Interfacial Degradation Mechanism of Nanostructured LiCoO<sub>2</sub> for Li<sub>6</sub>PS<sub>5</sub>Cl-Based All-Solid-State Batteries

Abstract

Interfacial degradation of Li6PS5Cl (LPSCl) with oxide cathode materials during cycling, particularly the formation of interfacial voids, leads to poor electrochemical performance. The formation of these voids is driven by two distinct mechanisms: the volumetric changes of oxide cathode materials during cycling and the volumetric shrinkage of LPSCl due to oxidative decomposition. However, the relative contribution of each route to void formation remains ambiguous, especially for nanostructured cathode materials. This study highlights the predominant influence of oxidative decomposition of LPSCl on the nanostructured LiCoO2 surface in the formation of interfacial voids when compared to the volumetric changes of LiCoO2 between charging and discharging. The interfacial degradation behavior is compared between bare LiCoO2 and LiCoO2-Li2SnO3 core-shell nanoparticles. Both types of nanoparticles exhibit comparable absolute volume changes of LiCoO2 during cycling, due to their similar particle sizes and reversible capacities, effectively ruling out the impact of volumetric changes of LiCoO2 on void formation. However, LiCoO2-Li2SnO3 shows mitigated interfacial void formation compared to bare LiCoO2, resulting in improved electrochemical performance. This is attributed to the fact that LiCoO2-Li2SnO3 suppresses the oxidative decomposition of LPSCl due to the enhanced chemical stability of Li2SnO3 with LPSCl. This reveals that the oxidative decomposition of LPSCl on the nanostructured LiCoO2 surface contributes more significantly to void formation than the volume change of LiCoO2. These findings provide valuable insights into the degradation mechanisms of nanostructured cathode materials.