Synergistic effect of NaTi2(PO4)(3) and MXene synthesized in situ for high-performance sodium-ion capacitors

The rapid growth of industries that use electrical energy requires novel energy storage systems that are low-cost, reliable, and have improved capacity and power. Sodium-ion capacitors (SICs) have attracted considerable attention as next-generation energy storage systems because they comprise sodium, which is a relatively inexpensive resource, and have high energy and power. Battery-type materials for SICs need to be studied due to their poor rate performance and lifespan. This study reports a NaTi2(PO4)(3)/MXene (NTP/MXene) composite as a battery-type anode material for high-performance SICs. The NTP/MXene composite is synthesized via the in situ growth of NTP, with poor electrical conductivity, on the surface of MXene, with a two-dimensional structure and high electrical conductivity. The in situ synthesized NTP/MXene composite exhibits better rate performance and cyclic stability than NTP or MXene. These improved electrochemical properties are attributed to the synergistic effect of the pseudocapacitive characteristics of MXene and the battery characteristics of NTP. An SIC assembled with the NTP/MXene composite and activated carbon affords a high energy density of 112.1 Wh kg(-1) and a high power density of 9.5 kW kg(-1). Furthermore, it exhibits excellent long-term capacity retention of 78 % even after 10,000 cycles.