Developing Dual-Graphite Batteries with Pure 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate Ionic Liquid as the Electrolyte

In this work, a novel dual-graphite battery (DGB) based on a pure 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMImTfO) ionic liquid electrolyte is constructed. Within a charge/discharge voltage range of 1.0-3.9 V and at a current of 400 mA g(-1), batteries with dual-natural-graphite electrodes exhibit a high discharge plateau above 3.0 V with an initial discharge capacity of 46.2 mAh g(-1), delivering a capacity retention of 71.0 % after 100 cycles. Comparative studies between the natural graphite and the synthetic graphite (KS6) electrodes are also conducted. Charge-discharge tests reveal that the dual natural-graphite battery presents a higher discharge voltage plateau and better retention than the dual KS6-graphite battery. To confirm the principle of the dual-graphite systems, a cyclic voltammetry test is conducted. The results demonstrate that the EMIm(+) cation exhibits an even more stable intercalation/de-intercalation behavior than the TfO- anion. Further tests, including ex situ X-ray diffraction and ex situ Raman spectroscopy, are performed to reveal the mechanism of TfO- and EMIm(+) intercalation into graphite, both demonstrating a reversible process.