Lithium ion battery

Abstract

The invention relates to the technical field of batteries, in particular to a lithium ion battery. The lithium ion battery comprises an electrolyte, a negative plate and a positive plate, the electrolyte comprises a fluorinated solvent, and the weight content of the fluorinated solvent is f wt% on the basis of the total weight of the electrolyte; the ratio of the width of the negative plate to the width of the positive plate is g, and the lithium ion battery meets the following relational expression: f / g is greater than or equal to 2 and less than or equal to 30. According to the lithium ion battery disclosed by the invention, by controlling the relationship between the weight content of the fluorinated solvent in the electrolyte and the width ratio of the positive plate and the negative plate, the fluorinated solvent can form an SEI film rich in LiF on the surfaces of the positive electrode and the negative electrode and the edge of the negative plate, and the SEI film rich in LiF is relatively thin and relatively high in toughness; the short circuit risk caused by burrs on the edge of the negative plate can be reduced, meanwhile, the diffusion speed of lithium ions in the electrolyte is increased, the lithium precipitation condition is improved, and therefore the safety performance and cycling stability of the battery are improved.

Description

Technical Field

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

[0002] In recent years, lithium-ion batteries have made significant progress in energy density, safety, charging speed, cycle life, etc. These advances provide better support and guarantee for their wide application in various application scenarios. However, the lithium plating problem of lithium-ion batteries has an impact on the cycle performance and safety performance of the battery, which has hindered the further development of lithium-ion batteries. Summary of the invention

[0003] The lithium deposition problem of lithium-ion batteries can be solved by adding functionalized solvents to the electrolyte. The functionalized solvents have specific functional groups that can improve the safety and cycle performance of the battery. For example, by adding fluorinated solvents to organic solvents, the organic solvent's ability to dissolve lithium salts can be improved, while the stability of the electrolyte can be improved, thereby improving the lithium deposition of the battery and improving the safety and cycle performance of the battery. However, after cutting, burrs will appear on the edge of the negative electrode sheet, which will increase the risk of battery short circuit and affect the safety and cycle performance of the battery.

[0004] In order to overcome the above technical problems existing in the prior art, the present invention provides a lithium ion battery. The lithium ion battery of the present invention controls the relationship between the weight content of the fluorinated solvent in the electrolyte and the width ratio of the positive and negative electrode sheets, so that the fluorinated solvent can form a LiF-rich SEI film on the surface of the positive and negative electrodes and the edge of the negative electrode sheet. The LiF-rich SEI film is relatively thin and has high toughness, which can reduce the short circuit risk caused by the burrs on the edge of the negative electrode sheet, and at the same time increase the diffusion rate of lithium ions in the electrolyte, improve the lithium precipitation situation, thereby improving the safety performance and cycle stability of the battery.

[0005] The present invention provides a lithium ion battery, wherein the lithium ion battery comprises an electrolyte, a negative electrode sheet and a positive electrode sheet, wherein the electrolyte comprises a fluorinated solvent, and the weight content of the fluorinated solvent is f wt% based on the total weight of the electrolyte; the ratio of the width of the negative electrode sheet to the width of the positive electrode sheet is g, and the lithium ion battery satisfies the following relationship: 2≤f / g≤30.

[0006] Through the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0007] The lithium ion battery of the present invention can improve the stability of the interface between the positive and negative electrode sheets and the electrolyte by controlling the relationship between the weight content of the fluorinated solvent in the electrolyte and the ratio of the width of the positive and negative electrode sheets, reduce the concentration polarization of the electrolyte and the polarization phenomenon of the electrochemical reaction during lithium insertion and extraction, and can especially form a SEI film with strong toughness around the burrs of the negative electrode sheet, so that the current of the burr part of the negative electrode sheet is more uniform, reduce the short circuit risk caused by the burrs on the edge of the negative electrode sheet, and improve the cycle performance and safety performance of the battery. At the same time, during the cycle process, the fluorinated solvent in the electrolyte can repair the SEI film in time, so that the battery maintains a high cycle performance, improve the transmission rate of lithium ions in the electrolyte, and improve the lithium precipitation situation.

[0008] Other features and advantages of the present invention will be described in detail in the following detailed description.

[0009] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Shown is a schematic diagram of the stacked negative electrode sheet and positive electrode sheet of the present invention.

[0011] Figure 2 Shown is a schematic structural diagram of the negative electrode sheet of the present invention.

[0012] Figure 3 Shown is a schematic structural diagram of the positive electrode current collector of the present invention.

[0013] Figure 4 FIG. 1 is a schematic diagram of a tab in one embodiment of the present invention. DETAILED DESCRIPTION

[0014] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention. In this article, unless otherwise specified, the data range includes the endpoints.

[0015] It should be noted that the numerical expressions such as "first" and "second" in the present disclosure are only used to distinguish different substances or usage methods, and do not represent the difference in order.

[0016] The present invention provides a lithium ion battery, wherein the lithium ion battery comprises an electrolyte, a negative electrode sheet and a positive electrode sheet, wherein the electrolyte comprises a fluorinated solvent, and the weight content of the fluorinated solvent is f wt% based on the total weight of the electrolyte; the ratio of the width of the negative electrode sheet to the width of the positive electrode sheet is g, and the lithium ion battery satisfies the following relationship: 2≤f / g≤30.

[0017] Figure 1 The figure shows a schematic diagram of a stacked negative electrode sheet and a positive electrode sheet. In order to illustrate the relative relationship between the width of the negative electrode sheet and the width of the positive electrode sheet, Figure 1 The separator is omitted in the figure, but it exists in lithium-ion batteries and can separate the positive electrode from the negative electrode. Figure 1 As shown, the width b1 of the negative electrode sheet 1 is greater than the width b2 of the positive electrode sheet 2, and the ratio of the width of the negative electrode sheet to the width of the positive electrode sheet is g=b2 / b1. In the present invention, the width is the length along the width direction.

[0018] The lithium-ion battery of the present invention can be a lithium-ion battery with a core-wound structure or a lithium-ion battery with a laminated structure. Before winding, the positive electrode sheet and the negative electrode sheet can be Figure 1 As shown in the figure, the layers are stacked and wound to form a roll core, wherein a separator is provided between the positive electrode sheet and the negative electrode sheet to separate the positive electrode sheet from the negative electrode sheet; in a lithium-ion battery with a stacked structure, the positive electrode sheet and the negative electrode sheet can also be as shown in the figure. Figure 1 Place them in layers as shown, and repeat as shown Figure 1 The positive electrode sheet and the negative electrode sheet shown form a laminated battery cell, wherein a separator is provided between the positive electrode sheet and the negative electrode sheet to separate the positive electrode sheet from the negative electrode sheet.

[0019] The electrolyte of the present invention includes a fluorinated solvent. During the first discharge, the fluorinated solvent forms a solvation sheath around the lithium ions. The fluorinated solvent has a high anion concentration in the sheath, which increases the LUMO energy level of the anions, and can promote the SEI film to be rich in LiF. The LiF-rich SEI film has a higher Young's modulus and a more uniform lithium ion flux, and can make lithium dendrites tend to grow in a planar manner, thereby making the interface between the electrolyte and the positive and negative electrode sheets more stable, and reducing the concentration polarization of the electrolyte and the electrochemical polarization phenomenon of lithium insertion and extraction.

[0020] By controlling the relationship between the weight content of the fluorinated solvent in the electrolyte and the ratio of the width of the positive and negative electrode sheets, it is possible to ensure that the fluorinated solvent forms a LiF-rich SEI film at the edge burrs of the negative electrode sheet. The SEI film is thin, has high toughness and low impedance, can promote the diffusion and transmission of ions, improve the lithium precipitation at the interface between the negative electrode sheet and the electrolyte, and after satisfying a specific relationship, the SEI film can be continuously repaired during the cycle process, ensuring that the SEI film near the burrs of the negative electrode sheet has a high stability, avoiding local polarization of the surface of the negative electrode sheet caused by uneven current in the burr part of the negative electrode sheet, reducing the risk of short circuit caused by burrs on the edge of the negative electrode sheet, and at the same time improving the transmission rate of lithium ions in the electrolyte, so that the battery can maintain long cycle performance and high safety performance.

[0021] The lithium-ion battery can satisfy the following relationship: 2≤f / g≤30 (for example, 2, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28 or 30). When f / g<2, the content of the fluorinated solvent is low or the ratio of the width of the negative electrode sheet to the width of the positive electrode sheet is too high. The content of the fluorinated solvent in the electrolyte is too low, and the LiF-rich SEI film cannot be formed on the positive and negative electrode surfaces, and the SEI film cannot be repaired in time during the cycle, resulting in that the polarization and short circuit problems caused by the burrs of the negative electrode sheet cannot be effectively improved. The ratio of the width of the negative electrode sheet to the width of the positive electrode sheet is too high, which will lead to a reduction in the effective surface area of ​​the electrode and an increase in the burrs of the negative electrode, which greatly increases the micro-short circuit during the cycle. When f / g>30, the content of fluorinated solvent is high or the ratio of the width of the negative electrode sheet to the width of the positive electrode sheet is too low. If the content of fluorinated solvent is too high, the viscosity of the electrolyte increases, which increases the risk of lithium deposition in the battery. If the ratio of the width of the negative electrode sheet to the width of the positive electrode sheet is too low, the lithium embedding ability of the negative electrode sheet will be weaker than that of the positive electrode sheet. At the same time, a higher content of fluorinated solvent will further slow down the rate at which lithium ions are embedded in the negative electrode sheet, making the lithium ion embedding rate of the negative electrode sheet even slower.

[0022] In the present invention, by controlling the ratio of the weight content of the fluorinated solvent in the electrolyte to the width of the positive and negative electrode sheets, the battery can achieve the advantages of higher safety performance and more stable cycle performance compared with the prior art. In order to further improve the effect, one or more of the technical features can be further optimized.

[0023] In one example, the lithium ion battery satisfies the following relationship: 6≤f / g≤15.

[0024] In one example, 3wt%≤fwt%≤30wt% (e.g., 3wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt% or 30wt%). Controlling the weight content of the fluorinated solvent in the electrolyte within the above range can make the viscosity of the electrolyte moderate, increase the transfer rate of lithium ions in the electrolyte, increase the solubility of lithium salts in the electrolyte, improve the conductivity of the electrolyte, and improve the cycle stability of the battery.

[0025] In one example, 5 wt % ≤ f wt % ≤ 20 wt %.

[0026] In one example, the fluorinated solvent includes one or more of fluorinated carbonate, fluorinated carboxylate, fluorinated ether, fluorinated benzene, fluorinated phosphate and fluorinated olefin. The fluorinated solvent has a high dielectric constant, which is conducive to the dissolution and dissociation of lithium salts, thereby improving the cycle performance of the battery, and can also form a protective film on the surface of the positive electrode current collector to inhibit the corrosion of the positive electrode current collector (aluminum foil).

[0027] In one example, the number of fluorine substitutions in the fluorinated solvent is ≤2 (e.g., 1 or 2). When the number of fluorine substitutions in the fluorinated solvent is greater than 2, the viscosity of the electrolyte increases, resulting in easy lithium precipitation in the electrolyte, and the structure of the fluorinated solvent is unstable. During the cycle, the fluorine element in the fluorinated solvent is easy to break bonds to form HF to corrode the positive electrode sheet, so it is necessary to control the number of fluorine substitutions in the fluorinated solvent to be ≤2.

[0028] In one example, the fluorocarbonate includes monofluoroethylene carbonate and / or monofluoroethyl methyl carbonate.

[0029] In one example, the fluorocarboxylic acid ester includes one or more of ethyl monofluoroacetate, dimethyl difluoroacetate, ethyl difluoroacetate (DFEA), and vinyl difluoroacetate.

[0030] In one example, the fluorinated ether includes one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane ether (DTDL) and octafluoropentyl-tetrafluoroethyl ether.

[0031] In one example, the fluorobenzene includes one or more of fluorobenzene and 1,2-difluorobenzene.

[0032] In one example, the fluorophosphate ester includes one or more of tris(2,2,2-trifluoroethyl) phosphate and bis(2,2,2-trifluoroethyl)-ethyl phosphate.

[0033] In one example, the fluoroolefin includes one or more of 1,2-difluoroethylene, monofluoroethylene and monofluoropropylene.

[0034] In one example, 1.01≤g≤1.08 (e.g., 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08). By controlling the ratio of the width of the negative electrode sheet to the width of the positive electrode sheet, the effective surface area of ​​the electrode can be increased, the available capacity of the electrode active material can be increased, and thus the energy density of the battery can be improved.

[0035] In one example, 1.03≤g≤1.06.

[0036] In one example, the ratio n of the area of ​​the negative electrode sheet to the area of ​​the positive electrode sheet is (1.01-1.12):1 (e.g., 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11 or 1.12). By controlling the ratio of the area of ​​the negative electrode sheet to the area of ​​the positive electrode sheet, the effective surface area of ​​the electrode can be increased, the available capacity of the electrode active material can be increased, and thus the energy density of the battery can be improved.

[0037] In one example, n is (1.03-1.08):1.

[0038] In one example, 1.01≤g≤1.08 and n is (1.01-1.12):1. The values ​​of g and n may be the same or different. When the values ​​of g and n are the same, it means that the ratio of the width of the negative electrode sheet to the width of the positive electrode sheet and the ratio of the area of ​​the negative electrode sheet to the area of ​​the positive electrode sheet are the same, and the lengths of the positive electrode sheet and the negative electrode sheet are the same; when the values ​​of g and n are different, it means that the ratio of the width of the negative electrode sheet to the width of the positive electrode sheet and the ratio of the area of ​​the negative electrode sheet to the area of ​​the positive electrode sheet are different, and the lengths of the positive electrode sheet and the negative electrode sheet are different.

[0039] In one example, 1.03≤g≤1.06 and n is (1.03-1.08):1.

[0040] like Figure 2 As shown, the negative electrode sheet 1 includes a negative electrode collector 11 and a negative electrode active material layer, the negative electrode collector 11 includes a single-sided area 111 and a double-sided area 112, the negative electrode active material layer includes a first negative electrode active material layer 121, a second negative electrode active material layer 122 and a third negative electrode active material layer 123, in the single-sided area 111, the third negative electrode active material layer 123 is located on the surface of one side of the negative electrode collector, and in the double-sided area 112, the first negative electrode active material layer 121 and the second negative electrode active material layer 122 are respectively located on the surfaces of both sides of the negative electrode collector 11.

[0041] When the lithium-ion battery is a lithium-ion battery with a roll-core structure, the single-sided area is located at the tail of the roll-core structure.

[0042] In one example, the thickness of the third negative electrode active material layer in the single-sided area is h, in μm, and the lithium-ion battery satisfies the following relationship: 0.1≤f / h≤0.7 (for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 or 0.7).

[0043] In the single-sided area of ​​the negative electrode sheet, since the negative electrode active material layer is only coated on one side of the negative electrode current collector, the current density is high, which can easily cause local overheating of the negative electrode sheet and aggravate the lithium precipitation on the surface of the negative electrode sheet. The inventor of the present invention has found through research that by controlling the relationship between the weight content of the fluorinated solvent in the electrolyte and the thickness of the third negative electrode active material layer in the single-sided area, a LiF-rich SEI film with low impedance can be formed on the surface of the single-sided area, thereby alleviating the lithium precipitation on the surface of the negative electrode sheet caused by local overheating. At the same time, the fluorinated solvent makes the lithium ions desolvate faster, which can accelerate the deintercalation of lithium ions and avoid the deposition of transition metals and the side reaction of electrolyte decomposition.

[0044] In one example, the lithium-ion battery satisfies the following relationship: 0.23≤f / h≤0.5.

[0045] In one example, 30 μm ≤ h μm ≤ 75 μm. Controlling h within the above range can avoid increasing the difficulty of lithium extraction on the surface of the negative electrode due to excessive thickness. At the same time, a moderate thickness can enable the battery to have a higher energy density while maintaining higher performance.

[0046] In one example, 40 μm≤h μm≤68 μm.

[0047] In one example, the second negative electrode active material layer and the third negative electrode active material layer are located on the same side of the negative electrode current collector, the thickness of the first negative electrode active material layer is the same as or different from the thickness of the second negative electrode active material layer, and the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer is 1:(0.8-0.99). By controlling the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material, the overall thickness of the negative electrode active material layer in the negative electrode sheet can be within a suitable range, and the thickness of the third negative electrode active material layer can be made thinner, thereby helping to reduce the transmission path of electrons and ions, improve the electronic conductivity and ion conductivity of the battery, thereby reducing the internal impedance of the battery and improving the lithium precipitation situation, thereby improving the charge and discharge efficiency and cycle performance of the battery.

[0048] In one example, a ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer is 1:(0.86-0.96).

[0049] In one example, the components of the first negative electrode active material layer, the second negative electrode active material layer, and the third negative electrode active material layer and the weight content of each component may be the same or different.

[0050] In one example, the second negative electrode active material layer and the third negative electrode active material layer have the same components and the same weight content of each component.

[0051] In one example, the first negative electrode active material layer and the second negative electrode active material layer have different components and different weight contents of each component.

[0052] In one example, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a carbon-based material and / or a silicon-based material.

[0053] In one example, the carbon-based material includes at least one of natural graphite, artificial graphite, mesocarbon microbeads, soft carbon and hard carbon.

[0054] In one example, the silicon-based material may include at least one of silicon, silicon oxygen, silicon carbon, and silicon alloy.

[0055] In one example, the negative electrode active material layer includes a negative electrode conductor and a negative electrode binder.

[0056] In one example, the negative electrode conductive agent includes at least one of conductive carbon black (Super P), acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes and metal powder.

[0057] In one example, the negative electrode binder includes at least one of styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol and polyvinylidene fluoride.

[0058] In one example, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode active material is 96wt%-98wt% (for example, 96wt%, 96.5wt%, 97wt%, 97.5wt% or 98wt%), the weight content of the negative electrode conductor is 0.5wt%-2wt% (for example, 0.5wt%, 1wt%, 1.5wt% or 2wt%), and the weight content of the negative electrode binder is 1wt%-2wt% (for example, 1wt%, 1.2wt%, 1.5wt%, 1.8wt% or 2wt%).

[0059] In one example, the negative electrode current collector includes a polymer layer and copper foil layers located on both sides of the polymer layer, and the polymer layer includes PP and / or PE.

[0060] In order to further improve the safety of the battery, the negative electrode current collector of the present invention adopts a composite current collector, such as Figure 3 As shown, the negative electrode current collector 11 includes a polymer layer 113 and copper foil layers 114 located on both sides of the polymer layer.

[0061] In one example, the composition of the polymer layer includes PP and / or PE.

[0062] According to research, the stronger the polarity of the solvent in the electrolyte, the greater the degree of corrosion to the copper foil. The electrolyte of the present invention includes a fluorinated solvent which is a weakly polar substance. After the fluorinated solvent undergoes a passivation reaction on the surface of the copper foil, a protective film can be formed. The protective film can improve the stability of the copper foil in the electrolyte environment and further reduce the degree of corrosion of the electrolyte on the negative electrode collector. That is, through the synergistic effect of the negative electrode composite current collector and the fluorinated solvent in the electrolyte, the degree of corrosion of the electrolyte on the negative electrode collector can be further reduced, and the corrosion resistance of the negative electrode collector can be improved.

[0063] In one example, the copper foil layer is copper foil.

[0064] In one example, the thickness of the copper foil layer is 0.3 μm-1.5 μm (for example, 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm or 1.5 μm). The thickness of the copper foil layer is the single-sided thickness. If there are copper foil layers on both sides of the polymer layer, and the thickness of the copper foil layers on both sides is the same, then the thickness of the copper foil layer is the thickness of the copper foil layer on either side.

[0065] In one example, the polymer layer has a thickness of 4 μm-8 μm (eg, 4 μm, 5 μm, 6 μm, 7 μm, or 8 μm).

[0066] In one example, the thickness t1 of the copper foil layer is 0.3 μm-1.5 μm, and the thickness of the polymer layer is 4 μm-8 μm. Controlling the thickness of the copper foil layer and the polymer layer within the above range can ensure that the thickness of the copper foil layer is thinner, thereby accelerating the electron transfer rate. The thickness of the polymer layer in the middle position is moderate, which can enhance the mechanical strength of the negative electrode collector and improve the structural stability of the battery. In addition, the polymer layer has excellent corrosion resistance and high temperature resistance, and can maintain stable performance under extreme working conditions. Compared with conventional current collectors such as pure copper foil current collectors, the negative electrode current collector of the present invention is thinner, has better conductivity, stronger heat dissipation energy, and is of moderate weight, which can improve the weight energy density of the battery.

[0067] In one example, the lithium-ion battery includes a negative electrode ear, and the area of ​​the negative electrode ear is s, in units of mm 2, the lithium-ion battery satisfies the following relationship: 0.1≤f / s≤3 (for example, 0.1, 0.5, 1, 1.5, 2, 2.5 or 3).

[0068] The area s of the pole ear is the area where the pole ear overlaps the pole piece. In the present invention, the lithium-ion battery includes a negative pole ear, and the area s of the pole ear is the area of ​​the positive pole ear. Figure 4 As shown, the area of ​​the negative electrode tab 31 of the negative electrode sheet 1 and the overlapping portion 41 of the negative electrode sheet 1 is the area s of the tab.

[0069] When used for a long time, the tabs are in the electrolyte environment and will be affected by electrochemical corrosion. Corrosion will make the surface of the tabs rough, thereby increasing resistance and affecting battery performance and efficiency. Currently, the purpose of corrosion prevention is achieved by covering the tabs with adhesive tape. However, due to current overload at the edge of the tab, the negative electrode sheet quickly de-inserts lithium, resulting in severe lithium deposition at the edge of the tab.

[0070] In order to solve the above-mentioned technical problems existing in the tabs, the present invention controls the relationship between the weight content of the fluorinated solvent in the electrolyte and the size of the tabs. The fluorinated solvent forms a protective layer near the negative electrode tab, which conducts ions but not electrons. This can reduce the overload current near the tabs, accelerate the deintercalation of lithium ions, and thus reduce lithium plating.

[0071] When f / s<0.1, the weight content of fluorinated solvent in the electrolyte is low, and the film formation at the edge interface of the pole ear is unstable under high pressure, and the protective layer is repaired in time when it is damaged. When f / s>3, the weight content of fluorinated solvent in the electrolyte is too high, and the viscosity of the electrolyte is relatively large. During the high-rate charge and discharge process, the transmission rate of lithium ions in the electrolyte is seriously slowed down, and there is a risk of increasing lithium precipitation in the pole ear; if the size of the pole ear is too small, if the current transmission density is too large, it will increase the resistance at the pole ear, resulting in local overheating and increasing the risk of battery insecurity.

[0072] In one example, the lithium-ion battery satisfies the following relationship: 0.4≤f / s≤1.

[0073] In an example, 10≤s≤30 (eg, 10, 15, 20, 25, or 30).

[0074] When s>30, the area of ​​the tab is too large, and the increased space occupied by the tab leads to an increase in the size of the battery, which will be particularly affected when the battery is integrated in a limited space. Tabs with too large an area will increase the weight of the battery, reduce the energy density and power density of the battery, and increase the corresponding cost. However, the area of ​​the tab cannot be too small. When s<10, the current carrying capacity is insufficient: as a current conduction channel, if the tab is too small, it may not be able to carry enough current, resulting in excessive current density, increasing the resistance at the tab, and affecting the battery's charge and discharge performance. In addition, tabs with smaller areas will limit the diffusion and heat dissipation of heat, which will cause local overheating of the battery and accelerate battery aging and damage.

[0075] In one example, 15≤s≤25.

[0076] In one example, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on one side or both sides of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material, a positive electrode conductive agent and a positive electrode binder.

[0077] In one example, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate and lithium-rich manganese.

[0078] In one example, the positive electrode conductive agent includes at least one of conductive carbon black (Super P), acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes and metal powder.

[0079] In one example, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, and polyethylene oxide.

[0080] In one example, based on the total weight of the positive electrode active material layer, the weight content of the positive electrode active site is 96wt%-98.5wt%, the weight content of the positive electrode conductor is 0.5wt%-2wt%, and the weight content of the positive electrode binder is 0.5wt%-2wt%.

[0081] In one example, the electrolyte further includes lithium salt, ethylene carbonate (EC), propylene carbonate (PC), an organic solvent and additives.

[0082] In one example, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium bisfluorosulfonyl imide (LiTFSI), lithium bistrifluoromethylsulfonyl imide, lithium difluorobisoxalatophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, tris(trifluoromethylsulfonyl)methyl lithium and lithium bis(trifluoromethylsulfonyl)imide. The lithium salt can affect the basic physical and chemical properties of the electrolyte and is an important component in the electrolyte that affects the characteristics of the lithium ion battery. The lithium salt has the function of conducting lithium ions and can improve the conductivity of the electrolyte.

[0083] The ethylene carbonate (EC) can form a SEI film on the negative electrode sheet during the first charge and discharge process, thereby improving the efficiency of subsequent lithium ion deintercalation at the negative electrode and reducing the occurrence of side reactions.

[0084] The propylene carbonate (PC) has a relatively high dielectric constant, can promote the dissociation of lithium salts, and greatly improve the conductivity of ions in the electrolyte.

[0085] In one example, the organic solvent includes one or more of propyl propionate (PP), ethyl propionate (EP), ethyl butyrate (EB), ethyl acetate (EA), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC).

[0086] In one example, the additive includes one or more of 1,3-propane sultone (PS), 1,3-acrylonitrile lactone (PST), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), adiponitrile (ADN), succinonitrile (SN), fluoroethylene carbonate (FEC) and 1,3,6-hexane trinitrile (HTCN). Among them, succinonitrile (SN) and 1,3,6-hexane trinitrile (HTCN) mainly complex with cobalt ions in the positive electrode sheet to protect the positive electrode material from dissolution and release under high voltage; VC and PS preferentially form a film on the surface of the negative electrode sheet to make the SEI film stronger.

[0087] In one example, based on the total weight of the electrolyte, the weight content of the lithium salt is 10-21wt%, the weight content of the EC is 0-15wt%, the weight content of the PC is 7-15wt%, the weight content of the organic solvent is 30-60wt%, and the weight content of the additive is 15-25wt%.

[0088] The present invention will be described in detail below by way of examples. The examples described in the present invention are only a part of the examples of the present invention, rather than all of the examples. Based on the examples in the present invention, all other examples obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0089] The following examples are used to illustrate the lithium ion battery of the present invention.

[0090] Example 1

[0091] (1) Preparation of positive electrode

[0092] The positive electrode active material (lithium cobalt oxide), positive electrode conductive agent (Super P), and positive electrode binder (polyvinylidene fluoride (PVDF)) are dispersed in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 98:1.2:0.8, and fully stirred to form a uniform positive electrode slurry. The positive electrode slurry is coated on both sides of the positive electrode collector (conventional aluminum foil), and then dried, rolled, cut (cutting size is 6.5cm*120cm), cleaned (cleaned area is 3*5mm), and attached with ear glue to obtain a positive electrode sheet, wherein the width of the positive electrode sheet is 118mm and the area of ​​the positive electrode sheet is 104481mm 2 .

[0093] (2) Preparation of negative electrode

[0094] The negative electrode active material (graphite), negative electrode conductive (Super P), a negative electrode binder (1.5 parts by weight of styrene-butadiene rubber (SBR) and 0.5 parts by weight of thickener sodium carboxymethyl cellulose (CMC)) are dispersed in an appropriate amount of deionized water in a weight ratio of 97:1:2, and are fully stirred to form a uniform negative electrode slurry. The negative electrode slurry is coated on the surface of the negative electrode collector (conventional copper foil) to form a negative electrode active material layer, wherein a first negative electrode active material layer and a second negative electrode active material layer are coated on both sides of the negative electrode collector, the thickness of the first negative electrode active material layer is 51.2 μm, the thickness of the second negative electrode active material layer is 51.2 μm, and a third negative electrode active material layer is coated on one side of the single-sided area of ​​the negative electrode collector (on the same side of the negative electrode collector as the second negative electrode active material layer), the thickness of the third negative electrode active material layer is 49.1 μm, and then dried, rolled, cut (cutting size is 6.8 cm*120.5 cm), cleaned, and attached with ear glue to obtain a negative electrode sheet.

[0095] Among them, the width of the negative electrode sheet is 123mm, and the area of ​​the negative electrode sheet is 109456mm 2 The thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer is 1:0.959, and the area of ​​the negative electrode tab is 15 mm 2 .

[0096] (3) Preparation of electrolyte

[0097] Component preparation: fluorinated solvent: ethyl difluoroacetate (DFEA) (wherein the number of fluorine substitutions in the fluorinated solvent is 2), 12 parts by weight; EC, 10 parts by weight; PC, 10 parts by weight; organic solvent: PP, 35 parts by weight; lithium salt: lithium hexafluorophosphate, 15 parts by weight; additives: PS, 3 parts by weight, FEC, 8 parts by weight; SN, 2 parts by weight, HTCN, 3 parts by weight, ADN (2 parts by weight), a total of 18 parts by weight.

[0098] In a glove box (H2O < 0.01ppm, O2 < 0.01ppm, Ar atmosphere), EC / PC / PP / DFEA were mixed evenly, and then fully dried lithium salt was added thereto. After dissolution, additives were added and stirred evenly. After passing the moisture and free acid tests, the required electrolyte was obtained.

[0099] (4) Diaphragm

[0100] The diaphragm consists of a substrate layer and coatings on both sides of the substrate layer. The substrate layer is made of PP / PE, the coating on one side of the substrate layer is PVDF, and the coating on the other side of the substrate layer is PMMA.

[0101] (5) Preparation of lithium-ion batteries

[0102] The positive electrode sheet of step (1), the separator of step (4), and the negative electrode sheet of step (2) are wound to obtain a bare cell without liquid injection, and the bare cell is placed in an outer packaging foil. The electrolyte of step (3) is injected into the dried bare cell, and the desired lithium-ion battery is obtained through vacuum packaging, standing, formation, shaping, sorting and other processes.

[0103] Among them, the ratio g of the width of the negative electrode sheet to the width of the positive electrode sheet is 1.04, the ratio n of the area of ​​the negative electrode sheet to the area of ​​the positive electrode sheet is 1.05, f / g=12 / 1.04=11.51, f / h=0.244, f / s=0.8.

[0104] Example 2

[0105] The method is carried out in accordance with Example 1, except that the negative electrode current collector is a composite current collector, including a polymer layer and copper foil layers on both sides of the polymer layer, wherein the polymer layer is PP, the thickness of the polymer layer is 6 μm, and the thickness of the copper foil layer is 1 μm.

[0106] Example 3 Group

[0107] This group of embodiments is used to illustrate the impact when f / g changes.

[0108] Example 3a

[0109] Refer to Example 1, except that the weight content of the fluorinated solvent in the electrolyte is f%=5%, and accordingly, f / g=4.8, f / h=0.102, and f / s=0.333.

[0110] Example 3b

[0111] Refer to Example 1, except that the weight content of the fluorinated solvent in the electrolyte is f%=18%, and accordingly, f / g=17.27, f / h=0.367, and f / s=1.2.

[0112] Example 3c

[0113] The process is carried out with reference to Example 1, except that the weight content of the fluorinated solvent in the electrolyte is f%=31%, and accordingly, f / g=29.81, f / h=0.631, and f / s=2.067.

[0114] Example 3d

[0115] Refer to Example 1, except that the weight content of the fluorinated solvent in the electrolyte is f%=3%, and accordingly, f / g=2.88, f / h=0.061, and f / s=0.2.

[0116] Example 3e

[0117] The method is carried out in accordance with Example 1, except that the width of the negative electrode sheet is 126.5 mm and the area of ​​the negative electrode sheet is 112571 mm. 2 , the width of the positive electrode sheet is 118.2mm, and the area of ​​the positive electrode sheet is 104658mm 2 , accordingly, g=1.07, n=1.08, f / g=11.21.

[0118] Example 3f

[0119] The method is carried out in accordance with Example 1, except that the width of the negative electrode sheet is 119.5 mm and the area of ​​the negative electrode sheet is 106341 mm 2 , the width of the positive electrode sheet is 118.3mm, and the area of ​​the positive electrode sheet is 104746mm 2 , accordingly, g=1.01, n=1.02, f / g=11.88.

[0120] Example 3g

[0121] The method is carried out in accordance with Example 1, except that the width of the negative electrode sheet is 130.1 mm and the area of ​​the negative electrode sheet is 115774 mm 2 , the width of the positive electrode sheet is 118.3mm, and the area of ​​the positive electrode sheet is 104746mm 2, accordingly, g=1.1, n=1.11, f / g=10.91.

[0122] Example 4 Group

[0123] This group of embodiments is used to illustrate the impact when f / h changes.

[0124] Example 4a

[0125] Refer to Example 1, except that the thickness h of the third negative electrode active material layer is 41.2 μm. In order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer is adaptively adjusted to 43 μm, then f / h=0.291.

[0126] Example 4b

[0127] Refer to Example 1, except that the thickness h of the third negative electrode active material layer is 67.4 μm. In order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer is adaptively adjusted to 70.3 μm, then f / h=0.178.

[0128] Example 4c

[0129] Refer to Example 1, except that the weight content of the fluorinated solvent in the electrolyte is 25%, the thickness h of the third negative electrode active material layer is 31.3 μm, and in order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer is adaptively adjusted to 32.6 μm, then f / g=23.98, f / h=0.799, f / s=1.667.

[0130] Example 4d

[0131] Refer to Example 1, except that the thickness h of the third negative electrode active material layer is 74.6 μm. In order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer is adaptively adjusted to 77.8 μm, then f / h=0.161.

[0132] Example 4e

[0133] Refer to Example 1, except that the thickness h of the third negative electrode active material layer is 28.5 μm. In order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer is adaptively adjusted to 29.7 μm, then f / h=0.421.

[0134] Example 4c

[0135] Refer to Example 1, except that the weight content of the fluorinated solvent in the electrolyte is 3%, the thickness h of the third negative electrode active material layer is 78.8 μm, and in order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer is adaptively adjusted to 82.2 μm, then f / g=2.88, f / h=0.038, f / s=0.2.

[0136] Example 5 Group

[0137] This group of embodiments is used to illustrate the influence produced when the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer is changed.

[0138] Example 5a

[0139] The same method is carried out as in Example 1, except that the thickness h of the third negative electrode active material layer is 50.4 μm, and the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer is 1:0.984, and f / h=0.238.

[0140] Example 5b

[0141] The same method is carried out as in Example 1, except that the thickness h of the third negative electrode active material layer is 44.3 μm, and the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer is 1:0.865, and f / h=0.271.

[0142] Example 5c

[0143] The same method is carried out as in Example 1, except that the thickness h of the third negative electrode active material layer is 41.8 μm, and the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer is 1:0.816, and f / h=0.287.

[0144] Example 5d

[0145] The same method is used as in Example 1, except that the thickness h of the third negative electrode active material layer is 62.1 μm, and the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer is 1:1.213, and f / h=0.193.

[0146] Example 5e

[0147] The same method is used as in Example 1, except that the thickness h of the third negative electrode active material layer is 535.7 μm, and the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer is 1:0.697, and f / h=0.336.

[0148] Example 6 Group

[0149] This group of embodiments is used to illustrate the impact when f / s changes.

[0150] Example 6a

[0151] The same method is carried out as in Example 2, except that the area s of the tab is 10 mm 2 , then f / s=1.2.

[0152] Example 6b

[0153] The same method is carried out as in Example 2, except that the area s of the tab is 8 mm 2 , then f / s=1.5.

[0154] Example 6c

[0155] The same method is carried out as in Example 2, except that the area s of the tab is 40 mm 2 , then f / s=0.3.

[0156] Example 6d

[0157] The same method is carried out as in Example 2, except that the area s of the tab is 30 mm 2 , then f / s=0.4.

[0158] Example 6e

[0159] The same method is carried out as in Example 2, except that the weight content of the fluorinated solvent in the electrolyte is 30%, and the area s of the tab is 10 mm 2 , then f / g=28.78, f / h=0.611, f / s=3.

[0160] Example 6f

[0161] The same method is carried out as in Example 2, except that the weight content of the fluorinated solvent in the electrolyte is 30%, and the area s of the tab is 8 mm 2 , then f / g=28.78, f / h=0.611, f / s=3.75.

[0162] Example 6g

[0163] The same method is carried out as in Example 2, except that the area s of the tab is 25 mm 2 , then f / s=0.48.

[0164] Example 7 Group

[0165] This group of examples is used to illustrate the effects produced when the fluorinated solvent is changed.

[0166] Example 7a

[0167] The process is carried out in accordance with Example 1, except that the fluorinated solvent is monofluorobenzene (the number of fluorine substitutions in the fluorinated solvent is 1).

[0168] Example 7b

[0169] The process is carried out in accordance with Example 1, except that the fluorinated solvent is octafluoropentyl-tetrafluoroethyl ether (the number of fluorine substitutions in the fluorinated solvent is 12).

[0170] Example 7c

[0171] The process is carried out in accordance with Example 1, except that the fluorinated solvent is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (the number of fluorine substitutions in the fluorinated solvent is 8).

[0172] Comparative Example 1

[0173] Refer to Example 1, except that the weight content of the fluorinated solvent in the electrolyte is 33%, then, f / g=31.73, f / h=0.672, f / s=0.367.

[0174] Comparative Example 2

[0175] Refer to Example 1, except that the weight content of the fluorinated solvent in the electrolyte is 1.5%, the thickness h of the third negative electrode active material layer is 12 μm, and in order to keep the thickness ratio of the first negative electrode active material layer to the third negative electrode active material layer basically unchanged, the thickness of the first negative electrode active material layer is adaptively adjusted to 12.5 μm, then f / g=1.44, f / h=0.125, f / s=0.05.

[0176] Comparative Example 3

[0177] The process is carried out in accordance with Example 1, except that no fluorinated solvent is added to the electrolyte.

[0178] Comparative Example 4

[0179] The same is done as in Example 1, except that the width of the positive electrode sheet is the same as the width of the negative electrode sheet, and the area of ​​the positive electrode sheet is the same as the area of ​​the negative electrode sheet.

[0180] Test Case

[0181] The lithium ion batteries obtained in the embodiments and comparative examples were tested as follows:

[0182] 1. Cycle performance test

[0183] Place the lithium-ion battery at 25°C, first discharge it to 3V at 0.2C, then charge it to 4.48V at 0.5C, record the capacity and thickness of the fully charged state, discharge it to 3V at 0.2C, then charge it to 4.48V at 1C constant current, then charge it to the upper limit voltage (4.53V) at 0.7C, then charge it to 0.05C at 4.53V constant voltage, let it stand for 5 minutes; then discharge it to 3V at 0.7C constant current, let it stand for 5 minutes, this is a charge and discharge cycle. Charge / discharge it 1000T in this way, and record the performance parameters of the lithium-ion battery during the cycle, including capacity retention rate and appearance abnormality. After the cycle, disassemble the battery to observe the lithium precipitation.

[0184] Capacity retention rate = 1000T capacity / initial capacity*100%.

[0185] Lithium deposition: Charge the battery to 4.48V at 0.5C, then disassemble the battery and observe whether there are grayish white dots or flakes on the top, bottom, surface, and arc of the negative electrode interface. When there are no grayish white dots or flakes, there is no lithium deposition. When the area of ​​grayish white dots or flakes accounts for less than 10% of the electrode area, it is slight lithium deposition. When the area of ​​grayish white dots or flakes accounts for ≥10% of the electrode area, it is lithium deposition.

[0186] 2. Safety performance test -25℃ external short circuit

[0187] The battery is fully charged at 0.5C (100% SOC), cut off at 0.05C, and left to stand for 10 minutes. The voltage, internal resistance, and thickness of the fully charged state (100% SOC) are tested at 25±5℃. The battery cell is placed in an environment of 25℃±5℃ for another 30 minutes, and the positive and negative poles are short-circuited. The short-circuit resistance is ≤50mΩ. The voltage and the temperature rise of the battery cell body are monitored. The test is terminated when the battery temperature drops below 20% of the peak temperature or the test time is greater than 24 hours. If the battery explodes or catches fire, it means that it has failed. A total of 10 battery samples were tested, and the test results are expressed as "passed test / 10". For example, "8 / 10" means that 8 out of 10 tests passed.

[0188] The obtained results are recorded in Table 1.

[0189] Table 1

[0190]

[0191]

[0192] As can be seen from Table 1, through the comparative examples and the embodiments, it can be seen that the capacity retention rate of the lithium-ion battery in the embodiment is significantly improved, and the safety pass rate is significantly improved, which means that the safety performance and cycle stability performance of the battery can be improved by controlling the relationship between the weight content of the fluorinated solvent in the electrolyte and the ratio of the width of the positive and negative electrodes.

[0193] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A lithium ion battery, characterized in that: The lithium-ion battery comprises an electrolyte, a negative electrode sheet and a positive electrode sheet, wherein the electrolyte comprises a fluorinated solvent, and the weight content of the fluorinated solvent is fwt% based on the total weight of the electrolyte; the ratio of the width of the negative electrode sheet to the width of the positive electrode sheet is g, and the lithium-ion battery satisfies the following relationship: 2≤f / g≤30.

2. The lithium ion battery according to claim 1, wherein The lithium ion battery satisfies the following relationship: 6≤f / g≤15; and / or, the fluorinated solvent comprises one or more of fluorinated carbonates, fluorinated carboxylates, fluorinated ethers, fluorinated benzenes, fluorinated phosphates and fluorinated olefins; and / or, 1.01≤g≤1.08, preferably 1.03≤g≤1.06; and / or, 3wt%≤fwt%≤30wt%, preferably 5wt%≤fwt%≤20wt%; And / or, the ratio n of the area of ​​the negative electrode sheet to the area of ​​the positive electrode sheet is (1.01-1.12):1, preferably (1.03-1.08):

1.

3. The lithium ion battery according to claim 1, wherein The negative electrode sheet includes a negative electrode collector and a negative electrode active material layer, the negative electrode collector includes a single-sided area and a double-sided area, the negative electrode active material layer includes a first negative electrode active material layer, a second negative electrode active material layer and a third negative electrode active material layer, in the single-sided area, the third negative electrode active material layer is located on the surface of one side of the negative electrode collector, in the double-sided area, the first negative electrode active material layer and the second negative electrode active material layer are respectively located on the surfaces of both sides of the negative electrode collector, the thickness of the third negative electrode active material layer in the single-sided area is h, in μm, then the lithium ion battery satisfies the following relationship: 0.04≤f / h≤0.

9.

4. The lithium ion battery according to any one of claims 1 to 3, wherein: The fluorocarbonate includes monofluoroethylene carbonate and / or monofluoroethyl methyl carbonate; and / or, the fluorocarboxylic acid ester comprises one or more of ethyl monofluoroacetate, dimethyl difluoroacetate, ethyl difluoroacetate and vinyl difluoroacetate; and / or, the fluoroether comprises one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane ether and octafluoropentyl-tetrafluoroethyl ether; And / or, the fluorobenzene includes one or more of monofluorobenzene and 1,2-difluorobenzene; and / or, the fluorophosphate comprises one or more of tris(2,2,2-trifluoroethyl)phosphate and bis(2,2,2-trifluoroethyl)-ethyl phosphate; and / or, the fluoroolefin comprises one or more of 1,2-difluoroethylene, monofluoroethylene and monofluoropropylene; And / or, the number of fluorine substitutions in the fluorinated solvent is ≤2.

5. The lithium ion battery according to claim 3, wherein: The lithium ion battery satisfies the following relationship: 0.1≤f / h≤0.7; and / or, 30 μm ≤ h μm ≤ 75 μm, preferably 40 μm ≤ h μm ≤ 68 μm; And / or, the second negative electrode active material layer and the third negative electrode active material layer are located on the same side of the negative electrode current collector, the thickness of the first negative electrode active material layer is the same as or different from the thickness of the second negative electrode active material layer, and the ratio of the thickness of the first negative electrode active material layer to the thickness of the third negative electrode active material layer is 1:(0.8-0.99).

6. The lithium ion battery according to claim 3, wherein: The negative electrode current collector comprises a polymer layer and copper foil layers located on both sides of the polymer layer, and the polymer layer comprises PP and / or PE.

7. The lithium ion battery according to claim 6, wherein: The thickness of the copper foil layer is 0.3 μm-1.5 μm; And / or, the polymer layer has a thickness of 4 μm-8 μm.

8. The lithium ion battery according to claim 7, wherein: The lithium-ion battery comprises a negative electrode ear, the area of ​​the negative electrode ear is s, in units of mm 2 , then the lithium-ion battery satisfies the following relationship: 0.1≤f / s≤3.

9. The lithium ion battery according to claim 8, wherein: The lithium ion battery satisfies the following relationship: 0.4≤f / s≤1; And / or, 10≤s≤30.

10. The lithium ion battery according to claim 3, wherein: The negative electrode sheet active material layer includes a negative electrode active material, and the negative electrode active material includes a carbon-based material and / or a silicon-based material; the carbon-based material includes at least one of natural graphite, artificial graphite, mesophase carbon microbeads, soft carbon and hard carbon; the silicon-based material may include at least one of silicon, silicon oxygen, silicon carbon and silicon alloy.

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