Negative electrode plates, electrochemical apparatus, and electronic equipment

Abstract

This invention provides negative electrode plates, electrochemical devices, and electronic equipment that can guarantee excellent discharge capacity, rapid charging performance, and cycle performance, and that combine excellent energy density, cycle performance, and storage performance. [Solution] The rate of decrease P0 of the specific surface area of ​​the negative electrode plate is 12% to 18%, where P0 = 1 - P, which is the ratio of the specific surface area of ​​the negative electrode plate at the second press density to the specific surface area of ​​the negative electrode plate at the first press density, and the porosity ε of the electrode plate of the negative electrode plate is 13% or more, and the porosity of the electrode plate is the porosity of the electrode plate of the negative electrode plate at the second press density.

Description

[Technical Field]

[0001] This invention relates to a negative electrode plate, an electrochemical apparatus, and electronic equipment. [Background technology]

[0002] Conventional natural graphite, such as flake graphite, possesses high capacity and high press density, but its inherent defects make practical applications extremely difficult. On the other hand, it is very difficult for synthetic graphite to exceed a capacity of 360 mAh / g, and even when fabricated into electrode plates, it is very difficult to exceed a press density of 1.70 g / cc. Even if these are forcibly achieved, the dynamic characteristics become extremely poor. Compared to conventional natural and synthetic graphite, microcrystalline natural graphite possesses the essential characteristics of high capacity and good dynamic characteristics, and has an extremely promising application prospect in high-capacity rapid-charging lithium-ion batteries.

[0003] Chinese patent application CN110380050A employs a pitch immersion filling method to improve the intrinsic powder press density of microcrystalline graphite. However, this process reduces the pores in the material itself, significantly degrading the material's dynamic properties. Furthermore, the effect of increased press density on the electrode plate is limited, and lithium-ion batteries containing such batteries cannot guarantee excellent discharge capacity, fast charging performance, and cycle performance. Therefore, it is extremely important to realize a method that achieves excellent discharge capacity, fast charging performance, and cycle performance simultaneously in lithium-ion batteries using graphite as the negative electrode material. [Overview of the project] [Problems that the invention aims to solve]

[0004] To address the shortcomings of existing lithium-ion batteries containing graphite material, which cannot guarantee excellent discharge capacity, fast charging performance, and cycle performance, the present invention provides a negative electrode plate, an electrochemical apparatus, and electronic equipment. An electrochemical apparatus (particularly a lithium-ion battery) incorporating these can guarantee excellent discharge capacity, fast charging performance, and cycle performance, and can simultaneously achieve excellent energy density, cycle performance, and storage performance. [Means for solving the problem]

[0005] To achieve the above objective, the present invention employs the following technical solution. In a first embodiment, the present invention provides a negative electrode plate, wherein the rate of reduction P0 of the specific surface area of ​​the negative electrode plate is 12% to 18%, where P0 = 1 - P, and P is the ratio of the specific surface area of ​​the negative electrode plate at a second press density to the specific surface area of ​​the negative electrode plate at a first press density. The electrode plate porosity ε of the negative electrode plate is 13% or more, and the electrode plate porosity is the electrode plate porosity of the negative electrode plate at the second press density. The second press density is 1.80 g / cc or the limit press density of the negative electrode plate, and the first press density is 1.65 g / cc.

[0006] In a second embodiment, the present invention provides an electrochemical apparatus including the negative electrode plate.

[0007] In a third embodiment, the present invention provides electronic equipment including the electrochemical apparatus. [Effects of the Invention]

[0008] The advantageous effects of the present invention are as follows: The present invention provides a negative electrode plate, and through the control and design of parameters such as the rate of reduction of the specific surface area of ​​the negative electrode plate and the porosity of the electrode plate at a press density of 1.80 g / cc, an electrochemical device (particularly a lithium-ion battery) including the negative electrode plate can guarantee excellent discharge capacity, rapid charging performance, and cycle performance, and can also achieve excellent energy density, cycle performance, and storage performance simultaneously.

Mode for Carrying Out the Invention

[0009] Hereinafter, the present invention will be further described by way of examples, but the present invention is not limited to the scope of the above examples. For experimental methods where specific conditions are not specified in the following examples, they are selected according to conventional methods and conditions or according to the product specifications. Negative electrode plate

[0010] In the negative electrode plate provided by the first aspect of the present invention, the decreasing rate P0 of the specific surface area of the negative electrode plate is 12% to 18%. Here, P0 = 1 - P, and P is the ratio of the specific surface area of the negative electrode plate at the second press density to the specific surface area of the negative electrode plate at the first press density. The electrode plate porosity ε of the negative electrode plate is 13% or more. Here, the electrode plate porosity is the electrode plate porosity of the negative electrode plate at the second press density. The second press density is 1.80 g / cc or the limit press density of the negative electrode plate, and the first press density is 1.65 g / cc.

[0011] In the present invention, the specific surface area of the negative electrode plate is obtained by measuring based on Chinese National Standard GB / T 19587-2017.

[0012] In the present invention, the "negative electrode plate at the second press density" can be obtained by the following method A or B. Method A: Press the negative electrode plate in the lithium-uninserted state to a press density of 1.80 g / cc, and the appearance of the negative electrode plate is good without wavy wrinkles at the ends. Method B: Press the negative electrode plate in the lithium-uninserted state to a press density of the limit press density, and the appearance of the negative electrode plate is good without wavy wrinkles at the ends. At this time, the limit press density is less than 1.80 g / cc.

[0013] In the present invention, the "negative electrode plate at the first press density" can be obtained by the following method. Press the negative electrode plate in the lithium-uninserted state to a press density of 1.65 g / cc, and the appearance of the negative electrode plate is good without wavy wrinkles at the ends.

[0014] In the present invention, the decreasing rate of the specific surface area of the negative electrode plate is the comprehensive result of the particle orientation, degree of bending, and inter-particle voids in the negative electrode plate, and represents the ability of the negative electrode plate to maintain a particle orientation, degree of bending, and inter-particle voids approximated to those under normal pressing density under an extremely high pressing density. The smaller the decreasing rate of the specific surface area of the negative electrode plate, the more stable the structure of the negative electrode plate. When the decreasing rate of the specific surface area of the negative electrode plate is excessively small, it indicates that the hardness of the negative electrode plate is excessively large and deformation is difficult to occur, which affects the pressing density of the negative electrode plate.

[0015] In some preferred embodiments, the decreasing rate of the specific surface area of the negative electrode plate is 13% - 17%, and the P0 is, for example, 12.5%, 12.7%, 13.2%, 13.3%, 13.5%, 13.7%, 13.9%, 14.1%, 14.5%, 14.7%, 14.9%, 15%, 15.2%, 15.3%, 15.9%, 16.4%, 16.7%, 17.2%, 17.7% or 17.8%.

[0016] In the present invention, the porosity of the electrode plate of the negative electrode plate refers to the ratio of the volume of the voids in the negative electrode plate to the apparent volume of the negative electrode plate.

[0017] In the present invention, the porosity of the electrode plate can be obtained by measurement based on Chinese national standard GB21650.1 - 2008.

[0018] In some preferred embodiments, the porosity of the electrode plate at the second pressing density of the negative electrode plate is 18% - 26%, for example, 18.2%, 19.3%, 20.5%, 20.6%, 20.9%, 21.2%, 22.2%, 22.5%, 22.7%, 23.1%, 23.2%, 23.5%, 23.6%, 23.9%, 24.1%, 24.2%, 24.3%, 25.2% or 25.6%.

[0019] In a specific embodiment, the negative electrode plate satisfies the following. The decreasing rate of the specific surface area of the negative electrode plate is 14.7%, and the porosity of the electrode plate of the negative electrode plate is 23.6%.

[0020] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 12.5%, and the porosity of the electrode plate of the negative electrode plate is 25.2%.

[0021] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 17.8%, and the porosity of the electrode plate of the negative electrode plate is 19.3%.

[0022] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 13.2%, and the porosity of the electrode plate of the negative electrode plate is 24.1%.

[0023] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 15.9%, and the porosity of the electrode plate of the negative electrode plate is 22.2%.

[0024] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 13.9%, and the porosity of the electrode plate of the negative electrode plate is 23.9%.

[0025] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 13.5%, and the porosity of the electrode plate of the negative electrode plate is 24.3%.

[0026] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 16.4%, and the porosity of the electrode plate of the negative electrode plate is 20.5%.

[0027] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 14.1%, and the porosity of the electrode plate of the negative electrode plate is 23.9%.

[0028] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 15.2%, and the porosity of the electrode plate of the negative electrode plate is 24.2%.

[0029] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 13.3%, and the porosity of the electrode plate of the negative electrode plate is 21.2%.

[0030] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 17.2%, and the porosity of the electrode plate of the negative electrode plate is 20.6%.

[0031] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 12.7%, and the porosity of the electrode plate of the negative electrode plate is 22.5%.

[0032] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 12%, and the porosity of the electrode plate of the negative electrode plate is 25.6%.

[0033] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 13.7%, and the porosity of the electrode plate of the negative electrode plate is 23.2%.

[0034] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 16.7%, and the porosity of the electrode plate of the negative electrode plate is 20.9%.

[0035] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 17.7%, and the porosity of the electrode plate of the negative electrode plate is 18.2%.

[0036] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 15.3%, and the porosity of the electrode plate of the negative electrode plate is 22.7%.

[0037] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 15%, and the porosity of the electrode plate of the negative electrode plate is 23.1%.

[0038] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 14.9%, and the porosity of the electrode plate of the negative electrode plate is 23.5%.

[0039] In a specific implementation plan, the negative electrode plate satisfies the following conditions: The rate of reduction of the specific surface area of ​​the negative electrode plate is 14.5%, and the porosity of the electrode plate of the negative electrode plate is 23.1%.

[0040] In the present invention, the adhesive force F of the negative electrode plate N This refers to the connection strength between the active material layer in the negative electrode plate and the current collector.

[0041] In several alternative implementations, the adhesive force F of the negative electrode plate N The range is 25-50N, for example, 27N, 28N, 31N, 32N, 33N, 34N, 35N, 38N, 39N, 40N, 41N, 43N, or 45N.

[0042] In this invention, the adhesive strength of the negative electrode plate is obtained by measuring it according to the following method. The negative electrode plate to be measured is cut into a long strip (length × width = 10 cm × 3 cm) and bonded to a long strip of quartz glass plate (the area is slightly larger than that of the negative electrode plate) with VHB tape attached. The negative electrode plate is rolled three times repeatedly using a dedicated small circular roller to ensure that the negative electrode plate and VHB are sufficiently bonded. A universal testing machine is used, and the standard method of measuring adhesive strength at 180° is selected to measure the magnitude of the adhesive strength of the negative electrode plate, and the average value is taken after measuring each sample three times.

[0043] In one selective embodiment, the negative electrode plate includes a negative electrode current collector, a first active material layer is provided on at least one surface of the negative electrode current collector, a second active material layer is provided on the first active material layer, the first active material layer includes a first graphite material and a first binder, the second active material layer includes a second graphite material and a second binder, and the Dv50 grain size of the first graphite material is larger than the Dv50 grain size of the second graphite material.

[0044] In one preferred embodiment, the difference between the Dv50 particle size of the first graphite material and the Dv50 particle size of the second graphite material is 3 to 7 μm, preferably 4.5 to 5.5 μm, for example, 5 μm.

[0045] In one preferred embodiment, the particle crushing strength F1 of the first graphite material is 30-36 mN, for example, 31 mN, 33 mN, 34 mN, or 35 mN.

[0046] In one preferred embodiment, the particle crushing strength F2 of the second graphite material is 20-30 mN, for example, 22 mN, 24 mN, or 27 mN.

[0047] In the present invention, the particle crushing strength refers to the critical pressure at which a single particle of the material will fracture when pressure resistance is measured.

[0048] In the present invention, the particle crushing strength can be obtained by measuring it using the Xiamen Yuanneng Technology Single Particle Mechanical Performance Measurement System (SPFT2000), and the specific measurement method is as follows: 0.5 g of graphite material is added to a beaker containing 20 mL of anhydrous ethanol, and ultrasonic dispersion is performed for 5 minutes to obtain a dispersion. 100 μL of the above dispersion is dropped onto a glass slide, and the glass slide is transferred to the SPFT2000 sample observation stage. A single particle is positioned using the optical microscope of the SPFT2000, the indenter is lowered at a constant speed, and the stress transition point during the particle compression process is recorded as the particle crushing strength.

[0049] In one preferred embodiment, the carbon content of the first graphite material is 99.9% or more, where the percentage is the mass percentage of the first graphite material.

[0050] In one preferred embodiment, the carbon content of the second graphite material is 99.9% or more, where the percentage is the mass percentage of the second graphite material.

[0051] In one preferred embodiment, the Dv50 particle size of the first graphite material is 14 to 18 μm, for example, 16 μm.

[0052] In one preferred embodiment, the Dv50 particle size of the second graphite material is 9 to 13 μm, for example, 11 μm.

[0053] In one preferred embodiment, the first graphite material is a microcrystalline graphite material.

[0054] In one preferred embodiment, the second graphite material is a microcrystalline graphite material.

[0055] In one preferred embodiment, the content of the first binder is 1.3% to 1.8%, for example, 1.5%, where the percentage is the mass percentage of the first active material layer.

[0056] In one preferred embodiment, the content of the second binder is 0.7% to 1.2%, for example, 1.1%, where the percentage is the mass percentage of the second active material layer.

[0057] Here, the types of the first and second binders are not particularly limited and may be independently selected from one or more of the following: polyvinylidene fluoride, polyvinyl fluoride, polyvinyl alcohol, carboxymethylcellulose, starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene ternary copolymer and its sulfonates, styrene-butadiene rubber (SBR), fluororubber, and various copolymers, for example, SBR.

[0058] In one preferred embodiment, the content of the first graphite material is 20% or more, preferably 50% or more, for example 96.2%, 96.5%, or 96.7%, where the percentage is the mass percentage of the first active material layer.

[0059] In one preferred embodiment, the content of the second graphite material is 20% or more, preferably 50% or more, for example 96.3%, 96.8%, or 96.9%, where the percentage is the mass percentage of the second active material layer.

[0060] In one preferred embodiment, the mass ratio of the first active material layer to the second active material layer is 1:(0.4~2.5), for example, 1:0.43, 1:0.67, 1:1, 1:1.5, or 1:2.33.

[0061] In one preferred embodiment, the thickness of the first active material layer is 50 to 120 μm, for example, 55 μm.

[0062] In one preferred embodiment, the thickness of the second active material layer is 50 to 110 μm, for example, 55 μm.

[0063] In some implementations, the first active material layer further contains a thickening agent, where the content of the thickening agent is, for example, 1.2%, and the percentage is the mass percentage of the first active material layer.

[0064] In some implementations, the second active material layer further contains a thickening agent, where the content of the thickening agent is, for example, 1.2%, and the percentage is the mass percentage of the second active material layer.

[0065] Here, the thickening agent may be any thickening agent commonly used in the preparation of negative electrode plates in this field, such as sodium carboxymethylcellulose (CMC).

[0066] In some implementations, the first active material layer further contains a conductive agent, where the content of the conductive agent is, for example, 0.8%, and the percentage is the mass percentage of the first active material layer.

[0067] In some implementations, the second active material layer further contains a conductive agent, where the content of the conductive agent is, for example, 0.8%, and the percentage is the mass percentage of the second active material layer.

[0068] Here, the conductive agent is not particularly limited and can be any agent that is conductive and does not cause a chemical change in the battery. For example, it may be a specific example of a conductive agent such as natural graphite or artificial graphite, carbon-based materials such as carbon black (Super P), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber, metal powder or metal fiber such as copper, nickel, aluminum, or silver, conductive whiskers such as zinc oxide whiskers or potassium titanate whiskers, conductive metal oxides such as titanium dioxide, or conductive polymers such as polyphenylene derivatives. The conductive agent is, for example, conductive carbon SP.

[0069] In several specific implementation plans, the mass ratio of the first graphite material, conductive agent, first binder, and thickener in the first active material layer is 96.5:0.8:1.5:1.2.

[0070] In several specific implementation plans, the mass ratio of the first graphite material, conductive agent, first binder, and thickener in the first active material layer is 96.7:0.8:1.3:1.2.

[0071] In several specific implementation plans, the mass ratio of the first graphite material, conductive agent, first binder, and thickener in the first active material layer is 96.2:0.8:1.8:1.2.

[0072] In several specific implementation plans, the mass ratio of the second graphite material, conductive agent, second binder, and thickener in the second active material layer is 96.9:0.8:1.1:1.2.

[0073] In several specific implementation plans, the mass ratio of the second graphite material, conductive agent, second binder, and thickener in the second active material layer is 96.3:0.8:0.7:1.2.

[0074] In several specific implementation plans, the mass ratio of the second graphite material, conductive agent, second binder, and thickener in the second active material layer is 96.8:0.8:1.2:1.2.

[0075] In the present invention, the negative electrode current collector may be a conventional negative electrode current collector in the art. The negative electrode current collector is a metal foil having a thickness of 3 to 500 micrometers, which serves as a substrate for supporting the first active material layer and the second active material layer. There are no particular restrictions on the material, as long as it has high electrical conductivity and does not cause chemical reactions in the secondary battery system. For example, it may be a foil material formed by surface treating nickel, titanium, aluminum, silver, stainless steel, carbon, etc. The negative electrode current collector usually has a smooth surface, but the adhesion between the first active material layer and the current collector can be improved by forming fine grooves or the like on its surface. In addition to foil materials, the negative electrode current collector can be any one or more of the various forms such as film, mesh, porous, foam, or nonwoven fabric in combination. Generally, the negative electrode current collector is copper foil.

[0076] In one preferred embodiment, the method for preparing the negative electrode plate includes the following steps: S1, a first negative electrode slurry layer is applied to at least one surface of the negative electrode current collector, the first negative electrode slurry layer comprising a first graphite material and a first binder. S2, a second negative electrode slurry layer is applied onto the first negative electrode slurry layer, the second negative electrode slurry layer comprising a second graphite material and a second binder. S3 is dried and cold-pressed to obtain the result.

[0077] In some more preferred embodiments, the coating density of the first negative electrode slurry layer is 0.055 g / cm³. 2 Larger, preferably 0.14 g / cm³ 2 Larger, for example, 0.60 g / cm³ 2 That is the case.

[0078] In some more preferred embodiments, the coating density of the second negative electrode slurry layer is 0.055 g / cm³. 2 Larger, preferably 0.14 g / cm³ 2 Larger, for example, 0.60 g / cm³ 2 That is the case.

[0079] In some more preferred embodiments, in step S1, the first graphite material is obtained by pre-treating a first graphite precursor, the pre-treatment comprising surface oxidation and / or carboxylation.

[0080] In some more preferred embodiments, in step S2, the second graphite material is obtained by pre-treating a second graphite precursor, the pre-treatment comprising surface oxidation and / or carboxylation.

[0081] In some preferred embodiments, the first graphite precursor may be microcrystalline graphite.

[0082] In some preferred embodiments, the second graphite precursor may be microcrystalline graphite. Microcrystalline graphite

[0083] In the present invention, the microcrystalline graphite preferably satisfies the following conditions: La ≤ 72 nm, Lc ≤ 15 nm. Here, La is the lattice constant on the 110 plane of the graphite crystal in the microcrystalline graphite, Lc is the lattice constant on the 002 plane of the graphite crystal in the microcrystalline graphite, and F p ≥ 15 mN, F p is the particle crushing strength.

[0084] In some preferred embodiments, La ≤ 60 nm.

[0085] In some specific embodiments, the first graphite precursor is microcrystalline graphite, and the La is, for example, 68 nm, 70 nm, 71 nm or 72 nm.

[0086] In some specific embodiments, the second graphite precursor is microcrystalline graphite, and the La is, for example, 66 nm, 68 nm, 69 nm or 70 nm.

[0087] In some preferred embodiments, Lc ≤ 12 nm.

[0088] In some specific embodiments, the first graphite precursor is microcrystalline graphite, and the Lc is, for example, 13 nm, 14 nm or 15 nm.

[0089] In some specific embodiments, the second graphite precursor is microcrystalline graphite, and the Lc is, for example, 12 nm, 13 nm or 14 nm.

[0090] In some preferred embodiments, 15 mN ≤ Fp ≤ 25 mN.

[0091] In some specific embodiments, the first graphite precursor is microcrystalline graphite, and the Fp is, for example, 23 mN or 25 mN.

[0092] In some specific embodiments, the second graphite precursor is microcrystalline graphite, and the Fp is, for example, 20 mN or 21 mN.

[0093] In some preferred embodiments, the particle size distribution symmetry of the microcrystalline graphite satisfies 0 < S ≤ 0.1, preferably 0 < S ≤ 0.07.

[0094] In some specific embodiments, the first graphite precursor is microcrystalline graphite, and the particle size distribution symmetry is, for example, 0.012, 0.023, 0.035 or 0.038.

[0095] In some specific embodiments, the second graphite precursor is microcrystalline graphite, and the particle size distribution symmetry is, for example, 0.028, 0.032, 0.046 or 0.052.

[0096] In some preferred embodiments, the sphericity of the microcrystalline graphite is preferably 0.5 - 1.0.

[0097] In some specific embodiments, the first graphite precursor is microcrystalline graphite, and the sphericity of the microcrystalline graphite is, for example, 0.90 or 0.91.

[0098] In some specific embodiments, the second graphite precursor is microcrystalline graphite, and the sphericity of the microcrystalline graphite is, for example, 0.88 or 0.89.

[0099] In some preferred embodiments, the carbon content of the microcrystalline graphite is 99.9% or more, and the percentage is the mass percentage in the microcrystalline graphite.

[0100] In one preferred embodiment, the Dv50 particle size of the first graphite precursor is 14-18 μm, for example, 16 μm.

[0101] In one preferred embodiment, the Dv50 particle size of the second graphite precursor is 9 to 13 μm, for example, 11 μm.

[0102] Here, La is obtained by calculation using formula (1). Here, λ is 0.0027 nm, β is the full width at half maximum, and θ is obtained by calculation based on formula (2). The specific measurement methods for β and d(110) are as follows: The graphite material and 50 mL of n-hexane are added to a beaker, ultrasonic vibration is performed for 5 minutes, then 100 μL of the solution is drawn up using a micropipette and dropped onto a copper mesh for TEM observation, and the copper mesh is quickly dried before observation. Diffraction observation is selected using a TEM and standardization is performed to obtain β and d(110).

number

number

[0103] Here, Lc is obtained by calculation using formula (3). Here, λ is 0.0027 nm, β is the full width at half maximum, and θ′ is obtained by calculation based on formula (4). The specific measurement methods for β and d(002) are as follows: The graphite material and 50 mL of n-hexane are added to a beaker, ultrasonic vibration is performed for 5 minutes, then 100 μL of the solution is drawn up using a micropipette and dropped onto a copper mesh for TEM observation, and the copper mesh is quickly dried before observation. Diffraction observation is selected using a TEM and standardization is performed to obtain β and d(002).

number

number

[0104] Here, the particle crushing strength (F p ) refers to the critical pressure at which a single particle of the material fractures during pressure resistance measurement. The particle crushing strength can be obtained by measurement using Xiamen Yuanneng Technology Single Particle Mechanical Performance Measurement System (SPFT2000), and the specific measurement method is as follows: 0.5 g of graphite material was added to a beaker containing 20 ml of anhydrous ethanol, and ultrasonic dispersion was performed for 5 minutes to obtain a dispersion. 100 μL of the above dispersion was dropped onto a glass slide, and the glass slide was transferred to the SPFT2000 sample observation stage. A single particle was positioned using the SPFT2000 optical microscope, and the indenter was lowered at a constant speed, and the stress transition point during the particle compression process was recorded as the particle crushing strength.

[0105] Here, the particle size distribution symmetry (S) was obtained by calculation using equation (5). Here, D(3,4) and Dv50 are obtained by measurement based on GB / T 41949-2022. The smaller the particle size distribution symmetry, the better the particle size distribution symmetry, and the higher the peak of the differential curve of the particle size volume distribution.

number

[0106] Here, the sphericity (D) refers to the ratio of the surface area of ​​a sphere of the same volume as the material particle to the surface area of ​​the material particle. Generally, the closer a particle is to a sphere in shape, the closer its sphericity is to 1. The sphericity of a sphere is equal to 1, while the sphericity of other objects is less than 1. The sphericity is measured according to GB / T 37406-2019.

[0107] In some specific implementation plans, the method for preparing the microcrystalline graphite includes the following steps: (I) A first mixing was performed with the microcrystalline graphite precursor and the binder, and a second mixing was performed by adding a solvent to obtain a mixture. Here, the temperature of the first mixing was 5 to 20°C, which is below the softening point of the binder. (II) The mixture is pressed to obtain a microcrystalline graphite green body. (III) The microcrystalline graphite green body is laid on the surface of the graphitization furnace, a graphitization heat-insulating material is laid on the microcrystalline graphite green body, and the graphitization treatment is performed, thereby obtaining a microcrystalline graphitized body from the microcrystalline graphite green body through the graphitization treatment. (IV) The microcrystalline graphitized material is subjected to pulverization.

[0108] Here, selectively, the temperature of the first mixture is 8 to 15°C below the softening point of the binder, for example, 10°C.

[0109] Here, selectively, in step (I), the fixed carbon content of the microcrystalline graphite precursor is 88% to 91%.

[0110] Here, selectively in step (I), the Dv50 particle size of the microcrystalline graphite precursor is 6 to 8 μm, for example, 7 μm.

[0111] Here, selectively in step (I), the mass ratio of the microcrystalline graphite precursor to the binder is (2-7):1, preferably (4-7):1, for example, 5:2.

[0112] Here, selectively in step (I), the binder comprises one or more of petroleum pitch, phenolic resin, epoxy resin, and coal tar.

[0113] Here, selectively, in step (I), the softening point of the binder is 100 to 250°C, preferably 100 to 130°C, for example, 110°C.

[0114] Here, selectively, in step (I), the solvent is selected from one or more of xylene, toluene, and n-hexane.

[0115] Here, selectively in step (I), the solid content of the mixture is 40% to 60%, for example 45%, where the percentage is the mass percentage of the solid component of the mixture relative to the total mass of the mixture.

[0116] Here, selectively, in step (I), the first mixing method is stirring, where the stirring time is preferably 0.5 to 2 hours, for example 1 hour, and the stirring speed is preferably 30 to 90 r / min.

[0117] Here, selectively, in step (I), the second mixing method is stirring, where the stirring time is preferably 0.5 to 2 hours, for example 1 hour, the stirring speed is preferably 60 to 120 r / min, and the stirring temperature is preferably room temperature.

[0118] Here, selectively, in step (I), the method for preparing the microcrystalline graphite precursor includes the following steps: The microcrystalline graphite ore is subjected to water washing and flotation, followed by coarse grinding and spheroidizing treatment to obtain the graphite precursor. Here, the time for the spheroidizing treatment is preferably 4 to 24 hours, and the spheroidizing treatment is preferably carried out using a honeycomb mill.

[0119] Here, selectively in step (II), the press is an isotropic hydrostatic press, where the duration of the isotropic hydrostatic press is preferably 18 to 30 hours, for example 24 hours, and the pressure of the isotropic hydrostatic press is preferably 150 to 300 MPa, for example 200 MPa.

[0120] Here, selectively, in step (III), the temperature of the graphitization treatment is greater than 1600°C.

[0121] Here, selectively, in step (III), the time for the graphitization treatment is 18 to 40 hours, preferably 24 to 36 hours.

[0122] Here, selectively, in step (III), the graphitized heat-insulating material is petroleum coke and / or pitch coke.

[0123] Here, selectively, in process (III), the graphitization equipment is a graphitization furnace. Here, selectively, step (IV) includes sieving and magnetic separation after the grinding process. Electrochemical apparatus

[0124] An electrochemical apparatus provided in a second aspect of the present invention includes the negative electrode plate described above.

[0125] In the present invention, the electrochemical apparatus is preferably a battery.

[0126] In one selective implementation, the electrochemical apparatus is a lithium-ion battery, and the lithium-ion battery includes the negative electrode plate, the positive electrode plate, the separator, and the electrolyte. Positive plate

[0127] In the present invention, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer installed on at least one surface of the positive electrode current collector.

[0128] In the present invention, the positive electrode active material in the positive electrode active material layer may be any positive electrode active material conventionally used in this field, such as one or more of lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, and lithium cobalt oxide.

[0129] In some selective implementations, the positive electrode active material layer further includes a binder.

[0130] Here, the type of binder is not particularly limited and can be arbitrarily selected from one or more types of polyvinylidene fluoride, polyvinyl fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose, starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene ternary copolymer and its sulfonates, styrene-butadiene rubber (SBR), fluororubber, and various copolymers, for example, PVDF.

[0131] In some selective implementations, the binder content is 1% to 10%, for example, 1.8%, where the percentage is the mass percentage of the positive electrode active material layer.

[0132] In some selective implementations, the positive electrode active material layer further includes a conductive agent.

[0133] Here, the type of conductive agent is not particularly limited and is a reagent used to ensure that the electrode has good charge and discharge performance. It may be arbitrarily selected from graphite materials such as natural graphite and artificial graphite, carbon black materials such as carbon black SP, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride powder, aluminum powder, and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, and conductive metal oxides such as titanium dioxide or polyphenylene derivatives.

[0134] In one specific implementation plan, the conductive agent is conductive carbon SP.

[0135] In some selective implementations, the content of the conductive agent is 0.2% to 3%, for example, 1.2%, where the percentage is the mass percentage of the positive electrode active material layer.

[0136] In several specific implementation plans, the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer is 97:1.2:1.8.

[0137] In the present invention, the positive electrode current collector may be a conventional positive electrode current collector in the art. The positive electrode current collector is a metal foil having a thickness of 3 to 500 micrometers, which serves as a substrate for supporting the positive electrode active material layer. The material is not particularly limited and should have high conductivity and not cause chemical reactions in the secondary battery system. For example, it may be a foil material formed after surface treatment of nickel, titanium, aluminum, silver, stainless steel, carbon, etc. The positive electrode current collector usually has a smooth surface, but the adhesion between the positive electrode active material layer and the current collector can be improved by forming fine grooves or the like on its surface. In addition to foil materials, the positive electrode current collector can be any one or more of the various forms such as film, mesh, porous, foam, or nonwoven fabric, in combination. Generally, the positive electrode current collector is aluminum foil.

[0138] In some implementations, the method for preparing the positive electrode plate includes thoroughly stirring and mixing each component of the positive electrode active material layer in a solvent to make it homogeneous, then coating the resulting positive electrode slurry onto at least one surface of a positive electrode current collector, drying it, and pressing it with a roll press.

[0139] In some selective implementations, the solvent comprises one or more of N-methylpyrrolidone (NMP), dimethyl carbonate, ethylene carbonate, and diethylene carbonate, for example, NMP. Separator

[0140] In the present invention, the separator in the electrocore may be a separator that has been conventionally used in this field.

[0141] In some alternative implementations, the separator may be made of polypropylene film or polyethylene film.

[0142] Here, the permeability of the separator may be 180 to 380 s / 100 mL.

[0143] Here, the porosity of the separator may be 30% to 50%.

[0144] Here, the thickness of the separator may be 9 to 18 μm.

[0145] In one specific implementation plan, the separator is a polyethylene film, the thickness of the separator is 11 μm, the air permeability of the separator is 230 s / 100 mL, and the porosity of the separator is 40%. electrolyte

[0146] In some implementations, the electrolyte may be an electrolyte commonly used in batteries in this art, and generally comprises a non-aqueous solvent, a lithium salt, and additives.

[0147] In some implementations, the method for preparing the lithium-ion battery includes the following steps: stacking a positive electrode plate, a separator, and a negative electrode plate in sequence, positioning the separator between the positive and negative electrode plates to provide isolation; then enclosing them in an aluminum plastic film, injecting the electrolyte after drying, and finally preparing a soft pack battery through processes such as sealing, standing, and chemical conversion. electronic equipment

[0148] An electronic device provided in a third aspect of the present invention includes the electrochemical apparatus described above.

[0149] Exemplary examples of the electronic devices described in the present invention include, but are not limited to, mobile devices (e.g., mobile phones, tablet computers, laptop computers, video cameras, portable printers / copiers, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems and backup power supplies, etc.

[0150] Based on a foundation consistent with common sense in this field, the above-mentioned preferred conditions may be combined in any way, that is, to obtain preferred examples of the present invention.

[0151] All reagents and raw materials used in this invention are commercially available.

[0152] Example 1 1. Preparation of the first graphite material and the second graphite material (1) Preparation of the first graphite precursor and the second graphite precursor (I) Microcrystalline graphite ore (purchased from Lutang Graphite Processing Plant, Chen Prefecture, Hunan Province; type number: Grade 1 Earthy Graphite; raw ore carbon content >85%) was subjected to initial water washing and flotation to achieve a fixed carbon content of 90%, and after coarse grinding, it was subjected to a spheroidization treatment for 6 hours using a honeycomb mill to obtain a microcrystalline graphite precursor with a spheroidity of 0.83 (Dv50 particle size of 7 μm). The above-mentioned microcrystalline graphite precursor was mixed with petroleum pitch with a softening point of 110°C (purchased from Liaoning Xinde New Materials Technology Co., Ltd., model number XD-110) in a mass ratio of 5:2. The mixture was heated to 10°C (100°C) below the softening point and stirred for 1 hour (stirring speed of 15 r / min to 20 r / min). Then, an appropriate amount of xylene solvent was added to aid in the dispersion of the petroleum pitch, and stirring was continued for 1 hour to obtain a mixture (solid content 45%). (II) The mixture was then added to a 40 × 30 cm × 30 cm rubber mold, pressed under a hydrostatic pressure of 200 MPa for 24 hours, and then demolded to obtain a microcrystalline graphite embryo. (III) The above-mentioned microcrystalline graphite crude material was laid on the surface of the Acheson graphitization furnace as a graphitization insulation material, and then another layer of petroleum coke was laid before graphitization was carried out. The graphitization temperature was 3000°C and the graphitization time was 36 hours. During this process, the microcrystalline graphite crude material formed microcrystalline graphitized bodies. (IV) The above-mentioned microcrystalline graphitized material was extracted and crushed, first filtered through a 250-mesh sieve, then shaped, and then sieved again through a 325-mesh sieve. The material that was not sieved was designated as material A, and the material that was sieved was designated as material B. Material A was subjected to crushing, shaping, sieving, and magnetic separation, and the Dv50 particle size was controlled to 16 μm to obtain the first graphite precursor (carbon content 99.9%, La 70 nm, Lc 14 nm, particle crushing strength F). p A value of 23 mN was obtained, with a particle size distribution symmetry S of 0.023 and a sphericity D of 0.90. Material B was crushed, shaped, sieved, and magnetically separated to control the Dv50 particle size to 11 μm, and a second graphite precursor (carbon content 99.9%, La 68 nm, Lc 13 nm, particle crushing strength F) was obtained. p A value of 20 mN was obtained, along with a particle size distribution symmetry S of 0.032 and a sphericity D of 0.88. (2) Surface oxidation treatment and carboxylation treatment are performed on the first graphite precursor and the second graphite precursor obtained above, respectively, and the specific steps are as follows. S0-1, Surface oxidation treatment The first graphite precursor described above was placed in a rotary kiln and subjected to a surface oxidation treatment for 1 hour at a temperature of 800°C with air flowing through it. The second graphite precursor described above was also placed in a rotary kiln and subjected to a surface oxidation treatment for 20 minutes at a temperature of 800°C with air flowing through it. S0-2, Carboxylation treatment 20 L of a 5 mol / L chloroacetic acid solution was placed in the room, then 3 kg of the first graphite precursor that had undergone the surface oxidation treatment described above was added, the temperature was raised to 60°C and stirred for 8 hours, the powder was collected after filtration, the temperature was then raised to 240°C at a rate of 2°C / min under vacuum, and the temperature was maintained for 2 hours to obtain the first graphite material (Dv50 particle size 16 μm, carbon content 99.9%). 20 L of a chloroacetic acid solution with a concentration of 2 mol / L was placed in the solution, then 3 kg of the second graphite precursor that had undergone the surface oxidation treatment described above was added, the temperature was raised to 60°C and stirred for 8 hours, the powder was collected after filtration, the temperature was then raised to 240°C at a rate of 2°C / min under vacuum, and the temperature was maintained for 2 hours to obtain the second graphite material (Dv50 particle size 11 μm, carbon content 99.9%).

[0153] 2. Preparation of the negative electrode plate S1. The obtained first graphite material, conductive agent (conductive carbon SP), first binder SBR, and thickener CMC were mixed in a mass ratio of 96.5:0.8:1.5:1.2 (total 100 parts by mass), and then 82 parts by mass of deionized water were added and mixed uniformly to obtain the first negative electrode slurry. The first negative electrode slurry was coated onto copper foil to form the first negative electrode slurry layer (coating density 0.60 g / cm³). 2 ) formed. S2. The obtained second graphite material, conductive agent (conductive carbon SP), second binder SBR, and thickener CMC were mixed in a mass ratio of 96.9:0.8:1.1:1.2 (total 100 parts by mass), and then 82 parts by mass of deionized water were added and mixed uniformly to obtain the second negative electrode slurry. Furthermore, the second negative electrode slurry was coated onto the first negative electrode slurry layer, and the second negative electrode slurry layer (coating density 0.60 g / cm³) was formed. 2 ) formed. In S3, after drying, a negative electrode plate was obtained by first performing a primary cold press to set the press density to the first press density, and then by performing a secondary cold press to set the press density to the second press density. In this plate, the first negative electrode slurry layer formed the first active material layer, and the second negative electrode slurry layer formed the second active material layer. The mass ratio of the first active material layer to the second active material layer was 5:5, and the thickness of both the first and second active material layers was 55 μm.

[0154] 3. Preparation of lithium-ion batteries A battery core was obtained by winding a positive electrode plate, a separator, and a negative electrode plate, and then the core was packaged in a package shell and electrolyte was injected to manufacture a soft pack battery. The preparation of the positive electrode plate included the following steps: The positive electrode active material NCM622, PVDF, and conductive carbon SP were mixed in a mass ratio of 97:1.8:1.2 (total 100 parts by mass), and then 82 parts by mass of NMP were added to obtain a positive electrode slurry. The obtained positive electrode slurry was coated onto at least one surface of an aluminum foil, dried, and compressed with a roll press to obtain the plate. In this configuration, the separator is a thin polyethylene film with a thickness of 11 μm, an air permeability of 230 s / 100 mL, and a porosity of 40%. In this process, a commercially available electrolyte (manufacturer: Xinya Shanshan New Materials Technology (Quzhou) Co., Ltd., model number: E3) was adopted.

[0155] Example 2 The only difference between Example 2 and Example 1 is as follows: In the preparation of the first graphite material and the second graphite material, the surface oxidation treatment temperature in step S0-1 was 600°C in both cases, and all other conditions were the same as in Example 1.

[0156] Example 3 The only difference between Example 3 and Example 1 is the following: In the preparation of the first graphite material and the second graphite material, the surface oxidation treatment temperature in step S0-1 was 1000°C in both cases, and all other conditions were the same as in Example 1.

[0157] Example 4 The only difference between Example 4 and Example 1 is the following: In the preparation of the first and second graphite materials, the surface oxidation treatment time of the first graphite precursor in step S0-1 is 0.5 hours, and all other conditions are the same as in Example 1.

[0158] Example 5 The only difference between Example 5 and Example 1 is the following: In the preparation of the first and second graphite materials, the surface oxidation treatment time for the second graphite precursor in step S0-1 is 30 min, and all other conditions are the same as in Example 1.

[0159] Example 6 The only difference between Example 6 and Example 1 is as follows: In the preparation of the first and second graphite materials, the surface oxidation treatment time for the second graphite precursor in step S0-1 is 10 min, and all other conditions are the same as in Example 1.

[0160] Example 7 The only difference between Example 7 and Example 1 is the following: In the preparation of the first and second graphite materials, the concentration of chloroacetic acid in step S0-2 is 4 mol / L, and all other conditions are the same as in Example 1.

[0161] Example 8 The only difference between Example 8 and Example 1 is the following: In the preparation of the first and second graphite materials, the concentration of chloroacetic acid in step S0-2 is 3 mol / L, and all other conditions are the same as in Example 1.

[0162] Example 9 The only difference between Example 9 and Example 1 is the following: In the preparation of the first and second graphite materials, the concentration of chloroacetic acid in step S0-2 is 1.5 mol / L, and all other conditions are the same as in Example 1.

[0163] Example 10 The only difference between Example 10 and Example 1 is as follows: In the preparation of the negative electrode plate, during step S1, the mass ratio of the first graphite material, conductive agent, first binder, and thickener is 96.7:0.8:1.3:1.2, and all other conditions are the same as in Example 1.

[0164] Example 11 The only difference between Example 11 and Example 1 is as follows: In the preparation of the negative electrode plate, during step S1, the mass ratio of the first graphite material, conductive agent, first binder, and thickener is 96.2:0.8:1.8:1.2, and all other conditions are the same as in Example 1.

[0165] Example 12 The only difference between Example 12 and Example 1 is as follows: In the preparation of the negative electrode plate, during step S2, the mass ratio of the second graphite material, conductive agent, second binder, and thickener is 96.3:0.8:0.7:1.2, and all other conditions are the same as in Example 1.

[0166] Example 13 The only difference between Example 13 and Example 1 is the following: In the preparation of the negative electrode plate, during step S2, the mass ratio of the second graphite material, conductive agent, second binder, and thickener is 96.8:0.8:1.2:1.2, and all other conditions are the same as in Example 1.

[0167] Example 14 The only difference between Example 14 and Example 1 is the following: In the preparation of the negative electrode plate, the mass ratio of the first active material layer and the second active material layer in step S3 is 3:7, and all other conditions are the same as in Example 1.

[0168] Example 15 The only difference between Example 15 and Example 1 is the following: In the preparation of the negative electrode plate, the mass ratio of the first active material layer and the second active material layer in step S3 is 4:6, and all other conditions are the same as in Example 1.

[0169] Example 16 The only difference between Example 16 and Example 1 is the following: In the preparation of the negative electrode plate, the mass ratio of the first active material layer and the second active material layer in step S3 is 6:4, and all other conditions are the same as in Example 1.

[0170] Example 17 The only difference between Example 17 and Example 1 is the following: In the preparation of the negative electrode plate, the mass ratio of the first active material layer and the second active material layer in step S3 is 7:3, and all other conditions are the same as in Example 1.

[0171] Example 18 The difference between Example 18 and Example 1 is as follows: In the preparation of the first and second graphite precursors, material A in step (IV) was subjected to grinding, shaping, sieving, and magnetic separation to control the Dv50 particle size to 18 μm. The first graphite precursor (carbon content 99.9%, La 71 nm, Lc 15 nm, particle crushing strength F) p A value of 25 mN, particle size distribution symmetry S of 0.012, and sphericity D of 0.91 were obtained. Other conditions were the same as in Example 1.

[0172] Example 19 The difference between Example 19 and Example 1 is as follows: In the preparation of the first and second graphite precursors, material B in step (IV) was subjected to grinding, shaping, sieving, and magnetic separation to control the Dv50 particle size to 13 μm, and the second graphite precursor (carbon content 99.9%, La 69 nm, Lc 14 nm, particle crushing strength F) was obtained. p A value of 21 mN, particle size distribution symmetry S of 0.028, and sphericity D of 0.89 were obtained. Other conditions were the same as in Example 1.

[0173] Example 20 The difference between Example 20 and Example 1 is as follows: When preparing the first and second graphite precursors, step (I) involves heating to 5°C (105°C) below the softening point and stirring for 1 hour. All other conditions are the same as in Example 1. The obtained first graphite precursor had a carbon content of 99.9%, La at 68 nm, Lc at 13 nm, and particle crushing strength F. p The strength is 23 mN, the particle size distribution symmetry S is 0.035, and the sphericity D is 0.90. The obtained second graphite precursor had a carbon content of 99.9%, La at 66 nm, Lc at 12 nm, and a particle crushing strength F. p The strength is 20 mN, the particle size distribution symmetry S is 0.046, and the sphericity D is 0.88.

[0174] Example 21 The difference between Example 21 and Example 1 is as follows: When preparing the first and second graphite precursors, step (I) involves heating to 20°C (90°C) below the softening point and stirring for 1 hour. All other conditions are the same as in Example 1. The obtained first graphite precursor had a carbon content of 99.9%, La at 72 nm, Lc at 15 nm, and a particle crushing strength F. p The strength is 23 mN, the particle size distribution symmetry S is 0.038, and the sphericity D is 0.90. The obtained second graphite precursor had a carbon content of 99.9%, La at 70 nm, Lc at 13 nm, and a particle crushing strength F. p The strength is 20 mN, the particle size distribution symmetry S is 0.052, and the sphericity D is 0.88.

[0175] Comparative Example 1 The only difference between this comparative example and Example 1 is as follows: During the preparation of the negative electrode plate, the temperature during step S0-1 and the surface oxidation treatment was 500°C in all cases, and all other conditions were the same as in Example 1.

[0176] Comparative Example 2 The only difference between this comparative example and Example 1 is as follows: During the preparation of the negative electrode plate, the temperature during step S0-1 and the surface oxidation treatment was 1100°C in all cases, and all other conditions were the same as in Example 1.

[0177] Comparative Example 3 The only difference between this comparative example and Example 1 is as follows: During the preparation of the negative electrode plate, the time for surface oxidation treatment of the first graphite precursor in step S0-1 was 0.2 hours, while all other conditions were the same as in Example 1.

[0178] Comparative Example 4 The only difference between this comparative example and Example 1 is as follows: During the preparation of the negative electrode plate, the surface oxidation treatment time of the second graphite precursor in step S0-1 is 5 minutes, while all other conditions are the same as in Example 1.

[0179] Comparative Example 5 The only difference between this comparative example and Example 1 is as follows: During the preparation of the negative electrode plate, the surface oxidation treatment time of the second graphite precursor in step S0-1 was 40 min, while all other conditions were the same as in Example 1.

[0180] Comparative Example 6 The only difference between this comparative example and Example 1 is as follows: During the preparation of the negative electrode plate, no surface oxidation treatment was performed on the second graphite precursor in step S0-1, and all other conditions were the same as in Example 1.

[0181] Comparative Example 7 The only difference between this comparative example and Example 1 is as follows: During the preparation of the negative electrode plate, the concentration of chloroacetic acid in step S0-2 is 2 mol / L, and all other conditions are the same as in Example 1.

[0182] Comparative Example 8 The only difference between this comparative example and Example 1 is as follows: During the preparation of the negative electrode plate, the concentration of chloroacetic acid in step S0-2 is 5 mol / L, and all other conditions are the same as in Example 1.

[0183] Comparative Example 9 The only difference between this comparative example and Example 1 is as follows: During the preparation of the negative electrode plate, the concentration of chloroacetic acid in step S0-2 is 1 mol / L, and all other conditions are the same as in Example 1.

[0184] Comparative Example 10 The only difference between this comparative example and Example 1 is as follows: During the preparation of the negative electrode plate, in step S1, the mass ratio of the first graphite material, conductive agent, first binder, and thickener was 96.0:0.8:2.0:1.2, and all other conditions were the same as in Example 1.

[0185] Comparative Example 11 The only difference between this comparative example and Example 1 is as follows: During the preparation of the negative electrode plate, in step S1, the mass ratio of the first graphite material, conductive agent, first binder, and thickener was 96.9:0.8:1.1:1.2, and all other conditions were the same as in Example 1.

[0186] Comparative Example 12 The only difference between this comparative example and Example 1 is as follows: During the preparation of the negative electrode plate, in step S2, the mass ratio of the second graphite material, conductive agent, second binder, and thickener was 96.7:0.8:1.3:1.2, and all other conditions were the same as in Example 1.

[0187] Comparative Example 13 The only difference between this comparative example and Example 1 is as follows: During the preparation of the negative electrode plate, in step S2, the mass ratio of the second graphite material, conductive agent, second binder, and thickener was 97.5:0.8:0.5:1.2, and all other conditions were the same as in Example 1.

[0188] Comparative Example 14 The differences between this comparative example and Example 1 are as follows: During the preparation of the negative electrode plate, only the second negative electrode slurry was coated onto the negative electrode current collector to obtain a second active material layer (thickness 110 μm), and the first active material layer was absent. All other conditions were the same as in Example 1.

[0189] Comparative Example 15 The differences between this comparative example and Example 1 are as follows: During the preparation of the negative electrode plate, only the first negative electrode slurry was coated onto the negative electrode current collector to obtain the first active material layer (thickness 110 μm), and there was no second active material layer. All other conditions were the same as in Example 1.

[0190] Comparative Example 16 The differences between this comparative example and Example 1 are as follows: During the preparation of the negative electrode plate, steps S1 and S2 are replaced with the following steps. S1. The obtained second graphite material, conductive agent (conductive carbon SP), second binder SBR, and thickener CMC were mixed in a mass ratio of 96.9:0.8:1.1:1.2 (total 100 parts by mass), and then 82 parts by mass of deionized water were added and mixed uniformly to obtain the second negative electrode slurry. Furthermore, the second negative electrode slurry was coated onto copper foil to form the second negative electrode slurry layer (coating density 0.60 g / cm³). 2 ) forms. S2. The obtained first graphite material, conductive agent (conductive carbon SP), first binder SBR, and thickener CMC were mixed in a mass ratio of 96.5:0.8:1.5:1.2 (total 100 parts by mass), and then 82 parts by mass of deionized water were added and mixed uniformly to obtain the first negative electrode slurry. The first negative electrode slurry was coated onto the second negative electrode slurry layer, and the first negative electrode slurry layer (coating density 0.60 g / cm³) 2 ) forms. Other conditions are the same as in Example 1.

[0191] Comparative Example 17 The differences between this comparative example and Example 1 are as follows: The preparation of the negative electrode plate is replaced with the following steps. S1. The obtained first graphite material, conductive agent (conductive carbon SP), first binder SBR, and thickener CMC were mixed in a mass ratio of 96.5:0.8:1.5:1.2 (total 100 parts by mass), and then 82 parts by mass of deionized water were added and mixed uniformly to obtain the first negative electrode slurry. S2. The obtained second graphite material, conductive agent (conductive carbon SP), second binder SBR, and thickener CMC were mixed in a mass ratio of 96.9:0.8:1.1:1.2 (total 100 parts by mass), and then 82 parts by mass of deionized water were added and mixed uniformly to obtain the second negative electrode slurry. After mixing the first negative electrode slurry and the second negative electrode slurry, the mixture is coated onto the copper foil to form a negative electrode slurry layer (coating density 0.60 g / cm³). 2 ) formed. In step S3, drying was performed, and then a negative electrode plate at a first press density was obtained by primary cold pressing, followed by a negative electrode plate at a second press density by secondary cold pressing. Here, the negative electrode slurry layer formed an active material layer with a thickness of 110 μm. Other conditions are the same as in Example 1.

[0192] Comparative Example 18 The differences between this comparative example and Example 1 are as follows: In the preparation of the negative electrode plate, a commercially available graphite material (purchased from Shanghai Shanshan Technology Co., Ltd., model number FSN-1) is used as the negative electrode material. The specific preparation process is as follows. Graphite material, conductive agent (conductive carbon SP), binder SBR, and thickener CMC were mixed in a mass ratio of 96.5:0.8:1.5:1.2 (total 100 parts by mass), and then 82 parts by mass of deionized water were added and mixed uniformly to obtain a negative electrode slurry. The negative electrode slurry was coated onto copper foil to form a negative electrode slurry layer (coating density 0.60 g / cm³). 2 ) formed. After drying, a negative electrode plate at a first press density was obtained by primary cold pressing, and then a negative electrode plate at a second press density was obtained by secondary cold pressing. Here, the negative electrode slurry layer forms an active material layer with a thickness of 110 μm. Other conditions are the same as in Example 1.

[0193] Comparative Example 19 The differences between this comparative example and Example 1 are as follows: In the preparation of the negative electrode plate, the first and second graphite materials were replaced with commercially available microcrystalline graphite (particle size 6.7 μm, particle crushing strength 14 mN, purchased from Shenzhen Beite Rui New Energy Materials Co., Ltd., model number WJ-1), and all other conditions were the same as in Example 1.

[0194] Some of the parameters in Examples 1-21 and Comparative Examples 1-19 are shown in Table 1.

[0195] Effect Example 1 For the first and second graphite precursors in Examples 1, 18-19, and 20-21, the lattice constants La and Lc, particle crushing strength, particle size distribution symmetry S, and sphericity D were measured. For the first and second graphite materials in Examples 1-21 and Comparative Examples 1-19, the particle crushing strength was measured. The specific measurement methods are as follows.

[0196] (1) Lattice constants La and Lc The obtained sample to be measured is used as the measurement sample. The sample to be measured and 50 mL of n-hexane are added to a beaker, ultrasonic vibration is performed for 5 minutes, then 100 μL of the solution is drawn up with a pipette and dropped onto a copper mesh for TEM observation. After the copper mesh is quickly dried, observation is performed. Selective diffraction observation and localization were performed using TEM to obtain the d(110) and half-width β of the sample. Then, based on equation (6), where λ is 0.0027 nm, θ could be calculated, i.e., equation (7).

number

number

number

number

[0197] (2) Particle size distribution symmetry S Referring to the Chinese national standard GB / T 41949-2022, the graphite material was measured using a laser particle size diffractometer (Malvern 3000). From the measurement results, the D(3,4) and Dv50 particle size data were directly read, and then S was obtained by calculation based on formula (10).

number

[0198] Effect Example 2 The specific surface area reduction rate, electrode plate porosity, and electrode plate adhesive strength F for the negative electrode plates in Examples 1-21 and Comparative Examples 1-19. N Furthermore, the limiting press density was measured, and the specific measurement method is as follows. (1) Limiting press density of the negative electrode plate Under conditions where the appearance of the negative electrode plate is well maintained, a roll press is used to roll-press the negative electrode plate. When the thickness of the negative electrode plate no longer decreases even when the pressure of the roll press is increased, the thickness of the negative electrode plate after roll pressing is measured with a micrometer and the thickness d is recorded. Then, a unit area of ​​the negative electrode plate is cut out, and after subtracting the mass of the copper foil contained therein, the mass is recorded as w. In this case, the limiting press density of the negative electrode plate is P = w / d. The limiting press density of the negative electrode plate evaluates the energy density index of the negative electrode plate. The limiting press densities of the negative electrode plates for each example and comparative example are shown in Table 1.

[0199] (2) Decrease rate of the specific surface area of ​​the negative electrode plate The negative electrode plate was cut into 2cm x 2cm negative electrode plates, and the specific surface area of ​​the negative electrode plate at the first and second press densities was measured according to the Chinese national standard GB / T 19587-2017. The ratio of the specific surface area of ​​the electrode plate at the second press density to that at the first press density is denoted as P, and the rate of reduction of the specific surface area of ​​the electrode plate is P0 = 1 - P. Table 1 shows the first and second press densities for each example and comparative example.

[0200] (3) Porosity of the electrode plate of the negative electrode plate In the first step, a negative electrode plate is obtained at the second press density. The method is the same as the method for obtaining the electrode plate in the measurement of the rate of reduction of the specific surface area of ​​the negative electrode plate described above. In the second step, measurements were taken in reference to the Chinese national standard GB21650.1-2008, and the porosity could be directly read.

[0201] (4) Adhesion force F of the negative electrode plate N The negative electrode plate to be measured is cut into long strips (length × width = 10 cm × 3 cm) and bonded to a long strip of quartz glass plate (slightly larger in area than the negative electrode plate) with VHB tape applied. The negative electrode plate is rolled three times using a dedicated small circular roller to ensure sufficient adhesion between the negative electrode plate and the VHB. A universal testing machine is used, and the standard method for 180° adhesion strength measurement is selected to measure the adhesion strength of the negative electrode plate. Each sample is measured three times and the average value is taken.

[0202] The specific measurement results are shown in Table 1.

[0203] Effect Example 3 Discharge capacity, initial efficiency, rapid charging time, number of cycles, and storage days were measured for the lithium-ion batteries prepared in Examples 1 to 21 and Comparative Examples 1 to 19. The specific measurement methods are as follows. (1)Discharge capacity At 25°C, the battery is first activated by performing one charge-discharge cycle at 0.1C within the operating voltage range of 2.7V (discharge termination voltage) to 4.3V (charge termination voltage). Then, the lithium-ion battery prepared above is connected to a Blue Electric Charge / Discharge Measurement Device, and a long-term cycle of charge-discharge is performed to measure its charge and discharge capacities. The operating voltage range for battery measurement is 2.7V (discharge termination voltage) to 4.3V (charge termination voltage), and the measurement rate is 0.3C. Initial efficiency = Discharge capacity / Charge capacity × 100%.

[0204] (2) Quick charging time The battery cell is directly charged to an 8% SOC state with a current of 0.33C. Then, based on the measured three-electrode window of the battery cell, the charging windows of 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% are defined as C1, C2, C3, C4, C5, C6, C7, and C8, respectively, and the battery is charged to 80% by step charging. That is, C1 is used from 8% to 10%, C2 is used from 10% to 20%, and so on. The charging time from 8% to 80% SOC state is recorded as the evaluation criterion for rapid charging capability, and the calculation formula is T=(0.02 / C1+0.1 / C2+0.1 / C3+0.1 / C4+0.1 / C5+0.1 / C6+0.1 / C7+0.1 / C8)×60.

[0205] (3) Number of cycles At 25°C, the battery is first activated by performing one charge-discharge cycle at 0.1C. The lithium-ion battery prepared above is then connected to a blue electrical charge-discharge measuring device. A long-term cycle is then performed at a rate of 0.3C, continuing until the ratio of the capacity after the nth cycle to the capacity after the first cycle at 0.3C falls below 80%. The capacity retention rate after the (n-1)th cycle is defined as 80%, the number of cycles is recorded as (n-1), and the measurement is stopped.

[0206] (4) Storage period At 25°C, the constant volume was recorded as C0 with a current of 0.33C. The battery cells were then stored under high-temperature conditions of 60°C, and thereafter, the cells were removed at 7-day intervals and their capacities were measured at room temperature to determine C1, C2, ... C. n Recorded as C n The storage time is the number of days until the C0 level first falls below 80%.

[0207] The measurement results are shown in Table 2.

[0208] [Table 1] JPEG2026082702000012.jpg157160

[0209] [Table 2] JPEG2026082702000014.jpg124139 Note: In Table 1, " / " indicates that the condition parameter is not involved in the specific experiment.

[0210] According to Tables 1 and 2, the specific surface area reduction rate P0 of the negative electrode plates obtained in Examples 1 to 21 is between 12% and 17.8%, the porosity ε of the electrode plates is between 18.2% and 25.6%, and the limiting press density of the negative electrode plates can reach 1.8 g / cc or more. The lithium-ion battery containing the said negative electrode plates can guarantee excellent discharge capacity, rapid charging performance, and cycle performance, and combines excellent energy density, cycle performance, and storage performance. Specifically, the discharge capacity of the lithium-ion battery can reach 358 mAh / g or more, the discharge time can reach 20 minutes or less, and the number of cycles can reach 2200 or more. On this basis, the initial efficiency can reach 90% or more, and the storage period can reach 280 days or more.

[0211] Through research, the inventors discovered that only when a negative electrode plate having a specific specific surface area reduction rate and electrode plate porosity as described in the present invention can a lithium-ion battery be guaranteed to have excellent discharge capacity, rapid charging performance, and cycle performance, and to possess excellent energy density, cycle performance, and storage performance. If the specific surface area reduction rate and electrode plate porosity of the negative electrode plate are excessive or insufficient, the resulting lithium-ion battery cannot be guaranteed to possess the above-mentioned excellent electrochemical performance.

[0212] Compared to Example 1, the rate of reduction P0 of the specific surface area of ​​the negative electrode plate obtained in Comparative Example 1 was too small, the critical press density of the negative electrode plate was clearly reduced, the rapid charging time of the lithium-ion battery containing it was extended, and the discharge capacity, number of cycles, initial efficiency, and storage days were all clearly deteriorated.

[0213] Compared to Example 1, the specific surface area reduction rate P0 of the negative electrode plate obtained in Comparative Example 2 was excessively large, the limiting press density of the negative electrode plate was relatively high, and although the lithium-ion battery containing it had relatively high discharge capacity and initial efficiency, the rapid charging time of the lithium-ion battery was clearly extended, and the number of cycles and storage days were significantly reduced.

[0214] Compared to Example 1, the rate of reduction P0 of the specific surface area of ​​the negative electrode plates obtained in Comparative Examples 3-4 and 6-7 was too small. Although the discharge capacity of the lithium-ion batteries containing these plates was considerable, the limiting press density of the negative electrode plates was clearly reduced in all cases, resulting in a clear deterioration of the rapid charging time, cycle count, initial efficiency, and storage days of the lithium-ion batteries.

[0215] Compared to Example 1, the specific surface area reduction rate P0 of the negative electrode plate obtained in Comparative Example 5 was excessively large, and the limiting press density of the negative electrode plate was considerable. Although the lithium-ion battery containing it had relatively high discharge capacity and initial efficiency, the rapid charging time of the lithium-ion battery was significantly longer, and the number of cycles and storage days were drastically reduced.

[0216] Compared to Example 1, the rate of reduction P0 of the specific surface area of ​​the negative electrode plate obtained in Comparative Example 8 was excessively large, the critical press density of the negative electrode plate was clearly reduced, the discharge capacity of the lithium-ion battery containing it decreased, the rapid charging time was significantly extended, and the number of cycles, initial efficiency, and storage days were all clearly deteriorated.

[0217] Compared to Example 1, the rate of reduction P0 of the specific surface area of ​​the negative electrode plate obtained in Comparative Example 9 was too small. Although the rapid charging time and discharge capacity of the obtained lithium-ion battery were comparable, the limiting press density of the negative electrode plate was clearly reduced, the number of cycles of the lithium-ion battery decreased significantly, and both the initial efficiency and storage days were clearly worsened.

[0218] Compared to Example 1, the rate of reduction P0 of the specific surface area of ​​the negative electrode plates obtained in Comparative Examples 10 and 14 was insufficient, the limiting press density of the negative electrode plates was clearly reduced in all cases, the rapid charging time of the lithium-ion batteries containing them was significantly extended, and the discharge capacity, number of cycles, initial efficiency, and storage days were all clearly deteriorated.

[0219] Compared to Example 1, the rate of reduction P0 of the specific surface area of ​​the negative electrode plates obtained in Comparative Examples 11-12 was excessively large. Although the discharge capacity of the resulting lithium-ion batteries was considerable, the limiting press density of the negative electrode plates was clearly reduced, the rapid charging time of the lithium-ion batteries was clearly extended, and the number of cycles, initial efficiency, and storage days all decreased significantly.

[0220] Compared to Example 1, the rate of reduction P0 of the specific surface area of ​​the negative electrode plate obtained in Comparative Example 13 was excessively large, the critical press density of the negative electrode plate was clearly reduced, the discharge capacity of the lithium-ion battery containing it deteriorated, and the rapid charging time, number of cycles, initial efficiency, and storage days were all clearly worsened.

[0221] Compared to Example 1, the rate of reduction P0 of the specific surface area of ​​the negative electrode plate obtained in Comparative Example 15 was excessively large. Although the critical press density of the negative electrode plate and the discharge capacity of the lithium-ion battery were relatively good, the rapid charging time of the lithium-ion battery deteriorated significantly, and the number of cycles, initial efficiency, and storage days all clearly worsened.

[0222] Compared to Example 1, the specific surface area reduction rate P0 of the negative electrode plates obtained in Comparative Examples 16-17 was excessively large, and the porosity e of the electrode plates was insufficient. Although the discharge capacity of the lithium-ion battery was relatively good, the limiting press density of the negative electrode plate decreased, the rapid charging time of the lithium-ion battery deteriorated significantly, and the number of cycles, initial efficiency, and storage days all decreased considerably.

[0223] Compared to Example 1, the specific surface area reduction rate P0 of the negative electrode plate obtained in Comparative Example 18 was excessively large, and the porosity e of the electrode plate was insufficient. Although the number of cycles and initial efficiency of the lithium-ion battery were relatively good, the critical press density of the negative electrode plate was clearly worsened, the discharge capacity of the lithium-ion battery was significantly reduced, the rapid charging time was significantly extended, and the storage days were clearly reduced.

[0224] Compared to Example 1, the rate of reduction P0 of the specific surface area of ​​the negative electrode plate obtained in Comparative Example 19 was too small, the critical press density of the negative electrode plate was clearly reduced, the rapid charging time of the lithium-ion battery containing it was significantly extended, the discharge capacity and cycle count decreased significantly, and the initial efficiency and storage days were clearly deteriorated.

[0225] Although specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely examples and that the scope of protection of the present invention is limited by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and substance of the present invention, and all such changes and modifications are within the scope of protection of the present invention. [Industrial applicability]

[0226] This invention relates to a negative electrode plate, an electrochemical apparatus, and electronic equipment.

Claims

1. A negative electrode plate, wherein the rate of reduction P of the specific surface area of ​​the negative electrode plate ０ The percentage is between 12% and 18%. P ０ = 1 - P, where P is the ratio of the specific surface area of ​​the negative electrode plate at the second press density to the specific surface area of ​​the negative electrode plate at the first press density. The porosity ε of the electrode plate of the negative electrode plate is 13% or more, and the porosity of the electrode plate is the porosity of the electrode plate of the negative electrode plate at the second press density. A negative electrode plate characterized in that the second press density is 1.80 g / cc or the limit press density of the negative electrode plate, and the first press density is 1.65 g / cc.

2. The negative electrode plate according to claim 1, characterized in that it satisfies one or more of the following conditions a to c. a, the above P ０ The percentage is between 13% and 17%. b. The above ε is between 18% and 26%. c. Adhesion force F of the negative electrode plate Ｎ The value is 25-50N.

3. The negative electrode plate according to claim 1, wherein the negative electrode plate includes a negative electrode current collector, a first active material layer is provided on at least one surface of the negative electrode current collector, a second active material layer is provided on the first active material layer, the first active material layer includes a first graphite material and a first binder, the second active material layer includes a second graphite material and a second binder, and the Dv50 particle size of the first graphite material is larger than the Dv50 particle size of the second graphite material.

4. The negative electrode plate according to claim 3, characterized in that the first graphite material and the second graphite material satisfy one or more of the following conditions a to i. a. The difference between the Dv50 particle size of the first graphite material and the Dv50 particle size of the second graphite material is 3 to 7 μm. b. Particle crushing strength F of the first graphite material １ The value is 30-36 mN. c. Particle crushing strength F of the second graphite material ２ The value is 20-30 mN. d. The carbon content of the first graphite material is 99.9% or more, where the percentage is the mass percentage of the first graphite material. e. The carbon content of the second graphite material is 99.9% or more, where the percentage is the mass percentage of the second graphite material. f. The Dv50 particle size of the first graphite material is 14 to 18 μm. g. The Dv50 particle size of the second graphite material is 9 to 13 μm. h, the first graphite material is a microcrystalline graphite material. i. The second graphite material is a microcrystalline graphite material.

5. The negative electrode plate according to claim 3, characterized in that the first active material layer and the second active material layer satisfy one or more of the following conditions a to g. a. The content of the first binder is 1.3% to 1.8%, where the percentage is the mass percentage of the first active material layer. b. The content of the second binder is 0.7% to 1.2%, where the percentage is the mass percentage of the second active material layer. c. The content of the first graphite material is 20% or more, where the percentage is the mass percentage of the first active material layer. d. The content of the second graphite material is 20% or more, where the percentage is the mass percentage of the second active material layer. e. The mass ratio of the first active material layer to the second active material layer is 1:(0.4 to 2.5). f. The thickness of the first active material layer is 50 to 120 μm. g) The thickness of the second active material layer is 50 to 110 μm.

6. The negative electrode plate according to claim 3, characterized in that the method for preparing the negative electrode plate includes the following steps. S1, A first negative electrode slurry layer is applied to at least one surface of the negative electrode current collector, wherein the first negative electrode slurry layer comprises the first graphite material and the first binder. S2, a second negative electrode slurry layer is applied onto the first negative electrode slurry layer, and the second negative electrode slurry layer comprises the second graphite material and the second binder. S3. The negative electrode plate is dried and cold-pressed to obtain the negative electrode plate.

7. The negative electrode plate according to claim 6, characterized in that the first graphite material and the second graphite material satisfy one or more of the following conditions a to d. a. The coating density of the first negative electrode slurry layer is 0.055 g / cm³. ２ Larger. b. The coating density of the second negative electrode slurry layer is 0.055 g / cm³. ２ Larger. c. In step S1, the first graphite material is obtained by pre-treating the first graphite precursor, wherein the pre-treatment includes surface oxidation treatment and / or carboxylation treatment. d. In step S2, the second graphite material is obtained by pre-treating the second graphite precursor, wherein the pre-treatment includes surface oxidation treatment and / or carboxylation treatment.

8. The negative electrode plate according to claim 7, characterized in that the first graphite precursor and the second graphite precursor each independently satisfy one or two of the following conditions a to b. a. The first graphite precursor and the second graphite precursor each independently satisfy the following conditions: La ≤ 72 nm, Lc ≤ 15 nm, where La is the lattice constant of the 110 plane and Lc is the lattice constant of the 002 plane, F ｐ ≥ 15 mN, F ｐ is the particle crushing strength, b. The method for preparing the first graphite precursor and the second graphite precursor each independently includes the following steps. (I) A first mixing is performed on the microcrystalline graphite precursor and the binder, and a solvent is added and a second mixing is performed to obtain a mixture. Here, the temperature of the first mixing is 5 to 20°C, which is below the softening point of the binder. (II) The mixture is pressed to obtain a microcrystalline graphite green. (III) The microcrystalline graphite green body is laid on the surface of the graphitization furnace, and a graphitization heat-insulating material is laid on the microcrystalline graphite green body to perform the graphitization treatment, thereby obtaining a microcrystalline graphitized body from the microcrystalline graphite green body after the graphitization treatment. (IV) The microcrystalline graphitized body is subjected to pulverization.

9. An electrochemical apparatus characterized by comprising a negative electrode plate as described in any one of claims 1 to 8.

10. An electronic device, characterized by including the electrochemical apparatus described in claim 9.

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