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

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.