High‐Performance Hybrid Supercapacitor Based on Graphene‐Wrapped Li₄Ti₅O₁₂ and Activated Carbon

Abstract Hybridizing battery and supercapacitor technologies have the potential to overcome the limitations of the currently prevailing energy‐storage systems. Combining high‐power capacitive electrodes from supercapacitors with the high‐energy intercalation electrodes in lithium‐ion batteries provides the opportunity to create a single device that can deliver both high energy and high power. Although energy densities in such hybrid systems easily exceed those found in supercapacitors, the kinetic imbalance between capacitive and intercalation electrodes remains a bottleneck to achieving the desired performance. This imbalance is eliminated through the use of graphene‐wrapped Li 4 Ti 5 O 12 from a simple, one‐step process as a high‐power anode in a new hybrid supercapacitor. The new hybrid supercapacitors are capable of delivering a high specific energy of up to 50 Wh kg −1 and can even maintain an energy of approximately 15 Wh kg −1 at a 20 s charge/discharge rate.