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EP-4738456-A1 - NEGATIVE ELECTRODE SHEET, ELECTROCHEMICAL DEVICE, AND PREPARATION METHOD FOR NEGATIVE ELECTRODE SHEET

EP4738456A1EP 4738456 A1EP4738456 A1EP 4738456A1EP-4738456-A1

Abstract

A negative electrode sheet, an electrochemical device, and a preparation method for the negative electrode sheet, relating to the technical field of secondary batteries. The negative electrode sheet comprises a current collector and a negative electrode active material layer. The negative electrode active material layer is located on at least one side of the current collector, and the negative electrode active material layer comprises a first active material layer and a second active material layer; the first active material layer and the second active material layer are stacked in the direction close to the current collector; and the structural stability parameter ratio S1/S2 of the first active material layer to the second active material layer satisfies 0.01-10.0. According to the negative electrode sheet, the electrochemical device, and the preparation method for the negative electrode sheet, by adjusting structural stability parameters of a double-layer structure in the negative electrode active material layer, the negative electrode active material layer forms a structure having a gradually decreasing hardness in the direction close to the current collector, so as to effectively optimize the pore distribution and the structural stability of the negative electrode active material layer, thereby improving the fast charging, cycle and storage performance of a lithium ion battery.

Inventors

  • WANG, YANQING
  • SUN, Huayu
  • LIU, YONGXING

Assignees

  • AESC Hebei Co., Ltd.
  • AESC HUBEI CO., LTD.
  • AESC Jiangsu Co., Ltd.
  • AESC ORDOS CO., LTD.
  • AESC Shanghai Co., Ltd.

Dates

Publication Date
20260506
Application Date
20240628

Claims (11)

  1. A negative electrode sheet, characterized in comprising: a current collector; a negative electrode active material layer located on at least one side of the current collector and comprising a first active material layer and a second active material layer stacked in a direction close to the current collector, wherein a structural stability parameter ratio S 1 /S 2 of the first active material layer to the second active material layer satisfies 0.01-10.0.
  2. The negative electrode sheet according to claim 1, characterized in that a negative electrode material in the negative electrode active material layer comprises a graphite material.
  3. The negative electrode sheet according to claim 1, characterized in that the structural stability parameter ratio S 1 /S 2 of the first active material layer to the second active material layer satisfies 0.1-5.0.
  4. The negative electrode sheet according to claim 1, characterized in that a structural stability parameter S 1 of the first active material layer is 3-16.
  5. The negative electrode sheet according to claim 1, characterized in that the negative electrode active material layer satisfies 6.5 ≤ τ − ε V OI P ≤ 80 , wherein τ is a tortuosity of the negative electrode active material layer, ε is a porosity of the negative electrode active material layer, P is a compaction density of the negative electrode active material layer, V OI is a stacking orientation degree of negative electrode material particles in the negative electrode active material layer.
  6. The negative electrode sheet according to claim 5, characterized in that the negative electrode active material layer satisfies 20 ≤ τ − ε V OI P ≤ 60 .
  7. The negative electrode sheet according to claim 1, characterized in that a compaction density of the negative electrode active material layer is 1.65-1.75 g/cm 3 .
  8. A preparation method for the negative electrode sheet according to any one of claims 1 to 7, characterized in comprising: mixing a first negative electrode material with a binder, a conductive agent, and a thickening agent to form a slurry and obtaining a first active material layer slurry; mixing a second negative electrode material with a binder, a conductive agent, and a thickening agent to form a slurry and obtaining a second active material layer slurry; and coating the second active material layer slurry and the first active material layer slurry on at least one side of the current collector in sequence, and after coating, obtaining the negative electrode sheet through drying, compaction, die cutting, and punching, wherein a hardness of the first negative electrode material is greater than a hardness of the second negative electrode material.
  9. The preparation method for the negative electrode sheet according to claim 8, characterized in that a structural stability parameter ratio S 1 /S 2 of the first negative electrode material to the second negative electrode material satisfies 0.01-10.0.
  10. The preparation method for the negative electrode sheet according to claim 8, characterized in that an average particle size Dv50 of the first negative electrode material is 11-17µm, and an average particle size Dv50 of the second negative electrode material is 16-19µm.
  11. An electrochemical device, characterized in comprising a positive electrode sheet, a separator, an electrolyte, and the negative electrode sheet according to any one of claims 1 to 7.

Description

TECHNICAL FILED The invention relates to the technical field of secondary batteries, and specifically relates to a negative electrode sheet, an electrochemical device, and a preparation method of the negative electrode sheet. RELATED ART In the conventional lithium ion battery system, the charging capability, cycle performance, processing performance, and safety performance of lithium ion batteries are determined by the negative electrode to a considerable extent. At present, the optimization strategies for negative electrode sheets focus on aspects such as compaction density, areal density, and active material ratio most of the time. However, as cell performance gradually approaches bottlenecks, we need to specifically refine the influence of electrode sheet levels on the cell performance, so as to more effectively improve the performance of corresponding cells from an intrinsic level. Currently, simply adjusting the compaction density, areal density, and active material ratio of the negative electrode materials no longer provides significant space for optimizing cell fast charging and cycle performance. It is necessary to reasonably consider the physical and chemical characteristics of the negative electrode sheets and optimize the distribution and orientation of particles and pores in the negative electrode active material layer by comprehensively adjusting the material ratio, hardness distribution, and compaction density of the negative electrode active material layer. The kinetic balance of the negative electrode sheets may be improved in this way, and the fast charging and cycle performance of the lithium ion batteries may thus be further optimized. Therefore, it is necessary to design a negative electrode sheet, an electrochemical device, and a preparation method of the negative electrode sheet to solve the above problems. SUMMARY In view of the above disadvantages of the related art, the invention provides a negative electrode sheet, an electrochemical device, and a preparation method of the negative electrode sheet, which comprehensively adjusts a material ratio, hardness distribution, and compaction density of the negative electrode active material layer in the negative electrode sheet, so that the technical problems of difficulty in comprehensively optimizing the distribution and orientation of particles and pores in the negative electrode active material layer and effectively balancing the kinetic performance of the negative electrode sheet found in the related art can be improved. To achieve the above objectives and other related objectives, the invention provides a negative electrode sheet including a current collector and a negative electrode active material layer. Herein, the negative electrode active material layer is located on at least one side of the current collector, and the negative electrode active material layer includes a first active material layer and a second active material layer. The first active material layer and the second active material layer are stacked in a direction close to the current collector, and a structural stability parameter ratio S1/S2 of the first active material layer to the second active material layer satisfies 0.01-10.0. In an embodiment of the invention, a negative electrode material in the negative electrode active material layer includes a graphite material. In an embodiment of the invention, the structural stability parameter ratio S1/S2 of the first active material layer to the second active material layer satisfies 0.1-5.0. In an embodiment of the invention, a structural stability parameter S1 of the first active material layer is 3-16. In an embodiment of the invention, the negative electrode active material layer satisfies 6.5≤τ−εVOIP≤80, wherein τ is a tortuosity of the negative electrode active material layer, ε is a porosity of the negative electrode active material layer, P is a compaction density of the negative electrode active material layer, VOI is a stacking orientation degree of negative electrode material particles in the negative electrode active material layer. In an embodiment of the invention, the negative electrode active material layer satisfies 20≤τ−εVOIP≤60. In an embodiment of the invention, a compaction density of the negative electrode active material layer is 1.65-1.75 g/cm3. Another aspect of the invention provides a preparation method for the negative electrode sheet, and the preparation method includes the following steps. A first negative electrode material is mixed with a binder, a conductive agent, and a thickening agent to form a slurry, and a first active material layer slurry is obtained. A second negative electrode material is mixed with a binder, a conductive agent, and a thickening agent to form a slurry, and a second active material layer slurry is obtained. The second active material layer slurry and the first active material layer slurry are coated on at least one side of the current collector in sequence, an