Ionic Liquid Based Electrolytes for High Temperature Lithium-Ion Batteries
In this work, we demonstrate that the IL Pyr13TFSI with an addition of LiTFSI is a potential electrolyte family for HT-LIBs. These electrolytes possess high thermal stability, up to 350°C, wide electrochemical stability windows, 0-5 V vs Li+/Li°, and ionic conductivities of the order of 10-3 S cm-1 at RT and 10-2 S cm-1 at HT (above 80°C). The LiTFSI0.2Pyr13TFSI0.8 electrolyte shows promising electrochemical stability in a LFP half-cell at 80°C delivering an average discharge capacity of 145 mAh g-1 at 1C (Fig.1). Additional doping of the IL based electrolytes with cyclic carbonates such as propylene carbonate (PC) and/or vinylene carbonate (VC), creating hybrid electrolytes, further improves the cycling performance in terms of capacity, stability and Coulombic efficiency. This is attributed mainly to a decrease in viscosity, leading to higher ionic conductivities and a better wetting of the electrode, and VC has the additional advantage of forming a stable SEI.
High Temperature Lithium-ion Batteries is a project funded by the Swedish Energy Agency and the collaboration between Chalmers University of Technology, Lund University, Uppsala University and Scania CV AB was created within the Swedish Hybrid Vehicle Centre.
Fig. 1 Specific capacity of LFP half-cells using IL based electrolytes cycled between 2.5 to 4.2 V vs Li+/Li° at 80°C and 1C rate. The open and closed circles represent the charge and discharge capacities, respectively.