Alkaline capacity decay induced vacancy-rich LDH for high-performance magnesium ions hybrid supercapacitor

Transition metal double hydroxides (LDHs) are among the most promising electrode materials in electrochemical energy storage. In this study, we synthesized electrodeposited nickel-cobalt layered double hydroxide (NiCo-LDH) to investigate the significant capacity gap in LDHs at different scan rates in an alkaline electrolyte. Experimental results demonstrate that the degradation of capacity at high scan rates is primarily attributed to the slow ion diffusion and the decreased reversibility of active metal ions. Furthermore, by exploiting the low reversibility of the deprotonation reaction at high scan rates, a NiCo-LDH with enriched hydrogen vacancies (H_v-rich LDH) was obtained. Consequently, the H_v-rich LDH, when used as the cathode in a magnesium ions hybrid supercapacitor (Mg-HSC), exhibits a high specific capacity of 94.97mAh g^-1 at a current density of 1 A g^-1 and maintains a significant capacity of 41.90 mAh g^-1 even at 20 A g^-1. Moreover, a Mg-HSC device assembled with an H_v-rich LDH cathode and a VS₂ anode delivers a high energy density of 48.44 Wh kg^-1 and a power density of 937.49 W kg^-1, demonstrating its practical application value. This work not only provides a theoretical basis for the defect design of LDHs but also expands their applicability.