In this paper, a battery-supercapacitor system is developed and its electrochemical performance is investigated. The battery-supercapacitor system is composed of a separated LiFePO4/activated carbon cathode and a separated Li4Ti5O12/activated carbon anode onto both sides of a piece of aluminum foil. We demonstrated the superior electrochemical performance of this battery-supercapacitor system, such as its energy density of 4.9-48.5 Wh/kg, power density of 167.7-5243.2 W/kg, rate capability of 73.9% at a current density of 20 A and cycle life (91.5% after 1800 cycles) which outperforms that of a hybrid supercapacitor. This can be explained by the synergistic effect of a Faradaic and non-Faradaic system in a single cell. The results clearly show that the battery-supercapacitor system, including a LiFePO4 cathode/Li4Ti5O12 anode and an activated carbon anode/activated carbon cathode, has great potential for use in advanced energy storage devices. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.