Cation-Exchange-Induced Enhanced Capacitive Performance of Ternary ZnCoNi Carbonate Hydroxides for High-Energy-Density Hybrid Supercapacitors

The development of high-performance electrode materials is critical for advancing the energy density of hybrid supercapacitors. Herein, a cation exchange strategy is proposed to optimize the electrochemical properties of a ternary ZnCoNi carbonate hydroxide (ZnCoNi-CH) electrode. The selective Ni2+-for-Zn2+ cation exchange in an ethanol solution effectively preserved the original morphology of the ZnCoNi-CH nanoarray while enhancing structural defects and synergistic bimetallic effects. The cation-exchanged electrode (ZnCoNi-CH-ex) exhibited a significantly increased areal capacity of 3.80 C cm–2 at 10 mA cm–2, surpassing that of the pristine ZnCoNi-CH electrode (2.55 C cm–2). XPS and EPR analyses revealed that cation exchange modulated the valence states of Ni3+/Ni2+ and Co3+/Co2+, promoting electron transfer and surface redox activity. Structural defects introduced during the exchange process created high-index crystal planes, facilitating electrolyte penetration and charge transport. As a result, the ZnCoNi-CH-ex electrode demonstrated superior rate capability (60.7% capacity retention at 100 mA cm–2) and exceptional cycling stability (94.7% capacity retention after 12,000 cycles at 50 mA cm–2). When integrated into an all-solid-state hybrid supercapacitor with activated carbon, the device delivered a high energy density of 1.0 mWh cm–2 at a power density of 9 mW cm–2, maintaining 105.9% capacity retention after 15,000 cycles. Theoretical calculations confirmed that cation exchange narrowed the bandgap and reduced OH– adsorption energy, synergistically enhancing conductivity and reaction kinetics. This work establishes an effective strategy for tuning the electronic structure and interfacial properties of electrode materials for high-performance hybrid supercapacitors.