Dual ion carrier storage through the addition of Mg²⁺ for high-energy and long-life zinc-ion hybrid capacitor

Cation additive can efficiently enhance the total electrochemical capabilities of zinc ion hybrid capacitors (ZHCs). However, their energy storing mechanisms are still under debated in zinc-based systems. Herein, we assemble several Zn // AC devices with different concentration electrolytes and investigate their electrochemical reaction dynamic behaviors. The zinc ion capacitor with Mg²⁺ mixed solution provides 82 mAh g^-1 capacity at 1A g^-1 and maintains 91% of original capacitance after 10,000 cycling. It is superior to the other assembled zinc ion devices in single component electrolyte. It demonstrates that the double ion storage mechanism enables superior rate performance and long cycle lifetime in ZHCs.