Cathode Materials for Sodium‐Ion Capacitors

The ever-increasing requirements for large-scale green energy storage create an urgent need to design novel rechargeable technologies with low-cost and sustainable properties. Because of the abundance of sodium (Na) resources and integration of the advantages of batteries and supercapacitors, sodium-ion capacitors (SICs) have aroused extensive concerns in recent years, and impressive research progress has been made in exploring high-performance electrode materials for SICs. Here, the selection and design of the structure and chemistry of materials for SIC cathode are comprehensively reviewed. Types and characteristics of cathode materials are divided into electrical double-layer capacitor (EDLC), pseudocapacitive, and battery-type cathode materials, covering the impact of various sodium storage kinetics on the electrochemical performance of SIC. The sodium storage mechanism and performance of these cathode materials are related to critical structural/chemical factors, including crystal structure, grain size, porosity, morphology, surface chemistry, as well as heteroatom doping. Furthermore, potential future research directions and a perspective toward the practical application of materials for SIC cathode are also provided.