Synergistic Structural Doping and Compositing of CoNi Layered Double Hydroxide Nanosheets for High-Duration, Large-Energy-Density Asymmetric Supercapacitors

The enhancement of energy storage capabilities in metal hydroxides relies on the improvement of their intrinsic conductivity and structural stability. In this study, we propose an approach to tackle these challenges by incorporating structural doping with magnesium and compositing with carbon nanotubes (CNTs) through a mechanochemical method. Initially, CNTs are mixed with magnesium acetate (Mg(Ac)2) to form a CNT/Mg(Ac)2 mixture, which is then annealed to yield a CNT/MgO mixture. Subsequent ion-exchange reaction at room temperature transforms the magnesium oxide component into CoNi LDH, leveraging the differences in solubility product constants (Ksp) between magnesium hydroxide and nickel cobalt hydroxides. The resultant CNT/CoNi LDH composite displays a nanosheet morphology and uniform distribution of components facilitated by the CNT compositing. As an electrode material for asymmetric supercapacitor energy storage, the CNT/CoNi LDH1–10 exhibits enhanced energy storage performance relative to pristine CoNi LDH, with increased capacitance in both three-electrode and asymmetric configurations as well as higher energy density. Additionally, the structural doping confers exceptional cycling stability to the CNT/CoNi LDH1–10, maintaining nearly 100% capacitance retention after 90,000 charge/discharge cycles. This study introduces a versatile approach for fabricating doped and composited CoNi LDH materials and their mixed oxide counterparts with potential applications in catalysis, energy storage, and other domains.