Hybridization of electrochemical capacitors and rechargeable batteries: An experimental analysis of the different possible approaches utilizing activated carbon, Li4Ti5O12 and LiMn2O4

Electrochemical hybrid energy storage devices have been developed and investigated with considerable effort in recent years. The idea is to combine the high specific energy of the battery component together with the high specific power of the capacitor component within one system. We realized laboratory scale electrochemical cells based on a capacitor material (activated carbon) and two battery materials (LiMn2O4 and Li4Ti5O12). We investigate hybrid systems following a serial and a parallel approach with two different mass ratios of battery materials over activated carbon.The investigated systems are compared in terms of Ragone plot and pulse performance. The results clearly show that the parallel hybridization of electrochemical capacitors and lithium-ion batteries is superior to the serial approach. Parallel hybrids provide both, high specific energy and power, and they outperform both the battery and the capacitor for pulsed applications. By contrast the serial hybrid can slightly increase the specific energy with respect to the capacitor but the specific power is comparable to the power of the battery, and it does not provide any benefit with pulsed applications.

► Different hybridization approaches of electrochemical storage devices were compared.
► Serial hybrids do not improve the battery or the capacitor.
► Parallel hybrids provide both high specific energy and specific power.
► Parallel hybrids outperform the other systems for pulsed applications.