Lithium-Metal Batteries Using Sustainable Electrolyte Media and Various Cathode Chemistries

Lithium-metal batteries employing concentrated glyme-based electrolytes and two different cathode chemistries are herein evaluated in view of a safe use of the highly energetic alkali-metal anode. Indeed, diethylene-glycol dimethyl-ether (DEGDME) and triethylene-glycol dimethyl-ether (TREGDME) dissolving lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate (LiNO₃) in concentration approaching the solvents saturation limit are used in lithium batteries employing either a conversion sulfur-tin composite (S:Sn 80:20 w/w) or a Li⁺ (de)insertion LiFePO₄ cathode. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) clearly show the suitability of the concentrated electrolytes in terms of process reversibility and low interphase resistance, particularly upon a favorable activation. Galvanostatic measurements performed on lithium-sulfur (Li/S) batteries reveal promising capacities at room temperature (25 °C) and a value as high as 1300 mAh g_S ^-1 for the cell exploiting the DEGDME-based electrolyte at 35 °C. On the other hand, the lithium-LiFePO₄ (Li/LFP) cells exhibit satisfactory cycling behavior, in particular when employing an additional reduction step at low voltage cutoff (i.e., 1.2 V) during the first discharge to consolidate the solid electrolyte interphase (SEI). This procedure allows a Coulombic efficiency near 100%, a capacity approaching 160 mAh g^-1, and relevant retention particularly for the cell using the TREGDME-based electrolyte. Therefore, this work suggests the use of concentrated glyme-based electrolytes, the fine-tuning of the operative conditions, and the careful selection of active materials chemistry as significant steps to achieve practical and safe lithium-metal batteries.