Secondary battery and electric device

Abstract

This application relates to a secondary battery and an electrical device, belonging to the field of electrochemical energy storage technology. The secondary battery of this application includes an electrode and a separator. The electrode includes a composite current collector and an active material layer disposed on at least one side of the composite current collector. A conductive layer is located between a polymer layer and the active material layer. The composite current collector includes a polymer layer and a conductive layer located on at least one side of the polymer layer. The polymer layer includes a first polymer and inorganic non-metallic particles. The inorganic non-metallic particles include oxides and / or sulfides. The active material layer includes an active material and a thermal runaway suppression material. The thermal runaway suppression material includes conductive metal particles and a second polymer coated on the surface of the conductive metal particles. The melting point of the first polymer is greater than that of the second polymer. The secondary battery of this application has high thermal safety.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, specifically to secondary batteries and electrical devices. Background Technology

[0002] Because secondary batteries are widely used in various products, such as transportation vehicles, wearable products for consumer and industrial applications, portable devices and energy storage devices, they are almost ubiquitous in all aspects of people's daily lives. However, accidents involving secondary batteries are frequently reported, such as fires and explosions of mobile phone batteries and electric vehicles. These are all because there is still a lack of comprehensive and effective solutions to the safety issues of secondary batteries.

[0003] The primary cause of fires and explosions in secondary batteries is thermal runaway, which is mainly caused by heat—specifically, the exothermic reaction resulting from the gradual thermal decomposition of various substances within the battery, including the solid electrolyte interface (SEI), electrolyte, binder, and positive and negative electrode active materials. Currently, common methods to improve the thermal safety of secondary batteries include positive electrode material modification, separator coating, module design, and BMS management. These methods, however, place high demands on material preparation and design. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of the prior art and provide a secondary battery and an electrical device.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: In a first aspect, a secondary battery is provided, including an electrode and a separator, wherein the electrode includes a composite current collector and an active material layer disposed on at least one side surface of the composite current collector; The composite current collector includes a polymer layer and a conductive layer located on at least one side of the polymer layer, wherein the conductive layer is located between the polymer layer and the active material layer; The polymer layer comprises a first polymer and inorganic non-metallic particles; The inorganic non-metallic particles include oxides and / or sulfides; The active material layer includes an active material and a thermal runaway suppression material; the thermal runaway suppression material includes conductive metal particles and a second polymer coated on the surface of the conductive metal particles; The melting point of the first polymer is greater than that of the second polymer.

[0006] In some embodiments, the particle size D50 of the inorganic non-metallic particles is D I The particle size D50 of the conductive metal particles is D M The following relationship is satisfied: 0.95≤D I / D M≤1, D M ≤100nm.

[0007] In some embodiments, the volumetric thermal expansion coefficients of the first polymer and the inorganic non-metallic particles are each independently 10~20 ppm / ℃.

[0008] In some embodiments, the mass of the inorganic non-metallic particles is 5-10% of the mass of the polymer layer.

[0009] In some embodiments, the melting point of the first polymer is ≥150°C.

[0010] In some embodiments, the melting point of the second polymer is 100-120°C.

[0011] In some embodiments, the first polymer includes polar groups.

[0012] In some embodiments, the polymer layer has pores; the pore size is 1~1.5μm.

[0013] In some embodiments, the thickness of the polymer layer is 1~10 μm.

[0014] In some embodiments, the mass percentage of the thermal runaway suppression material is 0.1% to 1%, based on the mass of the active material layer.

[0015] In some embodiments, the conductive metal particles are made of at least one of copper, copper alloy, silver, silver alloy, nickel, nickel alloy, gold, aluminum, aluminum alloy, zinc, zinc alloy, iron, iron alloy, palladium, and palladium alloy.

[0016] In some embodiments, the conductive metal particles are polygonal in shape.

[0017] In some embodiments, the first polymer and the second polymer each independently include at least one of polyacrylic acid, polyacrylic acid derivatives, polyacrylate, polyacrylate derivatives, poly(meth)acrylate, poly(meth)acrylate derivatives, polyethylene, polyethylene derivatives, polystyrene, polystyrene derivatives, polyacrylamide, polyacrylamide derivatives, polyacrylonitrile, polyacrylonitrile derivatives, polyimide, polyurethane, polyester, and polyvinylidene fluoride.

[0018] In some embodiments, the oxide includes at least one of calcium oxide, titanium dioxide, aluminum oxide, and magnesium peroxide.

[0019] In some embodiments, the sulfide includes at least one of zinc sulfide, magnesium sulfide, and lithium sulfide.

[0020] Secondly, an electrical device is provided, including the aforementioned secondary battery.

[0021] Compared with the prior art, the beneficial effects of this application are as follows: When a short circuit occurs inside the secondary battery of this application, a local high temperature (temperature greater than the melting point of the second polymer) and a local large current will be generated. Under the action of high temperature, the second polymer will melt and release conductive metal particles in the thermal runaway suppression material. Under the excitation of the local large current, the conductive metal particles will come into contact with the conductive layer in the composite current collector and undergo local electro-corrosion, melting through the local conductive layer and causing a local open circuit, so that the short circuit overheating area is within the local area, reducing the risk of thermal spread. At the same time, under the action of high temperature, the conductive metal particles will chemically react with the inorganic non-metallic particles in the polymer layer to form a coating layer (such as a metal sulfide layer and / or a metal oxide layer) on the surface of the conductive metal particles and adhere to the polymer layer, enhancing the adsorption force between the conductive metal particles and the first polymer, reducing the number of conductive metal particles falling into the electrolyte, reducing the risk of conductive metal particles causing secondary short circuits, thereby improving the thermal safety of the secondary battery. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the cross-section of the electrode. Figure 2 This is a schematic diagram of the composite current collector cross-section; Figure 3 This is a schematic diagram of the cross-section of the active material layer; Figure 4 This is a schematic diagram of the structure of a thermal runaway suppression material; Figure 5 This is a schematic diagram of a composite current collector.

[0023] Figure label: 10. Composite current collector; 20. Active material layer; 101. Polymer layer; 102. Conductive layer; 103. First polymer; 104. Inorganic non-metallic particles; 105. Pores; 201. Active material; 202. Thermal runaway suppression material; 2021. Conductive metal particles; 2022. Second polymer. Detailed Implementation

[0024] To facilitate understanding of this application, a more complete description will be provided below. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0025] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0026] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0027] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1-5” is disclosed, the described range should be interpreted as including ranges “1-4”, “1-3”, “1-2”, “1-2 and 4-5”, “1-3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0028] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0029] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has 'a' parts by mass and component B has 'b' parts by mass, it means that the mass ratio of component A to component B is a:b. It is important to understand that, unlike mass percentage content, the sum of the mass parts of all components is not limited to 100 parts.

[0030] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0031] In one aspect, a secondary battery is provided, comprising electrodes and a separator, such as... Figure 1 As shown, the electrode includes a composite current collector 10 and an active material layer 20 disposed on at least one side surface of the composite current collector 10; like Figure 2 As shown, the composite current collector 10 includes a polymer layer 101 and a conductive layer 102 located on at least one side of the polymer layer 101, with the conductive layer 102 located between the polymer layer 101 and the active material layer 20. The polymer layer 101 includes a first polymer 103 and inorganic non-metallic particles 104; The inorganic non-metallic particles include oxides and / or sulfides; like Figure 3 As shown, the active material layer 20 includes an active material 201 and a thermal runaway suppression material 202; as Figure 4 As shown, the thermal runaway suppression material 202 includes conductive metal particles 2021 and a second polymer 2022 coated on the surface of the conductive metal particles; The melting point of the first polymer is greater than that of the second polymer.

[0032] When a short circuit occurs inside the secondary battery of this application, local high temperature (temperature greater than the melting point of the second polymer) and local large current are generated. Under the action of high temperature, the second polymer melts and releases conductive metal particles in the thermal runaway suppression material. Under the excitation of local large current, the conductive metal particles come into contact with the conductive layer in the composite current collector and undergo local electro-corrosion, melting through the local conductive layer and causing a local open circuit. This keeps the short-circuit overheating area within a local area, reducing the risk of thermal propagation. At the same time, under the action of high temperature, the conductive metal particles react chemically with the inorganic non-metallic particles in the polymer layer to form a coating layer (such as a metal sulfide layer and / or a metal oxide layer) on the surface of the conductive metal particles and adhere to the polymer layer. This enhances the adsorption force between the conductive metal particles and the first polymer, reduces the number of conductive metal particles falling into the electrolyte, and reduces the risk of conductive metal particles causing a secondary short circuit, thereby improving the thermal safety of the secondary battery.

[0033] In some embodiments, the particle size D50 of the inorganic non-metallic particles is D I The particle size D50 of the conductive metal particles is D M The following relationship is satisfied: 0.95≤D I / D M ≤1, D M ≤100nm.

[0034] In this application, the particle size D50 of the inorganic non-metallic particles and the conductive metal particles satisfies the above relationship, which can increase the specific surface area of ​​the inorganic non-metallic particles, so that the inorganic non-metallic particles can fully cover the surface of the conductive metal particles, improve the chemical reaction rate between the inorganic non-metallic particles and the conductive metal particles, and thus improve the thermal safety of the secondary battery.

[0035] Specifically, DI / D M It can be a range of values ​​consisting of one or any two of the following: 0.95, 0.955, 0.96, 0.965, 0.97, 0.975, 0.98, 0.985, 0.99, 0.995, and 1.

[0036] Specifically, D M It can be a range of values ​​consisting of one or any two of the following: 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, and 100 nm.

[0037] In this application, the particle size D50 of inorganic non-metallic particles and conductive metal particles can be detected by the following method: The particle size of inorganic non-metallic particles and conductive metal particles is measured using a scanning electron microscope (SEM). First, the sample is brittlely fractured under liquid nitrogen conditions to form a natural fracture surface. The conductivity is enhanced by gold plating or low vacuum mode. Then, high-resolution images are acquired under appropriate accelerating voltage and magnification. Multiple regions are randomly sampled, and the average particle size and distribution are statistically analyzed to obtain the particle size D50 of inorganic non-metallic particles and conductive metal particles.

[0038] In some embodiments, the volumetric thermal expansion coefficients of the first polymer and the inorganic non-metallic particles are each independently 10~20 ppm / ℃.

[0039] In this application, the volumetric thermal expansion coefficients of the first polymer and the inorganic non-metallic particles are within the above-mentioned range, which is beneficial to improving the thermodynamic compatibility between the first polymer and the inorganic non-metallic particles, reducing interface separation caused by thermal stress, and further improving the thermal safety of the secondary battery.

[0040] Specifically, the volumetric thermal expansion coefficient of the first polymer can be a range of one or any combination of 10 ppm / ℃, 11 ppm / ℃, 12 ppm / ℃, 13 ppm / ℃, 14 ppm / ℃, 15 ppm / ℃, 16 ppm / ℃, 17 ppm / ℃, 18 ppm / ℃, 19 ppm / ℃, and 20 ppm / ℃.

[0041] Specifically, the volumetric thermal expansion of inorganic non-metallic particles can be a range of one or any combination of two of the following: 10 ppm / ℃, 11 ppm / ℃, 12 ppm / ℃, 13 ppm / ℃, 14 ppm / ℃, 15 ppm / ℃, 16 ppm / ℃, 17 ppm / ℃, 18 ppm / ℃, 19 ppm / ℃, and 20 ppm / ℃.

[0042] In this application, the volumetric thermal expansion coefficients of the first polymer and the inorganic non-metallic particles can be tested through the following aspects: Fix the sample under the probe of the TMA instrument, ensuring there are no gaps at the contact surface, set the heating rate (e.g., 5–10°C / min), and record the dimensional changes (ΔL) at different temperatures.

[0043] Calculate the coefficient of linear expansion: α = 1 / L0·(dL / dT), where L0 is the initial length and dL / dT is the rate of change of size. Assuming the material is isotropic, the coefficient of volume expansion is 3α.

[0044] In some embodiments, the mass of the inorganic non-metallic particles is 5 to 10% of the mass of the polymer layer; for example, it can be a range of one or any two of 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%.

[0045] In this application, the mass of the inorganic non-metallic particles is within the above-mentioned range, which can reduce the agglomeration effect of the inorganic non-metallic particles, and at the same time, can enable the inorganic non-metallic particles to fully react chemically with the conductive metal particles, thereby further improving the thermal safety of the secondary battery.

[0046] In some embodiments, the melting point of the first polymer is ≥150°C; for example, 150~350°C, specifically a range of one or any two of 150°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 320°C, and 350°C.

[0047] The melting point of the first polymer is within the above range, which makes it difficult for the polymer layer to melt when the secondary battery is short-circuited, thereby improving the thermal stability of the polymer layer and thus improving the thermal safety of the secondary battery.

[0048] In some embodiments, the melting point of the second polymer is 100-120°C; for example, it may be a range of one or any combination of 100°C, 102°C, 105°C, 107°C, 110°C, 113°C, 115°C, 118°C, and 120°C.

[0049] In this application, the melting point of the second polymer is within the above-mentioned range, which allows the second polymer to melt at 100~120°C, releasing conductive metal particles in the thermal runaway suppression material. This helps to reduce the short-circuit occurrence temperature of the secondary battery and improve the thermal safety of the secondary battery.

[0050] In some embodiments, the first polymer includes polar groups.

[0051] In this application, the first polymer includes polar groups, which can increase the compatibility between the first polymer and inorganic non-metallic particles, reduce the migration or precipitation of inorganic non-metallic particles in the polymer layer, and at the same time, the polar groups can form hydrogen bonds or covalent bonds with the surface of inorganic non-metallic particles, thereby improving the bonding strength between the first polymer and inorganic non-metallic particles.

[0052] Specifically, the polar group includes at least one of carboxyl, hydroxyl, amino, and acid anhydride groups.

[0053] It is understandable that, taking amino, hydroxyl, and carboxyl groups as examples, these groups can form hydrogen bonds or covalent bonds with hydroxyl groups on the surface of oxides (such as aluminum oxide). Similarly, taking anhydride groups as an example, these groups can form coordination bonds with metal ions on the surface of oxides (such as zinc oxide).

[0054] It is understood that those skilled in the art can introduce polar groups into the first polymer using modification methods known in the art; for example, carboxyl groups can be introduced into the surface of the first polymer by plasma treatment; or by mixing the first polymer, maleic anhydride and an initiator and then performing melt extrusion to obtain a first polymer with maleic anhydride groups introduced.

[0055] In some implementations, such as Figure 5 As shown, the polymer layer 101 has pores 105, and the conductive layer 102 can be deposited on the polymer layer 101 by deposition.

[0056] In some embodiments, the pore size is 1 to 1.5 μm; for example, it can be a range of one or any combination of 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm.

[0057] In this application, the pore size of the polymer layer is within the above-mentioned range, which is beneficial for lithium-ion transport and at the same time restricts the migration of inorganic non-metallic particles, thereby improving the electrochemical performance of the secondary battery.

[0058] In this application, the pore size of the pores in the polymer layer can be tested using the following method: The sample can be cut into thin slices to ensure a flat cross-section. The sample surface is then plated with gold to enhance conductivity. The sample is then placed in the SEM sample chamber, the accelerating voltage and working distance are adjusted, and the SEM image is processed using image software to identify the pore size in the pore region. The pore size is then calculated through the processing of the SEM image.

[0059] In some embodiments, the thickness of the polymer layer is 1 to 10 μm; for example, it can be a range of one or any combination of 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm.

[0060] In this application, the thickness of the polymer layer is within the above-mentioned range, which allows the composite current collector to maintain a certain mechanical strength and have good structural stability while being relatively thin and light.

[0061] In this application, the thickness of the polymer layer can be tested using the following method: the thickness of the polymer layer is measured using a scanning electron microscope (SEM). First, the sample is brittlely fractured under liquid nitrogen conditions to form a natural fracture surface. The conductivity is enhanced by gold plating or low vacuum mode. Then, high-resolution images are acquired under appropriate accelerating voltage and magnification. Multiple areas are randomly sampled, and the average thickness is calculated to obtain the thickness of the polymer layer.

[0062] In some embodiments, the mass percentage of the thermal runaway suppression material is 0.1% to 1% based on the mass of the active material layer; for example, it can be a range of one or any combination of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%.

[0063] In this application, the mass percentage of the thermal runaway suppression material is within the above-mentioned range. When a short circuit occurs in the secondary battery, the conductive metal particles have a sufficient number of reaction sites, which is beneficial to controlling the short-circuit overheating area of ​​the secondary battery, thereby improving the thermal safety of the secondary battery.

[0064] In some embodiments, the thermal runaway suppression material is at least one of a circular or arc-shaped form. Circular and / or arc-shaped thermal runaway suppression materials can slide between the voids in the active material layer, making it easier to migrate from the active material layer to the conductive layer; this is beneficial for improving the thermal safety of the secondary battery.

[0065] In some embodiments, the conductive metal particles are made of at least one of copper, copper alloy, silver, silver alloy, nickel, nickel alloy, gold, aluminum, aluminum alloy, zinc, zinc alloy, iron, iron alloy, palladium, and palladium alloy.

[0066] like Figure 4 As shown, in some embodiments, the conductive metal particles are polygonal in shape; for example, they can be at least one of triangle, rhombus, and pentagon. Polygonal conductive metal particles can increase the short-circuit contact area, so that a larger current can be generated at the short-circuit location, promoting the melting and penetration of the conductive layer by the conductive metal particles and preventing further occurrence of short circuits.

[0067] In some embodiments, those skilled in the art can prepare the thermal runaway suppression material using known methods, such as free radical polymerization, spray drying, fluidized bed coating, etc.

[0068] Taking free radical polymerization as an example, the preparation method of the thermal runaway suppression material includes the following steps: A mixture containing conductive metal particles and a redox initiator composition is prepared, and a monomer solution is added. The monomer is then free-radical polymerized on the surface of the conductive metal particles to form a second polymer.

[0069] Specifically, the monomer includes at least one of acrylic acid, acrylic acid derivatives, acrylates, acrylate derivatives, ethylene, ethylene derivatives, styrene, styrene derivatives, acrylamide, acrylamide derivatives, acrylonitrile, and acrylonitrile derivatives.

[0070] Specifically, the mixture may also include a surfactant, which has hydrophilic and lipophilic groups, and can attach the second polymer to the surface of the conductive metal particles to improve the structural stability of the thermal runaway suppression material.

[0071] Taking spray drying as an example, the preparation method of the thermal runaway suppression material includes the following steps: The second polymer is added to a solvent and dissolved to obtain a solution of the second polymer; Conductive metal particles are added to the second polymer solution and stirred until homogeneous. The resulting mixture is then spray-dried to obtain a thermal runaway suppression material.

[0072] In some embodiments, the inorganic non-metallic particles exist in the first polymer in a dispersed state, an interfacial bonded state, and an aggregated state; preferably, they are in an interfacial bonded state.

[0073] The dispersed state refers to inorganic non-metallic particles dispersed in the first polymer, without significant adhesion.

[0074] The interface-bound state refers to the inorganic non-metallic particles binding with the first polymer through chemical bonds or physical adsorption to form an interface layer.

[0075] Agglomerated state refers to inorganic non-metallic particles that are not sufficiently dispersed and are clustered together.

[0076] Interfacial bonding can enhance the interfacial compatibility between inorganic non-metallic particles and the first polymer, reduce interfacial defects, and improve electrical conductivity.

[0077] In some embodiments, the first polymer and the second polymer each independently include at least one of polyacrylic acid, polyacrylic acid derivatives, polyacrylate, polyacrylate derivatives, poly(meth)acrylate, poly(meth)acrylate derivatives, polyethylene, polyethylene derivatives, polystyrene, polystyrene derivatives, polyacrylamide, polyacrylamide derivatives, polyacrylonitrile, polyacrylonitrile derivatives, polyimide, polyurethane, polyester, and polyvinylidene fluoride.

[0078] In some embodiments, the oxide includes a metal oxide, specifically, the metal oxide includes at least one of calcium oxide, titanium dioxide, aluminum oxide, and magnesium peroxide.

[0079] In some embodiments, the sulfide includes a metal sulfide, specifically, the metal sulfide includes at least one of zinc sulfide, magnesium sulfide, and lithium sulfide.

[0080] In some embodiments, the polymer layer further includes a conductive agent, which includes at least one of a metallic material, a conductive polymer, and a carbon material. For example, as a metallic material, at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys can be used. As a conductive polymer, at least one of polyaniline, polythiophene, polyacetylene, and polypyrrole can be used. As a carbon material, at least one of carbon black, graphite, acetylene black (e.g., KETCHENTM black or DENKATM black), carbon fiber, carbon nanotubes, and graphene can be used.

[0081] It is understood that those skilled in the art can prepare composite current collectors using known methods.

[0082] Specifically, the preparation method of the composite current collector includes the following steps: A composite material is obtained by melt blending a first polymer, inorganic non-metallic particles, and an optional conductive agent. The composite material is prepared into a polymer layer, and a conductive layer is formed on at least one side surface of the polymer layer to obtain a composite current collector.

[0083] In some embodiments, the melt blending temperature is 200–400°C, for example, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 320°C, 340°C, 360°C, 380°C, or 400°C.

[0084] In some embodiments, the conductive layer comprises at least one of a metallic material, a conductive polymer, and a carbon material. For example, as a metallic material, at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys may be used. As a conductive polymer, at least one of polyaniline, polythiophene, polyacetylene, and polypyrrole may be used. As a carbon material, at least one of carbon black, graphite, acetylene black (e.g., KETCHENTM black or DENKATM black), carbon fiber, carbon nanotubes, and graphene may be used.

[0085] In some embodiments, the active material layer further includes a binder and a conductive agent.

[0086] In some embodiments, the adhesive 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).

[0087] In some embodiments, the conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] It is understood that when the electrode is a positive electrode, the active material is a positive active material.

[0089] In some embodiments, the positive electrode active material is selected from LiCoO2, LiNiO2, and LiNi x Mn y O2, Li 1+ z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al z At least one of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, and LiMnPO4, wherein each x is independently from 0.2 to 0.9; each y is independently from 0.1 to 0.45; and each z is independently from 0 to 0.2. The positive electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as positive electrode active materials.

[0090] In some embodiments, the positive electrode active material is selected from LiCoO2, LiNiO2, and LiNi x Mn y O2, Li 1+z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al z At least one of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, LiFeO2, and LiFePO4, wherein each x is independently 0.4 to 0.6; each y is independently 0.2 to 0.4; and each z is independently 0 to 0.1.

[0091] In some embodiments, the positive electrode active material is Li 1+x Ni a Mn b Co c Al (1-a-b-c) O2; where -0.2≤x≤0.2, 0≤a<1, 0≤b<1, 0≤c<1 and a+b+c≤1.

[0092] In some embodiments, the positive electrode active material has the general formula Li 1+x Ni a Mn b Co c Al (1-a-b-c) O2, where 0.33≤a≤0.92, 0.33≤a≤0.9, 0.33≤a≤0.8, 0.5≤a≤0.92, 0.5≤a≤0.9, 0.5≤a≤0.8, 0.6≤a≤0.92 or 0.6≤a≤0.9; 0≤b≤0.5, 0≤b≤0.3, 0.1≤b≤0.5, 0.1≤b≤0.4, 0.1≤b≤0.3, 0.1≤b≤0.2 or 0.2≤b≤0.5; 0≤c≤0.5, 0≤c≤0.3, 0.1≤c≤0.5, 0.1≤c≤0.4, 0.1≤c≤0.3, 0.1≤c≤0.2 or 0.2≤c≤0.5.

[0093] In some embodiments, the positive electrode active material is doped with a dopant selected from at least one of Fe, Ni, Mn, Al, Mg, Zn, Ti, La, Ce, Sn, Zr, Ru, Si, and Ge. In some embodiments, the dopant is not Fe, Ni, Mn, Mg, Zn, Ti, La, Ce, Ru, Si, or Ge. In some embodiments, the dopant is not Al, Sn, or Zr.

[0094] In some embodiments, the positive electrode active material may include LiNi. 0.33 Mn 0.33 Co 0.33 O2, LiNiO2, LiNi0.4 Mn 0.4 Co 0.2 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.7 Mn 0.15 Co 0.15 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2, LiNi 0.92 Mn 0.04 Co 0.04 O2, LiNi 0.8 Co 0.15 Al 0.05 At least one of O2.

[0095] It is understandable that when the electrode is a negative electrode, the active material is a negative electrode active material.

[0096] In some embodiments, the negative electrode active material may include natural graphite particles, synthetic graphite particles, hard carbon, soft carbon, mesophase carbon microspheres (MCMB), Sn, SnO2, SnO, Li4Ti5O 12 The negative electrode active material is selected from at least one of LTO, Si material, silicon-carbon (Si-C) composite material, silicon-nitrogen (Si-N) composite material, and silicon-oxygen (Si-O) composite material. The negative electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as negative electrode active materials for batteries.

[0097] In some embodiments, the secondary battery also includes an electrolyte.

[0098] In some embodiments, the electrolyte includes a non-aqueous solvent and a lithium salt.

[0099] In some embodiments, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.

[0100] In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0101] In some embodiments, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.

[0102] In some embodiments, the chain carbonate compound may include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof.

[0103] In some embodiments, the cyclic carbonate compound may include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof.

[0104] In some embodiments, the fluorocarbonate compound may include at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0105] In some embodiments, the carboxylic acid ester compound may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate.

[0106] In some embodiments, the ether compound may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0107] In some embodiments, the non-aqueous solvent may also include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0108] In some embodiments, the secondary battery further includes a separator located between the positive electrode and the negative electrode.

[0109] The separator is positioned between the positive and negative electrodes to prevent internal short circuits in the secondary battery, allowing electrolyte ions to pass freely without affecting the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. The separator used in this application can be any separator known in the prior art. For example, the type of separator can include, but is not limited to, at least one of woven membranes, nonwoven membranes, microporous membranes, composite membranes, rolled membranes, and spun membranes. The material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester, cellulose, polyimide (PI), polyamide (PA), spandex, and aramid. Polyester can include, but is not limited to, polyethylene terephthalate (PET) film.

[0110] In some embodiments, the diaphragm includes a substrate layer. The substrate layer may include, but is not limited to, at least one of a nonwoven fabric, membrane, or composite membrane having a porous structure. The material of the substrate layer may include, but is not limited to, at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. In some embodiments, the substrate layer may include, but is not limited to, at least one of a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane.

[0111] In some embodiments, the separator further includes a surface treatment layer disposed on at least one surface of the substrate layer. The surface treatment layer may include, but is not limited to, at least one of a polymer layer, an inorganic layer, and a layer formed by a mixture of polymers and inorganic substances. The polymer layer includes polymers. This application does not particularly limit the polymer, as long as it achieves the purpose of this application. For example, the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymers, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene). The inorganic layer includes inorganic particles and a binder. This application does not particularly limit the inorganic particles and binder, as long as it achieves the purpose of this application. For example, the inorganic particles may include, but are not limited to, at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. As another example, the binder may include, but is not limited to, at least one of the binders used in the above-mentioned positive electrode material layer or negative electrode material layer.

[0112] In some embodiments, the present application does not have a particular limitation on the thickness of the diaphragm, as long as the purpose of the present application can be achieved. For example, the thickness of the diaphragm is 3 μm to 20 μm.

[0113] Secondly, an electrical device is provided, including the aforementioned secondary battery.

[0114] The electrical device used in this application is not particularly limited and can be any electrical device known in the prior art.

[0115] The application of the secondary battery in this application is not particularly limited, and it can be used in any electrical device known in the prior art. According to some embodiments of this application, the electrical device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, and android robots.

[0116] Example 1 <Preparation of Composite Current Collectors> Polyethylene terephthalate (PET, melting point 260℃, coefficient of volumetric thermal expansion = 10ppm / ℃), alumina (particle size = 50nm, coefficient of volumetric thermal expansion = 10ppm / ℃) and carbon nanotubes were melt-blended at 250℃ in a mass ratio of 93:5:2 to prepare a polymer layer with a thickness of 3.5μm and a pore size of 1μm in the polymer layer. A composite current collector was obtained by depositing 1 μm thick copper metal onto both sides of the polymer layer using vacuum magnetron sputtering.

[0117] <Preparation of Thermal Runaway Suppression Materials> Polyethylene (melting point 120℃) and xylene are added to a container at a mass ratio of 10:1 to dissolve the polyethylene and obtain a polyethylene solution. Triangular aluminum particles (particle size D50=60nm) were added to a polyethylene solution, stirred evenly, and then spray-dried to obtain a thermal runaway suppression material.

[0118] <Preparation of Negative Electrode Sheets> Artificial graphite, conductive carbon black, thickener (hydroxyethyl cellulose (HEC)), binder (polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC)) and thermal runaway suppression material were added to deionized water at a mass ratio of 94.5:1:1.75:2.25:0.5 and mixed evenly to obtain a negative electrode slurry. The obtained negative electrode slurry was coated on both sides of the composite current collector, air-dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, the negative electrode sheet was obtained. The total thickness of the negative electrode active material layer on both sides was 40 μm.

[0119] <Preparation of the positive electrode> The positive electrode active material LiFePO4, conductive carbon black and polyvinylidene fluoride (PVDF) are mixed uniformly at a mass ratio of 97.5:1:1.5 and uniformly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform positive electrode slurry. The obtained positive electrode slurry is coated on both sides of the positive electrode current collector aluminum foil, and after baking, rolling and cutting, a positive electrode sheet is obtained, wherein the total thickness of the positive electrode active layer on both sides is 70 μm.

[0120] <Preparation of the diaphragm> Using a 12μm thick polyethylene microporous film as the substrate, inorganic alumina powder, polyvinylpyrrolidone, and deionized water were mixed evenly in a weight ratio of 3:1.5:5.5 to prepare an inorganic slurry. The inorganic slurry was then coated on both sides of the substrate and dried to form an inorganic layer with a thickness of 5μm, thus obtaining the diaphragm.

[0121] <Preparation of Electrolyte> At room temperature, in an argon-filled glove box (H2O < 1 ppm, O2 < 1 ppm), ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate were mixed uniformly in a volume ratio of 1.2:1:4:4, and water was removed using a 4 Å molecular sieve to obtain a mixed solvent. Lithium salt LiPF6 was added to the mixed solvent and mixed uniformly to obtain an electrolyte. The molar concentration of LiPF6 was 1 mol / L.

[0122] <Preparation of Secondary Batteries> The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrode. After winding, hot pressing and shaping, and welding of the tabs, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte prepared above is injected into the dried battery, and the battery is allowed to stand, form, and be tested for capacity to complete the preparation of the secondary battery.

[0123] Example 2 Except for the particle size D50 of the triangular aluminum particles in the <Preparation of Thermal Runaway Suppression Material>, which differs from that in Example 1, all other aspects are the same as in Example 1. In this example, the particle size D50 of the triangular aluminum particles is 63 nm.

[0124] Example 3 Except for the particle size D50 of the triangular aluminum particles in the <Preparation of Thermal Runaway Suppression Material>, which differs from that in Example 1, all other aspects are the same as in Example 1. In this example, the particle size D50 of the triangular aluminum particles is 67 nm.

[0125] Example 4 Except for the particle size D50 of the triangular aluminum particles in the <Preparation of Thermal Runaway Suppression Material>, which differs from that in Example 1, all other aspects are the same as in Example 1. In this example, the particle size D50 of the triangular aluminum particles is 70 nm.

[0126] Example 5 Except for the particle size D50 of the triangular aluminum particles in "Preparation of Thermal Runaway Suppression Material" and the particle size D50 of the alumina in "Preparation of Composite Current Collector", all other dimensions are the same as in Example 1. In this example, the particle size D50 of the triangular aluminum particles is 20 nm; the particle size D50 of the alumina is 20 nm.

[0127] Example 6 Except for the particle size D50 of the triangular aluminum particles in "Preparation of Thermal Runaway Suppression Material" and the particle size D50 of the alumina in "Preparation of Composite Current Collector", all other dimensions are the same as in Example 1. In this example, the particle size D50 of the triangular aluminum particles is 100 nm; the particle size D50 of the alumina is 100 nm.

[0128] Example 7 Except for the particle size D50 of the triangular aluminum particles in "Preparation of Thermal Runaway Suppression Material" and the particle size D50 of the alumina in "Preparation of Composite Current Collector", all other dimensions are the same as in Example 1. In this example, the particle size D50 of the triangular aluminum particles is 150 nm; the particle size D50 of the alumina is 150 nm.

[0129] Example 8 Except for the difference in the volumetric thermal expansion coefficients of alumina and PET in the <Preparation of Composite Current Collector> compared to Example 1, all other aspects are the same as in Example 1. In this example, the volumetric thermal expansion coefficient of alumina is 20 ppm / ℃, and the volumetric thermal expansion coefficient of PET is 20 ppm / ℃.

[0130] Example 9 Except for the difference in the volumetric thermal expansion coefficients of alumina and PET in the <Preparation of Composite Current Collector> compared to Example 1, all other aspects are the same as in Example 1. In this example, the volumetric thermal expansion coefficient of alumina is 18 ppm / ℃, and the volumetric thermal expansion coefficient of PET is 18 ppm / ℃.

[0131] Example 10 Except for the difference in the volumetric thermal expansion coefficients of alumina and PET in the <Preparation of Composite Current Collector> compared to Example 1, all other aspects are the same as in Example 1. In this example, the volumetric thermal expansion coefficient of alumina is 16 ppm / ℃, and the volumetric thermal expansion coefficient of PET is 16 ppm / ℃.

[0132] Example 11 Except for the mass ratio of PET, alumina, and carbon nanotubes in the <Preparation of Composite Current Collector>, which differs from Example 1, everything else is the same as in Example 1. In this example, the mass ratio of PET, alumina, and carbon nanotubes is 88:10:2.

[0133] Example 12 Except for the mass ratio of PET, alumina, and carbon nanotubes in the <Preparation of Composite Current Collector>, which differs from Example 1, everything else is the same as in Example 1. In this example, the mass ratio of PET, alumina, and carbon nanotubes is 85:13:2.

[0134] Example 13 Except for the difference in the mass ratio of PET, alumina, and carbon nanotubes in the <Preparation of Composite Current Collector> compared to Example 1, everything else is the same as in Example 1. In this example, the mass ratio of PET, alumina, and carbon nanotubes is 96:2:2.

[0135] Example 14 Except for the use of anhydride-modified PET instead of PET in the <Preparation of Composite Current Collector>, everything else is the same as in Example 1. The preparation method of anhydride-modified PET in this example is as follows: Polyethylene terephthalate (PET, melting point 260℃, coefficient of volumetric thermal expansion = 10ppm / ℃) particles were dissolved in chloroform, and then SnCl2 catalyst and maleic anhydride were added sequentially. The grafting reaction was carried out at 180℃. After the reaction was completed, the product was filtered and dried to obtain anhydride-modified PET. The mass of the catalyst was 2% of the mass of PET, and the mass of the maleic anhydride was 1.5% of the mass of PET.

[0136] Example 15 Except for the pore size of the polymer layer in the <Preparation of Composite Current Collector>, which differs from Example 1, everything else is the same as in Example 1. In this example, the pore size of the polymer layer is 1.5 μm.

[0137] Example 16 Except for the pore size of the polymer layer in the <Preparation of Composite Current Collector>, which differs from Example 1, everything else is the same as in Example 1. In this example, the pore size of the polymer layer is 2 μm.

[0138] Example 17 Except for the pore size of the polymer layer in the <Preparation of Composite Current Collector>, which differs from Example 1, everything else is the same as in Example 1. In this example, the pore size of the polymer layer is 0.5 μm.

[0139] Example 18 Except for the difference in the mass ratio of artificial graphite, conductive carbon black, thickener, binder, and thermal runaway suppression material in the <Preparation of Negative Electrode Sheet> compared to Example 1, all other aspects are the same as in Example 1. In this example, the mass ratio of artificial graphite, conductive carbon black, thickener, binder, and thermal runaway suppression material is 94.9:1:1.75:2.25:0.1.

[0140] Example 19 Except for the difference in the mass ratio of artificial graphite, conductive carbon black, thickener, binder, and thermal runaway suppression material in the <Preparation of Negative Electrode Sheet> compared to Example 1, all other aspects are the same as in Example 1. In this example, the mass ratio of artificial graphite, conductive carbon black, thickener, binder, and thermal runaway suppression material is 94:1:1.75:2.25:1.

[0141] Example 20 Except for the difference in the mass ratio of artificial graphite, conductive carbon black, thickener, binder, and thermal runaway suppression material in the <Preparation of Negative Electrode Sheet> compared to Example 1, all other aspects are the same as in Example 1. In this example, the mass ratio of artificial graphite, conductive carbon black, thickener, binder, and thermal runaway suppression material is 93.5:1:1.75:2.25:1.5.

[0142] Example 21 Except for the shape of the aluminum particles in the <Preparation of Thermal Runaway Suppression Material>, which differs from that in Example 1, all other aspects are the same as in Example 1. In this example, the aluminum particles are pentagonal in shape.

[0143] Example 22 Except for the shape of the aluminum particles in the <Preparation of Thermal Runaway Suppression Material>, which differs from that in Example 1, all other aspects are the same as in Example 1. In this example, the aluminum particles are circular.

[0144] Example 23 <Preparation of Composite Current Collectors> Polymethyl methacrylate (melting point 150℃, volumetric thermal expansion coefficient = 15ppm / ℃), lithium aluminum sulfide (particle size = 50nm, volumetric thermal expansion coefficient = 15ppm / ℃) and carbon nanotubes were melt-blended at 220-280℃ in a mass ratio of 93:5:2 to prepare a polymer layer with a thickness of 4.5μm and a pore size of 1μm in the polymer layer. A composite current collector was obtained by depositing 1 μm thick aluminum metal onto both sides of the polymer layer using vacuum magnetron sputtering.

[0145] <Preparation of Thermal Runaway Suppression Materials> Polyethylene (melting point 120℃) and xylene are added to a container at a mass ratio of 10:1 to dissolve the polyethylene and obtain a polyethylene solution. Triangular copper particles (particle size D50=60nm) were added to a polyethylene solution, stirred until homogeneous, and then spray-dried to obtain a thermal runaway suppression material.

[0146] <Preparation of Negative Electrode Sheets> Artificial graphite, conductive carbon black, thickener (hydroxyethyl cellulose (HEC)), and binder (polyvinylidene fluoride (PVDF) and carboxymethyl cellulose (CMC)) were added to deionized water in a mass ratio of 95:1:1.75:2.25 and mixed evenly to obtain a negative electrode slurry. The obtained negative electrode slurry was coated on both sides of a 4.5 μm thick copper foil for negative electrode current collectors. After drying at room temperature, it was transferred to an oven for further drying. Then, it was cold-pressed and slit to obtain a negative electrode sheet. The total thickness of the negative electrode active material layer on both sides was 40 μm.

[0147] <Preparation of the positive electrode> The positive electrode active material LiFePO4, conductive carbon black, polyvinylidene fluoride (PVDF) and thermal runaway suppression material are mixed uniformly in a mass ratio of 97:1:1.5:0.5 and uniformly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform positive electrode slurry. The obtained positive electrode slurry is coated on both sides of the composite current collector aluminum foil, and after baking, rolling, and cutting, a positive electrode sheet is obtained, wherein the total thickness of the positive electrode active layer on both sides is 70 μm.

[0148] <Preparation of the diaphragm> Using a 12μm thick polyethylene microporous film as the substrate, inorganic alumina powder, polyvinylpyrrolidone, and deionized water were mixed evenly in a weight ratio of 3:1.5:5.5 to prepare an inorganic slurry. The inorganic slurry was then coated on both sides of the substrate and dried to form an inorganic layer with a thickness of 5μm, thus obtaining the diaphragm.

[0149] <Preparation of Electrolyte> At room temperature, in an argon-filled glove box (H2O < 1 ppm, O2 < 1 ppm), ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate were mixed uniformly in a volume ratio of 1.2:1:4:4, and water was removed using a 4 Å molecular sieve to obtain a mixed solvent. Lithium salt LiPF6 was added to the mixed solvent and mixed uniformly to obtain an electrolyte. The molar concentration of LiPF6 was 1 mol / L.

[0150] <Preparation of Secondary Batteries> The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrode. After winding, hot pressing and shaping, and welding of the tabs, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte prepared above is injected into the dried battery, and the battery is allowed to stand, form, and be tested for capacity to complete the preparation of the secondary battery.

[0151] Example 24 <Preparation of Composite Current Collectors> Polyimide (melting point 334℃, volumetric thermal expansion coefficient = 14ppm / ℃), inorganic non-metallic particles, and carbon nanotubes were melt-blended at 220–280℃ in a mass ratio of 93:5:2 to prepare a polymer layer with a thickness of 3.5μm and pore size of 1μm. The inorganic non-metallic particles were a mixture of zinc sulfide and calcium oxide in a mass ratio of 1:1, with both zinc sulfide and calcium oxide having a particle size D50 of 60nm. The volumetric thermal expansion coefficients of zinc sulfide and calcium oxide were both 14ppm / ℃. The first composite current collector was obtained by depositing 1 μm thick copper metal onto both sides of the polymer layer using vacuum magnetron sputtering.

[0152] The second composite current collector was obtained by depositing 1 μm thick aluminum metal onto both sides of the polymer layer using vacuum magnetron sputtering.

[0153] <Preparation of Thermal Runaway Suppression Materials> Polyethylene (melting point 120℃) and xylene are added to a container at a mass ratio of 10:1 to dissolve the polyethylene and obtain a polyethylene solution. Triangular silver particles (particle size D50=60nm) were added to a polyethylene solution, stirred until homogeneous, and then spray-dried to obtain a thermal runaway suppression material.

[0154] <Preparation of Negative Electrode Sheets> Artificial graphite, conductive carbon black, thickener (hydroxyethyl cellulose (HEC)), binder (polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC)) and thermal runaway suppression material were added to deionized water at a mass ratio of 94.5:1:1.75:2.25:0.5 and mixed evenly to obtain a negative electrode slurry. The obtained negative electrode slurry was coated on both sides of the first composite current collector, air-dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, the negative electrode sheet was obtained. The total thickness of the negative electrode active material layer on both sides was 40 μm.

[0155] <Preparation of the positive electrode> The positive electrode active material LiFePO4, conductive carbon black, polyvinylidene fluoride (PVDF) and thermal runaway suppression material are mixed uniformly in a mass ratio of 97:1:1.5:0.5 and uniformly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform positive electrode slurry. The obtained positive electrode slurry is coated on both sides of the second composite current collector, and after baking, rolling, and cutting, a positive electrode sheet is obtained, wherein the total thickness of the positive electrode active layer on both sides is 70 μm.

[0156] <Preparation of the diaphragm> Using a 12μm thick polyethylene microporous film as the substrate, inorganic alumina powder, polyvinylpyrrolidone, and deionized water were mixed evenly in a weight ratio of 3:1.5:5.5 to prepare an inorganic slurry. The inorganic slurry was then coated on both sides of the substrate and dried to form an inorganic layer with a thickness of 5μm, thus obtaining the diaphragm.

[0157] <Preparation of Electrolyte> At room temperature, in an argon-filled glove box (H2O < 1 ppm, O2 < 1 ppm), ethylene carbonate, propylene carbonate, diethyl carbonate, and propyl propionate were mixed uniformly in a volume ratio of 1.2:1:4:4, and water was removed using a 4 Å molecular sieve to obtain a mixed solvent. Lithium salt LiPF6 was added to the mixed solvent and mixed uniformly to obtain an electrolyte. The molar concentration of LiPF6 was 1 mol / L.

[0158] <Preparation of Secondary Batteries> The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrode. After winding, hot pressing and shaping, and welding of the tabs, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte prepared above is injected into the dried battery, and the battery is allowed to stand, form, and be tested for capacity to complete the preparation of the secondary battery.

[0159] Comparative Example 1 Except for the preparation of the composite current collector, which differs from Example 1, all other steps are the same as in Example 1. The preparation of the composite current collector in this comparative example includes the following steps: Polymethyl methacrylate (melting point 150℃, coefficient of volumetric thermal expansion = 14ppm / ℃) and carbon nanotubes were melt-blended at 250℃ in a mass ratio of 98:2 to prepare a polymer layer with a thickness of 3.5μm and a pore size of 1μm in the polymer layer. A composite current collector was obtained by depositing 1 μm thick copper metal onto both sides of the polymer layer using vacuum magnetron sputtering.

[0160] Comparative Example 2 Except for the preparation of the negative electrode sheet, which differs from Example 1, all other steps are the same as in Example 1. The preparation of the negative electrode sheet in this comparative example includes the following steps: artificial graphite, conductive carbon black, thickener, and binder are added to deionized water in a mass ratio of 95:1:1.75:2.25 and mixed evenly to obtain a negative electrode slurry; the obtained negative electrode slurry is coated onto both sides of the composite current collector, air-dried at room temperature, then transferred to an oven for further drying, and finally cold-pressed and slit to obtain the negative electrode sheet; wherein, the total thickness of the negative electrode active material layer on both sides is 40 μm.

[0161] Comparative Example 3 Except for the preparation of the composite current collector and the preparation of the negative electrode sheet, which differ from Example 1, all other steps are the same as in Example 1. The preparation of the composite current collector and the preparation of the negative electrode sheet in this comparative example include the following steps: <Preparation of Composite Current Collectors> Polyethylene (melting point 120℃, volumetric thermal expansion coefficient = 12ppm / ℃), alumina (particle size = 50nm, volumetric thermal expansion coefficient = 12ppm / ℃) and carbon nanotubes were melt-blended at 220-280℃ in a mass ratio of 93:5:2 to prepare a polymer layer with a thickness of 3.5μm and pore size of 1μm in the polymer layer. A composite current collector was obtained by depositing 1 μm thick copper metal onto both sides of the polymer layer using vacuum magnetron sputtering.

[0162] <Preparation of Thermal Runaway Suppression Materials> Polymethyl methacrylate (melting point 150℃) and xylene are added to a container at a mass ratio of 10:1 to dissolve the polyethylene and obtain a polyethylene solution. Triangular aluminum particles (particle size D50=50μm) were added to a polyethylene solution, stirred until homogeneous, and then spray-dried to obtain a thermal runaway suppression material.

[0163] The parameters for each embodiment and comparative example are shown in Table 1.

[0164] Table 1 Performance testing (1) Maximum temperature: The temperature sensing wire is placed at the center of the large surface of the secondary battery and measured in real time with a data acquisition instrument. The sampling frequency is 0.1s, and the temperature change during the secondary battery test is recorded. (2) Voltage change: The voltage acquisition line is connected to the positive and negative tabs of the secondary battery and connected to the data acquisition instrument. The sampling frequency is 0.1s. The voltage change during the secondary battery test is recorded, and the voltage values ​​before and after the test are compared as the cell voltage difference. (3) Needle penetration test: Place the secondary battery on the needle penetration stand and penetrate it with a 1mm ceramic needle at a speed of 2mm / s. Record the temperature and voltage changes of the secondary battery and whether it catches fire.

[0165] The test results are shown in Table 2.

[0166] Table 2 As can be seen from the experimental data in Table 1, the maximum temperature of the secondary battery of this application is ≤240℃, the voltage change is ≤60mV, and no fire was ignited during the nail penetration test; indicating that the secondary battery of this application has high thermal safety.

[0167] The experimental data from Examples 1 and Comparative Examples 1-3 show that the absence of inorganic non-metallic particles in the polymer layer, the absence of thermal runaway suppression materials in the active material layer, or the lower melting point of the first polymer than that of the second polymer will lead to a decrease in the maximum temperature of the secondary battery, an increase in voltage variation, and even the possibility of ignition during the nail penetration test. This indicates that adding inorganic non-metallic particles to the polymer layer, adding thermal runaway suppression materials to the active material layer, and making the melting point of the first polymer higher than that of the second polymer will help to obtain a secondary battery with high thermal safety.

[0168] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A secondary battery, characterized in that, The electrode includes an electrode sheet and a separator, wherein the electrode sheet includes a composite current collector and an active material layer disposed on at least one surface of the composite current collector; The composite current collector includes a polymer layer and a conductive layer located on at least one side of the polymer layer, wherein the conductive layer is located between the polymer layer and the active material layer; The polymer layer comprises a first polymer and inorganic non-metallic particles; The inorganic non-metallic particles include oxides and / or sulfides; The active material layer includes an active material and a thermal runaway suppression material; the thermal runaway suppression material includes conductive metal particles and a second polymer coated on the surface of the conductive metal particles; The melting point of the first polymer is greater than that of the second polymer.

2. The secondary battery as described in claim 1, characterized in that, The particle size D50 of the inorganic non-metallic particles is D I The particle size D50 of the conductive metal particles is D M The following relationship is satisfied: 0.95≤D I / D M ≤1, D M ≤100nm.

3. The secondary battery as described in claim 1, characterized in that, The volumetric thermal expansion coefficients of the first polymer and the inorganic non-metallic particles are each independently 10~20 ppm / ℃.

4. The secondary battery as described in claim 1, characterized in that, The mass of the inorganic non-metallic particles is 5-10% of the mass of the polymer layer.

5. The secondary battery as described in claim 1, characterized in that, The first polymer has a melting point ≥150°C; and / or the second polymer has a melting point of 100~120°C.

6. The secondary battery as described in claim 1, characterized in that, The first polymer includes polar groups.

7. The secondary battery as described in claim 1, characterized in that, The polymer layer has pores; the pore size is 1~1.5μm; and / or the thickness of the polymer layer is 1~10μm.

8. The secondary battery as described in claim 1, characterized in that, Based on the mass of the active material layer, the mass percentage of the thermal runaway suppression material is 0.1% to 1%.

9. The secondary battery as described in claim 1, characterized in that, The conductive metal particles are made of at least one of the following materials: copper, copper alloy, silver, silver alloy, nickel, nickel alloy, gold, aluminum, aluminum alloy, zinc, zinc alloy, iron, iron alloy, palladium, and palladium alloy. And / or, the conductive metal particles are polygonal in shape; And / or, the first polymer and the second polymer each independently comprise at least one of polyacrylic acid, polyacrylic acid derivatives, polyacrylate, polyacrylate derivatives, poly(meth)acrylate, poly(meth)acrylate derivatives, polyethylene, polyethylene derivatives, polystyrene, polystyrene derivatives, polyacrylamide, polyacrylamide derivatives, polyacrylonitrile, polyacrylonitrile derivatives, polyimide, polyurethane, polyester, and polyvinylidene fluoride. And / or, the oxide includes at least one of calcium oxide, titanium dioxide, aluminum oxide, and magnesium peroxide; And / or, the sulfide includes at least one of zinc sulfide, magnesium sulfide, and lithium sulfide.

10. An electrical device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 9.

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