Secondary batteries and electronic devices

Abstract

To provide a secondary battery in which the interface stability of a wound cell in a charging and discharging process can be secured and the lithium deposition in a cycle process can be reduced, and its application.SOLUTION: A secondary battery includes at least a housing, and a wound cell disposed in the housing and including a negative electrode plate, a positive electrode plate, and a separator. When a state of charge (SOC) is 100%, the wound cell satisfies the following condition. L1 represents a thickness of the negative electrode plate when an initial SOC is 0%, X1 represents a longitudinal expansion rate of the negative electrode plate, L2 represents a width of the wound cell, and X2 represents a lateral expansion rate of the wound cell. By the secondary battery and its application according to the present invention, the lithium deposition in a cycle process can be reduced and the cycle performance of the secondary battery can be improved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the technical field of secondary batteries, and more particularly to secondary batteries and their applications. [Background technology]

[0002] With the rapid development of smart grids, electric vehicles, and portable electronic products, secondary batteries such as lithium-ion batteries have become one of the most widely used power batteries. Lithium-ion batteries are widely used in various electric vehicles due to their advantages, such as high operating voltage, long cycle life, no memory effect, low self-discharge, and environmental friendliness. Lithium-ion battery cells are classified into laminated cells, wound cells, etc., depending on the cell formation method. Wound cells are more common among power batteries. However, due to the special structure of wound cells, lithium deposition at the interface is prone to occur during charge-discharge cycles. Summary of the Invention [Problem to be solved by the invention]

[0003] The present invention aims to provide a secondary battery that can ensure the interface stability of a wound cell during charge / discharge processes, reduce lithium deposition during cycling processes, and improve the cycle performance of the secondary battery, and uses thereof. [Means for solving the problem]

[0004] In order to solve the above technical problems, the present invention is realized by the following technical solutions:

[0005] One aspect of the present invention provides a secondary battery. The secondary battery includes at least a case and a wound cell disposed in the case, the wound cell including a negative electrode plate, a positive electrode plate, and a separator. When the state of charge (SOC) is 100%, the wound cell satisfies the following conditions:

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[0006] In one embodiment of the present invention, the value range of L1 satisfies 60 μm≦L1≦200 μm, and the value range of L2 satisfies 80 mm≦L2≦400 mm.

[0007] In one embodiment of the present invention, when the number of cycles of the secondary battery is within 1 to 60 and the SOC is 100%, the wound cell satisfies the following conditions.

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[0008] In one embodiment of the present invention, the negative electrode plate includes a negative electrode active material, the negative electrode active material including one of graphite or graphite doped with a silicon material, and the silicon material including at least one of silicon monoxide or silicon.

[0009] In one embodiment of the present invention, the positive plate includes an active positive material, which includes at least one of a nickel-cobalt-manganese ternary material or a modified nickel-cobalt-manganese ternary material.

[0010] In one embodiment of the present invention, the general formula for the nickel-cobalt-manganese ternary material is LiNi x Co y Mn 1-x-y O2, where 0.5≦x≦0.9 and 0.01≦y≦0.2.

[0011] In one embodiment of the present invention, the general formula of the modified nickel-cobalt-manganese ternary material is LiNi x Co y Mn 1-x-y M zO2, wherein 0.5≦x≦0.95, 0.01≦y≦0.2, 0<z≦0.1、1-x-y> 0, and M is at least selected from one of C, Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, or Zn.

[0012] In one embodiment of the present invention, the secondary battery further includes an electrolyte, the electrolyte being filled in the wound cell and between the wound cell and the housing, the electrolyte including a lithium salt, and the lithium salt including lithium hexafluorophosphate.

[0013] In one embodiment of the present invention, the electrolyte further comprises an additive, and the additive comprises at least one of 1,3-propane sultone, ethylene sulfate, fluoroethylene carbonate, or vinylene carbonate.

[0014] The present invention further provides an electronic device including a secondary battery. [Effects of the Invention]

[0015] In consideration of the above, embodiments of the present invention provide a secondary battery and its application. The secondary battery and its application alleviate problems such as wrinkling of the electrode pieces and interface degradation, ensure interface stability of the wound cell during charging and discharging, optimize ion transport paths, and optimize problems such as lithium deposition and heat generation caused by uneven electrode piece current density distribution during charging and discharging on one or both electrode pieces. This significantly reduces the risk of cracking in the corner regions of the wound cell during cycling, easing the difficulty of processing during cell winding and assembly, thereby improving the performance of the secondary battery. The positive electrode active material layer is prevented from peeling, improving the cycle characteristics of the secondary battery. The negative electrode active material layer is prevented from peeling, contributing to the stabilization of the negative electrode plate structure and improving the wettability of the electrolyte, thereby improving the electrochemical performance of the secondary battery. The lithium deposition during cycling can be reduced, improving the cycle performance of the secondary battery. [Brief explanation of the drawings]

[0016] In order to more clearly describe the technical solutions of the embodiments of the present invention, the drawings necessary for describing the embodiments are described below. Needless to say, the drawings in the following description are only some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative efforts. [Figure 1] 1 is a schematic diagram showing a secondary battery as a soft-pack battery according to an embodiment of the present invention. [Figure 2] FIG. 1 is a schematic diagram illustrating an ion battery as a hard-shell battery according to another embodiment of the present invention. [Figure 3] FIG. 1 is a schematic diagram illustrating a wound cell according to an embodiment of the present invention. [Figure 4] FIG. 2 is a schematic diagram showing a negative electrode plate according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described with reference to specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details of this specification can be modified or changed in various ways based on various viewpoints and applications without departing from the spirit of the present invention.

[0018] It should be noted that this invention may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, the embodiments are provided herein so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0019] The technical solutions of the present invention will be described in more detail below with reference to some embodiments and drawings. The embodiments described in this specification are not all of the embodiments of the present invention, but only constitute a part thereof. All other embodiments that can be achieved by those skilled in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of the present invention.

[0020] The present invention provides an electronic device. The electronic device includes at least one secondary battery for supplying power. The electronic device may be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electronic toy, a power tool, or the like. In one embodiment of the present invention, the vehicle is, for example, a new energy vehicle, which may be a pure electric vehicle, a hybrid vehicle, or a range-extended vehicle. The spacecraft may include an airplane, a rocket, a space shuttle, a spaceship, or the like. The electronic toys may include stationary or mobile electric toys such as game consoles, electric car toys, electric boat toys, and electric plane toys. The power tools may include electric metal cutting tools such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, as well as electric grinding tools, electric assembly tools, and electric railway tools. The present invention does not limit the types and processes of the electric devices.

[0021] During the charge and discharge process of a secondary battery, the negative electrode active material in the secondary battery repeatedly expands and contracts during the cycle, shocking the material and causing the wound cell to contract and expand in various directions. If the space retained within the wound cell is insufficient, the electrode pieces are likely to have insufficient space for expansion. This can result in wrinkling of the electrode plates, deterioration of the interface, and even self-discharge of deposited lithium, which can lead to safety issues such as short circuits. As a result, the development of secondary batteries has been limited.

[0022] Referring to FIGS. 1 and 2 , the present invention provides a secondary battery applicable to electronic devices. The secondary battery includes a housing 10 and a wound cell 11. The wound cell 11 is disposed inside the housing 10. The wound cell 11 includes a negative electrode plate, a positive electrode plate, a separator, etc. The separator is disposed between the negative electrode plate and the positive electrode plate. An electrolyte is filled inside the wound cell 11 and between the wound cell 11 and the housing 10. The secondary battery further includes a first electrode 12 and a second electrode 13, which are separately disposed on the same side of the housing 10 and connected to the electrode tabs of the negative electrode plate and the positive electrode plate, respectively, inside the wound cell 11, thereby functioning as the positive and negative electrodes of the secondary battery. This improves space utilization within the housing 10 and simplifies the cell structure, facilitating connection of multiple cells in a cell module. According to another embodiment of the present invention, the first electrode 12 and the second electrode 13 are disposed, for example, at two opposite ends of the housing 10. That is, the cell can be formed with tabs on one or both sides to meet different usage requirements in different environments. The present invention does not limit the type or shape of the secondary battery. In one embodiment of the present invention, the secondary battery may be, for example, a soft-pack battery or a hard-shell battery. In the present invention, the secondary battery may be, for example, a lithium-ion battery or a sodium-ion battery. In this embodiment, a lithium-ion battery will be described as an example of the secondary battery.

[0023] Referring to FIG. 1, in one embodiment of the present invention, the secondary battery is, for example, a soft-pack battery. The housing 10 of the soft-pack battery is made of a soft film such as a polyimide film, an aluminum plastic film, or a polyethylene film. Specifically, after forming a wound cell 11, the outside of the wound cell is covered with a soft film, an electrolyte is injected, and the opening is sealed. In this manner, a soft-pack battery is formed.

[0024] Referring to FIG. 2 , in one embodiment of the present invention, the secondary battery is a hard-shell battery, such as a prismatic or cylindrical battery. The housing 10 of the hard-shell battery may be, for example, circular, square, or rectangular with rounded corners. The housing 10 may be, for example, an aluminum or steel housing. One end of the housing 10 is sealed and the other end is open. The housing 10 forms a cavity for accommodating a wound cell. The wound cell is placed inside the housing 10, an electrolyte is injected, and the battery is assembled to form a hard-shell battery. In the hard-shell battery, an explosion-proof valve 14 is disposed between the first electrode 12 and the second electrode 13, for example, at a predetermined distance from each of the first electrode 12 and the second electrode 13, at a midpoint between the first electrode 12 and the second electrode 13. When the cell is operating normally, the explosion-proof valve 14 may activate a ventilation function to allow air to circulate between the inside and outside of the cell while preventing the passage of particles. If thermal runaway occurs in the cell, the pressure difference between the inside and outside of the cell reaches the explosion-proof threshold, and the explosion-proof valve opens, allowing both gas and solid matter to be discharged from the cell, thereby improving the safety performance of the cell.

[0025] In one embodiment of the present invention, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer coated on at least one or both sides of the positive electrode current collector, for example, to improve the capacity performance of the cell. The positive electrode current collector may be, for example, a foil material such as nickel, titanium, aluminum, nickel, silver, stainless steel, or carbon that has been surface-treated. In addition to foil materials, the positive electrode current collector may be in the form of a film, mesh, porous material, foam, nonwoven fabric, or a combination of two or more. The thickness of the positive electrode current collector is, for example, 8 μm to 15 μm. In this embodiment, the positive electrode current collector is, for example, aluminum foil.

[0026] In one embodiment of the present invention, the positive electrode active material layer may contain, for example, a positive electrode active material, a conductive agent, an adhesive, etc. Furthermore, the mass ratio of the positive electrode active material, the conductive agent, and the adhesive, with the total mass of the positive electrode active material layer being 100%, is, for example, 94.5% to 97.8%, 1.2% to 3.5%, and 1% to 2%. The positive electrode active material contains at least one positive electrode active material, such as a nickel-cobalt-manganese ternary material or a modified nickel-cobalt-manganese ternary material. Furthermore, the general formula of the nickel-cobalt-manganese ternary material is LiNi x Co y Mn 1-x-y O2, where 0.5≦x≦0.9 and 0.01≦y≦0.2, and the general formula of the modified nickel-cobalt-manganese ternary material is LiNi x Co y Mn 1-x-y M zIt is O2, where 0.5 ≦ x ≦ 0.95, 0.01 ≦ y ≦ 0.2, 0 < z ≦ 0.1, and M is at least selected from one of C, Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W or Zn. The modified nickel-cobalt-manganese ternary material can be modified by performing at least one of doping, coating, or structure control. The conductive agent is selected from any one or more of, for example, conductive carbon black (Super P, SP), acetylene black, carbon nanotubes (Carbon Nanotubes, CNT), mesophase carbon microspheres, or graphene. The adhesive is selected from any one or more of, for example, polyvinylidene fluoride (Poly vinylidene Fluoride, PVDF), polyacrylic acid (Polyacrylic Acid, PAA), polyamide (Polyamide, PA), polyacrylonitrile (Polyacrylonitrile, PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (Polymethyl Methacrylate, PMMA), ethylene-propylene-diene terpolymer (PMMA), or polyhexafluoropropylene. In one embodiment of the present invention, the conductive agent is selected from, for example, conductive carbon black and carbon nanotubes, the adhesive is selected from, for example, polyvinylidene fluoride, and the mass ratios of the positive electrode active material, carbon nanotubes, conductive carbon black, and polyvinylidene fluoride are, for example, 94.5% - 97.8%, 0.2% - 1.5%, 1% - 2%, 1% - 2%. By using a plurality of conductive agents in combination, the formation of a conductive network can be promoted, the shedding of the positive electrode active material layer can be suppressed, and the cycle performance of the secondary battery can be improved.

[0027] In one embodiment of the present invention, the negative electrode plate includes, for example, a negative electrode current collector and a negative electrode active material layer coated on at least one or both sides of the negative electrode current collector to improve the capacity performance of the cell. The negative electrode current collector is selected from a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, a stainless steel current collector, or the like, and the thickness of the negative electrode current collector is, for example, 8 μm to 15 μm. In this embodiment, the negative electrode current collector is, for example, copper foil.

[0028] In one embodiment of the present invention, the negative electrode active material layer may contain, for example, a negative electrode active material, an adhesive, a conductive agent, a thickener, and the like. Furthermore, the mass ratios of the negative electrode active material, the conductive agent, the adhesive, and the thickener, relative to the total mass of the negative electrode active material layer being 100%, are, for example, 93.4% to 97.8%, 0.6% to 2.6%, 0.8% to 1.5%, and 0.8% to 2.5%. The negative electrode active material may include, for example, graphite or graphite doped with a silicon material. The graphite may be, for example, natural graphite or artificial graphite. The silicon material in the silicon-doped graphite may include, but is not limited to, at least one of silicon monoxide and silicon. The adhesive may be selected from, for example, one or more of polyvinylidene fluoride, polyamide, polypropylene, polyacrylate, polyvinyl ether, polymethyl methacrylate, polyhexafluoropropylene, or polymerized styrene butadiene rubber (SBR). The conductive agent may be selected from, for example, one or more of conductive carbon black, acetylene black, carbon nanotubes, mesophase carbon microspheres, graphene, or the like. The thickener may be selected from, for example, one or more of carboxymethyl cellulose sodium (CMC), polyacrylic acid, or the like. In one embodiment of the present invention, the conductive agent is selected from, for example, conductive carbon black or carbon nanotubes, the adhesive is selected from, for example, polymerized styrene butadiene rubber, and the thickener is selected from, for example, carboxymethyl cellulose sodium or polyacrylic acid. The mass proportions of the negative electrode active material, carbon nanotubes, conductive carbon black, polyvinylidene fluoride, sodium carboxymethyl cellulose, and polyacrylic acid are, for example, 94.5% to 97.8%, 0% to 1.2%, 0.6% to 1.4%, 0.8% to 1.5%, 0.8% to 1.5%, and 0% to 1%. The combined use of multiple thickeners and multiple conductive agents suppresses the detachment of the negative electrode active material layer, contributes to stabilizing the structure of the negative electrode plate, and improves the wettability of the electrolyte, thereby improving the electrochemical performance of the secondary battery.

[0029] In one embodiment of the present invention, the separator is, for example, one of polyethylene (PE) film, polypropylene (PP) film, glass fiber film, composite film, etc. The thickness of the separator is, for example, 9 μm to 15 μm. An electrolyte is filled between the positive electrode plate, the negative electrode plate, and the separator, and between the wound cell and the housing. The electrolyte contains a lithium salt, and the lithium salt includes LiPF6. The present invention does not limit the type of electrolyte, and a commercially available LiPF6 electrolyte may be selected. In one embodiment of the present invention, the electrolyte contains an organic solvent, a lithium salt, an additive, etc. The organic solvent includes, for example, one of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC), and diethyl carbonate (DEC), etc., or a combination of at least two of them. Examples of lithium salts include LiPF 6 The additive includes at least one film-forming additive, such as 1,3-propane sultone (PS), ethylene diamine tetradecanoate (DTD), fluoroethylene carbonate (FEC), or vinylene carbonate (VC). In this embodiment, the organic solvent is a mixed solution of EC, EMC, and DEC in a volume ratio of 1:1:1. In a glove box under an argon atmosphere with a water content of less than 10 ppm, thoroughly dried lithium hexafluorophosphate is dissolved in the mixed solution, and then 1,3-propane sultone and vinylene carbonate are added and mixed uniformly to obtain an electrolyte. The concentration of LiPF6 is 1 mol / L, and the mass content of 1,3-propane sultone in the electrolyte is 0.1% to 3%, and the mass content of vinylene carbonate is 0.1% to 3%.

[0030] The present invention also provides a method for manufacturing a secondary battery. In this method, a positive electrode active material, a conductive agent, and an adhesive are mixed according to their mass ratios, and then a positive electrode solvent is added and stirred until the system is homogeneous to obtain a positive electrode slurry. The positive electrode solvent is, for example, selected from N-methylpyrrolidone (NMP). The positive electrode slurry is uniformly applied to at least one surface of a positive electrode current collector. After drying, the mixture is processed by rolling, cutting, etc. to obtain a positive electrode plate. A negative electrode active material, a conductive agent, an adhesive, and a thickener are mixed according to their mass ratios, and then a negative electrode organic solvent is added and mixed uniformly to obtain a negative electrode slurry. The negative electrode solvent is, for example, selected from deionized water. The negative electrode slurry is applied to at least one surface of a negative electrode current collector. After drying, the mixture is processed by rolling, cutting, etc. to obtain a negative electrode plate. A separator, a positive electrode plate, a separator, and a negative electrode plate are arranged in this order. Next, each component is wound in the same direction to obtain a wound cell. The wound cell is placed in a housing, an electrolyte is poured in, and the opening is sealed. In this way, a secondary battery is obtained.

[0031] Referring to FIG. 3, in one embodiment of the present invention, the wound cell 11 is circular or rectangular with rounded edges. In this embodiment, the wound cell 11 has, for example, a rectangular shape with rounded edges. In the wound cell 11, two flat regions with large opposing areas are called flat regions, and the two flat regions are arranged opposite each other, with the region connecting both ends of the flat regions being called a corner region. The width of the wound cell 11 is L2. When the secondary battery is adjusted to a state of charge (SOC) of 100%, the wound cell satisfies the following conditions:

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[0032] Referring to FIGS. 3 and 4, in one embodiment of the present invention, when testing the lateral expansion coefficient X2 of a wound cell, a computed tomography (CT) test is performed on a cell at the beginning of life to verify the length of the negative plate. That is, the test is performed at the early stage of the cell's life. Three locations are selected: the top, middle, and bottom of the coated area 103 of the negative plate. In this embodiment, for example, the A1-A1, A2-A2, and A3-A3 positions are selected on the negative plate in the flat area of ​​the innermost layer of the cell, while being careful to avoid the thin-walled area 104. In the wound cell 11, the width of the flat area of ​​the negative plate at the innermost periphery of the wound cell, i.e., the distance D1 from point A to point B at the innermost periphery of the negative plate in FIG. 3, is marked with high accuracy. After cycling the wound cell, a CT test is performed again in the same manner. That is, the width of the flat area of ​​the innermost periphery of the negative plate, i.e., the distance D2 from point A to point B after cycling, is marked. The data of the lateral expansion coefficient X2 of the wound cell can be obtained by calculation based on the formula X2=(D2-D1) / D1. In this embodiment, the width of the wound cell is measured using, for example, a Vernier scale.

[0033] Referring to FIGS. 3 and 4, in one embodiment of the present invention, the negative electrode plate 101 of the wound cell 11 includes multiple negative electrode tabs 102, a coated region 103, and a thinned region 104. The coated region 103 is located at the center of the negative electrode plate 101, the thinned region 104 is located on both sides of the coated region 103, and the negative electrode tabs 102 are located on the same side of the thinned region 104, away from the coated region 103. In one embodiment of the present invention, for example, after rolling the negative electrode plate 101, the thickness of the coated region 103 is defined as the thickness of the negative electrode plate at an initial SOC of 0%. Similarly to the transverse expansion coefficient test, a CT test is also performed on the cell at BOL to verify the cross-sectional condition of the negative electrode plate. That is, the test is performed at an early stage of the cell's life, and the thickness M1 of the negative electrode plate at the innermost layer of the cell is read and calculated. After cycling the wound cell, a CT inspection is performed in a similar manner. That is, the thickness M2 of the innermost negative electrode plate is also marked. Furthermore, the data of the longitudinal expansion coefficient X1 of the negative electrode plate is obtained by calculation based on the formula X1=(M1-M2) / M2. In this embodiment, the thickness of the negative electrode plate is measured using, for example, a micrometer.

[0034] The present invention will be described in more detail below with reference to examples. However, it should be noted that such examples should not be construed as limiting. Appropriate modifications can be made without departing from the gist of the present invention, and all such modifications are included in the scope of the present invention.

[0035] Example 1 Preparation of positive electrode plate: LiNi as positive electrode active material 0.5 Co 0.2 Mn 0.3 O2, carbon nanotubes and conductive carbon black as conductive agents, and polyvinylidene fluoride as adhesive were mixed in a mass ratio of 96%:1%:1.5%:1.5% (96%). After uniformly mixing the positive electrode active material, adhesive, and conductive agent, N-methylpyrrolidone was added as a solvent and stirred until the mixture became uniform and transparent. This yielded a positive electrode slurry. The positive electrode slurry was uniformly applied to a 13 μm aluminum foil current collector, baked, and dried. Next, the mixture was rolled and cut to obtain a positive electrode plate.

[0036] Preparation of negative electrode plate: Artificial graphite was used as the negative electrode active material, carbon nanotubes and conductive carbon black were used as conductive agents, polymerized styrene butadiene rubber was used as the adhesive, and sodium carboxymethyl cellulose and polyacrylic acid were used as thickeners in a mass ratio of 95.2%:0.4%:0.8%:1.6%:1.0%:1.0%. Next, deionized water was added and thoroughly stirred to obtain negative electrode slurry. The negative electrode slurry was uniformly applied to 13 μm copper foil, sintered, rolled, and cut to obtain a negative electrode plate. The thickness of the negative electrode plate at an initial SOC of 0% was 150 μm.

[0037] Separator selection: 13 μm polyethylene was selected as the separator.

[0038] Preparation of electrolyte: EC, EMC, and DEC were mixed in a volume ratio of 1:1:1 to obtain a mixed solution. Thoroughly dried lithium hexafluorophosphate was dissolved in the mixed solution in an argon atmosphere glove box with a moisture content of less than 10 ppm. Next, 1,3-propane sultone and vinylene carbonate were added and mixed uniformly to obtain an electrolyte. The concentration of LiPF6 was 1 mol / L, and the mass content of 1,3-propane sultone and vinylene carbonate in the electrolyte was 1% and 0.5%, respectively.

[0039] Battery fabrication: A positive electrode plate, a separator, and a negative electrode plate were stacked in this order, with the separator positioned between the positive and negative electrodes to act as a separator. The components were wound to obtain a wound cell. The wound cell had a width of 122 mm. The structure was then placed in a housing and transferred to a vacuum oven for drying. An electrolyte was then injected, and the housing was sealed. A secondary battery was obtained after the processes of standing, hot pressing, cold pressing, molding, clamping, and capacity grading. The secondary battery was cycled, with the cycle number being 1.

[0040] Example 2 The width of the wound cell was 150 mm, and the number of cycles of the secondary battery was 20. The other operations were the same as in Example 1.

[0041] Example 3 The width of the wound cell was 90 mm, and the number of cycles of the secondary battery was 40. The other operations were the same as in Example 1.

[0042] Comparative Example 1 The width of the negative electrode plate at an initial SOC of 0% was 300 μm. The width of the wound cell was 70 mm, and the number of cycles of the secondary battery was 1. Other operations were the same as in Example 1.

[0043] Comparative Example 2 The number of cycles of the secondary battery was 20. Other operations were the same as those in Comparative Example 1.

[0044] Comparative Example 3 The number of cycles of the secondary battery was 40. The other operations were the same as those in Comparative Example 1.

[0045] In the present invention, the data and capacity retention rates of the secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3 after different cycle numbers were tested. Table 1 shows the test results.

[0046] In one embodiment of the present invention, the capacity retention rate is calculated as follows: At a temperature of 25°C, a secondary battery is charged to 4.2 V at a constant current of 1 C, and then discharged to 2.5 V at a constant current of 1 C, and this is taken as the discharge capacity at the first cycle. By periodically charging and discharging the battery according to the above conditions, the discharge capacities after different numbers of cycles can be obtained. The capacity retention rate after cycling can be calculated using the following formula: Capacity retention rate (%) = (discharge capacity after the corresponding number of cycles / discharge capacity after 1 cycle) × 100%. Here, when the number of cycles is 1, the capacity retention rate is 100%.

[0047] [Table 1]

[0048] Referring to Table 1 in combination with Comparative Examples 1 to 3, when the width of the wound cell and the width of the negative electrode plate exceeded the above numerical ranges, the wound cell did not satisfy the following conditions within the number of cycles and at 100% SOC.

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[0049] Referring to Table 1 in combination with Examples 1 to 3 and Comparative Examples 1 to 3, when the width of the wound cell and the width of the negative electrode plate are within the above-mentioned numerical ranges, the number of cycles is within the above-mentioned ranges, and the SOC is 100%, if the wound cell satisfies the following conditions, as the number of cycles increases, the effect on the capacity retention rate of the secondary battery decreases and the capacity retention rate of the secondary battery increases.

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[0050] In consideration of the above, embodiments of the present invention provide a secondary battery and its use. The design of the wound cell reduces issues such as wrinkling of the electrode pieces and interface degradation, ensures interface stability of the wound cell during charging and discharging, optimizes ion transport paths, and eliminates issues such as lithium deposition and heat generation caused by uneven electrode piece current density distribution during charging and discharging on one or both electrode pieces. This significantly reduces the risk of cracking at the corners of the wound cell during cycling, easing the difficulty of processing the cell during winding and assembly, thereby improving the performance of the secondary battery. Optimizing the composition of the positive electrode active material layer reduces shedding of the positive electrode active material layer and improves the cycle characteristics of the secondary battery. Optimizing the composition of the negative electrode active material layer reduces shedding of the negative electrode active material layer, contributing to the structural stability of the negative electrode plate and improved electrolyte wettability, thereby improving the electrochemical performance of the secondary battery. Lithium deposition during cycling can be reduced, improving the cycle performance of the secondary battery.

[0051] The above description merely illustrates exemplary embodiments and examples of the present application and describes relevant technical principles. Those skilled in the art should understand that the scope of the disclosure contained in the present invention is not limited to the technical solution formed by a specific combination of the above technical features, but also encompasses other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the concept of the present invention, for example, (but not limited to) technical solutions formed by replacing the above features with technical features having similar functions disclosed in the present invention.

[0052] Except for the technical features described herein, the remaining technical features are known to those skilled in the art, and in order to highlight the innovative features of the present invention, the remaining features will not be described again in this specification. [Industrial Applicability]

[0053] The secondary battery can be applied to electronic devices, and can ensure the interface stability of wound cells during charge and discharge processes, reduce lithium precipitation during cycling processes, and improve the cycling performance of secondary batteries. [Explanation of symbols]

[0054] 10: Housing 11: Wound cell 12: First electrode 13: Second electrode 14: Explosion-proof valve 101: Negative plate 102: Negative electrode tab 103: Covered Area 104: Thin area.

Claims

1. The housing and a wound cell disposed within the housing and including a negative electrode plate, a positive electrode plate, and a separator; At least The positive electrode plate includes a positive electrode active material, and the positive electrode active material includes a nickel-cobalt-manganese ternary material; the negative electrode plate includes a negative electrode active material, the negative electrode active material including graphite, At a state of charge (SOC) of 100%, the wound cell satisfies the following conditions: Secondary battery. [Equation 1] In the formula, L1 represents the thickness of the negative electrode plate at an initial SOC of 0%, X1 represents the longitudinal expansion coefficient of the negative electrode plate, L2 represents the width of the wound cell, and X2 represents the lateral expansion coefficient of the wound cell, the unit of L1 is μm, the unit of L2 is μm, the value range of L1 satisfies 60 μm≦L1≦200 μm, and the value range of L2 satisfies 80 mm≦L2≦400 mm.

2. When the cycle number of the secondary battery is within 1 to 60 and the SOC is 100%, the wound cell satisfies the following condition: The secondary battery according to claim 1 . [Equation 2]

3. The general formula of the nickel-cobalt-manganese ternary material is LiNi ｘ Co ｙ Mn １－ｘ－ｙ O ２ wherein 0.5≦x≦0.9 and 0.01≦y≦0.2; The secondary battery according to claim 1 .

4. The general formula of the nickel-cobalt-manganese ternary material is LiNi ｘ Co ｙ Mn １－ｘ－ｙ M ｚ O ２ wherein 0.5≦x≦0.95, 0.01≦y≦0.2, 0<z≦0.1, 1−x−y>0, and M is at least one selected from the group consisting of C, Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, and Zn. The secondary battery according to claim 1 .

5. the secondary battery further includes an electrolyte, the electrolyte being filled in the wound cell and between the wound cell and a housing, the electrolyte including a lithium salt, and the lithium salt including lithium hexafluorophosphate; The secondary battery according to claim 1 .

6. The electrolyte solution further includes an additive, and the additive includes at least one of 1,3-propane sultone, ethylene sulfate, fluoroethylene carbonate, or vinylene carbonate. The secondary battery according to claim 5 .

7. An electronic device comprising the secondary battery according to any one of claims 1 to 6.

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