A long cycle negative electrode sheet and a lithium ion battery comprising the same

Abstract

Disclosed are a long cycle negative electrode sheet and a lithium ion battery including the same. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes silicon oxide particles. The silicon oxide particles satisfy the following relationships: D i ≤ 35 μm (I), d i ≤ 25 μm (II), 0.45 ≤ (ΣE j 2 ) / (ΣD i 2 ) ≤ 0.75 (III), (ΣF k 2 ) / (ΣD i 2 ) ≥ 0.37 (IV), and the blending amount of the silicon oxide particles satisfies the following relationship: 0.05 ≤ (ΣF k 2 ) / S ≤ 0.47 (V). The lithium ion battery has a high energy density characteristic and a long cycle life at a charge condition of 0.1 C to 1.0 C.

Description

Technical Field

[0001] This invention belongs to the field of energy storage and relates to a long-cycle negative electrode and a lithium-ion battery including the negative electrode. Background Technology

[0002] In recent years, consumers have increasingly demanded higher driving ranges for electronic products and electric vehicles, which in turn places higher demands on the energy density of lithium-ion batteries, the energy carriers. At room temperature, silicon's reversible capacity is approximately ten times that of graphite, thus silicon oxide particles, with silicon as the active component, show great promise for high-energy-density batteries. Adding a certain proportion of silicon oxide particles to a graphite anode system can effectively increase the specific capacity of the anode, thereby improving the battery's energy density. However, the introduction of silicon oxide particles leads to a decrease in the anode's cycle performance. Therefore, how to construct lithium-ion batteries with high energy density and long cycle life has become a pressing challenge in the development of anode materials and battery design. Summary of the Invention

[0003] To improve the above-mentioned technical problems, the present invention provides a long-cycle negative electrode and a lithium-ion battery including the negative electrode.

[0004] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0005] A negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer being disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer comprising silicon oxide particles;

[0006] The silicon oxide particles satisfy the following relationship:

[0007] D i ≤35μm(I),

[0008] d i ≤25μm (II),

[0009] 0.45≤(ΣE j 2 ) / (ΣD i 2 )≤0.75 (III),

[0010] (ΣF k 2 ) / (ΣD i 2 ≥0.37 (IV),

[0011] Furthermore, the mixing amount of silicon oxide particles satisfies the following relationship:

[0012] 0.05≤(ΣFk 2 ) / S≤0.47 (V);

[0013] Where Σ represents the summation of the data, and D i d represents the circumcircle diameter of any silicon oxide particle. i E represents the diameter of the inscribed circle of any silicon oxide particle. j D represents i The circumcircle diameter of silicon oxide particles ≥9μm, F k d i The outer circle diameter of silicon oxide particles ≥4μm, i, j, k represent the particle number, and S represents the cross-sectional area of ​​the negative electrode active material layer in the observation area.

[0014] According to the present invention, in the negative electrode, the specific surface area of ​​the silicon oxide particles is less than or equal to 1.2 m². 2 / g.

[0015] According to the present invention, the mass percentage of silicon oxide particles relative to the negative electrode active material layer is approximately 5 wt% to 25 wt%.

[0016] According to the present invention, in the negative electrode sheet, the thickness L of the negative electrode active material layer satisfies 30μm≤L≤100μm.

[0017] According to the present invention, the silicon oxide particles contain Si and O elements, and the molar ratio x (mol / mol) of O to Si elements satisfies 0.7 ≤ x ≤ 1.4.

[0018] According to the present invention, at least a portion of the surface of the silicon oxide particles contains a coating layer.

[0019] The present invention also provides silicon oxide particles for the above-mentioned negative electrode, the particles comprising at least the following characteristics:

[0020] (1)D v max≤35;

[0021] (2) 9.0≤D v 50≤13.0;

[0022] (3) BET≤1.2;

[0023] in:

[0024] D v max represents the maximum particle size of the silicon oxide particles, in μm;

[0025] D v 50 represents the median particle size of the silicon oxide particles, in μm;

[0026] BET represents the specific surface area of ​​the silicon oxide particles, in m². 2 / g.

[0027] The present invention also provides a lithium-ion battery, wherein the lithium-ion battery includes the above-mentioned negative electrode sheet.

[0028] According to the present invention, after the lithium-ion battery undergoes 1 to 5 charge-discharge cycles, the negative electrode plate undergoes irreversible expansion, at which time the negative electrode plate satisfies the following relationship:

[0029] D i ≤44μm

[0030] d i ≤32μm,

[0031] 0.45≤(ΣE j ' 2 ) / (ΣD i ' 2 )≤0.75,

[0032] (ΣF k ' 2 ) / (ΣD i ' 2 )≥0.37,

[0033] 0.06≤(ΣF k ' 2 ) / S'≤0.53,

[0034] 39μm≤L'≤130μm

[0035] Where Σ represents the summation of the data, and D i ' represents the circumcircle diameter of any silicon oxide particle, d i ' represents the diameter of the inscribed circle of any silicon oxide particle, E j ' indicates D i 'The circumcircle diameter of silicon oxide particles ≥11.2μm, F k ' indicates d i 'The outer circle diameter of silicon oxide particles ≥5.0μm, i, j, k represent the particle number, S' represents the cross-sectional area of ​​the negative electrode in the observation area, and L' represents the thickness of the active material layer.

[0036] Beneficial effects of the present invention

[0037] Silicon oxide particles generate inert silicate components during initial lithium intercalation, which act as a buffer against expansion during cycling. Therefore, silicon oxide particles exhibit higher cycle stability than pure silicon particles under the same size conditions. Nevertheless, in research on constructing high-energy-density lithium-ion batteries, the inventors unexpectedly discovered that even using a negative electrode containing silicon oxide particles did not achieve ideal cycle performance. Further analysis revealed that this performance deficiency was due to flaws in the material selection and design of the hybrid negative electrode. To prevent excessive concentration of expansion stress during cycling, a common approach is to reduce the maximum particle size D of the silicon oxide particles... v The maximum diameter (max) is controlled at around 13 μm, making it less than or equal to the median particle size (D) of the graphite particles. v 50, which facilitates the uniform filling of silicon oxide particles between graphite particles, thereby reducing local stress and strain. However, when using the above approach, the particle size of silicon oxide particles is significantly smaller than that of graphite particles, thus possessing a larger specific surface area. For example, when the maximum particle size D of the silicon oxide particles... v max is 13μm, D v When the thickness is 5μm, the specific surface area is approximately 3m². 2 / g; and when the maximum particle size D of the graphite particles v The maximum value is 35μm, D v When the thickness is 15 μm, the specific surface area is approximately 1 m². 2 / g. Considering the large volume change of silicon oxide particles during lithium insertion / extraction cycles, the surface SEI film will continuously break down and repair itself. A large specific surface area often leads to more side reactions, thus accelerating the degradation rate of lithium-ion batteries. Therefore, increasing the particle size of silicon oxide particles as much as possible, while ensuring that local strain does not cause electrode deformation, can help improve cycle performance. On the other hand, among all three-dimensional geometries, spheres have the smallest specific surface area, and silicon oxide particles are usually formed from the fragmentation of bulk materials, including various irregular shapes such as rods, plates, and polyhedra. This characteristic results in a large specific surface area. Therefore, controlling the shape of silicon oxide particles is also an important approach to adjusting specific surface area and cycle performance.

[0038] In view of this, the present invention provides a long-cycle negative electrode and a lithium-ion battery based on the negative electrode, which has high energy density characteristics and long cycle life under charging conditions of 0.1C to 1.0C. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the circumcircle and incircle of the silicon oxide particles in this invention.

[0040] Figure 2 The volume-based particle size distribution curve of the silicon oxide particles in Example 1 is shown.

[0041] Figure 3 This is a SEM image of the silicon oxide particles from Example 1 (taken using secondary electron mode).

[0042] Figure 4 This is a SEM cross-sectional image (taken using backscattered electron mode) of the negative electrode sheet in Example 4; in the figure: 41 represents silicon oxide particles, 42 represents graphite, and 43 represents copper foil. The circumcircle of the silicon oxide particles is marked with a circular dashed line in the figure.

[0043] Figure 5 This is a SEM cross-sectional image of the negative electrode sheet in Example 4 (taken using backscattered electron mode). The inscribed circles of some silicon oxide particles are marked with dashed lines; the diameter of the inscribed circles of these particles is ≥4 μm. Detailed Implementation

[0044] [Negative electrode sheet and its preparation]

[0045] As mentioned above, the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer being disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer comprising silicon oxide particles.

[0046] The silicon oxide particles satisfy the following relationship:

[0047] D i ≤35μm (I),

[0048] d i ≤25μm (II),

[0049] 0.45≤(ΣE j 2 ) / (ΣD i 2 )≤0.75 (III),

[0050] (ΣF k 2 ) / (ΣD i 2 ≥0.37 (IV),

[0051] Where Σ represents the summation of the data, and D i d represents the circumcircle diameter of any silicon oxide particle. i E represents the diameter of the inscribed circle of any silicon oxide particle. j D represents i The circumcircle diameter of silicon oxide particles ≥9μm, F k d iThe outer circle diameter of silicon oxide particles ≥4μm, where i, j, and k represent the particle number.

[0052] In this invention, the above relationship is based on cross-sectional photographs of silicon oxide particles, wherein the photographs are scanning electron microscope (SEM) characterization results of the cross-section of the negative electrode sheet, and the length of the negative electrode sheet in the observation area is ≥150μm.

[0053] In this invention, the circumcircle represents the smallest circle with the largest diameter that can completely enclose the silicon oxide particles. The incircle represents the largest circle with the largest diameter that can be completely enclosed by the silicon oxide particles. (See schematic diagram below.) Figure 1 As shown.

[0054] This invention defines the particle size of silicon oxide particles in the negative electrode using equations (I) and (II). When the above conditions are met, the silicon oxide particle size is moderate, and its volume change during cycling will not cause significant deformation of the electrode; when D exists... i >35μm or d i When silicon oxide particles are larger than 25 μm, the absolute value of the volume change of these particles during cycling is large, which may lead to excessive stress in local areas and the risk of bulging of the active material layer. This will worsen the electrical contact between the active material layer and the current collector, thereby accelerating the decay of the battery's cycle capacity.

[0055] This invention defines not only the particle size distribution of silicon oxide particles but also their shape through equations (III) and (IV). Any cross-section of a sphere is circular, with the inscribed and circumscribed circles having equal diameters. For irregular geometric shapes, the closer the inscribed and circumscribed circles are to each other, the closer the shape is to a circle. For example, when the circumscribed circle diameter is 1, the inscribed circle diameter of an equilateral triangle is 0.5, that of a square is 0.71, that of a regular hexagon is 0.87, and that of a circle is 1. In view of this, this invention unexpectedly discovers that, given a fixed circumscribed circle size for the cross-sectional shape of silicon oxide particles, the inscribed circle diameter must be sufficiently large. At this point, the overall shape of the silicon oxide particles is closer to a sphere, thus effectively reducing side reactions occurring on the surface of the silicon oxide particles. When equations (III) and (IV) are satisfied, the electrode contains an appropriate proportion of D... i ≥9μm and sufficient proportion of d i Silicon oxide particles with a diameter ≥4 μm, where the specific surface area of ​​the silicon oxide particles is less than or equal to 1.2 m². 2 / g (The specific surface area of ​​conventionally used silicon oxide is generally greater than 1.2m²) 2 / g), fewer side reactions; when (ΣE) j 2 ) / (ΣD i2 When (ΣE) < 0.45, the overall particle size of silicon oxide particles is small, the specific surface area is large, and there are more surface side reactions; when (ΣE) < 0.45, the overall particle size of silicon oxide particles is small, the specific surface area is large, and there are more surface side reactions; j 2 ) / (ΣD i 2 When (ΣF) > 0.75, the overall particle size of silicon oxide particles is relatively large, which easily exacerbates the uneven stress distribution inside the electrode, leading to electrode deformation. This, in turn, worsens the electrical contact between the active material layer and the current collector, thereby accelerating the battery cycle capacity decay. k 2 ) / (ΣD i 2 When the specific surface area (SSA) is less than 0.37, the overall shape of the silicon oxide particles deviates too far from spherical, for example, there are many rod-shaped or plate-shaped particles. In this case, the specific surface area of ​​the silicon oxide particles is generally greater than 1.2 m². 2 / g, with numerous side reactions.

[0056] In one specific embodiment, the amount of silicon oxide particles mixed in the negative electrode sheet satisfies the following relationship:

[0057] 0.05≤(ΣF k 2 ) / S≤0.47 (V);

[0058] Where Σ represents the summation of the data, F k d i The outer circle diameter of silicon oxide particles ≥4μm, k represents the number of the silicon oxide particle, and S represents the cross-sectional area of ​​the negative electrode active material layer in the SEM image observation area.

[0059] Studies have found that when the doping amount of silicon oxide particles satisfies this relationship, the mass percentage of silicon oxide particles relative to the active material layer is approximately 5 wt% to 25 wt%.

[0060] Studies have found that when the mass percentage of silicon oxide particles is approximately 5wt%–25wt%, the silicon oxide particles can be relatively uniformly dispersed among the graphite particles, resulting in lower local stress; when (ΣF k 2 When (ΣF) / S < 0.05, the silicon oxide particle content is too low, which cannot guarantee that the lithium-ion battery has a high energy density; when (ΣF) / S < 0.05, the silicon oxide particle content is too low, which cannot guarantee that the lithium-ion battery has a high energy density. k 2 When ) / S > 0.47, the silicon oxide particle content is too high, which easily leads to particle aggregation areas, exacerbates local expansion, worsens the electrical contact of active materials, and causes the battery capacity to decay faster.

[0061] In one specific embodiment, the thickness L of the active material layer in the negative electrode sheet satisfies 30μm≤L≤100μm. When the active material layer is within this thickness range, the uniformity of coating and the overall dynamics of the battery electrode sheet can be guaranteed. When L<30μm, the coating is too thin, and phenomena such as coating scraping are prone to occur, making it impossible to guarantee the uniformity of the electrode sheet; when L>100μm, the electrode sheet is too thick, resulting in severe polarization effects, which can easily lead to phenomena such as lithium plating on the electrode sheet, and accelerate the decay of the battery cycle capacity.

[0062] In one specific embodiment, the silicon oxide particles contain Si and O elements, and the molar ratio x (mol / mol) of O to Si satisfies 0.7 ≤ x ≤ 1.4. Examples include 0.7, 0.8, 1.0, 1.2, 1.4, or any value within the range of the aforementioned pairwise values. When this relationship is satisfied, the silicon oxide particles exhibit high specific capacity and a stable structure. When x < 0.7, the silicate inert matrix formed after lithium intercalation in the silicon oxide particles is small, resulting in poor cycle stability. When x > 1.4, the oxygen content in the silicon oxide particles is too high, leading to increased irreversible reactions, reduced specific capacity, and hindering the achievement of high energy density targets. The cross-sectional photograph of the negative electrode sheet can be obtained by cutting perpendicularly to the surface of the negative electrode sheet using an ion milling device and observing the cross-section using a scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS). The length of the negative electrode sheet in the observation area is ≥ 150 μm.

[0063] According to the present invention, at least a portion of the surface of the silicon oxide particles (e.g., a coating ratio greater than 0 and less than or equal to 100%) contains a coating layer, specifically a carbon coating layer. For example, the material of the carbon coating layer is selected from one or more of graphite, amorphous carbon, graphene, and carbon nanotubes.

[0064] Furthermore, the negative electrode active material layer also includes other negative electrode materials. For example, the other negative electrode materials are one or more selected from graphite, hard carbon, and soft carbon materials.

[0065] Furthermore, the negative electrode active material layer also includes a conductive agent. For example, the conductive agent is one or more selected from carbon black (Super P), acetylene black, Ketjen black, carbon fiber, single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs).

[0066] Furthermore, the negative electrode active material layer also includes a binder. For example, the binder is selected from one or more of carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polytetrafluoroethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber (SBR), and epoxy resin.

[0067] Furthermore, the negative electrode current collector is selected from one or more of copper foil, carbon-coated copper foil, and perforated copper foil.

[0068] The present invention also provides a method for preparing the above-mentioned negative electrode sheet, comprising:

[0069] Silicon oxide particles, optional other negative electrode materials, conductive agents and binders are mixed to obtain a negative electrode slurry. The negative electrode slurry is coated on a current collector, dried and sliced, then dried again, and finally rolled and slit to obtain a negative electrode sheet.

[0070] According to the present invention, the negative electrode slurry further contains a solvent. For example, the solvent is water.

[0071] According to the present invention, the drying temperature is 70 to 90°C, and exemplarily 70°C, 80°C, and 90°C.

[0072] According to the present invention, the drying temperature is 90 to 110°C, exemplarily 90°C, 100°C, or 110°C; the drying time is 8 to 24 hours, exemplarily 8 hours, 10 hours, 12 hours, or 24 hours, or any value within the range of the aforementioned pairs of values.

[0073] [Silicon oxide particles and their preparation]

[0074] The present invention also provides silicon oxide particles for the above-mentioned negative electrode, the particles comprising at least the following characteristics:

[0075] (1)D v max≤35;

[0076] (2) 9.0≤D v 50≤13.0;

[0077] (3) BET≤1.2.

[0078] in:

[0079] D v max represents the maximum particle size of the silicon oxide particles, in μm;

[0080] D v 50 represents the median particle size of the silicon oxide particles, in μm;

[0081] BET represents the specific surface area of ​​the silicon oxide particles, in m². 2 / g.

[0082] In some embodiments, the median particle size Dv50 of the silicon oxide particles satisfies: 9.0 ≤ Dv50 ≤ 11.0.

[0083] In some embodiments, the median particle size Dv50 of the silicon oxide particles satisfies: 11.0 < Dv50 ≤ 13.0.

[0084] In some embodiments, the molar ratio x of O and Si elements in the silicon oxide particles satisfies: 1.0 ≤ x ≤ 1.4, for example, 1.0, 1.1, 1.2, 1.4 or any point within the range of the aforementioned pairwise values.

[0085] In some embodiments, the molar ratio x of O and Si elements in the silicon oxide particles satisfies: 0.7 ≤ x < 1.0. Examples include 0.7, 0.8, 0.9, or any value within the range of the aforementioned pairwise values.

[0086] This invention also provides a method for preparing the above-mentioned silicon oxide particles, the method comprising:

[0087] 1) Mix silicon powder and silica powder at a Si / SiO2 molar ratio of 0.33 to 3.00 to obtain a mixture;

[0088] 2) In 10 -6 ~10 -4 The mixture is reacted for 4 to 10 hours at a pressure of MPa and a temperature of 1000–1200°C to generate gas.

[0089] 3) The gas is condensed to obtain a solid;

[0090] 4) The solid is pulverized to obtain powder A;

[0091] 5) Carbon coating treatment is applied to powder A to obtain powder B;

[0092] 6) Perform particle size classification on powder B to obtain the silicon oxide particles.

[0093] According to the present invention, in step 1), the mixing can be carried out by a horizontal mixer, an air-flow mixer or a horizontal ball mill.

[0094] According to the present invention, the pulverization in step 4) includes primary pulverization and secondary pulverization. The purpose of primary pulverization is to grind the solid into powder, and the purpose of secondary pulverization is to grind away the sharp edges of the powder particles, making the particle shape tend towards spherical. The primary pulverization can be carried out by a horizontal ball mill, and the secondary pulverization can be carried out by a vibrating ball mill. The container material used for both primary and secondary pulverization is stainless steel, and the grinding balls can be made of stainless steel or zirconium oxide. In both primary and secondary pulverization, the total filling volume of the solid to be pulverized and the grinding balls is 25% to 40% of the container. In primary pulverization, the diameter of the grinding balls is 1 to 2 cm, the mass ratio of the solid to be pulverized to the grinding balls is 0.05 to 0.15, the container rotation frequency is 200 to 300 rpm, and the ball milling time is 8 to 12 hours. In secondary pulverization, the diameter of the grinding balls is 0.3 to 1 cm, the mass ratio of the solid to be pulverized to the grinding balls is 0.3 to 0.5, the container vibration frequency is 400 to 800 rpm, and the ball milling time is 5 to 8 hours.

[0095] According to the present invention, in step 5), the carbon coating method includes chemical vapor deposition.

[0096] According to the present invention, the chemical vapor deposition method includes the following steps: calcining powder A at high temperature in a carbon source gas atmosphere to prepare powder B.

[0097] Preferably, the carbon source gas can be a mixture of argon and acetylene (C2H2). For example, the proportion of acetylene (C2H2) in the mixture is 3% to 20%, such as 3%, 5%, 8%, 10%, 15%, 20%, or any value within the range of the aforementioned pairs.

[0098] According to the present invention, the mass ratio of carbon source gas to silicon oxide particles flowing per minute is 0.05% to 0.4%, exemplarily 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, or any value within the range of the aforementioned pairs of values.

[0099] Preferably, the temperature of the high-temperature calcination treatment is 600–800°C, exemplarily 600°C, 700°C, or 800°C; the time of the high-temperature calcination treatment is 3–60 min, exemplarily 3 min, 5 min, 8 min, 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min. Further, the heating rate of the high-temperature calcination treatment is 5–15°C / min, exemplarily 5°C / min, 10°C / min, or 15°C / min.

[0100] Preferably, the high-temperature calcination treatment is carried out in an inert gas atmosphere, such as a nitrogen or argon atmosphere.

[0101] According to an exemplary embodiment of the present invention, the carbon coating method includes the following steps:

[0102] i) Under argon protection, powder A is heated to 600-800℃;

[0103] ii) Introduce an argon / acetylene mixture with a C2H2 content of 3-20% for a reaction time of 3-60 min;

[0104] iii) Under argon protection, the mixture is naturally cooled to room temperature to obtain powder B.

[0105] According to the present invention, in step 6), the purpose of the particle size classification process is to obtain D v max and D v 50 Powders that meet the aforementioned requirements, and the methods used include airflow classification.

[0106] [Lithium-ion battery]

[0107] The present invention also provides a lithium-ion battery comprising the above-described negative electrode.

[0108] According to the present invention, after the lithium-ion battery undergoes 1 to 5 charge-discharge cycles, the negative electrode plate undergoes irreversible expansion, at which time the negative electrode plate satisfies the following relationship:

[0109] D i ≤44μm

[0110] d i ≤32μm,

[0111] 0.45≤(ΣE j ' 2 ) / (ΣD i ' 2 )≤0.75,

[0112] (ΣF k ' 2 ) / (ΣD i ' 2 )≥0.37,

[0113] 0.06≤(ΣF k ' 2 ) / S'≤0.53,

[0114] 39μm≤L'≤130μm.

[0115] Where Σ represents the summation of the data, and D i ' represents the circumcircle diameter of any silicon oxide particle, d i ' represents the diameter of the inscribed circle of any silicon oxide particle, E j ' indicates Di 'The circumcircle diameter of silicon oxide particles ≥11.2μm, F k ' indicates d i 'The outer circle diameter of silicon oxide particles ≥5.0μm, i, j, k represent the particle number, S' represents the cross-sectional area of ​​the negative electrode in the observation area, and L' represents the thickness of the active material layer.

[0116] According to the present invention, the lithium-ion battery further includes a positive electrode.

[0117] According to the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer coated on the surface of the positive current collector. Preferably, the positive active material layer includes a positive electrode material.

[0118] According to the present invention, the current collector is selected from one or more of aluminum foil, carbon-coated aluminum foil, and perforated aluminum foil.

[0119] According to the present invention, the cathode material is selected from one or more of lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium iron silicate, lithium cobalt oxide (LCO), nickel-cobalt-manganese ternary materials, nickel-manganese / cobalt-manganese / nickel-cobalt binary materials, lithium manganese oxide, and lithium-rich manganese-based materials.

[0120] According to the present invention, the lithium-ion battery further includes a separator. For example, the separator is selected from one or more of polyethylene separators or polypropylene separators.

[0121] According to the present invention, the lithium-ion battery further includes an electrolyte. Preferably, the electrolyte is a non-aqueous electrolyte, which includes a solvent and a lithium salt.

[0122] For example, the solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC).

[0123] For example, the lithium salt is selected from one or more of LiPF6, LiBF4, LiSbF6, LiClO4, LiCF3SO3, LiAlO4, LiAlCl4, Li(CF3SO2)2N, LiBOB and LiDFOB.

[0124] According to the present invention, the lithium-ion battery further includes a packaging shell. For example, the packaging shell is selected from one or more of aluminum-plastic film, aluminum shell, and steel shell.

[0125] In this invention, the median particle size Dv50 of silicon oxide particles can be determined using a laser particle size analyzer. For example, a Malvern particle size analyzer can be used for measurement, and the testing steps are as follows: disperse silicon oxide particles in deionized water containing a dispersant (such as nonylphenol polyoxyethylene ether, content ~0.03% wt) to form a mixture, sonicate the mixture for 2 minutes, and then place it in the Malvern particle size analyzer for testing.

[0126] The BET (Brunauer-Emmett-Teller) surface area of ​​silicon oxide particles can be measured using the BET test method. For example, it can be measured using a Tri Star II surface area analyzer.

[0127] The molar ratio x of O to Si in silicon oxide particles can be determined using energy dispersive spectroscopy (EDS). For example, an Oxford energy dispersive spectroscopy instrument can be used for testing.

[0128] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0129] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0130] The electrical performance testing methods for silicon oxide particles, negative electrode sheets, and lithium-ion batteries in the following embodiments and comparative examples of the present invention are as follows:

[0131] 1. Button cell battery manufacturing and testing methods:

[0132] Silicon oxide particles, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), carbon black (Super P), and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 85:2:5.5:7:0.5. Deionized water was added, and a negative electrode slurry was obtained under vacuum stirring. This slurry was coated onto copper foil, dried at 80°C, sliced, and then transferred to a 100°C vacuum oven for 12 hours of drying. After rolling in the drying environment, the compaction density was approximately 1.4 g / cm³. 3 Then, a punching machine was used to make round discs with a diameter of about 1.2 cm.

[0133] Under an inert atmosphere, 13 wt% of fully dried lithium hexafluorophosphate (LiPF6) and 10 wt% of fluoroethylene carbonate (FEC) were rapidly added to ethylene carbonate (EC), and the mixture was stirred until homogeneous to obtain the desired electrolyte.

[0134] In a glove box, a coin cell is assembled using a lithium metal sheet as the counter electrode, a polyethylene membrane as the separator, and an electrolyte.

[0135] Using the LAND testing system, the material was discharged to 0.005V at a current of 50mA / g, allowed to stand for 10 minutes, and then charged to 1.5V at 50mA / g. The specific capacity and initial efficiency of the negative electrode material were then calculated.

[0136] 2. Full Battery Fabrication and Testing Methods

[0137] Silicon oxide particles, D v 50% of 15μm graphite, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), carbon black (Super P), and single-walled carbon nanotubes (SWCNTs) were mixed at a mass ratio of y:(96-y):1.5:1.5:0.9:0.1. Deionized water was added, and the mixture was stirred under vacuum to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a 6μm thick copper foil, dried at 80℃, and then transferred to a 100℃ vacuum oven for 12 hours. After rolling and slitting, the negative electrode sheet was obtained.

[0138] Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), and carbon black (Super P) were mixed at a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until a homogeneous positive electrode slurry was formed. The positive electrode slurry was then uniformly coated onto an aluminum foil with a thickness of 12 μm. The coated aluminum foil was baked in an oven and then dried in an oven at 120°C for 8 hours at a density of 4.0 g / cm³. 3 The compaction density is achieved by rolling, followed by slitting to obtain the desired positive electrode sheet. The positive electrode sheet is smaller than the negative electrode sheet to avoid lithium deposition at the edges of the negative electrode sheet. The initial delithiation capacity of the positive electrode sheet per unit area is 2% lower than the initial lithium insertion capacity of the negative electrode sheet, ensuring that the negative electrode sheet has sufficient lithium storage sites and preventing lithium deposition.

[0139] Under an inert atmosphere, a mixed solution was prepared according to the mass ratio of EC:PC:PP:LiPF6:FEC:PS = 13:13:50:15:5:4, and stirred evenly to obtain the desired electrolyte.

[0140] An 8μm thick polyethylene diaphragm was selected.

[0141] A pre-lithiated negative electrode is obtained by attaching a layer of lithium foil to the surface of the negative electrode through a rolling method, which enables the initial efficiency of the pre-lithiated negative electrode to reach 91.2% to 92.2% in coin cell testing.

[0142] The prepared positive electrode, separator, and pre-lithiated negative electrode are stacked in sequence, ensuring that the separator is positioned between the positive and negative electrodes and provides isolation. Then, the cells are wound to obtain bare cells without electrolyte filling. The bare cells are placed in an aluminum-plastic film casing, and the prepared electrolyte is injected into the dried cells. After vacuum sealing, settling, formation, shaping, and sorting, the desired lithium-ion battery is obtained.

[0143] The LAND testing system was used, and the test temperature was 25°C.

[0144] Charge the battery at a constant current of 0.7C to 4.45V, charge it at a constant voltage of 0.05C, let it stand for 10 minutes, and then discharge it at 0.2C to 3.0V to obtain the discharge capacity and discharge energy. Use the discharge capacity as the nominal capacity and the discharge energy as the battery energy.

[0145] The battery was charged at a constant current of 0.7C to 3.88V and then at a constant voltage of 0.02C. The thickness of the battery at this point was measured and taken as the initial thickness. The initial volume of the battery was calculated by multiplying its initial thickness by its length and width. The energy density of the battery was calculated by dividing its energy by its initial volume.

[0146] Charge at a constant current of 0.7C to 4.45V, charge at a constant voltage of 0.05C, let stand for 10 minutes, discharge at 1C to 3.0V, let stand for 10 minutes, and repeat this charge and discharge cycle. The highest discharge capacity in the first three weeks is the initial capacity of the battery. The ratio of the capacity at each step to the initial capacity is the capacity retention rate of the battery. Cycle until the capacity retention rate is less than 80%.

[0147] Example

[0148] 1. Preparation and physicochemical parameters of silicon oxide particles

[0149] The following is an exemplary method for preparing silicon oxide particles:

[0150] 1) Mix silicon powder and silica powder at a Si / SiO2 molar ratio of 0.33 to 3.00 to obtain a mixture;

[0151] 2) In 2×10 -5 The mixture was subjected to MPa pressure and 1050℃ temperature for 6 hours to generate gas.

[0152] 3) The gas is condensed to obtain a solid;

[0153] 4) The solid is pulverized to obtain powder A;

[0154] 5) Carbon coating treatment is applied to powder A to obtain powder B;

[0155] 6) Perform particle size classification on powder B to obtain the silicon oxide particles.

[0156] in:

[0157] Step 4) involves pulverization, which includes primary pulverization and secondary pulverization. In primary pulverization, the total filling volume of the material to be pulverized and the grinding balls is 30% of the container, the diameter of the grinding balls is 1.5 cm, the mass ratio of the material to be pulverized to the grinding balls is 0.1, and the pulverization time is 10 h. In secondary pulverization, the total filling volume of the material to be pulverized and the grinding balls is 30% of the container, the diameter of the grinding balls is 0.5 cm, the mass ratio of the material to be pulverized to the grinding balls is 0.4, and the pulverization time is 6 h.

[0158] In step 5), the proportion of acetylene (C2H2) in the mixed gas is 5%, the mass ratio of carbon source gas to silicon oxide particles flowing per minute is 0.2%, the calcination temperature is 700℃, and the calcination time is 15min.

[0159] Table 1 presents the preparation parameters for each embodiment and comparative example, including the Si / SiO2 molar ratio in step 1) and the vibration frequency of the ball mill during the secondary grinding in step 4). Table 1 also provides the physicochemical parameters of the silicon oxide particles for each embodiment and comparative example, including the O / Si molar ratio x and the maximum particle size D. v max, median particle size D v 50. Specific surface area (BET), specific capacity of silicon oxide particles, and initial efficiency.

[0160] In the primary crushing processes of Examples 1-3 and Comparative Examples 1-5, the container rotation frequency was 250 rpm; in the primary crushing process of Comparative Example 6, the container rotation frequency was 500 rpm.

[0161] Table 1

[0162]

[0163] The silicon oxide particles in Examples 1-3 all satisfy the limitations of this invention, wherein:

[0164] Example 1 serves as the baseline group; the difference between Example 2 and Example 1 lies in the O / Si molar ratio, with Example 1 ranging from 1.0 to 1.4 and Example 2 ranging from 0.7 to 1.0; the difference between Example 3 and Example 1 lies in the particle size, with Example 1 having a smaller D... v 50 is in the range of 9.0 to 11.0 μm, D in Example 3 v 50 is in the range of 11.0 to 13.0 μm.

[0165] The silicon oxide particles of Comparative Examples 1-6 do not fully meet the limitations of this invention. These characteristics are indicated in bold italics in the table, wherein: the O / Si molar ratio of Comparative Example 1 is greater than 1.4; the O / Si molar ratio of Comparative Example 2 is less than 0.7; in Comparative Example 3, the vibration frequency of the container during secondary crushing is too low, resulting in poor crushing effect and low D of the silicon oxide particles. v 50 is greater than 13.0 μm; in Comparative Examples 4 and 5, during the secondary grinding process, the vibration frequency of the container was too high, and the grinding intensity was too great, resulting in a D-value of the silicon oxide particles. v For particles smaller than 9.0 μm, and due to the reduced particle size and increased specific surface area, the BET values ​​are all greater than 1.2 μm. 2 / g; In Comparative Example 6, the rotation frequency of the container during the primary crushing step was increased, while the secondary crushing step was omitted. In this case, the silicon oxide particles retained more angularity, and the BET was greater than 1.2m. 2 / g.

[0166] As can be seen from Table 1:

[0167] The O / Si molar ratio of the silicon oxide particles in Examples 1, 3, and Comparative Examples 3-6 was 1.12, and their specific capacity and first-efficiency were similar, at 1570-1610 mAh / g and 74%-75%, respectively.

[0168] In Comparative Example 1, Example 1, Example 2 and Comparative Example 2, the molar ratio of O / Si decreased sequentially to 1.55, 1.12, 0.91 and 0.66, respectively. The corresponding specific capacity and first-efficiency also increased sequentially. The reason for this phenomenon is that the lower the oxygen content, the fewer irreversible reactions involving oxygen.

[0169] Figure 2 The figure shows the volume-based particle size distribution curve of the silicon oxide particles in Example 1. The curve shows that particles with a diameter ≥ 9.8 μm account for approximately 50% of the total volume of the silicon oxide particles, with the largest particle size being approximately 28 μm. This particle size distribution control increases the proportion of larger-diameter silicon oxide particles, thus helping to reduce the specific surface area of ​​the silicon oxide particles.

[0170] Figure 3 This is a SEM image (taken using secondary electron mode) of the silicon oxide particles from Example 1. As can be seen from the image, there are very few flake-shaped, rod-shaped, wedge-shaped, or sharply angled silicon oxide particles, thus ensuring that the silicon oxide particles have a small specific surface area.

[0171] 2. Preparation and physical properties of the negative electrode sheet

[0172] The following is an example of a method for preparing a negative electrode:

[0173] Silicon oxide particles, D v50 μm graphite, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), carbon black (Super P), and single-walled carbon nanotubes (SWCNTs) were mixed at a mass ratio of y:(96-y):1.5:1.5:0.9:0.1, and deionized water was added. The mixture was then stirred under vacuum to obtain a negative electrode slurry. The slurry was prepared at 8 mg / cm³. 2 The areal density was determined by uniformly coating the negative electrode slurry onto a 6μm thick copper foil, drying it at 80℃, and then transferring it to a 100℃ vacuum oven for 12 hours to achieve an areal density of 1.6 g / cm³. 3 The compaction density is rolled and then cut to obtain the negative electrode sheet.

[0174] Table 2 shows the preparation conditions of the negative electrode sheets for Examples 4-7 and Comparative Examples 5-11, including the silicon oxide particles used and their doping amounts. The doping amount of the silicon oxide particles was obtained using the formula y / 96. Table 2 also provides the physical properties of the negative electrode sheets, including the circumscribed circle diameter D. i The maximum value, the diameter of the inscribed circle d i The maximum value, (ΣE) j 2 ) / (ΣD i 2 ), (ΣF k 2 ) / (ΣD i 2 ), (ΣF k 2 ) / S, thickness of active material layer L.

[0175] For example, such as Figure 4 and Figure 5 The image shown is a SEM cross-sectional photograph of the negative electrode sheet of Embodiment 4 of the present invention. In the figure, 41 represents silicon oxide particles and 42 represents graphite. Then, D... i The value d can be obtained by measuring the circumcircle diameter of each silicon oxide particle. i E can be obtained by measuring the inscribed circle diameter of each silicon oxide particle. j D can be measured i The outer circle diameter of silicon oxide particles ≥9μm is obtained, F k It can be determined by d i The outer circle diameter of silicon oxide particles ≥4 μm is obtained; S represents the cross-sectional area of ​​the negative electrode active material layer in the SEM image observation area; then, the outer circle diameter D of each silicon oxide particle is measured. i Each D i The circumscribed circle diameter E of silicon oxide particles ≥9μm j Each d i The circumcircle diameter F of silicon oxide particles ≥4μmk By squaring each part and then summing them, we can obtain ΣE. j 2 ,ΣD i 2 and ΣF k 2 Then, (ΣE) is calculated. j 2 ) / (ΣD i 2 ), (ΣF k 2 ) / (ΣD i 2 ), (ΣF k 2 The value of ) / S.

[0176] Table 2

[0177]

[0178] The negative electrode sheets of Examples 4 to 7 all meet the limitations of this invention, wherein: Example 4 is the baseline group; the difference between Example 5 and Example 4 is only that the silicon oxide particles used in Example 5 have a lower O / Si molar ratio; the difference between Example 6 and Example 4 is that the silicon oxide particles used in Example 6 have a lower secondary vibration frequency during synthesis, therefore D v max and D v 50 is relatively large, and the proportion of large-diameter particles is also relatively high, therefore the corresponding (ΣE) j 2 ) / (ΣD i 2 ) and (ΣF k 2 ) / (ΣD i 2 ) is larger; the difference between Example 7 and Example 4 is that its (ΣF k 2 The ratio is higher, meaning that more silicon oxide particles are incorporated.

[0179] The negative electrode sheets of Comparative Examples 7-15 do not fully meet the limitations of this invention (these features are indicated in bold italics in Table 2), wherein: the O / Si molar ratio of the silicon oxide particles used in Comparative Example 7 is greater than 1.4; the O / Si molar ratio of the silicon oxide particles used in Comparative Example 8 is less than 0.7; and the D of the negative electrode sheet in Comparative Example 9... i The maximum value is greater than 35μm, d i The maximum value is greater than 25 μm, (ΣE j 2 ) / (ΣD i 2 () greater than 0.75, (ΣF) k2 ) / (ΣD i 2 The value is less than 0.37. Comparative analysis shows that the silicon oxide particles used in this negative electrode experienced excessively low vibration frequencies during the secondary grinding process, resulting in insufficient removal of the particle edges and corners. This leads to a larger circumscribed circle diameter and also causes (ΣF) to... k 2 ) / (ΣD i 2 The value of ΣE decreases relatively; in Comparative Example 10, the negative electrode's (ΣE) value decreases relatively. j 2 ) / (ΣD i 2 Less than 0.45, (ΣF k 2 ) / (ΣD i 2 The value is less than 0.37. This is because the vibration frequency of the silicon oxide particles used in the negative electrode is too high during the secondary crushing process, resulting in an excessively small particle size. Consequently, the parameters related to the circumscribed circle and inscribed circle do not meet the requirements. (ΣE) of the negative electrode in Comparative Example 11... j 2 ) / (ΣD i 2 ), (ΣF k 2 ) / (ΣD i 2 The difference between the ΣF values ​​in Comparative Example 10 and Comparative Example 12 is lower because the silicon oxide particles used in this negative electrode undergo a higher vibration frequency during the secondary crushing process, resulting in smaller particle sizes. k 2 ) / (ΣD i 2 The value is less than 0.37 because the silicon oxide particles used in this negative electrode are only fined by single-stage grinding, and the rotation frequency of the container during grinding is too high, resulting in the particles retaining more sharp edges; in Comparative Example 13, the negative electrode (ΣF) k 2 The (ΣF) / S ratio is too low, which is due to insufficient silicon oxide particle doping; in Comparative Example 14, the negative electrode (ΣF) k 2 The S / S ratio is too high, which is due to excessive doping of silicon oxide particles; the active material layer of the negative electrode in Comparative Example 15 is greater than 100 μm.

[0180] from Figure 4 (or Figure 5 As can be seen from the cross-section of the negative electrode in Example 4, the electrode includes a high proportion of D. i ≥9μm and d iWith silicon oxide particles ≥4μm, this design can effectively reduce side reactions on the surface of silicon oxide particles and improve the cycle stability of the electrode when the silicon oxide particle doping content is high (5% to 25%).

[0181] 3. Preparation and physical properties of lithium-ion batteries

[0182] The lithium-ion battery was obtained according to the aforementioned preparation method.

[0183] In the preparation of the pre-lithiated negative electrode, a 5μm thick striped lithium foil was used, i.e., lithium foil segments and blank segments were alternately and repeatedly distributed. The widths of the lithium foil segments and blank segments in each example and comparative example are as follows: Example 8, Example 10, Comparative Examples 18-21 and Comparative Example 24, lithium foil segment width 0.2cm, blank segment width 0.8cm; Example 9 and Comparative Example 17, lithium foil segment width 0.15cm, blank segment width 0.85cm; Example 11, lithium foil segment width 0.5cm, blank segment width 0.5cm; Comparative Example 16, lithium foil segment width 0.3cm, blank segment width 0.7cm; Comparative Example 22, no lithium replenishment; Comparative Example 23, lithium foil segment width 0.8cm, blank segment width 0.2cm.

[0184] Perform two charge-discharge cycles according to the aforementioned cycle regime, disassemble the battery, and obtain the negative electrode sheet.

[0185] Table 3 shows the physical properties of the negative electrode sheets of the lithium-ion batteries in Examples 8-11 and Comparative Examples 16-24 after two cycles, including the circumscribed circle diameter D. i The maximum value of ', the diameter of the inscribed circle d i The maximum value of ', (ΣE) j ' 2 ) / (ΣD i ' 2 ), (ΣF k ' 2 ) / (ΣD i ' 2 ), (ΣF k ' 2 ) / S、Thickness of active material layer L'.

[0186] Table 3

[0187]

[0188] The conclusions drawn from the data in Table 3 are similar to those in Table 2, and will not be repeated here.

[0189] 4. Cycle performance of lithium-ion batteries

[0190] Table 4 shows the energy density and cycle number of the lithium-ion batteries of Examples 8-11 and Comparative Examples 16-24 when the capacity retention rate is 80%.

[0191] Table 4

[0192]

[0193] As can be seen from Table 4, the negative electrode sheets of Examples 4-7 and the corresponding lithium-ion batteries of Examples 8-11 meet all the characteristics described in this invention, with energy densities all above 740 Wh / L and cycle counts all above 750 cycles; the negative electrode sheet of Comparative Example 7 and the lithium-ion battery of Comparative Example 16 have excessively high O / Si molar ratios in their silicon oxide particles, resulting in battery energy densities less than 700 Wh / L; the negative electrode sheet of Comparative Example 8 and the lithium-ion battery of Comparative Example 17 have excessively low O / Si molar ratios in their silicon oxide particles, resulting in battery cycle counts less than 500 cycles; the negative electrode sheet of Comparative Example 9 has a low D... i d i 、(ΣE j 2 ) / (ΣD i 2 ), (ΣF k 2 ) / (ΣD i 2 The D of the lithium-ion battery in Comparative Example 18 and Comparative Example 18 i '、d i '、(ΣE j ' 2 ) / (ΣD i ' 2 ), (ΣF k ' 2 ) / (ΣD i ' 2 None of them meet the limitations of this invention, and the battery cycle count is less than 600 cycles; the negative electrode of Comparative Example 10 has (ΣE) j 2 ) / (ΣD i 2 ), (ΣF k 2 ) / (ΣD i 2 ) and Comparative Example 19's lithium-ion battery (ΣE) j ' 2 ) / (ΣD i ' 2 ), (ΣF k ' 2 ) / (ΣD i ' 2 None of these meet the limitations of this invention; the battery cycle life is only about 600 cycles. The negative electrode of Comparative Example 11 has (ΣE) j 2 ) / (ΣD i2 ), (ΣF k 2 ) / (ΣD i 2 ), (ΣF k 2 (ΣE) / S and Comparative Example 20's lithium-ion battery j ' 2 ) / (ΣD i ' 2 ), (ΣF k ' 2 ) / (ΣD i ' 2 ), (ΣF k ' 2 Neither ΣF nor S meets the limitations of this invention, and the battery cycle life is only about 500 cycles; the negative electrode of Comparative Example 12 has (ΣF) k 2 ) / (ΣD i 2 ) and Comparative Example 21's lithium-ion battery (ΣF k ' 2 ) / (ΣD i ' 2 None of them meet the limitations of this invention, and the battery cycle count is less than 550 cycles; the negative electrode of Comparative Example 13 (ΣF) k 2 (ΣF) / S and Comparative Example 22's lithium-ion battery k ' 2 The (ΣF) / S does not meet the limitations of this invention, and the battery energy density is lower than 700Wh / L; the negative electrode of Comparative Example 14 has (ΣF) k 2 (ΣF) / S and Comparative Example 23's lithium-ion battery k ' 2 The L of the negative electrode in Comparative Example 15 and the L' of the lithium-ion battery in Comparative Example 23 do not meet the limitations of this invention, and the battery cycle count is less than 500 cycles.

[0194] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes silicon oxide particles. The silicon oxide particles satisfy the following relationship: D i ≤35μm(I), d i ≤25 μm(II), 0.45≤(ΣE j 2 ) / (ΣD i 2 )≤0.75(III), (S.F. k 2 ) / (ΣD i 2 )≥0.37(IV), Where Σ represents the summation of the data, and D i d represents the circumcircle diameter of any silicon oxide particle. i E represents the diameter of the inscribed circle of any silicon oxide particle. j D represents i The circumcircle diameter of silicon oxide particles ≥9μm, F k d i The outer diameter of silicon oxide particles ≥4μm, where i, j, and k represent the particle numbers; the doping amount of silicon oxide particles in the negative electrode sheet satisfies the following relationship: 0.05≤(ΣF k 2 ) / S≤0.47(V); Where Σ represents the summation of the data, F k d i The outer circle diameter of silicon oxide particles ≥4μm, k represents the number of silicon oxide particles, and S represents the cross-sectional area of ​​the active material layer in the observation area. The thickness L of the negative electrode active material layer satisfies 30μm≤L≤100μm; The silicon oxide particles contain Si and O elements, and the molar ratio x (mol / mol) of O to Si elements satisfies 0.7 ≤ x ≤ 1.4; The specific surface area of ​​the silicon oxide particles is less than or equal to 1.2 m². 2 / g.

2. The negative electrode sheet according to claim 1, characterized in that, The mass percentage of silicon oxide particles relative to the negative electrode active material layer is 5 wt% to 25 wt%.

3. The negative electrode sheet according to any one of claims 1-2, characterized in that, At least a portion of the surface of the silicon oxide particles contains a coating layer.

4. The negative electrode sheet according to claim 3, characterized in that, The coating layer is a carbon coating layer, and the material of the carbon coating layer is selected from one or more of graphite, amorphous carbon, graphene, and carbon nanotubes.

5. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in any one of claims 1-4.

6. The lithium-ion battery according to claim 5, characterized in that, After 1 to 5 charge-discharge cycles, the negative electrode of the lithium-ion battery satisfies the following relationship: D i ’≤44μm, d i ’≤32μm, 0.45≤(ΣE j ' 2 ) / (ΣD i ' 2 )≤0.75, (S.F. k ' 2 ) / (ΣD i ' 2 )≥0.37, 0.06≤(ΣF k ' 2 ) / S'≤0.53, 39μm≤L'≤130μm Where Σ represents the summation of the data, and D i ' represents the circumcircle diameter of any silicon oxide particle, d i ' represents the diameter of the inscribed circle of any silicon oxide particle, E j ' indicates D i 'The circumcircle diameter of silicon oxide particles ≥11.2μm, F k ' indicates d i 'The outer circle diameter of silicon oxide particles ≥5.0μm, i, j, k represent the particle number, S' represents the cross-sectional area of ​​the negative electrode in the observation area, and L' represents the thickness of the active material layer.

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