A novel modification approach for natural graphite anode of Li-ion batteries

To improve the rate capability and cyclability of natural graphite anode for Li-ion batteries, a novel modification approach was developed. The modification approach included two steps: (a) high-energy ball milling in a rotary autoclave containing alumina balls, H₃ PO₄ and ethanol; (b) coating with pyrolytic carbon from phenlic resin. The treated graphite shows obvious improvement compared with the original natural graphite in electrochemical properties such as cyclability and rate capability, especially at high current density. The primary reasons leading to the improvement in rate capability and cyclability are that the diffusion impedance of Li⁺ in graphite is reduced due to the fact that P filtered into graphite layers can mildly increase interlayer distances, and the fact that the structural stability of graphite surface is enhanced since the coated pyrolytic carbon can depress the co-intercalation of solvated lithium ion.