Anode electrode and electrochemical device

Abstract

The application discloses an anode pole piece and an electrochemical device, and relates to the field of electrochemical energy storage. The anode pole piece comprises at least two of a bottom active layer, a middle active layer and a top active layer, the surface density of holes in the bottom active layer, the middle active layer and the top active layer increases in turn, and the average pore diameter of the holes in the bottom active layer, the middle active layer and the top active layer is 5%-10%, 15%-20% and 25%-30% of the Dv50 particle size of the active material respectively. By controlling the hole density and the gradient increase of the pore diameter from inside to outside in the anode active layer, the application is beneficial to improving the liquid retention and inhibiting the volume expansion, promoting the gradual infiltration of the electrolyte, optimizing the transmission channel of lithium ions, improving the lithium ion transmission rate and the discharge capacity, and improving the lithium precipitation performance and the cycle life of the battery as a whole.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage, and more particularly to anode plates and electrochemical devices. Background Technology

[0002] Currently, lithium-ion battery electrode structures mainly employ traditional coated electrodes, such as directly coating a mixture of active materials, conductive agents, and binders onto the current collector. With the increasing demand for high energy density and high power density in batteries, continuous exploration and optimization of electrode structures are needed to improve lithium-ion transport efficiency. However, electrode structures still have many limitations in lithium-ion channel construction, making it difficult to meet the ever-growing performance requirements.

[0003] The main technical challenge in electrode structure lies in the increasing compaction density of lithium-ion battery electrodes, which leads to smaller and smaller internal pores. Simultaneously, the reduced porosity of the electrolyte, coupled with the poor electrolyte retention of silicon-doped cells, results in insufficient electrolyte retention, hindering the rapid migration of lithium ions and failing to effectively guarantee the battery's cycle life and overall performance. Summary of the Invention

[0004] This invention provides an anode electrode and an electrochemical device. By containing a large number of pores in the anode active layer, the liquid retention of the electrode electrolyte is effectively improved, while also reserving expandable space to buffer the volume expansion of the electrode during cycling and reduce lithium plating. At the same time, controlling the pore density and pore size of the anode active layer to increase gradually from the inside to the outside can improve the effect of electrolyte penetration and optimize the lithium ion transport channels, thereby improving the lithium ion transport rate and discharge capacity, and improving the overall lithium plating performance and cycle life of the electrochemical device.

[0005] To address the aforementioned technical problems, one objective of this invention is to provide an anode electrode, comprising a current collector and an anode active layer. The anode active layer includes at least two of a bottom active layer, a middle active layer, and a top active layer, which are sequentially stacked away from the current collector. Each of the bottom, middle, and top active layers includes pores, with the areal density of the pores in the bottom active layer being 1.3 × 10⁻⁶. 6 ~2.2×10 6 pcs / cm 3 The areal density of the pores in the central active layer is 1.7 × 10⁻⁶. 6 ~2.8×10 6 pcs / cm 3 The areal density of the pores in the top active layer is 2.2 × 10⁻⁶. 6 ~3.0×10 6 pcs / cm 3 ; The average pore size of the pores in the bottom active layer, middle active layer, and top active layer satisfies the following relationship: 5% × S ≤ B 底 ≤10%×S; 15%×S≤B 中 ≤20%×S; 25%×S≤B 顶 ≤30%×S; In the formula, B 底 B represents the average pore size in the bottom active layer. 中 B represents the average pore size of the agent in the middle active layer. 顶 denoted as the average pore size in the top active layer; S is the Dv50 particle size of the active material in the bottom, middle, or top active layer.

[0006] In some embodiments, S is the Dv50 particle size of the active material in the bottom or middle active layer that is in contact with the current collector.

[0007] In some embodiments, the active materials in the bottom active layer, the middle active layer and the top active layer are each independent and include at least one of carbon-based materials, tin-based materials and silicon-based materials.

[0008] In some embodiments, the active materials in the bottom active layer and the middle active layer comprise 5%-50% silicon-based material and the balance carbon-based material by mass; the active materials in the top active layer comprise carbon-based material.

[0009] In some embodiments, the silicon-based material comprises porous amorphous carbon and / or porous crystalline material, and silicon and / or silicon oxide, wherein the silicon and / or silicon oxide is supported in the porous amorphous carbon and / or porous crystalline material.

[0010] In some embodiments, the carbon-based compound includes at least one of natural graphite, artificial graphite, surface-modified natural graphite, hard carbon, soft carbon, and mesophase carbon microspheres.

[0011] In some embodiments, the tin-based material includes at least one of Sn, SnO2, and SnO.

[0012] In some embodiments, the silicon-based material includes at least one of Si materials, silicon-carbon composite materials, silicon-nitrogen composite materials, and silicon-oxygen composite materials.

[0013] In some embodiments, the bottom active layer, the middle active layer, and the top active layer are all formed by drying a slurry comprising a pore-forming agent and active materials. The slurry of the bottom active layer comprises a pore-forming agent comprising 0.5%-1% of the total mass of the active materials in the anode active layer, the slurry of the middle active layer comprises a pore-forming agent comprising 1.5%-2% of the total mass of the active materials in the anode active layer, and the slurry of the top active layer comprises a pore-forming agent comprising 2.5%-3% of the total mass of the active materials in the anode active layer.

[0014] In some embodiments, the Dv50 particle size of the pore-forming agent in the slurry of the bottom active layer, middle active layer, and top active layer satisfies the following relationship: 5%×S≤D 底 ≤10%×S; 15%×S≤D 中 ≤20%×S; 25%×S≤D 顶 ≤30%×S; In the formula, D 底 Dv50 particle size of the pore-forming agent in the slurry of the bottom active layer; D 中 Dv50 particle size of the pore-forming agent in the slurry of the middle active layer; D 顶 denoted as Dv50 particle size of the pore-forming agent in the slurry of the top active layer; S is the Dv50 particle size of the active material in the bottom active layer, middle active layer, or top active layer.

[0015] In some embodiments, the pore-forming agent includes at least one selected from iodine, camphor, naphthalene, p-dichlorobenzene, hexachloroethane, anthracene, and phenanthrene.

[0016] In some embodiments, the slurry baking temperature of the bottom active layer, the middle active layer and the top active layer is 80-150 °C.

[0017] In some embodiments, the Dv50 particle size of the active material in the bottom active layer, middle active layer and top active layer is independent and ranges from 6 to 20 μm.

[0018] In some embodiments, the Dv50 particle size of the active material in the bottom active layer is 6-8 μm; the Dv50 particle size of the active material in the middle active layer is 9-12 μm; and the Dv50 particle size of the active material in the top active layer is 14-16 μm.

[0019] In some embodiments, the thicknesses of the bottom active layer, the middle active layer, and the top active layer are each independent and are 20-30 μm.

[0020] In some embodiments, the thickness of the anodic active layer is 40-90 μm.

[0021] To address the aforementioned technical problems, a second objective of this invention is to provide an electrochemical device, including an anode plate.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. This application contains a large number of pores in the anode active layer to store electrode liquid, thereby increasing the liquid retention capacity and reducing lithium plating. The pores can also serve as expandable spaces to buffer volume expansion. At the same time, by controlling the pore density and pore size to gradually increase from the inside to the outside in different active layers, it can not only effectively help the electrolyte to gradually and fully penetrate from the outside to the inside, but also optimize the lithium ion transport channels, improve the lithium ion transport rate and discharge capacity, thereby improving the overall lithium plating performance and cycle life of the electrochemical device.

[0023] 2. This application employs a gradient design of pore-forming agents with different contents and particle sizes in different active layers. After high-temperature baking, the agents can be completely volatilized to form a gradient increase in pore density and pore size in different active layers, thereby optimizing the lithium-ion transport channels in the anode electrode. The pore-forming agents can be completely volatilized and leave no residue during the baking process in the cell manufacturing process. This not only saves pore construction process steps but also avoids the side reaction effects between the anode and the electrode liquid. The preparation process is simple, and the lithium-ion batteries used in the anode electrode have excellent overall performance. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the anode electrode structure in Embodiment 1 of the present invention; The reference numerals in the accompanying drawings are as follows: 1. Anode current collector; 2. Bottom active layer; 3. Middle active layer; 4. Top active layer; 5. Hole. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0028] As used in this article: In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0029] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0030] In the description of this invention, it should be understood that the terms "upper", "lower", "left", "right", "top", "bottom", etc., indicating orientation or positional relationship are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0031] The term "D50" refers to the diameter of the particles that occupy 50% of the volume when the particles are arranged in ascending order of diameter. It means that particles with a diameter greater than or less than this value each account for 50%, and is also known as the median diameter or median particle size.

[0032] The term "pore-forming agent" refers to an additive that forms a porous structure inside a material through decomposition to generate gas or dissolution and removal. It is classified into organic pore-forming agents, inorganic pore-forming agents, and composite pore-forming agents. The content and particle size of the pore-forming agent directly affect the porosity, pore size, and mechanical properties.

[0033] This application provides an anode electrode, including a current collector and an anode active layer. The anode active layer includes at least two of a bottom active layer, a middle active layer, and a top active layer, which are stacked sequentially away from the current collector. Each of the bottom, middle, and top active layers includes pores, and the areal density of the pores in the bottom active layer is 1.3 × 10⁻⁶. 6 ~2.2×10 6 pcs / cm 3 The areal density of the pores in the central active layer is 1.7 × 10⁻⁶. 6 ~2.8×10 6 pcs / cm 3 The areal density of the pores in the top active layer is 2.2 × 10⁻⁶. 6 ~3.0×106 pcs / cm 3 ; The average pore size of the pores in the bottom active layer, middle active layer, and top active layer satisfies the following relationship: 5%×S≤B 底 ≤10%×S; 15%×S≤B 中 ≤20%×S; 25%×S≤B 顶 ≤30%×S; In the formula, B 底 B represents the average pore size in the bottom active layer. 中 B represents the average pore size of the agent in the middle active layer. 顶 denoted as the average pore size in the top active layer; S is the Dv50 particle size of the active material in the bottom, middle, or top active layer.

[0034] This application constructs multiple active layers in the anode active layer, forming numerous pores in different active layers. This allows for the storage of electrode electrolyte, increasing electrolyte retention and reducing lithium plating. The remaining pores also serve as expandable spaces to buffer the volume expansion during electrode cycling. Furthermore, this application controls the pore density and pore size of different active layers to increase gradually from the inside out, facilitating the gradual and thorough penetration of the electrolyte from the outside in. This prevents voids within the active layers due to insufficient electrolyte penetration, which can obstruct the continuous current path and affect battery capacity and charge / discharge efficiency. The gradient pore density and pore size also optimize lithium-ion transport channels, improving lithium-ion transport rate and discharge capacity, thereby enhancing the overall lithium plating performance and cycle life of the electrochemical device.

[0035] In some implementations, the areal density gradient of the pores in the bottom active layer, middle active layer, and top active layer increases progressively.

[0036] In some embodiments, the areal density of the pores in the bottom active layer is 1.3 × 10⁻⁶. 6 pcs / cm 3 1.4×10 6 pcs / cm 3 1.5×10 6 pcs / cm 3 1.6×10 6 pcs / cm 3 1.7×10 6 pcs / cm 3 1.8×10 6 pcs / cm 3 1.9×10 6 pcs / cm 3 2.0×10 6 pcs / cm 3 2.1×10 6 pcs / cm3 2.2×10 6 pcs / cm 3 The range of values ​​between any one of them or any two of them.

[0037] In some embodiments, the areal density of the pores in the central active layer is 1.7 × 10⁻⁶. 6 pcs / cm 3 1.8×10 6 pcs / cm 3 1.9×10 6 pcs / cm 3 2.0×10 6 pcs / cm 3 2.1×10 6 pcs / cm 3 2.2×10 6 pcs / cm 3 2.3×10 6 pcs / cm 3 2.4×10 6 pcs / cm 3 2.5×10 6 pcs / cm 3 2.6×10 6 pcs / cm 3 2.7×10 6 pcs / cm 3 2.8×10 6 pcs / cm 3 The range of values ​​between any one of them or any two of them.

[0038] In some embodiments, the areal density of the pores in the top active layer is 2.2 × 10⁻⁶. 6 pcs / cm 3 2.3×10 6 pcs / cm 3 2.4×10 6 pcs / cm 3 2.5×10 6 pcs / cm 3 2.6×10 6 pcs / cm 3 2.7×10 6 pcs / cm 3 2.8×10 6 pcs / cm 3 2.9×10 6 pcs / cm 3 3.0×10 6 pcs / cm 3 The range of values ​​between any one of them or any two of them.

[0039] It should be noted that the areal density of the pores in the bottom, middle, and top active layers was measured using scanning electron microscopy (SEM), including the following steps: (1) The cross section of the electrode sample was photographed by SEM to obtain a high-resolution secondary electron image. The pores appeared as black areas in the image, and the active material and conductive agent appeared as gray / white clumps. (2) Use image processing software to binarize the SEM image, set the holes to black and the solid material to white. The software can automatically identify and count the number, area, perimeter, etc. of the black area (holes). (3) Calculation of pore density: Count the number of pores in the image area (known area) to directly calculate "pores / square micrometer" or "pores / square centimeter".

[0040] In some embodiments, the average pore size B of the slurry in the bottom active layer 底 It is a range of values ​​between any one of 5%×S, 6%×S, 7%×S, 8%×S, 9%×S, and 10%×S.

[0041] In some embodiments, the average pore size B of the slurry in the central active layer 中 It is a range of values ​​between any one of 15%×S, 16%×S, 17%×S, 18%×S, 19%×S, and 20%×S.

[0042] In some embodiments, the average pore size B of the slurry in the top active layer 顶 It is a range of values ​​between any one of 25%×S, 26%×S, 27%×S, 28%×S, 29%×S, and 30%×S.

[0043] This application controls the pore size of the pores in different active layers of the anode to increase gradually from the inside to the outside, with the bottom active layer having a smaller pore size than the outer layer. This helps the electrolyte to gradually and fully penetrate from the outside to the inside, preventing voids in the internal pores of the active layer due to insufficient electrolyte penetration rate. This improves the absorption efficiency of the electrolyte, increases the electrolyte retention capacity, and also optimizes the lithium-ion transport channels, improving the lithium-ion transport rate and enhancing the lithium plating performance and cycle stability of the cell. In addition, the bottom active layer also provides mechanical support to maintain the stability of the active layer structure during cycling.

[0044] It should be noted that the average pore size of the pores in the bottom, middle, and top active layers was determined using mercury intrusion porosimetry, including the following steps: Electrode samples with individually coated bottom, middle, or top active layers are placed in a dedicated sample tube. Under vacuum, pressure is gradually applied to the system to force mercury into the pores. The instrument records the volume of mercury entering at different pressures. Based on the relationship between pressure and the amount of mercury entering, the pore size and pore size distribution at the bottom can be directly obtained.

[0045] In some embodiments, S is the Dv50 particle size of the active material in the bottom or middle active layer that is in contact with the current collector.

[0046] This application adjusts the particle size of the pore-forming agent in different layers based on the particle size of the active material in the bottommost active layer closest to the current collector. This is because the particle size of the active material in the bottommost active layer is usually set to be larger or equivalent to that in the middle and top active layers. Designing the particle size of the pore-forming agent based on the active material with a larger particle size can ensure that the pore size formed after baking and volatilization is larger, thereby improving wettability.

[0047] In some embodiments, the active materials in the bottom active layer, the middle active layer, and the top active layer are each independent and include at least one of carbon-based materials, tin-based materials, and silicon-based materials.

[0048] In some embodiments, the active materials in the bottom and middle active layers comprise 5%-50% by mass of silicon-based materials and the remainder of carbon-based materials; the active materials in the top active layer comprise carbon-based materials.

[0049] In some embodiments, the mass fraction of silicon-based material in the active materials of the bottom active layer and the middle active layer is any one or a range between any two of 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, and 50%.

[0050] In some embodiments, the silicon-based material comprises porous amorphous carbon and / or porous crystalline material, and silicon and / or silicon oxide, wherein the silicon and / or silicon oxide is supported in the porous amorphous carbon and / or porous crystalline material.

[0051] In some embodiments, the carbon-based compound includes at least one of natural graphite, artificial graphite, surface-modified natural graphite, hard carbon, soft carbon, and mesophase carbon microspheres.

[0052] In some embodiments, the tin-based material includes at least one of Sn, SnO2, and SnO.

[0053] In some embodiments, the silicon-based material includes at least one of Si materials, silicon-carbon composite materials, silicon-nitrogen composite materials, and silicon-oxygen composite materials.

[0054] In some embodiments, the bottom active layer, the middle active layer, and the top active layer are all formed by drying a slurry comprising a pore-forming agent and active materials. The slurry of the bottom active layer comprises a pore-forming agent comprising 0.5%-1% of the total mass of the active materials in the anode active layer, the slurry of the middle active layer comprises a pore-forming agent comprising 1.5%-2% of the total mass of the active materials in the anode active layer, and the slurry of the top active layer comprises a pore-forming agent comprising 2.5%-3% of the total mass of the active materials in the anode active layer.

[0055] In some embodiments, the Dv50 particle size of the pore-forming agent in the slurry of the bottom active layer, middle active layer, and top active layer satisfies the following relationship: 5%×S≤D 底 ≤10%×S; 15%×S≤D 中 ≤20%×S; 25%×S≤D 顶 ≤30%×S; In the formula, D 底 Dv50 particle size of the pore-forming agent in the slurry of the bottom active layer; D 中 Dv50 particle size of the pore-forming agent in the slurry of the middle active layer; D 顶 S represents the Dv50 particle size of the pore-forming agent in the slurry of the top active layer; S represents the Dv50 particle size of the active material in the bottom active layer, middle active layer, or top active layer. In some embodiments, the pore-forming agent includes at least one of iodine, camphor, naphthalene, p-dichlorobenzene, hexachloroethane, anthracene, and phenanthrene.

[0056] In some embodiments, the slurry baking temperature for the bottom active layer, the middle active layer, and the top active layer is 80-150 °C.

[0057] In some embodiments, the baking temperature of the slurry for the bottom active layer, the middle active layer, and the top active layer is any one or a range between any two of 80 ℃, 85 ℃, 90 ℃, 95 ℃, 100 ℃, 105 ℃, 110 ℃, 115 ℃, 120 ℃, 125 ℃, 130 ℃, 135 ℃, 140 ℃, 145 ℃, and 150 ℃.

[0058] In some embodiments, the pore-forming agent in the slurry of the bottom active layer accounts for any one or any two of the following values: 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1% of the total mass of the active material in the anode active layer.

[0059] In some embodiments, the pore-forming agent in the slurry of the middle active layer accounts for any one or any two of the following values: 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2% of the total mass of the active material in the anode active layer.

[0060] In some embodiments, the pore-forming agent in the slurry of the top active layer accounts for any one or any two of the range of 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, and 3% of the total mass of the active material in the anode active layer.

[0061] This application controls the content and particle size of the pore-forming agent in different active layers of the anode active layer to increase gradually from the inside to the outside. After the pore-forming agent is volatilized by high-temperature baking, a large number of pores will remain in the active layer. The pore density and pore size of the active layer at the bottom are lower than those on the outside, which can help the electrolyte to gradually and fully penetrate from the outside to the inside and optimize the lithium ion transport channel, reduce the existence of internal voids. At the same time, the lower porosity of the bottom active layer can also provide mechanical support to maintain the stability of the active layer structure during cycling.

[0062] It should be noted that the pore-forming agent content in the slurry of the bottom active layer, middle active layer, and top active layer was tested using the ethanol release-ultraviolet spectrophotometry method. The pore-forming agent in the ethanol-released coating can be determined by reading the solution concentration through the absorption peak, and the pore-forming agent content in the sample can be calculated. The specific steps include: (1) Standard curve: Prepare an ethanol solution containing pore-forming agent of 0-60 mg / L, scan UV-Vis, take the absorbance at λmax = 290nm, and plot the Ac standard curve (linear range above 0.999). (2) Sample release: Weigh 30 mg of sample, add 10 mL of anhydrous ethanol, shake at 25 °C in the dark for 2 h, then centrifuge to collect the supernatant and record the volume as V (L); (3) Measure the A value at 290 nm in the supernatant and substitute it into the Ac standard curve to obtain the concentration c (mg / L); (4) Calculate the mass of pore-forming agent (mg) according to the following formula: c × V (L) × dilution factor; Pore-forming agent content (wt%) = (pore-forming agent mass / sample mass) × 100; repeated 3 times, RSD < 3%.

[0063] It should be noted that the Dv50 particle size of the pore-forming agent in the slurry of the bottom active layer, middle active layer, and top active layer is determined by laser diffraction or scanning electron microscopy to measure the particle size distribution. In some embodiments, the shape of the pore-forming agent in the slurry of the bottom active layer, middle active layer, and top active layer includes, but is not limited to, at least one of square, rectangular, rhomboid, hexagonal, circular, and irregular shapes.

[0064] In some embodiments, the Dv50 particle size of the active material in the bottom active layer, middle active layer and top active layer is independent and ranges from 6 to 20 μm.

[0065] In some embodiments, the Dv50 particle size of the active material in the bottom active layer, the middle active layer and the top active layer are each independent and are within the range of any one or any two of 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm and 20 μm.

[0066] In some embodiments, the Dv50 particle size of the active material in the bottom active layer is 6-8 μm; the Dv50 particle size of the active material in the middle active layer is 9-12 μm; and the Dv50 particle size of the active material in the top active layer is 14-16 μm.

[0067] This application controls the particle size of the active material in different active layers of the anode active layer to increase in a gradient from the inside to the outside, which can form a more suitable particle size difference with the particle size of the corresponding pore-forming agent. During preparation, the small-particle-size pore-forming agent can coat the surface of the large-particle-size active material to achieve uniform dispersion. This can avoid the excessive particle size difference between the pore-forming agent and the active layer, which would lead to uneven accumulation and dispersion, resulting in uneven pore distribution and affecting the transport and cycling performance of lithium ions.

[0068] It should be noted that the Dv50 particle size of the active materials in the bottom active layer, middle active layer and top active layer was measured using laser diffraction.

[0069] In some implementations, the thicknesses of the bottom active layer, the middle active layer, and the top active layer are each independent and are 20-30 μm.

[0070] In some embodiments, the thicknesses of the bottom active layer, the middle active layer, and the top active layer are each independent and are within the range of any one or any two of 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, and 30 μm.

[0071] In some embodiments, the thickness of the anolyte active layer is 40-90 μm.

[0072] In some embodiments, the thickness of the anolyte active layer is any one or a range between any two of 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, and 90 μm.

[0073] It should be noted that the thicknesses of the bottom active layer, middle active layer, top active layer, and anolyte active layer were all measured using two-dimensional microscopy or scanning electron microscopy (SEM).

[0074] In some embodiments, the current collector is a metal foil, preferably a copper foil.

[0075] In some embodiments, the bottom active layer, the middle active layer, and the top active layer include a main material, which includes an active material, a conductive agent, and a binder.

[0076] In some embodiments, the main materials of the bottom active layer, the middle active layer and the top active layer are each independent and include 86%-99% active material, 0.5%-5.9% binder, 0.3%-4.7% conductive agent and 0.2%-4% dispersant by mass fraction.

[0077] In some embodiments, the conductive agent includes, but is not limited to, at least one of conductive carbon black, graphite, expanded graphite, graphene, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanofibers, carbon nanotubes, activated carbon, and mesoporous carbon.

[0078] In some embodiments, the adhesive includes, but is not limited to, at least one of 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.

[0079] This application also provides a method for preparing an anode electrode, including the following steps: Active materials, conductive agents, binders, and pore-forming agents are mixed in proportions for the bottom active layer, middle active layer, and top active layer, and then dissolved evenly in water to obtain bottom active layer slurry, middle active layer slurry, and top active layer slurry, respectively. The bottom active layer slurry, middle active layer slurry, and top active layer slurry are sequentially coated on the surface of the current collector and baked dry to form the bottom active layer, middle active layer, and top active layer, respectively. After cold pressing and slitting, the anode electrode is prepared.

[0080] In some implementations, the baking temperature is 80-150 °C.

[0081] This application also provides an electrochemical device, including an anode plate.

[0082] In some embodiments, a cathode electrode, a diaphragm, and an electrolyte are also included.

[0083] In some embodiments, the electrochemical device includes any apparatus in which an electrochemical reaction occurs to interconvert chemical energy into electrical energy, and specific, non-limiting examples include all types 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.

[0084] 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.

[0085] To further illustrate the present invention, the following detailed description is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention. Unless otherwise specified, the raw materials used in the following embodiments and comparative examples are all commercially available, and the same raw materials were used in parallel experiments.

[0086] Example 1 Anode plate, such as Figure 1 As shown, it includes an anode current collector and an anode active layer disposed on both sides of the current collector. The anode current collector is a copper foil. The anode active layer includes a bottom active layer, a middle active layer and a top active layer stacked sequentially along the direction away from the current collector. The thickness of the bottom active layer, the middle active layer and the top active layer is 20 μm. The bottom active layer, middle active layer, and top active layer are all formed by baking a slurry containing the main material and a pore-forming agent at 130 °C. The pore-forming agent in the slurry of the bottom active layer, middle active layer, and top active layer is iodine. The main material includes 98.2% active material, 0.4% carbon nanotubes, 0.8% styrene-butadiene rubber, and 0.6% sodium hydroxymethyl cellulose dispersant. The active material in the bottom active layer includes 15% silicon carbide and the balance graphite, the active material in the middle active layer includes 15% silicon carbide and the balance graphite, and the active material in the top active layer includes graphite. The content of pore-forming agent in the slurry of the bottom active layer, middle active layer, and top active layer satisfies the following relationship: M 底 =0.5%×H,M 中 =1.5%×H; M 顶 =2.5%×H; where M底 M represents the content of pore-forming agent in the bottom active layer slurry; 中 M represents the content of pore-forming agent in the middle active layer slurry; 顶 H represents the content of pore-forming agent in the top active layer slurry; H represents the total mass of active materials in the anode active layer. The Dv50 particle size of the active material in the bottom active layer is S 底 The Dv50 particle size of the active material in the middle active layer is S 中 The Dv50 particle size of the top active material is S 顶 S 底 S 中 S 顶 All are 10 μm; The Dv50 particle size of the pore-forming agent in the bottom active layer, middle active layer, and top active layer slurry satisfies the following relationship: D 底 =5%×S,D 中 =15%×S;D 顶 =25%×S; where D is the formula. 底 Dv50 particle size of the pore-forming agent in the bottom active layer slurry; D 中 Dv50 particle size of the pore-forming agent in the middle active layer slurry; D 顶 Dv50 is the particle size of the pore-forming agent in the top active layer slurry; S is S 底 .

[0087] The above-mentioned method for preparing the anode electrode includes the following steps: Active materials, carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, and pore-forming agents are mixed in proportions for the bottom active layer, middle active layer, and top active layer, respectively. Then, they are dissolved evenly in deionized water to obtain bottom active layer slurry, middle active layer slurry, and top active layer slurry with a solid content of 40%. The bottom active layer slurry, middle active layer slurry, and top active layer slurry are sequentially coated on the surface of copper foil and baked and dried at 130 °C to form the bottom active layer, middle active layer, and top active layer, respectively. After cold pressing and slitting, the anode electrode is prepared.

[0088] Example 2-3 The anode electrode differs from that in Example 1 in that the content of the pore-forming agent M in the bottom active layer slurry is [not specified]. 底 The content of pore-forming agent M in the middle active layer slurry 中 The content of pore-forming agent M in the top active layer slurry 顶 The differences are used to change the areal density of the pores in the bottom active layer, middle active layer and top active layer.

[0089] Examples 4-5 The anode electrode differs from that in Example 1 in that the Dv50 particle size D of the pore-forming agent in the bottom active layer slurry is... 底 The Dv50 particle size D of the pore-forming agent in the middle active layer slurry 中 The Dv50 particle size D of the pore-forming agent in the top active layer slurry 顶 The differences are used to change the areal density of the pores in the bottom active layer, middle active layer and top active layer.

[0090] Example 6 The anode electrode differs from that in Example 1 in that the Dv50 particle size S of the active material in the bottom active layer is... 底 The Dv50 particle size S of the active material in the middle active layer 中 The Dv50 particle size S of the active material in the top active layer 顶 The differences are used to change the areal density of the pores in the bottom active layer, middle active layer and top active layer.

[0091] Examples 7-8 The anode electrode differs from that in Example 1 in that the Dv50 particle size S of the active material in the bottom active layer is... 底 The Dv50 particle size S of the active material in the middle active layer 中 and the Dv50 particle size S of the active material in the top active layer 顶 And S is different, so as to achieve the change of the areal density of the pores in the bottom active layer, the middle active layer and the top active layer.

[0092] Example 9 The anode electrode differs from that in Example 1 in that camphor is used as the pore-forming agent in the bottom active layer, middle active layer, and top active layer slurry.

[0093] Example 10 The anode electrode differs from that in Example 1 in that the pore-forming agent in the bottom active layer, middle active layer and top active layer slurry is naphthalene.

[0094] Example 11 The anode electrode differs from that in Example 1 in that the thickness of the bottom active layer is 0, while the thicknesses of the middle and top active layers are both 30 μm, and S is S. 中 .

[0095] Example 12 The anode electrode differs from that in Example 1 in that the thickness of the middle active layer is 0, while the thicknesses of the bottom and top active layers are both 30 μm.

[0096] Example 13 The anode electrode differs from that in Example 1 in that the thickness of the top active layer is 0, while the thicknesses of the bottom and middle active layers are both 30 μm.

[0097] Example 14 The anode electrode differs from that in Example 1 in that the active materials in the bottom active layer, middle active layer and top active layer all include 10% silicon carbon by mass and the remainder graphite.

[0098] Comparative Example 1 The anode electrode differs from that in Example 1 in that the content of pore-forming agent in the bottom active layer, middle active layer and top active layer slurry is 0.

[0099] Comparative Examples 2-4 The anode electrode differs from that in Example 1 in that the content of the pore-forming agent M in the bottom active layer slurry is [not specified]. 底 The content of pore-forming agent M in the middle active layer slurry 中 The content of pore-forming agent M in the top active layer slurry 顶 The differences are used to change the areal density of the pores in the bottom active layer, middle active layer and top active layer.

[0100] Comparative Examples 5-7 The anode electrode differs from that in Example 1 in that the Dv50 particle size D of the pore-forming agent in the bottom active layer slurry is... 底 The Dv50 particle size D of the pore-forming agent in the middle active layer slurry 中 The Dv50 particle size D of the pore-forming agent in the top active layer slurry 顶 The differences are used to change the areal density of the pores in the bottom active layer, middle active layer and top active layer.

[0101] Comparative Example 8 The anode electrode differs from that in Example 1 in that the content of the pore-forming agent M in the bottom active layer slurry is [not specified]. 底 The content of pore-forming agent M in the top active layer slurry 顶 The Dv50 particle size D of the pore-forming agent in the bottom active layer slurry 底 The Dv50 particle size D of the pore-forming agent in the top active layer slurry 顶 The differences are used to change the areal density of the pores in the bottom active layer, middle active layer and top active layer.

[0102] The pore density of the bottom active layer and the content of pore-forming agent in the slurry of the anode plates in the above embodiments and comparative examples are M. 底 And the Dv50 particle size D of the pore-forming agent 底 The pore density of the middle active layer and the content of pore-forming agent in the slurry (M) 中 And the Dv50 particle size D of the pore-forming agent 中The pore density of the top active layer and the content of pore-forming agent in the slurry (M) 顶 And the Dv50 particle size D of the pore-forming agent 顶 The Dv50 particle size S of the active material in the bottom active layer 底 The Dv50 particle size S of the active material in the middle active layer 中 The Dv50 particle size S of the active material in the top active layer 顶 Both S are shown in Table 1 below.

[0103] Table 1 - Parameter settings of the anode plates in the embodiments and comparative examples of this application The anode plates prepared in the above embodiments and comparative examples are used to assemble electrochemical devices, including the following steps: (1) Lithium cobalt oxide, acetylene black, carbon nanotubes and polyvinylidene fluoride were mixed in a mass ratio of 97.6:0.7:0.5:1.2 and fully dissolved in N-methylpyrrolidone solvent to obtain a cathode paste with a solid content of 74%. The cathode paste was uniformly coated on aluminum foil, baked at 120 °C, and then cold-pressed and slit to prepare a cathode electrode sheet. (2) Mix ethylene carbonate, propylene carbonate, diethyl carbonate and propyl propionate in a volume ratio of 1:1:3:3 to obtain a mixed solvent, dissolve lithium salt LiPF6 in the mixed solvent at a concentration ratio of 1 mol / L to prepare an electrolyte. (3) The cathode electrode, separator and anode electrode are wound together to form a bare cell. The separator is a PE film with a ceramic coating on the surface. Then, the electrolyte is injected and sealed. After vacuum sealing, standing, formation, degassing and trimming, the cell is prepared.

[0104] Performance testing 1. Cyclic Capacity Retention Rate Test: The cells assembled with anode plates from the examples and comparative examples were subjected to cyclic charge-discharge tests. The charging mode was constant current charging at 2 C to 4.5 V, followed by constant voltage charging to 0.05 C; the discharging mode was constant current discharging at 0.7 C to 3.0 V. The test ended when the capacity retention rate was 80%, and the number of cycles at this time was recorded. The test results are shown in Table 2 below.

[0105] 2. Discharge capacity test: The cells assembled with anode plates of the examples and comparative examples were charged and discharged according to the following method: constant current charging at 0.5 C to 4.5 V, followed by constant voltage charging to 0.05 C cutoff; then constant current discharging at 0.2 C to 3.0 V cutoff. The discharge capacity was tested and the test results are shown in Table 2 below.

[0106] 3. Lithium plating window test: The cells assembled with the anode plates of the examples and comparative examples were subjected to cyclic charge and discharge at room temperature. They were charged with a constant current of 2-4 C to 4.5 V, then charged with a constant voltage to 0.05 C; and then discharged with a constant current of 1 C to 3.0 V. The charge and discharge cycle was repeated for 20 cycles. The charging current at which lithium plating first appeared during the cyclic charge and discharge with a current window of 2-4 C can be used as the lithium plating window of the battery. The test results are shown in Table 2 below.

[0107] Table 2 - Performance test results of the anode electrode assembled cells of the embodiments and comparative examples of this application As shown in Table 2, in Example 1 of this application, a pore-forming agent is doped into the anode active layer. After baking and volatilization, the remaining pores can store the electrolyte, increasing the electrolyte retention and reducing lithium plating. The remaining pores can also serve as expandable spaces to buffer volume expansion. Simultaneously, controlling the pore-forming agent content and particle size of different active layers with a gradient increase from the inside to the outside not only effectively helps the electrolyte gradually and fully penetrate from the outside to the inside, but also optimizes the lithium-ion transport channels, improving the lithium-ion transport rate and discharge capacity, thereby comprehensively improving the lithium plating performance and cycle life of the electrochemical device. In contrast, the anode active layer of Comparative Example 1 is not doped with a pore-forming agent. After high-temperature baking, it cannot form pores through volatilization. Therefore, the electrolyte retention of the anode electrode is low, resulting in severe lithium plating after long cycles, a low lithium plating window, and the electrode does not build pores to improve lithium-ion transport efficiency, leading to low discharge capacity and low cycle life.

[0108] In Comparative Examples 2-3, the particle size of the pore-forming agent in different active layers increases from the inside out. Unlike Example 1, in Comparative Example 2, the content of the pore-forming agent in each active layer is consistent. After high-temperature baking, the pore density remaining after the pore-forming agent volatilizes in different active layers is basically the same. Due to the limited permeation rate of the electrolyte in the active layer, when the electrolyte permeates from the outside in, the insufficient permeation rate leads to voids inside the active layer. These voids block the continuous current path, thus affecting the battery's discharge capacity and cycle capacity retention. In Comparative Example 3, the content of the pore-forming agent in different active layers decreases from the inside out, resulting in an even lower permeation rate of the electrolyte from the outside in. The voids in the bottom active layer are difficult to completely fill with electrolyte, and the existing voids reduce the battery's discharge capacity and cycle performance.

[0109] Compared to Example 1, in Comparative Example 4, the content of pore-forming agent in different active layers increases from the inside to the outside, but the content of pore-forming agent in different layers is too high. In Comparative Example 7, the particle size of pore-forming agent in different active layers increases from the inside to the outside, but the particle size of pore-forming agent in different layers is too large. Ultimately, this results in excessive pore density or excessive pore size left by the volatilization of the anode active layers after high-temperature baking in Comparative Examples 4 and 7, leading to excessive capacity loss and affecting the overall mechanical support strength of the anode active layer. The electrode is prone to collapse, which squeezes the electrolyte, exacerbates lithium plating, and reduces the discharge capacity and cycle capacity retention rate simultaneously.

[0110] In Comparative Examples 5-6, the pore-forming agent content in different active layers increases from the inside out. Unlike Example 1, in Comparative Example 5, the particle size of the pore-forming agent in each active layer is uniform, resulting in identical pore sizes after high-temperature baking and subsequent volatilization. However, the pore size of the top active layer in Comparative Example 5 is smaller than that in Example 1, leading to lower electrolyte absorption efficiency and slower lithium-ion migration rate, thus reducing the rate capability. In Comparative Example 6, the particle size of the pore-forming agent in different active layers decreases from the inside out. Smaller external pore sizes hinder electrolyte penetration, while larger internal pore sizes result in incomplete electrode liquid penetration, potentially disrupting the conductive network. Furthermore, poor internal support makes lithium deposition more likely in later stages of cycling, leading to a sharp decrease in cycle capacity.

[0111] Compared to Example 1, the content and particle size of the pore-forming agent in different active layers of Comparative Example 8 are the same. Since the electrolyte has a limited penetration rate on the active layer, it cannot fully fill the internal pores in a short time when the electrolyte penetrates from the outside to the inside. The presence of voids inside the active layer will block the continuous path of the current, thereby affecting the discharge capacity and cycle capacity retention rate of the battery.

[0112] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. An anode plate, characterized in that, The device includes a current collector and an anode active layer. The anode active layer comprises at least two of a bottom active layer, a middle active layer, and a top active layer, which are stacked sequentially away from the current collector. Each of the bottom, middle, and top active layers includes pores, and the areal density of the pores in the bottom active layer is 1.3 × 10⁻⁶. 6 ~2.2×10 6 pcs / cm 3 The areal density of the pores in the central active layer is 1.7 × 10⁻⁶. 6 ~2.8×10 6 pcs / cm 3 The areal density of the pores in the top active layer is 2.2 × 10⁻⁶. 6 ~3.0×10 6 pcs / cm 3 ; The average pore size of the pores in the bottom active layer, middle active layer, and top active layer satisfies the following relationship: 5% × S ≤ B 底 ≤10%×S; 15%×S≤B 中 ≤20%×S; 25%×S≤B 顶 ≤30%×S; In the formula, B 底 B represents the average pore size in the bottom active layer. 中 B represents the average pore size of the agent in the middle active layer. 顶 denoted as the average pore size in the top active layer; S is the Dv50 particle size of the active material in the bottom, middle, or top active layer.

2. The anode plate as described in claim 1, characterized in that, S represents the Dv50 particle size of the active material in the bottom or middle active layer that is in contact with the current collector.

3. The anode plate as described in claim 1, characterized in that, The active materials in the bottom and middle active layers include 5%-50% silicon-based materials and the remainder carbon-based materials by mass; the active materials in the top active layer include carbon-based materials.

4. The anode plate as described in claim 1, characterized in that, The bottom active layer, middle active layer, and top active layer are all formed by drying a slurry comprising a pore-forming agent and active materials. The slurry of the bottom active layer comprises a pore-forming agent comprising 0.5%-1% of the total mass of the active materials in the anode active layer. The slurry of the middle active layer comprises a pore-forming agent comprising 1.5%-2% of the total mass of the active materials in the anode active layer. The slurry of the top active layer comprises a pore-forming agent comprising 2.5%-3% of the total mass of the active materials in the anode active layer.

5. The anode plate as described in claim 4, characterized in that, The Dv50 particle size of the pore-forming agent in the slurry of the bottom active layer, middle active layer, and top active layer satisfies the following relationship: 5%×S≤D 底 ≤10%×S; 15%×S≤D 中 ≤20%×S; 25%×S≤D 顶 ≤30%×S; In the formula, D 底 Dv50 particle size of the pore-forming agent in the slurry of the bottom active layer; D 中 Dv50 particle size of the pore-forming agent in the slurry of the middle active layer; D 顶 denoted as Dv50 particle size of the pore-forming agent in the slurry of the top active layer; S is the Dv50 particle size of the active material in the bottom active layer, middle active layer, or top active layer.

6. The anode plate as described in claim 4, characterized in that, The pore-forming agent includes at least one of iodine, camphor, naphthalene, p-dichlorobenzene, hexachloroethane, anthracene, and phenanthrene.

7. The anode plate as described in claim 1, characterized in that, The Dv50 particle size of the active materials in the bottom active layer, middle active layer and top active layer are independent and range from 6 to 20 μm.

8. The anode plate as described in claim 7, characterized in that, The Dv50 particle size of the active material in the bottom active layer is 6-8 μm; the Dv50 particle size of the active material in the middle active layer is 9-12 μm; and the Dv50 particle size of the active material in the top active layer is 14-16 μm.

9. The anode plate as described in claim 1, characterized in that, The thicknesses of the bottom active layer, the middle active layer, and the top active layer are each independent and are 20-30 μm; And / or, the thickness of the anode active layer is 40-90 μm.

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

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