High-spatiotemporal-resolution operando strain imaging enabling degradation diagnosis in lithium-metal batteries

Understanding the structural evolution and failure mechanisms of electrodes is vital for advancing high-energy-density lithium batteries. However, real-time visualization of internal degradation processes under realistic conditions remains a major challenge. Here, we report an operando distributed strain imaging approach based on intrinsic Rayleigh backscattering to reveal the distinct stress evolution of Li-metal batteries (LMBs) with PVDF-based solid polymer electrolyte (SPE) and carbonate-based liquid electrolyte (LE). Distinct from conventional fiber Bragg grating (FBG)-based point strain monitoring, this distributed imaging method provides high spatiotemporal resolution and stress sensitivity, enabling non-destructive, full-area detection of interfacial inhomogeneity in lithium deposition beyond the reach of conventional electrochemical signals. Using this technique, we achieve continuous stress imaging over the full life cycle (>1600 h) in pouch-type LMBs, enabling life-cycle tracking of degradation evolution and uncovering an anomalous “V-shaped” stress trajectory during lithium deposition. Notably, NCM811|LE|Li batteries exhibit a maximum local strain of 441 µε after 120 h, more than twice that of NCM811|SPE|Li (164 µε). Large-area mapping further reveals that the PVDF-based SPE facilitates homogeneous Li + flux and uniform deposition. This Rayleigh-backscattering-enabled imaging offers a powerful diagnostic method for quantifying interfacial stress dynamics and real-time assessment of state of health in high-energy-density lithium batteries. Distributed Rayleigh-optical frequency domain reflectometry (OFDR) strain imaging reveals distinct chemo-mechanical degradation between NCM811|LE|Li and NCM811|SPE|Li pouch cells under industrial low stack pressure. Download: Download high-res image (201KB) Download: Download full-size image