Redox‐Level Design for High‐Energy‐Density Chloride Electrodes

In this study, 3d transition metal chlorides are evaluated exhibiting high Li diffusivity, as determined by high‐throughput computational screening, and create a redox electron orbital energy‐level diagram to explain their working potentials and reversibility‐decreasing Cl‐release behavior. The redox‐level diagram enables the design of high‐potential chloride electrode materials that suppress Cl release by adjusting the transition metal environment of the redox center. Li 2 FeCl 4 , containing elementally strategically ideal Fe, exhibits a high energy density of 330 Wh (kg‐cathode) −1 via redox‐level‐tuning partial O coordination (Li 2.2 FeCl 3.8 O 0.2 ). This energy density is the highest recorded value for Fe‐based solid‐state batteries offering high safety and high charge/discharge rates. First‐principles calculations confirm and correlate this high energy density to Fe redox‐level tuning and capacity development up to the Cl‐release potential. This redox‐level tuning approach can be extended to other electrode material systems, including oxides, sulfides, and halides, to develop high‐energy‐density batteries.