Temperature effect on graphite KS44

Abstract

Graphite Lonza KS44 in a solution 1 M LiClO4 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 ºC. 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 ºC shows a long voltage plateau at 0.7 Vvs. 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.

Keywords

• graphite
• lithiation
• reversible capacity
• galvanostatic charging
• solid electrolyte layer