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Enhanced Ion Transport in an Ether Aided Super Concentrated Ionic Liquid Electrolyte for Long-Life Practical Lithium Metal Battery Applications

preprint
submitted on 30.06.2020 and posted on 02.07.2020 by Urbi Pal, Fangfang Chen, Derick Gyabang, Thushan Pathirana, Binayak Roy, Robert Kerr, Douglas Macfarlane, Michel Armand, Patrick C. Howlett, Maria Forsyth
We explore a novel ether aided superconcentrated ionic liquid electrolyte; a combination of ionic liquid, N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (C3mpyrFSI) and ether solvent, 1,2 dimethoxy ethane (DME) with 3.2 mol/kg LiFSI salt, which offers an alternative ion-transport mechanism and improves the overall fluidity of the electrolyte. The molecular dynamics (MD) study reveals that the coordination environment of lithium in the ether aided ionic liquid system offers a coexistence of both the ether DME and FSI anion simultaneously and the absence of ‘free’, uncoordinated DME solvent. These structures lead to very fast kinetics and improved current density for lithium deposition-dissolution processes. Hence the electrolyte is used in a lithium metal battery against a high mass loading (~12 mg/cm2) LFP cathode which was cycled at a relatively high current rate of 1mA/cm2 for 350 cycles without capacity fading and offered an overall coulombic efficiency of >99.8 %. Additionally, the rate performance demonstrated that this electrolyte is capable of passing current density as high as 7mA/cm2 without any electrolytic decomposition and offers a superior capacity retention. We have also demonstrated an ‘anode free’ LFP-Cu cell which was cycled over 50 cycles and achieved an average coulombic efficiency of 98.74%. The coordination chemistry and (electro)chemical understanding as well as the excellent cycling stability collectively leads toward a breakthrough in realizing the practical applicability of this ether aided ionic liquid electrolytes in lithium metal battery applications, while delivering high energy density in a prototype cell.

Funding

This work is financially supported by the Australia-India Strategic Research Fund (AISRF, grant agreement No.48515). Professors Maria Forsyth and Douglas MacFarlane thank the ARC for their respective Australian Laureate Fellowship (FL110100013 and FL120100019). The authors acknowledge the Australian Research Council (ARC) for funding via the Australian Centre for Electromaterials Science, grant CE140100012. Dr. Fangfang Chen acknowledges the assistance of computational resources provided at the NCI National Facility systems at the Australian National University through the National Computational Merit Allocation Scheme supported by the Australian Government.

History

Email Address of Submitting Author

upal@deakin.edu.au

Institution

Institute for Frontier Materials, Deakin University

Country

Australia

ORCID For Submitting Author

0000-0001-5962-5185

Declaration of Conflict of Interest

The authors declare no competing financial interest.

Version Notes

First version

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