In Situ Observation of Thermally Activated and Localized Li Leaching from Lithiated Graphite

Temperature is known to impact Li-ion battery performance and safety, however, understanding of its effect has largely been limited to uniform high or low temperatures. While the insights gathered from such research are important, limited information is available on the effects of non-uniform temperatures. In this paper, the effect of a microscale, temperature hotspot on a Li-ion battery was characterized using in situ micro-Raman spectroscopy, in situ optical microscopy and thermal simulations. Our results show that mild temperature heterogeneity induced by the micro-Raman laser can cause Li to leach out from LiC6 and LiC12 in the absence of an applied current. The leached Li is found to be localized to the temperature hotspot and is not observed upon uniform heating indicating that temperature heterogeneity is responsible for causing Li leaching. It is proposed that temperature heterogeneity induces spatial heterogeneity in graphite's degree of lithiation which can lead to Li leaching.