Negative plate, preparation method thereof and lithium ion battery

Abstract

The present application relates to the technical field of lithium ion batteries, and discloses a negative electrode plate, which comprises: a negative electrode current collector, which is treated by an oxidation treatment device so as to make the surface of the negative electrode current collector contain a polar oxygen-containing functional group; the negative electrode coating comprises a negative electrode coating material coated on the surface of at least one side of the negative electrode current collector, the negative electrode coating material comprises a negative electrode active substance, and the negative electrode active substance comprises a carbon material and an aluminum oxide coating layer coating the carbon material; the negative electrode coating material also comprises a negative electrode binder, and the negative electrode binder comprises at least one of polyacrylic acid, a polyacrylic acid derivative, sodium carboxymethyl cellulose, polyacrylonitrile, polystyrene-acrylic acid and butadiene styrene rubber. Therefore, the binding force of a pole piece interface can be effectively improved, so that the mechanical stability of the pole piece is ensured, and the rate capability and the cycling stability of the pole piece can be improved. The invention further discloses a preparation method of the negative plate and a lithium ion battery.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a negative electrode sheet and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] Currently, with the widespread application of lithium-ion batteries in new energy vehicles, energy storage systems, and portable electronic devices, the requirements for their energy density, rate performance, and cycle life continue to increase. Among them, the negative electrode, as a key carrier for lithium ion storage and release in the battery structure, has a direct impact on the performance of lithium-ion batteries due to its interfacial chemical stability, structural integrity, and ion / electron transfer efficiency. Graphite-based negative electrode materials are the primary choice for lithium-ion battery negative electrodes due to their low lithium insertion potential, high reversible capacity, and good conductivity.

[0003] However, due to the strong hydrophobicity of the graphite surface, the electrolyte wettability is insufficient, resulting in uneven initial interface film formation, which is not conducive to the formation of a dense solid electrolyte interface (SEI) film, affecting battery performance. To this end, the related art provides a negative electrode material, which includes graphite, and has pores on the surface and / or inside the graphite. By adjusting the internal and / or surface pore volume, specific surface area, etc., the capacity and rate performance of the negative electrode material can be improved.

[0004] During the implementation of the embodiments of the present disclosure, it was found that at least the following problems exist in the related art:

[0005] The above method can improve the battery performance to a certain extent. However, under the preparation conditions of high compaction and high load, the graphite negative electrode sheet is prone to peeling between the active material and the copper foil current collector; especially in the long cycle and repeated charge and discharge process, the accumulation of interfacial stress will aggravate the damage of the electrode structure, resulting in insufficient electrode interface bonding force, affecting its mechanical stability, causing polarization increase and capacity drop, thereby affecting its rate performance and cycle stability.

[0006] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to ordinary technicians in this field. Summary of the Invention

[0007] In order to provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. The summary is not an extensive review, nor is it intended to identify key / critical elements or delineate the scope of protection of these embodiments, but rather serves as a prelude to the detailed description that follows.

[0008] The embodiments of the present disclosure provide a negative electrode sheet and a preparation method thereof, and a lithium-ion battery, which can effectively improve the bonding force of the electrode sheet interface, thereby ensuring its mechanical stability, and further improving its rate performance and cycle stability.

[0009] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode coating. The negative electrode current collector is treated by an oxidation treatment device so that the surface of the negative electrode current collector contains polar oxygen-containing functional groups, including one or more of hydroxyl groups, carboxyl groups, and carbonyl groups. The negative electrode coating includes a negative electrode coating material coated on at least one side of the negative electrode current collector, the negative electrode coating material includes a negative electrode active material, the negative electrode active material includes a carbon material and an alumina coating layer coating the carbon material. The average thickness of the alumina coating layer is 5nm to 50nm, and the mass of the alumina coating layer is 0.5% to 5% of the mass of the active material. The negative electrode coating material also includes a negative electrode binder, the negative electrode binder includes at least one of polyacrylic acid, a polyacrylic acid derivative, sodium carboxymethyl cellulose, polyacrylonitrile, polystyrene-acrylic acid, and styrene-butadiene rubber, wherein the mass of the negative electrode binder is 1% to 3% of the mass of the negative electrode sheet.

[0010] Optionally, the surface of the negative electrode current collector is determined to contain polar oxygen-containing functional groups by the following method:

[0011] In the infrared spectrum of the negative electrode current collector, at 3200 cm -1 ~3600cm -1 Between 1700cm -1 ~1725cm -1 Between and 500cm -1 ~600cm -1 There are characteristic peaks between them; among them, 3200cm -1 ~3600cm -1 The characteristic peak at 1700 cm corresponds to the stretching vibration of hydroxyl groups. -1 ~1725cm -1 The characteristic peak at 500 cm corresponds to the carbonyl stretching vibration. -1 ~600cm -1 The characteristic peaks correspond to the Cu-O lattice vibration.

[0012] Optionally, the floating mass percentage of the negative electrode active material is ≤9.5%, and the floating mass percentage of the negative electrode active material is calculated by the following formula:

[0013] m f / m t ×100%;

[0014] Among them, m f is the mass of floating carbon material, mt is the total mass of carbon material.

[0015] Optionally, the aluminum oxide coating layer is determined to coat the carbon material by:

[0016] In the X-ray photoelectron spectrum of the negative electrode active material, there is an Al2p characteristic peak between 74.0 eV and 75.5 eV, and there is an O1s characteristic peak between 530.0 eV and 533.0 eV.

[0017] Optionally, the carbon material includes one or more of artificial graphite, natural graphite, soft carbon or hard carbon; the negative electrode coating further includes a negative electrode conductive agent, and the negative electrode conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black.

[0018] Optionally, the surface of the negative electrode coating is punched by laser punching, mechanical punching or laser scoring.

[0019] Optionally, a plurality of pores are provided on the negative electrode coating, wherein the spacing between adjacent pores is 0.1 mm to 2 mm, the pore diameter is 40 μm to 100 μm, and the ratio of the pore depth to the thickness of the negative electrode coating is 0.2 to 0.85.

[0020] Optionally, the negative electrode sheet has a sheet resistance R≤4.0×10 -3 Ω·cm 2 .

[0021] Optionally, the compaction density of the negative electrode sheet is 1.3 g / cm 3 ~1.75g / cm 3 .

[0022] Optionally, the peeling force N of the negative electrode sheet is ≥10.5 N / m.

[0023] In some embodiments, the method for preparing the negative electrode sheet comprises the following steps:

[0024] Preparation of negative electrode current collector: The negative electrode current collector was cleaned and then placed in an oxidation treatment device. It was irradiated at an ozone concentration of 30 ppm and a temperature of 25°C for 15 minutes to cause surface oxidation reaction of the negative electrode current collector to generate polar oxygen-containing functional groups.

[0025] Preparation of a negative electrode coating material: Aluminum nitrate, a carbon material, and a solvent are configured into a mixed solution, and after stirring and ultrasonic dispersion, the pH value of the mixed solution is adjusted to 4 to 5 to obtain a suspension system solution; the suspension system solution is dried at a temperature of 100°C to remove the solvent; the dried suspension system is treated at a temperature of 650°C for 2 hours in an inert gas environment, and then mixed with a negative electrode binder and a negative electrode conductive agent in a set ratio to obtain a negative electrode coating material of an aluminum oxide-coated carbon material;

[0026] Preparation of negative electrode sheet: coating the negative electrode coating material on at least one side of the negative electrode current collector, drying and cold pressing to obtain the negative electrode sheet.

[0027] In some embodiments, the lithium-ion battery includes a positive electrode sheet and a negative electrode sheet as described in the above embodiments.

[0028] Optionally, the positive electrode sheet includes a positive electrode current collector and a positive electrode coating coated with at least one layer containing a positive electrode active material; the positive electrode active material includes lithium nickel cobalt manganese oxide (Li1Ni x Co y Mn z M b O2) and lithium iron phosphate; wherein, 0.70≤x≤0.95, 0.15≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1; the element M includes one or more of Zr, W, Ti, Al, Sr, B and Nd.

[0029] Optionally, the lithium-ion battery further includes: an electrolyte including a lithium salt, a solvent and an additive; the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatoborate and lithium bis(trifluoromethylsulfonyl)imide; the solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate and ethyl methyl carbonate; the additive includes one or more of fluoroethylene carbonate, bis(fluoroethylene carbonate), vinyl sulfate, vinyl sulfite, vinyl carbonate and vinyl carbonate.

[0030] Optionally, the charging characteristics of the lithium-ion battery are as follows: the lithium-ion battery is discharged to 2.5V at 25°C, and after standing for 6 hours, it is charged to 4.2V at a constant current of 1C and 6C respectively. Correspondingly, the constant current section charging capacity is Q1 and Q6, wherein the charging capacity retention rate Q R ≥85%, Q R =Q6 / Q1.

[0031] Optionally, after 1000 cycles at 1C rate at 25°C, the capacity decay rate Q d <11%.

[0032] Optionally, the ratio of the capacity of the negative electrode sheet to the capacity of the positive electrode sheet is 1.02 to 1.15.

[0033] The negative electrode sheet and its preparation method, as well as the lithium-ion battery provided by the embodiments of the present disclosure can achieve the following technical effects:

[0034] This application uses oxidation treatment equipment to treat the negative electrode current collector, which can make the surface of the negative electrode current collector contain polar oxygen-containing functional groups. Compared with untreated negative electrode current collectors, it has better hydrophilicity and can enhance the interfacial interaction with polar aqueous binders, thereby significantly enhancing the interfacial adhesion between the active material and the binder and current collector. At the same time, the use of polyacrylic acid or polyacrylic acid derivatives as its binder can further enhance the interfacial bonding strength. Therefore, it can reduce the electronic contact resistance and improve the diffusivity of lithium ions while improving the overall mechanical strength of the electrode.

[0035] Furthermore, the negative electrode active material includes a carbon material and an alumina coating layer that coats the carbon material. The alumina coating layer can form a stable and uniform inorganic interface layer, effectively inhibit the repeated rupture of the SEI film, and alleviate the volume expansion of the carbon material during the lithium insertion and deinsertion process, thereby improving the cycle stability.

[0036] Therefore, through the above-mentioned structural optimization, the physical and chemical coupling relationship between the internal phase of the electrode and its interface is significantly improved, the interface impedance and polarization are reduced, and thus better capacity retention and cycle stability can be achieved under high rate and long life conditions.

[0037] The above general description and the following description are exemplary and explanatory only and are not intended to limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] One or more embodiments are exemplarily described by corresponding drawings. These exemplary descriptions and drawings do not limit the embodiments. Elements with the same reference numerals in the drawings are shown as similar elements. The drawings do not constitute a scale limitation. In addition,

[0039] Figure 1 This is a schematic flow chart of a method for preparing a negative electrode sheet provided by an embodiment of the present disclosure;

[0040] Figure 2 is a schematic structural diagram of a lithium-ion battery provided by an embodiment of the present disclosure;

[0041] Figure 3 is a schematic structural diagram of a lithium-ion battery provided by an embodiment of the present disclosure;

[0042] Figure 4Schematic diagram of an expanded lithium-ion battery provided by an embodiment of the present disclosure.

[0043] Reference numerals:

[0044] 1-positive terminal; 10-battery cell; 11-positive column; 12-negative terminal; 2-shell; 3-negative electrode; 4-diaphragm; 5-positive electrode. DETAILED DESCRIPTION

[0045] In order to be able to understand the features and technical content of the embodiments of the present disclosure in more detail, the implementation of the embodiments of the present disclosure is described in detail below in conjunction with the accompanying drawings. The accompanying drawings are for reference only and are not used to limit the embodiments of the present disclosure. In the following technical description, for the sake of convenience of explanation, a full understanding of the disclosed embodiments is provided through multiple details. However, one or more embodiments can still be implemented without these details. In other cases, to simplify the drawings, well-known structures and devices can be simplified for display.

[0046] In the description and claims of the embodiments of the present disclosure, as well as in the accompanying drawings, the terms "first," "second," and the like are used to distinguish similar items and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate to describe the embodiments of the present disclosure herein. In addition, the terms "including," "having," and any variations thereof are intended to cover non-exclusive inclusions.

[0047] In the embodiments of the present disclosure, the terms "upper", "lower", "inside", "middle", "outside", "front", "back" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. These terms are mainly intended to better describe the embodiments of the present disclosure and their embodiments, and are not intended to limit the indicated devices, elements or components to having a specific direction, or to be constructed and operated in a specific direction. Moreover, in addition to being used to indicate directions or positional relationships, some of the above terms may also be used to indicate other meanings. For example, the term "upper" may also be used to indicate a certain dependency or connection relationship in certain circumstances. For those of ordinary skill in the art, the specific meanings of these terms in the embodiments of the present disclosure can be understood according to specific circumstances.

[0048] Furthermore, the terms "disposed," "connected," and "fixed" should be interpreted broadly. For example, "connected" can mean a fixed connection, a removable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection, an indirect connection through an intermediary, or an internal connection between two devices, elements, or components. Those skilled in the art will understand the specific meanings of these terms in the embodiments of this disclosure based on the specific circumstances.

[0049] Unless otherwise stated, the term "plurality" means two or more.

[0050] In the embodiment of the present disclosure, the character " / " indicates that the preceding and following objects are in an "or" relationship. For example, A / B means: A or B.

[0051] The term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0052] It should be noted that, unless there is any conflict, the embodiments and features in the embodiments of the present disclosure can be combined with each other.

[0053] Due to its low lithium insertion potential, high reversible capacity and good conductivity, graphite materials are widely used in battery negative electrodes. However, graphite materials also have many problems. For example, the graphite surface is highly hydrophobic, resulting in insufficient wettability with the electrolyte, which is not conducive to the formation of a uniform and dense solid electrolyte interface film. This will aggravate the initial irreversible capacity loss and increase the film formation side reaction, thereby affecting the battery cycle stability. For example, under the preparation conditions of high compaction and high load, the graphite negative electrode is prone to peeling between the active material and the copper foil current collector. Especially during long-term repeated charge and discharge, the interfacial stress accumulates, which will aggravate the damage of the electrode structure, resulting in increased polarization and a sudden drop in capacity.

[0054] Therefore, in order to further improve the above problems. The embodiment of the present disclosure provides a negative electrode sheet, including a negative electrode current collector and a negative electrode coating. The negative electrode current collector is treated by an oxidation treatment device so that the surface of the negative electrode current collector contains polar oxygen-containing functional groups, including one or more of hydroxyl groups, carboxyl groups and carbonyl groups; the negative electrode coating includes a negative electrode coating material coated on at least one side of the negative electrode current collector, the negative electrode coating material includes a negative electrode active substance, the negative electrode active substance includes a carbon material and an alumina coating layer coated with the carbon material; wherein the average thickness of the alumina coating layer is 5nm to 50nm, and the mass of the alumina coating layer is 0.5% to 5% of the mass of the active substance; the negative electrode coating material also includes a negative electrode binder, the negative electrode binder includes at least one of polyacrylic acid, a polyacrylic acid derivative, sodium carboxymethyl cellulose, polyacrylonitrile, polystyrene-acrylic acid and styrene-butadiene rubber, wherein the mass of the negative electrode binder is 1% to 3% of the mass of the negative electrode sheet.

[0055] Using the negative electrode provided by the embodiments of the present disclosure, the present application treats the negative electrode current collector through an oxidation treatment device, which can make the surface of the negative electrode current collector contain polar oxygen-containing functional groups. Compared with the untreated negative electrode current collector, it has better hydrophilicity and can enhance the interfacial interaction with the polar aqueous binder, thereby significantly enhancing the interfacial adhesion between the active material and the binder and current collector. At the same time, the use of polyacrylic acid or a polyacrylic acid derivative as the binder can further enhance the interfacial bonding strength. Therefore, it can reduce the electronic contact resistance and improve the diffusivity of lithium ions while improving the overall mechanical strength of the electrode.

[0056] Furthermore, the negative electrode active material includes a carbon material and an alumina coating layer that coats the carbon material. The alumina coating layer can form a stable and uniform inorganic interface layer, effectively inhibit the repeated rupture of the SEI film, and alleviate the volume expansion of the carbon material during the lithium insertion and deinsertion process, thereby improving the cycle stability.

[0057] Therefore, through the above-mentioned structural optimization, the physical and chemical coupling relationship between the internal phase of the electrode and its interface is significantly improved, the interface impedance and polarization are reduced, and thus better capacity retention and cycle stability can be achieved under high rate and long life conditions.

[0058] Optionally, the surface of the negative electrode current collector is determined to contain polar oxygen-containing functional groups by the following method:

[0059] In the infrared spectrum of the negative electrode current collector, at 3200 cm -1 ~3600cm -1 Between 1700cm -1 ~1725cm -1 Between and 500cm -1 ~600cm -1 There are characteristic peaks between them.

[0060] Here, at 3200cm -1 ~3600cm -1 There are characteristic peaks between them, indicating that under the action of oxidation, water vapor in the air or organic matter adsorbed on the surface is oxidized and formed, corresponding to the stretching vibration of hydroxyl (-OH).

[0061] At 1700cm -1 ~1725cm -1 There is a characteristic peak between them, indicating that the organic pollutants or oxidation intermediates on the surface of the negative electrode current collector are further oxidized, corresponding to the stretching vibration of the carbonyl group (C=O).

[0062] At 500cm -1 ~600cm -1There is a characteristic peak between the two, indicating that the surface of the negative electrode current collector already contains oxides, corresponding to the metal (-O) lattice vibration. Among them, the negative electrode current collector can be copper foil, and here it is the Cu-O lattice vibration of copper oxide.

[0063] Optionally, the floating mass percentage of the negative electrode active material is ≤9.5%, and the floating mass percentage of the negative electrode active material is calculated by the following formula:

[0064] m f / m t ×100%;

[0065] Among them, m f is the mass of floating carbon material, m t is the total mass of carbon material.

[0066] Here, because graphite has a low hydrophilicity, it tends to float in water. After being treated with alumina, the graphite's hydrophilicity increases, significantly increasing its buoyancy. Therefore, the percentage of anode active material that floats can be used to assess the integrity of the alumina coating on the carbon material.

[0067] Optionally, the aluminum oxide coating layer is determined to coat the carbon material by:

[0068] In the X-ray photoelectron spectrum of the negative electrode active material, there is an Al2p characteristic peak between 74.0 eV and 75.5 eV, and there is an O1s characteristic peak between 530.0 eV and 533.0 eV.

[0069] Here, X-ray photoelectron spectroscopy (XPS) can microscopically detect whether the graphite surface has an aluminum oxide coating. The presence of Al2p and O1s characteristic peaks and the binding energy can be used to determine the valence state of Al and O, thereby confirming that the carbon material is coated with aluminum oxide. The excitation source for data acquisition is a monochromatic Al target (AlKα, 1486.6eV), and the binding energy is corrected for charge using C1s (284.8eV).

[0070] Optionally, the carbon material includes one or more of artificial graphite, natural graphite, soft carbon or hard carbon.

[0071] Optionally, the negative electrode coating further includes a negative electrode conductive agent, and the negative electrode conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black.

[0072] Optionally, the surface of the negative electrode coating is punched by laser punching, mechanical punching or laser scoring.

[0073] Optionally, a plurality of pores are provided on the negative electrode coating, wherein the spacing between adjacent pores is 0.1 mm to 2 mm, the pore diameter is 40 μm to 100 μm, and the ratio of the pore depth to the thickness of the negative electrode coating is 0.2 to 0.85.

[0074] This can effectively alleviate the expansion stress of the pole piece and improve structural stability. Here, the introduced channels can, to a certain extent, buffer the stress concentration caused by volume expansion, thereby improving cycle life and structural integrity.

[0075] Furthermore, it can improve electrolyte wettability and diffusion efficiency, shorten the lithium ion diffusion path, and enhance rate performance. Specifically, the pores can form direct ion transmission channels, shortening the lithium ion diffusion path within the active material, accelerating the reaction rate, and improving capacity retention at high rates.

[0076] Optionally, the negative electrode sheet has a sheet resistance R≤4.0×10 -3 Ω·cm 2 .

[0077] Optionally, the compaction density of the negative electrode sheet is 1.3 g / cm 3 ~1.75g / cm 3 .

[0078] This effectively optimizes the electrode microstructure, improves electronic conductivity, increases the first-cycle coulombic efficiency, and reduces electrode expansion. Therefore, it not only ensures the battery's energy density but also its rate performance, thereby improving structural stability and cycle life.

[0079] Optionally, the peeling force N of the negative electrode sheet is ≥10.5 N / m.

[0080] Combine Figure 1 As shown, the embodiment of the present disclosure also provides a method for preparing a negative electrode sheet, comprising the following steps:

[0081] Preparation of negative electrode current collector: The negative electrode current collector was cleaned and then placed in an oxidation treatment device. It was irradiated at an ozone concentration of 30 ppm and a temperature of 25°C for 15 minutes to cause surface oxidation reaction of the negative electrode current collector to generate polar oxygen-containing functional groups.

[0082] Preparation of a negative electrode coating material: Aluminum nitrate, a carbon material, and a solvent are configured into a mixed solution, and after stirring and ultrasonic dispersion, the pH value of the mixed solution is adjusted to 4 to 5 to obtain a suspension system solution; the suspension system solution is dried at a temperature of 100°C to remove the solvent; the dried suspension system is treated at a temperature of 650°C for 2 hours in an inert gas environment, and then mixed with a negative electrode binder and a negative electrode conductive agent in a set ratio to obtain a negative electrode coating material of an aluminum oxide-coated carbon material;

[0083] Preparation of negative electrode sheet: coating the negative electrode coating material on at least one side of the negative electrode current collector, drying and cold pressing to obtain the negative electrode sheet.

[0084] The embodiments of the present disclosure further provide a lithium-ion battery, comprising a positive electrode sheet and a negative electrode sheet as described in the above embodiments.

[0085] The specific structure of the negative electrode sheet refers to the above embodiments. Since the lithium-ion battery adopts all the technical solutions of all the above embodiments, it has at least all the technical effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0086] Optionally, the positive electrode sheet includes a positive electrode current collector and a positive electrode coating coated with at least one layer containing a positive electrode active material; the positive electrode active material includes lithium nickel cobalt manganese oxide (Li1Ni x Co y Mn z M b O2) and lithium iron phosphate; wherein, 0.70≤x≤0.95, 0.15≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1; the element M includes one or more of Zr, W, Ti, Al, Sr, B and Nd.

[0087] Optionally, the lithium-ion battery further includes: an electrolyte including a lithium salt, a solvent and an additive; the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatoborate and lithium bis(trifluoromethylsulfonyl)imide; the solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate and ethyl methyl carbonate; the additive includes one or more of fluoroethylene carbonate, bis(fluoroethylene carbonate), vinyl sulfate, vinyl sulfite, vinyl carbonate and vinyl carbonate.

[0088] Optionally, the charging characteristics of the lithium-ion battery are as follows: the lithium-ion battery is discharged to 2.5V at 25°C, and after standing for 6 hours, it is charged to 4.2V at a constant current of 1C and 6C respectively. Correspondingly, the constant current section charging capacity is Q1 and Q6, wherein the charging capacity retention rate Q R ≥85%, Q R =Q6 / Q1.

[0089] Optionally, after 1000 cycles at 1C rate at 25°C, the capacity decay rate Q d <11%.

[0090] Optionally, the ratio of the capacity of the negative electrode sheet to the capacity of the positive electrode sheet is 1.02 to 1.15. In this way, a slight negative electrode overload design can be effectively achieved in lithium-ion batteries, ensuring safety while taking into account energy density and cycle performance.

[0091] Furthermore, the ratio of the negative electrode's capacity to the positive electrode's capacity is 1.02 to 1.15, preventing lithium metal deposition at the positive electrode during the final stages of charging due to a lack of lithium ion embedding, reducing the risk of lithium plating and improving battery safety. This also avoids excessive negative electrode charge, which can lead to reduced energy density and cost. Therefore, the battery combines high initial efficiency, long life, and consistent grouping, making it suitable for practical applications requiring high energy density and long cycle life.

[0092] In the embodiment of the present disclosure, the lithium-ion battery further includes a shell, and the positive electrode sheet and the negative electrode sheet are encapsulated in the shell. Figures 2 to 4 As shown, the lithium-ion battery specifically includes a cylindrical shell 2, the interior of which is used to accommodate the battery cell, wherein the top is the positive terminal 1, the bottom is the negative terminal 12, and the positive terminal 1 is provided with a positive column 11. Specifically, Figure 3 shows a schematic structural diagram of the lithium-ion battery in this application, Figure 4 FIG1 shows a schematic diagram of the lithium-ion battery in the present application. Figure 4 As shown in the stacking, then winding to form Figure 3 The cylindrical battery cell 10 shown has the electrode end at the cylinder axis at the beginning of winding and at the outer surface of the cylinder at the end of winding. The positive electrode sheet 5 comprises a strip of positive electrode foil, a positive electrode coating applied to the surface of the positive electrode foil strip, and a first hollow foil region. The negative electrode sheet 3 comprises a strip of negative electrode foil, a negative electrode coating applied to the surface of the negative electrode foil strip, and a second hollow foil region. The first and second hollow foil regions are perpendicular to the winding direction and are formed by flattening or cutting and stacking to form the top and bottom end faces of the lithium-ion battery.

[0093] On this basis, an embodiment of the present disclosure provides a method for preparing a lithium-ion battery, comprising:

[0094] Preparation of positive electrode sheet: Mix the positive electrode coating materials, apply them on both sides of the aluminum foil, dry and cold press to obtain the positive electrode sheet;

[0095] Preparation of negative electrode sheet: Mix the negative electrode coating material and apply it on both sides of the copper foil. Then, a depression of a certain depth is opened in the negative electrode coating. After drying and cold pressing, the negative electrode sheet is obtained.

[0096] Preparation of battery cells: The positive and negative electrode sheets are rolled and slit, and then wound together with the separator to obtain battery cells;

[0097] Assembling lithium-ion batteries: Welding the tabs of the lithium-ion battery to the electrical connectors, placing them into the battery case, and performing the electrolyte injection, sealing, and formation processes to obtain a lithium-ion battery.

[0098] In addition, an embodiment of the present disclosure provides an electrical device, comprising a lithium-ion battery for providing power as described in the present application.

[0099] The present invention is further explained below with reference to the following examples.

[0100] Example 1

[0101] This embodiment 1 provides a method for preparing a lithium ion battery as follows:

[0102] Preparation of positive electrode sheet: Select positive electrode active material (Li1Ni 0.8 Co 0.1 Mn 0.1 O2), conductive carbon black, carbon nanotubes and polyvinylidene fluoride (PVDF) are thoroughly stirred and mixed in an N-methylpyrrolidone solvent system in a mass ratio of 96:1:1:2 to obtain a positive electrode coating material; the positive electrode coating material is then coated on a 12.0 μm thick aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.

[0103] Preparation of negative electrode sheet: including preparation of negative electrode current collector and preparation of negative electrode coating material.

[0104] Among them, the preparation of the negative electrode current collector includes: cleaning the surface of the copper foil with ethanol to remove oil and related organic impurities, and then placing it in a UV ultraviolet ozone catalytic oxidation device, and irradiating it for 15 minutes under the conditions of ozone concentration of 30ppm and temperature of 25°C. In this way, high-energy UV induces O2 in the air to be converted into O3, and decomposes to form active oxygen atoms. These active oxygen can react with the copper surface to generate polar oxygen-containing functional groups such as hydroxyl (-OH), carboxyl (-COOH), and carbonyl (C=O).

[0105] The preparation of the negative electrode coating material includes: preparing Al(NO3)3 into a 0.1 mol / L ethanol / water mixed solution to form an aluminum salt solution, then adding graphite powder to the aluminum salt solution at a mass ratio of 50:1, stirring and ultrasonically dispersing, so that the precursor aluminum source is uniformly adsorbed on the graphite surface, and then adjusting the pH to 4-5 to promote the hydrolysis and deposition of the precursor. The resulting suspension system is dried at a temperature of 100°C to remove the solvent, and finally the dried suspension system is treated at a temperature of 650°C for 2 hours in an inert gas environment to convert the precursor into a dense and continuous alumina coating layer to obtain a negative electrode active material.

[0106] Anode active material (aluminum oxide coating amount of 2.0%), carbon nanotubes, sodium carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) were selected and stirred in deionized water at a mass ratio of 96:1.5:1:1.5 to form a cathode coating material. The cathode coating material was then applied to both sides of the copper foil, dried and cold pressed to form an anode sheet. The compaction density was 1.5 g / cm 3 .

[0107] Preparation of an electrolyte: 1 mol / L lithium hexafluorophosphate, ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were selected and mixed in a mass ratio of 15:15:20:50 to obtain an electrolyte.

[0108] Preparation of the diaphragm: A high-porosity diaphragm is selected, in which the thickness of the base film polyethylene PE is 9 μm, the thickness of the ceramic coating on both sides of the base film is 1.0 μm, and the thickness of the polyvinylidene fluoride (PVDF) coating is 1.0 μm.

[0109] Assembling the lithium-ion battery: The positive and negative electrode sheets are rolled and slit separately, then wound together with the separator to form a cylindrical battery core. This core is then welded to the electrical connector and assembled into the battery casing. After completing the injection, sealing, and formation processes, the lithium-ion battery of this example is obtained. The casing is cylindrical, with dimensions of 21.0 mm in diameter and 70.0 mm in length.

[0110] Example 2

[0111] Example 2 provides a lithium-ion battery, which differs from Example 1 in that the amount of aluminum oxide coating on the graphite surface of the negative electrode active material in the negative electrode coating is 1.0%. All other aspects are the same as Example 1.

[0112] Example 3

[0113] Example 3 provides a lithium-ion battery, which differs from Example 1 in that the amount of aluminum oxide coating on the graphite surface of the negative electrode active material in the negative electrode coating is 1.5%. Other aspects are the same as Example 1.

[0114] Example 4

[0115] Example 4 provides a lithium-ion battery, which differs from Example 1 in that the amount of aluminum oxide coating on the graphite surface of the negative electrode active material in the negative electrode coating is 2.5%. All other aspects are the same as Example 1.

[0116] Example 5

[0117] Example 5 provides a lithium-ion battery, which differs from Example 1 in that the amount of aluminum oxide coating on the graphite surface of the negative electrode active material in the negative electrode coating is 3%. Other aspects are the same as Example 1.

[0118] Example 6

[0119] Example 6 provides a lithium-ion battery. The difference between this example and Example 1 is that the copper foil current collector is oxidized for 5 minutes. Other aspects are the same as Example 1.

[0120] Example 7

[0121] Example 7 provides a lithium-ion battery. The difference between this example and Example 1 is that the copper foil current collector is oxidized for 10 minutes, and the rest is the same as Example 1.

[0122] Example 8

[0123] Example 8 provides a lithium-ion battery. The difference between this example and Example 1 is that the copper foil current collector is oxidized for 20 minutes, and the rest is the same as Example 1.

[0124] Example 9

[0125] Example 9 provides a lithium-ion battery. The difference between this example and Example 1 is that the copper foil current collector is oxidized for 25 minutes. Other aspects are the same as Example 1.

[0126] Example 10

[0127] Example 10 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass ratio of the negative electrode active material, carbon nanotubes, sodium carboxymethyl cellulose and polyacrylic acid is 96:1.5:2:0.5, and the rest is the same as Example 1.

[0128] Example 11

[0129] Example 11 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass ratio of the negative electrode active material, carbon nanotubes, sodium carboxymethyl cellulose and polyacrylic acid is 96:1.5:1.5:1, and the rest is the same as Example 1.

[0130] Example 12

[0131] Example 12 provides a lithium-ion battery. The difference between this example and Example 1 is that the mass ratio of the negative electrode active material, carbon nanotubes, sodium carboxymethyl cellulose and polyacrylic acid is 96:1.5:0.5:2, and the rest is the same as Example 1.

[0132] Comparative Example 1

[0133] Comparative Example 1 provides a lithium-ion battery. The difference between this comparative example and Example 1 is that the graphite surface of the negative electrode active material in the negative electrode coating is not coated with aluminum oxide. Other aspects are the same as Example 1.

[0134] Comparative Example 2

[0135] Comparative Example 2 provides a lithium-ion battery. The difference between this comparative example and Example 1 is that the copper foil current collector is not oxidized, and the other aspects are the same as Example 1.

[0136] Comparative Example 3

[0137] Comparative Example 3 provides a lithium-ion battery. The difference between this comparative example and Example 1 is that the negative electrode coating material includes a negative electrode active material, carbon nanotubes, sodium carboxymethyl cellulose and styrene-butadiene rubber, and the mass ratio is 96:1.5:1:1.5, which are fully stirred and mixed in an N-methylpyrrolidone solvent system. The rest is the same as Example 1.

[0138] The lithium-ion batteries of Examples 1 to 12 and Comparative Examples 1 to 3 were subjected to corresponding tests.

[0139] This embodiment provides a lithium-ion battery pretreatment method, comprising the following steps:

[0140] Discharge the lithium-ion battery at a constant current to 2.5V. Ensure the battery is in a safe state to reduce the risk of short circuits or thermal runaway during disassembly. Disassemble the battery and remove the negative electrode from the cylindrical cell in a glove box under a pure argon or other inert atmosphere. Use tweezers or a suitable tool to peel the electrode away, avoiding damage to the active material layer.

[0141] Cut the removed negative electrode sheet into appropriate sizes and soak it in an anhydrous dimethyl carbonate (DMC) solution for 30 minutes to dissolve and remove residual electrolyte and possible byproducts. Remove the electrode and wipe the surface with a dust-free wipe. Then replace the anhydrous dimethyl carbonate (DMC) solution and repeat the soaking and wiping process three times to ensure that there are no residual contaminants on the electrode surface.

[0142] Rinse the electrode with anhydrous ethanol and wipe it again to further remove the solvent and impurities.

[0143] After cleaning, a portion of the electrodes were placed in a glove box for 48 hours to ensure that they were completely dry to prevent subsequent tests from being interfered with by residual solvents. This portion of the electrodes was used for diaphragm resistance testing and peel force testing.

[0144] After drying the other electrode, use a plastic scraper or blade to scrape the negative electrode active material, ensuring that the collected powder is not contaminated. Transfer the scraped powder to a centrifuge tube filled with anhydrous ethanol and ultrasonically disperse it in an ultrasonic cleaner for 30 minutes to further remove any residual electrolyte, binder, and impurities.

[0145] After ultrasonic treatment, the sample was centrifuged at 5000 rpm for 2 min, the supernatant was removed, and the powder was re-dispersed with anhydrous ethanol. Ultrasonic dispersion was performed again using an ultrasonic cleaner for 10 min, and then centrifuged again. This process was repeated three times to ensure the purity of the powder sample.

[0146] The precipitate was collected and transferred to a vacuum drying oven and dried at 80°C for 12 hours to ensure that the residual solvent was completely removed. The dried powder was placed in a sealed bag or a sealed sample box and immediately taken out of the glove box. This part of the electrode was quickly tested for the floating rate of the negative electrode active material.

[0147] This embodiment also provides a method for testing the sheet resistance of a negative electrode sheet, using a resistance test system model RM2610 to measure the sheet resistance of the negative electrode sheet. The resistance test system has 45 probes arranged in a square matrix, with one probe serving as a ground probe.

[0148] The test method includes the following steps:

[0149] Place the test sample on the test device and use a pressure gauge to adjust the pressure applied by the probe to ensure good contact between the probe and the test sample. The contact area is 0.01 cm 2 .

[0150] During the test, the 20 outer probes apply a constant current, causing it to flow through the surface, interface, and current collector of the negative electrode sheet. Simultaneously, the 25 central probes measure voltage changes in real time. The sheet resistance is calculated using Ohm's law and fitting analysis.

[0151] In the front, middle and rear sections of the above-mentioned electrode, 9 square grids were randomly selected for diaphragm resistance measurement, and the obtained resistance values ​​were recorded as R1, R2, R3, R4, R5, R6, R7, R8, and R9 respectively. By calculating the average value of the above resistance values, the average diaphragm resistance R of the negative electrode sheet actually tested was obtained, R = (R1+R2+R3+R4+R5+R6+R7+R8+R9) / 9.

[0152] This embodiment also provides a method for testing the peeling force of a negative electrode sheet, comprising the following steps:

[0153] Use double-sided tape to fix the test sample on a flat thin steel plate, making sure the tape is attached to the center of the steel plate. Here the test sample is a long strip.

[0154] Then peel off the protective layer of the double-sided tape, stick the test sample on the double-sided tape, and use a pressure roller to evenly press the test sample to ensure good adhesion;

[0155] Then tear off the unpasted end, bend the natural end of the torn test sample upward, and clamp it in the upper fixture of the tensile testing machine to perform a 180° peel test. Record the tensile force curve. The stage where the tensile force changes by no more than 10% is selected as the stable peeling stage.

[0156] The ratio of the average tensile force of the section to the width of the test sample was calculated to obtain the peel strength of the negative electrode sheet.

[0157] Peel force tests were performed on the front, middle, and back sections of the electrode sheet, and the resulting peel force values ​​were recorded as N1, N2, and N3, respectively. The average peel force N of the actual negative electrode sheet tested was calculated by averaging these peel force values, where N = (N1 + N2 + N3) / 3.

[0158] This embodiment also provides a method for testing the floating mass percentage of active material in a negative electrode sheet, comprising the following steps:

[0159] Take M1 mass of negative electrode active material and add it to a mixed electrolyte containing ethylene carbonate and methyl carbonate in a ratio of 3:7. Let it stand for 3 minutes and take out the negative electrode active material floating on the electrolyte.

[0160] Rinse with ethanol, then centrifuge and dry to obtain a mass M2. The floating mass percentage is M1 / M2×100%.

[0161] This embodiment also provides a method for testing the rate performance of a lithium-ion battery. The lithium-ion battery is discharged to 2.5V and placed in a constant temperature box at 25°C for 6 hours. The test is performed according to the following steps:

[0162] Under the condition of 1C charging rate, constant current and constant voltage charging to 4.2V, the cut-off current is 0.1C, and it is left to stand for 30 minutes. The capacity of constant current charging to 4.2V is Q1;

[0163] At a discharge rate of 1C, discharge at a constant current until the voltage reaches 2.5V, with a cutoff current of 0.1C, and then let it stand for 30 minutes.

[0164] Under the condition of 6C charging rate, constant current and constant voltage charging to 4.2V, cut-off current is 0.1C, and it is left to stand for 30 minutes. The capacity of constant current charging to 4.2V is Q6;

[0165] At a discharge rate of 1C, discharge at a constant current until the voltage reaches 2.5V, with a cutoff current of 0.1C, and then let it stand for 30 minutes.

[0166] Here, the capacity retention rate Q of the lithium-ion battery is calculated by Q1 and Q6. R , where Q R =Q6 / Q1×100%.

[0167] This embodiment also provides a method for testing the cycling performance of a lithium-ion battery. The lithium-ion battery is placed in a constant temperature box at 25° C. for 6 hours and tested according to the following steps:

[0168] Charging steps: At a 0.1C charge rate, charge at constant current to 4.2V, then switch to constant voltage charging until the current drops to 0.01C; let it sit for 30 minutes after charging is completed;

[0169] Discharge steps: Discharge to 2.5V at a discharge rate of 0.1C.

[0170] Repeat the above charging and discharging steps for 1000 cycles.

[0171] The discharge capacity Q1 and Q2 of the battery after 1 cycle and 1000 cycles 1000 Calculate the capacity decay rate Q of lithium-ion batteries d , Q d =(Q1-Q 1000 )×100%.

[0172] After Examples 1 to 12 and Comparative Examples 1 to 3 were subjected to the above tests, the corresponding sheet resistance, peeling force, floating mass percentage, capacity retention rate, and capacity decay rate were obtained. The relevant data are shown in Table 1 below:

[0173]

[0174] Table 1

[0175] In Table 1, by comparing Examples 1 to 5, it can be seen that as the amount of aluminum oxide coating on the graphite surface gradually increases to 2%, the membrane resistance of the negative electrode sheet is significantly reduced, the peeling force and capacity retention rate are simultaneously improved, and the floating mass percentage and capacity attenuation rate both show a downward trend, indicating that the interface conductivity, adhesion and structural stability of the negative electrode sheet are improved.

[0176] However, when the alumina coating content continues to increase to 3%, the above performance parameters all show varying degrees of decline. The fundamental reason is that the alumina surface is rich in polar oxygen-containing functional groups, such as hydroxyl (–OH) and carboxyl (–COOH), which have better hydrophilicity than ordinary graphite surfaces. They can form hydrogen bonds and electrostatic interactions with the carboxyl (–COOH) in polyacrylic acid binders, thereby significantly enhancing the interfacial adhesion between the active material and the binder and current collector, reducing electronic contact resistance and improving the diffusion behavior of lithium ions.

[0177] In addition, an appropriate amount of alumina coating can also form a stable and uniform inorganic interface layer on the surface of the graphite particles, effectively inhibiting the repeated rupture of the SEI film and alleviating the volume expansion of the graphite during the lithium insertion and removal process, thereby improving the cycle stability. However, when the alumina coating amount is too high, such as exceeding 2.5%, the alumina coating layer tends to be dense and continuous, and part of the alumina coating layer may even block the effective contact between the graphite and the electrolyte, thereby limiting the rapid insertion and removal of lithium ions, significantly increasing the interfacial impedance, causing the membrane resistance to rebound, and affecting the rate performance and cycle stability.

[0178] In Table 1, by comparing Example 1 and Example 6 to Example 9, it can be seen that the time for the oxidation treatment equipment to treat the negative electrode current collector will also affect the performance of the negative electrode sheet. As the treatment time increases, the performance of the negative electrode sheet gradually improves and then gradually decreases. Here, when the treatment time is short, such as less than 15 minutes, fewer oxygen-containing functional groups are generated on the surface of the copper foil. When the treatment time is long, such as more than 15 minutes, a thicker copper oxide will form on the surface of the copper foil, which hinders electron conduction and lithium ion diffusion, but leads to increased film resistance and deterioration of interface contact, thereby affecting rate performance and cycle performance. Therefore, the overall performance of the negative electrode current collector after 15 minutes of treatment is the best. The introduction of oxygen-containing functional groups on the surface of the copper foil can significantly improve the hydrophilicity of its surface, enhance the wetting and mechanical bonding of the current collector to the coating layer, thereby improving the peeling force and structural stability. At the same time, the improved interfacial electrical contact is also conducive to rapid electron transmission and reduced membrane resistance.

[0179] In Table 1, a comparison of Examples 1, 10, and 12 shows that the amount of polyacrylic acid binder used also affects the performance of lithium-ion batteries. Here, as the polyacrylic acid content increases, its capacity retention and capacity decay rates rise and fall to varying degrees. The polyacrylic acid binder's molecular chain contains a high proportion of carboxyl groups (–COOH), which can form hydrogen bonds or coordination bonds with the oxide layer on the copper foil surface and the surface of the negative electrode active material, significantly enhancing the overall adhesion of the electrode and facilitating the kinetic transport of lithium ions. Therefore, an appropriate amount of polyacrylic acid binder can effectively build a uniform conductive network, which helps reduce resistance, improve rate capability, and cycle stability. However, when the polyacrylic acid binder content is high and the sodium carboxymethyl cellulose (CMC) content is low, the dispersion stability of the slurry is poor, which in turn affects the overall performance of the lithium-ion battery. Therefore, when the polyacrylic acid binder content is 1.5%, the overall performance of the lithium-ion battery is optimal.

[0180] In Table 1, by comparing Example 1 and Comparative Examples 1 to 3, it can be seen that when the graphite surface is not coated with alumina, the negative electrode current collector is not oxidized, and the polyacrylic binder is adjusted to styrene-butadiene rubber (SBR), the diaphragm resistance, peeling force, floating mass percentage, capacity retention rate and capacity attenuation rate will be affected to varying degrees.

[0181] In summary, the present application can effectively improve the bonding force of the electrode interface by optimizing the structure of the negative electrode current collector and the negative electrode coating, thereby ensuring its mechanical stability, and further improving its rate performance and cycle stability.

[0182] The above description and the accompanying drawings sufficiently illustrate the embodiments of the present disclosure to enable those skilled in the art to practice them. Other embodiments may include structural and other changes. The embodiments represent only possible variations. Unless expressly required, individual components and functions are optional, and the order of operations may vary. Portions and features of some embodiments may be included in or replace portions and features of other embodiments. The embodiments of the present disclosure are not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes may be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A negative electrode sheet, characterized in that: include: The negative electrode current collector is treated by an oxidation treatment device so that the surface of the negative electrode current collector contains polar oxygen-containing functional groups, including one or more of hydroxyl groups, carboxyl groups and carbonyl groups; A negative electrode coating, comprising a negative electrode coating material coated on at least one side of the negative electrode current collector, the negative electrode coating material comprising a negative electrode active material, the negative electrode active material comprising a carbon material and an alumina coating layer coating the carbon material; wherein the average thickness of the alumina coating layer is 5 nm to 50 nm, and the mass of the alumina coating layer is 0.5% to 5% of the mass of the active material; The negative electrode coating material also includes a negative electrode binder, which includes at least one of polyacrylic acid, polyacrylic acid derivatives, sodium carboxymethyl cellulose, polyacrylonitrile, polystyrene-acrylic acid and styrene-butadiene rubber, wherein the mass of the negative electrode binder is 1% to 3% of the mass of the negative electrode sheet.

2. The negative electrode sheet according to claim 1, characterized in that: The presence of polar oxygen-containing functional groups on the surface of the negative electrode current collector was determined by the following method: In the infrared spectrum of the negative electrode current collector, at 3200 cm -1 ~3600cm -1 Between 1700cm -1 ~1725cm -1 Between and 500cm -1 ~600cm -1 There are characteristic peaks between them; Among them, 3200cm -1 ~3600cm -1 The characteristic peak at 1700 cm corresponds to the stretching vibration of hydroxyl groups. -1 ~1725cm -1 The characteristic peak at 500 cm corresponds to the carbonyl stretching vibration. -1 ~600cm -1 The characteristic peaks correspond to the Cu-O lattice vibration.

3. The negative electrode sheet according to claim 1, characterized in that: The floating mass percentage of the negative electrode active material is ≤9.5%, and the floating mass percentage of the negative electrode active material is calculated by the following formula: m f / m t ×100%; Among them, m f is the mass of floating carbon material, m t is the total mass of carbon material.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The aluminum oxide coating layer is used to determine whether the carbon material is coated by the following method: In the X-ray photoelectron spectrum of the negative electrode active material, there is an Al2p characteristic peak between 74.0 eV and 75.5 eV, and there is an O1s characteristic peak between 530.0 eV and 533.0 eV.

5. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The carbon material includes one or more of artificial graphite, natural graphite, soft carbon or hard carbon; the negative electrode coating also includes a negative electrode conductive agent, and the negative electrode conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The surface of the negative electrode coating is punched by laser punching, mechanical punching or laser scoring.

7. The negative electrode sheet according to claim 6, wherein the negative electrode coating is provided with a plurality of pores, wherein: The distance between adjacent pores is 0.1 mm to 2 mm, the pore diameter is 40 μm to 100 μm, and the ratio of the pore depth to the thickness of the negative electrode coating is 0.2 to 0.

85.

8. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The sheet resistance of the negative electrode is R≤4.0×10 -3 Ω·cm 2 .

9. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The compaction density of the negative electrode sheet is 1.3 g / cm 3 ~1.75g / cm 3 .

10. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The peeling force N of the negative electrode sheet is greater than or equal to 10.5 N / m.

11. A method for preparing a negative electrode sheet according to any one of claims 1 to 10, characterized in that: The following steps are involved: Preparation of negative electrode current collector: Cleaning the negative electrode current collector and then placing it in an oxidation treatment device to cause surface oxidation reaction of the negative electrode current collector to generate polar oxygen-containing functional groups; Preparation of negative electrode coating material: aluminum nitrate, carbon material and solvent are configured into a mixed solution, and after stirring and dispersing, the pH value of the mixed solution is adjusted to 4-5 to obtain a suspension system solution; The suspension system solution is dried, and then mixed with a negative electrode binder and a negative electrode conductor according to a set ratio to obtain a negative electrode coating material of an aluminum oxide-coated carbon material; Preparation of negative electrode sheet: coating the negative electrode coating material on at least one side of the negative electrode current collector, drying and cold pressing to obtain the negative electrode sheet.

12. A lithium ion battery, characterized in that: The invention comprises a positive electrode sheet and a negative electrode sheet as claimed in any one of claims 1 to 10.

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