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

Abstract 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.