Highly Efficient Chlorine Fixation Based on Organic Selenium for 3.7-V Aqueous Batteries

The limited high-potential cathode materials for aqueous batteries have hindered their improvement in energy density improvement. Chlorine-based batteries with Cl⁰ to Cl^- redox reaction (ClRR) are promising for high-performance aqueous batteries due to their high redox potential and large theoretical capacity. However, the inherent gas-liquid conversion feature of ClRR and poor Cl fixation can cause Cl₂ leakage, reducing battery reversibility and raising safety concerns. Herein, we utilize a Se-based organic molecule, polymerized benzoselenadiazole (poly-PhSe), as the Cl-anchoring agent and realize an atomic level-Cl fixation through chalcogen-halogen coordinating chemistry, achieving a highly reversible ClRR with extra-low Cl₂ emission and a notably high-discharge voltage (3.7 V when paired with a graphite anode). The promoted Cl fixation and multivalence conversion of Se contribute to a three-electron conversion process, resulting in a significantly high-discharge capacity of up to 344 mAh g^-1 with an average output voltage of 1.79 V and a high Coulombic efficiency of 99.1%. Based on the superior reversibility of the developed poly-PhSe electrode with ClRR, a remarkable rate performance and cycling performance (with a capacity retention of 84.6% after 850 cycles) are achieved. Significantly, the pouch cell delivers a record areal capacity of up to 5.3 mAh cm^-2, demonstrating great potential for practical applications. This chalcogen-halogen coordination chemistry between the Se electrode and Cl provides new insight for developing reversible and efficient batteries with halogen redox reactions.