Dual solvents with different coordination strengths for localized high concentration electrolytes in lithium metal batteries

Localized high-concentration electrolytes (LHCEs) can stabilize lithium metal batteries (LMBs) through anion-rich solvation structure and robust interphase formation. However, conventional LHCEs release free 1,2-dimethoxyethane (DME) through persistent solvent exchange, causing cathode degradation at high voltage. Here, we propose a ternary LHCE ( ter -LHCE), which combines a rationally designed weakly-solvating cosolvent, 1,1,1,3,3,3-hexafluoro-2-(2-methoxyethoxy)-2-(trifluoromethyl)propane (HFMTFP) with the diluent bis(2,2,2-trifluoroethyl) ether (BTFE) and primary solvent DME, to suppress dynamic DME release for enhanced interfacial stability. HFMTFP establishes an energetically hierarchical solvation structure that confines DME within the Li + solvation sheath, thereby enhancing the oxidative stability of ter -LHCE. The coexistence of coordinated and free HFMTFP promotes inorganic-rich interphases at the Li metal anode and nickel-rich cathode. LMB full cells with ter -LHCE achieved 91.6% capacity retention over 250 cycles at 2C with a 4.4 V cut-off condition. This work highlights the effectiveness of integrating weakly-solvating cosolvents into LHCEs to regulate the solvation dynamics for practical high-voltage LMBs.