Revealing the electrochemical-mechanical correspondence between electrode films and 20 Ah prismatic Li-ion batteries via optical fiber monitoring

Revealing the connections and corresponding relationships between changes in the electrodes and cell-level strain variation can enhance the accurate estimation of state of charge (SOC), state of health (SOH), cycling life, safety and other key factors of the large capacity prismatic batteries. By utilizing Fiber Bragg Grating (FBG) sensors and a "Zero-strain" lithium titanate (LTO) electrode, we directly monitored the strain behaviors of LiFePO4 (LFP) and graphite electrodes. These strain measurements were further connected to the non-monotonic strain variation observed in a 20 Ah LFP||Graphite prismatic cell monitored by surface-implanted FBGs, whicih confirms that the strain variation results from electrode deformation. Furthermore, we demonstrate the feasibility of accurately estimating SOC and SOH of the prismatic cell based on strain profiles, achieving an absolute error below 3% and a relative error below 10% for SOC estimation, as well as the ability to indicate capacity degradation method for SOH monitoring. These results encourage the utilization of FBG strain monitoring in actual engineering applications.