In Search of the Best Solid Electrolyte-Layered Oxide Pairing for Assembling Practical All-Solid-State Batteries

All-solid-state batteries have largely attracted interest as they can boost the energy density of today's Li-ion batteries by 50% provided that several fundamental/practical roadblocks be solved. Focusing on the interface between the solid electrolyte and cathode active material (CAM), we herein studied the chemical/electrochemical compatibility of the coated layered oxide LiNi0.6Mn0.2Co0.2O2 with the three main inorganic electrolyte contenders, these being lithium thiophosphate (β-Li3PS4), argyrodite (Li6PS5Cl), and halide (Li3InCl6). Such electrolytes were prepared by either solvent-free or solution chemistry and paired with the CAM to form a composite which was further tested by assembling solid-state batteries using Li0.5In as a negative electrode. Among the electrolytes prepared by dry routes, the best performing one was found to be Li6PS5Cl followed by β-Li3PS4 and lastly Li3InCl6. In contrast, no general trend of benefit or detriment was observed when switching to the solution route as it resulted in either performance improvement or deterioration depending on the electrolyte. Additionally, they show a strong dependence on the battery performance upon the presence of carbon additives. Lastly, we unraveled a pronounced chemical/electrochemical incompatibility of Li3InCl6 toward Li6PS5Cl and β-Li3PS4, hence questioning the design of hetero-structural cell architectures. Altogether, we hope these findings to provide guidance in the proper pairing of electrode–electrolyte components for designing highly performing solid-state batteries.