Mechanism Exploration of Li₂S–Li₂O–LiI Positive Electrodes with High Capacity and Long Cycle Life via TEM Observation

High Resolution Image Download MS PowerPoint Slide All-solid-state rechargeable batteries with Li 2 S-based positive electrode active materials have received much attention due to their safety and high capacity. Since Li 2 S has quite a low electronic and ionic conductivity, Li 2 S in the positive electrode is combined with conductive agents, such as conductive carbons and sulfide solid electrolytes, to improve its cycle performance. Recently, we developed a remarkable Li 2 S-based positive electrode active material: Li 2 S–Li 2 O–LiI. Particularly, Li 2 S-(66.7Li 2 O·33.3LiI) exhibited high capacity and long-term cycle performance. In this research, we investigated the microstructural changes of the Li 2 S-(66.7Li 2 O·33.3LiI) positive electrode by using transmission electron microscopy (TEM) to clarify the long-term cycling factor. TEM observation revealed that Li 2 S becomes amorphous after charge processes, while the Li 2 S antifluorite structure is restored after discharge processes, indicating reversible microstructural changes in Li 2 S. Moreover, we discovered that numerous Li 2 S nanocrystals can maintain a size of less than 10 nm during discharge processes. This factor significantly contributes to the long-term rechargeability of these active materials.