Enhanced low temperature performances of expanded commercial mesocarbon microbeads (MCMB) as lithium ion battery anodes

Expanded mesocarbon microbeads (EMCMB) are prepared by oxidizing pristine mesocarbon microbeads (MCMB). The d(002) value calculated from X-ray diffraction results shows that the average interlayer distance of MCMB increases after oxidizing modification. The increased interlayer distance facilitates Li+ insertion kinetics, which causes an extraordinarily improved capacity of EMCMB (100 mAh g(-1)) at -40 degrees C, compared with pristine MCMB (almost no capacity at -40 degrees C). The facilitated Li+ insertion kinetics is analyzed by electrochemical impedance spectroscopy (EIS). EIS results demonstrate that both charge-transfer resistance and Li+ diffusion resistance of the EMCMB decrease obviously. The diffusion coefficients of Li+ in MCMB and EMCMB at -40 degrees C calculated from EIS are 2.46 x 10(-17) cm(2) s(-1) and 1 x 10(-15) cm(2) s, respectively. (C) 2012 Elsevier B.V. All rights reserved.