Solid-state lithium metal batteries represent a critical frontier in energy storage technology, yet persistent interfacial instability between Li metal anode and solid electrolytes generates detrimental electrochemical-mechanical interactions that undermine cycling durability. To resolve this fundamental challenge, here we establish an innovative real-time strain monitoring that directly correlates micro-mechanical evolution with interfacial degradation during Li plating/stripping. It reveals that Li plating induces significant microstrain accumulation, while stripping processes only partially release mechanical stress. Systematic analysis identifies three characteristic strain evolution periods during cycling: initial linear growth, intermediate stabilization, and terminal exponential escalation prior to cell failure. Post-mortem characterization attributes the final strain surge to synergistic cumulative dendrite propagation, dead lithium agglomeration, and SEI disintegration. Parametric studies demonstrate that elevated cell stack pressure from 200 KPa to 3500 KPa reduced initial strain growth cycle by 50% and stabilized strain value by 47.8%, whereas doubling current density prolongs 10-fold linear growth period and increases 4-fold plateau strain one, severely curtailing battery longevity. Crucially, we establish predictive correlations between strain trajectory patterns and electrochemical failure signature. This mechano-analytical platform enables non-destructive interrogation of interfacial dynamics, providing an operational protocol for failure diagnosis and pressure-current parameter optimization to achieve durable solid-state battery systems.
