Influence of surface treatment on the Li doping/undoping reaction at a mesophase low temperature carbon fiber

In an attempt to improve the Li insertion/extraction rates of a low-temperature disordered carbon having a very high Li loading capacity, several surface modification methods were examined for a mesophase carbon fiber prepared at 800 °C. The electrochemical reaction rates were evaluated by cyclic voltammetry and potential step chronoamperometry (PSCA) in an electrolyte of propylene carbonate (PC) containing 1 M LiClO4 at an ambient temperature in a glove box filled with dried argon. trast to a well-graphitized carbon fiber, the vacuum deposition of a silver film on the 800 °C fiber surface revealed no appreciable rate-enhancing effect except at the lowest potential limit. Successive heating of the silver-deposited fiber in low-pressure oxygen, however, resulted in a remarkable rate enhancement. Using a single carbon fiber (10 μm in diameter), the chemical diffusion coefficient (Dchem) was evaluated by PSCA. The Dchem value was found to be increased up to one order of magnitude after the treatment, by which we could show that the low-temperature carbon has a capability to be put to practical use for the next generation of Li-ion batteries having enhanced capacity and power.