Experimental investigation of both flame retardancy and electrochemical performance of PYR13TFSI for lithium battery electrolytes

Abstract

The ionic liquid has attracted great attention in the development of electrochemical energy storage technology due to its designable structure and non-flammable nature. To comprehensively evaluate the potential feasibility of ionic liquid additives for the safety improvement of lithium-ion batteries, N-Methyl-N-propyl pyrrolidinium bis (trifluoromethanesulfonyl) imide (PYR₁₃TFSI) is employed in this study to reveal the additive effects on both flame retardancy and electrochemical performance. The flame retardancy of PYR₁₃TFSI is systematically investigated by SET test, pool flame, and jet flame. Analyses indicate PYR₁₃TFSI can significantly suppress the combustion of electrolytes by 80 wt% at ambient conditions and 90 wt% at high-temperature conditions due to the nature of non-volatility and non-flammability. Further experiments on the charge-discharge cycling tests show that the battery with no more than 80 wt% PYR₁₃TFSI has satisfactory cycling stability under various C-rate conditions. Further increasing the additive content will severely degrade the discharge capacities, particularly in high C-rate cycling tests. Indigo anhydride (IAN) is employed to improve the electrochemical performance of the electrolytes containing 90 wt% PYR₁₃TFSI. The results reveal that adding 1 % IAN can make the performance of the electrolyte with 90 wt% PYR₁₃TFSI close to or exceeds that with 80 wt% PYR₁₃TFSI. Therefore, it is recommended to add 90 wt% PYR₁₃TFSI and 1 wt% IAN to ensure the balance between flame retardant efficiency and electrochemical performance of electrolytes in lithium-ion batteries.