Secondary battery and use thereof

Abstract

The invention provides a secondary battery and an application thereof. The secondary battery at least comprises a shell, a first electrode and a second electrode, the winding battery cell is arranged in the shell, and the winding battery cell comprises a negative pole piece, a positive pole piece and a diaphragm; wherein in the 100% state of charge, the wound battery cell meets # imgabs0 #, L1 is the thickness of the negative pole piece under the initial 0% SOC, X1 is the longitudinal expansion rate of the negative pole piece, L2 is the width of the wound battery cell, and X2 is the transverse extension rate of the wound battery cell. According to the secondary battery and the application thereof provided by the invention, the lithium precipitation phenomenon in the cycle process can be reduced, and the cycle performance of the secondary battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a secondary battery and applications thereof. Background Art

[0002] With the rapid development of smart grids, electric vehicles, portable electronic products and other fields, secondary batteries, mainly lithium-ion batteries, have become one of the most widely used power batteries. Lithium-ion batteries have been 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. The cells in lithium-ion batteries are divided into laminated cells and wound cells according to the molding method. Wound cells account for a large proportion in power batteries, but due to the special structure of wound cells, it is easy to cause interfacial lithium deposition during the charge and discharge cycle. Summary of the invention

[0003] The present invention provides a secondary battery and application thereof, which can ensure the interface stability of a wound battery cell during the charge and discharge process, reduce lithium plating during the cycle process, and improve the cycle performance of the secondary battery.

[0004] To solve the above technical problems, the present invention is implemented through the following technical solutions.

[0005] The present invention provides a secondary battery, comprising at least:

[0006] a housing; and

[0007] A wound battery cell is arranged in the housing, wherein the wound battery cell comprises a negative electrode sheet, a positive electrode sheet and a separator;

[0008] Wherein, at 100% charge state, the wound battery cell satisfies: Wherein, L1 is the thickness of the negative electrode sheet at the initial 0% SOC, X1 is the longitudinal expansion rate of the negative electrode sheet, L2 is the width of the wound battery cell, and X2 is the lateral extension rate of the wound battery cell.

[0009] 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.

[0010] In one embodiment of the present invention, when the secondary battery has a cycle number of 1-60 and is at a 100% charge state, the wound battery cell satisfies:

[0011] In one embodiment of the present invention, the negative electrode plate includes a negative electrode active material, the negative electrode active material includes one of graphite or graphite-doped silicon materials, and the silicon material includes at least one of silicon monoxide or silicon.

[0012] In one embodiment of the present invention, the positive electrode plate includes a positive electrode active material, and the positive electrode active material includes at least one of a nickel-cobalt-manganese ternary material or a modified nickel-cobalt-manganese ternary material.

[0013] In one embodiment of the present invention, the general formula of the nickel-cobalt-manganese ternary material is LiNi x Co y Mn 1-x-y O 2 , where 0.5≤x≤0.9, 0.01≤y≤0.2.

[0014] 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 z O 2 , where 0.5≤x≤0.95, 0.01≤y≤0.2, 0<z≤0.1,1-x-y> 0, M is at least one selected from C, Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W or Zn.

[0015] In one embodiment of the present invention, the secondary battery further includes an electrolyte, the secondary battery further includes an electrolyte, the electrolyte is filled in the wound battery cell and between the wound battery cell and the shell, the electrolyte includes a lithium salt, and the lithium salt includes lithium hexafluorophosphate.

[0016] In one embodiment of the present invention, the electrolyte further includes an additive, and the additive includes at least one of 1,3-propane sultone, vinyl sulfate, fluoroethylene carbonate or vinylene carbonate.

[0017] The present invention also provides an electronic device, comprising the secondary battery mentioned above.

[0018] In summary, the present invention proposes a secondary battery and its application, which can reduce the problems of pole piece wrinkles and interface deterioration, ensure the interface stability of the wound battery cell during the charging and discharging process, optimize the ion transmission path, and optimize the problems of lithium precipitation and heat generation caused by the uneven distribution of pole piece current density in the single-sided pole ear or double-sided pole ear battery cell during the charging and discharging process, significantly reduce the risk of cracks in the corner area of ​​the wound battery cell during the cycle, and reduce the processing difficulty of the winding assembly of the battery cell, thereby improving the performance of the secondary battery. It can reduce the peeling of the positive electrode active material layer and improve the cycle performance of the secondary battery. It can reduce the peeling of the negative electrode active material layer, which is beneficial to improve the stability of the negative electrode sheet structure and the wettability of the electrolyte, and improve the electrochemical performance of the secondary battery. It can reduce the lithium precipitation phenomenon during the cycle and improve the cycle performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 It is a schematic diagram of a secondary battery that is a soft-pack battery in one embodiment of the present invention.

[0021] Figure 2 It is a schematic diagram of another embodiment of the present invention in which the ion battery is a hard shell battery.

[0022] Figure 3 Schematic diagram of a wound battery cell in one embodiment of the present invention.

[0023] Figure 4 Schematic diagram of a negative electrode sheet in one embodiment of the present invention.

[0024] Explanation of reference numerals: 10, casing; 11, wound battery cell; 12, first electrode; 13, second electrode; 14, explosion-proof valve; 101, negative electrode sheet; 102, negative electrode tab; 103, coating area; 104, thinning area. DETAILED DESCRIPTION

[0025] The following describes the embodiments of the present invention through specific examples, and 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, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0026] It should be understood that the present invention can be implemented in different forms and should not be interpreted as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make the disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0027] The technical solution of the present invention is further described in detail below in conjunction with several embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] The present invention provides an electronic device, the electronic device includes at least one secondary battery, and the secondary battery is used to provide electrical energy. Among them, the electronic device can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy and an electric tool, etc. In one embodiment of the present invention, the vehicle is, for example, a new energy vehicle, and the new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. Spacecraft include airplanes, rockets, space shuttles and spacecrafts, etc. Electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric airplane toys, etc. Electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators and electric planers, etc. The present invention specifically limits the types and steps of electronic devices.

[0029] During the charge and discharge process of secondary batteries, the negative electrode active materials in the secondary batteries expand and contract repeatedly during the cycle, which has a relatively large impact on the materials, causing the wound battery cells to shrink and expand in different directions. Once there is insufficient space reserved in the wound battery cells, it is easy for the pole pieces to have nowhere to expand, which in turn causes the pole pieces to wrinkle and the interface to deteriorate, seriously leading to safety problems such as lithium plating, self-discharge and even short circuit, limiting the development of secondary batteries.

[0030] See also Figure 1 to Figure 2 As shown, the present invention proposes a secondary battery that can be used in the above-mentioned electronic device. The secondary battery includes a shell 10 and a wound battery cell 11, and the wound battery cell 11 is arranged in the shell 10. Among them, the wound battery cell 11 includes a negative electrode sheet, a positive electrode sheet and a separator, etc. The separator is arranged between the negative electrode sheet and the positive electrode sheet, and the inside of the wound battery cell 11 and between the wound battery cell 11 and the shell 10 are filled with electrolyte. The secondary battery also includes a first electrode 12 and a second electrode 13, which are arranged at intervals on the same side of the shell 10, and are respectively connected to the tabs of the negative electrode sheet and the positive electrode sheet in the wound battery cell 11, as the positive and negative electrodes of the secondary battery, which can improve the space utilization rate in the shell 10, and simplify the structure of the battery cell, which is convenient for the connection of multiple batteries in the battery module. In another embodiment of the present invention, the first electrode 12 and the second electrode 13 are arranged at opposite ends of the shell 10, that is, the formed battery cell is a single-side tab or double-side tab battery cell to meet the use requirements of different environments. The present invention does not limit the type and shape of the secondary battery. In one embodiment of the present invention, the secondary battery is, for example, a soft-pack battery or a hard-shell battery. In the present invention, the secondary battery is, for example, a lithium-ion battery, or a sodium-ion battery. In this embodiment, the secondary battery is described by taking a lithium-ion battery as an example.

[0031] See also Figure 1As shown, in one embodiment of the present invention, the secondary battery is, for example, a soft-pack battery, and the shell 10 of the soft-pack battery is, for example, a soft-pack film such as a polyimide film, an aluminum-plastic film, and a polyethylene film. Specifically, after the wound battery cell 11 is formed, the soft-pack film is coated on the outside of the wound battery cell, and an electrolyte is injected and sealed to obtain a soft-pack battery.

[0032] See also Figure 2 As shown, in one embodiment of the present invention, the secondary battery is, for example, a hard shell battery, and also, for example, a square shell battery or a cylindrical battery. The shape of the shell 10 of the hard shell battery is, for example, a circle, a square or a rounded rectangle, and the shell 10 is, for example, an aluminum shell or a steel shell. One end of the shell 10 is sealed, and the other end is provided with an opening. The shell 10 forms a receiving cavity to accommodate the wound battery cell. The wound battery cell is placed in the shell 10, and the electrolyte is injected and assembled to obtain a hard shell battery. In the hard shell battery, an explosion-proof valve 14 is provided between the first electrode 12 and the second electrode 13, and for example, it is provided in the middle position of the first electrode 12 and the second electrode 13, and has a preset distance between the first electrode 12 and the second electrode 13, respectively. The explosion-proof valve 14 can open the ventilation function when the battery cell is working normally, so that the air flow inside and outside the battery cell can flow, and particulate matter cannot flow. When the battery cell has thermal runaway and the pressure difference inside and outside the battery cell reaches the explosion-proof preset value, the explosion-proof valve opens, and both gas and solid can be discharged from the inside of the battery cell to the outside of the battery cell through the explosion-proof valve, thereby improving the safety performance of the battery cell.

[0033] In one embodiment of the present invention, the positive electrode plate includes a positive current collector and a positive active material layer coated on at least one side of the positive current collector, and for example, both sides are coated with positive active material layers to improve the capacity performance of the battery cell. Among them, the positive current collector can be, for example, a foil formed by surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel or carbon. In addition to the foil, the positive current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam or non-woven fabric. Among them, the thickness of the positive current collector is, for example, 8μm-15μm. In this embodiment, the positive current collector is, for example, aluminum foil.

[0034] In one embodiment of the present invention, the positive electrode active material layer includes, for example, a positive electrode active material, a conductive agent, and a binder, and the mass proportion of the positive electrode active material, the conductive agent, and the binder is, for example, 94.5%-97.8%: 1.2%-3.5%: 1%-2% based on 100% of the total mass of the positive electrode active material layer. The positive electrode active material includes at least one of a nickel-cobalt-manganese ternary material or a modified nickel-cobalt-manganese ternary material, and the general formula of the nickel-cobalt-manganese ternary material is LiNi x Co y Mn 1-x-y O 2, where 0.5 ≤ x ≤ 0.9, 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 z O 2 , where 0.5 ≤ x ≤ 0.95, 0.01 ≤ y ≤ 0.2, 0 < z ≤ 0.1, M is selected from at least one of C, Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, or Zn, and the modification method of the modified nickel-cobalt-manganese ternary material includes at least one of doping, coating, or structure control, etc. The conductive agent is, for example, selected from any one or more of conductive carbon black (Super P, SP), acetylene black, carbon nanotubes (Carbon Nanotubes, CNT), mesophase carbon microspheres, or graphene, etc. The binder is, for example, selected from any one or more of polyvinylidene fluoride (Poly vinylidene Fluoride, PVDF), polyacrylic acid (Polyacrylic Acid, PAA), polyamide (Polyamide, PA), polyacrylonitrile (Polyacrylonitrile, PAN), polyacrylate, polyvinylether, polymethylmethacrylate (PolymethylMethacrylate, PMMA), ethylene-propylene-diene terpolymer (EPDM), or polyhexafluoropropylene, etc. In an embodiment of the present invention, the conductive agent is, for example, selected from conductive carbon black and carbon nanotubes, and the binder is, for example, selected from 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 multiple conductive agents in combination, it is beneficial to form a conductive network, reduce the peeling of the positive electrode active material layer, and improve the cycling performance of the secondary battery.

[0035] In an embodiment of the present invention, the negative electrode sheet includes, for example, a negative electrode current collector and a negative electrode active material layer coated on at least one side of the negative electrode current collector, or, for example, both sides are coated with the negative electrode active material layer to improve the capacity performance of the battery cell. The negative electrode current collector is, for example, selected from one of a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foam copper current collector, or a stainless steel current collector, etc., and the thickness of the negative electrode current collector is, for example, 8 μm - 15 μm. In this embodiment, the negative electrode current collector is, for example, a copper foil.

[0036] In one embodiment of the present invention, the negative electrode active material layer includes a negative electrode active material, a binder, a conductive agent, a thickener, etc., and the mass proportion of the negative electrode active material, the conductive agent, the binder and the thickener is, for example, 93.4%-97.8%: 0.6%-2.6%: 0.8%-1.5%: 0.8%-2.5% based on 100% of the total mass of the negative electrode active material layer. The negative electrode active material, for example, includes one of graphite or graphite-doped silicon materials, wherein the graphite is, for example, natural graphite or artificial graphite, and the silicon material in the graphite-doped silicon material includes, but is not limited to, at least one of silicon oxide or silicon. The binder is, for example, selected from any one or more of polyvinylidene fluoride, polyamide, polypropylene, polyacrylate, polyvinyl ether, polymethyl methacrylate, polyhexafluoropropylene or styrene butadiene rubber (SBR). The conductive agent is, for example, selected from any one or more of conductive carbon black, acetylene black, carbon nanotubes, mesophase carbon microspheres or graphene. The thickener is, for example, selected from any one or more of sodium carboxymethyl cellulose (CMC) or polyacrylic acid. In one embodiment of the present invention, the conductive agent is, for example, selected from conductive carbon black and carbon nanotubes, the adhesive is, for example, selected from styrene-butadiene rubber, the thickener is, for example, selected from sodium carboxymethyl cellulose and polyacrylic acid, and the mass proportion of the negative electrode active material, carbon nanotubes, conductive carbon black, polyvinylidene fluoride, sodium carboxymethyl cellulose and polyacrylic acid is, for example, 94.5%-97.8%: 0-1.2%: 0.6%-1.4%: 0.8%-1.5%: 0.8%-1.5%: 0%-1%. By sharing a variety of thickeners and a variety of conductive agents, the peeling of the negative electrode active material layer is reduced, which is beneficial to improve the stability of the negative electrode sheet structure and the wettability of the electrolyte, and improve the electrochemical performance of the secondary battery.

[0037] In one embodiment of the present invention, the separator is, for example, a polyethylene film (PE), a polypropylene film (PP), a glass fiber film, a polyethylene film or a composite film, and the thickness of the separator is, for example, 9 μm-15 μm. The electrolyte is filled between the positive electrode sheet, the negative electrode sheet and the separator, and between the wound battery cell and the shell. The electrolyte includes a lithium salt, and the lithium salt includes lithium hexafluorophosphate (LiPF 6). The present application does not specifically limit the type of electrolyte, and any commercial lithium hexafluorophosphate electrolyte can be selected. In one embodiment of the present invention, the electrolyte includes an organic solvent, a lithium salt, and an additive, wherein the organic solvent includes, for example, any one of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC) or diethyl carbonate (DEC), or a combination of at least two thereof. The lithium salt is, for example, lithium hexafluorophosphate, and the additive includes, for example, at least one of film-forming additives such as 1,3-propane sultone (PS), vinyl sulfate (DTD), fluoroethylene carbonate (Fluoroethylene carbonate, FEC) or vinyl 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 an argon atmosphere glove box with a water content of <10ppm, fully dried lithium hexafluorophosphate is dissolved in the mixed solution, and then 1,3-propane sultone and vinylene carbonate are added and mixed to obtain an electrolyte, wherein LiPF 6 The concentration is 1 mol / L, the mass content of 1,3-propane sultone in the electrolyte is 0.1%-3%, and the mass content of vinylene carbonate in the electrolyte is 0.1%-3%.

[0038] The present invention also provides a method for preparing a secondary battery, wherein the positive electrode active material, the conductive agent and the binder are mixed according to a mass ratio, and then a positive electrode solvent is added and stirred until the system is uniform to obtain a positive electrode slurry. The positive electrode solvent is selected from N-methylpyrrolidone (NMP), for example. The positive electrode slurry is evenly coated on at least one side of the positive electrode collector, and after drying, rolling, slitting and other processes are performed to obtain a positive electrode sheet. The negative electrode active material, the conductive agent, the binder and the thickener are mixed according to a mass ratio, and then a negative electrode solvent is added and mixed evenly to obtain a negative electrode slurry, and the negative electrode solvent is selected from deionized water, for example. The negative electrode slurry is coated on at least one side of the negative electrode collector, and after drying, rolling, slitting and other processes are performed to obtain a negative electrode sheet. The separator, positive electrode sheet, separator and negative electrode sheet are stacked in order, then wound in the same direction and finished to obtain a wound battery cell, which is placed in a shell, injected with electrolyte, and sealed to obtain a secondary battery.

[0039] See also Figure 3 As shown, in one embodiment of the present invention, the wound battery cell 11 is, for example, circular or rounded rectangular. In this embodiment, the wound battery cell 11 is, for example, a rounded rectangular, and two straight areas with large faces facing each other in the wound battery cell 11 are defined as straight areas. The two straight areas are arranged opposite to each other, and the area connected at both ends of the straight area is defined as a corner area. Among them, the width of the wound battery cell 11 is L2. Among them, in the secondary battery, when the secondary battery is adjusted to 100% state of charge (State of Charge, SOC), the wound battery cell satisfies: Among them, L1 is the thickness of the negative electrode sheet at the initial 0% SOC, that is, the thickness of the negative electrode sheet when the secondary battery is assembled and not under any working conditions, X1 is the longitudinal expansion rate of the negative electrode sheet, L2 is the width of the wound battery cell, and X2 is the lateral extension rate of the wound battery cell. Among them, the value range of L1 satisfies: 60μm≤L1≤200μm, and the value range of L2 satisfies: 80mm≤L2≤400mm. When the secondary battery has a cycle number of 1-60, for example, and is in a 100% charged state, when the wound battery cell satisfies the above formula, it can ensure the interface stability of the battery cell during the charging and discharging process, optimize the ion transmission path, and optimize the problems of lithium precipitation or heat generation caused by uneven distribution of the current density of the electrode sheet during the charging and discharging process of the single-sided or double-sided output ear battery cell, significantly reduce the risk of cracks in the corner area of ​​the battery cell during the cycle, and can reduce the processing difficulty of the battery cell winding assembly.

[0040] See also Figure 3 to Figure 4 As shown, in one embodiment of the present invention, when testing the lateral extension rate X2 of the wound battery cell, the BOL (Beginning of Life) battery cell is subjected to a computed tomography (CT) test to show the length state of the negative electrode sheet, that is, the test is performed at the beginning of the life of the battery cell, and the top, middle and bottom three points in the coating area 103 of the negative electrode sheet are selected. In this embodiment, for example, the negative electrode sheet in the innermost straight area of ​​the battery cell is selected at the A1-A1 position, the A2-A2 position and the A3-A3 position, and the thinning area 104 is avoided. The wound battery cell 11 is marked with high precision to measure the width of the straight area of ​​the innermost negative electrode sheet of the wound battery cell, that is, Figure 3 In the figure, the distance D1 from point A to point B of the innermost negative electrode sheet is measured. After the winding cell is cycled for a certain number of times, the CT test is performed again in the same way, and the width of the straight area of ​​the innermost negative electrode sheet is also marked, that is, the distance D2 from point A to point B after the cycle. The data of the lateral extension rate X2 of the wound cell can be obtained by calculation using the formula: X2 = (D2-D1) / D1. In this embodiment, the width of the wound cell is measured, for example, using a vernier caliper.

[0041] See also Figure 3 to Figure 4As shown, in one embodiment of the present invention, the negative electrode sheet 101 in the wound battery cell 11 includes a plurality of negative electrode tabs 102, a coating area 103 and a thinning area 104, wherein the coating area 103 is arranged in the middle of the negative electrode sheet 101, the thinning area 104 is arranged on both sides of the coating area 103, and the negative electrode tabs 102 are arranged on the same side of the thinning area 104 away from the coating area 103. In one embodiment of the present invention, for example, after the negative electrode sheet 101 is rolled, the thickness of the coating area 103 is defined as the thickness of the negative electrode sheet at the initial 0% SOC. When testing the longitudinal expansion rate X1 of the negative electrode sheet, similar to the longitudinal expansion rate test method, the BOL battery cell is subjected to a CT test to show the cross-sectional state of the negative electrode sheet, that is, the test is performed at the early stage of the life of the battery cell, for example, the thickness M1 of the negative electrode sheet is read and calculated in the innermost layer of the battery cell. After the winding cell cycle, the CT test is performed again in the same way, and the thickness of the innermost negative electrode sheet is marked as M2. The longitudinal expansion rate X1 of the negative electrode sheet can be obtained by calculation using the formula: X1 = (M1-M2) / M2. In this embodiment, the thickness of the negative electrode sheet is measured by, for example, a micrometer.

[0042] Hereinafter, the present invention will be explained in more detail by citing examples, which should not be construed as limiting. Appropriate modifications may be made within the scope consistent with the gist of the present invention, all of which fall within the technical scope of the present invention.

[0043] Example 1

[0044] Preparation of positive electrode sheet: LiNi 0.5 Co 0.2 Mn 0.3 O 2 , conductive carbon nanotubes and conductive carbon black, and adhesive polyvinylidene fluoride are mixed in a mass ratio of 96%: 1%: 1.5%: 1.5%. After the positive electrode active material, adhesive and conductive agent are evenly mixed, solvent N-methylpyrrolidone is added and stirred until uniform and transparent to obtain positive electrode slurry. The positive electrode slurry is evenly coated on a 13μm aluminum foil current collector, dried, and then rolled and cut to obtain a positive electrode sheet.

[0045] Preparation of negative electrode sheet: Mix the negative electrode active material artificial graphite, the conductive agent carbon nanotube and conductive carbon black, the adhesive styrene butadiene rubber, and the thickener sodium carboxymethyl cellulose and polyacrylic acid in a mass ratio of 95.2%: 0.4%: 0.8%: 1.6%: 1.0%: 1.0%, add deionized water, and stir thoroughly to obtain negative electrode slurry. The negative electrode slurry is evenly coated on a 13μm copper foil, and the negative electrode sheet is obtained after drying, rolling, and slitting. Among them, the thickness of the negative electrode sheet at the initial 0% SOC is 150μm.

[0046] Selection of diaphragm: 13 μm polyethylene was selected as the diaphragm.

[0047] Preparation of electrolyte: EC, EMC and DEC were mixed in a volume ratio of 1:1:1 to obtain a mixed solution. In an argon atmosphere glove box with a water content of <10ppm, fully dried lithium hexafluorophosphate was dissolved in the mixed solution. 1,3-propane sultone and vinylene carbonate were then added and mixed to obtain an electrolyte. Among them, LiPF 6 The concentration of is 1 mol / L, the mass content of 1,3-propane sultone in the electrolyte is 1%, and the mass content of vinylene carbonate in the electrolyte is 0.5%.

[0048] Preparation of battery: stack the positive electrode sheet, separator and negative electrode sheet in sequence, place the separator between the positive electrode sheet and the negative electrode sheet to play an isolating role, and wind up to obtain a wound battery cell, and the width of the wound battery cell is 122mm. Then place it in a shell, transfer it to a vacuum oven for drying, inject electrolyte and seal it, and after standing, hot and cold pressing, formation, clamping and capacity division processes, obtain a secondary battery, and cycle the secondary battery, and the number of cycles is 1.

[0049] Example 2

[0050] The width of the wound battery cell is 150 mm, the number of cycles of the secondary battery is 20, and other operations are consistent with Example 1.

[0051] Example 3

[0052] The width of the wound battery cell is 90 mm, the number of cycles of the secondary battery is 40, and other operations are consistent with Example 1.

[0053] Comparative Example 1

[0054] The thickness of the negative electrode sheet at the initial 0% SOC is 300 μm, the width of the wound battery cell is 70 mm, the number of cycles of the secondary battery is 1, and other operations are consistent with Example 1.

[0055] Comparative Example 2

[0056] The number of cycles of the secondary battery was 20, and other operations were consistent with those of Comparative Example 1.

[0057] Comparative Example 3

[0058] The number of cycles of the secondary battery was 40, and other operations were consistent with Comparative Example 1.

[0059] In the present invention, the data and cycle capacity retention rate of the secondary batteries at different cycle numbers in Examples 1-3 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1.

[0060] In one embodiment of the present invention, the cycle capacity retention rate is when the temperature is 25°C, the secondary battery is charged to 4.2V at a constant current of 1C, and discharged to 2.5V at a constant current of 1C. The discharge capacity of the secondary battery at this time is tested, which is the discharge capacity of the first cycle. The battery is cycled according to the above conditions to obtain the discharge capacity of different cycle numbers. The capacity retention rate after the cycle is calculated according to the following formula: Capacity retention rate (%) = (discharge capacity corresponding to the number of cycles / discharge capacity of the first cycle) × 100%. When the number of cycles is 1, the capacity retention rate is 100%.

[0061] Table 1. Performance of secondary batteries in Examples 1-3 and Comparative Examples 1-3

[0062]

[0063] Please refer to Table 1. In combination with Comparative Examples 1-3, it can be seen that when the width of the wound cell and the thickness of the negative electrode sheet exceed the value range, the secondary battery does not meet the following conditions within the cycle number and at 100% charge state: At this time, as the number of cycles increases, the cycle capacity retention rate of the secondary battery decreases rapidly, and the capacity of the secondary battery decays seriously. That is, when the formula calculation result exceeds 0.0255%, it is very easy to cause wrinkles on the negative electrode interface, the interface deteriorates during the cycle expansion process, and lithium precipitation increases, which in turn causes various safety problems, and the performance of the secondary battery cannot be guaranteed.

[0064] As shown in Table 1, it can be seen from the combination of Examples 1-3 and Comparative Examples 1-3 that when the width of the wound cell and the thickness of the negative electrode sheet are within the value range, the secondary battery is within the number of cycles and at 100% charge state, the wound cell meets the following conditions: When the number of cycles increases, the impact on the cycle capacity retention rate of the secondary battery is small, and the cycle capacity retention rate of the secondary battery is high. Therefore, by designing the structure of the wound battery cell, it is possible to reduce problems such as electrode wrinkles and interface degradation, ensure the interface stability of the wound battery cell during the charge and discharge process, optimize the ion transmission path, and optimize the problems of lithium precipitation and heat generation caused by uneven distribution of electrode current density in the single-sided or double-sided electrode tab cells during the charge and discharge process. The risk of cracks in the corner area of ​​the wound battery cell during the cycle process is significantly reduced, and the processing difficulty of the cell winding assembly can be reduced, thereby improving the performance of the secondary battery.

[0065] In summary, the present invention proposes a secondary battery and its application. By designing a wound battery cell, it is possible to reduce problems such as electrode wrinkles and interface degradation, ensure the interface stability of the wound battery cell during the charge and discharge process, optimize the ion transmission path, and optimize the problems of lithium precipitation and heat generation caused by uneven distribution of electrode current density in the single-sided or double-sided electrode cell during the charge and discharge process. The risk of cracks in the corner area of ​​the wound battery cell during the cycle process is significantly reduced, and the processing difficulty of the battery cell winding assembly can be reduced, thereby improving the performance of the secondary battery. By optimizing the components of the positive electrode active material layer, the peeling of the positive electrode active material layer can be reduced, and the cycle performance of the secondary battery can be improved. By optimizing the components of the negative electrode active material layer, the peeling of the negative electrode active material layer can be reduced, which is beneficial to improve the stability of the negative electrode sheet structure and the wettability of the electrolyte, and improve the electrochemical performance of the secondary battery. It can reduce the lithium precipitation phenomenon during the cycle process and improve the cycle performance of the secondary battery.

[0066] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept, such as a technical solution formed by replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

[0067] Except for the technical features described in the specification, the remaining technical features are known technologies to those skilled in the art. In order to highlight the innovative features of the present invention, the remaining technical features will not be described here in detail.

Claims

1. A secondary battery, It is characterized in that At least: case; as well as A wound battery cell is arranged in the housing, wherein the wound battery cell comprises a negative electrode sheet, a positive electrode sheet and a separator; Wherein, at 100% charge state, the wound battery cell satisfies: Wherein, L1 is the thickness of the negative electrode sheet at the initial 0% SOC, X1 is the longitudinal expansion rate of the negative electrode sheet, L2 is the width of the wound battery cell, and X2 is the lateral extension rate of the wound battery cell.

2. The secondary battery according to claim 1, It is characterized in that The value range of L1 satisfies: 60μm≤L1≤200μm, and the value range of L2 satisfies: 80mm≤L2≤400mm.

3. The secondary battery according to claim 1, It is characterized in that When the secondary battery has a cycle number of 1 to 60 and is at a 100% charge state, the wound battery cell meets the following requirements:

4. The secondary battery according to claim 1, It is characterized in that The negative electrode plate includes a negative electrode active material, wherein the negative electrode active material includes one of graphite or graphite-doped silicon materials, and the silicon material includes at least one of silicon monoxide or silicon.

5. The secondary battery according to claim 1, It is characterized in that The positive electrode plate includes a positive electrode active material, and the positive electrode active material includes at least one of a nickel-cobalt-manganese ternary material or a modified nickel-cobalt-manganese ternary material.

6. The secondary battery according to claim 5, It is characterized in that The general formula of the nickel-cobalt-manganese ternary material is LiNi x Co y Mn 1-x-y O 2 , where 0.5≤x≤0.9, 0.01≤y≤0.

2.

7. The secondary battery according to claim 5, It is characterized in that The general formula of the modified nickel-cobalt-manganese ternary material is LiNi x Co y Mn 1-x-y M z O 2 , where 0.5≤x≤0.95, 0.01≤y≤0.2, 0<z≤0.1,1-x-y> 0, M is at least one selected from C, Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W or Zn.

8. The secondary battery according to claim 1, It is characterized in that The secondary battery further includes an electrolyte, the electrolyte is filled in the wound battery core and between the wound battery core and the shell, the electrolyte includes a lithium salt, and the lithium salt includes lithium hexafluorophosphate.

9. The secondary battery according to claim 8, It is characterized in that The electrolyte further includes an additive, wherein the additive includes at least one of 1,3-propane sultone, vinyl sulfate, fluoroethylene carbonate, or vinylene carbonate.

10. An electronic device, It is characterized in that A secondary battery comprising the secondary battery according to any one of claims 1 to 9.

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