Engineering the Artificial Cathode-Electrolyte Interphase Coating for Solid-State Batteries via Tailored Annealing

Solid-state batteries with nickel-rich layered oxide cathode active materials (CAMs) and sulfide-based solid electrolytes (SEs) are emerging as promising candidates for next-generation energy-storage systems. However, both active and electrolyte materials suffer from poor (electro)chemical compatibility, leading to severe degradation at the SE|CAM interface which is highly detrimental to the long-term cycling stability. Inspired by the natural cathode-electrolyte interphase (CEI), a novel coating concept involves formation of a protective, artificial CEI coating prior to cell assembly. Here, we investigate the oxidative annealing process after coating Li₃PS₄ as precursor onto polycrystalline LiNi_0.85Co_0.10Mn_0.05O₂ (NCM85). A combination of microscopic (scanning transmission electron microscopy, STEM), spectroscopic/spectrometric (X-ray photoelectron spectroscopy, XPS, low energy ion scattering, LEIS, and time-of-flight secondary ion mass spectrometry, ToF-SIMS), and electrochemical methods reveals that the composition, morphology, and performance of the coating can be tailored by controlled annealing in oxidizing atmosphere. The effect on coating quality and its stabilizing effect on the SE|CAM interface are examined. Only a morphologically and compositionally optimized coating can successfully prevent interfacial degradation, highlighting the need for tailored process parameters to fully exploit the coating potential. The optimization is supported by an efficient benchmarking framework combining electrochemical and analytical methods, which can serve as a basis for further systematic coating studies.