battery

Abstract

The application provides a battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator in a laminated and wound arrangement. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer disposed thereon, the negative electrode active layer comprising a silicon-based material. The positive electrode sheet comprises a single-side coated region and a double-side coated region, the single-side coated region being disposed close to a tail portion of the positive electrode sheet. The single-side coated region is provided with a positive electrode active layer on one side surface close to a winding center of the wound electrode body, and at least part of the single-side coated region is located in an outermost turn of the wound electrode body. The positive electrode active layer of the single-side coated region located in the outermost turn of the wound electrode body is provided with a functional coating away from at least part of an area on a surface of the positive electrode current collector, the functional coating comprising flame-retardant particles. The electrolyte comprises a carboxylic ester compound and a cyclic carbonate compound, the mass percentage content of the carboxylic ester compound being a, and the mass percentage content of the cyclic carbonate compound being b, wherein a and b satisfy: 0.5≤a / b≤10.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a battery. Background Technology

[0002] To meet market demands, lithium-ion batteries are constantly striving for higher capacity and energy density. Based on this, silicon-based materials, with their superior theoretical specific capacity, have become a research hotspot in anode materials.

[0003] However, silicon undergoes a volume expansion of up to 300% during lithium insertion / extraction. This massive volume change disrupts the stability of the solid electrolyte interface (SEI) on the negative electrode surface. During battery hot-box testing, the unstable decomposition of the SEI film leads to increased heat and gas generation within the cell, causing cell bulging and deformation, as well as deformation of the separator corresponding to the single-sided coating area of ​​the outermost positive electrode. This increases the risk of contact between the single-sided coating area of ​​the outermost positive electrode and the negative electrode. Furthermore, the separator corresponding to the single-sided coating area of ​​the outermost positive electrode is the first to come into contact with the high-temperature environment during hot-box testing, making it more prone to shrinkage and short circuits at the positive and negative electrode contact points. This exacerbates thermal runaway problems such as battery explosions and combustion. Therefore, effectively improving the hot-box safety performance while maintaining good electrochemical performance has become a core challenge driving the large-scale commercial application of silicon-based anodes.

[0004] In related technologies, there is a limited ability to pass the thermal test of batteries. Summary of the Invention

[0005] In view of this, embodiments of this application provide a battery to solve the problem of limited pass rate in hot box tests of batteries in related technologies.

[0006] In a first aspect, embodiments of this application provide a battery comprising: a positive electrode, a negative electrode, an electrolyte, and a separator arranged in a stacked and wound configuration. The positive and negative electrode are wound together with the separator to form a wound electrode body having a flat portion and a curved portion. The negative electrode includes a negative current collector and a negative active layer disposed on the negative current collector, the negative active layer comprising a silicon-based material. The positive electrode includes a positive current collector and a positive active layer disposed on the positive current collector, the positive electrode including a single-sided coating region and a double-sided coating region, the single-sided coating region being disposed near the tail of the positive electrode. The positive active layer is disposed on one side surface of the single-sided coating region near the winding center of the wound electrode body, at least a portion of the single-sided coating region being located at the outermost edge of the wound electrode body. At least a portion of the surface of the positive active layer of the single-sided coating region located at the outermost edge of the wound electrode body away from the positive current collector is provided with a functional coating, the functional coating comprising flame-retardant particles. The electrolyte comprises carboxylic acid esters and cyclic carbonates, with the mass percentage of carboxylic acid esters being 'a' and the mass percentage of cyclic carbonates being 'b', wherein 'a' and 'b' satisfy the condition: 0.5 ≤ a / b ≤ 10.

[0007] In conjunction with the first aspect above, in one possible implementation, a and b satisfy: 1≤a / b≤8; and / or, a is 5%~70% and b is 5%~50%.

[0008] In conjunction with the first aspect above, in one possible embodiment, the carboxylic acid ester compound includes one or more of ethyl propionate, propyl propionate, propyl acetate, isopropyl acetate, ethyl acetate, ethyl butyrate, methyl propionate, methyl formate, 2,2-difluoroethyl acetate, and ethyl 2,2-difluoroethyl acetate; and / or, the cyclic carbonate compound includes one or more of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and difluoroethylene carbonate (DFEC).

[0009] In conjunction with the first aspect described above, in one possible embodiment, the diaphragm comprises a porous base membrane and a polymer adhesive layer disposed on at least one surface thereon. The surface of the polymer adhesive layer forms a plurality of pore structures, the area ratio A of the pore structures in the unit area of ​​the polymer adhesive layer being 10% to 90%, preferably 30% to 70%; and / or, the porous base membrane comprises at least one of polyethylene and polypropylene; and / or, the polymer adhesive layer comprises at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), poly(p-phenylene terephthalamide) (PPTA), polyimide (PI), and poly(p-phenylenebenzodioxazole) (PBO).

[0010] In conjunction with the first aspect above, in one possible implementation, the thickness h1 of the porous base membrane is 3 μm to 15 μm, preferably 4 μm to 11 μm; and / or, the porosity K of the porous base membrane is 30% to 65%, preferably 35% to 55%; and / or, the thickness h2 of the polymer adhesive layer is 0.5 μm to 5 μm, preferably 1 μm to 4 μm.

[0011] In conjunction with the first aspect above, in one possible implementation, the flame-retardant particles comprise at least one of inorganic or organic flame-retardant materials; further, the inorganic flame-retardant material comprises one or more of aluminum hydroxide, magnesium hydroxide, boron nitride, zinc borate, barium metaborate, antimony trioxide, silicon dioxide, layered silicates, alumina, borosilicate, aluminum phosphate, and zirconium phosphate; and / or, the organic flame-retardant material comprises one or more of melamine, melamine cyanurate, melamine polyphosphate, and ammonium polyphosphate.

[0012] In conjunction with the first aspect above, in one possible embodiment, the median particle size Dv50 of the flame-retardant particles is 0.01 μm to 3 μm; and / or, the functional coating further includes a binder, which further includes one or more of homopolymer polyvinylidene fluoride (PVDF), modified polyvinylidene fluoride, polyimide (PI), polyamide-imide (PAI), styrene-butadiene rubber (SBR), modified styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, potassium carboxymethyl cellulose, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polyvinyl alcohol, polyacrylonitrile, polyacrylamide, polyacrylic acid-acrylonitrile copolymer and its derivatives, acrylic acid-acrylamide and its derivatives, acrylic acid-acrylate copolymer, acrylic acid-acrylonitrile-acrylamide copolymer, polymethacrylate and styrene-acrylic emulsion; and / or, the swelling degree B of the binder in the electrolyte is <50%, preferably, B <30%.

[0013] In conjunction with the first aspect above, in one possible implementation, the peel strength between the functional coating of the single-sided coating area of ​​the positive electrode and the separator is Fc1, and the peel strength between the separator and the negative electrode is Fa. Fc1 and Fa satisfy: Fc1 < Fa. Preferably, Fc1 and Fa satisfy: 1 ​​< Fa / Fc1 ≤ 8. Further, Fa is 8 N / m to 40 N / m. Preferably, Fa is 15 N / m to 35 N / m. And / or, Fc1 is 4 N / m to 25 N / m. Preferably, Fc1 is 6 N / m to 20 N / m. And / or, the peel strength between the positive active layer of the double-sided coating area of ​​the positive electrode and the separator is Fc2. Fc2 is 10 N / m to 30 N / m. Further, Fc1 and Fc2 satisfy: Fc1 < Fc2.

[0014] In conjunction with the first aspect described above, in one possible implementation, the thickness of the functional coating is h3. The single-sided coating area of ​​the positive electrode sheet has a first surface and a second surface disposed opposite to each other along the thickness direction of the positive electrode sheet. The first surface faces the winding center of the wound electrode body, and the second surface is away from the winding center of the wound electrode body. The functional coating is located on the first surface. The first surface of the single-sided coating area of ​​the positive electrode sheet with the functional coating has a plurality of recesses, and the second surface has protrusions corresponding to the recesses. The height D of each protrusion satisfies: 1 μm ≤ D ≤ 40 μm; the relationship between D and h3 satisfies: 0.08 ≤ D / h3 ≤ 60, preferably 0.2 ≤ D / h3 ≤ 40; and / or, h3 satisfies: 0.3 μm ≤ h3 ≤ 20 μm; and / or, the equivalent circle diameter S of the protrusion is defined as: 0.5 mm ≤ S ≤ 2 mm, preferably 1 mm ≤ S ≤ 2 mm; and / or, the center distance P between two adjacent protrusions satisfies: 1.2S ≤ P ≤ 4S.

[0015] In conjunction with the first aspect described above, in one possible implementation, the negative electrode sheet includes a negative electrode active layer, which comprises bulk silicon-carbon material. The number m of bulk silicon-carbon material with a length greater than 2 μm is 5 to 50 per 1000 μm², preferably 10 to 30 per 1000 μm²; and / or, the ratio C of the average thickness to the average length of the bulk silicon-carbon material is 0.05 to 0.3, preferably 0.1 to 0.2.

[0016] Secondly, embodiments of this application provide an electrical device that includes the battery in any of the above embodiments.

[0017] In hot-box testing, the enormous heat generated by a short circuit between the positive and negative electrodes is a key factor leading to battery thermal runaway. By applying a functional coating to the surface of the positive electrode, an additional functional coating separates the positive and negative electrodes when the separator contracts due to heat, thereby reducing the probability of a short circuit. Furthermore, in wound electrode bodies, the core may bulge and deform violently during hot-box testing, making it easier for a short circuit to occur between the core and the negative electrode. Applying a functional coating to the single-sided coating area of ​​the outermost positive electrode can improve the problem of poor furnace temperature pass rate during hot-box safety testing. However, the application of this functional coating increases the migration path of lithium ions and reduces the migration efficiency of lithium ions between the positive and negative electrodes. At the same time, the application of the functional coating on one side of the positive electrode will lead to poor electrolyte wettability of the positive electrode active layer in that area, resulting in a poorer lithium insertion / extraction rate of the positive electrode. Consequently, lithium ions inserted into the corresponding negative electrode area are not timely, leading to the problem of black spot lithium plating after battery cycling. Therefore, it is necessary to combine methods to improve lithium ion transport kinetics to improve the problem of localized black spot lithium plating in the battery.

[0018] According to the technical solution of this application, the electrolyte contains an appropriate proportion of low-viscosity carboxylic acid ester compounds, which can provide a strong penetration driving force, thereby improving the electrolyte wettability of the positive electrode's single-sided area, and thus improving the problem of slow lithium insertion / extraction rates and the resulting black spots on the negative electrode. Simultaneously, the inclusion of low-viscosity carboxylic acid ester compounds in the electrolyte reduces the migration resistance of lithium ions, lowers the ohmic internal resistance during charging and discharging, reduces battery heat generation, and makes it easier for the low-viscosity electrolyte to fill the micropores of the electrode, increasing the electrolyte-solid phase contact area. The electrolyte itself can act as a micro-convection medium, faster dissipating heat from localized hot spots on the electrode from the battery interior, which is beneficial for improving internal heat dissipation. This can improve the battery's furnace temperature performance while preventing the occurrence of localized black spots on the negative electrode. However, carboxylic acid esters have relatively poor chemical stability, low flash points, and are more volatile and flammable. Adding an appropriate proportion of cyclic carbonate compounds to the electrolyte offers better stability, high boiling and ignition points, and high dielectric constants. This allows for better dissociation of lithium salts, promoting the formation of a dense and stable SEI film on the silicon-based anode surface, ensuring battery cycle performance. Furthermore, cyclic carbonates can work synergistically with carboxylic acid esters to better balance furnace temperature performance and lithium insertion / extraction rates, thus improving the problem of black spot lithium plating after battery cycling. In addition, at higher temperatures, cyclic carbonates themselves decompose. The decomposition products of cyclic carbonates such as EC (electrodeionized aluminum carbonate) and CO2 can also act as a gas-phase flame retardant, improving the battery's thermal safety.

[0019] According to the technical solution of this application, the mass percentage of carboxylic acid ester compounds is 'a', and the mass percentage of cyclic carbonate compounds is 'b', where a and b satisfy: 0.5 ≤ a / b ≤ 10. Controlling the ratio of these two substances in the electrolyte within this range ensures a suitable proportion of low-viscosity carboxylic acid esters to provide strong penetration driving force, while a suitable proportion of cyclic carbonates maintains the necessary lithium salt dissociation and SEI film quality. This allows for better synergy between the two to improve furnace temperature performance and lithium insertion / extraction rates, thereby better guaranteeing battery cycle performance. If a / b is too small, it means the mass percentage of cyclic carbonates is too high or the mass percentage of carboxylic acid ester compounds is too low, resulting in a high electrolyte viscosity, making it difficult to fully wet the dense functional coating in a short time. This will cause the lithium insertion / extraction rate of the single-sided region of the positive electrode with the functional coating to lag behind that of the double-sided region, resulting in insufficient lithium ion insertion in the corresponding region of the negative electrode, forming black spots on the negative electrode. If the a / b ratio is too high, it means that the proportion of carboxylic acid esters or cyclic carbonates is too high. Although the wettability is excellent, insufficient cyclic carbonates will lead to a decrease in lithium-ion conductivity, which will affect the overall kinetics. On the other hand, more importantly, the stability of carboxylic acid ester organic compounds (such as PP and EP) in the electrolyte is generally lower than that of cyclic carbonates (such as EC) in the electrolyte. At high temperatures, carboxylic acid ester organic compounds are prone to oxidation and gas production, thereby reducing battery safety. Controlling the ratio of the two within the above-mentioned range can improve the safety of battery hot box testing while addressing the lithium plating problem. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of a wound electrode body according to an embodiment of this application.

[0021] Figure 2 for Figure 1 Schematic diagram of the cross-sectional structure along DD.

[0022] Figure 3 This is a schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application.

[0023] Figure 4 This is a partial structural schematic diagram of a positive electrode sheet according to an embodiment of this application.

[0024] Figure 5 This is a schematic diagram of the structure of a negative electrode sheet according to an embodiment of this application.

[0025] Figure 6 This is a schematic diagram of a battery structure according to an embodiment of this application.

[0026] Figure 7 This is another structural schematic diagram of a battery provided according to one embodiment of this application.

[0027] Figure 8 This is a scanning electron microscope (SEM) schematic diagram of a functional coating provided according to an embodiment of this application.

[0028] Figure label: 100. Battery; 10. Wound electrode body; 101. Flat portion; 102. Bending portion; 11. Positive electrode sheet; 111. Positive electrode current collector; 112. Positive electrode active layer; 113. Single-sided coating area; 113a. First surface; 113b. Second surface; 114. Double-sided coating area; 115. Functional coating; 116. Recess; 117. Protrusion; 12. Negative electrode sheet; 121. Negative electrode current collector; 122. Negative electrode active layer; 13. Separator. Detailed Implementation

[0029] Embodiments of this application provide a battery to address the problem of limited pass rate in hot box tests of batteries in related technologies.

[0030] The battery and electrical device according to embodiments of this application will now be described with reference to the accompanying drawings.

[0031] Exemplary battery refer to Figures 1 to 8 As shown, in a first aspect, embodiments of this application provide a battery 100, which includes: a positive electrode 11, a negative electrode 12, an electrolyte, and a separator 13 arranged in a stacked and wound manner. The negative electrode 12 includes a negative current collector 121 and a negative active layer 122 disposed on the negative current collector 121, the negative active layer 122 comprising a silicon-based material. The positive electrode 11 and the negative electrode 12 are wound together with the separator 13 to form a wound electrode body 10 having a flat portion 101 and a curved portion 102. The positive electrode 11 includes a positive current collector 111 and a positive active layer 112 disposed on the positive current collector 111, the positive electrode 11 including a single-sided coating region 113 and a double-sided coating region 114, the single-sided coating region 113 being disposed near the tail of the positive electrode 11. A positive electrode active layer 112 is disposed on the surface of the single-sided coating area 113 near the winding center of the wound electrode body 10, and at least a portion of the single-sided coating area 113 is located on the outermost ring of the wound electrode body 10. At least a portion of the surface of the positive electrode active layer 112 of the single-sided coating area 113 located on the outermost ring of the wound electrode body 10, away from the positive electrode current collector 111, is provided with a functional coating 115, which includes flame-retardant particles. The electrolyte includes carboxylic acid ester compounds and cyclic carbonate compounds, with the mass percentage of the carboxylic acid ester compounds being 'a' and the mass percentage of the cyclic carbonate compounds being 'b', wherein a and b satisfy: 0.5 ≤ a / b ≤ 10. For example, a / b is 0.8, 2, 3, 4, 5, 6, 7, 8, or 9.

[0032] According to the technical solution of this application, by providing a functional coating 115 on the surface of the positive electrode 11, when the separator 13 shrinks due to heat, there is another layer of functional coating 115 between the positive and negative electrodes to separate the positive electrode 11 and the negative electrode 12, thereby reducing the probability of internal short circuits. Moreover, during the hot box test of the wound electrode body 10, when the core bulges and deforms violently, internal short circuits are more likely to occur. Providing a functional coating 115 on the single coating area of ​​the outermost positive electrode can improve the problem of poor furnace temperature pass rate of the battery 100 in the hot box safety test.

[0033] However, the application of the functional coating 115 increases the migration path of lithium ions and reduces the migration efficiency of lithium ions between the positive and negative electrode sheets 12. At the same time, the application of the functional coating 115 on one side of the positive electrode sheet 11 will cause the electrolyte wettability of the positive electrode active layer 112 in that area to deteriorate, resulting in a lower lithium insertion / extraction rate of the positive electrode. This will cause the lithium ions inserted into the corresponding negative electrode area to be delayed, leading to the problem of black spot lithium plating after battery 100 cycles. Therefore, it is necessary to combine methods to improve the lithium ion transport kinetics to improve the problem of local black spot lithium plating in battery 100.

[0034] According to the technical solution of this application, the electrolyte contains an appropriate proportion of low-viscosity carboxylic acid ester compounds, which can provide a strong penetration driving force, thereby improving the electrolyte wettability of the positive electrode's single-sided area, and thus improving the problem of slow lithium insertion / extraction rates and the resulting black spots on the negative electrode. Simultaneously, the inclusion of low-viscosity carboxylic acid ester compounds in the electrolyte reduces the migration resistance of lithium ions, lowers the ohmic internal resistance during charging and discharging, and reduces heat generation in the battery 100. Furthermore, the low-viscosity electrolyte more easily fills the micropores of the electrode, increasing the electrolyte-solid phase contact area. The electrolyte itself can act as a micro-convection medium, more quickly removing heat from local hot spots on the electrode from the inside of the battery 100, which is beneficial for improving heat dissipation inside the battery 100. This can improve the furnace temperature performance of the battery 100 while preventing the local black spot problem on the negative electrode. However, carboxylic acid esters have relatively poor chemical stability, low flash points, and are more volatile and flammable. Adding an appropriate proportion of cyclic carbonate compounds to the electrolyte provides better stability, high boiling and ignition points, and high dielectric constants. This allows for better dissociation of lithium salts, promoting the formation of a dense and stable SEI film on the silicon-based negative electrode 12, ensuring the cycle performance of battery 100. Furthermore, cyclic carbonates can work synergistically with carboxylic acid esters to better balance furnace temperature performance and lithium insertion / extraction rates, thus improving the problem of black spot lithium plating after battery 100 cycling. In addition, at higher temperatures, cyclic carbonates themselves decompose. The decomposition products of cyclic carbonates such as EC (electrodeionized aluminum oxide) and CO2 can also act as a gas-phase flame retardant, improving the thermal safety of battery 100.

[0035] According to the technical solution of this application, the mass percentage of carboxylic acid ester compounds is 'a', and the mass percentage of cyclic carbonate compounds is 'b', where a and b satisfy: 0.5 ≤ a / b ≤ 10. Controlling the ratio of these two substances in the electrolyte within this range ensures a suitable proportion of low-viscosity carboxylic acid esters to provide strong penetration driving force, while a suitable proportion of cyclic carbonates maintains the necessary lithium salt dissociation and SEI film quality. This allows for better synergy between the two to improve furnace temperature performance and lithium insertion / extraction rates, thereby better guaranteeing the cycle performance of battery 100. If a / b is too small, it means the mass percentage of cyclic carbonates is too high or the mass percentage of carboxylic acid ester compounds is too low, resulting in a high electrolyte viscosity, making it difficult to fully wet the dense functional coating 115 in a short time. This will cause the lithium insertion / extraction rate of the positive electrode single-sided region with functional coating 115 to lag behind that of the double-sided region, resulting in insufficient lithium ion insertion in the corresponding negative electrode region, forming negative electrode black spots. If the a / b ratio is too high, it means that the proportion of carboxylic acid esters or cyclic carbonates is too high. Although the wettability is excellent, insufficient cyclic carbonates will lead to a decrease in lithium-ion conductivity, which will affect the overall kinetics. On the other hand, more importantly, the stability of carboxylic acid ester organic compounds (such as PP and EP) in the electrolyte is usually lower than that of cyclic carbonates (such as EC) in the electrolyte. At high temperatures, carboxylic acid ester organic compounds are prone to oxidation and gas production, thereby reducing the safety of Battery 100. Controlling the ratio of the two within the above range can improve the safety of Battery 100 hot box testing while addressing the lithium plating problem.

[0036] In some embodiments, a and b satisfy: 1 ​​≤ a / b ≤ 8, for example, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, or 7.5. In one example, a is 5% to 70%, for example, 7%, 10%, 20%, 30%, 40%, 50%, or 60%, and b is 5% to 50%, for example, 5%, 10%, 15%, 25%, 35%, or 45%.

[0037] This allows for better adjustment of the electrolyte viscosity while ensuring its stability. It ensures that the electrolyte contains an appropriate proportion of low-viscosity carboxylic acid ester organic compounds to provide strong penetration driving force, while also containing an appropriate proportion of cyclic carbonate compounds to maintain the necessary lithium salt dissociation degree and SEI film quality. This allows the two to work together to improve furnace temperature performance and lithium insertion / extraction efficiency, thereby reducing the risk of black spot lithium plating after 100 cycles of the battery.

[0038] It should be noted that, in this application, the method for testing the mass content of carboxylic acid esters and cyclic carbonates in the electrolyte can be as follows: the electrolyte sample in the battery is detected by gas chromatography-mass spectrometry (GS-MS), compared with the spectrum of the standard sample or searched in the mass spectrometry library, and then the content of the above electrolyte components is calculated by plotting a standard curve using the commonly used external standard method or internal standard method.

[0039] It is understood that the electrolyte may also contain other conventional components, such as linear carbonates, such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC), etc., as per conventional settings in the art, and will not be elaborated here.

[0040] In some embodiments, the carboxylic acid ester compounds include one or more of ethyl propionate, propyl propionate, propyl acetate, isopropyl acetate, ethyl acetate, ethyl butyrate, methyl propionate, methyl formate, 2,2-difluoroethyl acetate, and ethyl 2,2-difluoroethyl acetate.

[0041] It should be noted that when a carboxylic acid ester compound comprises multiple components, the content of different components can be set as needed, and this application does not impose any restrictions on this.

[0042] In some embodiments, the cyclic carbonate compounds include one or more of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and difluoroethylene carbonate (DFEC).

[0043] It should be noted that when cyclic carbonate compounds include multiple components, the content of different components can be set as needed, and this application does not impose any restrictions on this.

[0044] In some embodiments, the separator 13 includes a porous base membrane and a polymer adhesive layer disposed on at least one surface thereon. In one example, the polymer adhesive layer may be an oil-based adhesive layer, i.e., the polymer adhesive particles are dissolved by a non-aqueous organic solvent, such as N-methylpyrrolidone. Multiple pore structures are formed on the surface of the polymer adhesive layer. These pore structures not only provide rapid longitudinal permeation channels for the electrolyte, enhancing lithium-ion transport kinetics and mitigating the interfacial black spot problem caused by impaired lithium-ion insertion, but their pore wall structure also allows for strong physical anchoring with the electrode under hot-pressing conditions, thereby providing excellent peel strength. The area ratio A of the pore structure in the polymer adhesive layer per unit area is 10% to 90%, for example, 20%, 30%, 40%, 50%, 60%, 70%, or 80%.

[0045] By controlling the proportion of the pore structure within this range, sufficient mechanical strength can be provided while ensuring ionic conductivity. When A is below 10%, the adhesive layer is too dense, resulting in low liquid retention of the separator 13 in the later stages of battery 100 cycling, leading to localized liquid shortages and exacerbating localized lithium plating. When A is above 90%, the adhesive layer structure strength decreases, resulting in insufficient effective bonding area with the electrode, leading to reduced peel strength and increasing the lithium-ion transport distance between the positive and negative electrodes 12, which in turn increases the risk of black spot lithium plating in battery 100. Within the above range, an optimal balance between adhesion and wettability can be achieved.

[0046] Preferably, A is 30% to 70%, for example, 35%, 45%, 55% or 65%. Controlling the proportion of the pore structure within this range can better ensure ionic conductivity while providing sufficient bonding area to guarantee the adhesion performance between the electrode and the separator 13.

[0047] The method for testing the proportion of pore structures can be described below. Discharge battery 100 to 0% SOC, then disassemble battery 100 and remove separator 13. Using a scanning electron microscope (SEM), randomly select at least five fields of view at different locations on the surface of separator 13 to acquire images. Adjust the imaging voltage of the SEM to ensure sufficient contrast in the images to clearly distinguish the pore areas (dark areas) of the pore structure from the solid areas (bright areas) of the polymer adhesive layer. The statistical area of ​​a single field of view should be no less than 100 μm². Use image analysis software (e.g., ImageJ, NanoMeasurer, Matlab, etc.) to calculate the percentage of black pixels in the dark areas relative to the total number of pixels in the entire image. This percentage is the proportion of pore structures in that field of view.

[0048] In one example, the porous base membrane includes at least one of polyethylene and polypropylene. The porous base membrane in this application can be a dry-stretched or wet-stretched microporous membrane.

[0049] In one example, the polymer adhesive layer includes at least one of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), poly(p-phenylene terephthalamide) (PPTA), polyimide (PI), and poly(p-phenylenebenzodioxazole) (PBO).

[0050] Preferably, the separator 13 further includes ceramic particles, which can synergize with the flexibility of the polymer adhesive layer to balance toughness and stiffness, reducing the risk of the separator 13 being punctured. Furthermore, the ceramic particles can improve the heat resistance of the separator 13, thereby enhancing its thermal stability and preventing short circuits caused by separator 13 shrinkage, thus improving the furnace temperature performance of the battery 100. Then, the ceramic particles can adsorb the electrolyte, making the electrolyte distribution more uniform at the electrode and separator 13 interface, reducing interfacial impedance. The ceramic particles can be alumina (Al2O3), boehmite (AlOOH, hydrated alumina), silicon dioxide (SiO2), zirconium oxide (ZrO2), or barium titanate (BaTiO3), etc.

[0051] In some embodiments, the thickness h1 of the porous base film is 3 μm to 15 μm, for example, 4 μm, 6 μm, 8 μm, 12 μm, or 14 μm. This ensures the heat resistance of the separator 13 while shortening the lithium-ion transport path, reducing the thermal shrinkage rate of the separator 13 and the risk of puncture, thereby improving the electrical performance of the battery 100. Preferably, h1 is 4 μm to 11 μm, for example, 5 μm, 7 μm, or 9 μm, to better balance adhesion energy and porosity.

[0052] The porosity K of the porous membrane is 30% to 65%, for example, 40%, 45%, 55%, or 60%, to ensure electrolyte retention. Appropriate porosity ensures sufficient wetting and storage of the electrolyte, providing ample and continuous channels for ion transport between the positive and negative electrodes. Preferably, K is 35% to 55%, for example, 38%, 42%, 46%, or 52%, to better ensure electrolyte retention.

[0053] In one example, the thickness h2 of the polymer adhesive layer is 0.5 μm to 5 μm, for example, 0.8 μm, 1 μm, 2 μm, 3 μm or 4 μm, to ensure peel strength. Preferably, h2 is 1 μm to 4 μm, for example, 1.5 μm, 2.5 μm or 3.5 μm.

[0054] Within the aforementioned range, the thickness h2 of the polymer adhesive layer ensures the bonding stability between the positive electrode 11 and / or the negative electrode 12 and the separator 13, effectively shortening the lithium-ion transport path and reducing the risk of lithium plating. Excessive thickness of the polymer adhesive layer increases the ion migration path, while insufficient thickness reduces the adhesion between the positive electrode 11 and / or the negative electrode 12 and the separator 13, increasing the risk of lithium plating after 100 cycles.

[0055] In some embodiments, the functional coating 115 includes flame-retardant particles and a binder. The flame-retardant particles include at least one of inorganic or organic flame-retardant materials. The blending of the flame-retardant particles and the binder ensures stable bonding with the positive electrode active layer 112 of the single-sided coating area 113 of the positive electrode sheet 11, while also ensuring a firm bond with the separator 13 and preventing the formation of an ion-blocking layer. Furthermore, the flame-retardant particles can block heat transfer during furnace temperature testing of the battery 100, reducing the risk of fire and explosion and further improving the furnace temperature performance of the battery 100.

[0056] It should be noted that the content of each component in the functional coating 115 is set according to the conventional settings in the art. For example, the mass percentage of flame retardant particles in the functional coating 115 can be 5%-95%, which will not be elaborated here.

[0057] In one example, the inorganic flame retardant material includes one or more of aluminum hydroxide, magnesium hydroxide, boron nitride, zinc borate, barium metaborate, antimony trioxide, silicon dioxide, layered silicates, alumina, borosilicate, aluminum phosphate, and zirconium phosphate. In one example, the organic flame retardant material includes one or more of melamine, melamine cyanurate, melamine polyphosphate, and ammonium polyphosphate.

[0058] It should be noted that, in this application, flame-retardant materials do not only refer to flame-retardant materials in the traditional sense, but may also include materials that only have heat insulation functions.

[0059] It should be noted that, in this application, "flame-retardant particles" refers to materials added to the functional coating 115 on the positive electrode sheet that can absorb heat from the surface of the burning material through endothermic decomposition, release water vapor, decompose heat molecules, and form an insoluble oxide layer to inhibit the combustion reaction and reduce the local temperature; or, by releasing non-flammable inert gases to form a heat-insulating and oxygen-barrier protective layer; or, by expanding in volume after heating to form a porous carbon layer to isolate heat and oxygen transfer; or, by absorbing gases or liquids produced by combustion through physical adsorption; or, by promoting the reaction of negative oxygen ions during combustion; or, by blocking the heat conduction path, blocking the flame and heat spread, and reducing the heat transfer rate through heat insulation, thereby inhibiting or delaying the thermal runaway reaction of the battery during furnace temperature testing by exhibiting one or more of the above-mentioned flame-retardant effects at high temperatures.

[0060] Specifically, the flame-retardant particles include at least one of inorganic flame-retardant materials and organic flame-retardant materials. The inorganic flame-retardant materials include one or more of aluminum hydroxide, zinc borate, barium metaborate, antimony trioxide, borosilicate, aluminum phosphate, zirconium phosphate, silicon dioxide, layered silicates, magnesium oxide, magnesium hydroxide, aluminum oxide, silicon carbide, boron nitride, and aluminum titanate. The organic flame-retardant materials include melamine cyanurate (MCA), melamine phosphate (MP), melamine borate (MB), and ammonium polyphosphate (APP).

[0061] In some embodiments, flame-retardant particles such as aluminum hydroxide and magnesium hydroxide can absorb a large amount of heat through decomposition reactions, thereby reducing the local temperature of the battery and achieving flame-retardant function.

[0062] In some embodiments, melamine cyanurate (MCA), melamine phosphate (MP), melamine borate (MB), and ammonium polyphosphate (APP) can expand in volume upon heating to form a porous carbon layer, which isolates heat and oxygen transfer, thereby playing a flame-retardant role.

[0063] In other embodiments, materials such as silicon carbide, boron nitride, layered silicates, and magnesium oxide can be melted or sintered at high temperatures to form a dense ceramic layer, absorbing heat and releasing water vapor to block flames and the spread of heat.

[0064] The processes and specific mechanisms by which the flame-retardant particles exert their flame-retardant effect vary, and will not be listed one by one here. It should be noted that the types of flame-retardant particles are not limited to the above-mentioned substances. Any material with the above-mentioned mechanism can be used as the flame-retardant particles in this application.

[0065] In some embodiments, the median particle size Dv50 of the flame-retardant particles is 0.01 μm to 3 μm, for example, 0.01 μm, 0.012 μm, 0.015 μm, 0.018 μm, 0.022 μm, 0.03 μm, 0.05 μm, 0.15 μm, 0.3 μm, 0.5 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, or 2.5 μm. This ensures the formation of a uniform functional coating 115 that does not affect lithium-ion transport.

[0066] By controlling the Dv50 of the flame-retardant particles, a dense and uniform functional coating 115 without sharp, hard protrusions is ensured, thereby achieving efficient flame retardancy while guaranteeing the interface stability and cycle safety of the battery 100. If the Dv50 of the flame-retardant particles is too small, severe agglomeration occurs, making it difficult to deagglomerate using conventional dispersion methods. This results in an uneven functional coating 115, and after the battery 100 expands during cycling, the agglomerated flame-retardant particles have weak adhesion and are prone to detachment, becoming potential danger zones in the event of thermal runaway. Conversely, if the Dv50 is too large, single large particles or a few protruding particles can easily puncture the separator 13 after rolling, causing a short circuit. Furthermore, excessively large particles increase the porosity of the coating, reducing the flame-retardant effect. In this application, "median particle size" refers to the particle size value corresponding to 50% of the cumulative volume on the cumulative distribution curve from smallest to largest volume in the volume-based particle size distribution.

[0067] In this application, the particle size of the flame-retardant particles can be tested using laser particle size analysis, specifically according to GB / T 19077-2016 "Particle Size Analysis - Laser Diffraction Method". Of course, the method for testing the particle size of flame-retardant particles is not limited to this. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) can also be used to magnify the area on the positive electrode sheet with the functional coating 115 at high magnification (e.g., magnification to 30,000x to 100,000x) to obtain a high-resolution image of the flame-retardant particles. Then, image processing software can be used to test and statistically analyze the particle size of 50 to 100 flame-retardant particles, and the Dv50 of the flame-retardant particles can be calculated.

[0068] In one example, the binder includes one or more of the following: homopolymer polyvinylidene fluoride (PVDF), modified polyvinylidene fluoride, polyimide (PI), polyvinylidene fluoride-hexafluoropropylene copolymer, polyamide-imide (PAI), styrene-butadiene rubber (SBR), modified styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, potassium carboxymethyl cellulose, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polyvinyl alcohol, polyacrylonitrile, polyacrylamide, polyacrylic acid-acrylonitrile copolymer and its derivatives, acrylic acid-acrylamide and its derivatives, acrylic acid-acrylate copolymer, acrylic acid-acrylonitrile-acrylamide copolymer, polymethacrylate, and styrene-acrylic emulsion.

[0069] In one example, the swelling degree B of the binder in the functional coating 115 in the electrolyte is less than 50%, for example, 45%, 35%, 25%, 15%, 5%, or 1%. Preferably, B is less than 30%, for example, 28%, 23%, 19%, 14%, 7%, or 3%.

[0070] Thus, the low-swelling binder, upon contact with the electrolyte, can still effectively anchor the flame-retardant particles to the surface of the single-sided coating area 113 of the positive electrode 11. During hot pressing, it generates certain intermolecular forces or physical interlocking with the adhesive layer of the separator 13 (e.g., an oil-based separator 13), forming a stable integrated structure of "positive electrode 11 - functional coating 115 - separator 13". This structure ensures the uniformity of the interfacial current distribution, thereby fundamentally reducing the problem of black spot lithium plating on the negative electrode 12 corresponding to the area where the functional coating 115 is located on the single-sided coating area 113 of the positive electrode 11. Furthermore, due to the low swelling degree of the binder, it can maintain its original structure in the electrolyte and will not clog the gaps between the flame-retardant particles due to excessive expansion. These gaps are interconnected with the macroporous structure of the separator 13, forming a highly efficient lithium-ion transport channel, reducing ion transport resistance and the risk of lithium plating, while ensuring that the battery 100 has low internal resistance and excellent rate discharge performance.

[0071] The test method for the swelling degree of the binder in functional coating 115 can refer to the following steps.

[0072] 1. After discharging the battery to 0% SOC, disassemble the battery to obtain the positive electrode 11. Cut a 2 cm × 2 cm positive electrode 11 with a functional coating 115 on one side as the test sample. Soak it in dimethyl carbonate (DMC) for 24 h and dry it in an oven at 80 ℃ for 12 h to obtain the dried and separated test sample. Weigh the initial mass of each dried and separated test sample and record it as M0.

[0073] 2. Completely immerse the sample to be tested in a sealed container containing sufficient electrolyte. The electrolyte is prepared by dissolving LiPF6 in a 1:1 volume ratio of propyl propionate (PP) / ethylene carbonate (EC) solvent and adding 20 wt% fluoroethylene carbonate (FEC). The LiPF6 content in the electrolyte is 1 mol / L. Place the container in a constant temperature oven at 60℃±2℃ for 24 hours to accelerate the swelling equilibrium process.

[0074] 3. Remove the sample and wipe off the residual electrolyte on the surface of the sample with lint-free paper. Weigh the mass of the sample after swelling and record it as M1.

[0075] 4. Calculate the mass swelling rate: Mass swelling rate = (M1 - M0) / M0 × 100%.

[0076] If the binder powder in the functional coating is available, the swelling degree of the binder in the functional coating can be tested by following the steps below.

[0077] Step 1: Place the adhesive powder to be tested in a mold and prepare a dense and flat film by hot pressing. Cut at least three standard-sized circular or square samples from the prepared film and record their initial dimensions (thickness, diameter, etc.).

[0078] Step 2: Weigh the initial mass of each dried sample and record it as M0. Measure the density of the dried sample using a density gradient column or a gas displacement densitometer (e.g., Archimedes' principle) and record it as ρ0. From this, the initial volume of the sample, V0 = M0 / ρ0, can be calculated.

[0079] Step 3: Completely immerse the sample in a sealed container containing sufficient electrolyte. This electrolyte should have the same composition as the electrolyte used in the battery. For example, the electrolyte could be LiPF6 dissolved in a 1:1 volume ratio of propyl propionate (PP) / ethylene carbonate (EC) solvent, with the addition of 20 wt% fluoroethylene carbonate (FEC). The LiPF6 content in the electrolyte should be 1 mol / L. Place the container in a constant temperature oven at 60℃±2℃ for 24 hours to accelerate the swelling equilibrium process. Afterward, remove the sample, remove any residual electrolyte, and immediately weigh it after swelling, recording this as M1. Then, immediately place the sample into a density bottle containing a known volume of inert solvent (a solvent that dissolves the electrolyte but does not swell the binder, such as n-hexane, used for oil-based binders). Measure the volume V1 of the swollen sample by the increase in volume.

[0080] Step 4, calculate the degree of swelling. Mass swelling = (M1-M0) / M0×100%; Volume swelling rate = (V1-V0) / V0×100%.

[0081] In some embodiments, the peel strength between the functional coating 115 of the single-sided coating area 113 of the positive electrode 11 and the separator 13 is Fc1, and the peel strength between the separator 13 and the negative electrode is Fa, wherein Fc1 and Fa satisfy: Fc1 < Fa. Preferably, Fc1 and Fa satisfy: 1 ​​< Fa / Fc1 ≤ 8, for example 1.5, 2, 3, 4, 6 or 7.

[0082] During the charging and discharging process of battery 100, the positive and negative electrode materials will expand and contract to different degrees, with the silicon-based material of the negative electrode expanding more dramatically. The peel strength Fa between the separator 13 and the negative electrode sheet 12 is set to be relatively high. Simultaneously, Fc1 < Fa, when battery 100 expands, the relatively small adhesive force between the functional coating 115 of the single-sided coating area 113 of the positive electrode sheet 11 and the separator 13 allows for slight slippage of this area relative to the separator 13. This reduces the risk of excessive shear or compressive forces on the functional coating 115 of the single-sided coating area 113 of the positive electrode when the negative electrode expands excessively, thereby increasing the risk of the functional coating 115 detaching and improving the thermal safety of battery 100.

[0083] In one example, Fa is 8 N / m to 40 N / m, for example, 10 N / m, 15 N / m, 20 N / m, 30 N / m or 35 N / m. Preferably, Fa is 15 N / m to 35 N / m, for example, 18 N / m, 21 N / m, 25 N / m, 28 N / m or 33 N / m.

[0084] In one example, Fc1 is 4 N / m to 25 N / m, for example, 5 N / m, 8 N / m, 10 N / m, 15 N / m or 20 N / m. Preferably, Fc1 is 6 N / m to 20 N / m, for example, 7 N / m, 9 N / m, 11 N / m, 14 N / m or 17 N / m.

[0085] In one example, the peel strength between the positive electrode active layer 112 and the separator 13 in the double-sided coating region 114 of the positive electrode 11 is Fc2, where Fc2 is 10 N / m to 30 N / m, for example, 12 N / m, 14 N / m, 18 N / m, 20 N / m, 24 N / m, or 28 N / m. In one example, Fc1 and Fc2 satisfy: Fc1 ≤ Fc2. Preferably, Fc1 < Fc2.

[0086] Thus, the peel strength Fc1 between the functional coating 115 on the single-sided coating area 113 and the separator 13 is less than the peel strength Fc2 between the positive active layer 112 and the separator 13 on the double-sided coating area 114 of the positive electrode 11. On the one hand, this ensures that the ion transport path between the double-sided coating area 114 of the positive electrode 11, the separator 13, and the negative electrode 12 is as small as possible, thus maximizing the capacity of the battery 100. On the other hand, during lithium intercalation and expansion of the negative electrode, the expansion force is transmitted layer by layer. When the peel strength between the double-sided coating area 114 of the positive electrode 11 and the separator 13 is high, it can resist expansion stress, absorb some of the expansion stress transmitted inside the cell, and act as a buffer to dissipate stress. Meanwhile, the peel strength Fc1 between the functional coating 115 on the single-sided coating area 113 and the separator 13 is relatively low. When the remaining stress is transferred to the functional coating 115 on the single-sided coating area 113 of the positive electrode 11, where the peel strength is weakest, it can reduce the additional internal stress generated by the mechanical constraint of the separator 13 on the functional coating 115 on the single-sided coating area 113 of the positive electrode 11. Moreover, the low peel strength at this interface allows for a certain degree of controllable micro-slippage, preventing the internal stress from being superimposed on the expansion stress of the battery 100 and increasing the risk of the functional coating 115 falling off. In addition, the micro-slippage between the functional coating 115 on the single-sided coating area 113 of the positive electrode 11 and the separator 13 forms a microspace. This microspace is beneficial for storing electrolyte and reduces the risk of black spot lithium plating on the negative electrode corresponding to the positive electrode single-sided coating area 113 with the functional coating 115.

[0087] In some embodiments, the thickness of the functional coating 115 is h3. The single-sided coating area 113 of the positive electrode 11 has a first surface 113a and a second surface 113b disposed opposite to each other along the thickness direction of the positive electrode 11. The first surface 113a faces the winding center of the wound electrode body 10, and the second surface 113b is away from the winding center of the wound electrode body 10. The functional coating 115 is located on the first surface 113a. A plurality of recesses 116 are provided on the first surface 113a of the single-sided coating area 113 of the positive electrode 11 with the functional coating 115, and a protrusion 117 corresponding to the recesses 116 is provided on the second surface 113b. The height D of each protrusion 117 satisfies: 1 μm ≤ D ≤ 40 μm, for example, 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, or 30 μm. By controlling D within this range, it is possible to ensure that an effective liquid storage unit of sufficient depth is formed within the functional coating 115, while simultaneously forming a stress relief zone on the positive electrode 11. When the battery 100 expands, the stress relief zone can be flattened to improve the breakage problem of the positive electrode 11. At the same time, it avoids the excessive height of the protrusion 117, which would damage the current collector of the positive electrode 11 and the structure of the flame-retardant particles in the functional coating 115 when the protrusion 117 is set, thus achieving a balance between the electrical performance and safety of the battery 100.

[0088] The relationship between D and h3 satisfies: 0.08 ≤ D / h3 ≤ 60, for example, 0.1, 0.5, 1, 5, 10, 20, 30, 40 or 50. Preferably, 0.2 ≤ D / h3 ≤ 40.

[0089] By controlling the D / h3 ratio, it is possible to avoid situations where the D / h3 is too small, resulting in a shallow protrusion 117 or an excessively thick functional coating 115. On the one hand, this would prevent the effective storage of electrolyte in the single-sided positive electrode area, thus failing to effectively reduce the probability of lithium plating on the negative electrode 12 opposite the single-sided coating area 113 of the positive electrode 11 with the functional coating 115. On the other hand, it would have limited effect on improving the overall fracture stress of the positive electrode 11. Conversely, if the D / h3 ratio is too large, the protrusion 117 would be too deep or the functional coating 115 too thin, potentially causing excessive damage to the structure of the flame-retardant particles in the functional coating 115 or the structure of the positive electrode active material. This would reduce the thermal safety and electrical performance of the battery 100 and create new stress concentration points at the root of the protrusion 117, increasing the risk of electrode breakage. Meeting these conditions ensures that the protrusion 117 structure is deep enough to redistribute the stress within the positive electrode 11. When the positive electrode 11 is subjected to stress, the presence of the protrusion 117 can effectively disperse the stress into a larger volume of active material matrix, thereby reducing the risk of electrode breakage.

[0090] In this application, the testing method for h3 can be referred to the following description.

[0091] After discharging the fully charged battery to 0% SOC, use ceramic scissors to cut along the thickness direction of the positive electrode 11. Cut the sample of the single-sided coating area 113 of the outermost ring of the positive electrode 11 of the discharged wound electrode body 10 into samples suitable for detection by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) (for example, cut the above area into 2 cm × 10 cm pieces). A 2 cm sample was used as a test sample. The cross-section of the sample was then polished using an argon ion polisher. The polished cross-section was magnified to an appropriate magnification (e.g., 1000x) using a scanning electron microscope. Energy dispersive spectroscopy (EDS) was then used to identify characteristic elements (e.g., silicon, magnesium, phosphorus, aluminum, zinc, barium, boron, etc.) of the flame-retardant particles in the functional coating 115 to distinguish the interface between the functional coating 115 and the positive electrode active layer 112. SEM was then used to randomly measure the straight-line distance between the upper surface of the functional coating 115 away from the positive electrode active layer 112 and the interface between the functional coating 115 and the positive electrode active layer 112 at multiple different locations (e.g., 10 locations) within the magnified cross-section (reference). Figure 8 The thickness of the functional coating 115 can be obtained by calculating and averaging the 10 measured thickness values ​​of the functional coating 115. It can be understood that if the interface between the functional coating 115 and the positive electrode active layer 112 is uneven, the straight-line distance between the highest point of the functional coating 115 away from the positive electrode active layer 112 and the lowest point of the functional coating 115 near the positive electrode active layer 112 is used as the thickness value of the functional coating 115.

[0092] In this application, the height D of the protrusion 117 is defined as the height of the vertex of the protrusion 117 above the reference plane in the thickness direction of the positive electrode 11. The reference plane is the plane containing the second surface 113b of the positive electrode 11.

[0093] In one example, the equivalent circle diameter S of the protrusion 117 is defined to satisfy: 0.5 mm ≤ S ≤ 2 mm, for example, 0.8 mm, 1.0 mm, 1.4 mm or 1.8 mm. Preferably, 1 mm ≤ S ≤ 2 mm, for example, 1.2 mm, 1.4 mm, 1.6 mm or 1.8 mm.

[0094] If the diameter S is too small, it is easily filled by the functional coating 115 particles, losing its purpose of liquid storage and causing significant compression of the functional coating 115, increasing the risk of lithium plating. If the diameter S is too large, the adhesion stability between the separator 13 and the positive electrode 11 decreases, increasing the risk of localized lithium plating. When the equivalent circular diameter S of the protrusion 117 is within the above range, it can both allow the formation of a concave portion 116 on the functional coating 115 that matches the size of the protrusion 117, improving the liquid storage effect of the functional coating 115 and reducing the risk of lithium plating in the battery 100, and ensure that the equivalent circular diameter S of the protrusion 117 is not too small, which would cause significant localized compression of the functional coating 115, leading to localized detachment of the functional coating 115 or localized stress concentration points on the positive electrode 11, causing the positive electrode 11 to break.

[0095] In one example, the center distance P between two adjacent protrusions 117 satisfies: 1.2S≤P≤4S, for example, 1.4, 1.8, 2, or 3.

[0096] In this way, the center distances P and S between two adjacent protrusions 117 satisfy the above range, which can ensure the connection stability between the recessed portion and the non-recessed portion 116 on the functional coating 115, prevent the functional coating 115 from falling off, and also make the protrusions 117 form a uniformly distributed macroscopic reinforcement area on the surface of the positive electrode 11. When the battery 100 expands, it can effectively redistribute the linear stress or point stress into surface stress to avoid stress concentration that could cause the positive electrode 11 to break.

[0097] In this application, the equivalent circle diameter S of the convex portion 117 can be determined using the following test method.

[0098] After discharging the battery to 0% SOC, the battery is disassembled to obtain the positive electrode 11. A 2 cm × 2 cm positive electrode 11 with a protrusion 117 is cut along the thickness direction of the positive electrode 11. The cut positive electrode 11 is magnified to an appropriate magnification (e.g., 500x) using a scanning electron microscope to obtain a clear SEM image of the positive electrode 11 with the protrusion. Using image processing software, a measurement line is drawn along the height direction of the protrusion 117, and the height of the protrusion 117 is calculated based on the image pixel information and the known magnification. Similarly, in the SEM image, the diameter of the protrusion 117 is measured using image processing software. By randomly measuring the circumscribed circle diameters of 10 different protrusions 117, the average value is calculated (the maximum and minimum values ​​can be removed, and the average of the remaining values ​​is taken) to obtain the equivalent circular diameter S of the protrusion 117.

[0099] It should be noted that when the protrusion 117 is irregular in shape, the straight-line distance between the two farthest points of a single protrusion 117 is measured as the equivalent circle diameter S of the protrusion 117.

[0100] In this application, the method for measuring the center distance P between two adjacent protrusions 117 can be referred to the following description. After discharging the battery to 0% SOC, the battery is disassembled to obtain the positive electrode 11. A test sample of the positive electrode 11 with protrusions 117 and a diameter of 2 cm × 2 cm is cut along the thickness direction of the positive electrode 11. The test sample of the cut positive electrode 11 is magnified to an appropriate magnification (e.g., 500 times) using a scanning electron microscope. Ten to twenty (e.g., 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20) protrusions 117 are randomly selected on the surface of the test sample. The distance between the centers of two adjacent protrusions 117 among the above 10 to 20 protrusions 117 is measured, and the average value is taken (the maximum and minimum values ​​can be removed and the average value of the remaining values ​​is taken), which is the center distance P between two adjacent protrusions 117.

[0101] It should be noted that when two adjacent protrusions 117 are irregularly shaped, the straight-line distance between the highest points of the two adjacent protrusions 117 is measured as the center distance P between the two adjacent protrusions 117.

[0102] In some embodiments, the negative electrode 12 includes a negative electrode active layer 122, which comprises bulk silicon-carbon material. The number m of bulk silicon-carbon material with a length greater than 2 μm is 5 to 50 per 1000 μm², for example, 10, 15, 20, 30, or 40 per 1000 μm². Preferably, m is 10 to 30 per 1000 μm², for example, 14, 18, 24, or 28 per 1000 μm².

[0103] When m meets the above range, the bulk silicon-carbon material in the negative electrode active layer 122 has a larger specific surface area and a shorter lateral diffusion path for lithium ions, thus exhibiting better ion transport kinetics. This helps to improve the lithium insertion / extraction rate of the negative electrode, making lithium ions more uniformly distributed on the surface of the negative electrode sheet 12, and further suppressing the "black spots" and lithium plating problems caused by local kinetic sluggishness. If the number m of bulk silicon-carbon material with a longest dimension greater than 2μm in the unit surface area of ​​the negative electrode sheet 12 is too small, the improvement in the lithium insertion rate of the bulk silicon-carbon material will not be significant, and the effect on improving lithium plating will be limited. If m is too large, it will lead to an excessively large specific surface area of ​​the bulk silicon-carbon material, resulting in violent side reactions, increased heat generation, continuous growth and thickening of the SEI film, and consumption of a large amount of lithium source and electrolyte, leading to lithium plating and deterioration of the thermal safety performance of the battery 100.

[0104] In some embodiments, the ratio C of the average thickness to the average length of the bulk silicon carbide material is 0.05 to 0.3, for example, 0.08, 0.1, 0.12, 0.2 or 0.25. Preferably, B is 0.1 to 0.2, for example, 0.11, 0.13, 0.16 or 0.18.

[0105] Bulk silicon-carbon materials with an average thickness-to-average length ratio C (i.e., flatness) below 0.05 are too thin, making them prone to breakage during electrode rolling, reducing their lithium intercalation capacity and increasing the risk of lithium plating. Flatness above 0.3 results in an excessively large component of expansion behavior perpendicular to the negative electrode current collector 121 (i.e., the thickness direction of the battery 100), potentially causing continuous compression of the separator 13 and increasing the risk of puncture. Controlling the flatness between 0.05 and 0.3, particularly within the preferred range of 0.1 to 0.2, guides the bulk silicon-carbon material to primarily undergo "in-plane expansion" parallel to the current collector direction during charging and discharging, thereby suppressing its "vertical expansion" towards the separator 13. This reduces the risk of the separator 13 being punctured due to stress concentration, compromising its integrity, increasing the risk of shrinkage during hot-box testing, and reducing the thermal safety performance of the battery 100.

[0106] After discharging battery 100 to 0% SOC, battery 100 is disassembled to obtain negative electrode 12. Negative electrode 12 is cut along its thickness direction to obtain a cross-section of negative electrode 12. Under a scanning electron microscope, 20 different regions of the cross-section of negative electrode 12 are randomly selected and each is magnified to 1000 times to obtain 20 SEM cross-sectional images of negative electrode 12. The length and thickness of any 5 blocky silicon-carbon materials in each SEM image are measured and averaged. The length and thickness of the blocky silicon-carbon materials in the 20 different regions of negative electrode 12 SEM cross-sectional images are calculated and averaged again to obtain the average length and average thickness of the blocky silicon-carbon materials.

[0107] The length (L) of the bulk silicon-carbon material is defined as the maximum Feret diameter. This is achieved by measuring the length of a single bulk silicon-carbon particle on the plane of the negative electrode current collector 121 using a pair of parallel calipers that are continuously rotated. The maximum Feret diameter is defined as the length (L) of the single bulk silicon-carbon particle. The average length of the bulk silicon-carbon material is obtained by measuring the lengths of multiple bulk silicon-carbon materials (e.g., 50 bulk silicon-carbon materials can be tested) and then calculating the average value.

[0108] The thickness (T) of bulk silicon carbide material is defined as the smallest caliper dimension of the bulk silicon carbide material perpendicular to the direction of the maximum Feret diameter, i.e., the thickness of a single bulk silicon carbide particle. The average thickness of the bulk silicon carbide material can be obtained by measuring the thickness of multiple bulk silicon carbide materials (e.g., testing the thickness of 50 bulk silicon carbide materials) and then calculating the average value.

[0109] It should be noted that, for clarity, the entire structure of the battery 100 described above is not depicted. To achieve its necessary functions, those skilled in the art can configure other structures according to specific application scenarios, and the embodiments of this application do not impose such limitations. Similarly, for clarity, the entire preparation process and technology of the battery 100 described above is not depicted. To realize the preparation of the battery 100, those skilled in the art can select preparation engineering and processes according to specific application scenarios, and the embodiments of this application do not impose such limitations.

[0110] Exemplary electrical equipment Secondly, this application provides an electrical device that includes the aforementioned battery 100. Exemplarily, this electrical device can be a charging device or a power-consuming device. For example, the electrical device can be a pure electric vehicle, a hybrid electric vehicle, a range-extended electric vehicle, or a drone, etc.

[0111] The battery 100 provided according to the embodiments of this application has the corresponding effects of the battery 100 described above, as detailed above, and will not be repeated here.

[0112] It should be understood that the term "comprising" and its variations used in the embodiments of this application are open-ended, meaning "including but not limited to". The term "according to" means "at least partially according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least another embodiment". The term "a plurality of" means "more than one", which implies covering two, three or more cases.

[0113] It should be understood that although terms such as "first" or "second" may be used in embodiments of this application to describe various elements, such as a first positive electrode active material layer and a second positive electrode active material layer, these elements are not defined by these terms, which are only used to distinguish one element from another.

[0114] The scope of protection of the embodiments of this application is not limited to the above embodiments. Any variations or substitutions that can be conceived by those skilled in the art within the technical scope disclosed in the embodiments of this application should be included within the scope of protection of the embodiments of this application. Therefore, the scope of protection of the embodiments of this application should be determined by the scope of the claims.

[0115] The present application is described in detail below with reference to specific embodiments, which are used to understand rather than limit the present application.

[0116] Unless otherwise specified, all materials and reagents used in the following examples are commercially available. Unless otherwise specified, the processing procedures and techniques involved are conventional technical methods.

[0117] Example 1 Preparation of negative electrode sheet 12: Negative electrode active material (i.e., negative electrode active material, graphite and bulk silicon-carbon composite material), sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black are dispersed in deionized water at a mass percentage of 58% (graphite):35% (bulk silicon-carbon composite material):2.5%:1.5%:3, and mixed evenly to obtain a slurry. The prepared negative electrode slurry is uniformly coated onto copper foil, dried at 100°C, and then rolled and slit to obtain negative electrode sheet 12. The negative electrode active material is a graphite and silicon-carbon composite material. In the negative electrode active layer 122, the silicon content A is 15.75 wt%, and the silicon content in the bulk silicon-carbon composite material is 45 wt%. The silicon content in the negative electrode active layer 122 is varied by controlling the proportion of the bulk silicon-carbon composite material in the negative electrode active material and the silicon content in the bulk silicon-carbon composite material.

[0118] Preparation of positive electrode 11: Lithium nickel cobalt manganese oxide (NCM), polyvinylidene fluoride (PVDF), and carbon black (conductive agent) are mixed in a mass percentage ratio of 97.2:1.8:1. An appropriate amount of N-methylpyrrolidone is added as a solvent, and the mixture is stirred until homogeneous, forming a uniformly dispersed electrode slurry with a solid content of 65 wt%. The prepared positive electrode slurry is uniformly coated onto aluminum foil and then rolled and slit to form the positive electrode 11. The positive electrode 11 includes a single-sided coating area 113 and a double-sided coating area 114. Then, following a conventional winding structure, the positive electrode 11, negative electrode 12, and separator 13 are used to fabricate a wound electrode body 10. A functional coating 115 is provided on the surface of the positive active layer 112 of the outermost single-sided coating area 113 of the wound electrode body 10, away from the positive current collector 111. The functional coating 115 comprises silica flame-retardant particles and a binder polyacrylic acid, wherein the silica and polyacrylic acid are mixed in a mass percentage ratio of 3:7, and the solvent is water.

[0119] Then, the wound electrode body 10 is housed in the casing and made into battery 100 through steps such as encapsulation, liquid injection, formation, secondary sealing, and capacity testing.

[0120] Electrolyte preparation: In an argon-filled glove box (moisture <1 ppm, oxygen <1 ppm), add 35 wt% propyl propionate (a carboxylic acid ester compound) and 25 wt% propylene carbonate (a cyclic carbonate compound) as organic solvent, based on the total mass of the electrolyte, and mix to form a homogeneous solution. Slowly add 10 wt% lithium hexafluorophosphate (LiPF6) as the lithium salt, and 8 wt% fluoroethylene carbonate. The remainder is ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 2:1 mass ratio as solvent. After stirring until homogeneous, the electrolyte is obtained. It should be noted that the amount of solvent in the electrolyte can be adjusted, for example, by adjusting the amount of ethylene carbonate (EC) and dimethyl carbonate (DMC), to change the amount of carboxylic acid ester compounds and cyclic carbonate compounds in the electrolyte. The remaining components of the electrolyte are set according to standard procedures and will not be described further here.

[0121] The electrolyte comprises propyl propionate and propylene carbonate. The mass percentage of propyl propionate is a = 35%, and the mass percentage of propylene carbonate is b = 25%, with a / b = 1.4. The pore structure of the separator 13 accounts for A = 30%. The thickness of the porous base membrane is h1 = 4 μm. The thickness of the polymer adhesive layer is h2 = 1 μm. The porosity of the porous base membrane is K = 35%. The thickness of the functional coating 115 is H3 = 0.3 μm. The median particle size Dv50 of the flame-retardant particles in the functional coating 115 is Dv50 = 0.015 μm, and the flame-retardant particles are silica. The swelling degree of the binder in the electrolyte is B = 25%. The peel strength Fc1 between the functional coating 115 and the separator 13 is 20 N / m, and the peel strength Fa between the separator 13 and the negative electrode 12 is 35 N / m. Fa / Fc1 = 1.75. The peel strength between the positive electrode active layer 112 and the separator 13 is Fc2 = 24 N / m. The peel strength between the functional coating 115 of the single-sided coating area 113 and the separator 13 is Fc = 5 N / m, and the peel strength between the separator 13 and the negative electrode 12 is Fa = 15 N / m, Fa / Fc = 3. The height D of the protrusion 117 on the first surface 113a of the single-sided coating area 113 of the positive electrode 11 with the functional coating 115 is 30 μm, D / h3 = 30, h3 = 1 μm. The equivalent circle diameter S of the protrusion 117 is 1.5 mm, P = 1.5S. The number of bulk silicon carbide materials larger than 2 μm is 30 per 1000 μm². The ratio of the average thickness to the average length of the bulk silicon carbide materials is C = 0.2.

[0122] Example 2 This embodiment is based on Example 1, except that the electrolyte includes propyl propionate, ethyl propionate, and propylene carbonate. The median particle size Dv50 of the flame-retardant particles in the functional coating 115 is 1.2 μm, and the flame-retardant particles are melamine cyanurate.

[0123] Example 3 This embodiment is based on Example 1, except that the electrolyte includes ethyl propionate, propylene carbonate, and fluoroethylene carbonate. The flame-retardant particles are magnesium hydroxide.

[0124] Example 4 This embodiment is based on Example 1, except that the electrolyte includes propyl propionate, isopropyl acetate, propylene carbonate, and ethylene carbonate. The flame-retardant particles are melamine cyanurate and silica, wherein the median particle size Dv50 of melamine cyanurate is 1.2 μm, and the median particle size Dv50 of silica is 0.015 μm.

[0125] Example 5 This embodiment is based on Example 1, except that the electrolyte includes propyl propionate + ethyl propionate + propylene carbonate + ethylene carbonate + fluoroethylene carbonate, and the flame retardant particles are silicon dioxide.

[0126] Example 6 This embodiment is based on Example 1, except that the mass percentage of propyl propionate a = 5%, the mass percentage of propylene carbonate b = 10%, and a / b = 0.5.

[0127] Example 7 This embodiment is based on Example 1, except that the electrolyte includes 2,2-difluoroethyl acetate + propylene carbonate + fluoroethylene carbonate, and the flame-retardant particles are aluminum phosphate. a=70%, b=7.1%, a / b=9.86. The pore structure of the separator 13 accounts for A=90%. The thickness of the porous base membrane is h1=15 μm. The porosity of the porous base membrane is K=65%. The thickness of the polymer adhesive layer is h2=5 μm. The Dv50 of the flame-retardant particles is 3 μm. The peel strength Fc1 between the functional coating 115 and the separator 13 is 25 N / m, and the peel strength Fa between the separator 13 and the negative electrode 12 is 40 N / m, Fa / Fc1=1.6. The peel strength Fc2 between the positive electrode active layer 112 and the separator 13 is 30 N / m. The height D of the protrusion 117 on the first surface 113a of the single-sided coating area 113 of the positive electrode 11 is 40 μm, h3 is 5 μm, D / h3 is 8, the equivalent circle diameter S of the protrusion 117 is 2 mm, and P is 2S. The number of bulk silicon-carbon materials larger than 2 μm is 50 per 1000 μm². The ratio of the average thickness to the average length of the bulk silicon-carbon materials is C = 0.3.

[0128] Example 8 This embodiment is based on Example 1, except that the electrolyte includes 2,2-difluoroethyl acetate + propylene carbonate + fluoroethylene carbonate, and the flame-retardant particles are boron nitride. a=25%, b=50%, a / b=0.5. The pore structure ratio of the 13-porous membrane is A=10%. The thickness of the porous base membrane is h1=3.5 μm. The porosity of the porous base membrane is K=30%. The thickness of the polymer adhesive layer is h2=0.5 μm. The Dv50 of the flame-retardant particles is 0.01 μm. The swelling degree of the binder in the electrolyte is B=49%. The peel strength Fc1 between the functional coating 115 and the membrane 13 is 4 N / m, and the peel strength Fa between the membrane 13 and the negative electrode 12 is 8 N / m, Fa / Fc1=2. The peel strength Fc2 between the positive electrode active layer 112 and the membrane 13 is 6 N / m. The height D of the protrusion 117 on the first surface 113a of the single-sided coating area 113 of the positive electrode 11 is 1.1 μm, h3 is 13 μm, D / h3 is 0.08, the equivalent circle diameter S of the protrusion 117 is 0.5 mm, and P is 4S. The number of bulk silicon-carbon materials larger than 2 μm is 5 per 1000 μm². The ratio of the average thickness to the average length of the bulk silicon-carbon materials is C = 0.05.

[0129] Example 9 This embodiment is based on Example 1, except that the electrolyte includes 2,2-difluoroethyl acetate + ethyl butyrate + ethylene carbonate + propylene carbonate + fluoroethylene carbonate, and the flame-retardant particles are aluminum hydroxide. a=40%, b=5%, a / b=8. The pore structure of the separator 13 accounts for A=70%. The thickness of the porous base membrane h1=7 μm. The porosity of the porous base membrane K=45%. The thickness of the polymer adhesive layer h2=3 μm. The Dv50 of the flame-retardant particles=1.8 μm. The swelling degree of the binder in the electrolyte B=5%. The peel strength Fc1 between the functional coating 115 and the separator 13 is 10 N / m, and the peel strength Fa between the separator 13 and the negative electrode 12 is 15 N / m, Fa / Fc1=1.5. The peel strength Fc2 between the positive electrode active layer 112 and the separator 13 is 12 N / m. The height D of the protrusion 117 on the first surface 113a of the single-sided coating area 113 of the positive electrode 11 is 18 μm, h3 is 0.3 μm, D / h3 is 60, and the equivalent circle diameter S of the protrusion 117 is 1.3 mm, P is 1.2S. The number of bulk silicon-carbon materials larger than 2 μm is 25 per 1000 μm². The ratio of the average thickness to the average length of the bulk silicon-carbon materials is C = 0.15.

[0130] Example 10 This embodiment is based on embodiment 5, except that the proportion of the 13-pore structure of the diaphragm is A=8%.

[0131] Example 11 This embodiment is based on embodiment 5, except that the proportion of the 13-pore structure of the diaphragm is A=93%.

[0132] Example 12 This embodiment is based on Example 5, except that the polymer adhesive layer thickness h2 = 0.3 μm.

[0133] Example 13 This embodiment is based on Example 5, except that the polymer adhesive layer thickness h2 = 6 μm.

[0134] Example 14 This embodiment is based on Embodiment 5, except that the thickness of the porous base film is h1=2 μm.

[0135] Example 15 This embodiment is based on Embodiment 5, except that the thickness of the porous base film is h1=16 μm.

[0136] Example 16 This embodiment is based on Embodiment 5, except that the porosity K of the porous base membrane is 28%.

[0137] Example 17 This embodiment is based on Embodiment 5, except that the porosity K of the porous base membrane is 69%.

[0138] Example 18 This embodiment is based on Embodiment 5, except that the Dv50 of the flame-retardant particles is 0.008 μm.

[0139] Example 19 This embodiment is based on Embodiment 5, except that the flame-retardant particles have a Dv50 of 4 μm.

[0140] Example 20 This embodiment is based on Embodiment 5, except that the swelling degree B of the adhesive in the electrolyte is 53%.

[0141] Example 21 This embodiment is based on embodiment 5, except that the peel strength between the functional coating 115 and the diaphragm 13 is Fc1=3 N / m and Fa / Fc1=11.7.

[0142] Example 22 This embodiment is based on embodiment 5, except that the peel strength between the functional coating 115 and the diaphragm 13 is Fc1=28 N / m and Fa / Fc1=1.25.

[0143] Example 23 This embodiment is based on embodiment 5, except that the peel strength between the diaphragm 13 and the negative electrode 12 is Fa=7N / m and Fa / Fc1=0.35.

[0144] Example 24 This embodiment is based on embodiment 5, except that the peel strength between the separator 13 and the negative electrode 12 is Fa=42N / m and Fa / Fc1=2.1.

[0145] Example 25 This embodiment is based on Embodiment 5, except that the peel strength between the positive electrode active layer 112 and the separator 13 is Fc2 = 8 N / m, and Fc1 > Fc2.

[0146] Example 26 This embodiment is based on Embodiment 5, except that the peel strength Fc2 between the positive electrode active layer 112 and the separator 13 is 35 N / m.

[0147] Example 27 This embodiment is based on embodiment 5, except that the height D of the protrusion 117 is 0.7 μm and D / h3 is 0.7.

[0148] Example 28 This embodiment is based on embodiment 5, except that the height D of the protrusion 117 is 43 μm and D / h3 is 43.

[0149] Example 29 This embodiment is based on embodiment 5, except that the height of the protrusion 117 is D=0.5 μm, h3=10 μm, and D / h3=0.05.

[0150] Example 30 This embodiment is based on embodiment 5, except that the height of the protrusion 117 is D=21 μm, h3=0.3 μm, and D / h3=70.

[0151] Example 31 This embodiment is based on embodiment 5, except that the equivalent circle diameter S of the protrusion 117 is 0.4 mm.

[0152] Example 32 This embodiment is based on embodiment 5, except that the equivalent circle diameter S of the protrusion 117 is 2.5 mm.

[0153] Example 33 This embodiment is based on embodiment 5, except that P=1.1S.

[0154] Example 34 This embodiment is based on embodiment 5, except that P=5S.

[0155] Example 35 This embodiment is based on Embodiment 5, except that the number of bulk silicon-carbon materials larger than 2 μm is 3 per 1000 μm².

[0156] Example 36 This embodiment is based on Embodiment 5, except that the number of bulk silicon-carbon materials larger than 2 μm is 54 per 1000 μm².

[0157] Example 37 This embodiment is based on Embodiment 5, except that the ratio of the average thickness to the average length of the bulk silicon-carbon material is C=0.03.

[0158] Example 38 This embodiment is based on Embodiment 5, except that the ratio of the average thickness to the average length of the bulk silicon-carbon material is C=0.5.

[0159] Comparative Example 1 This embodiment is based on Example 5, except that the mass percentage of the carboxylic acid ester compound is a=4% and a / b=0.4.

[0160] Comparative Example 2 This embodiment is based on Example 5, except that the mass percentage of the carboxylic acid ester compound is a=75% and a / b=15.

[0161] Comparative Example 3 This embodiment is based on Example 5, except that the mass percentage of the cyclic carbonate compound is b=4.8% and a / b=4.8.

[0162] Comparative Example 4 This embodiment is based on Example 5, except that the mass percentage of the cyclic carbonate compound is b=53% and a / b=0.75.

[0163] Material property testing 1. h1, h2, D, h3 and P were obtained by microscopy or scanning electron microscopy.

[0164] 2. Furnace temperature test conditions and methods (including sample quantity): 1) Sample grouping: 100 samples of 10 batteries were tested for each embodiment; 2) Test methods: The experiment was conducted at 25 ℃±5 ℃ using the following steps: a. Discharge to the lower limit voltage at 0.2C.

[0165] b. Let stand for 5 minutes.

[0166] c. Charge to the upper limit voltage at 0.7C, with a cutoff current of 0.02C.

[0167] d. Test the voltage, internal resistance, and thickness of a fully charged 100 battery at 25℃ + 5℃, and take a picture before the test.

[0168] e. Place the fully charged battery 100 in an oven and heat it at a rate of 5 ℃ / min ± 2 ℃ / min. When the temperature inside the oven reaches 130 ℃, keep it at that temperature for 10 min.

[0169] f. Continue heating using this procedure. After the oven temperature reaches 131℃ and 132℃, maintain the temperature for 10 minutes and observe the failure status of battery 100.

[0170] Experimental results: If the temperature rises to 131℃ or 132℃ and the battery 100 does not catch fire or explode during the 10-minute heat preservation process, it is considered to have passed the furnace temperature performance test. For example, 2P / 10T means that 2 out of 10 batteries 100 pass the test, that is, 2 out of the 10 tested batteries 100 pass the furnace temperature test as described above.

[0171] 3. Test conditions and methods for 1000T cycle performance at room temperature (including the number of samples): 1) Sample grouping: The number of samples for each embodiment is 5.

[0172] 2) Test methods: Conduct the experiment at 25℃±+5℃ using the following steps: a. Charge at a constant current rate of 2C, cut off at a rate of 0.05C, and then discharge at a constant current rate of 4C, with a voltage range of 2.0V to 4.3V. This constitutes one charge-discharge cycle.

[0173] Experimental results: After 1000 cycles and 5 minutes of rest, the lithium-ion battery 100 was disassembled.

[0174] 4. Peel strength test between electrode and diaphragm 13 (peel strength test) After discharging the battery to 0% SOC, disassemble the battery. Take the separator 13 (25 mm wide) and the corresponding electrode area (e.g., separator and negative electrode, or separator and positive electrode double-sided area, or separator and positive electrode single-sided coated area with functional coating) (25 mm wide) and heat-press them together under a certain pressure (e.g., 1 MPa) and temperature (e.g., 90 °C). Cut them into standard samples (e.g., 25 mm wide, the bonding length between separator 13 and electrode is not less than 30 mm, and the clamping area at both ends is not less than 10 mm). Perform a peel test on a universal tensile testing machine at a peel angle of 180° and a rate of 300 mm / min. Record the flat peel strength during the stable peel stage and calculate the peel strength per unit width of the sample (N / m). Peel strength = average force value / test sample width. Each sample should be tested at least 3 times and the average value should be taken.

[0175] 5. High-temperature (45℃) 600T battery lithium plating test: 1) Sample grouping: The number of samples for each embodiment is 5.

[0176] 2) Test methods: At an environment of 45℃±5℃, after placing battery 100 in a constant temperature test chamber for 1 hour to reach a constant temperature, conduct the test according to the following steps: a) Discharge at a constant current of 0.2C to the lower limit voltage; let stand for 5 minutes, then charge at 0.5C to the upper limit voltage of 4.53V, and then charge at a constant voltage until the current drops to 0.02C. Let stand for 5 minutes, then discharge at a constant current of 0.2C to the lower limit voltage of 3V. Record this discharge capacity as the initial capacity (D0).

[0177] b) Place battery 100 in a 45℃ constant temperature chamber for stepped charging: charge at a constant current of 3C to 4.35V, then charge at a constant current of 2.5C to 4.35V, followed by constant voltage charging until the current reaches 1.8C; charge at a constant current of 1.8C to 4.4V, then charge at a constant voltage until the current reaches 1.5C; charge at a constant current of 1.5C to 4.5V, then charge at a constant voltage until the current reaches 1.2C; charge at a constant current of 1.2C to 4.58V, then charge at a constant voltage until the current reaches 0.25C. After standing for 5 minutes, disassemble lithium-ion battery 100.

[0178] The criteria for judging the degree of lithium plating in lithium-ion batteries 100 are as follows: Five batteries 100 that have undergone 1000T cycling at room temperature and five batteries 100 that have undergone 600T cycling at high temperature are tested respectively. With batteries 100 fully charged, they are disassembled. The presence of black spots on the negative electrode 12 corresponding to the area with the functional coating 115 on the single-sided coating area 113 of the positive electrode 11 in each battery 100 is observed. The total area of ​​the negative electrode 12 corresponding to the area with the functional coating 115 on the single-sided coating area 113 of the positive electrode 11 in each battery 100 is recorded as S. The area of ​​the black spot on the negative electrode 12 corresponding to this area is plotted and statistically analyzed using graphical analysis software (e.g., ImageJ, NanoMeasurer, Matlab, ParticleMetric, etc.) and recorded as S1. The area of ​​the black spot on the negative electrode 12 is calculated as S1 / S. 100%.

[0179] The degree of lithium plating in a single battery 100 is determined by the area of ​​black spots appearing on the negative electrode 12. A 0% black spot area on the negative electrode 12 is considered no lithium plating. A black spot area greater than 0% and less than or equal to 10% is considered slight lithium plating, which has a relatively small impact on the battery 100 and allows for normal use. A black spot area greater than 10% and less than or equal to 50% is considered moderate lithium plating, and a black spot area greater than 50% and less than or equal to 100% is considered severe lithium plating. Experimental results: 1 / 5 indicates that one out of five tested batteries 100 exhibited lithium plating, with the degree of lithium plating further defined by the area of ​​the black spots in that battery 100. For example, in Example 6, the result of lithium plating after 1000T cycling at room temperature is 0 / 5, which means that no lithium plating occurred in any of the 5 tested batteries 100. The result of lithium plating after 600T cycling at high temperature is 1 / 5, which means that one battery 100 has slight black spot lithium plating on one side. This means that one of the 5 tested batteries 100 has lithium plating, and that battery 100 has slight black spot lithium plating.

[0180] Table 1 shows the test results.

[0181] Table 1 The data above shows that when the ratio of a to b satisfies 0.5 ≤ a / b ≤ 10, the furnace temperature performance of the battery and the problem of lithium plating in black spots can be improved.

Claims

1. A battery, characterized in that, include: A positive electrode, a negative electrode, and a separator are stacked and wound together. The positive electrode and the negative electrode are wound together with the separator to form a wound electrode body having a flat portion and a curved portion. The negative electrode includes a negative current collector and a negative active layer disposed on the negative current collector. The negative active layer is made of silicon-based material. The positive electrode includes a positive current collector and a positive active layer disposed on the positive current collector. The positive electrode includes a single-sided coating area and a double-sided coating area. The single-sided coating area is located near the tail of the positive electrode. The positive active layer is disposed on one side of the single-sided coating area near the winding center of the wound electrode body. At least a portion of the single-sided coating area is located on the outermost ring of the wound electrode body. At least a portion of the positive active layer on the surface of the single-sided coating area located on the outermost ring of the wound electrode body away from the positive current collector is provided with a functional coating, which includes flame-retardant particles. The battery further includes an electrolyte comprising a carboxylic acid ester compound and a cyclic carbonate compound, wherein the mass percentage of the carboxylic acid ester compound is a and the mass percentage of the cyclic carbonate compound is b, wherein a and b satisfy the condition: 0.5 ≤ a / b ≤ 10.

2. The battery according to claim 1, characterized in that, a and b satisfy: 1 ​​≤ a / b ≤ 8; and / or a ranges from 5% to 70%, and b ranges from 5% to 50%.

3. The battery according to claim 1, characterized in that, The carboxylic acid ester compounds include one or more of ethyl propionate, propyl propionate, propyl acetate, isopropyl acetate, ethyl acetate, ethyl butyrate, methyl propionate, methyl formate, 2,2-difluoroethyl acetate, and ethyl 2,2-difluoroethyl acetate; and / or The cyclic carbonate compounds include one or more of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and difluoroethylene carbonate (DFEC).

4. The battery according to claim 1, characterized in that, The diaphragm comprises a porous base membrane and a polymer adhesive layer disposed on at least one surface thereon, wherein The polymer adhesive layer has multiple porous structures formed on its surface, and the area ratio A of the porous structures in the unit area of ​​the polymer adhesive layer is 10%~90%, preferably A is 30%~70%; and / or, The porous base membrane includes at least one of polyethylene and polypropylene; and / or The polymer adhesive layer includes at least one of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), poly(p-phenylene terephthalamide) (PPTA), polyimide (PI), and poly(p-phenylenebenzodioxazole) (PBO).

5. The battery according to claim 4, characterized in that, The thickness h1 of the porous base film is 3 μm to 15 μm, preferably 4 μm to 11 μm; and / or The porosity K of the porous base membrane is 30%~65%, preferably 35%~55%; and / or The thickness h2 of the polymer adhesive layer is 0.5 μm to 5 μm, preferably 1 μm to 4 μm.

6. The battery according to claim 1, characterized in that, The flame-retardant particles include at least one of inorganic or organic flame-retardant materials; further, The inorganic flame retardant material includes one or more of the following: aluminum hydroxide, magnesium hydroxide, boron nitride, zinc borate, barium metaborate, antimony trioxide, silicon dioxide, layered silicates, alumina, boehmite, aluminum phosphate, and zirconium phosphate; and / or The organic flame retardant material includes one or more of melamine, melamine cyanurate, melamine polyphosphate, and ammonium polyphosphate.

7. The battery according to claim 6, characterized in that, The median particle size Dv50 of the flame-retardant particles is 0.01 μm to 3 μm; and / or, the functional coating further includes a binder, and the binder further includes one or more of the following: homopolymer polyvinylidene fluoride (PVDF), modified polyvinylidene fluoride, polyimide (PI), polyamide-imide (PAI), styrene-butadiene rubber (SBR), modified styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, potassium carboxymethyl cellulose, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, polyvinyl alcohol, polyacrylonitrile, polyacrylamide, polyacrylic acid-acrylonitrile copolymer and its derivatives, acrylic acid-acrylamide and its derivatives, acrylic acid-acrylate copolymer, acrylic acid-acrylonitrile-acrylamide copolymer, polymethacrylate, and styrene-acrylic emulsion; and / or The swelling degree of the binder in the electrolyte is B < 50%, preferably B < 30%.

8. The battery according to claim 1, characterized in that, The peel strength between the functional coating of the positive electrode single-sided coating area and the separator is Fc1, and the peel strength between the separator and the negative electrode is Fa. Fc1 and Fa satisfy: Fc1 < Fa. Preferably, Fc1 and Fa satisfy: 1 ​​< Fa / Fc1 ≤ 8. Further, Fa is 8 N / m to 40 N / m. Preferably, Fa is 15 N / m to 35 N / m, and / or Fc1 is 4 N / m to 25 N / m, preferably 6 N / m to 20 N / m; and / or The peel strength between the positive electrode active layer and the separator in the double-sided coated area of ​​the positive electrode sheet is Fc2, where Fc2 is 10 N / m to 30 N / m. Further... The Fc1 and Fc2 satisfy the condition: Fc1 < Fc2.

9. The battery according to claim 1, characterized in that, The thickness of the functional coating is h3. The single-sided coating area of ​​the positive electrode sheet has a first surface and a second surface that are arranged opposite to each other along the thickness direction of the positive electrode sheet. The first surface faces the winding center of the wound electrode body, and the second surface is away from the winding center of the wound electrode body. The functional coating is located on the first surface. The first surface of the single-sided coating area of ​​the positive electrode sheet with the functional coating has a plurality of recesses, and the second surface has a protrusion corresponding to the recesses. The height D of each of the protrusions satisfies: 1 μm ≤ D ≤ 40 μm, and the relationship between D and h3 satisfies: 0.08 ≤ D / h3 ≤ 60, preferably 0.2 ≤ D / h3 ≤ 40, and / or, The h3 satisfies: 0.3 μm ≤ h3 ≤ 20 μm; and / or The equivalent circular diameter S of the convex portion is defined to satisfy: 0.5 mm ≤ S ≤ 2 mm, preferably, 1 mm ≤ S ≤ 2 mm, and / or, The center distances P and S between two adjacent protrusions satisfy: 1.2S ≤ P ≤ 4S.

10. The battery according to any one of claims 1 to 9, characterized in that, The negative electrode includes a negative electrode active layer, wherein the negative electrode active layer comprises bulk silicon-carbon material. The number m of bulk silicon-carbon materials with a length greater than 2 μm is 5 to 50 per 1000 μm², preferably 10 to 30 per 1000 μm²; and / or The ratio C of the average thickness to the average length of the bulk silicon-carbon material is 0.05 to 0.3, preferably 0.1 to 0.2.

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