The Effect of Temperature and SEI Formation on the Nucleation and Growth of Electrochemically Plated Lithium

Abstract

Understanding the nucleation and growth process during electroplating of lithium metal is essential for enabling long cycle life in lithium metal batteries. The morphology of electrochemically plated lithium is strongly correlated with Coulombic efficiency and cycle life, and the nucleation and growth of lithium is dictated by the nature of the substrate, the characteristics of the solid electrolyte interphase (SEI), and temperature. However, there is a lack of knowledge about how these factors affect fundamental nucleation and growth processes, especially at temperatures other than room temperature. In this work, we investigate the nucleation, growth, and morphology evolution of lithium metal under different temperature conditions. Stainless steel and antimony metal are used as substrates to compare growth surfaces that are inert with those that form alloys with lithium. Ex situ SEM is used to explore the morphology evolution at temperatures ranging from -20 °C to 20 °C. In order to better track the particle size evolution over time, we use an electrolyte solution tailored to cause Li to deposit as spherical particles (a 1:1 (v/v) 1,3-dioxolane (DOL) and 1,2 dimethoxyethane (DME) mixture with 1M LiTFSI and 0.8M LiNO3). We find that as temperature increases, the particle size also increases. Furthermore, growth on lithiated antimony films results in larger average particle sizes than on stainless steel. Our experiments also show that the extent and nature of the initial SEI growth on the substrate plays a controlling role in determining the Li morphology and uniformity of growth, and prolonged growth of the SEI was found to increase the Coulombic efficiency during the first few cycles. These results highlight the sensitivity of Li to cycling conditions and temperature, and they indicate that careful control is necessary to attain high-efficiency cycling in Li metal batteries.