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

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.