Research progress in Na-ion capacitors

Research activities on the development of organic Na-ion hybrid electrochemical capacitors (NICs) are described in this review. In particular, more emphasis is given on the development of battery type electrodes (faradaic mechanism), for example, hard carbons, Na2Ti3O7, etc. Also, equal importance is given for the exploration of non-faradaic type counter electrodes derived from bio-mass and polymer precursors. In the recent past, Mxenes have attracted attention as promising candidates for cathodes and anodes for electrochemical energy storage devices. Accordingly, efficient utilization of such Mxenes as positive and negative electrodes in an NIC assembly is given along with their synthetic procedure. Furthermore, the symmetric configuration of other Na-ion based organic supercapacitor is also given in detail.