Recent advances in anode materials for sodium - and potassium-ion hybrid capacitors

With the advent of the post-lithium-ion era, sodium- and potassium-based energy storage devices are intensively focused in the recent years. The novel sodium- and potassium-ion hybrid capacitors couple with the merits of supercapacitors and secondary batteries and thus are widely explored. A typical hybrid capacitor is generally constructed by combining a battery-type anode and a capacitive-type cathode, which presents both high energy density and power features. The design and fabrication of anode materials with high rate capability and long life to match the capacitive cathode is a critical issue. In this short review, the newly developed anode materials in nonaqueous capacitors are systematically analyzed. Based on a comprehensive summarization, the challenges for further practical applications of anode materials are prospected.