Multifunctional Coatings on Sulfide-Based Solid Electrolyte Powders with Enhanced Processability, Stability, and Performance for Solid-State Batteries.

Sulfide-based solid-state electrolytes (SSEs) exhibit many tantalizing properties including high ionic conductivity and favorable mechanical properties that motivate their use in next-generation solid-state batteries. However, widespread adoption of these materials is hindered by their intrinsic instability under ambient conditions, which makes them difficult to process at scale, as well as by (electro)chemical instability at the Li||SSE and cathode||SSE interfaces, which limits cell performance and lifetime. We leverage atomic layer deposition (ALD) to grow thin, oxide-based coatings on argyrodite (Li 6 PS 5 Cl) powders to address both issues simultaneously. We demonstrate that thin films of aluminum oxide (Al 2 O 3 ) can be directly grown onto argyrodite particles using trimethyl aluminum and H 2 O with minimal chemical modification of the underlying material. These coatings enable exposure of powders to pure and H 2 O-saturated oxygen environments for ≥4 hours with little to no reactivity, compared with significant degradation of the uncoated powder. Furthermore, pellets fabricated from coated powders exhibit ionic conductivities up to 2 × higher than those made from uncoated material, with a simultaneous decrease in electronic conductivity and significant suppression of Li 2 S and Li 3 P formation observed at the Li-SSE interface. These benefits result in significantly improved room temperature cycle life at high capacity and current density (≥150 cycles at 1 mAh/cm 2 per cycle and 0.5 mA/cm 2 ). We hypothesize that these enhanced properties derive from improved electronic and chemical properties at intergranular boundaries, as well as improved Li metal adhesion at the interface. This work points to a completely new framework for designing active, stable, and scalable materials for next-generation solid-state batteries. This article is protected by copyright. All rights reserved.