In Operando Raman Spectroscopy Reveals Li-Ion Solvation in Lithium Metal Batteries

Abstract

Inhomogeneous lithium (Li) deposition and unstable solid electrolyte interphase are the main causes of short cycle life and safety issues in Li metal batteries (LMBs). Developing a 3D structured matrix current collector and novel electrolyte are feasible strategies to tackle these issues. Ether-based electrolytes are widely used in LMBs. However, a fundamental understanding of Li-ion coordination and solvent remains incomplete. Here, lithiophilic Ag-Cu mesh is designed as the current collector to boost rapid Li-ion flux and Li metal nucleation. Meanwhile, dimethoxyethane (DME)/dioxolane (DOL) are used as complex solvents to enable lower interfacial resistance. The solvation structures at the interfaces of different collectors with different electrolytes are investigated. By applying in operando Raman spectroscopy, it is demonstrated that bis(trifluoromethylsulfonyl)imide TFSI^–and DME molecules are highly coordinated with Li⁺ compared with DOL molecules. Furthermore, lithiophilic 3D Ag-Cu mesh tunes Li⁺ solvation/desolvation, resulting in a uniform deposition. The Ag-Cu mesh/Li symmetric cells demonstrate long-term cycling life up to 1200 h and Coulombic efficiency of 98.6% over 200 cycles at 1 mA cm⁻². The Ag-Cu mesh/Li||LiNi_0.8Co_0.1Mn_0.1O₂ cells exhibit an initial discharge capacity of 208.7 mAh g⁻¹ at 1.0 C with a capacity retention of 76.1% after 500 cycles.