Improvement of overcharge performance using Li4Ti5O12 as negative electrode for LiFePO4 power battery

Liquid state soft packed LiFePO4 cathode lithium ion cells with capacity of 2 Ah were fabricated using graphite or Li4Ti5O12 as negative electrodes to investigate the 3 C/10 V overcharge characteristics at room temperature. The LiFePO4/Li4Ti5O12 cell remained safe after the 3 C/10 V overcharge test while the LiFePO4/graphite cell went to thermal runaway. Temperature and voltage variations during overcharge were recorded and analyzed. The cells after overcharge were disassembled to check the changes of the separated cell components. The results showed that the Li4Ti5O12 as anode active material for LiFePO4 cell showed obvious safety advantage compared with the graphite anode. The lithium ionic diffusion models of Li4Ti5O12 anode and graphite anode were built respectively with the help of morphology characterizations performed by scanning electron microscopy. It was found that the different particle shapes and lithium ionic diffusion modes caused different lithium ionic conductivities during overcharge process.