Secondary battery and electric device

Abstract

The present application belongs to the technical field of secondary batteries, and specifically relates to a secondary battery and an electric device. The secondary battery comprises an electrode sheet, wherein the electrode sheet comprises a current collector and an active substance layer disposed on at least one side of the current collector, the active substance layer comprises a main region and a thinned region, the thinned region is located at an outer edge of the main region, and a flame-retardant layer including a flame-retardant material is disposed between the thinned region and the current collector. The flame-retardant layer including the flame-retardant material is disposed between the thinned region and the current collector, so that when the temperature of the battery is excessively high, a flame retardant can absorb heat to reduce the temperature of the battery. Moreover, formed thermal decomposition products adhere to the surface of the electrode sheet, so that a good flame-retardant effect is achieved, thereby effectively improving the safety performance of the battery.

Description

A secondary battery and electrical device

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411753106.9, filed on November 28, 2024, entitled "A Secondary Battery and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application belongs to the field of secondary battery technology, specifically relating to a secondary battery and an electrical device. Background Technology

[0004] With the widespread use of lithium-ion batteries and the rapid development of sodium-ion batteries, battery safety has become a critical issue. Currently, the risk of thermal runaway in batteries is high; once thermal runaway occurs, it can lead to fires or even explosions, seriously threatening people's lives and property. To mitigate the thermal runaway problem, existing technologies often involve doping flame-retardant materials into the positive or negative electrode materials. However, while these flame-retardant materials improve battery safety, they often sacrifice the battery's volumetric energy density, making it difficult to achieve a balance between the two. Summary of the Invention

[0005] Therefore, this application provides a positive electrode active material, a secondary battery, and an electrical device, with the aim of improving the electrochemical kinetics of the thinned region while exerting a flame-retardant effect, thereby balancing high energy density and battery safety performance.

[0006] To achieve the above objectives, according to one aspect of this application, a secondary battery is provided, comprising an electrode, the electrode including a current collector and an active material layer disposed on at least one side of the current collector, the active material layer comprising:

[0007] Main area;

[0008] A thinning zone is located at the outer edge of the main body area, and a flame-retardant layer containing flame-retardant material is provided between the thinning zone and the current collector.

[0009] Optionally, the flame-retardant material includes flame-retardant particles and a conductive layer distributed on at least a portion of the surface of the flame-retardant particles.

[0010] Optionally, the thickness of the conductive layer is 2-20 nm, and the conductive layer accounts for 1%-10% of the mass of the flame-retardant particles.

[0011] Optionally, the flame-retardant particles have a Dv10 of 50-150nm, a Dv50 of 100-500nm, and a Dv99 of 300-900nm.

[0012] Optionally, the flame-retardant material satisfies at least one of the following conditions:

[0013] (1) The conductive layer comprises one or more of conductive carbon black, graphene, carbon nanotubes and conductive polymers;

[0014] (2) The flame-retardant particles include one or more of polyphosphazene particles, ammonium polyphosphate particles, phosphate particles, red phosphorus particles and organic phosphorus particles.

[0015] Optionally, the flame-retardant layer may also include 1%-5% of an adhesive.

[0016] Optionally, the thickness of the flame-retardant layer on the side away from the main body area is greater than the thickness on the side closer to the main body area.

[0017] Optionally, the minimum single-sided thickness of the thinning zone is 40-53 μm, the maximum single-sided thickness is 59-70 μm, and the width is 5-15 mm.

[0018] Optionally, the minimum single-sided thickness of the flame-retardant layer is 1-5 μm, the maximum single-sided thickness is 10-20 μm, and the width is 5-15 mm.

[0019] Optionally, the total thickness of the thinned area and the flame-retardant layer is substantially the same as the thickness of the main body area.

[0020] According to two aspects of this application, this application also provides an electrical device, including a secondary battery as described in any of the above claims, wherein the secondary battery serves as a power supply for the electrical device.

[0021] The technical solution of this application has the following advantages:

[0022] The secondary battery provided in this application includes an electrode sheet, which includes a current collector and an active material layer disposed on at least one side of the current collector. The active material layer includes a main region and a thinned region, with the thinned region located at the outer edge of the main region. A flame-retardant layer containing a flame-retardant material is disposed between the thinned region and the current collector. By disposing of a flame-retardant layer containing a flame-retardant material between the thinned region and the current collector, the flame retardant can absorb heat and reduce the battery temperature when the battery temperature is too high. Simultaneously, the formed thermal decomposition products adhere to the electrode sheet surface, providing a good flame-retardant effect and effectively improving the battery's safety performance. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 is a schematic diagram of the negative electrode sheet provided in Embodiment 1 of this application;

[0025] Figure 2 is a schematic diagram of the structure of a positive electrode sheet according to a specific embodiment of this application;

[0026] 1. Current collector; 2. Main body area; 3. Thinned area; 4. Flame retardant layer; 5. Ceramic layer. Detailed Implementation

[0027] The following will clearly and completely describe the concept and technical effects of this application in conjunction with embodiments, so as to fully understand the purpose, features and effects of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the scope of protection of this application.

[0028] The embodiments of this application are described in detail below. The described embodiments are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0029] In the description of this application, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0030] In the description of this application, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0031] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0032] Existing lithium / sodium-ion batteries suffer from thermal runaway safety issues. Once thermal runaway occurs, it can lead to fires or even explosions, seriously threatening people's lives and property. Current technologies often address this by incorporating flame-retardant materials into the positive or negative electrode materials. However, while these flame-retardant materials improve battery safety, they often sacrifice the battery's volumetric energy density, making it difficult to achieve a balance between the two. Furthermore, the temperature at the electrode tabs is relatively high during battery use, making it a potential starting point for thermal runaway, and traditional safety measures are insufficiently targeted at the electrode tabs.

[0033] In a typical embodiment of this application, a secondary battery is provided, including an electrode. The electrode includes a current collector and an active material layer disposed on at least one side of the current collector. The active material layer includes:

[0034] Main area;

[0035] A thinning zone is located at the outer edge of the main body area, and a flame-retardant layer containing flame-retardant material is provided between the thinning zone and the current collector.

[0036] This application incorporates a flame-retardant layer containing flame-retardant material between the thinned area and the current collector. When the battery temperature is too high, the flame retardant can absorb heat and reduce the battery temperature. Simultaneously, the resulting thermal decomposition products adhere to the electrode surface, providing excellent flame retardancy and effectively improving the battery's safety performance.

[0037] In some embodiments, the total thickness of the thinned region and the flame-retardant layer is substantially the same as the thickness of the main body region. By controlling the total thickness of the thinned region and the flame-retardant layer to be substantially the same as the thickness of the main body region, the spare space in the thinned region can be utilized without increasing the electrode thickness or creating new spare space in the thickness direction. This appropriately thick flame-retardant layer can improve the interfacial contact of the thinned region and reduce internal resistance, thereby improving electrochemical kinetics and thus increasing the first-cycle coulombic efficiency and cycle capacity retention. While maintaining a high volumetric energy density, it significantly improves the safety performance of the battery. Especially at the relatively high-temperature tabs, it can promptly exert a flame-retardant effect, preventing thermal runaway from spreading from the tabs, further improving battery safety, and simultaneously improving the electrochemical kinetics of the electrode thinning region.

[0038] In this application, "the total thickness of the thinned area and the flame-retardant layer is substantially the same as the thickness of the main body area" means that the difference between the total thickness of the thinned area and the flame-retardant layer and the thickness of the main body area is within ±5% of the thickness of the main body area.

[0039] In some alternative embodiments, the flame-retardant material includes flame-retardant particles and a conductive layer distributed on at least a portion of the surface of the flame-retardant particles. This structure forms a core-shell-like structure, with the conductive layer as the outer layer and the flame-retardant particles as the core. This arrangement can improve the conductivity of the flame-retardant particles and reduce the electrode resistance.

[0040] In some optional embodiments, the thickness of the conductive layer is 2-20 nm, and the conductive layer accounts for 1%-10% of the mass of the flame-retardant particles. A thickness and mass percentage of the conductive layer within these ranges can better improve electron conduction velocity, reduce the internal resistance of the flame-retardant layer, and improve the electrochemical kinetics of the thinned region. For example, the thickness of the conductive layer is 2 nm, 5 nm, 10 nm, or 20 nm, and the mass percentage of the conductive layer in the flame-retardant particles is 1%, 3%, 5%, 8%, or 10%, respectively. The thickness of the conductive layer is obtained by testing the flame-retardant material using transmission electron microscopy.

[0041] In some optional embodiments, the flame-retardant particles have a Dv10 of 50-150 nm, a Dv50 of 100-500 nm, and a Dv99 of 300-900 nm. Nanoscale flame-retardant particles are more sensitive to temperature, and the Dv10, Dv50, and Dv99 of the flame-retardant particles within the aforementioned ranges result in shorter flame-retardant reaction times, better coverage of endothermic and thermal decomposition products, and thus better flame-retardant effects. For example, the flame-retardant particles have Dv10 of 50 nm, 80 nm, 140 nm, and 150 nm, Dv50 of 100 nm, 210 nm, 400 nm, and 500 nm, and Dv99 of 300 nm, 600 nm, and 900 nm.

[0042] In some alternative embodiments, the conductive layer comprises one or more of conductive carbon black, graphene, carbon nanotubes, and conductive polymers. The materials of the conductive layer can improve the conductivity of the flame-retardant particles and enhance the electrochemical performance of the electrode thinning region. The conductive polymer includes at least one of polyethylene, polythiophene, and polyaniline.

[0043] In some optional embodiments, the flame-retardant particles include one or more of polyphosphazene particles, ammonium polyphosphate particles, phosphate particles, red phosphorus particles, and organophosphorus particles. The phosphates include at least one of zirconium phosphate, calcium phosphate, and zinc phosphate; the organophosphorus particles include at least one of guanidine phosphonate, phosphate esters, and phosphites. The phosphate esters include at least one of tricresyl phosphate (TCP), triphenyl phosphate (TPP), resorcinol bis(diphenyl phosphate) (RDP), and bisphenol A bis(diphenyl phosphate) (BDP). These flame-retardant particles play a crucial flame-retardant role when the battery is about to experience thermal runaway, inhibiting heat diffusion and preventing battery fire by absorbing heat, cooling, and forming thermal decomposition products that adhere to the electrode surface.

[0044] In some optional embodiments, the flame-retardant layer further includes 1%-5% of a binder. The aforementioned percentage of binder strengthens the contact between the flame-retardant layer and the current collector, preventing the flame-retardant layer from detaching during battery use and reducing powder shedding and poor contact in the thinned area. For example, the flame-retardant layer may further include 1%, 3%, or 5% of a binder. The binder may include at least one of polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR).

[0045] In some optional embodiments, the thickness of the flame-retardant layer on the side away from the main body region of the active material layer is greater than the thickness on the side closer to the main body region. That is, the thickness of the flame-retardant layer on the side closer to the tab is greater than the thickness on the side farther from the tab. This can further improve the flame-retardant effect.

[0046] In some optional embodiments, the minimum single-sided thickness of the active material layer thinning region is 40-53 μm, the maximum single-sided thickness is 59-70 μm, and the width is 5-15 mm. For example, the minimum single-sided thickness of the active material layer thinning region is 40 μm, 45 μm, 50 μm, and 53 μm, the maximum single-sided thickness is 59 μm, 60 μm, 65 μm, and 70 μm, and the width is 5 mm, 10 mm, and 15 mm. Controlling the minimum single-sided thickness, maximum single-sided thickness, and width of the active material layer thinning region within the above range provides usable space for coating the flame-retardant layer in the thinned region without reducing the amount of active material, thus enabling the battery to maintain a high volumetric energy density.

[0047] In some optional embodiments, the minimum single-sided thickness of the flame-retardant layer is 1-5 μm, the maximum single-sided thickness is 10-20 μm, and the width is 5-15 mm. For example, the minimum single-sided thickness of the flame-retardant layer is 1 μm, 3 μm, or 5 μm, the maximum single-sided thickness is 10 μm, 15 μm, or 20 μm, and the width is 5 mm, 10 mm, or 15 mm. Controlling the minimum single-sided thickness, maximum single-sided thickness, and width of the flame-retardant layer within the above range provides usable space for coating the flame-retardant layer in the thinned area without reducing the amount of active material, thus enabling the battery to maintain a high volumetric energy density.

[0048] In some alternative embodiments, the electrode includes a positive electrode or a negative electrode. When the electrode is a positive electrode, the flame-retardant layer 4 is located on the side away from the current collector and at the outer edge of the active material layer thinning area, and a ceramic layer 5 is disposed thereon, as shown in Figure 2. The ceramic layer is disposed at the above position to prevent burrs on the edge of the electrode from scratching and to provide heat insulation.

[0049] According to two aspects of this application, this application also provides an electrical device including the secondary battery described in any of the foregoing claims, wherein the secondary battery serves as a power supply for the electrical device. The secondary battery of this application includes, but is not limited to, lithium-ion secondary batteries and sodium-ion secondary batteries.

[0050] Electrical equipment refers to any device that can utilize electrical energy and convert it into mechanical energy, heat energy, light energy, or one or more other forms of energy, such as electric motors, electric heaters, and electric light sources. Specifically, it can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, and energy storage systems. Mobile devices can include mobile phones, laptops, drones, robot vacuum cleaners, and e-cigarettes; electric vehicles can include pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks.

[0051] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application.

[0052] Example 1

[0053] This embodiment provides a secondary battery, the preparation method of which is as follows:

[0054] A. Preparation of the negative electrode sheet:

[0055] (1) Preparation of flame retardant slurry

[0056] Flame-retardant particles (polyphosphazene, particle size parameters shown in Table 1) were dispersed in N-methylpyrrolidone to form a 10 wt% polyphosphazene nanoparticle suspension. A conductive agent (conductive carbon black) was added to the polyphosphazene suspension and stirred until homogeneous, forming a mixture with a conductive layer coating the flame-retardant particles. The mass of the conductive carbon black was 5% of the mass of the polyphosphazene nanoparticles. A binder, polyvinylidene fluoride (PVDF), was added to the mixture, and stirring was continued until homogeneous to obtain a flame-retardant slurry. The mass of the binder was 3% of the total mass of the conductive agent and flame-retardant particles.

[0057] (2) Preparation of flame retardant layer

[0058] The flame-retardant slurry obtained in step (1) is applied to the edge area along the length of the current collector (copper foil), and after drying, a current collector containing a flame-retardant layer is formed.

[0059] (3) Preparation of active material layer slurry

[0060] The negative electrode active material graphite, conductive agent (conductive carbon black) and binder (styrene-butadiene rubber SBR) are dispersed in deionized water at a mass ratio of 94:3:3 and mixed evenly to obtain an active material layer slurry.

[0061] (4) Preparation of negative electrode sheet

[0062] The active material layer slurry obtained in step (3) is coated onto the current collector containing the flame retardant layer obtained in step (2), forming an active material layer containing a main area and a thinned area on the current collector. After drying, a negative electrode sheet is obtained. In the negative electrode sheet, the thinned area of ​​the active material layer is coated on the flame retardant layer and located at the outer edge of the main area, so that the thickness of the flame retardant layer and the thinned area is the same as the thickness of the main body of the active material layer.

[0063] The negative electrode sheet of this embodiment is shown in Figure 1, including a current collector 1 and active material layers disposed on both sides of the current collector 1. The active material layer includes a thinned region 3 and a main body region 2. A flame-retardant layer 4 is disposed between the thinned region 3 and the current collector 1. Two flame-retardant layers 4 are disposed, symmetrically arranged along a central axis parallel to the length direction of the current collector 1. The thickness of the flame-retardant layer gradually decreases from the side furthest from the main body region towards the side closer to the main body region. The thickness of the flame-retardant layer abutting the main body region is the minimum single-sided thickness, denoted as H1; the thickness of the flame-retardant layer furthest from the main body region is the maximum thickness, denoted as H2; the width of the flame-retardant layer on one side is denoted as W1. Two thinned regions 3 are disposed, symmetrically arranged along a central axis parallel to the length direction of the current collector. The thickness of the thinned regions 3 gradually increases from the side furthest from the main body region 2 towards the side closer to the main body region 2. The thickness of the thinning zone furthest from the main body area is the minimum thickness, denoted as H3; the thickness of the thinning zone that abuts the main body area is the maximum thickness, denoted as H4; the width of a single thinning zone is denoted as W2, and the thickness of the main body area is denoted as H5. Specific parameters are shown in Table 1.

[0064] B. Preparation of the positive electrode sheet

[0065] The positive electrode active material LiFePO4, conductive agent carbon nanotubes, and binder PVDF were dispersed in NMP solvent at a mass ratio of 96:2:2 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto a positive electrode current collector aluminum foil, and after baking, cold pressing, and cutting, a positive electrode sheet was obtained.

[0066] C. Preparation of electrolyte

[0067] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed uniformly in a mass ratio of 1:1:1 to obtain an organic solvent. LiPF6 was dissolved in the above organic solvent and mixed uniformly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage content of LiPF6 was 13%.

[0068] D. Preparation of secondary batteries

[0069] The above-mentioned positive electrode sheet, PP / PE / PP composite separator and negative electrode sheet are stacked in sequence and wound to obtain a cell assembly. The cell assembly is placed in an aluminum shell for welding and baking. After adding the above-mentioned electrolyte, it is sealed to complete the battery preparation.

[0070] Examples 2-3

[0071] The preparation process is basically the same as in Example 1. The difference is that the type of flame-retardant particles in step (1) of the negative electrode preparation process is adjusted to prepare a negative electrode containing flame-retardant materials with different flame-retardant particles.

[0072] Examples 4-5

[0073] The preparation process is basically the same as in Example 1. The difference is that the type of conductive agent in step (1) of the negative electrode preparation process is adjusted to prepare a negative electrode containing flame-retardant materials with different conductive layers.

[0074] Examples 6-7

[0075] The preparation process is basically the same as in Example 1. The difference is that the amount of conductive agent in step (1) of the negative electrode preparation process is adjusted to prepare negative electrode sheets with different conductive layer ratios (i.e., the mass percentage of the conductive layer to the flame retardant particles).

[0076] Examples 8-9

[0077] The preparation process is basically the same as in Example 1. The difference is that different flame-retardant particles with different particle size parameters are used in step (1) of the negative electrode preparation process to obtain different negative electrode sheets.

[0078] Examples 10-11

[0079] The preparation process is basically the same as in Example 1. The difference is that the amount of binder in step (1) of the negative electrode preparation process is adjusted to prepare negative electrode sheets with different binder ratios (i.e., the mass percentage of the binder in the flame retardant layer).

[0080] Examples 12-13

[0081] The preparation process is basically the same as in Example 1. The difference is that the width of the flame retardant layer and the active material layer thinning area in steps (1) and (2) of the negative electrode sheet is adjusted to obtain negative electrode sheets with different characteristics.

[0082] Examples 14-17

[0083] The preparation process is basically the same as in Example 1. The difference is that the corresponding structures of the gaskets of the flame retardant layer and active material layer coating equipment in steps (1) and (2) of the negative electrode preparation process are adjusted to prepare negative electrode sheets with different thicknesses of flame retardant layer and active material layer thinning area.

[0084] Comparative Example 1

[0085] The preparation process is basically the same as in Example 1, except that the negative electrode sheet is not coated with a flame retardant layer.

[0086] Comparative Example 2

[0087] The preparation process is basically the same as in Example 1. The difference is that in step (4) of preparing the negative electrode sheet, the active material layer slurry is coated between the two flame retardant layers, and the thinned area of ​​the prepared negative electrode sheet is adjacent to the flame retardant layer, rather than on the flame retardant layer. Specific parameters are shown in Table 1.

[0088] Performance testing

[0089] 1. Energy density

[0090] At 25°C, the battery was charged to 3.65V at a rate of 0.33C, and then discharged to 2.0V at a rate of 0.33C. The discharge energy was recorded, and the mass energy density of the battery was obtained by dividing the discharge energy by the mass energy of the battery.

[0091] 2. Initial charge / discharge efficiency

[0092] The newly assembled battery was charged to 3.25V at 0.2C at 45℃, then charged to 3.65V at 0.33C at 25℃. The total charging capacity was recorded. Finally, the battery was discharged to 2.0V at 0.33C at 25℃, and the discharge capacity was recorded. The first charge-discharge efficiency was obtained by dividing the total charging capacity by the discharge capacity.

[0093] 3. Cyclic performance testing

[0094] At 25°C, the battery was charged at a rate of 1C to 3.65V, and then discharged at a rate of 1C to 2.0V. The discharge capacity of each cycle was recorded. After 300 cycles, the ratio of the discharge capacity of the 300th cycle to the discharge capacity of the first cycle was calculated to obtain the capacity retention rate after 300 cycles.

[0095] 4. Flame retardant properties

[0096] A fully charged battery is heated from 25°C to 180°C at a rate of 5°C / min and held for 30 minutes. The battery's state is recorded. Batteries that catch fire have poor flame retardant performance. Batteries that do not catch fire but have an open explosion-proof valve have average flame retardant performance. Batteries that do not catch fire and have an closed explosion-proof valve have good flame retardant performance.

[0097] 5. Needle prick test

[0098] Insert a 3mm diameter steel needle into the center of the large surface of a fully charged battery at a 45° angle and a speed of 25mm / s. Observe for 1 hour. If the battery does not catch fire or explode, it passes the needle penetration test. If the battery catches fire or explodes, it fails the needle penetration test.

[0099] 6. Thermal diffusion test

[0100] Three batteries are connected in series to form a simple module, with 1mm thick U-shaped frames separating the batteries. In a sealed box at room temperature, a 1000W heating element is used to trigger thermal runaway of the first battery on the left. The thermal runaway of adjacent batteries is recorded. If adjacent batteries do not catch fire or explode, the thermal runaway test is passed. If adjacent batteries catch fire or explode, the thermal runaway test is not passed.

[0101] Table 1

[0102] Table 2

[0103] The test results show that the battery prepared using the electrode structure of this application has high energy density, high charge and discharge efficiency, high cycle performance, and high safety performance.

[0104] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A secondary battery, wherein, The electrode includes a current collector and an active material layer disposed on at least one side of the current collector, the active material layer comprising: Main area; A thinning zone is located at the outer edge of the main body area, and a flame-retardant layer containing flame-retardant material is provided between the thinning zone and the current collector.

2. The secondary battery according to claim 1, wherein, The flame-retardant material includes flame-retardant particles and a conductive layer distributed on at least a portion of the surface of the flame-retardant particles.

3. The secondary battery according to claim 2, wherein, The thickness of the conductive layer is 2-20 nm, and the conductive layer accounts for 1%-10% of the mass of the flame-retardant particles.

4. The secondary battery according to claim 2, wherein, The flame-retardant particles have a Dv10 of 50-150nm, a Dv50 of 100-500nm, and a Dv99 of 300-900nm.

5. The secondary battery according to claim 2, wherein, The flame-retardant material meets at least one of the following conditions: (1) The conductive layer comprises one or more of conductive carbon black, graphene, carbon nanotubes and conductive polymers; (2) The flame-retardant particles include one or more of polyphosphazene particles, ammonium polyphosphate particles, phosphate particles, red phosphorus particles and organic phosphorus particles.

6. The secondary battery according to claim 1, wherein, The flame-retardant layer also includes 1%-5% adhesive.

7. The secondary battery according to claim 1, wherein, The thickness of the flame-retardant layer on the side away from the main body area is greater than the thickness on the side closer to the main body area.

8. The secondary battery according to claim 7, wherein, The minimum single-sided thickness of the thinning zone is 40-53 μm, the maximum single-sided thickness is 59-70 μm, and the width is 5-15 mm.

9. The secondary battery according to claim 7, wherein, The minimum single-sided thickness of the flame-retardant layer is 1-5μm, the maximum single-sided thickness is 10-20μm, and the width is 5-15mm.

10. The secondary battery according to any one of claims 1-9, wherein, The total thickness of the thinned area and the flame-retardant layer is basically the same as the thickness of the main body area.

11. An electrical appliance, wherein, The device includes the secondary battery as described in any one of claims 1-10, wherein the secondary battery serves as the power supply for the electrical equipment.

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