Boosted electrochemical performance of NiCoMn-based layered double hydroxide induced by creating metal-S bonds for hybrid supercapacitors

The reasonable and designed synthesis of cathodes, especially regulating their components and micro-structures, could efficiently enhance their intrinsic activity and exposed reaction sites for high-performance supercapacitors. Herein, NiCoMn-based ternary layered double hydroxide with metal-S (M-S) bonds (named as NiCoMn-LDH/S) is prepared via hydrothermal and ion-exchange methods. The M-S bonds created by ion exchange between LDH and moderate S^2- at relatively low temperatures (ensuring appropriate sulfurization degree) have noticeable effects on performance regulation of the cathodes, as the surface electron density, bandgap and the active sites of original LDH are effectively modulated, which are revealed by theoretical and experimental results. The prepared product possesses a high specific capacity of 275.1 mAh·g^-1, as well as admirable rate performance and cycling stability. In addition, the corresponding hybrid supercapacitor delivers a competitive energy density of 44.6 Wh·kg^-1 at a power density of 831 W·kg^-1, and presents long-term cycling stability of 81% initial capacity retention after 50,000 cycles. Moreover, the supercapacitor also possesses promising charge storage performance even at low ambient temperatures, which addresses the issues of low temperature performance faced by most typical supercapacitors. This study has proposed a high-quality LDH-based cathode with enhanced electrochemical activity for hybrid supercapacitors, which is significant for the development of aqueous charge storage devices.