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

Abstract

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. Li2FeCl4, containing elementally strategically ideal Fe, exhibits a high energy density of 330 Wh (kg-cathode)−1 via redox-level-tuning partial O coordination (Li2.2FeCl3.8O0.2). 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.