Negative pole piece and electrochemical device and electronic device comprising same

Abstract

The invention discloses a negative pole piece and an electrochemical device and an electronic device comprising the same, and belongs to the technical field of energy storage. The negative pole piece comprises a negative current collector and a negative active material layer arranged on at least one surface of the negative current collector; the negative electrode active material layer comprises a bottom layer, a middle layer and a surface layer which are sequentially arranged on the surface of the negative electrode current collector, the bottom layer comprises a three-dimensional carbon material, the middle layer comprises a two-dimensional carbon material, and the surface layer comprises a one-dimensional carbon material; the thickness of the bottom layer, the thickness of the middle layer and the thickness of the surface layer are H3, H2 and H1 respectively, and the formula that H1: H2: H3 = (0.5-2): (1-3): (5-10) is met. According to the present invention, by constructing the continuous Li < + > transmission channel from the surface layer to the bottom layer, the Li < + > is not easily accumulated at the interface, such that the concentration polarization is reduced, the charge transmission dynamics is improved, and the cycle performance of the electrochemical device is improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and more specifically, to a negative electrode and an electrochemical and electronic device comprising the same. Background Technology

[0002] In traditional lithium-ion batteries, the negative electrode is mainly composed of single-layer and multi-layer sheet graphite. However, this type of negative electrode can often only be used in batteries with lower energy density because the active material at the bottom of the electrode does not easily come into contact with the electrolyte. This results in a longer lithium-ion migration path, increased concentration polarization, and poorer charge transport dynamics, ultimately causing the battery capacity to fall short of the design value. In addition, in the later stages of cycling, it is prone to problems such as interface lithium plating and deterioration of charging capacity, which further hinders the improvement of battery energy density. Summary of the Invention

[0003] The purpose of this application is to overcome the shortcomings of existing technologies and provide a negative electrode sheet and an electrochemical and electronic device comprising it. This application achieves this by constructing a continuous Li from the surface to the bottom layer. + The transmission channel enables Li + It is less likely to accumulate at the interface, which reduces concentration polarization, improves charge transport kinetics, and thus improves the cycle performance of the electrochemical device.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0005] The first aspect of this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a bottom layer, a middle layer and a top layer disposed sequentially on the surface of the negative electrode current collector. The bottom layer includes a three-dimensional carbon material (3D carbon material), the middle layer includes a two-dimensional carbon material (2D carbon material), and the top layer includes a one-dimensional carbon material (1D carbon material).

[0006] The thicknesses of the bottom layer, middle layer, and top layer are H3, H2, and H1, respectively, satisfying: H1:H2:H3=(0.5-2):(1-3):(5-10).

[0007] In some implementations, H, H1, H2, and H3 satisfy: H = H1 + H2 + H3, H1:H2:H3 = 1:(1-2):(7-9).

[0008] In some implementations, H satisfies: 50μm≤H≤300μm.

[0009] In some implementations, H1, H2, and H3 satisfy the following conditions: 5μm≤H1≤30μm, 10μm≤H2≤70μm, and 25μm≤H3≤200μm.

[0010] In some embodiments, the one-dimensional carbon material includes at least one of carbon nanowires, carbon nanofibers, and graphene nanoribbons.

[0011] In some embodiments, the two-dimensional carbon material includes at least one of graphene, expanded graphite, and artificial graphite.

[0012] In some embodiments, the three-dimensional carbon material includes at least one of graphene aerogel, graphite foam, and spherical graphite.

[0013] In some embodiments, the length of the one-dimensional carbon material is L nm and the diameter is R nm, wherein L and R satisfy: 50 ≤ L / R ≤ 150.

[0014] In some implementations, L and R satisfy: 500nm≤L≤2000nm, 3nm≤R≤40nm.

[0015] In some embodiments, the peak intensity ratio of the Raman spectrum of the two-dimensional carbon material is Id / Ig, where Id / Ig satisfies: 0.1 ≤ Id / Ig ≤ 0.8; the lateral dimension of the two-dimensional carbon material is X, where X satisfies: 0.5 μm ≤ X ≤ 10 μm. Id is the D peak intensity of the Raman spectrum of the two-dimensional carbon material, and Ig is the G peak intensity of the Raman spectrum of the two-dimensional carbon material.

[0016] In some embodiments, the specific surface area of ​​the three-dimensional carbon material is 20-100 m². 2 / g, with a porosity of 20-60% and a compressive strength of 2.0-3.5t / g.

[0017] In some embodiments, the total compaction density of the negative electrode sheet is P, wherein P satisfies: 1.6 g / cm³ 3 ≤P≤1.9g / cm 3 .

[0018] In some embodiments, the compaction density of the one-dimensional carbon material is P1, the compaction density of the two-dimensional carbon material is P2, and the compaction density of the three-dimensional carbon material is P3. P, P1, P2, and P3 satisfy the following condition: P = P1*H1 / H + P2*H2 / H + P3*H3 / H. Furthermore, P1, P2, and P3 satisfy the condition: 0.6 g / cm³. 3 ≤P1≤1.0g / cm 3 1.2g / cm 3 ≤P2≤1.6g / cm 3 1.8g / cm 3 ≤P3≤2.0g / cm 3 .

[0019] A second aspect of this application provides an electrochemical device comprising the negative electrode sheet described above.

[0020] A third aspect of this application provides an electronic device including the electrochemical device described above.

[0021] The beneficial effects of this application are as follows:

[0022] This application utilizes one-dimensional carbon materials as a "conductive highway" to rapidly conduct electrons / Li + Two-dimensional carbon materials as "Li + A "diffusion bridge" connects 1D and 3D carbon material structures; the three-dimensional carbon material serves as the "lithium storage host," balancing capacity and stability, thereby constructing a continuous Li-mass structure from the surface to the bottom. + The transmission channel enables Li + It is less likely to accumulate at the interface, which reduces concentration polarization, improves charge transport kinetics, and thus improves the cycle performance of the electrochemical device. Attached Figure Description

[0023] The embodiments described in this application are not limited to the accompanying drawings, which are only some of the embodiments described herein. Those skilled in the art can obtain drawings of other embodiments based on the content of this application.

[0024] Figure 1 This is a schematic diagram of the negative electrode sheet described in this application. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0027] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0028] In this application, there are no particular restrictions on the specific dispersion and mixing methods.

[0029] Unless otherwise specified, all components, raw materials, or instruments used in the embodiments and comparative examples of this application are commercially available.

[0030] General definition

[0031] The term "binder" refers to a substance used to bond inorganic fillers to or to each other in a porous substrate material. Any organic binder that can bond inorganic fillers to or to each other in a porous substrate material may be used herein. Some non-limiting examples of organic binders include polyesters, polyamides, polyacrylic acid, polyethers, polyimides, polyolefins, rubbers, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, cellulose, cellulose derivatives, latexes, and combinations thereof.

[0032] Negative electrode active material: As used herein and in the claims, the term "negative electrode active material" (also known as anodic active material) is defined as a material that is electrochemically active in a negative electrode or anode. Active material should be understood as a material capable of capturing and releasing Li and / or Na ions when subjected to voltage changes over a predetermined time period.

[0033] I. Negative electrode

[0034] This application provides a negative electrode sheet, which includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector. The negative active material layer includes a bottom layer, a middle layer, and a top layer disposed sequentially on the surface of the negative current collector. The bottom layer includes a three-dimensional carbon material, the middle layer includes a two-dimensional carbon material, and the top layer includes a one-dimensional carbon material.

[0035] In some embodiments, the negative current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is a copper foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0036] In some embodiments, the one-dimensional carbon material includes at least one of carbon nanowires, carbon nanofibers, and graphene nanoribbons.

[0037] In some embodiments, the two-dimensional carbon material includes at least one of graphene, expanded graphite, and artificial graphite.

[0038] In some embodiments, the three-dimensional carbon material includes at least one of graphene aerogel, graphite foam, and spherical graphite.

[0039] In this application, the negative electrode active material layer comprises a surface layer, a middle layer, and a bottom layer, forming a gradient transport path from high conductivity to high storage capacity. Specifically, the one-dimensional carbon material in the surface layer rapidly conducts electrons / Li through axial conduction. + Solving the surface dynamics bottleneck; the two-dimensional carbon material in the middle layer expands the Li... + A diffusion channel balances defects and conductivity; the three-dimensional carbon material in the underlying layer provides high-capacity storage and volume expansion buffering, offering more transport paths for lithium ions to the underlying active material. Therefore, this application uses one-dimensional carbon material as a "conductive highway" for rapid electron / Li ion exchange. + Two-dimensional carbon materials as "Li + A "diffusion bridge" connects 1D and 3D structures; three-dimensional carbon materials serve as the "lithium storage host," balancing capacity and stability, thereby constructing a continuous Li-mass structure from the surface to the bottom. + The transmission channel enables Li + It is less likely to accumulate at the interface, which reduces concentration polarization, improves charge transport kinetics, and thus improves the cycle performance of the electrochemical device.

[0040] In some implementations, the thicknesses of the bottom layer, middle layer, and top layer are H3, H2, and H1, respectively, and the total thickness of the bottom layer, middle layer, and top layer is H. The H, H1, H2, and H3 satisfy: H = H1 + H2 + H3, H1:H2:H3 = (0.5-2):(1-3):(5-10), for example, it can be 0.5:1:5, 0.5:1:8, 0.5:1:10, 0.5:2:5, 0.5:2:8, 0.5:2:10, 0.5:3:5, 0.5:3:8, 0.5:3:10, 1:1:5, 1:1:8, 1:1:10, 1:2:5, 1:2:10, 1:3:5, 1:3:10, 2:1:5, 2:1:10, 2:2:5, or a range consisting of any two of these values.

[0041] In this application, if the surface layer is too thin, it will hinder electron conduction, increasing interfacial impedance and resulting in an insufficient charging window; if the surface layer is too thick, it will reduce energy density and cause insufficient electrolyte wetting; if the middle layer is too thin, it will cause uneven lithium-ion diffusion and local lithium deposition; if the middle layer is too thick, the densely stacked 2D carbon layer will hinder ion diffusion; if the bottom layer is too thin, the ion and electron diffusion rates will decrease, reducing rate performance; if the bottom layer is too thick, excessive electrolyte adsorption will occur, leading to more side reactions and reducing coulombic efficiency. Therefore, this application, by controlling the thickness of the surface, middle, and bottom layers within the above-mentioned ranges, is beneficial for shortening the lithium-ion transport path, improving lithium-ion transport efficiency, reducing interfacial impedance, improving electrolyte wettability on the negative electrode, improving the liquid retention of the negative electrode, increasing the compaction density of the negative electrode, reducing the occurrence of side reactions, and effectively improving the coulombic efficiency, rate performance, and cycle performance of the electrochemical device.

[0042] In some implementations, H, H1, H2, and H3 satisfy: H1:H2:H3 = 1:(1-2):(7-9).

[0043] In some implementations, H satisfies: 50μm≤H≤300μm, for example, it can be 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 150μm, 200μm, 250μm, 300μm or a range of any two of these values.

[0044] In some implementations, H1 satisfies: 5μm≤H1≤30μm, for example, it can be 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 22μm, 25μm, 28μm, 30μm or a range of any two of these values.

[0045] In some implementations, H2 satisfies: 10μm≤H2≤70μm, for example, it can be a range of 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm or any two of these values.

[0046] In some implementations, H3 satisfies: 25μm≤H3≤200μm, for example, it can be 25μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, 120μm, 150μm, 180μm, 200μm or any two of these values.

[0047] In some embodiments, the mass percentage of the one-dimensional carbon material in the negative electrode sheet is 5% ≤ W1 ≤ 15%. For example, it can be 5%, 6%, 8%, 10%, 12%, 14%, 15%, or a range of any two of these values.

[0048] In some embodiments, the mass percentage of the two-dimensional carbon material in the negative electrode sheet is 5% ≤ W2 ≤ 30%. For example, it can be 5%, 10%, 15%, 20%, 25%, 30%, or any two of these values.

[0049] In some embodiments, the mass percentage of the three-dimensional carbon material in the negative electrode sheet is 40% ≤ W3 ≤ 80%. For example, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any two of these values.

[0050] In some embodiments, the length of the one-dimensional carbon material is L nm and the diameter is R nm, wherein L and R satisfy: 50 ≤ L / R ≤ 150, for example, it can be 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150 or any two of these values.

[0051] In some implementations, L satisfies: 500nm ≤ L ≤ 2000nm, for example, it can be a range of 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, 1600nm, 1700nm, 1800nm, 1900nm, 2000nm or any two of these values.

[0052] In some implementations, R satisfies: 3nm≤R≤40nm, for example, it can be a range of 3nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm or any two of these values.

[0053] In this application, if the length L of the one-dimensional carbon material is too large, it is prone to entanglement and agglomeration, leading to difficulties in dispersion and a decrease in the uniformity of slurry coating; if the length L is too small, it is difficult to form a continuous conductive path, resulting in reduced electron transport efficiency; if the diameter R of the one-dimensional carbon material is too large, it weakens the directional conductivity of the one-dimensional material; if the diameter R is too small, the mechanical strength is insufficient, and it is prone to breakage during rolling or cycling. Therefore, by controlling the length and diameter of the one-dimensional carbon material within the above-mentioned ranges, it is beneficial to improve the cycling performance and rate performance of the electrochemical device.

[0054] In some embodiments, the peak intensity ratio of the Raman spectrum of the two-dimensional carbon material is Id / Ig, where Id / Ig satisfies: 0.1 ≤ Id / Ig ≤ 0.8, and can be, for example, a range of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or any two of these values. Id represents the D peak intensity of the Raman spectrum of the two-dimensional carbon material, and Ig represents the G peak intensity of the Raman spectrum of the two-dimensional carbon material.

[0055] In this application, the Id / Ig test method is as follows: a 532nm laser is used as the excitation source, and the laser power is controlled below 1mW to avoid thermal effects. Before testing, a standard silicon wafer with a diameter of 520.7cm is used. -1 Characteristic peaks were used to calibrate the Raman spectrometer. Spectra were acquired at least five randomly selected locations on the surface of the sample. After baseline correction of the obtained raw spectra, the D peak (approximately 1350 cm⁻¹) was selected. -1) and G peak (approximately 1580cm) -1 The peak value of Id / Ig is the average value of all measurement points.

[0056] In some embodiments, the lateral dimension of the two-dimensional carbon material is X, which satisfies: 0.5μm≤X≤10μm, for example, it can be 0.5μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or any two of these values.

[0057] The lateral dimensions of the two-dimensional carbon material described in this application can be statistically characterized using scanning electron microscopy (SEM). The specific method is as follows: the sample is dispersed in a volatile solvent such as ethanol, ultrasonically treated to form a uniform dispersion, and then drop-coated onto a silicon wafer with a silicon oxide layer (approximately 300 nm thick) or a substrate covered with a conductive layer (such as gold or platinum). Observation is performed after the solvent has completely evaporated. At least five SEM images with clear contrast are acquired at different fields of view using an accelerating voltage of 5 kV to 10 kV and a secondary electron imaging mode. The projected contours of no fewer than 50 independent layers are randomly measured using image analysis software (such as ImageJ), and their lateral dimensions are defined as the maximum Feret diameter within the discernible boundary of the layer projection. The final lateral dimension is the arithmetic mean of all measurement results and its distribution range.

[0058] In this application, if the Id / Ig ratio is too small, it indicates that the crystallinity is too high and the defect sites are insufficient, resulting in a reduction in lithium-ion adsorption active sites and a decrease in reversible capacity; if the Id / Ig ratio is too large, there are too many defects, and the sp 2 Disruption of the carbon network leads to decreased conductivity and increased resistance to electron transport. If the lateral dimension X is too small, it is difficult to form a continuous conductive network, resulting in broken electron conduction paths; if the lateral dimension X is too large, the layers become densely packed, hindering electrolyte wetting and impeding lithium-ion diffusion. Therefore, controlling the Id / Ig ratio and lateral dimension of the two-dimensional carbon material within the above-mentioned ranges is beneficial to improving the cycle performance of the electrochemical device.

[0059] In some embodiments, the specific surface area of ​​the three-dimensional carbon material is 20-100 m². 2 / g, for example, could be 20m 2 / g、30m 2 / g、40m 2 / g, 50m 2 / g、60m 2 / g、70m 2 / g、80m 2 / g、90m 2 / g, 100m 2 / g or a range consisting of any two of its values.

[0060] In some embodiments, the porosity of the three-dimensional carbon material is 20-60%, for example, it can be a range of 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any two of these values.

[0061] In some embodiments, the compressive strength of the three-dimensional carbon material is 2.0-3.5 t / g, for example, it can be 2.0 t / g, 2.1 t / g, 2.2 t / g, 2.3 t / g, 2.4 t / g, 2.5 t / g, 2.6 t / g, 2.7 t / g, 2.8 t / g, 2.9 t / g, 3.0 t / g, 3.1 t / g, 3.2 t / g, 3.3 t / g, 3.4 t / g, 3.5 t / g, or any two of these values.

[0062] In this application, if the specific surface area of ​​the three-dimensional carbon material is too small, there are insufficient active sites, leading to reduced capacity and limited rate performance; if the specific surface area is too large, side reactions are aggravated (such as excessive SEI growth), coulombic efficiency decreases, and electrolyte consumption is too rapid. If the porosity is too low, there are insufficient lithium-ion transport channels, resulting in increased polarization during fast charging; if the porosity is too high, the mechanical strength is insufficient, leading to structural collapse during rolling or cycling, and making it difficult to achieve the required compaction density. If the compressive strength is too low, the electrode is prone to deformation, and the interfacial contact deteriorates; if the compressive strength is too high, it is usually accompanied by excessively low porosity, sacrificing ion transport kinetics. Therefore, controlling the specific surface area, porosity, and compressive strength of the three-dimensional carbon material within the above-mentioned ranges is beneficial to improving the cycling performance of the electrochemical device.

[0063] In some embodiments, the total compaction density of the negative electrode sheet is P, wherein P satisfies: 1.6 g / cm³ 3 ≤P≤1.9g / cm 3 For example, it could be 1.6 g / cm³ 3 1.62g / cm 3 6.5g / cm 3 6.8g / cm 3 1.7g / cm 3 1.75g / cm 3 1.78g / cm 3 1.8g / cm 3 1.85g / cm 3 1.9g / cm 3 Or a range consisting of any two of these values.

[0064] In this application, when the electrode compaction density is too low, the electrode structure is too porous, resulting in low utilization of active materials, insufficient volumetric energy density, and poor interfacial contact, significantly increasing electron transport impedance. Conversely, excessively high compaction density will over-compress the pore structure, hindering lithium-ion transport and exacerbating charge-discharge polarization, while also deteriorating the electrode's mechanical properties. Therefore, controlling the total compaction density of the electrode within the aforementioned range is beneficial for improving the cycle performance of the electrochemical device.

[0065] In some embodiments, the compaction density of the one-dimensional carbon material is P1, the compaction density of the two-dimensional carbon material is P2, and the compaction density of the three-dimensional carbon material is P3, satisfying: P1 < P2 < P3. By controlling P1 < P2 < P3, the rate performance and cycle performance of the electrochemical device can be further improved.

[0066] In some implementations, P, P1, P2, and P3 satisfy: P = P1 * H1 / H + P2 * H2 / H + P3 * H3 / H.

[0067] In some embodiments, P1 satisfies: 0.6 g / cm³ 3 ≤P1≤1.0g / cm 3 For example, it could be 0.6 g / cm³ 3 0.65g / cm 3 0.7g / cm 3 0.75g / cm 3 0.8g / cm 3 0.85g / cm 3 0.9g / cm 3 0.95g / cm 3 1.0g / cm 3 Or a range consisting of any two of these values.

[0068] In some embodiments, P2 satisfies: 1.2 g / cm³ 3 ≤P2≤1.6g / cm 3 For example, it could be 1.2 g / cm³. 3 1.25g / cm 3 1.3g / cm 3 1.35g / cm 3 1.4g / cm 3 1.45g / cm 3 1.5g / cm 3 1.55g / cm 3 1.6g / cm 3 Or a range consisting of any two of these values.

[0069] In some embodiments, P3 satisfies: 1.8 g / cm³3 ≤P3≤2.0g / cm 3 For example, it could be 1.8 g / cm³ 3 1.85g / cm 3 1.9g / cm 3 1.95g / cm 3 2.0g / cm 3 Or a range consisting of any two of these values.

[0070] In some embodiments, the surface layer further includes a negative electrode binder and a thickener, wherein the mass percentage of the negative electrode binder in the surface layer is 1.0-1.5%, preferably 1.2%; and the mass percentage of the thickener is 0.5-1.2%, preferably 0.8%.

[0071] In some embodiments, the intermediate layer further includes a negative electrode binder and a thickener, wherein the mass percentage of the negative electrode binder in the intermediate layer is 0.8-1.2%, preferably 1.0%; and the mass percentage of the thickener is 0.8-1.2%, preferably 1.0%.

[0072] In some embodiments, the substrate further includes a negative electrode binder and a thickener, wherein the negative electrode binder comprises 0.5-1.0% by mass, preferably 0.9%, and the thickener comprises 1.0-1.5% by mass, preferably 1.1%.

[0073] In some embodiments, the negative electrode binder includes at least one of the following: polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. This application is not limited to the above materials and also includes other materials that can be used as battery negative electrode binders.

[0074] In some embodiments, the thickener includes at least one of sodium carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, polyacrylic acid, sodium polyacrylate, sodium alginate, guar gum, xanthan gum, carrageenan, gellan gum, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, and acrylic copolymers.

[0075] This application does not impose any particular restrictions on the source of one-dimensional, two-dimensional, or three-dimensional carbon materials, as long as they can achieve the purpose of this application. For example, in some embodiments, the one-dimensional carbon materials such as carbon nanowires, carbon nanofibers, and graphene nanoribbons can be purchased from suppliers such as Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., Beijing Boyu High-Tech New Materials Technology Co., Ltd., or Shenzhen Jinglü Technology Co., Ltd.; the two-dimensional carbon materials such as graphene, expanded graphite, and artificial graphite can be purchased from suppliers such as Jinan Shengquan Group Co., Ltd., Qingdao Haoxin New Energy Technology Co., Ltd., or Xiamen Kaina Graphene Technology Co., Ltd.; and the three-dimensional carbon materials such as graphene aerogel, graphite foam, and spherical graphite can be purchased from suppliers such as the Institute of Metal Research, Chinese Academy of Sciences, Ningbo CRRC New Energy Technology Co., Ltd., or Inner Mongolia Ruisheng New Energy Co., Ltd.

[0076] Preparation method of negative electrode sheet

[0077] 1. Preparation of the base slurry:

[0078] Add the three-dimensional carbon material, negative electrode binder, and thickener to mixing tank 1 in a mass ratio of (96-98):(0.5-2):(0.5-2), and then add solvent and mix thoroughly.

[0079] 2. Preparation of intermediate layer slurry:

[0080] Two-dimensional carbon material, negative electrode binder, and thickener are added to mixing tank 2 in a mass ratio of (96-98):(0.5-2):(0.5-2), and then solvent is added and mixed thoroughly.

[0081] 3. Preparation of surface slurry:

[0082] One-dimensional carbon material, negative electrode binder, and thickener are added to mixing tank 3 in a mass ratio of (96-98):(0.5-2):(0.5-2), and then solvent is added and mixed thoroughly.

[0083] 4. Preparation of negative electrode sheet:

[0084] The slurry in mixing tanks 1, 2, and 3 is coated onto copper foil in the order of bottom layer, middle layer, and top layer by extrusion coating, and then baked and rolled to obtain the negative electrode sheet.

[0085] II. Electrochemical Device

[0086] This application provides an electrochemical device comprising the aforementioned negative electrode. In some embodiments, the electrochemical device further includes a positive electrode, a membrane, and an electrolyte, wherein the membrane is located between the positive and negative electrodes.

[0087] The electrochemical device of this application includes any device in which an electrochemical reaction occurs, and specific examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0088] positive electrode

[0089] The electrochemical device of this application includes a positive electrode, wherein the positive electrode includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector.

[0090] In some implementations, the type of positive current collector is not particularly limited, and it may be any material known to be suitable for use as a positive current collector.

[0091] In some implementations, the positive current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper.

[0092] There are no particular restrictions on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.

[0093] In some embodiments, the positive electrode active layer includes a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0094] In some embodiments, the positive electrode active material is selected from LiCoO2, LiNiO2, and LiNi x Mn y O2, Li 1+ z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al zThe group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, LiMnPO4 and combinations thereof, wherein each x is independently 0.2 to 0.9; each y is independently 0.1 to 0.45; and each z is independently 0 to 0.2.

[0095] In some embodiments, the positive electrode active material is Li 1+x Ni a Mn b Co c Al (1-a-b-c) O2; where -0.2≤x≤0.2, 0≤a<1, 0≤b<1, 0≤c<1 and a+b+c≤1.

[0096] In some embodiments, the positive electrode active material has the general formula Li 1+x Ni a Mn b Co c Al (1-a-b-c) O2, where 0.33≤a≤0.92, 0.33≤a≤0.9, 0.33≤a≤0.8, 0.5≤a≤0.92, 0.5≤a≤0.9, 0.5≤a≤0.8, 0.6≤a≤0.92 or 0.6≤a≤0.9; 0≤b≤0.5, 0≤b≤0.3, 0.1≤b≤0.5, 0.1≤b≤0.4, 0.1≤b≤0.3, 0.1≤b≤0.2 or 0.2≤b≤0.5; 0≤c≤0.5, 0≤c≤0.3, 0.1≤c≤0.5, 0.1≤c≤0.4, 0.1≤c≤0.3, 0.1≤c≤0.2 or 0.2≤c≤0.5.

[0097] In some embodiments, the positive electrode active material is doped with a dopant selected from the group consisting of Fe, Ni, Mn, Al, Mg, Zn, Ti, La, Ce, Sn, Zr, Ru, Si, Ge, and combinations thereof.

[0098] In some embodiments, the positive electrode active material includes LiNi. 0.33 Mn 0.33 Co 0.33 O2(NMC333), LiNi 0.4 Mn 0.4 Co 0.2 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2(NMC532), LiNi 0.6 Mn 0.2 Co 0.2O2(NMC622), LiNi 0.7 Mn 0.15 Co 0.15 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2(NMC811), LiNi 0.92 Mn 0.04 Co 0.04 O2, LiNi 0.8 Co 0.15 Al 0.05 At least one of O2 (NCA) and LiNiO2 (LNO).

[0099] In some embodiments, the positive electrode binder includes binder materials comprising at least one of the following: polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. This application is not limited to the above materials and also includes other materials that can be used as battery positive electrode binders.

[0100] In some embodiments, the positive electrode conductive agent includes at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon tubes, carbon nanotubes, activated carbon, and mesoporous carbon. This application is not limited to the above materials, but also includes other materials that can be used as positive electrode conductive agents in batteries.

[0101] diaphragm

[0102] The separator separates the negative and positive electrodes and provides a pathway for lithium-ion migration. The use of the separator is not particularly limited, as long as it is a separator commonly used in lithium-ion secondary batteries. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte permeability are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes formed from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc.) or laminated structures with two or more layers. Alternatively, nonwoven fabrics formed from conventional porous nonwoven fabrics (e.g., glass fibers with high melting points, polyethylene terephthalate fibers, etc.) can be used. Furthermore, coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can be used, and can optionally be used as single-layer or multi-layer structures.

[0103] Generally, a diaphragm includes a substrate and a coating applied to the surface of the substrate.

[0104] electrolytes

[0105] The electrochemical device of this application also includes an electrolyte.

[0106] In some embodiments, the electrolyte includes at least one of a gel electrolyte, a solid electrolyte, and a liquid electrolyte.

[0107] In some embodiments, the liquid electrolyte includes a non-aqueous solvent and a lithium salt.

[0108] In some embodiments, the lithium salt includes at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.

[0109] In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0110] In some embodiments, the carbonate compound includes at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.

[0111] In some embodiments, the chain carbonate compound includes diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. Examples of fluorinated carbonate compounds are at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0112] In some embodiments, examples of carboxylic acid ester compounds are at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate.

[0113] In some embodiments, examples of ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0114] In some embodiments, the non-aqueous solvent also includes at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0115] III. Electronic Devices

[0116] This application also provides an electronic device, including the electrochemical device described in this application.

[0117] The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the electrochemical device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, android robots, etc.

[0118] The following uses a lithium-ion battery as an example and combines specific embodiments to illustrate the preparation of a lithium-ion battery. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0119] Example 1

[0120] The method for preparing a lithium-ion battery includes the following steps:

[0121] 1. Preparation of the base slurry:

[0122] Three-dimensional carbon material (spherical graphite), negative electrode binder (SBR), and thickener (CMC) are added to mixing tank 1 at a mass ratio of 98:0.9:1.1. Then, deionized water is added and the mixture is stirred thoroughly until homogeneous. The weight ratio of three-dimensional carbon material to deionized water is 2:1.

[0123] 2. Preparation of intermediate layer slurry:

[0124] Two-dimensional carbon material (sheet artificial graphite), negative electrode binder (SBR), and thickener (CMC) are added to mixing tank 2 at a mass ratio of 98:1.0:1.0. Then, deionized water is added and the mixture is stirred thoroughly until homogeneous. The weight ratio of two-dimensional carbon material to deionized water is 2:1.

[0125] 3. Preparation of surface slurry:

[0126] One-dimensional carbon material (carbon nanowires), negative electrode binder (SBR), and thickener (CMC) are added to mixing tank 3 at a mass ratio of 98:1.2:0.8. Then, deionized water is added and the mixture is stirred thoroughly until homogeneous. The weight ratio of one-dimensional carbon material to deionized water is 2:1.

[0127] 4. Preparation of negative electrode sheet:

[0128] The slurry in mixing tanks 1, 2, and 3 is coated onto copper foil in the order of bottom layer, middle layer, and top layer by extrusion coating. The coating weight of the three layers is controlled, and then the negative electrode sheet is obtained by baking and rolling. The final ratio of the surface layer thickness H1: middle layer thickness H2: bottom layer thickness H3 of the electrode sheet is 2:2:7.

[0129] (2) Preparation of positive electrode

[0130] The positive electrode material lithium cobalt oxide, the mixed conductive agent (Super P:KS-6:CNT = 6:3:1), and the binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 98:1.2:0.8. The mixture was then coated onto an Al foil, dried, rolled, and slit to obtain the positive electrode sheet.

[0131] (3) Preparation of the diaphragm

[0132] The PE surface is coated with ceramic as a release membrane.

[0133] (4) Preparation of electrolyte

[0134] A solution prepared by mixing lithium salt LiPF6 with a non-aqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP): ethylene carbonate (VC)) in a mass ratio of 25:25:15:31:4, with a mass ratio of 8:92) is used as the electrolyte for lithium batteries.

[0135] (5) Battery manufacturing

[0136] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for safety isolation. The electrode assembly is then wound up to form the electrode assembly. The electrode assembly is placed in a packaging shell, electrolyte is injected, and the package is sealed to obtain a lithium battery.

[0137] The parameters of the negative electrode are shown in Table 1.

[0138] Examples 2-7, Comparative Examples 1-8

[0139] The difference between Examples 2-7 and Example 1 is that the coating weights of the top, middle, and bottom layers are adjusted during extrusion coating, thereby changing the thickness ratio of the top, middle, and bottom layers.

[0140] Examples 8-13

[0141] The difference between Examples 8-13 and Example 1 is that one-dimensional carbon materials with different lengths and aspect ratios are selected when preparing the surface slurry.

[0142] Examples 14-19

[0143] The difference between Examples 14-19 and Example 1 is that different Id / Ig ratios and two-dimensional carbon materials with different lateral dimensions were selected when preparing the intermediate layer slurry.

[0144] Examples 20-25

[0145] The difference between Examples 20-25 and Example 1 is that different three-dimensional carbon materials with different specific surface areas, porosities, and compressive strengths were selected when preparing the bottom slurry.

[0146] Table 1

[0147]

[0148]

[0149] Test methods

[0150] 1. Test method for liquid retention coefficient:

[0151] Liquid retention coefficient = (weight of cell after double sealing - weight of cell before liquid injection) g / cell discharge capacity Ah.

[0152] 2. Test method for lithium plating window:

[0153] The battery cell is charged to 4.5V at a rate of XC (X = 1~10C, gradient rate charging) at room temperature of 25℃, discharged to 3.0V at 0.7C, and cycled for 50cls. The lithium plating window is the rate at which lithium plating does not occur at the cycle interface (for example, direct charging at 2.5C does not cause lithium plating, while direct charging at 2.7C causes lithium plating, so the lithium plating window is 2.5C).

[0154] 3. Test method for DC internal resistance:

[0155] Record the initial voltage V1 of the battery cell, discharge it with a constant current of 1A for 500ms, and record the discharge end voltage V2. The DC internal resistance is (V1-V2) / 1A.

[0156] 4. Method for testing gram capacity:

[0157] In this application, the specific capacity of the negative electrode material is tested using a half-cell system. The negative electrode material to be tested, a conductive agent, and a binder are mixed in a certain proportion to form the working electrode, and a coin cell is assembled using a lithium metal sheet as the counter electrode and a reference electrode. Under constant temperature conditions (e.g., 25°C), a constant current charge-discharge tester is used to conduct charge-discharge tests within a set voltage window (e.g., 0.01V-2.0V vs. Li+ / Li). The specific capacity of the material is calculated using the constant current discharge capacity, specifically: Specific capacity (mAh / g) = Discharge capacity (mAh) / Mass of active material of the negative electrode (g). The final result is the average value of multiple tests.

[0158] 5. Initial coulombic efficiency = initial discharge capacity / initial charge capacity × 100%.

[0159] 6. Test method for the number of cycles required to reduce degradation to 80% at 25℃:

[0160] The battery under test was subjected to continuous charge-discharge testing under a constant temperature environment of 25±2℃ and a constant current and constant voltage charging and discharging regime. The ratio of the discharge capacity after multiple cycles to the initial discharge capacity was calculated to obtain the capacity retention rate. The number of cycles corresponding to when the capacity retention rate first equals or falls below 80% is the test result.

[0161] The test results are shown in Table 2.

[0162] Table 2

[0163]

[0164]

[0165] As shown in Table 2, this application utilizes one-dimensional carbon materials as a "conductive highway" to rapidly conduct electrons / Li + Two-dimensional carbon materials as "Li + A "diffusion bridge" connects 1D and 3D structures; three-dimensional carbon materials serve as the "lithium storage host," balancing capacity and stability, thereby constructing a continuous Li-mass structure from the surface to the bottom. + The transmission channel enables Li + It is less likely to accumulate at the interface, which reduces concentration polarization, improves charge transport kinetics, and thus improves the cycle performance of the electrochemical device.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A negative electrode sheet, characterized in that, The present invention includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a bottom layer, a middle layer and a top layer disposed sequentially on the surface of the negative electrode current collector. The bottom layer includes a three-dimensional carbon material, the middle layer includes a two-dimensional carbon material and the top layer includes a one-dimensional carbon material. The thicknesses of the bottom layer, middle layer, and top layer are H3, H2, and H1, respectively, satisfying: H1:H2:H3=(0.5-2):(1-3):(5-10).

2. The negative electrode sheet according to claim 1, characterized in that, H1, H2, and H3 satisfy the following: H1:H2:H3 = 1:(1-2):(7-9); And / or, H1, H2, H3 satisfy: 50μm≤H1+H2+H3≤300μm; 5μm≤H1≤30μm, 10μm≤H2≤70μm, 25μm≤H3≤200μm.

3. The negative electrode sheet according to claim 1, characterized in that, The one-dimensional carbon material includes at least one of carbon nanowires, carbon nanofibers, and graphene nanoribbons; And / or, the two-dimensional carbon material includes at least one of graphene, expanded graphite, and artificial graphite; And / or, the three-dimensional carbon material includes at least one of graphene aerogel, graphite foam, and spherical graphite.

4. The negative electrode sheet according to claim 1, characterized in that, The length of the one-dimensional carbon material is Lnm and the diameter is Rnm, wherein L and R satisfy: 50≤L / R≤150.

5. The negative electrode sheet according to claim 4, characterized in that, The L and R satisfy the following conditions: 500nm≤L≤2000nm; 3nm≤R≤40nm.

6. The negative electrode sheet according to claim 1, characterized in that, The Raman spectrum of the two-dimensional carbon material has a peak intensity ratio of Id / Ig, where Id / Ig satisfies: 0.1≤Id / Ig≤0.8; the lateral dimension of the two-dimensional carbon material is X, where X satisfies: 0.5μm≤X≤10μm.

7. The negative electrode sheet according to claim 1, characterized in that, The specific surface area of ​​the three-dimensional carbon material is 20-100 m². 2 / g, with a porosity of 20-60% and a compressive strength of 2.0-3.5t / g.

8. The negative electrode sheet according to claim 1, characterized in that, The total compaction density of the negative electrode sheet is P, and P satisfies: 1.6 g / cm³ 3 ≤P≤1.9g / cm 3 .

9. An electrochemical device, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-8.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.

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