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

Abstract

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 LiClO 4 at an ambient temperature in a glove box filled with dried argon. In contrast 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 ( D chem) was evaluated by PSCA. The D chem 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.