Electrochemical cycling behavior of LiFePO4 cathode charged with different upper voltage limits
Electrochemical cycling behavior of LiFePO4 (LFP) cathode charged with different upper voltage limits has been studied. Reversible capacity of the cathode is not significantly increased by pushing up the charge voltage limit. However, charge voltage limit plays a role affecting the passivation film of the electrode. When cycled with low charge voltage limit, the passivation film is not well developed and the LFP electrode exhibits high surface impedance. When charged to extremely high voltage limit, oxidation of electrolyte produces carbon-based layer coating the LFP particles. The optimized charge voltage limits of 3.9 and 4.3 V are obtained under different experimental conditions. Long term cycling behavior of full cell is evaluated against MCMB anode. After 1000 electrochemical cycles, around 60% of the initial capacity is lost. Lithium inventory loss is found to be the main factor responsible for the cell failure. The impact of charge voltage limit on the cycling performance of LFP cathode is buried in the Li consumption during electrochemical cycles. Fe precipitation and the resultant impedance rise on the anode side, which are widely accepted to be responsible for the capacity decay of graphite/LFP full cells, is not observed in this study.