrane was placed in a vacuum drying oven at 80 °C and dried for 1 h to remove the residual solvent to obtain a fiber membrane.

[0153] Example 9

[0154] The preparation method of the separator and the secondary battery in this embodiment is basically the same as that in Example 1, except that:

[0155] In step (1), no silane coupling agent is added for modification.

[0156] Example 10

[0157] The preparation method of the separator and the secondary battery in this embodiment is basically the same as that in Example 1, except that:

[0158] In step (2), graphene oxide is not added.

[0159] Example 11

[0160] The preparation method of the separator and the secondary battery in this embodiment is basically the same as that in Example 1, except that:

[0161] Omit steps (7) and (8).

[0162] Comparative Example 1

[0163] A commercially available polypropylene separator (manufacturer: Shenzhen Zhongxing New Materials Technology Co., Ltd.; thickness: 20 μm) was used.

[0164] Comparative Example 2

[0165] Diaphragm:

[0166] (1) 10 g of nano-alumina (particle size 50 nm) and 10 g of nano-silica (particle size 20 nm) were added to 200 mL of anhydrous ethanol, and the two suspensions were ultrasonically dispersed for 30 min using an ultrasonic disperser with a power of 300 W and a frequency of 20 kHz. Then, 0.2 g of silane coupling agent KH-550 (2% of the mass of the inorganic particles) was slowly added to each of the two suspensions at a stirring speed of 300 rpm, and the stirring was continued for 1 h to allow the coupling agent to fully react with the surface of the nanoparticles. The pH value of the suspension was adjusted to 4.5 using 0.1 M hydrochloric acid. The above suspension was placed in a constant temperature water bath at 60°C and the stirring reaction was continued for 2 h. After the reaction was completed, the suspension was centrifuged at 8000 rpm for 10 min to collect the modified nanoparticles. Subsequently, the nanoparticles were washed three times with anhydrous ethanol, adding 100 mL of ethanol each time, stirring evenly and centrifuging to remove unreacted residues; finally, the washed nanoparticles were dried in a vacuum drying oven at 60°C for 12 h to obtain surface-modified nano-Al2O3 and SiO2.

[0167] (2) Add 15 g of polyamic acid (PAA) to 85 mL of N,N-dimethylformamide (DMF). At room temperature (25°C), a magnetic stirrer was used to stir at a speed of 500 rpm for 4 h until PAA was completely dissolved to form a transparent solution with a mass fraction of 15%; 0.75 g PVDF (molecular weight of about 530,000 g / mol, accounting for 5% of the mass of PAA) was added to the above PAA solution, and the stirring was continued at a speed of 500 rpm for 6 h to ensure that PVDF was uniformly dispersed in the solution to form a stable blend solution; 2.5 g each of the modified nano-Al2O3 and SiO2 obtained in step (1) was slowly added to the blend solution, and the stirring speed was increased to 600 rpm. Stirring was carried out while adding to prevent the agglomeration of nanoparticles; in order to further ensure the uniform dispersion of the nanomaterials in the solution, the mixed solution was placed in an ultrasonic disperser with a power of 200 W and intermittent ultrasonic treatment (working for 2 seconds and stopping for 2 seconds) was carried out for 1 h. During this process, the solution was placed in an ice bath to prevent the solution temperature from being too high due to ultrasound; 1 g of graphene oxide (GO) was added to 50 mL of DMF was ultrasonically dispersed for 1 h to form a 2 wt% GO dispersion; then, the GO dispersion was slowly poured into the spinning solution and stirred for 2 h to ensure that GO was evenly dispersed in the solution. The solution was placed in a vacuum degassing device and allowed to stand for 12 h to eliminate bubbles in the solution to obtain the spinning solution.

[0168] (3) A stainless steel needle with an inner diameter of 0.6 mm was selected as the nozzle and connected to the injection pump. The collector used a rotating drum with a diameter of 10 cm. The speed of the collector was set to 100 rpm, which was conducive to the orientation and uniformity of the fibers. The voltage was set to 18 kV, the distance between the nozzle and the collector was 15 cm, the solution flow rate was 0.5 mL / h, and the time was set to 4 h. Electrospinning was performed to prepare a fiber membrane precursor with a thickness of 12 μm. The fiber membrane precursor was subjected to an imidization reaction to convert polyamic acid (PAA) into polyimide (PI) to obtain a fiber membrane, namely a diaphragm. The diaphragm was placed in a vacuum drying oven with the temperature set to 80 °C and dried for 1 h to remove the residual solvent.

[0169] Among them, the imidization reaction includes a programmed temperature rising process and a cooling process; the programmed temperature rising process is divided into the following stages: stage 1, heating from 80°C to 150°C at a heating rate of 2°C / min, and keeping warm for 1 hour; stage 2, continuing to heat to 200°C, keeping warm for 1 hour, and further dehydration; stage 3: heating to 250°C, keeping warm for 1 hour; stage 4, finally heating to 350°C, keeping warm for 1 hour; during the entire heating process, nitrogen protection is maintained, and the nitrogen flow rate is 50mL / min; then the heating device is turned off, and the fiber membrane is allowed to cool naturally to room temperature in a nitrogen atmosphere. The fiber membrane is taken out and its color is observed to gradually change from light yellow to golden yellow, indicating that the imidization reaction is successfully completed.

[0170] (4) Use a plasma cleaning machine and set the parameters as follows: the gas type is oxygen, the flow rate is 100 cm 3 / min, power is 100W, and processing time is 5min; place the diaphragm flatly in the plasma reaction chamber, close the chamber door, and start the equipment for processing.

[0171] (5) Dissolve 1 g of polyvinylidene fluoride (PVDF) in 99 mL of DMF and stir for 6 h. Use a spin coater to evenly coat the PVDF solution on the surface of the diaphragm. The spin coating parameters are set to a speed of 3000 rpm and a time of 30 seconds. Place the coated diaphragm in an oven at 60°C and dry for 1 h to form a polyvinylidene fluoride layer on the surface of the diaphragm.

[0172] Secondary batteries:

[0173] The secondary battery is a lithium-ion battery, which includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator located between the two. The separator uses the above-mentioned separator. The positive electrode is prepared by coating a positive electrode slurry containing 96.8% lithium iron phosphate, 1.0% carbon black (SP), 0.4% carbon nanotubes (CNT), and 1.8% polyvinylidene fluoride (PVDF) on aluminum foil, based on a 100% solid content in the slurry. The negative electrode is prepared by coating a negative electrode slurry containing 95.5% graphite, 1.5% carbon black (SP), 1.2% carboxymethyl cellulose (CMC), and 1.8% styrene-butadiene rubber (SBR) on copper foil, based on a 100% solid content in the negative electrode slurry. The electrolyte is a 1.1 mol / L LiPF6 system, and the solvent is a carbonate system.

[0174] Performance Testing

[0175] (1) Physical properties test

[0176] a. Thickness test: The thickness of the diaphragms in the above-mentioned embodiments and comparative examples was measured at multiple points using a micrometer screw. The average value of the thickness at each point was the thickness of the corresponding diaphragm. The test results are shown in Table 1.

[0177] b. Porosity test: The porosity of the diaphragms in the above examples and comparative examples was calculated using a liquid absorption method. The test results are shown in Table 1.

[0178] c. Mechanical Properties Test: The diaphragms of the above embodiments and comparative examples were cut into 15 mm x 20 mm sizes and tested for tensile strength and elongation at break using a universal material testing machine. The test results are shown in Table 1.

[0179] d. Thermal Stability Test: The diaphragm was cut into a certain size and placed in a 150°C oven for 1 hour. The thermal shrinkage was calculated. The test results are shown in Table 1.

[0180] (2) Electrochemical performance test

[0181] a. Ionic Conductivity Test: At 25°C, the diaphragms of the above examples and comparative examples were cut into 24 mm x 24 mm squares. The cut diaphragm squares were immersed in electrolyte in a glove box. The diaphragms were then placed in a test mold and their AC impedance resistance was measured to obtain ionic conductivity. The test results are shown in Table 1.

[0182] b. Electrolyte Absorption Rate Test: The separators from the above examples and comparative examples were cut into 90 mm x 90 mm dimensions and immersed in electrolyte for 24 hours. The electrolyte absorption rate was calculated as the difference in weight before and after immersion compared to the percentage of the separator mass before immersion. The test results are shown in Table 1.

[0183] c. Interface impedance test: The separators of the above examples and comparative examples were assembled into lithium metal / separator / lithium metal symmetrical cells, and the initial interface impedance was tested. The test results are shown in Table 2.

[0184] d. Cycling Performance Test: At 25°C, the secondary batteries of the above examples and comparative examples were charged using a constant current constant voltage charging mode with a charging current of 0.5C and a voltage of 3.65V. The batteries were discharged using a constant current discharge mode with a discharge current of 0.5C and a discharge cutoff voltage of 2.5V. The capacity retention after 200 cycles was recorded. The test results are shown in Table 2.

[0185] e. Rate performance test: At 25°C, the battery cell was conditioned to 50% SOC at a current rate of 0.33C, discharged at 2C for 10 seconds, and its DCR data was recorded. Similarly, the DCR data of the battery cell at 50% SOC and 1C for 10 seconds at -10°C was measured. Rate testing was performed at a 5C discharge rate. The charge and discharge window of the lithium iron phosphate battery is 3.65 V to 2.5 V. The test results are shown in Table 2.

[0186] Table 1

[0187]

[0188] As shown in Table 1, by comparing Examples 1 to 11 with Comparative Examples 1 to 2, it can be seen that the diaphragm provided in the present application has a thinner thickness, higher porosity, higher electrolyte absorption rate, higher ionic conductivity, and lower interface impedance. The diaphragm has good thermal stability and maintains good tensile strength and ductility.

[0189] Table 2

[0190]

[0191] As shown in Table 2, by comparing Examples 1 to 11 with Comparative Examples 1 to 2, it can be seen that the separator provided by the present application, after being assembled into a battery, reduces the internal resistance of the battery and improves the cycle performance and rate performance of the battery.

[0192] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0193] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the technical concept of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A diaphragm, characterized in that: include: Fiber membrane; as well as The gel is arranged in the pores of the fiber membrane, and the gel comprises a silicone gel matrix and solid electrolyte particles dispersed in the silicone gel matrix.

2. The diaphragm according to claim 1, characterized in that The fiber membrane comprises: a polyimide matrix; and Inorganic modified particles are dispersed in the polyimide matrix, and surfaces of the inorganic modified particles have Si-O-Si bonds.

3. The diaphragm according to claim 2, characterized in that The fiber membrane also includes: Graphene oxide is dispersed in the polyimide matrix.

4. The diaphragm according to claim 1, characterized in that The average particle size of the solid electrolyte particles is 50 nm to 150 nm.

5. The diaphragm according to any one of claims 1 to 4, characterized in that: At least one of the following conditions is met: (1) In the gel, the mass ratio of the silicone gel matrix to the solid electrolyte particles is (0.2-0.72):1; (2) The thickness of the diaphragm is 5 μm to 15 μm; (3) The porosity of the diaphragm is 60% to 70%; (4) The tensile strength of the diaphragm is 100 MPa~200 MPa, and the elongation at break is 50%~150%; (5) The ionic conductivity of the membrane at 25°C is 2.0*10 -4 S / cm~1.8*10 -3 S / cm; (6) The electrolyte absorption rate of the diaphragm is 90% to 130%; (7) The thermal shrinkage of the diaphragm at 150°C is less than 1%.

6. A method for preparing a diaphragm, characterized in that: The following steps are involved: dispersing solid electrolyte particles in silica sol to obtain a composite sol solution; Filling the composite sol solution into the pores of the fiber membrane and performing a gelation treatment to obtain a diaphragm; The diaphragm includes the fiber membrane and a gel, and the gel includes a silicone gel matrix and the solid electrolyte particles dispersed in the silicone gel matrix.

7. The method for preparing a diaphragm according to claim 6, wherein: The step of filling the pores of the fiber membrane with the composite sol solution and performing gelation treatment to obtain a diaphragm specifically includes the following steps: placing the fiber membrane into the composite sol solution for immersion treatment, so that the composite sol solution fills the pores of the fiber membrane to obtain a sol-filled fiber membrane; The sol-filled fiber membrane is subjected to gelation treatment to obtain the separator.

8. The method for preparing a diaphragm according to claim 7, characterized in that: Before the step of gelling the sol-filled fiber membrane to obtain a diaphragm, the method includes the following steps: The sol-filled fiber membrane is taken out and hung vertically.

9. A secondary battery, characterized in that: The invention comprises a diaphragm according to any one of claims 1 to 5, or a diaphragm prepared by the method for preparing the diaphragm according to any one of claims 6 to 8.

10. An electrical device, characterized in that: Comprising the secondary battery as claimed in claim 9.

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