In situ stress monitoring unravels particle-scale microstructural evolution in aging LiFePO₄/graphite batteries

LiFePO₄/graphite (LFP/Gr) batteries are extensively used in energy storage. During cycling, the repeated lithiation/delithiation of active materials induces periodic stress fluctuations, which negatively impact electrochemical performance. Unveiling the correlation between stress evolution and electrode-level changes during long-term cycling is crucial for accurately estimating the state of health of the battery. Herein, a selfdeveloped high-precision in situ stress monitoring platform is used to track the stress evolution of LFP/Gr batteries over 500 cycles in real time. By combining the characterization of transmission electron microscopy(TEM) and X-ray photoelectron spectroscopy(XPS), it is found that the increase in the stress baseline during aging can reflect the thickening of the solid electrolyte interphase (SEI) on the Gr particles, while the change in the stresscurve amplitude indicates an increase in the cracking degree and proportion of LFP particles owing to the increased specific surface area of the cracked LFP particles that accelerate the phase-change rate on the positive electrode side. By establishing the connection between macroscopic stress features and electrode microstructures, this research provides experimental evidence for further stress-based battery state estimation technologies.

November 2024