Influence of LiNO₃ on the Lithium Metal Deposition Behavior in Carbonate‐Based Liquid Electrolytes and on the Electrochemical Performance in Zero‐Excess Lithium Metal Batteries

Abstract

Continuous lithium (Li) depletion shadows the increase in energy density and safety properties promised by zero-excess lithium metal batteries (ZELMBs). Guiding the Li deposits toward more homogeneous and denser lithium morphology results in improved electrochemical performance. Herein, a lithium nitrate (LiNO₃ ) enriched separator that improves the morphology of the Li deposits and facilitates the formation of an inorganic-rich solid-electrolyte interphase (SEI) resulting in an extended cycle life in Li||Li-cells as well as an increase of the Coulombic efficiency in Cu||Li-cells is reported. Using a LiNi_0.6 Co_0.2 Mn_0.2 O₂ positive electrode in NCM622||Cu-cells, a carbonate-based electrolyte, and a LiNO₃ enriched separator, an extension of the cycle life by more than 50 cycles with a moderate capacity fading compared to the unmodified separator is obtained. The relative constant level of LiNO₃ in the electrolyte, maintained by the LiNO₃ enriched separator throughout the cycling process stems at the origin of the improved performance. Ion chromatography measurements carried out at different cycles support the proposed mechanism of a slow and constant release of LiNO₃ from the separator. The results indicate that the strategy of using a LiNO₃ enriched separator instead of LiNO₃ as a sacrificial electrolyte additive can improve the performance of ZELMBs further by maintaining a compact and thus stable SEI layer on Li deposits.