Temperature-Derived Fe Dissolution of a LiFePO4/Graphite Cell at Fast Charging and High State-of-Charge Condition

Recently, the cathode materials employed in lithium-ion batteries are dominated by transition metal oxides, phosphates, and spinels which are known to undergo a rapid capacity fade due to the synergistic effect of transition metal dissolution and lithium plating, especially at higher operating voltages and at elevated temperatures. However, solutions to mitigate these issues are unavailable largely due to the incomplete understanding of the complexity of the capacity fade mechanism at high state-of-charge and fast charging rates. Herein, a comprehensive experimental evidence linking to the high cell temperature as the main origin of Fe dissolution in the LiFePO4/graphite cell is provided. After 400 complete charge-discharge cycles at 4C, Fe dissolution is accelerated and is shortly followed by the deposition of Fe on graphite anode, and the subsequent formation of Fe-catalyzed solid electrolyte interface layer at the anode. The dissolution-deposition process accounts for nearly 17-20% of the capacity loss against the initial capacity as observed in our experiments.