Highly Reversible Aqueous Anode‐Free Cadmium–Bromine Batteries

Abstract

ABSTRACT 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 Cd 2+ plating kinetics in an anode‐free Cd–Br battery, LiCl is introduced into CdSO 4 electrolyte to reconstruct the Cd 2+ 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.