Elucidating the impact of Li3InCl6-coated LiNi0.8Co0.15Al0.05O₂ on the electro-chemo mechanics of Li6PS5Cl-based solid-state batteries

Li6PS5Cl has attracted much attention due to its high Li-ion conductivity and ease in processibility, which allows large-scale applications of solid-state batteries. However, when combined with high-voltage cathodes, Li6PS5Cl suffers from detrimental side reactions. Due to the stability towards high voltages combined with a relatively high Li-ion conductivity Li3InCl6 has been considered as catholyte with the potential to compensate Li6PS5Cl shortcomings. Despite previous claims about its (electro)chemical instability, we hypothesize that Li3InCl6 remains a promising choice when (i) triple junctions between Li3InCl6, Li6PS5Cl, and Ni-rich cathodes are avoided and (ii) the cut-off voltage is below 3.6 V (vs Li/In). Therefore, a core-shell-structured cathode, i.e., LiNi0.8Co0.15Al0.05O₂ particles with a 100 nm thick pin-hole-free Li3InCl6 layer, has been developed using mechanofusion. When employed in a solid-state battery with a cut-off voltage of 3.58V (vs Li/In) a specific capacity enhancement of about 80 mAh/g at any C-rate (0.1 to 1C) was achieved. The stability of Li3InCl6 as well as its functionality to prevent Li6PS5Cl from decomposition and cathode particles from mechanical degradation has been demonstrated, by synchrotron operando XRD and, e.g., post-mortem analysis using Plasma FIB SEM and XPS. This study shows that Li3InCl6 can be used as catholyte when applied appropriately.