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CN-122000333-A - Modified graphite negative electrode material, preparation method thereof, negative electrode and lithium ion battery

CN122000333ACN 122000333 ACN122000333 ACN 122000333ACN-122000333-A

Abstract

The invention relates to a modified graphite anode material, a preparation method thereof, an anode and a lithium ion battery. The modified graphite anode material comprises graphite particles and an SEI precursor layer constructed by lithium salt uniformly coated on the surface of each graphite particle, wherein the lithium salt is in a crystalline structure, the thickness of the SEI precursor layer is 1-500 nm, and in the process of first charge and discharge of a battery, the lithium salt has electrochemical reaction in preference to electrolyte, so that inorganic phase SEI taking LiF and/or Li 3 PO 4 as main components is formed on the surface of the graphite particles in situ. The negative electrode material realizes active formation and uniform distribution of SEI, and even in a thick electrode, the surface of deep graphite particles can form a continuous SEI layer in the first charge and discharge and circulation process of a battery, thereby remarkably improving the first-week coulomb efficiency and the circulation life, improving the low-temperature and rate performance, and in addition, electrolyte can be easier to infiltrate the electrode, so that Li + is more smoothly transmitted in the thick electrode, and the electrochemical performance of the electrode is improved.

Inventors

  • LIU BOWEN
  • WANG XUEFENG
  • LV GUOCHENG

Assignees

  • 中国科学院物理研究所
  • 中国地质大学（北京）

Dates

Publication Date
20260508
Application Date
20260213

Claims (10)

  1. 1. The modified graphite anode material is characterized by comprising graphite particles and a Solid Electrolyte Interface (SEI) precursor layer which is constructed by lithium salt uniformly coated on the surface of each graphite particle; The lithium salt is in a crystalline structure, and the thickness of the SEI precursor layer is 1-500 nm; In the first charge and discharge process of the battery, the lithium salt reacts electrochemically in preference to the electrolyte, and inorganic phase SEI taking LiF and/or Li 3 PO 4 as main components is formed on the surface of the graphite particles in situ.
  2. 2. The modified graphite anode material of claim 1, wherein the lithium salt comprises one or more of lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium difluorophosphate (LiPO 2 F 2 ), lithium nitrate (LiNO 3 ), or lithium dioxaborate (LiBOB).
  3. 3. The modified graphite negative electrode material according to claim 1, wherein the lithium salt is distributed on the surface of graphite particles in an island-like crystal structure and/or a continuous dense crystal coating structure in the SEI precursor layer.
  4. 4. The modified graphite anode material of claim 1, wherein the SEI precursor layer is formed by incorporating lithium salt in the anode slurry preparation stage and coating the surface of each graphite particle by in-situ crystallization with solvent evaporation in the pole piece drying stage.
  5. 5. The modified graphite anode material of claim 1, wherein the modified graphite anode material is used for a thick electrode having a thickness in the range of 100-300 microns.
  6. 6. A method of preparing the modified graphite anode material of any one of claims 1 to 5, comprising: mixing graphite particles, a conductive agent, a binder and a solvent, and stirring to prepare a negative electrode slurry; Adding lithium salt into the negative electrode slurry and continuously stirring to uniformly disperse the lithium salt in the negative electrode slurry to form modified slurry; And in the drying process, the solvent volatilizes, and lithium salt is crystallized on the surfaces of graphite particles in situ to form SEI precursor layers uniformly coated on the surfaces of each graphite particle.
  7. 7. The method according to claim 6, wherein the drying time is 1 to 12 hours and the temperature is 60 to 120 ℃.
  8. 8. The method according to claim 6, wherein the lithium salt comprises one or more of lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium difluorophosphate (LiPO 2 F 2 ), lithium nitrate (LiNO 3 ) or lithium dioxalate borate (LiBOB); The addition amount of the lithium salt is 0.1-20wt% of the sum of the masses of the graphite particles, the conductive agent and the binder; The conductive agent comprises one or more of conductive carbon black, conductive graphite, conductive carbon nano tube, carbon fiber or conductive carbon composite material; the binder comprises one or more of sodium carboxymethylcellulose (CMC-Na), styrene Butadiene Rubber (SBR), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyacrylic acid (PAA) or copolymers thereof; The solvent comprises one or more of water, N-methyl pyrrolidone (NMP), ethanol, isopropanol or a mixed solvent system thereof.
  9. 9. A negative electrode, characterized in that the negative electrode comprises the modified graphite negative electrode material according to any one of claims 1 to 5.
  10. 10. A lithium ion battery comprising the modified graphite negative electrode material according to any one of claims 1 to 5, or comprising the negative electrode according to claim 9.

Description

Modified graphite negative electrode material, preparation method thereof, negative electrode and lithium ion battery Technical Field The invention relates to the technical field of graphite cathode materials, in particular to a modified graphite cathode material and a preparation method thereof, a cathode and a lithium ion battery. Background Graphite is the most commonly used negative electrode material of the current commercial lithium ion battery, and has lower lithium intercalation potential, a stable charge and discharge platform and reversible lithium ion intercalation/deintercalation capability. Meanwhile, the graphite has rich resources and low cost, and is suitable for large-scale application. With the rapid development of electronic devices and new energy automobile industries, the demand for lithium ion batteries with high energy density and rapid charging performance is increasing. The application of graphite to prepare thick electrodes can accommodate more active material, thereby significantly increasing battery energy density. However, as the thickness of the negative electrode sheet increases, the transmission distance of lithium ions in the electrode becomes long, resulting in a decrease in ion migration efficiency, and the polarization phenomenon is easily aggravated, thereby affecting the charge-discharge performance and cycle life of the battery. It is difficult in the prior art to balance the high energy density of thick electrodes with good ion transport properties. For the preparation and optimization of thick electrodes, various technical solutions are proposed in the prior publications. CN118676296a discloses a negative electrode sheet and a preparation method thereof, wherein electrolyte salt is introduced into one side of a thick electrode sheet far away from a current collector, so that the electrolyte distribution in the region is improved. However, in the method, the electrolyte salt is 1-250 mu m particles, the effect is mainly to improve ion contact on the macroscopic level of one side surface of the thick electrode sheet, the interface performance of deep graphite particles inside the thick electrode is still uneven, and the ion transmission efficiency and the cycling stability of the thick electrode are not improved essentially. CN119695084a proposes to prepare a thick electrode by forming a porous structure in the negative electrode slurry, so as to reduce the tortuosity of the lithium ion migration path inside the pole piece and improve the conduction rate of lithium ions in the pole piece and the rate capability of the battery cell. However, the method mainly relies on optimizing the pore structure of the slurry and the grading of graphite particles, the porous structure of the method is firstly improved by wetting and ion transmission of electrode surface particles, the interface performance of deep graphite particles inside a thick electrode is still uneven, and meanwhile, the porous structure can cause rheological fluctuation of the slurry to influence the coating uniformity. Therefore, the technique cannot fundamentally improve the SEI uniformity and overall ion transport efficiency of each graphite particle surface inside the thick electrode. CN118763284a enhances the fast fill rate performance by increasing the lithium ion desolvation capacity by adding low viscosity additives such as propionitrile, butyronitrile, FEC and ODA to the electrolyte. However, this solution relies on the diffusion of additives in the electrolyte to the surface of graphite particles during charge and discharge to form an SEI film, and for thick electrodes, deep graphite particles are far from the electrolyte phase, and the diffusion of additives is limited, so that it is difficult to form a uniform and continuous SEI layer on the surface of each particle. Therefore, the technology cannot fundamentally ensure the interface stability and the high-rate cycle performance of deep particles inside the thick electrode. CN118983399a improves the power output capability of conventional lithium batteries by introducing modified porous alumina into the negative electrode slurry. However, this approach mainly improves overall conductivity and structural stability, and there is still a limitation in the continuity of the ion transport channels inside the thick electrode. Meanwhile, porous alumina is additionally introduced to occupy part of the volume of active substances, so that the energy density of the thick pole piece is reduced. Therefore, this technique cannot fundamentally improve SEI uniform formation and overall ion transport efficiency of each graphite particle surface inside a thick electrode. In summary, although the prior art improves lithium ion transport on the surface layer or the whole structure of the thick electrode, the deep graphite particles inside the thick electrode still have the problems of insufficient wetting, uneven interface performance and low ion transport efficiency.