Operando Differential Electrochemical Pressiometry for Probing Electrochemo-Mechanics in All-Solid-State Batteries

Owing to an absence or lack of soft (and/or liquid) components, electrochemo-mechanical effects are imperative for all-solid-state batteries (ASBs) based on inorganic solid electrolytes (SEs). As this aspect has been overlooked, relevant investigation has remained scarce. In this work, the development of a new operando differential electrochemical pressiometry (DEP) for ASBs is reported. The time- (or capacity-) derivative differential pressure signals (dP/dt or dP/dQ) reflecting corresponding differential volume changes of electrode active materials feature the specific state of charges (SOCs). This finding leads to a precise estimation of the SOCs of graphite (Gr) electrodes in LiNi_0.70Co_0.15Mn_0.15O₂ (NCM)/Gr all-solid-state full cells using sulfide SEs with varying capacity ratios of negative to positive electrodes (n/p ratios); this is corroborated by complementary analysis using a three-electrode electrochemical cell and ex situ X-ray diffraction measurements. Furthermore, electrochemo-mechanical behaviors of NCM/Gr full cells with Gr electrodes employing SEs excluding or including reductively unstable Li₁₀GeP₂S₁₂ are investigated. Notable volume changes caused by lithiation of Li₁₀GeP₂S₁₂ are detected. Importantly, significantly delayed SOC for Gr caused by a severe side reaction with Li₁₀GeP₂S₁₂ is disclosed by the operando DEP result.