In operando neutron diffraction study of the temperature and current rate-dependent phase evolution of LiFePO₄in a commercial battery

In operando NPD data of electrodes in lithium-ion batteries reveal unusual LiFePO₄phase evolution after the application of a thermal step and at high current. At low current under ambient conditions the LiFePO₄to FePO₄two-phase reaction occurs during the charge process, however, following a thermal step and at higher current this reaction appears at the end of charge and continues into the next electrochemical step. The same behavior is observed for the FePO₄to LiFePO₄transition, occurring at the end of discharge and continuing into the following electrochemical step. This suggests that the bulk (or the majority of the) electrode transformation is dependent on the battery's history, current, or temperature. Such information concerning the non-equilibrium evolution of an electrode allows a direct link between the electrode's functional mechanism that underpins lithium-ion battery behavior and the real-life operating conditions of the battery, such as variable temperature and current, to be made.