Real-Time Monitoring of Strain Relaxation in Graphite Anode for Lithium-Ion Battery.

With the push for high energy density, lithium-ion batteries face growing challenges from mechanical strain in graphite anodes, arising from volume fluctuations during Li⁺ insertion and extraction. Current diagnostic limitations have impeded the comprehensive elucidation of internal strain evolution and its coupling with underlying ion transport mechanisms. In this study, an embedded fiber-optic sensing strategy is implemented to achieve real-time, distributed quantification of strain dynamics within the graphite electrode. This approach enables direct tracking of spatially heterogeneous strain accumulation and reveals a strain relaxation phenomenon intimately correlated with Li⁺ diffusion behavior. The relaxation process becomes particularly significant at high states of charge (> 80%) and exhibits strong thermally activated kinetics. To mitigate localized strain concentrations, a pitch-derived carbon coating strategy is further developed, yielding a 2.8 nm-thick amorphous carbon layer on graphite surfaces. Strain mapping demonstrates that the modified graphite (Gr@P) exhibits ≈22% enhancement in relaxation kinetics and a ≈47% improvement in distribution uniformity. Consequently, the Gr@P anode delivers improved mechanical integrity and electrochemical durability, retaining 86.7% capacity after 500 cycles at 2C -substantially surpassing the pristine graphite (55.0%). This work establishes a practical real-time methodology for mechanochemical interrogation, offering a viable pathway for the rational design of high-performance anodes.