Electrochemical Properties and Deposition/Dissolution Behavior of Li Metal Negative Electrode in VS<sub>4</sub>/Li Battery

In order to develop high-energy batteries, it is important to understand the charge/discharge characteristics of the Li-metal negative electrode when operating with high Li utilization; these characteristics determine the practical capacity of the negative electrode. In this study, electrochemical properties and deposition/dissolution behavior of Li metal negative electrodes in a VS4/Li battery with high Li utilization and current density were investigated. The potentials of the positive and negative electrodes were measured separately using a three-electrode cell. During discharge (Li dissolution) at the negative electrode, a semi-quantitative correlation was observed between the Coulombic efficiency and the capacity at which the slope of the potential curve increased sharply. The Coulombic efficiency of the negative electrode improved when vinylene carbonate (VC) or fluoroethylene carbonate (FEC) was added to the electrolyte. Granular particles were found to be deposited on the entire surface of the charged negative electrodes. The average particle size followed the order FEC addition > VC addition > no addition. A mixture of fine fibrous and cord-shaped residues was observed in the discharged negative electrode when the electrolyte was used without additives. In contrast, almost exclusively fibrous residues were observed when the FEC-added electrolyte was used. The cell capacity decreased mainly because of the Li depletion of the negative electrode without additives, while the capacity reduction was mainly attributed to the degradation of the positive electrode with additives.