The influence of surface inhomogeneity on the overcharge and lithium plating of graphite electrodes

Abstract

Abstract We seek to clarify phenomena involved in the overcharge of a graphite electrode in a lithium ion battery, including lithium (Li) plating. In Baker and Verbrugge (2019 J. Electrochem. Soc.), we developed a set of equations that can be used to treat Li plating and subsequent electro-dissolution, and we analyzed how the equation system behaved for a particle of graphite, a fundamental unit of the negative (porous) electrode in lithium ion cells. In this work, we employ the same governing equations, but we render them in a two-dimensional setting to examine the graphite-electrolyte interface, allowing us to clarify phenomena involved in Li plating over graphitic electrode elements in the absence of complicating factors associated with the architecture of a porous electrode. For a variety of reasons described in the Introduction of this work, the surface of graphite is nonuniform in terms of reaction rates for Li insertion and plating, and we show that when the electrode is subjected to constant-current charging, as is commonly employed, such nonuniformities lead to early Li plating over the highly reactive surfaces. These observations underscore the importance of maintaining a uniform electrode surface, especially when the cell is to be subjected to high rates of charge.