Cryolithionite‐based Pseudocapacitive Electrode for Sustainable Lithium‐ion Capacitors

Lithium‐ion insertion/deinsertion in anode at slow rates limits the power performance of energy storage devices. Here, a new pseudocapacitive electrode with high reversible capacity during cycling has been proposed for a lithium‐ion capacitor. The lithium‐fluoride garnet, namely Na3Fe2Li3F12, is obtained via precipitation from an aqueous solution at room temperature using abundant materials and exhibits a high discharge capacity of 746 mAh g‐1. After the first charging cycle, energy is stored via fast pseudocapacitive faradaic reactions which are facilitated by the nanocrystalline transport pathways with no structural modification to the electrode. The high stability window of F‐garnet allows extracting cell voltages of 2.2—3.2 V in a lithium‐ion capacitor where it is coupled with a porous carbon‐based positive electrode, with a high energy efficiency of 93 % maintained for 10000 charge/discharge cycles. This study opens new research direction concerning pseudocapacitive anode materials for the enhancing power performance and even replacing the traditional battery‐like anode materials.