Lithium deposition on graphite anode during long-term cycles and the effect on capacity loss

Abstract

Lithium deposition on the surface of a graphite anode during long-term cycles was evaluated using a LiCoO₂/graphite battery. The batteries were charged/discharged at 1 C and 25 °C within the voltage range of 2.75–4.2 V for 600, 700, 800, 900 and 1000 cycles. Scanning electron microscopy (SEM) results indicated that both solid electrolyte interphase (SEI) film and lithium deposition appeared on the surface of the cycled graphite anode. Dendritic and granular lithium deposits grew on the anode non-uniformly. Metallic lithium existed in the deposition according to differential scanning calorimetry (DSC) results. Capacity declined distinctly from the 800th cycle, corresponding with the growth of lithium deposits. An SEI film was formed on the surface of the lithium deposits. Results of X-ray photoelectron spectroscopy (XPS) test indicated that the composition of SEI film on the surface of the lithium deposits was the same as that of the SEI film on the surface of cycled graphite. Capacity loss from the electrolyte consumed by the formation of the SEI film was 23.61%, while the loss from other battery components was 76.39%. Formation of lithium deposits consumed active lithium in the battery and led to capacity loss. According to test results of the three-electrode cell, the average anode potential at the end of constant-current charging for full battery became more negative with the cycling, and this phenomenon was related to the generation of lithium deposits.