Anode foil based on anodized aluminum foil and method for manufacturing the same
By constructing a honeycomb-shaped nanoporous alumina layer in the negative electrode of a sodium-ion battery using anodic aluminum foil and embedding a high-energy-density phosphorus-doped material coating layer, the problems of large electrode elongation, poor adhesion and low peel strength were solved, achieving high energy density and stable battery performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING ELECTRIC VEHICLE
- Filing Date
- 2026-01-26
- Publication Date
- 2026-06-05
AI Technical Summary
Existing sodium-ion battery negative electrode sheets have excessive elongation after rolling, poor adhesion, and low peel strength, resulting in unstable cell performance. Furthermore, the theoretical specific capacity of hard carbon materials is low, making it difficult to meet the requirements for high energy density.
The negative electrode sheet is prepared by anodic aluminum foil. A honeycomb nanoporous aluminum oxide layer is constructed on the surface of the aluminum foil, and a coating layer of high specific energy phosphorus-doped material and hard carbon material is embedded. Combined with acid etching treatment, the thickness and pore size of the oxide layer are controlled, which improves the adhesion and peel strength between the electrode sheet and the current collector, while suppressing the volume expansion of the phosphorus-based material.
It significantly reduces the elongation of the electrode after rolling, improves the adhesion and peel strength between the electrode and the current collector, enhances the cycle stability and energy density of the battery, and strengthens the cycle performance and safety of the cell.
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Figure CN122158469A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of sodium-ion battery technology, specifically to a negative electrode sheet based on anodic aluminum foil and its preparation method. Background Technology
[0002] With the increasing demand for new energy vehicles, the demand for power batteries is also rising. Sodium-ion batteries, due to the advantages of sodium resources and price, are considered a highly promising electrochemical energy storage system. In sodium-ion batteries, the negative electrode, as a key component, plays a crucial role in storing and releasing sodium ions; its performance directly affects the battery's charge-discharge efficiency, cycle life, and energy density, among other core performance indicators.
[0003] However, during the development of the battery cell, the inventors discovered the following problems in the electrode preparation process: ① Due to the special morphology of hard carbon materials, the elongation of the material area is too large after the electrode is rolled. The excessive difference in elongation between the coated area and the blank area will first lead to more wrinkles after the electrode is rolled, which will affect the performance of the cell; secondly, it will lead to instability in the manufacturing process, high frequency of tape breakage, and greatly reduce production efficiency and yield.
[0004] ② Poor adhesion between the negative electrode material and the current collector leads to material loss at the edges of the electrode sheets after slitting or die-cutting processes, resulting in a high short-circuit rate after hot pressing of the electrode core. More importantly, the low peel strength causes the active electrode material to detach from the current collector during battery cycling, leading to battery failure.
[0005] ③ Hard carbon anode materials have a low theoretical specific capacity, making it difficult to match with high specific energy cathode materials to meet the requirements of high energy density sodium-ion batteries.
[0006] Patent application (CN115986062A) discloses multi-layered nanoporous gradient electrodes and their preparation methods, as well as lithium-ion batteries, such as... Figure 1 As shown (1-nanoporous layer, 2-first coating, 3-second coating, 4-uneven structure), the current collector of the electrode is anodized and reduced by argon to create a nanoporous surface, increasing the specific surface area and improving the adhesion between the current collector and the first coating slurry. By controlling the proportion of active materials in different coating layers, a concentration gradient is formed to control the energy density of the electrode, thereby improving the safety and fast-charging performance of the electrode. However, the reduction method used in this patent application uses an argon-hydrogen mixed gas to completely reduce the oxide layer, which only creates a chaotic rough surface on the aluminum foil to improve peel strength. It has no amorphous structure and the improvement effect is generally limited. At the same time, the double-layer electrode is coated using a conventional double-layer coating method, the main purpose of which is to improve the fast-charging performance of the cell by changing the areal density and compaction gradient of the upper and lower coating layers.
[0007] Based on this technical background, this invention studies a negative electrode sheet based on anodized aluminum foil and its preparation method. Summary of the Invention
[0008] To address the shortcomings of existing technologies, this invention provides a negative electrode sheet based on anodized aluminum foil and its preparation method. The negative electrode sheet uses anodizing to treat the aluminum foil, which yields a honeycomb-shaped nanoporous alumina layer. Then, acid etching is performed to control the thickness and pore size of the oxide layer, which not only improves the surface roughness of the aluminum foil but also enhances the adhesion between the electrode sheet and the current collector. Furthermore, the embedded design of the first coating layer suppresses the volume expansion of the phosphorus-based material during the electrode sheet's cycling process, thereby improving the cycle stability and safety of the battery.
[0009] To achieve the above objectives, a first aspect of the present invention provides a negative electrode sheet based on anodized aluminum foil, comprising: A honeycomb porous current collector includes a pure aluminum foil layer and a nanoporous alumina layer, wherein the nanoporous alumina layer is obtained by sequentially anodizing and acid etching the aluminum foil current collector. The first coating layer has an active material that is a high-specific-energy phosphorus-doped material, which is embedded in the porous structure of the nanoporous alumina layer. The second coating layer, made of hard carbon material, is applied over the first coating layer.
[0010] A second aspect of the present invention provides a method for preparing the above-mentioned negative electrode sheet based on anodized aluminum foil, comprising: The aluminum foil current collector is sequentially anodized and acid-etched to form a honeycomb porous current collector with a nanoporous alumina layer. The first coating slurry is applied to the surface of the honeycomb porous current collector and embedded inside the porous structure of the nanoporous alumina layer. The second coating layer slurry is applied onto the first coating layer to obtain the negative electrode sheet; The negative electrode sheet is rolled.
[0011] The beneficial effects of this invention include: (1) The negative electrode sheet based on anodic aluminum foil proposed in this invention uses anodic oxidation to process the aluminum foil to obtain a honeycomb nanoporous aluminum oxide layer. Then, through acid etching treatment, the thickness and pore size of the oxide layer are controlled, which not only improves the surface roughness of the aluminum foil, but also improves the adhesion between the electrode sheet and the current collector. At the same time, through the embedded design of the first coating layer, the volume expansion of the phosphorus-based material is suppressed during the cycle of the electrode sheet, thereby improving the cycle stability and safety of the battery.
[0012] (2) The negative electrode sheet based on anodic aluminum foil proposed in this invention can preferentially undergo micro-deformation of the nanoporous aluminum oxide layer on the current collector surface during the rolling of the electrode sheet, thereby reducing the elongation of the electrode sheet after rolling and improving the stability of the rolling process. At the same time, the negative electrode sheet of sodium-ion battery is modified from the perspectives of current collector structure control and coating design, so that the electrode sheet elongation after rolling is only 0.05% and the peel strength reaches 30 N / m. While ensuring process stability, the cycle performance and energy density of the battery cell are improved.
[0013] (3) The method for preparing the negative electrode based on anodic aluminum foil proposed in this invention mixes a certain proportion of high theoretical specific capacity red phosphorus material into the first coating layer, thereby improving the first efficiency and energy density of the sodium-ion battery.
[0014] (4) The method for preparing the negative electrode based on anodic aluminum foil proposed in this invention retains a honeycomb aluminum oxide thin layer on the surface of a portion of the pure aluminum foil by adjusting the concentration of the acidic solution and the corrosion time, so as to improve the peel strength of the electrode and suppress the volume expansion of the first coating after charge-discharge cycles.
[0015] (5) The method for preparing a negative electrode based on anodized aluminum foil proposed in this invention is as follows: the first coating layer is coated on the surface of the prepared aluminum foil using a gravure coating machine with a fixed thickness. It is a thin electrode doped with red phosphorus material. The theoretical capacity of phosphorus-based material is much higher than that of conventional hard carbon material. At the same time, the first coating layer is embedded in the honeycomb oxide layer. The honeycomb structure can suppress the volume expansion of phosphorus-based material and improve the material cycle performance.
[0016] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description
[0017] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings.
[0018] Figure 1 This is a schematic diagram of an existing multi-level nanoporous gradient electrode structure.
[0019] Figure 2 This is a schematic diagram of the honeycomb porous current collector structure based on anodized aluminum foil proposed in this invention.
[0020] Figure 3 This is a schematic diagram of the negative electrode sheet based on anodic aluminum foil proposed in this invention. Detailed Implementation
[0021] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.
[0022] This invention provides a negative electrode sheet based on anodized aluminum foil, such as... Figure 3 As shown, it includes: The honeycomb porous current collector includes a pure aluminum foil layer and a nanoporous alumina layer. The nanoporous alumina layer is obtained by sequentially anodizing and acid etching the aluminum foil current collector. The first coating layer has an active material that is a high-specific-energy phosphorus-doped material, which is embedded in the porous structure of the nanoporous alumina layer. The second coating layer, made of hard carbon material, is applied over the first coating layer.
[0023] The negative electrode sheet in this invention uses anodizing to treat aluminum foil, which yields a honeycomb-shaped nanoporous alumina layer. Then, acid etching is used to control the thickness and pore size of the oxide layer, which not only improves the surface roughness of the aluminum foil but also enhances the adhesion between the electrode sheet and the current collector. At the same time, the embedded design of the first coating layer suppresses the volume expansion of the phosphorus-based material during the cycle of the electrode sheet, thereby improving the cycle stability and safety of the battery.
[0024] According to the present invention, the aluminum foil current collector has a thickness of 6-16 μm, a purity of ≥99.9%, and a dyn value of 30-35 dyn / cm.
[0025] According to the present invention, the thickness of the pure aluminum foil layer is 1-2 μm; The thickness of the nanoporous alumina layer is 5-10 μm, and the pore size of its porous structure is 500-1000 nm, with a depth of 3-6 μm.
[0026] According to the present invention, the thickness of the first coating layer is 2-3 μm.
[0027] According to the present invention, the thickness of the negative electrode sheet is 250-280 μm, and the areal density is 200-250 mg / m³. 2 The compacted density is 0.9-1.1 g / m³. 3 .
[0028] In this invention, the nanoporous alumina layer on the current collector surface can preferentially undergo micro-deformation during the rolling of the electrode, reducing the elongation of the electrode after rolling and improving the stability of the rolling process. At the same time, the sodium-ion battery negative electrode is modified from the perspectives of current collector structure control and coating design, so that the electrode elongation after rolling is only 0.05% and the peel strength reaches 30 N / m. While ensuring process stability, the cycle performance and energy density of the cell are improved.
[0029] The present invention also provides a method for preparing the above-mentioned negative electrode sheet based on anodized aluminum foil, comprising: The aluminum foil current collector is sequentially anodized and acid-etched to form a honeycomb porous current collector with a nanoporous alumina layer. The first coating slurry is applied to the surface of the honeycomb porous current collector and embedded inside the porous structure of the nanoporous alumina layer. The second coating layer slurry is applied onto the first coating layer to obtain the negative electrode sheet; The negative electrode sheet is rolled.
[0030] In this invention, a certain proportion of high theoretical specific capacity red phosphorus material is mixed into the first coating layer, which improves the first efficiency and energy density of the sodium-ion battery.
[0031] According to the present invention, the process of sequentially anodizing and acid etching an aluminum foil current collector to form a honeycomb porous current collector with a nanoporous alumina layer includes: After removing oil and impurities from the surface of the aluminum foil current collector, it is placed in a dual-electrode electrolytic cell with the aluminum foil as the anode and the carbon plate as the cathode for anodizing treatment to obtain an aluminum oxide layer and a honeycomb porous aluminum oxide layer. The anodized aluminum foil current collector was cleaned with ultrapure water and dried. The dried aluminum foil current collector is immersed in an acidic solution to obtain a honeycomb porous current collector with a nanoporous alumina layer.
[0032] According to the present invention, the electrolyte in the dual-electrode electrolytic cell is a mixed solution of 0.5-2 mol / L oxalic acid and sulfuric acid; The anodizing process includes first applying a voltage of 5-10V for 0.5-2 minutes, followed by applying a voltage of 40-60V for 0.5-2 minutes. The thickness of the alumina layer is 1-2 μm, and the height of the honeycomb porous alumina layer is 5-10 μm; The concentration of the acidic solution is 1-5 mol / L; Soaking time is 1-2 minutes; The acidic solution is at least one of acetic acid or phosphoric acid.
[0033] According to the present invention, the first coating slurry comprises 90-98 wt% of a first active substance, 2-3 wt% of a conductive agent and 1-5 wt% of a binder; The first active material includes red phosphorus and hard carbon material, with a mass ratio of red phosphorus to hard carbon material of 1:8-10; The first coating layer slurry is applied by gravure coating.
[0034] In this invention, by controlling the concentration of the acidic solution and the corrosion time, a honeycomb-shaped alumina thin layer on the surface of a portion of the pure aluminum foil is retained, thereby improving the electrode peel strength and inhibiting the volume expansion of the first coating after charge-discharge cycles.
[0035] According to the present invention, the second coating slurry comprises 90-98 wt% of a second active substance, 2-3 wt% of a conductive agent, and 1-5 wt% of a binder; The second active material is hard carbon; The conductive agent is either superphosphorus or acetylene black; The adhesive is carboxymethyl cellulose and / or styrene-butadiene rubber; The compaction density of roller pressing is 0.9-1.1 g / m³. 3 .
[0036] In this invention, the first coating layer is applied to the surface of the prepared aluminum foil using a gravure coating machine with a fixed thickness. It is a thin-layer electrode doped with red phosphorus material. The theoretical capacity of phosphorus-based materials is much higher than that of conventional hard carbon materials. At the same time, the first coating layer is embedded in a honeycomb oxide layer. The honeycomb structure can suppress the volume expansion of phosphorus-based materials and improve the material's cycle performance.
[0037] The present invention will be described in more detail below through embodiments.
[0038] Example 1
[0039] This invention provides a negative electrode sheet based on anodized aluminum foil, such as... Figure 3 As shown, it includes: The honeycomb porous current collector includes a pure aluminum foil layer and a nanoporous alumina layer. The nanoporous alumina layer is obtained by sequentially anodizing and acid etching the aluminum foil current collector. The first coating layer has an active material that is a high-specific-energy phosphorus-doped material, which is embedded in the porous structure of the nanoporous alumina layer. The second coating layer, made of hard carbon material, is applied over the first coating layer.
[0040] In this embodiment, the honeycomb porous current collector structure is as follows: Figure 2 As shown.
[0041] This invention provides a method for preparing a negative electrode based on anodized aluminum foil. The core of this method lies in constructing a nanoporous alumina layer on the surface of the aluminum foil current collector through anodizing and acid etching, combined with a gradient composite slurry coating process, to achieve synergistic optimization of the electrode's mechanical and electrochemical properties. The specific steps are as follows: 1. Preparation of porous current collectors: A 15μm aluminum foil was selected and placed in a two-electrode electrolytic cell for anodic oxidation. The aluminum foil was used as the anode and the carbon plate as the cathode. The electrolyte was a 1 mol / L mixed solution of oxalic acid and sulfuric acid. In the first step, a voltage of 10V was applied for anodic oxidation for 1 min, and in the second step, a voltage of 60V was applied for anodic oxidation for 1 min, resulting in a 2μm thick Al2O3 substrate film with a height of 10μm and a pore size of 5μm. The resulting porous current collector was immersed in a 5 mol / L acetic acid solution for 1-2 min, resulting in a porous structure with a pore size of 500nm and a pore depth of 7μm. 2. Preparation of electrode sheet: Prepare the first coating layer slurry for the negative electrode. The slurry has the following mass percentages: 90-98 wt% active material, 2-3 wt% conductive agent, and 1-5 wt% binder. The active material in the first coating layer is a mixture of red phosphorus and hard carbon material in a mass ratio of 1:9. The conductive agent is either SuperP or acetylene black. The binder is either carboxymethyl cellulose (CMC) or styrene-butadiene rubber (SBR) or a mixture of both. The first coating layer is applied to the surface of the porous current collector using a gravure coating method, and the coating thickness is 2-3 μm. The first coating layer is embedded in the honeycomb-like pore structure of the current collector surface. A second coating slurry for the negative electrode is prepared, wherein the slurry mass percentage is 90-98 wt% of active material, 2-3 wt% of conductive agent, and 1-5 wt% of binder; the active material of the second coating layer is hard carbon, the conductive agent is either SuperP or acetylene black, and the binder is carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR). The second coating slurry is applied to the single-layer electrode from step two using an extrusion coating method. The electrode thickness is 250-280 μm, and the electrode areal density is 200-250 mg / m³. 2 ; The electrode sheets obtained in step four are then rolled to achieve a compaction density of 0.9-1.1 g / m³. 3 .
[0042] Example 2
[0043] This invention provides a method for preparing a negative electrode sheet based on anodized aluminum foil, the specific steps of which are as follows: 1. Preparation of porous current collectors: A 15μm aluminum foil was selected and placed in a two-electrode electrolytic cell for anodic oxidation. The aluminum foil was used as the anode and the carbon plate as the cathode. The electrolyte was a 1 mol / L mixed solution of oxalic acid and sulfuric acid. In the first step, a voltage of 10V was applied for anodic oxidation for 1 min, and in the second step, a voltage of 60V was applied for anodic oxidation for 1 min, resulting in an Al2O3 film with a thickness of 2μm, a height of 10μm, and a pore size of 5μm. The resulting porous current collector was immersed in a 10 mol / L acetic acid solution for 1-2 min, resulting in a porous structure with a pore size of 630nm and a pore depth of 3μm. 2. Preparation of electrode sheet: Prepare the first coating layer slurry for the negative electrode. The slurry has the following mass percentages: 90-98 wt% active material, 2-3 wt% conductive agent, and 1-5 wt% binder. The active material in the first coating layer is a mixture of red phosphorus and hard carbon material in a mass ratio of 1:9. The conductive agent is either SuperP or acetylene black. The binder is either carboxymethyl cellulose (CMC) or styrene-butadiene rubber (SBR) or a mixture of both. The first coating layer is applied to the surface of the porous current collector using a gravure coating method, and the coating thickness is 2-3 μm. The first coating layer is embedded in the honeycomb-like pore structure of the current collector surface. A second coating slurry for the negative electrode is prepared, wherein the slurry mass percentage is 90-98 wt% of active material, 2-3 wt% of conductive agent, and 1-5 wt% of binder; the active material of the second coating layer is hard carbon, the conductive agent is either SuperP or acetylene black, and the binder is carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR). The second coating slurry is applied to the single-layer electrode from step two using an extrusion coating method. The electrode thickness is 250-280 μm, and the electrode areal density is 200-250 mg / m³. 2 ; The electrode sheets obtained in step four are then rolled to achieve a compaction density of 0.9-1.1 g / m³. 3 .
[0044] Example 3
[0045] This invention provides a method for preparing a negative electrode sheet based on anodized aluminum foil, the specific steps of which are as follows: 1. Preparation of porous current collectors: A 15μm aluminum foil was selected and placed in a two-electrode electrolytic cell for anodic oxidation. The aluminum foil was used as the anode and the carbon plate as the cathode. The electrolyte was a 1 mol / L mixed solution of oxalic acid and sulfuric acid. In the first step, a voltage of 10V was applied for anodic oxidation for 1 min, and in the second step, a voltage of 60V was applied for anodic oxidation for 1 min, resulting in an Al2O3 film with a thickness of 2μm, a height of 10μm, and a pore size of 5μm. The resulting porous current collector was then immersed in a 15 mol / L acetic acid solution for 1-2 min, resulting in a porous structure with a pore size of 900nm and a pore depth of 1μm. 2. Preparation of electrode sheet: Prepare the first coating layer slurry for the negative electrode. The slurry has the following mass percentages: 90-98 wt% active material, 2-3 wt% conductive agent, and 1-5 wt% binder. The active material in the first coating layer is a mixture of red phosphorus and hard carbon material in a mass ratio of 1:9. The conductive agent is either SuperP or acetylene black. The binder is either carboxymethyl cellulose (CMC) or styrene-butadiene rubber (SBR) or a mixture of both. The first coating layer is applied to the surface of the porous current collector using a gravure coating method, and the coating thickness is 2-3 μm. The first coating layer is embedded in the honeycomb-like pore structure of the current collector surface. A second coating slurry for the negative electrode is prepared, wherein the slurry mass percentage is 90-98 wt% of active material, 2-3 wt% of conductive agent, and 1-5 wt% of binder; the active material of the second coating layer is hard carbon, the conductive agent is either SuperP or acetylene black, and the binder is carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR). The second coating slurry is applied to the single-layer electrode from step two using an extrusion coating method. The electrode thickness is 250-280 μm, and the electrode areal density is 200-250 mg / m³. 2 ; The electrode sheets obtained in step four are then rolled to achieve a compaction density of 0.9-1.1 g / m³. 3 .
[0046] Comparative Example 1
[0047] 15μm aluminum foil is selected and coated with a single layer of hard carbon paste. The paste contains 90-98 wt% active material, 2-3 wt% conductive agent, and 1-5 wt% binder by mass percentage. The electrode is rolled to a compaction density of 0.9-1.1 g / m³. 3 Assemble pouch cells.
[0048] Comparative Example 2: A 15μm aluminum foil is selected. The first coating layer is 2μm thick, and the slurry mass percentage is 90-98wt% active material, 2-3wt% conductive agent, and 1-5wt% binder. The active material in the first coating layer is red phosphorus and hard carbon material in a mass ratio of 1:9. The second coating layer is 250μm thick, and the slurry mass percentage is 90-98wt% active material, 2-3wt% conductive agent, and 1-5wt% binder. Rolling is performed until the compacted density is 0.9-1.1 g / m³. 3 Assemble soft-pack battery cells.
[0049] Table 1 Comparison results of Examples 1-3 and Comparative Examples 1-2
[0050] As can be seen from Table 1, compared with Comparative Examples 1-2, the negative electrode sheets of Examples 1-3 based on anodic aluminum foil, by treating the aluminum foil by anodic oxidation, can obtain a honeycomb-shaped nanoporous aluminum oxide layer. Then, by acid etching treatment, the thickness and pore size of the oxide layer can be controlled, which can not only improve the surface roughness of the aluminum foil, but also improve the adhesion between the electrode sheet and the current collector. At the same time, through the embedded design of the first coating layer, the cell cycle performance and energy density are improved while ensuring stability during the electrode sheet cycle.
[0051] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.
Claims
1. A negative electrode sheet based on anodized aluminum foil, characterized in that, include: A honeycomb porous current collector includes a pure aluminum foil layer and a nanoporous alumina layer, wherein the nanoporous alumina layer is obtained by sequentially anodizing and acid etching the aluminum foil current collector. The first coating layer has an active material that is a high-specific-energy phosphorus-doped material, which is embedded in the porous structure of the nanoporous alumina layer. The second coating layer, made of hard carbon material, is applied over the first coating layer.
2. The negative electrode sheet according to claim 1, characterized in that, The aluminum foil current collector has a thickness of 6-16 μm, a purity of ≥99.9%, and a dyn value of 30-35 dyn / cm.
3. The negative electrode sheet according to claim 1, characterized in that, The thickness of the pure aluminum foil layer is 1-2 μm; The thickness of the nanoporous alumina layer is 5-10 μm, and the pore size of its porous structure is 500-1000 nm, with a depth of 3-6 μm.
4. The negative electrode sheet according to claim 1, characterized in that, The thickness of the first coating layer is 2-3 μm.
5. The negative electrode sheet according to claim 1, characterized in that, The thickness of the negative electrode sheet is 250-280 μm, and the areal density is 200-250 mg / m³. 2 The compacted density is 0.9-1.1 g / m³. 3 .
6. A method for preparing a negative electrode sheet based on anodized aluminum foil according to any one of claims 1-5, characterized in that, include: The aluminum foil current collector is sequentially anodized and acid-etched to form a honeycomb porous current collector with a nanoporous alumina layer. The first coating slurry is applied to the surface of the honeycomb porous current collector and embedded inside the porous structure of the nanoporous alumina layer. The second coating layer slurry is applied onto the first coating layer to obtain the negative electrode sheet; The negative electrode sheet is rolled.
7. The preparation method according to claim 6, characterized in that, The process of sequentially anodizing and acid etching aluminum foil current collectors to form a honeycomb porous current collector with a nanoporous alumina layer includes: After removing oil and impurities from the surface of the aluminum foil current collector, it is placed in a dual-electrode electrolytic cell with the aluminum foil as the anode and the carbon plate as the cathode for anodizing treatment to obtain an aluminum oxide layer and a honeycomb porous aluminum oxide layer. The aluminum foil current collector after anodizing is cleaned with ultrapure water and dried. The dried aluminum foil current collector is immersed in an acidic solution to obtain a honeycomb porous current collector with a nanoporous alumina layer.
8. The preparation method according to claim 7, characterized in that, The electrolyte in the dual-electrode electrolytic cell is a mixed solution of 0.5-2 mol / L oxalic acid and sulfuric acid; The anodizing process includes first applying a voltage of 5-10V for anodizing for 0.5-2 minutes, followed by applying a voltage of 40-60V for anodizing for 0.5-2 minutes. The thickness of the alumina layer is 1-2 μm, and the height of the honeycomb porous alumina layer is 5-10 μm; The concentration of the acidic solution is 1-5 mol / L; The soaking time is 1-2 minutes; The acidic solution is at least one of acetic acid or phosphoric acid.
9. The preparation method according to claim 6, characterized in that, The first coating slurry comprises 90-98 wt% of a first active substance, 2-3 wt% of a conductive agent and 1-5 wt% of a binder; The first active material includes red phosphorus and hard carbon material, wherein the mass ratio of red phosphorus to hard carbon material is 1:8-10; The first coating layer slurry is applied by gravure coating.
10. The preparation method according to claim 9, characterized in that, The second coating slurry comprises 90-98 wt% of a second active substance, 2-3 wt% of a conductive agent, and 1-5 wt% of a binder; The second active material is hard carbon; The conductive agent is either superphosphorus or acetylene black. The adhesive is carboxymethyl cellulose and / or styrene-butadiene rubber; The compaction density of the roller press is 0.9-1.1 g / m³. 3 .