Analysis of Thermal Aging Paths for Large-Format LiFePO4/Graphite Battery

Long-term cycling performance of 60 Ampere-hour (Ah) LiFePO4/graphite batteries has been investigated at different temperatures. It is found that single cells and series connected modules cycled in proper thermal environment exhibit superior cycling stability over those cycled at both ends of operation temperature. This paper presents a comprehensive technique to identify capacity fade mechanisms of different thermal aging paths, including galvanostatic intermittent titration technique (GITT) analysis, electrochemical impedance spectra (EIS) analysis, and dQ/dV peak curves. The direct correlation between thermal conditions and the side reactions degree of the batteries provides an effective methodology to analyze the reason of capacity fade and to prolong the cycle life of LiFePO4/graphite batteries. Finally, the effects under different aging stages on the degradation elements are also examined.