Thermal-overdischarge coupling induced aging mechanisms in LiFePO4 batteries: insights from multi-scale electrochemical and material diagnostics

This study deciphers aging mechanisms in lithium iron phosphate (LiFePO4) batteries under coupled thermal-electrochemical stresses using a multi-scale approach. Industrial-grade LiFePO4/graphite pouch cells underwent accelerated aging across orthogonal temperature (25/45/65 °C) and discharge cut-off voltage (2.5/1.0/0.5 V) conditions. Integrating electrochemical diagnostics (DCIR, EIS, IC/DV) with post-mortem characterization (SEM/TEM/XRD/ToF-SIMS/μXRF) reveals that: (1) Elevated temperatures amplify lithium loss and SEI instability; (2) Deep over-discharge (≤1.0 V) triggers anode degradation via graphite structural collapse, copper dissolution, and SEI rupture; (3) Coupled stresses induce synergistic failure—manifested by DCIR transitions from linear to exponential growth—correlated microscopically with dead lithium accumulation, metal deposition percolation, and interfacial collapse; (4) Extreme conditions (65 °C/0.5 V) provoke atypical mechanisms including cathode FePO4 segregation and copper migration. The work establishes DCIR inflection as a non-destructive marker for failure-stage transition and provides fundamental insights into stress-coupled degradation pathways, advancing predictive models for LiFePO4 battery durability in energy storage systems.