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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 Clads 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. [ABSTRACT FROM AUTHOR]