Capacity loss induced by lithium deposition at graphite anode for LiFePO4/graphite cell cycling at different temperatures

Capacity fading of a commercial 18650 LiFePO4/graphite cell was investigated at different temperatures (25, 40, 50 and 60 °C) until 30% of its capacity was lost. Capacity decrease of the cell is in linear relationship with cycle number and the slope of the capacity-fading line is increased by elevating temperature. The capacity-fade mechanisms were investigated by using a combination of electrochemical, structural and inductively coupled plasma (ICP) techniques. Lithium inventory loss was found to be the main cause for the capacity loss. At the end of the cycling test, the amount of lithium precipitated on the graphite anode surface was determined. Most of the consumed lithium is found on the graphite anode, especially at high temperature condition, illustrating that the majority of lithium loss was ascribed to the side reactions at the graphite anode/electrolyte interface. Fe deposition at the graphite anode surface aroused from its dissolution into the electrolyte is not significant even when the cell is cycled at 50 °C condition.