A self-healing strategy to enhance the stability of high mass-loaded nickel-cobalt hydroxides for high energy hybrid supercapacitors

Nickel-cobalt hydroxides (NiCo-OH) with superb electrolyte ion diffusion efficiency and numerous Lewis-base sites display preferable capacity and development potential. However, the low active species utilization and poor structural stability limit the construction of its thick electrodes with high mass-loading, further impeding the high-efficiency energy storage applications. Herein, by inducing the spontaneous formation of a dense zeolitic imidazolate framework-67 (ZIF-67) layer on the NiCo-OH nanosheets, the cracks on its surface are successfully repaired to achieve structural self-healing, thereby preparing the NiCo-OH@ZIF-67-2 carbon cloth electrode (NCZ-2) with high mass-loading (59.7 mg cm- 2) and stability. Moreover, the NCZ-2 with abundant oxygen vacancies and defects achieves a high specific capacitance of 91.11 F cm-2 (43.92 C cm-2/1526.13 F g- 1) at 10 mA cm- 2. The ex-situ measurements also reveal the phase structure evolution and charge storage mechanism of NCZ-2 during charging and discharging, and its reversible de/hydrogenation process and enhanced electrochemical activity are confirmed via theoretical calculations. Subsequently, the assembled aqueous NCZ2//HACC hybrid supercapacitors exhibit excellent energy storage capacity with a high energy density of 2.36 mWh cm- 2 and a favorable capacitance retention of 103.2 % after 10,000 cycles. Thus, this study provides a new strategy for designing thick electrodes with high structural stability and capacitance, further promoting the advancement of practical applications for high-energy storage.