A zwitterionic salt with one sulfonate and two ether functional groups as an additive for lithium-ion battery electrolyte

Abstract

An imidazolium-based zwitterionic compound bearing two ether groups at the C-1 and C-2 positions and one sulfonate group at the C-3 position of the imidazolium ring was successfully synthesized. The compound was characterized using nuclear magnetic resonance spectroscopy and elemental analysis. The product (2.5 wt%) was added to a commercial electrolyte for lithium-ion batteries containing 1 M LiPF6 in ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (1:1:1 by volume). The resulting electrolyte had a slightly higher ionic conductivity in the range 10–70 °C than the model electrolyte, implying that the additive had a beneficial impact, possibly due to the C-2 rather than the C-1 ether group. Cyclic voltammetry analysis indicated that the electrochemical stability of the electrolyte did not change. The effect of the electrolyte additive on the cell’s 1C cycling performance was also examined: it was found that a stable discharge capacity was maintained for up to 100 cycles. Fourier transform infrared spectra of complexes formed by the synthesized product and LiPF6 at different ratios showed that the Li+ ions interacted with all the functional groups.