Multi-Valent Cation Strategies for Controlling Interphase Chemistry at the Lithium Metal Anode

The effectiveness of a solid electrolyte interphase (SEI) in lithium metal batteries (LMBs) is crucial for the reversible deposition and dissolution of lithium (Li). Herein, a multi-valent cation (MVC) is proposed approach to enable superior LMB performance without increasing conducting salt concentration, thus reducing the cost and environmental footprint of LMBs. In this approach, a minimal amount of magnesium carbonate (MgCO₃) of 0.05 m is added to a lithium hexafluorophosphate (LiPF₆) based electrolyte, which effectively scavenges hydrogen fluoride (HF) generated from hydrolysis of LiPF₆. Concurrently, the HF scavenging process dissolves MgCO₃ microparticles and releases Mg²⁺ cations. It is noteworthy that multivalent Mg²⁺ cations, due to their high charge density, enrich the electric double layer with anions that preferentially decompose to form an anion-derived SEI. Consequently, the MVC approach facilitates enhanced reversibility of Li metal deposition and dissolution, as well as stable galvanostatic cycling of LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811)||Li cells. This approach provides a highly effective pathway for designing anion-derived SEI, offering new insights into the control of Li metal interfaces.