Electrochemical Performance of Lithium Ion Capacitors Using Li<sup>+</sup>-Intercalated Mesocarbon Microbeads as the Negative Electrode

Abstract

Lithium ion capacitors (LICs) were fabricated using Li -intercalated mesocarbon microbeads (LMCMBs) as the negative electrode and commercial activated carbon (AC) as the positive electrode. The phase structure of LMCMB electrodes was characterized by X-ray diffraction (XRD). LMCMB electrodes retain their original graphite crystal structure when the capacity induced by initial Li + intercalation is less than 200 mAh·g-1. The charge-discharge performances of positive and negative electrodes and LICs were studied using a three-electrode cell. Using an LMCMB electrode as an anode, a stable working potential is obtained at lower voltage than using other electrodes, and the potential range of the positive electrode is extended to a lower range. The electrochemical performance of LMCMB/AC capacitors, including capacitance, cycle life, and efficiency, is improved compared with that of an MCMB/AC capacitor. The efficiency increases from less than 95% to nearly 100%, and the capacity retention is improved from 74.8% to nearly 100% for 100 cycles in a voltage range of 2.0 to 3.8 V. The stable capacity of LMCMB/AC capacitors with cycling is directly correlated to less polarization of AC during the charge storage process, which is caused in turn by the LMCMB negative electrode. Gravimetric energy densities as high as 85.6 1733 Acta Phys. ⁃Chim. Sin. 2012 Vol.28 and 97.9 Wh·kg-1 are obtained in voltage ranges of 2.0 to 3.8 V and 1.5 to 3.8 V, respectively.