In situ observation of thermally activated and localized Li leaching from lithiated graphite

TL;DR

This study investigates how microscale temperature hotspots cause localized lithium leaching from lithiated graphite in Li-ion batteries, revealing that temperature heterogeneity alone can induce lithium migration without applied current.

Contribution

The paper introduces in situ micro-Raman spectroscopy combined with optical microscopy and thermal simulations to analyze localized lithium leaching caused by microscale temperature hotspots.

Findings

Localized lithium leaching occurs at temperature hotspots.

Lithium metal remains localized near heated regions.

Heterogeneous temperature induces lithiation heterogeneity.

Abstract

Temperature is known to impact Li-ion battery performance and safety, however, understanding its effect on Li-ion batteries has largely been limited to uniform high or low temperatures. While the insights gathered from such research are important, much less information is available on the effects of non-uniform temperatures which more accurately reflect the environments that Li-ion batteries are exposed to in real world applications. In this paper, we characterize the impact of a microscale, temperature hotspot on a Li-ion battery using a combination of in situ micro-Raman spectroscopy, in situ optical microscopy and COMSOL Multiphysics thermal simulations. Our results show that mild temperature heterogeneity induced by the micro-Raman laser can cause lithium to locally leach out from different lithiated graphite phases (LiC6 and LiC12) in the absence of an applied current. The Li metal is found to be largely localized to the region heated by the micro-Raman laser and is not observed upon uniform heating to comparable temperatures suggesting that temperature heterogeneity is uniquely responsible for causing Li to leach out from lithiated graphite phases. A mechanism whereby localized temperature heterogeneity induced by the laser induces heterogeneity in the degree of lithiation across the graphite anode is proposed to explain the localized Li leaching. This study highlights the sensitivity of lithiated graphite phases to minor temperature heterogeneity in the absence of an applied current.