Insights into grain boundary in lithium-rich anti-perovskite as solid electrolytes

In all-solid-state lithium batteries, anti-perovskite solid electrolyte has high ionic conductivity and high stability with lithium metal anode. However, grain boundaries (GBs) contribute to undesirable resistance limiting ionic conductivity in anti-perovskite, and there is limited knowledge about the GBs in solid electrolyte, particularly at the atomic scale. Here, using density functional theory calculations we show that four symmetric tilt (3 and 5) GBs effects on structural characteristics and ions transport in anti-perovskite (Li3OCl) solid electrolyte. Using first-principles simulation, GBs are found to be relatively stable resulting in its high concentrations in Li₃OCl. Interestingly, the presence of GBs can improve compatibility with electrode, while it decreases the ionic conductivity and band gaps in Li₃OCl. Furthermore, it is noted that the 5 GBs structures are softer and higher ionic conductivity than 3 GBs, delivering a new insight that GBs types may importantly affect the softness and ionic conductivity in solid electrolyte. Significantly, we find that the easiest Li ion migration pathway is along GB direction in Li₃OCl with GBs structures. The present work uncovers the GBs behaviors in anti-perovskite solid electrolyte, which can help us to guide the design of high performance anti-perovskite solid electrolyte.