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

All-solid-state rechargeable batteries with Li2S-based positive electrode active materials have received much attention due to their safety and high capacity. Since Li2S has quite a low electronic and ionic conductivity, Li2S 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 Li2S-based positive electrode active material: Li2S-Li2O- LiI. Particularly, Li2S-(66.7Li(2)O center dot 33.3LiI) exhibited high capacity and long-term cycle performance. In this research, we investigated the microstructural changes of the Li2S-(66.7Li(2)O center dot 33.3LiI) positive electrode by using transmission electron microscopy (TEM) to clarify the long-term cycling factor. TEM observation revealed that Li2S becomes amorphous after charge processes, while the Li2S antifluorite structure is restored after discharge processes, indicating reversible micro-structural changes in Li2S. Moreover, we discovered that numerous Li2S 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.