Temperature effect on graphite KS44 lithiation in ethylene carbonate + propylene carbonate solution: Galvanostatic and impedance study

Abstract

Graphite Lonza KS44 in a solution 1 M LiC1O4 in a propoylene carbonate - ethylene carbonate (1 M:1 M) mixture was lithiated and delithiated galvanostatically at room temperature and at the elevated temperature of 55°C. Voltage-time profiles and complex impedance diagrams were recorded and are discussed for this particular system. It was confirmed that this type of graphite shows a relatively small current loss consumed by exfoliation, if lithiated at room temperature. However, the voltage-time curve of the first charging at 55°C shows a long voltage plateau at 0.7 V vs. Li/Li-, which corresponds to 540 mAh g-1 of irreversible capacity attributed to exfoliation. The solid electrolyte layer formed at elevated temperature, although less protecting in the sense of electrolyte reduction, shows a remarkably higher electrical resistance than that formed at room temperature. A comparison of the impedance diagrams of lithiated and delithiated samples allows the conclusion that mass transfer through the graphite, not that through the solid electrolyte layer, plays a dominant role in the mass transfer limitations.