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

Vittorio Marangon,Alberto Barlini,Jusef Hassoun,Luca Minnetti,Matteo Adami

doi:10.1021/acs.energyfuels.1c00927

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 gS–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.

Highlights

Li-ion batteries power a wide array of electronic devices, from portable systems such as laptops and smartphones to hybrid (HEVs) and fully electric vehicles (EVs).[1,2] The research on Li-ion batteries has led to the achievement of a remarkable energy density, i.e., 260 Wh kg−1, and a long cycle life.[3,4] an increasing demand for energy with the purpose of extending the driving range of EVs has renewed interest in the metallic lithium, which offers a high theoretical capacity (3860 mAh g−1) and the lowest redox potential (−3.04 V vs SHE) among the various electrodes proposed as the battery anode.[5]
Corresponding voltammograms (Figure 1a, c) show the typical profiles expected for the reversible multiple-step Li/S electrochemical process consisting of a first cycle with a different
This enhancement is likely justified by the electrochemical impedance spectroscopy (EIS) Nyquist plots reported in Figure 3b for DEGDME_HCE and in Figure 3d for TREGDME_HCE and by the results of the corresponding nonlinear least-squares (NLLS) analyses listed in Table 2.28,29 the data indicate for the two electrolytes a series of semicircles and lines ascribed to solid electrolyte interphase (SEI) layers, charge transfer processes, and diffusion phenomena occurring in the lithium cells at the various frequencies, with an overall initial resistance of about 300 Ω for DEGDME_HCE and 150 Ω for TREGDME_HCE decreasing to about 90 Ω and 80 Ω, respectively, upon the 10 Cyclic voltammetry (CV) cycles taken under consideration

Summary

■ INTRODUCTION

Li-ion batteries power a wide array of electronic devices, from portable systems such as laptops and smartphones to hybrid (HEVs) and fully electric vehicles (EVs).[1,2] The research on Li-ion batteries has led to the achievement of a remarkable energy density, i.e., 260 Wh kg−1, and a long cycle life.[3,4] an increasing demand for energy with the purpose of extending the driving range of EVs has renewed interest in the metallic lithium, which offers a high theoretical capacity (3860 mAh g−1) and the lowest redox potential (−3.04 V vs SHE) among the various electrodes proposed as the battery anode.[5]. (de)insertion mechanism associated with a LiFePO4 olivine cathode.[3,25] the present study focuses on the electrochemical performances of the new electrolytes in advanced lithium cells using the high-performance sulfur composite with low amount of electrochemically inactive, conductive tin metal (S:Sn 80:20 w/w)[26] and the advanced carbon-coated LiFePO4 cathode.[27] The results of the study may shed light on possible applications of the highly concentrated glyme-based electrolytes for achieving new rechargeable batteries with remarkable safety content using the highly energetic, yet challenging, lithium−metal anode. The synthesis of the sulfur composite (S:Sn 80:20) was achieved in a previous work through a physical mixing and melting process of elemental sulfur (80% wt, ≥99.5%, Riedel-de Haen ) and nanometric tin powder (20% wt,

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ REFERENCES

■ ACKNOWLEDGMENTS