Maxwell Protocol for Non‐Destructive Health Diagnosis of All‐Solid‐State Batteries

Abstract Sulfide‐based all‐solid‐state batteries (ASSBs) exhibit distinct degradation dynamics characterized by intricate interfacial cascade reactions that differ markedly from those of conventional lithium‐ion batteries (LIBs). Despite being technologically promising, these systems currently lack robust health diagnostic frameworks to capture their critical failure mechanisms. Various physicochemical analyses based on cell disassembly are available and provide useful health‐related information; but, because of their destructive nature, they render cells unusable for continuous health monitoring over long‐term cycling. Herein, we present a nondestructive diagnostic methodology founded on the Maxwell relations. This approach enables the precise detection of the delithiation heterogeneity in cathode active materials and quantifies internal void formation by measuring changes in the open‐circuit voltage (OCV) in response to temperature and pressure variations, respectively, without perturbing the cell operation. Our comprehensive thermodynamics analysis protocol establishes systematic criteria for classifying cells into one of three categories: reuse, recondition, or recycle. This nondestructive diagnostic methodology enables the sustainable utilization of ASSB technology based on efficient resource management.