Mixed Electrolytes of Organic Solvents and Ionic Liquid for Rechargeable Lithium-Ion Batteries

Mixed electrolytes formed by the combination of 1-butyl-1-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide (BMP-TFSI) ionic liquid and standard liquid electrolyte are prepared and characterized. Linear sweep voltammetry measurements demonstrate that these mixed systems exhibit a wide electrochemical stability window, allowing them to be suitable electrolyte for carbonaceous anode-based lithium-ion batteries. Lithium-ion cells composed of graphite anode and LiCoO₂ cathode are assembled using the mixed electrolytes, and their cycling performances are evaluated. The cell containing proper content of BMP-TFSI shows good cycling performance comparable to that of a cell assembled with organic electrolyte. The presence of BMP-TFSI in the mixed electrolyte contributes to the reduction of the flammability of electrolyte solution and the improvement of the thermal stability of charged Li₁-ₗCoO₂ in the electrolyte solution.