Capacitance‐Enhanced Battery: Integrating High‐Density Battery Capacity with Supercapacitive Swiftness in an Ultra‐Large MXene Architecture

Abstract The rapid advancement of electrochemical energy storage based on earth‐abundant sodium (Na) ions necessitates the seamless integration of high energy density and fast charge–discharge kinetics. A persistent challenge in this domain is the sluggish ion migration kinetics associated with the large ionic radii of Na + ions, which significantly impact high‐energy output applications, such as acceleration and climbing. Herein, a concept of Capacitance‐Enhanced Battery (CEB) is proposed that leverages an ultra‐large MXene framework interfaced with a Bi 2 S 3 @ZnS composite(hereafter abbreviated as BiZnS) to form a C@BiZnS@V 4 C 3 heterostructure for reaching a dynamic dual‐mechanism response. At low current densities, the system operates predominantly in a battery mode, wherein sodium‐ion alloying and conversion reactions within the BiZnS framework ensure high energy retention. At high current densities, the heterostructure facilitates a supercapacitive mode, where active sites at the MXene and BiZnS surfaces and interfaces engage in rapid ion adsorption–desorption, enabling instantaneous energy delivery. This dual functionality imparts exceptional electrochemical performance of the Na‐ion batteries, with a remarkable specific capacity of 270.4 mAh g −1 at an ultra‐high current density of 100 A g −1 and extraordinary durability, maintaining outstanding electrochemical stability over 10 000 cycles at 20 A g −1 . These findings underscore the transformative potential of CEBs and establish dual‐mechanism electrodes for next‐generation energy storage systems.