Improving the electrochemical performance of Li2S cathodes based on point defect control with cation/anion dual doping

Abstract

Li₂S is a promising cathode candidate for all-solid-state batteries (ASSBs) because of its high theoretical capacity and availability for coupling with a Li-free anode or an anode-less electrode. However, ionically insulating Li₂S leads to excess conductive additives, low sulfur utilization and sluggish kinetics, which hinders the implementation of high energy density potential by ASSBs. Improving the intrinsic conductivity of Li₂S is the key to solve this issue. In this study, PI₃-doped Li₂S cathodes were fabricated and the relationship between lithium vacancies and ionic conductivities was examined quantitatively by the time-of-flight (TOF) neutron diffraction. By cation–anion dual doping, the ionic conductivities of Li₂S–PI₃ materials were improved to 10⁻⁴ S cm⁻¹, which is desirable for the cathode without solid electrolytes added. Upon simply mixing with carbon, the Li₂S–PI₃–C cathode shows a high overall cathode capacity of 541 mA h g⁻¹ with a high S utilization of 82% at 0.05C and a capacity of 207 mA h g⁻¹ at 1C at room temperature, realizing high energy density with good rate performance.