Overcoming the Interfacial Challenges of LiFePO₄ in Inorganic All-Solid-State Batteries

All-solid-state batteries (ASSBs) are one of the most promising systems to enable long-lasting and thermally resilient next-generation energy storage. Ideally, these systems should utilize low-cost resources with reduced reliance on critical materials. Pursuing cobalt- and nickel-free chemistries, like LiFePO₄ (LFP), is a promising strategy. Morphological features of LFP essential for improved electrochemical performance are highlighted to elucidate the interfacial challenges when implemented in ASSBs, since adoption in inorganic ASSBs has yet to be reported. In this work, the compatibility of LFP with two types of solid-state electrolytes, Li₆PS₅Cl (LPSCl) and Li₂ZrCl₆ (LZC), are investigated. The potential existence of oxidative decomposition products is probed using a combination of structural, electrochemical, and spectroscopic analyses. Bulk and interfacial characterization reveal that the sulfide-based electrolyte LPSCl decomposes into insulative products, and electrochemical impedance spectroscopy is used to quantify the resulting impedance growth. However, through utilization of the chloride-based electrolyte LZC, high-rate and stable electrochemical performance is achieved at room temperature.