Operando optical monitoring of chemo-mechanical degradation in silicon-carbon anode batteries for state-of-health estimation

Silicon/carbon (Si/C) anodes are promising candidates for next-generation high-energy-density lithium-ion batteries (LIBs). However, severe volume changes lead to chemo-mechanical degradation, which is difficult to observe using conventional external monitoring approaches and hinders accurate state-of-health (SOH) estimation consequently. In this study, embedded Fiber Bragg Grating (FBG) sensors are employed for operando monitoring of the internal strain evolution of Si/C-anode pouch cells, enabling the investigation of chemo-mechanical degradation mechanisms and the development of a strain-informed SOH estimation framework. Crucially, Si/C-anode cells exhibit higher peak and irreversible strains compared with graphite-anode cells, indicating more severe mechanical deformation during cycling. Furthermore, aging experiments reveal that the accumulated irreversible strain serves as an effective indicator of interfacial degradation. Correlation analysis demonstrates that both reversible and irreversible strains exhibit strong linear relationships with capacity degradation, with Pearson coefficients of 0.991 and −0.973, respectively. Finally, mechanically interpretable strain features are incorporated into a Ridge-regression model for SOH estimation, achieving a root mean square error of 1.255%. This study establishes an internal strain-driven diagnostic framework for revealing chemo-mechanical degradation mechanisms and enabling accurate SOH estimation of high-energy-density LIBs.