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

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 battery capacitors 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 battery capacitor devices had a good cycle life performance at high rates. After 1000 cycles, the capacity loss of the DMLAC/Li4Ti5O12 hybrid battery capacitor device at 4C was no more than 4.8 %. Moreover, the capacity loss would be no more than 9.6 % after 2000 cycles at 8C.