Formation and Evolution of Lithium Metal Anode–Carbonate Electrolyte Interphases

The interphase layer between Li metal electrode and electrolyte is vital to the performance of Li metal batteries but is not adequately understood. To solve the efficiency and cyclability problems facing current Li metal anodes, strategies must be formulated upon updated knowledge of the interphase. We report our study of formation and evolution of the interphase layer in commercial carbonate electrolyte over cycles and as a function of additives, using Li||Cu cells as a model system. Side reactions with the electrolyte generate and continuously grow the interphase and set an unsatisfactory upper bound for the Coulombic efficiency. However, the cycle life of the cell is mostly determined by the structure and properties of the interphase layer. This understanding explains the positive additive effects observed in our prior work: Adding LiNO3 leads to a more porous and more ionically-conducting interphase layer and thus extends the cycle life; simultaneously adding LiNO3 and fluoroethylene carbonate reduces the reactivity of the electrolyte and thus improves the Coulombic efficiency.