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

## TL;DR

This paper introduces a low-cost method to improve lithium metal battery performance by using magnesium carbonate to control the chemical environment at the lithium anode.

## Contribution

A novel multi-valent cation strategy using MgCO3 to regulate the electric double layer and promote anion-derived SEI formation.

## Key findings

- Adding 0.05 m MgCO3 scavenges HF and releases Mg2+ cations.
- Mg2+ cations enrich anions in the interphase, leading to stable Li metal cycling.
- The approach enables dense Li deposits and extended cycle life in NMC811||Li cells.

## Abstract

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 LiNi0.8Mn0.1Co0.1O2 (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.

A multivalent‐cation strategy using suspension MgCO3‐containing electrolyte regulates the electric double layer to promote anion‐derived SEI formation on Li metal. CO3
2‐ scavenges HF while Mg2+ enriches anions in the interphase, enabling dense Li deposits, reduced overvoltage, and extended cycle life of NMC811||Li cells with minimal, low‐cost additive loading.