  Lithium-metal batteries employing concentrated glyme-based electrolytes and
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 in the lithium-sulfur (Li/S) batteries reveal promising
capacities at room temperature (25 {\deg}C) and a value as high as 1300 mAh
gS-1 for DEGDME-based electrolyte at 35 {\deg}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 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.

Applied Physics;Materials Science;Chemical Physics