Quantifying the local Li-ion diffusion over the grain boundaries of a protective coating, revealing the impact on the macroscopic Li-ion transport in an all-solid-state battery

Abstract The key challenge for solid-state-batteries is to design electrode-electrolyte interfaces that combine (electro)chemical and mechanical stability with facile Li-ion transport. Typically, this presents conflicting demands, the solid electrolyte-electrode interface-area should be maximized to facilitate high currents, while it should be minimized to reduce the parasitic interface reactions and enhance stability. Addressing these issues would greatly benefit from establishing the impact of interface coatings on local Li-ion transport over the grain boundaries. Here, the three-phase Li-ion transport, between solid electrolyte, coating and electrode is revealed using exchange-NMR, disentangling the detailed quantitative impact of the coating on the Li-ion transport in solid state batteries. A Li2S cathode is coated by LiI, providing a ductile and conductive interface with the argyrodite-sulfur electrolyte, where the exchange-NMR demonstrates that this enhances the interface transport to such an extent that the commonly applied nanosizing of the cathodic mixture can be abandoned. This leads to facile sulfur activation, preventing solid-electrolyte decomposition, in micron-sized cathodic mixtures, that can be related to the role of coatings on the Li-ion transport, providing perspectives for sulfur based solid-state-batteries.