Highly Reversible Aqueous Anode-Free Cadmium-Bromine Batteries

Aqueous anode-free zinc (Zn)-based batteries promise high energy density; however, their reversibility and lifespan are hampered by dendritic growth, hydrogen evolution, and poor Zn utilization (<20%). Cadmium (Cd), a close analogue of Zn, presents a viable alternative. Here, we systematically compare both Zn and Cd anodes in aqueous media, showing that Cd features dendrite-free deposition, suppressed side reactions, and stable cycling at anode utilization up to 75%. Benefiting from these advances, we demonstrate the first aqueous anode-free cadmium-bromine (Cd-Br) battery. To boost Cd²⁺ plating kinetics in an anode-free Cd-Br battery, LiCl is introduced into CdSO₄ electrolyte to reconstruct the Cd²⁺ solvation shell, resulting in accelerated desolvation and deposition kinetics. Consequently, anode-free Cd-Br coin cells achieve 87.6% capacity retention after 2000 cycles at 4 C, significantly superior to the anode-free Zn-Br coin cells with 12.4% retention after only 50 cycles and outperforming other reported aqueous anode-free systems. Moreover, scaled-up aqueous anode-free Cd-Br pouch cells exhibit stable cycling over 1250 cycles with capacity retention of 83.8% and high energy density of 157 Wh kg^-1, far exceeding that of state-of-the-art Zn-Mn and Zn-V pouch cells. This work establishes anode-free Cd-Br chemistry as a new paradigm in developing high-energy and highly reversible aqueous batteries.