Sustainable Low-Concentration Electrolyte Design for Practical Lithium Metal Batteries

Abstract

Low-concentration electrolytes (LCEs) offer a cost-effective and sustainable route toward practical lithium metal batteries (LMBs), yet their solvent-governed solvation and interfacial chemistry often result in unstable lithium deposition behavior. Herein, we uncover the decisive role of solvent molecular structure in dictating Li+ solvation environments and solid–electrolyte interphase (SEI) formation in LCEs. We demonstrate that cyclic ethers, compared with linear ethers, promote enhanced anion participation in the Li+ solvation sheath, thereby enabling the formation of inorganic-rich SEI layers and improving lithium stability. Nevertheless, their practical application is hindered by severe ring-opening polymerization. To address this issue, trace LiBH4 is introduced as an effective polymerization inhibitor, leading to a stabilized cyclic-ether-based LCE (0.2 M LiFSI in DOL + 0.02 M LiBH4). This electrolyte induces an anion-enriched primary solvation structure and a robust inorganic SEI, achieving highly reversible lithium plating/stripping with a Coulombic efficiency of up to 96.20%. Under practical conditions (11.5 mg cm–2, 50 μm Li), Li-LiFePO4 full cells deliver over 300 stable cycles with 94.3% capacity retention, and its feasibility is further validated in a 2 Ah pouch cell. This work provides an effective electrolyte design strategy for practical and sustainable LMBs.