Electrochemical performance of MCMB/(AC+LiFePO4) lithium-ion capacitors

Lithium-ion capacitors (LICs) were fabricated using mesocarbon microbeads (MCMB) as a negative electrode and a mixture of activated carbon (AC) and LiFePO4 as a positive electrode (abbreviated as LAC). The phase structure and morphology of LAC samples were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The electrochemical performance of the LICs was studied using cyclic voltammetry, charge-discharge rate measurements, and cycle performance testing. A LIC with 30 wt% LiFePO4 was found to have the best electrochemical performance with a specific energy density of 69.02 W h kg(-1) remaining at 4 C rate after 100 cycles. Compared with an AC-only positive electrode system, the ratio of practical capacity to theoretical calculated capacity of the LICs was enhanced from 42.22% to 56.59%. It was proved that adding LiFePO4 to AC electrodes not only increased the capacity of the positive electrode, but also improved the electrochemical performances of the whole LICs via Li+ pre-doping.