Surface modification of graphite by ion implantation for promoting the electrochemical property in Li-ion batteries

Nowadays, graphite is still the commercial anode material for Li-ion batteries although many kinds of anode materials have been reported. A great deal of efforts has been devoting to improving the specific gravimetric capacity of graphite by doping or preparing hierarchical structure. However, the volumetric capacity of graphite is not taken seriously compared to the specific gravimetric capacity. In this paper, a surface modification method, ion implantation, has been put forward to improve the volumetric capacity of graphite with high coulombic efficiency. After modification with 50 keV N⁺ ions at 1 × 10¹² ions/cm², the volumetric capacity of implanted graphite increases 29.6% (696 mAh/cm³) compared to that of pure graphite electrode (537 mAh/cm³) with a super-high initial coulombic efficiency of ~95.9%. Moreover, the influence of nitrogen doping and vacancies induced by N⁺ ions implantation on the improving of volumetric capacity is discussed. The implanted effects of graphite are also observed by HRTEM, GIXRD, Raman and XPS.