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

Abstract

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.

Figure 1

(a, c) Cyclic voltammetry (CV) and (b, d) electrochemical impedance spectroscopy (EIS) measurements performed on Li/electrolyte/S:Sn 80:20 cells employing either (a, b) DEGDME_HCE or (c, d) TREGDME_HCE. CV potential range, 1.8–2.8 V vs Li⁺/Li; scan rate, 0.1 mV s^–1. EIS carried out at the OCV of the cells and after 1, 5, and 10 voltammetry cycles (inset reports magnification); frequency range, 500 kHz–100 mHz; alternate voltage signal amplitude, 10 mV.

Figure 2

(a, c) Selected voltage profiles and (b, d) corresponding cycling trends at 25 and 35 °C of Li/electrolyte/S:Sn 80:20 cells employing either (a, b) DEGDME_HCE or (c, d) TREGDME_HCE. The cells are galvanostatically cycled using a voltage range between 1.9 and 2.8 V at the constant current rate of C/5 (1C = 1675 mA g_S^–1).

Figure 3

(a, c) Cyclic voltammetry (CV) and (b, d) electrochemical impedance spectroscopy (EIS) measurements performed on Li/electrolyte/LFP cells employing either (a, b) DEGDME_HCE or (c, d) TREGDME_HCE. CV potential range, 2.7–3.9 V vs Li⁺/Li; scan rate, 0.1 mV s^–1. EIS carried out at the OCV of the cells and after 1, 5, and 10 voltammetry cycles; frequency range, 500 kHz–100 mHz; alternate voltage signal amplitude, 10 mV.

Figure 4

(a, c) Voltage profiles and (b, d) corresponding cycling trends with Coulombic efficiency (right y-axis) related to Li/electrolyte/LFP cells employing either (a, b) DEGDME_HCE or (c, d) TREGDME_HCE galvanostatically cycled at the constant current rate of C/5 (1C = 170 mA g^–1) at room temperature (25 °C). Voltage range, 2.7–3.9 V.

Figure 5

(a, c) Voltage profiles and (b, d) corresponding cycling trends with Coulombic efficiency (right y-axis) related to Li/electrolyte/LFP cells employing either (a, b) DEGDME_HCE or (c, d) TREGDME_HCE galvanostatically cycled at room temperature (25 °C) at the constant current rate of C/5 (1C = 170 mA g^–1) in a voltage range between 1.2 and 3.9 V for the first cycle (inset in panels (a) and (c)) and between 2.7 and 3.9 V for the subsequent ones.

Figure 6

Cycling trends with Coulombic efficiency (right y-axis) related to (a) Li/DEGDME_HCE/S:Sn 80:20 and (b) Li/TREGDME_HCE/LFP cells galvanostatically cycled at 1C (1675 mA g_S^–1) and C/3 (1C = 170 mA g^–1), respectively. The Li/S cell was cycled at 35 °C by exploiting an electrolyte/sulfur ratio of 20 μL mg^–1 and a 1.6–2.8 V voltage range. The Li/LFP cell was cycled at room temperature (25 °C) by employing a 1.2–3.9 V voltage range for the first cycle and voltage limits of 2.7 and 3.9 V for the subsequent ones.