High-temperature capacity fading mechanism for LiFePO4/graphite soft-packed cell without Fe dissolution

• High-temperature capacity fading for LiFePO4/graphite soft-packed cell was studied.
• Temperature-dependent extent of surface structural disorder in graphite was found.
• Active lithium loss is still a dominating mechanism for irreversible capacity loss.
• Fast and continuous reformation/repairing mechanism of instable SEI was proposed.

Commercial electrolyte containing functional additives that completely suppress Fe dissolution from the LiFePO4 electrode was used in LiFePO4/graphite soft-packed cell for eliminating its catalysis to solid electrolyte interphase (SEI) formation. The results show that the cycle performances of assembled soft-packed full-cell were still temperature-dependent. Average Raman spectra show temperature-dependent extent of surface structural disorder in graphite, leading to higher interfacial resistance at elevated temperatures. Half-cell studies using cycled cathode at different temperatures reveal different lithiated LixFePO4. An accelerated mechanism of the operating temperature to reformation/repairing of SEI layer is proposed, which greatly consumes active lithium during cycling, therefore causes fast capacity loss at elevated temperatures.