Secondary battery and electric device

Abstract

The application provides a secondary battery and a power utilization device, and belongs to the technical field of electrochemical energy storage. The secondary battery comprises a positive electrode sheet, and the positive electrode sheet comprises: a positive electrode current collector, having a first region and a second region connected along a first direction of the positive electrode current collector; a positive electrode active material layer, arranged on the first region, and containing a positive electrode active material; an insulating layer, arranged on the second region, and containing ceramic particles; and a phase change layer, arranged on the insulating layer, and containing a phase change material. The secondary battery has the advantages of high energy density and improved safety performance.

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] Secondary batteries, such as lithium-ion batteries, are widely used in smartphones, wearable devices, consumer drones, and electric vehicles due to their advantages such as high energy density, long cycle life, and no memory effect. With the widespread application of lithium-ion batteries in these fields, market demands for their safety performance are increasing. However, lithium-ion batteries are susceptible to short circuits between the positive and negative electrodes due to mechanical abuse (e.g., crushing, puncture), thermal abuse (e.g., high temperature), and electrical abuse (e.g., overcharging, over-discharging), resulting in relatively poor safety performance.

[0003] Current methods for improving the safety performance of lithium-ion batteries all come at the cost of sacrificing the energy density of the batteries. Therefore, there is an urgent need to provide a technical means that can significantly improve the safety performance of lithium-ion batteries under the condition of higher energy density. 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 a positive electrode, said positive electrode comprising: The positive electrode current collector has a first region and a second region connected along a first direction of the positive electrode current collector; A positive electrode active material layer is disposed in the first region, and the positive electrode active material layer contains a positive electrode active material; An insulating layer is disposed in the second region, the insulating layer comprising ceramic particles; A phase change layer is disposed on the insulating layer, the phase change layer comprising a phase change material.

[0006] In some embodiments, the thickness of the insulating layer is 90%-95% of the thickness of the positive electrode active material layer, and the thickness of the phase change layer is 5%-10% of the thickness of the positive electrode active material layer.

[0007] In some embodiments, the width of the second region is 2-10 mm along the first direction of the positive current collector.

[0008] In some embodiments, the positive electrode further includes a mutually soluble region disposed in the second region, the mutually soluble region being located between the positive electrode active material layer and the insulating layer, the phase change layer being disposed on the mutually soluble region and the insulating layer, and the mutually soluble region comprising ceramic particles and the positive electrode active material.

[0009] In some embodiments, the thickness of the mutually soluble region is the same as the thickness of the insulating layer.

[0010] In some embodiments, the width of the miscible region along the first direction of the positive current collector is 0.01-0.5 mm.

[0011] In some embodiments, the secondary battery satisfies at least one of the following: (a) The thickness of the positive electrode active material layer is 20-100 μm; (b) The thickness of the insulating layer is 5-50 μm; (c) The thickness of the phase change layer is 1-10 μm; (d) The interlayer bonding strength between the insulating layer and the phase change layer is ≥0.5 MPa; (e) The ceramic particles comprise at least one of the following: silicon dioxide, boron oxide, magnesium oxide, copper oxide, nickel oxide, calcium oxide, aluminum oxide, titanium dioxide, zirconium oxide, vanadium oxide, lanthanum oxide, beryllium oxide, yttrium oxide, cerium oxide, silicon nitride, titanium nitride, aluminum nitride, boron nitride, magnesium nitride, zirconium nitride, silicon oxynitride, silicon carbide, boron carbide, tantalum carbide, vanadium carbide, zirconium carbide, tungsten carbide, molybdenum carbide, manganese carbide, iron carbide, titanium carbide, and niobium carbide; (f) The phase change temperature of the phase change material is 80-100℃.

[0012] In some embodiments, the secondary battery further includes a negative electrode sheet, which includes a negative current collector and a negative active material layer and a thermal expansion layer disposed on the same surface of the negative current collector, the thermal expansion layer being disposed around the edge of the negative active material layer.

[0013] In some embodiments, the thickness of the negative electrode active material layer is greater than or equal to the thickness of the thermal expansion layer.

[0014] In some embodiments, the thickness of the thermal expansion layer is 80%-100% of the thickness of the negative electrode active material layer.

[0015] In some embodiments, the thermal expansion layer includes thermally expanded graphite, ceramic fibers, and an adhesive.

[0016] In some embodiments, based on the mass of the thermally expanded layer, the mass percentage of the thermally expanded graphite is 60-80%, the mass percentage of the ceramic fiber is 10-30%, and the mass percentage of the adhesive is 3-10%.

[0017] In some embodiments, the initial expansion temperature of the thermally expandable graphite is 120-130°C.

[0018] In some embodiments, the thickness of the negative electrode active material layer is 50-100 μm.

[0019] In some embodiments, the width of the thermal expansion layer is 2-10 mm.

[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: This application provides an insulating layer and a phase change layer disposed on the insulating layer in the second region without the positive electrode active material layer. The coverage of the phase change layer can prevent the positive electrode current collector at the insulating layer from being exposed, reducing the short circuit between the positive electrode current collector and the negative electrode. When the secondary battery experiences a short circuit or overcharging, causing severe internal heat generation, the phase change layer absorbs heat and melts to form a buffer layer, thereby increasing the gap between the positive electrode and the negative electrode, and increasing the resistance to the shuttle between the positive electrode and the negative electrode for active ions (such as lithium ions). After the phase change layer melts, the insulating layer can effectively cover the empty foil area of ​​the positive electrode current collector in the positive electrode (i.e., the second region), thereby avoiding the short circuit mode between the positive electrode current collector and the negative electrode, achieving the effect of preventing thermal runaway and improving the safety performance of the secondary battery. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet in this application; Figure 2 This is a schematic diagram of the edge structure of the positive and negative electrode plates in the secondary battery of this application; Figure 3 This is a schematic diagram of the phase change layer change in the positive electrode sheet of the secondary battery of this application; Figure 4 This is a schematic diagram of the negative electrode sheet of this application; Figure 5 This is a schematic diagram of the phase change layer and thermal expansion layer changes of the positive electrode in the secondary battery of this application.

[0023] Figure description: Positive current collector 2, second region 3, first region 4, positive active material layer 401, insulating layer 301, phase change layer 302, mutually soluble region 303, negative current collector 5, thermal expansion layer 6, negative active material layer 7, separator 8, first direction X. 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] To further illustrate this application, the secondary battery and power-consuming device provided in this application will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of this application.

[0032] like Figure 1 and Figure 2 As shown, in a first aspect, this application provides a secondary battery, including a positive electrode, said positive electrode comprising: The positive electrode current collector 2 has a first region 4 and a second region 3 connected along a first direction (i.e., the width direction) of the positive electrode current collector 2; A positive electrode active material layer 401 is disposed in the first region 4, and the positive electrode active material layer contains a positive electrode active material; An insulating layer 301 is disposed in the second region 3, and the insulating layer 301 comprises ceramic particles; A phase change layer 302 is disposed on the insulating layer 301, and the phase change layer 302 contains a phase change material.

[0033] like Figure 3 As shown, this application provides an insulating layer and a phase change layer disposed on the insulating layer in a second region without a positive electrode active material layer. The phase change layer can prevent the positive electrode current collector at the insulating layer from being exposed, reducing the short circuit between the positive electrode current collector and the negative electrode. When the secondary battery experiences a short circuit or overcharging, causing severe internal heat generation, the phase change layer absorbs heat and melts to form a buffer layer, thereby increasing the gap between the positive and negative electrode plates and increasing the resistance to the shuttle movement of active ions (such as lithium ions) between the positive and negative electrode plates. After the phase change layer melts, the insulating layer can effectively cover the empty foil area of ​​the positive electrode current collector in the positive electrode plate (i.e., the second region), thereby avoiding the short circuit mode between the positive electrode current collector and the negative electrode plate, achieving the effect of preventing thermal runaway and improving the safety performance of the secondary battery.

[0034] In some embodiments, the phase change material includes at least one of saturated fatty acids, paraffin wax, and sugar alcohols. The saturated fatty acids are selected from saturated fatty acids with ≥18 carbon atoms, and the sugar alcohols may be selected from at least one of sorbitol, xylitol, and erythritol.

[0035] In some embodiments, the thickness of the insulating layer is 90%-95% of the thickness of the positive electrode active material layer, and the thickness of the phase change layer is 5%-10% of the thickness of the positive electrode active material layer.

[0036] In this application, based on the thickness of the positive electrode active material layer, the thickness percentages of the insulating layer and the phase change layer are within the above range, which can provide insulation protection for the second region of the positive electrode sheet, reduce the risk of short circuit between the positive electrode current collector and the negative electrode sheet, and improve the safety performance of the secondary battery.

[0037] Specifically, the thickness of the insulating layer can be a range of one or any two of the following: 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, and 95% of the thickness of the positive electrode active material layer.

[0038] Specifically, the thickness of the phase change layer can be a range of one or any two of the following: 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% of the thickness of the positive electrode active material layer.

[0039] In some embodiments, the width of the second region along the first direction of the positive current collector is 2-10 mm; for example, it can be a range of one or any two of 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 6.5 mm, 7 mm, 7.5 mm, 8 mm, 8.5 mm, 9 mm, 9.5 mm, and 10 mm.

[0040] In this application, along the first direction of the positive electrode current collector, when the sum of the widths of the first region and the second region is constant, the size of the second region affects the size of the first region, that is, the size of the positive electrode active material layer, and thus affects the energy density of the secondary battery. By controlling the width of the second region within the aforementioned range, not only can the safety performance of the secondary battery be improved, but it is also beneficial to balance the energy density of the secondary battery.

[0041] In some embodiments, the positive electrode sheet further includes a mutually soluble region 303 disposed in the second region 3. The mutually soluble region 303 is located between the positive electrode active material layer 401 and the insulating layer 301. The phase change layer is disposed on the mutually soluble region and the insulating layer. The mutually soluble region 303 contains ceramic particles and the positive electrode active material.

[0042] In this application, a mutually soluble region is provided between the positive electrode active material layer and the insulating layer, and a phase change layer is provided on the mutually soluble region and the insulating layer. The coverage of the phase change layer can prevent the positive electrode current collector at the junction of the positive electrode active material layer and the insulating layer from being exposed, thereby reducing the short circuit between the positive electrode current collector and the negative electrode sheet.

[0043] In some embodiments, the thickness of the mutually soluble region is the same as the thickness of the insulating layer.

[0044] In this application, the thickness of the mutually soluble region is the same as the thickness of the insulating layer, which is beneficial to improving the safety performance and cycle stability of the secondary battery.

[0045] In some embodiments, the width of the miscible region along the first direction of the positive current collector is 0.01-0.5 mm; for example, it can be a range of one or any combination of 0.01 mm, 0.05 mm, 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm, 0.5 mm.

[0046] In this application, when setting the insulating layer, the insulating layer slurry is first placed on the second region of the positive electrode current collector at a certain distance from the edge of the positive electrode active material layer. Because the insulating layer slurry is flowable and has surface tension, it spreads and levels towards the positive electrode active material layer until the edge of the insulating layer coincides with the edge of the positive electrode active material layer, i.e., the width of the intersoluble region is 0 mm. Alternatively, the insulating layer slurry spreads along the edge of the positive electrode active material layer to the surface of the positive electrode active material layer under the influence of suction, and then penetrates into the interior of the positive electrode active material layer under the influence of gravity, forming an intersoluble region. This intersoluble region has a width of 0.01-0.5 mm along the first direction of the positive electrode current collector. The surface of the aforementioned intersoluble region will exhibit a color close to that of the insulating layer and can be clearly observed and tested using a scanning electron microscope (SEM). Therefore, under the condition of controlling the amount of insulating layer, controlling the width of the intersoluble region within the above range is beneficial to improving the production process yield of the positive electrode sheet, while reducing the risk of lithium plating in the secondary battery, thereby improving the safety performance of the secondary battery, and also helps to take into account the energy density of the secondary battery.

[0047] In some embodiments, the thickness of the positive electrode active material layer is 20-100 μm; for example, it can be a range of one or any combination of 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm.

[0048] In some embodiments, the thickness of the insulating layer is 5-50 μm; for example, it can be a range of one or any combination of 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm.

[0049] In some embodiments, the thickness of the phase change layer is 1-10 μm; for example, it can be a range of one or any combination of two of the following: 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, and 10 μm.

[0050] In this application, the thicknesses of the positive electrode active material layer, the insulating layer, and the phase change layer are within the aforementioned range, which not only enables the secondary battery to have a higher energy density but also improves the safety performance of the secondary battery.

[0051] In some embodiments, the interlayer bonding strength between the insulating layer and the phase change layer is ≥0.5 MPa; for example, it can be a range of values ​​consisting of one or any two of 0.5 MPa, 0.7 MPa, 1 MPa, 1.3 MPa, 1.5 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, and 10 MPa.

[0052] In this application, the interlayer bonding strength between the insulating layer and the phase change layer is within the above-mentioned range. During the preparation of the positive electrode sheet, the risk of phase change layer detachment is reduced, the positive electrode current collector is not exposed, and the safety performance of the secondary battery is improved.

[0053] Specifically, the interlayer bonding strength between the insulating layer and the phase change layer can be tested using the following methods: (1) Test method: The 180° peel strength test method was adopted (refer to GB / T 2792-2014: Test method for peel strength of adhesive tape, ASTM D903: Standard test method for peel or anti-peel strength of adhesives), and the specific steps are as follows: (2) Sample preparation: Cut strips with a width of 25 mm and a length of 150 mm from the positive electrode sheet to ensure the integrity of the interface between the insulating layer and the phase change layer.

[0054] (3) Testing equipment: A universal tensile testing machine is used; (4) Test conditions: Peeling angle: 180°.

[0055] Peeling speed: 300 mm / min (or 50-500 mm / min range, adjusted according to specific needs).

[0056] Ambient temperature: 25±2°C, relative humidity: 50±5%.

[0057] Number of repetitions: at least 5 times, take the average; (5) Calculation formula: interlayer bonding strength (MPa) = (average peel force F (N) × 1000) / (sample width W (mm) × thickness t (mm)); where F is the force value in the stable peel stage and t is the phase change layer thickness.

[0058] In some embodiments, based on the mass of the miscible region, the mass percentage of the ceramic particles is 5-50%, for example, it can be a range of one or any combination of 5%, 7%, 10%, 13%, 15%, 18%, 20%, 22%, 25%, 27%, 30%, 33%, 35%, 38%, 40%, 42%, 45%, 47%, and 50%. In the insulating layer, the mass percentage of ceramic material within the above range ensures that the miscible region provides structural support while maintaining a certain level of electrochemical activity, controlling the insulation resistance of the insulating layer within the required range, improving the reliability of the insulating layer, and thus enhancing the safety performance of the secondary battery.

[0059] In some embodiments, the ceramic particles include at least one of silicon dioxide, boron oxide, magnesium oxide, copper oxide, nickel oxide, calcium oxide, aluminum oxide, titanium dioxide, zirconium oxide, vanadium oxide, lanthanum oxide, beryllium oxide, yttrium oxide, cerium oxide, silicon nitride, titanium nitride, aluminum nitride, boron nitride, magnesium nitride, zirconium nitride, silicon oxynitride, silicon carbide, boron carbide, tantalum carbide, vanadium carbide, zirconium carbide, tungsten carbide, molybdenum carbide, manganese carbide, iron carbide, titanium carbide, and niobium carbide.

[0060] The aforementioned ceramic particles not only exhibit good insulation properties at room temperature, but also at high temperatures. Therefore, even in the event of thermal runaway in a secondary battery, they help maintain good insulation between the positive electrode tab and the negative electrode sheet, thereby improving the safety performance of the secondary battery.

[0061] In some embodiments, the phase transition temperature of the phase change material is 80-100°C; for example, it can be a range of one or any combination of 80°C, 82°C, 85°C, 87°C, 90°C, 93°C, 95°C, 98°C, and 100°C. When the phase transition temperature of the phase change material is within the above range, the phase change layer can melt at 80-100°C to form a buffer layer, which helps reduce the probability of short circuits in the secondary battery and improves the safety performance of the secondary battery.

[0062] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0063] In this application, positive current collectors of different thicknesses can be purchased and selected by measuring with a micrometer.

[0064] The positive electrode material layer includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0065] The positive electrode material layer may further include a conductive agent and a positive electrode binder. This application does not impose any particular limitation on the types of conductive agents and positive electrode binders, as long as they achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The positive electrode binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and positive electrode binder in the positive electrode material layer; those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0066] In some implementations, such as Figure 2 and Figure 4 As shown, the secondary battery also includes a negative electrode sheet, which includes a negative current collector 5 and a negative active material layer 7 and a thermal expansion layer 6 disposed on the same surface of the negative current collector 5. The thermal expansion layer 6 is disposed around the negative active material layer 7.

[0067] like Figure 5 As shown, when a short circuit or overcharge occurs in a secondary battery, causing intense internal heat generation, the thermal expansion layer expands due to the heat, further increasing the gap between the positive and negative electrode plates, reducing the path of short circuit propagation, cutting off the heat spread of the electrode plates, and thus improving the safety performance of the secondary battery.

[0068] In some embodiments, the thermal expansion layer and the phase change layer have at least a partial overlap region in the projection of the phase change layer in the first direction; the phase change layer and the thermal expansion layer interact to increase the spacing between the positive electrode and the negative electrode, thereby improving the safety performance of the secondary battery.

[0069] It should be noted that there must be no gaps between the thermal expansion coating and the negative electrode active material layer; that is, the two coatings must be in contact with each other. In actual operation, partial miscibility between the thermal expansion coating and the negative electrode active material layer is permissible, but the width of the miscible portion must be less than or equal to 0.2 mm.

[0070] In some embodiments, the thickness of the negative electrode active material layer is greater than or equal to the thickness of the thermal expansion layer.

[0071] In some embodiments, the thickness of the thermal expansion layer is 80%-100% of the thickness of the negative electrode active material layer; for example, it can be a range of one or any two of 80%, 82%, 85%, 87%, 90%, 93%, 95%, 98%, 100%.

[0072] In this application, based on the thickness of the negative electrode active material layer, by controlling the thickness of the thermal expansion layer within the above range, the spacing between the positive electrode and the negative electrode can be increased more effectively, thereby improving the safety performance of the secondary battery.

[0073] In some embodiments, the thermal expansion layer includes thermally expanded graphite, ceramic fibers, and an adhesive.

[0074] In some embodiments, based on the mass of the thermally expanded layer, the mass percentage of the thermally expanded graphite is 60-80%, the mass percentage of the ceramic fiber is 10-30%, and the mass percentage of the adhesive is 3-10%.

[0075] In this application, by controlling the mass percentages of thermally expanded graphite, ceramic fiber, and binder in the thermal expansion layer within the aforementioned range, the obtained thermal expansion layer not only has good thermal expansion properties but also high structural integrity. This helps to disperse the stress between the negative electrode active material layer and the thermal expansion layer during the cold pressing process of the negative electrode sheet, while reducing the risk of the thermal expansion layer falling off, thereby improving the safety performance of the secondary battery.

[0076] Specifically, based on the mass of the thermally expanded layer, the mass percentage of the thermally expanded graphite can be a range of one or any two of 60%, 62%, 65%, 67%, 70%, 73%, 75%, 78%, and 80%.

[0077] Specifically, based on the mass of the thermal expansion layer, the mass percentage of the ceramic fiber can be a range of one or any two of the following: 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, and 30%.

[0078] Specifically, based on the mass of the thermal expansion layer, the mass percentage of the adhesive can be a range of one or any combination of 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%.

[0079] In some embodiments, the initial expansion temperature of the thermally expandable graphite is 120-130°C; for example, it can be a range of one or any combination of 120°C, 121°C, 122°C, 123°C, 124°C, 125°C, 126°C, 127°C, 128°C, 129°C, and 130°C.

[0080] In this application, by controlling the initial expansion temperature of thermally expanding graphite within the above-mentioned range, a layer temperature can be formed with the phase change layer, accurately responding to thermal runaway, improving the safety threshold, and thus enhancing the safety performance of the secondary battery.

[0081] In some embodiments, the thickness of the negative electrode active material layer is 50-100 μm; for example, it can be a range of one or any combination of 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm.

[0082] In some embodiments, the width of the thermal expansion layer is 2-10 mm; for example, it can be a range of one or any combination of 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm.

[0083] In this application, by controlling the width of the thermal expansion layer within the aforementioned range, the safety performance of the secondary battery is improved while maintaining a high energy density.

[0084] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0085] The negative electrode material layer includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase microcarbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-SnO alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0086] In some embodiments, the negative electrode material layer may further include a conductive agent and a negative electrode binder. This application does not particularly limit the types of conductive agents and negative electrode binders, as long as they achieve the purpose of this application. For example, they may be at least one of the aforementioned conductive agents and positive electrode binders. This application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, and negative electrode binder in the negative electrode material layer. Those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0087] In this application, as Figure 2 As shown, the secondary battery also includes a separator 8. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the separator material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The separator type may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0088] In some embodiments, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used.

[0089] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0090] In some embodiments, the inorganic layer comprises inorganic particles and a membrane binder. This application does not particularly limit the inorganic particles; for example, the inorganic particles may include at least one selected from 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, or barium sulfate. This application does not particularly limit the membrane binder; for example, the membrane binder may be at least one of the above-mentioned positive electrode binders. In some embodiments, the polymer layer comprises a polymer, the polymer material of which includes at least one selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0091] In this application, there is no particular limitation on the thickness of the diaphragm, as long as it can achieve the purpose of this application. For example, the thickness of the diaphragm can be from 3 μm to 30 μm.

[0092] In this application, the secondary battery also includes an electrolyte, which includes lithium salts and non-aqueous solvents.

[0093] This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, lithium bis(oxalato)borate (LiBOB), and lithium difluoroborate. This application also does not impose any particular limitation on the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application.

[0094] This application does not impose any particular restrictions on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0095] In some embodiments, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] The secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0103] The fabrication process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the fabrication process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. Alternatively, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0104] This application does not impose any particular limitation on the type of secondary battery; any secondary battery known in the prior art can be used. In some embodiments, the secondary battery may include, but is not limited to, lithium-ion batteries, sodium-ion batteries, nickel-metal hydride batteries, lithium polymer batteries, lithium-sulfur batteries, sodium-sulfur batteries, and lithium metal sulfide batteries.

[0105] Secondly, an electrical device is provided, including the aforementioned secondary battery. Therefore, the electrical device provided in this application has good performance. This application does not particularly limit the type of electrical device; it can be any electrical device known in the prior art. In some embodiments, the electrical device may include, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0106] Example 1 <Preparation of the positive electrode> Preparation of positive electrode active layer slurry: Lithium nickel cobalt manganese oxide, super P, and PVDF were added to NMP solvent in a mass ratio of 97:1:2 and stirred thoroughly to form a positive electrode active layer slurry with a solid content of 58% and a viscosity of 4000 mPa·s. Preparation of insulating slurry: Alumina ceramic particles and polyvinylidene fluoride binder are mixed evenly in deionized water at a mass ratio of 93:7 to obtain an insulating slurry with a solid content of 35%. Preparation of phase change layer slurry: Paraffin wax (phase change temperature is 80℃) and polyvinylidene fluoride binder are mixed evenly in deionized water at a mass ratio of 90:10 to obtain an insulating layer slurry with a solid content of 30%. Using a 10μm thick aluminum foil as the positive electrode current collector, a first region and a second region are connected on one surface of the positive electrode current collector along the first direction. Adhesive paper is applied to the second region, and positive electrode slurry is coated on the first region and dried at 85°C. The adhesive paper is then peeled off, and an insulating layer slurry is coated on the second region and dried at 85°C. Next, a phase change layer slurry is coated on the insulating layer and dried at 40°C. Then, the first and second regions are cold-pressed at a pressure of 90 tons. After the cold-pressing process, the foil is cut into sheets, and positive electrode tabs are obtained from the corresponding positions of the empty foil area to obtain the positive electrode sheet. The width of the second region along the first direction of the positive electrode current collector is 5mm, and the width of the interfacial region is 0mm. The thickness of the single-sided positive electrode active material layer is 50μm, the thickness of the single-sided insulating layer is 45μm, the thickness of the single-sided phase change layer is 5μm, and the interlayer bonding strength between the insulating layer and the phase change layer is 1MPa.

[0107] <Preparation of Negative Electrode Sheets> Artificial graphite, super P, CMC, and SBR were added to a deionized water solvent in a mass ratio of 96.5:0.5:1.2:1.8 and stirred thoroughly to form a negative electrode active material slurry with a solid content of 53% and a viscosity of 3000 mPa·s. The negative electrode active material slurry was then coated on both sides of a copper foil, dried, rolled, and cut into sheets. Negative electrode tabs were cut from the corresponding positions of the empty foil areas of the copper foil to obtain negative electrode sheets. The thickness of the single-sided negative electrode active layer was 50 μm.

[0108] <Preparation of Electrolyte> Lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1.5:1 to obtain an electrolyte, wherein the molar concentration of lithium hexafluorophosphate was 1 mol / L.

[0109] <Preparation of the diaphragm> A porous polyethylene film with a thickness of 7μm (supplied by Celgard) is used.

[0110] <Preparation of Secondary Batteries> The positive electrode, separator, and negative electrode prepared above are stacked in sequence, with the separator acting as a separator between the positive and negative electrode. Then, the four corners of the entire stacked structure are fixed with tape to obtain the electrode assembly of the stacked structure. The electrode assembly is placed in an aluminum-plastic film outer packaging foil and dehydrated at 80°C. The prepared electrolyte is then injected. After vacuum sealing, standing, formation, shaping, and capacity testing, a secondary battery is obtained. The formation temperature is 80°C, and the formation standing time is 2 hours.

[0111] Example 2-12 Except for the fact that in the "Preparation of Positive Electrode Sheet", the parameters of the positive electrode sheet are as shown in Table 1 by adjusting the width of the second region, the width of the intersoluble region, the thickness of the insulating layer and the thickness of the phase change layer along the first direction of the positive electrode current collector, the rest are the same as in Example 1.

[0112] Example 13 Except for the negative electrode sheet being prepared according to the following <Preparation of Negative Electrode Sheet>, the rest is the same as in Example 1.

[0113] <Preparation of Negative Electrode Sheets> Preparation of negative electrode active material layer slurry: Artificial graphite, super P, CMC and SBR were added to deionized water solvent in a mass ratio of 96.5:0.5:1.2:1.8 and stirred thoroughly to form a negative electrode active material layer slurry with a solid content of 53% and a viscosity of 3000 mPa·s. Preparation of thermal expansion layer slurry: Thermal expansion graphite (initial expansion temperature is 120℃), ceramic fiber (alumina-silica fiber) and binder polyvinylidene fluoride are added to deionized water at a mass ratio of 75:20:5 and stirred evenly to form a thermal expansion layer slurry with a solid content of 48%. The negative electrode active layer slurry is coated on the middle position of both sides of the copper foil and dried at 85°C to form the negative electrode active material layer. Then, the thermal expansion layer slurry is coated around the negative electrode active material layer on both sides of the copper foil, dried, rolled, and cut into sheets. The negative electrode tabs are then cut from the corresponding positions of the empty foil area of ​​the copper foil to obtain the negative electrode sheet. The thickness of the single-sided negative electrode active layer is 50μm, the thickness of the single-sided thermal expansion layer is 50μm, and the width of the thermal expansion layer is 5mm.

[0114] Examples 14-23 Except for the fact that in the <Preparation of Negative Electrode Sheet>, the parameters of the negative electrode sheet are as shown in Table 2 by adjusting the thickness of the single-sided thermal expansion layer, the width of the thermal expansion layer and the initial expansion temperature of the thermally expanded graphite, the rest are the same as in Example 13.

[0115] Table 1 Parameters of the positive electrode sheet Table 2 Parameters of the negative electrode sheet Comparative Example 1 Except for the positive electrode sheet prepared according to the following <Preparation of Positive Electrode Sheet>, the rest is the same as in Example 1.

[0116] <Preparation of the positive electrode> Preparation of positive electrode active layer slurry: Lithium nickel cobalt manganese oxide, super P, and PVDF were added to NMP solvent in a mass ratio of 97:1:2 and stirred thoroughly to form a positive electrode active layer slurry with a solid content of 58% and a viscosity of 4000 mPa·s. Preparation of insulating slurry: Alumina ceramic particles and polyvinylidene fluoride binder are mixed evenly in deionized water at a mass ratio of 93:7 to obtain an insulating slurry with a solid content of 35%. Using a 10μm thick aluminum foil as the positive electrode current collector, a first region and a second region are connected on one surface of the positive electrode current collector along the first direction. Adhesive paper is applied to the second region, and positive electrode slurry is coated on the first region. The mixture is then dried at 85°C. The adhesive paper is peeled off from the second region, and an insulating layer slurry is coated on the second region, which is then dried at 85°C. The first and second regions are then cold-pressed at a pressure of 90 tons. After cold pressing, the foil is cut into sheets, and positive electrode tabs are cut from corresponding positions in the empty foil area to obtain the positive electrode sheet. The width of the second region along the first direction of the positive electrode current collector is 5mm, and the width of the intersoluble region is 0mm. The thickness of the single-sided positive electrode active material layer is 50μm, and the thickness of the single-sided insulating layer is 50μm.

[0117] Comparative Example 2 Except for the positive electrode sheet prepared according to the following <Preparation of Positive Electrode Sheet>, the rest is the same as in Example 1.

[0118] <Preparation of the positive electrode> Preparation of positive electrode active layer slurry: Lithium nickel cobalt manganese oxide, super P, and PVDF were added to NMP solvent in a mass ratio of 97:1:2 and stirred thoroughly to form a positive electrode active layer slurry with a solid content of 58% and a viscosity of 4000 mPa·s. Preparation of phase change layer slurry: Paraffin wax (phase change temperature is 80℃) and polyvinylidene fluoride binder are mixed evenly in deionized water at a mass ratio of 90:10 to obtain an insulating layer slurry with a solid content of 30%. Using a 10μm thick aluminum foil as the positive electrode current collector, a first region and a second region are connected on one surface of the positive electrode current collector along the first direction. Adhesive paper is applied to the second region, and positive electrode slurry is coated on the first region and dried at 85℃. The adhesive paper is peeled off the second region, and phase change layer slurry is coated on the second region and dried at 40℃. Then, the first and second regions are cold-pressed at a pressure of 90 tons. After the cold-pressing process, the foil is cut into sheets, and positive electrode tabs are cut from the corresponding positions of the empty foil area to obtain the positive electrode sheet. The width of the second region along the first direction of the positive electrode current collector is 5mm, and the width of the intersoluble region is 0mm. The thickness of the single-sided positive electrode active material layer is 50μm, and the thickness of the single-sided phase change layer is 50μm.

[0119] Comparative Example 3 Except for the positive electrode sheet prepared according to the following <Preparation of Positive Electrode Sheet>, the rest is the same as in Example 1.

[0120] <Preparation of the positive electrode> Preparation of positive electrode active layer slurry: Lithium nickel cobalt manganese oxide, super P, and PVDF were added to NMP solvent in a mass ratio of 97:1:2 and stirred thoroughly to form a positive electrode active layer slurry with a solid content of 58% and a viscosity of 4000 mPa·s. Preparation of insulating slurry: Alumina ceramic particles and polyvinylidene fluoride binder are mixed evenly in deionized water at a mass ratio of 93:7 to obtain an insulating slurry with a solid content of 35%. Preparation of phase change layer slurry: Paraffin wax (phase change temperature is 80℃) and polyvinylidene fluoride binder are mixed evenly in deionized water at a mass ratio of 90:10 to obtain an insulating layer slurry with a solid content of 30%. Using a 10μm thick aluminum foil as the positive electrode current collector, a first region and a second region are connected on one surface of the positive electrode current collector along the first direction. Adhesive paper is applied to the second region, and positive electrode slurry is coated on the first region and dried at 85°C. The adhesive paper is peeled off the second region, and phase change layer slurry is coated on the second region and dried at 40°C. Then, insulating layer slurry is coated on the phase change layer and dried at 40°C. The first and second regions are then cold-pressed at a pressure of 90 tons. After the cold-pressing process, the foil is cut into sheets, and positive electrode tabs are cut from the corresponding positions of the empty foil area to obtain the positive electrode sheet. The width of the second region along the first direction of the positive electrode current collector is 5mm, and the width of the interfacial region is 0mm. The thickness of the single-sided positive electrode active material layer is 50μm, the thickness of the single-sided insulating layer is 5μm, the thickness of the single-sided phase change layer is 45μm, and the interlayer bonding strength between the insulating layer and the phase change layer is 1MPa.

[0121] Comparative Example 4 Except for the positive electrode sheet prepared according to the following <Preparation of Positive Electrode Sheet>, the rest is the same as in Example 1.

[0122] <Preparation of the positive electrode> Preparation of positive electrode active layer slurry: Lithium nickel cobalt manganese oxide, super P, and PVDF were added to NMP solvent in a mass ratio of 97:1:2 and stirred thoroughly to form a positive electrode active layer slurry with a solid content of 58% and a viscosity of 4000 mPa·s. Using a 10μm thick aluminum foil as the positive electrode current collector, a first region and a second region are connected on one surface of the positive electrode current collector along the first direction. The obtained positive electrode active layer slurry is coated on the first and second regions and dried at 85°C. Then, the first and second regions are cold-pressed at a pressure of 90 tons. After the cold-pressing process, the foil is cut into sheets, and positive electrode tabs are cut from the corresponding positions of the empty foil area to obtain the positive electrode sheet. The width of the second region along the first direction of the positive electrode current collector is 5mm, and the thickness of the single-sided positive electrode active material layer is 50μm.

[0123] Performance testing The performance of the secondary batteries in the above embodiments and comparative examples was tested using the following methods: (1) Energy density: a) Pretreatment: Charge the battery to 4.25V with constant current (1 / 3C), and then charge it to the cutoff current of 0.05C with constant voltage.

[0124] b) Discharge test: Discharge the battery to 3V at a 1C rate. During the discharge process, the test system will continuously record the battery voltage and current, and calculate the real-time energy and cumulative energy.

[0125] c) Record the discharge mass energy density: E = (battery capacity Q × average voltage V) / battery mass m; unit: Wh / kg. Where Q is in Ah, V is in V, and m is in kg.

[0126] (2) Safety performance: Safety performance was tested using a needle puncture test; the method for triggering thermal runaway by needle puncture is as follows. a) Needle material: steel; b) Needle diameter: 3mm; c) Needle tip shape: conical, with an angle of 30°; d) Needle insertion speed: 1 mm / s; e) Acupuncture location and direction: perpendicular to the electrode plate; f) Condition for stopping acupuncture: penetrating acupuncture.

[0127] The test results are shown in Table 3.

[0128] Table 3 As can be seen from the experimental data in Table 3, the secondary battery of this application improves the safety performance of the secondary battery while maintaining energy density.

[0129] 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, Includes a positive electrode plate, wherein the positive electrode plate comprises: The positive electrode current collector has a first region and a second region connected along a first direction of the positive electrode current collector; A positive electrode active material layer is disposed in the first region, and the positive electrode active material layer contains a positive electrode active material; An insulating layer is disposed in the second region, the insulating layer comprising ceramic particles; A phase change layer is disposed on the insulating layer, the phase change layer comprising a phase change material.

2. The secondary battery as described in claim 1, characterized in that, The thickness of the insulating layer is 90%-95% of the thickness of the positive electrode active material layer, and the thickness of the phase change layer is 5%-10% of the thickness of the positive electrode active material layer.

3. The secondary battery as described in claim 1, characterized in that, Along the first direction of the positive current collector, the width of the second region is 2-10 mm.

4. The secondary battery as described in claim 1, characterized in that, The positive electrode sheet further includes a mutually soluble region disposed in the second region. The mutually soluble region is located between the positive electrode active material layer and the insulating layer. The phase change layer is disposed on the mutually soluble region and the insulating layer. The mutually soluble region contains ceramic particles and positive electrode active material.

5. The secondary battery as described in claim 4, characterized in that, The thickness of the mutually soluble region is the same as the thickness of the insulating layer; and / or, along the first direction of the positive current collector, the width of the mutually soluble region is 0.01-0.5 mm.

6. The secondary battery as described in claim 1, characterized in that, Meet at least one of the following: (a) The thickness of the positive electrode active material layer is 20-100 μm; (b) The thickness of the insulating layer is 5-50 μm; (c) The thickness of the phase change layer is 1-10 μm; (d) The interlayer bonding strength between the insulating layer and the phase change layer is ≥0.5 MPa; (e) The ceramic particles comprise at least one of the following: silicon dioxide, boron oxide, magnesium oxide, copper oxide, nickel oxide, calcium oxide, aluminum oxide, titanium dioxide, zirconium oxide, vanadium oxide, lanthanum oxide, beryllium oxide, yttrium oxide, cerium oxide, silicon nitride, titanium nitride, aluminum nitride, boron nitride, magnesium nitride, zirconium nitride, silicon oxynitride, silicon carbide, boron carbide, tantalum carbide, vanadium carbide, zirconium carbide, tungsten carbide, molybdenum carbide, manganese carbide, iron carbide, titanium carbide, and niobium carbide; (f) The phase change temperature of the phase change material is 80-100℃.

7. The secondary battery as described in claim 1, characterized in that, The secondary battery further includes a negative electrode sheet, which includes a negative current collector and a negative active material layer and a thermal expansion layer disposed on the same surface of the negative current collector. The thermal expansion layer is disposed around the edge of the negative active material layer.

8. The secondary battery as described in claim 7, characterized in that, The thickness of the negative electrode active material layer is greater than or equal to the thickness of the thermal expansion layer.

9. The secondary battery as described in claim 8, characterized in that, The thickness of the thermal expansion layer is 80%-100% of the thickness of the negative electrode active material layer.

10. The secondary battery as described in claim 7, characterized in that, The thermal expansion layer comprises thermally expanded graphite, ceramic fibers, and an adhesive.

11. The secondary battery as described in claim 10, characterized in that, Based on the mass of the thermal expansion layer, the mass percentage of the thermally expanded graphite is 60-80%, the mass percentage of the ceramic fiber is 10-30%, and the mass percentage of the adhesive is 3-10%.

12. The secondary battery as described in claim 10, characterized in that, The initial expansion temperature of the thermally expandable graphite is 120-130℃.

13. The secondary battery as described in claim 7, characterized in that, The thickness of the negative electrode active material layer is 50-100 μm; And / or, the width of the thermal expansion layer is 2-10 mm.

14. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1-13.

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