<p>Lithium-ion batteries (LIBs) exhibit an intrinsic electrochemical-mechanical coupling effect, enabling the effective monitoring of lithium plating via the responses of mechanical signals. To reveal the electrochemical-mechanical coupling mechanism throughout the entire lithium plating process, fiber optic strain sensors were employed to systematically investigate the strain evolution behavior of LIBs during charging and the subsequent relaxation stage. The results show that under normal charging conditions without lithium plating, the cell strain exhibits a monotonic stress release and stabilizes during the relaxation stage. In contrast, under lithium plating conditions, including low-temperature and high C-rate charging, the cell strain exhibits a characteristic of increasing first and then decreasing during the relaxation stage, which is defined as a strain peak. Combined with the relaxation voltage analysis and electrochemical impedance spectroscopy (EIS) test results, this strain peak is confirmed to originate from the continuous kinetic process of the spontaneous dissolution of metallic lithium and the re-intercalation of Li⁺ into graphite. This process is driven by the potential difference between the metallic lithium deposited on the anode surface and the lithiated graphite. This reproducible strain characteristic is observed in various commercial cell systems, thus verifying the universality of the proposed mechanism. This study clarifies the intrinsic correlation between cell strain and the lithium dissolution − re-intercalation process during relaxation and deepens the understanding of the electrochemical-mechanical coupling mechanism. It also provides theoretical support for the strain-based lithium plating monitoring technique.</p>