Search

CN-122000296-A - Pole piece and cylindrical lithium ion battery

CN122000296ACN 122000296 ACN122000296 ACN 122000296ACN-122000296-A

Abstract

The application relates to a pole piece and a cylindrical lithium ion battery. The pole piece comprises a current collector and active material layers positioned on two sides of the current collector, wherein the content of at least one active material in the active material layers is gradually reduced from the head to the tail of the pole piece along the length direction of the pole piece. The application improves the expansion difference of the inner and outer ring pole pieces and improves the battery performance by regulating and controlling the formulation of the upper and lower layers of slurry and the thickness of the coating in the length direction.

Inventors

  • NIU YARU
  • XU SHIQI
  • ZHU GUANNAN

Assignees

  • 上海轩邑新能源发展有限公司

Dates

Publication Date
20260508
Application Date
20260213

Claims (10)

  1. 1. A pole piece comprises a current collector and active material layers positioned on two sides of the current collector, wherein, And along the length direction of the pole piece, gradually reducing the total content of at least one active substance in the active substance layer from the head part to the tail part of the pole piece.
  2. 2. The pole piece of claim 1, wherein the active material mass per unit area of at least one of the active materials gradually decreases from the beginning of the roll of the pole piece to the end of the roll along the length of the pole piece.
  3. 3. The pole piece according to claim 1 or 2, wherein the active material layer is a double layer structure containing an active material, comprising a bottom layer close to the current collector and an upper layer distant from the current collector; the bottom layer is a high-content active material layer, and the upper layer is a medium-low-content active material layer; The total thickness of the active material layer is unchanged from the beginning to the end of the roll of the pole piece along the length direction of the pole piece, the thickness of the bottom layer is gradually thinned, and the thickness of the upper layer is gradually increased; optionally, the pole piece is one or two of a negative pole piece and a positive pole piece.
  4. 4. A pole piece according to claim 3, wherein when the pole piece is a negative pole piece, the active substance comprises a silicon-based material; Optionally, the silicon-based material is selected from one or more of nano silicon, silicon oxide, pre-lithiated silicon oxide, pre-magnesia silicon oxide, silicon-carbon composite material; optionally, the mass ratio of the silicon-based material in the bottom layer is 10% -20%, and the mass ratio of the silicon-based material in the upper layer is 1% -5%.
  5. 5. The pole piece of claim 4, wherein the active material further comprises graphite; optionally, the graphite is selected from one or more of natural graphite and artificial graphite; optionally, the graphite is present in a ratio of (1-silicon based material) x 100%.
  6. 6. A pole piece according to claim 3, wherein when the pole piece is a positive pole piece, the active substance comprises a ternary material; optionally, the ternary material in the bottom layer is a high-nickel ternary active substance, and the ternary material in the upper layer is a medium-nickel ternary active substance; Optionally, the high nickel ternary active material is an 8-9 ternary material; Optionally, the middle nickel ternary active material is a 5-7 ternary material.
  7. 7. A pole piece according to claim 3, wherein the raw materials in the active material layer further comprise a conductive agent, a binder and a solvent; optionally, the conductive agent is selected from one or more of a carbon-based material, a metal-based material, a conductive polymer; optionally, the binder is selected from one or more of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethyleneoxy-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon; optionally, the solvent is deionized water or NMP.
  8. 8. The pole piece according to claim 7, wherein the mass ratio of active substance, conductive agent, binder in the bottom layer or the upper layer is (90-98): 0.5-5): 1-10% Along the length direction of the pole piece, from the beginning to the end of the pole piece, the thickness of the bottom layer is linearly reduced from 65% -51% to 35% -49%, and the thickness of the upper layer is linearly increased from 35% -49% to 51% -65%.
  9. 9. A cylindrical lithium ion battery comprising a pole piece according to any one of claims 1 to 8.
  10. 10. The cylindrical lithium ion battery of claim 9, wherein the cylindrical lithium ion battery further comprises a separator comprising a substrate layer and a surface treatment layer; Optionally, the substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide; optionally, the surface treatment layer is a ceramic layer, and the material of the ceramic layer is at least one of alumina and boehmite.

Description

Pole piece and cylindrical lithium ion battery Technical Field The application relates to the technical field of lithium ion batteries, in particular to a cylindrical battery and a pole piece. Background The cylindrical lithium ion battery is mainly formed by winding a positive plate, a negative plate and a diaphragm for isolating the positive plate from the negative plate to form a cylindrical winding core, wherein the winding core is arranged on a cylindrical shell, electrolyte is injected into the winding core to seal the winding core, and the cylindrical lithium ion battery is formed, wherein the positive plate and the negative plate are completely identical in active layers from the winding head to the winding tail in the length direction, for example, the active layers comprise active materials, conductive agents and adhesive in types and proportions. Under the design of the pole piece, because of the cylindrical structural characteristics, the positive and negative pole pieces of the inner layer (the winding head) and the outer layer (the winding tail) of the winding core are stressed differently in the charging and discharging process of the battery, so that the rebound of the pole pieces of the inner and outer layers, especially the rebound of the negative pole piece in the thickness direction of the pole piece is inconsistent. Finally, the performance difference of the inner layer and the outer layer of the cylindrical battery cell is caused, so that the performance attenuation of the battery cell is accelerated. Disclosure of Invention The following is a summary of the subject matter of the detailed description of the application. This summary is not intended to limit the scope of the application. In a first aspect of the application, a pole piece is provided, the pole piece comprising a current collector and active material layers on both sides of the current collector. In one exemplary embodiment, the total content of at least one active material in the active material layer gradually decreases from the beginning of the roll of the pole piece to the end of the roll of the pole piece along the length direction of the pole piece, and for example, the active material mass per unit area (i.e., areal density) or the overall distribution density of at least one active material gradually decreases from the beginning of the roll of the pole piece to the end of the roll of the pole piece along the length direction of the pole piece. In one exemplary embodiment, the active material layer is a double-layer structure including an active material-containing layer including a lower layer adjacent to the current collector and an upper layer distant from the current collector. In an exemplary embodiment, the active material content in the upper layer and the lower layer are different. In one exemplary embodiment, the bottom layer is a high active material layer and the upper layer is a medium low active material layer. In one exemplary embodiment, the thicknesses of the bottom layer and the upper layer vary gradually from the beginning of the roll of the pole piece to the end of the roll along the length of the pole piece. In an exemplary embodiment, the thickness of the bottom layer or the upper layer is gradually thinned and the thickness of the other layer is gradually increased from the beginning to the end of the roll of the pole piece along the length direction of the pole piece. In an exemplary embodiment, the total thickness of the active material layer is substantially constant from the beginning to the end of the roll of the pole piece along the length of the pole piece, the thickness of the bottom layer is gradually thinned, and the thickness of the upper layer is gradually increased, that is, by decreasing the thickness ratio of the high active material layer and increasing the thickness ratio of the low active material layer during double-layer coating. In an exemplary embodiment, the base layer and the upper layer are different in slurry formulation. In an exemplary embodiment, the pole piece is one or both of a negative pole piece and a positive pole piece. In one exemplary embodiment, the pole piece is a positive pole piece or a negative pole piece. In one exemplary embodiment, when the electrode sheet is a negative electrode sheet, the active material includes a silicon-based material. In an exemplary embodiment, the silicon-based material is selected from one or more of nano-silicon, silicon oxide, pre-lithiated silicon oxide, pre-magnesia silicon oxide, silicon-carbon composite materials. In one exemplary embodiment, the mass ratio of the silicon-based material in the bottom layer is 10% -20% (e.g., 20%), and the mass ratio of the silicon-based material in the upper layer is 1% -5% (e.g., 5%). In an exemplary embodiment, the active material further comprises graphite. In an exemplary embodiment, the graphite is selected from one or more of natural graphite and artificial graphite. In one exe