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

Graphite electrodes were electrochemically cycled in Li-ion cells at 50 and 60 degrees C in order to determine the changes in their surface properties in comparison to the electrodes tested at 25 degrees C. A 17% drop in planar capacity occurred during the first cycle at 60 degrees C compared to a 40% at 25 degrees 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 +/- 0.12 mAh cm(-2) was attained at 60 degrees C rather than 0.53 +/- 0.03 mAh cm(-2) at 25 degrees C. The SEI layer formed at 60 degrees C predominantly consisted of Li2CO3 and was devoid of residual LiClO4 detected at 25 degrees C. At 25 degrees C, the diffusion coefficient of Li+ (D-Li(+)) was calculated as 1.07 x 10(-8) cm(2) s(-1), whereas at 60 C, Dm* increased to 3.25 x 10(-8) cm(2) s(-1). A pre-treatment conducted at 60 degrees C enhanced the cyclic performance of graphite subsequently cycled at 25 degrees C; a Li2CO3-enriched SEI, generated during the 60 degrees C pre-treatment, covered the graphite surface uniformly and resulted in a 28% increase in battery capacity at 25 degrees C. (C) 2013 Elsevier Ltd. All rights reserved.