Effects of the LiFePO4 content and the preparation method on the properties of (LiFePO4+AC)/Li4Ti5O12 hybrid batterycapacitors

Abstract

Two composite cathode materials containing LiFePO4 and activated carbon (AC) were synthesized by an in-situ method and a direct mixing technique, which are abbreviated as LAC and DMLAC, respectively. Hybrid battery-capacitors LAC/Li4Ti5O12 and DMLAC/Li4Ti5O12 were then assembled. The effects of the content of LiFePO4 and the preparation method on the cyclic voltammograms, the rate of charge-discharge and the cycle performance of the hybrid batterycapacitors were investigated. The results showed the overall electrochemical performance of the hybrid battery-capacitors was the best when the content of LiFePO4 in the composite cathode materials was in the range from 11.8 to 28.5 wt. %, while the preparation method had almost no impact on the electrochemical performance of the composite cathodes and hybrid battery-capacitors. Moreover, the hybrid batterycapacitor devices had a good cycle life performance at high rates. After 1000 cycles, the capacity loss of the DMLAC/Li4Ti5O12 hybrid batterycapacitor device at 4 C was no more than 4.8 %. Moreover, the capacity loss would be no more than 9.6 % after 2000 cycles at 8?C.