The effect of electrochemically active element species on the stability of the layered cathode-sulfide electrolyte interface

Layered cathode materials are widely used in conventional lithium-ion batteries with liquid electrolytes. From LiCoO₂ (LCO) to Ni-rich (LiNi_xCo_yMn_zAl_{1−x−y−z}O₂, x ≥ 0.8) materials, different electrochemically active elements bring various properties to the cathodes and therefore they are employed in different fields. Although these layered material systems, composed of different transition metals (TMs), have been intensively studied, their electrochemical properties and interfacial stabilities when paired with promising sulfide solid electrolytes have not been systematically explored. Here, excluding the interference of redundant TMs, we prepared LiNi_xCo_1−xO₂ in an attempt to reveal the laws of reactivity at the interface between the layered cathode and the sulfide electrolyte. As a result of systematic analysis, overall, both chemical and electrochemical adverse reactions are proven to be aggravated with the increasing Ni/Co proportion. Compared to that when paired with liquid electrolytes, materials with a high Ni content exhibit much inferior electrochemical stability when paired with sulfide solid electrolytes. The introduction of Co enhances the interfacial stability, whereas the effect becomes less pronounced when the Co content in the system is half or more. This fundamental work deepens the insight into cathode/electrolyte interface deterioration and serves as a guide for designing an appropriate cathode for the up-and-coming all-solid-state lithium batteries (ASSLBs).