Lithium metal batteries (LMBs) offer high theoretical capacity (3860 mAh·g⁻¹) and a low electrode potential (-3.04 V vs. SHE). However, challenges such as inhomogeneous solid electrolyte interface (SEI) formation and high surface area lithium (HSAL) growth lead to low Coulombic efficiency, rapid capacity decay, and safety concerns. To address these issues, localized high-concentration electrolytes (LHCEs) were investigated. LHCEs combine the advantages of high-concentration electrolytes (HCEs), such as enhanced oxidative stability and suppressed aluminum dissolution, with a non-solvating diluent to improve ionic conductivity and reduce cost.

A comparative study was conducted using various electrolytes, including 1 M LiTFSI/DME (diluted electrolyte, DE), 5 M LiTFSI/DME (HCE), and a commercial carbonate-based electrolyte (1 M LiPF₆ in EC:EMC 3:7). Electrochemical performance was evaluated in LiNi₀.₈Co₀.₁Mn₀.₁O₂ (NCM811) || Li coin cells with low-excess Li electrodes (20 µm Li foil on Cu). Results showed that LHCE (1:2.2:2 LiTFSI:DME:TTE) demonstrated superior electrochemical performance with 82% capacity retention after 150 cycles and an average Coulombic efficiency of 99.8%.

Structural analysis via FT-Raman spectroscopy revealed that LHCE maintains a similar solvation structure to HCE, consisting of contact ion pairs (CIPs) and aggregated ion pairs (AGGs), but with higher ionic conductivity and lower viscosity. Scanning electron microscopy (SEM) images of cycled electrodes confirmed reduced HSAL formation with LHCE compared to HCE and carbonate-based electrolytes. The study concludes that LHCE offers a promising pathway for stabilizing lithium metal anodes in high-energy-density batteries.