Investigating battery-supercapacitor material hybrid configurations in energy storage device cycling at 0.1 to 10C rate

Battery-supercapacitor hybridisation enables safe charge-discharge operation at high C rate, up to the supercapacitor capacity, while maintaining battery lifetime. However, battery-supercapacitor systems in parallel connection require a DC/DC converter for voltage balance. Hybridisation at material level is explored in this study aiming to avoid the use of a DC/DC converter. Different battery-supercapacitor configurations, hybridised at material level, are investigated with the goal to maintain the long redox plateau of the battery and to self-balance without the need of DC/DC converter. Applying these principles to a LiFePO4 (LFP) battery, the best configuration was found to be a device with a Li anode and a composite LFP/activated carbon (AC) cathode reaching 180 mAh per gram of battery cathode. The device is cycled according to different schedules from 0.1C to 10C rate and the cathode and anode surface are characterised microstructurally and in terms of their chemical composition, after just fabricated and post-mortem after cycling according to different C rate schedules.