Aqueous Zinc-Chlorine Battery Modulated by a MnO₂ Redox Adsorbent

Aqueous zinc-chlorine battery with high discharge voltage and attractive theoretical energy density is expected to become an important technology for large-scale energy storage. However, the practical application of Zn-Cl₂ batteries has been restricted due to the Cl₂ cathode with sluggish kinetics and low Coulombic efficiency (CE). Here, an aqueous Zn-Cl₂ battery using an inexpensive and effective MnO₂ redox adsorbent (referred to Zn-Cl₂@MnO₂ battery) to modulate the electrochemical performance of the Cl₂ cathode is developed. Density functional theory calculations reveal that the existence of the intermediate state Cl_ads free radical catalyzed by MnO₂ on the Cl₂ cathode contributes to the charge storage capacity, which is the key to modulate the electrode and improve the electrochemical performance. Further analysis of the Cl₂ cathode kinetics discloses the adsorption and catalytic roles of the MnO₂ redox adsorbent. The Zn-Cl₂@MnO₂ battery displays an enhanced discharge voltage of 2.0 V at a current density of 2.5 mA cm^-2, and stable 1000 cycles with an average CE of 91.6%, much superior to the conventional Zn-Cl₂ battery with an average CE of only 66.8%. The regulation strategy to the Cl₂ cathode provides opportunities for the future development of aqueous Zn-Cl₂ batteries.