Research progress in nonaqueous lithium/sodium-ion capacitors

Lithium/sodium ion capacitors have been widely studied because they can combine the advanges of supercpacitors and lithium/sodium ion batteries. They have higher energy density than conventional capacitors and higher power density than lithium/sodium ion batteries. In this review, the working principle, development status, bottleneck problem and improvement method of lithium/sodium ion capacitors are introduced. We mainly focus on the comparion of the lithium/sodium storage properties of the same kind of electrode materials and the performance of the corresponding lithium/sodium ion capacitors. We also point out the recent R&D process that is mainly focus on the improvement on the capacity and kinetics imbalance between the positive and negative electrodes, and the aims are to construct high-performance lithium/sodium ion batteries having high energy density, high power density and long cycle stability. Finally, the future development of lithium/sodium ion capacitors is summarized and prospected.