Surface modification allows graphite anode to stand out

Graphite was the first commercialized anode material for lithium-ion batteries.
The first commercial lithium-ion battery model, developed by Sony in Japan in 1990, paired lithium cobalt oxide with graphite. After thirty years of development, graphite remains the most reliable and widely used anode material. Graphite surface modification has become the core improvement direction of high-safety lithium battery systems.

Graphite has a good layered structure, with carbon atoms arranged in a hexagonal pattern extending in two dimensions. The interlayer bonding force is van der Waals force, with an interlayer distance of 0.3354nm, exhibiting anisotropic characteristics.
Graphite, as an anode material for lithium-ion batteries, has high selectivity for electrolytes. However, its performance in high-current charge and discharge is poor. During the first charge and discharge cycle, solvated lithium ions insert between the graphite layers. These ions reduce and decompose to produce new substances, causing volume expansion. This can directly lead to the collapse of the graphite layers, worsening the cycling performance of the electrode.
Therefore, graphite modification is needed to improve its reversible capacity.
It also enhances the quality of the SEI film, increases compatibility with electrolytes, and improves cycling performance.

Currently, surface modification methods for graphite anodes mainly include mechanical ball milling, surface oxidation and halogenation, surface coating, and element doping.

Mechanical ball milling

The mechanical ball milling method changes the structure and morphology of the graphite anode surface through physical means. This increases the surface area and contact area, thereby improving lithium-ion storage and release efficiency.

• Reducing particle size: Mechanical ball milling can significantly reduce the particle size of graphite, giving the graphite anode material a larger specific surface area.
  Smaller particle sizes facilitate the rapid diffusion of lithium ions, improving the battery’s rate performance.
• Introducing new phases: During the ball milling process, graphite particles may undergo phase transitions due to mechanical forces. Such as the introduction of rhomboid equal new phase
  The presence of these new phases provides more lithium storage sites, enhancing the lithium storage capacity of graphite.
• Increasing porosity: Ball milling also creates numerous micropores and defects on the surface of graphite particles. These porous structures act as fast channels for lithium ions, improving their diffusion rate and the charging and discharging efficiency of the battery.
• Improving conductivity: Mechanical ball milling does not directly change the conductivity of graphite.
  It reduces the particle size and introduces porosity.
  This allows better contact between the graphite anode and the electrolyte.
  As a result, the conductivity and electrochemical performance of the battery improve.

Surface oxidation and halogenation treatment

Oxidation and halogenation treatments can improve the interfacial chemical properties of graphite anode materials.

Surface oxidation

Surface oxidation typically includes gas-phase oxidation and liquid-phase oxidation.

Gas-phase oxidation mainly uses air, O2, O3, CO2, C2H2, and other gases as oxidants. These gases react with graphite in a gas-solid interface reaction, reducing active sites on the graphite surface. This reduces the first-cycle irreversible capacity loss.
At the same time, it generates more micropores and nano-channels, increasing lithium-ion storage space. This helps improve reversible capacity and enhance graphite anode performance.

Liquid-phase oxidation mainly uses solutions of strong chemical oxidants like HNO3, H2SO4, and H2O2 to react with graphite. This improves its electrochemical performance.
However, improper control of the solution may cause graphite layers to collapse. Therefore, it’s important to consider whether the introduced impurities could harm electrode performance. Additionally, the reaction produces gases or solutions that are harmful to the environment, instruments, and equipment.

Surface halogenation

Through halogenation, C-F structures form on the surface of natural graphite, enhancing its structural stability. This prevents graphite layer shedding during cycling. Halogenation of natural graphite also reduces internal resistance, increases capacity, and improves charge-discharge performance.
Studies show that the modification effect depends heavily on the type of graphite used. Simply oxidizing or halogenating graphite offers limited electrochemical performance improvement and does not meet practical requirements. Thus, researchers combine oxidation or halogenation with coating to enhance graphite’s electrochemical performance, achieving better results.

Surface coating

Surface coating modification of graphite anode materials includes carbon, metal or non-metal, oxide, and polymer coatings.
Surface coating improves reversible capacity, first-cycle Coulombic efficiency, cycle performance, and high-current charge-discharge performance.

Element doping

Element doping refers to intentionally incorporating or loading certain metals or non-metals into graphite materials. This alters the material’s microstructure, enhancing the Li insertion/extraction capability of the graphite anode.
As a result, it improves the lithium storage capacity and cycling stability of graphite. Non-metal elements doped into graphite materials mainly include B, N, Si, P, S, etc. Metal elements include Fe, Co, Ni, Cu, Zn, Sn, Ag, etc., with various compound doping also being developed.

Conclusion

Surface modification technology improves the efficiency of lithium ion storage and release by altering the surface structure, morphology, and chemical properties of the graphite anode.
The development of this technology helps enhance the energy density, extend the cycle life, and improve the safety performance of lithium-ion batteries.

EPIC’s ball milling and classification equipment can also provide you with exclusive solutions for surface modification of graphite, helping you quickly solve problems.