High Energy Lithium Ion Capacitors Using Hybrid Cathodes Comprising Electrical Double Layer and Intercalation Host Multi-Layers

Abstract The ability to recharge and to deliver high capacity quickly is required for the next generation of lithium ion storage technologies, especially for pure electric vehicles. A new type of hybrid positive electrode for lithium ion capacitors is investigated that comprises discrete layers of high power capacitive activated carbon and high capacity insertion-type LiFePO4, with the aim of boosting energy density towards that of a lithium ion battery while preserving capacitor-like power capability over thousands of charge/discharge cycles. The electrochemical performance of these hybrid electrodes was investigated both as a function of the LiFePO4 weight fraction (its thickness in the multi-layered electrode arrangement) and its location within the multi-layer. The best performing hybrid positive electrode architecture delivered an attractive balance of an energy density of ~ 90 Wh/kg and a power density of ~ 15 kW/kg in a full lithium ion capacitor configuration, which outperformed other combinations of the same materials. The ability to produce a double-sided configuration of the hybrid layered electrode over 20 × 20 cm2 was demonstrated, confirming the potential scalability of layer-by-layer manufacture.