Cycling Performance and Kinetic Mechanism Analysis of a Li Metal Anode in Series-Concentrated Ether Electrolytes

Li metal batteries are facing unprecedented opportunities because of the urgent demand for high-energy-density rechargeable batteries as well as enormous challenges due to their low Coulombic efficiency and notorious safety issues. Recently, high-concentration electrolytes have attracted much attention owing to their superior properties. However, Li metal plating is an exceedingly complicated process including several elementary steps; it is not comprehensive enough to uncover the mystery of concentrated electrolytes by studying the structure of electrolytes, the existence of anions, cations, and solvent molecules using only conventional means. Here, we first report the apparent cycling performance of Li metal anode in series-concentrated LiTFSI/DOL-DME electrolytes. It shows that the Li metal anode in 4 M LiTFSI/DOL-DME electrolyte can operate 180 cycles stably at 2 mA cm^-2 with an average Coulombic efficiency of 98%, in which the Li plating layer is more compact and without dendrites. Subsequently, the kinetic parameters were obtained by the microelectrode technique. We found that appropriate mass transfer, interface, and surface step kinetic parameters (migration number, exchange current density, nucleation rate, and corrosion rate) and their good matching degree are favorable for the cycling of Li metal anodes. This work reveals the relationship between the elementary steps and the apparent cycling performance during the Li plating process under certain operating conditions; it is a major breakthrough in the study of high-concentration electrolytes and can provide a new perspective for future research.