Indium‐Mediated Electrolyte with Efficient Mg 2+ Transport and CO 2 Pathway Selection for Highly Reversible Mg–CO 2 Batteries

ABSTRACT Mg–CO 2 batteries present promising potential for integrated energy storage and carbon fixation, though their advancement is limited by slow cathodic CO 2 conversion kinetics and insufficient reversibility. Here, we report an In‐mediated electrolyte that couples solvation structure regulation with cathodic pathway control to realize highly reversible Mg─CO 2 chemistry in a conventional electrolyte system. Experimental and theoretical analyses demonstrate that, in addition to stabilizing the Mg anode and ensuring Mg 2+ transport, In species serve as an “electron sink and relay” to accelerate CO 2 conversion kinetics. They undergo preferential reduction prior to CO 2 , generating in situ atomically dispersed active sites that subsequently activate CO 2 via electron injection. This process directs the conversion pathway toward the formation of more reversible discharge products with favorable transport morphologies. As a result, the Mg─CO 2 battery delivers a long‐term cycling life of over 1300 h at 100 mA g −1 with a minimum voltage gap of 0.25 V during cycling, and maintains robust performance under extreme conditions, including 3000 mA g −1 rate capability and operation at −20°C. This concept of mediator‐enhanced electrolyte provides an effective route for a high‐performance Mg–CO 2 battery system.