Thermal cycling induced capacity enhancement of graphite anodes in lithium-ion cells

Abstract

Graphite electrodes were electrochemically cycled in Li-ion cells at 50 and 60°C in order to determine the changes in their surface properties in comparison to the electrodes tested at 25°C. A 17% drop in planar capacity occurred during the first cycle at 60°C compared to a 40% at 25°C and reduced the amount of damage that occurred to graphite due to a rapidly formed solid electrolyte interphase (SEI). During the following cycles, a planar capacity of 3.11±0.12mAhcm−2 was attained at 60°C rather than 0.53±0.03mAhcm−2 at 25°C. The SEI layer formed at 60°C predominantly consisted of Li2CO3 and was devoid of residual LiClO4 detected at 25°C. At 25°C, the diffusion coefficient of Li+ (DLi+) was calculated as 1.07×10−8cm2s−1, whereas at 60°C, DLi+ increased to 3.25×10−8cm2s−1. A pre-treatment conducted at 60°C enhanced the cyclic performance of graphite subsequently cycled at 25°C; a Li2CO3-enriched SEI, generated during the 60°C pre-treatment, covered the graphite surface uniformly and resulted in a 28% increase in battery capacity at 25°C.