Rechargeable Cadmium Metal Batteries Enabled by an Aqueous CdSO4 Electrolyte

Rechargeable aqueous cadmium (Cd) metal batteries enabled by the Cd plating and stripping behaviors of anode show great promise for next-generation energy storage applications due to the superior corrosion resistance, high specific capacity (476.5 mAh g^-1), suitable redox potential (-0.4 V vs standard hydrogen electrode), and cost-effectiveness of Cd anode. However, this field is still in its infancy, with limited scientific exploration and numerous unresolved challenges. Therefore, to bridge the existing research gap in the field of Cd metal batteries, this study conducted a comprehensive investigation into the electrochemical performance of the Cd metal, utilizing a stable and low-cost aqueous CdSO₄ solution as an electrolyte. It is revealed that the solvation structure of Cd²⁺ transitions from [Cd(H₂O)₉]²⁺ to [Cd(H₂O)₆(SO₄)₃]^4- as the CdSO₄ concentration increases from 0.5 to 3 M. This transition reduces the activity of H₂O around Cd²⁺, promotes charge transfer, and enhances desolvation/solvation kinetics during Cd plating/stripping processes. Consequently, when the concentration of CdSO₄ reached nearly saturated 3 M, the Cd anode presents optimal corrosion-resistant and dendrite-free capabilities, reflecting in durable Cd plating/stripping performance for over 2000 h with a high Coulombic efficiency of 99.7%. Furthermore, the Cd//V₂O₅ full cell achieves an ultralong cycle life, maintaining stable performance for 30,000 cycles with minimal capacity degradation. The high reversibility of the Cd anode and the exceptional performance of the full cell affirm the potential of aqueous CdSO₄ electrolyte as a foundation for the future development of Cd metal batteries, offering profound insights and guidance for advancing aqueous energy storage technology.