Convergent Intercalation of Tetrahexyl Ammonium and Spiro-bipyrrolidinium Cations into Graphite Electrodes from Propylene Carbonate

The quaternary alkyl ammonium (QAA) cation storage behavior of the graphite negative electrode in graphite/activated carbon (AC) is closely related to the formation of graphite intercalation compounds (GICs) during the charge and discharge process. In this work, spiro-(1,1′)-bipyrrolidinium tetrafluoroborate (SBPBF₄) and tetrahexyl ammonium tetrafluoroborate (THABF₄) dissolved in propylene carbonate (PC) were applied in graphite/AC capacitors. In situ X-ray diffraction and step-by-step QAA cation storage measurements displayed that both cations could take part in the formation of GICs, leading to the formation of a new type of GIC. Accordingly, the graphite/AC capacitor shows a satisfactory cycle performance. Moreover, the influence factor of the hierarchical and convergent intercalation behavior of mixed QAA cations was discussed in detail.