Preparation of spiro-type quaternary ammonium salt via economical and efficient synthetic route as electrolyte for electric double-layer capacitor

ZHOU Hong-ming(周宏明)^{1, 2}, SUN Wen-jiao(孙文佼)¹, LI Jian(李荐)^{1, 2}

(1. School of Materials Science and Engineering, Central South University, Changsha 410083, China;
2. Hunan Zhengyuan Institute for Energy Storage Materials and Devices, Changsha 410083, China)

Abstract:A spiro-type quaternary ammonium salt, spiro-(1,1′)-bipyrrolidinium tetrafluoroborate (SBP-BF₄) was successfully prepared by an economical and efficient three-step process comprising the cyclization reaction of 1,4-dibromobutane and pyrrolidine, and subsequent ion exchange pathway with KOH followed by neutralization reaction via HBF₄ in the system of ethanol solution. ¹H NMR, ¹³C NMR, FI-IR and XPS analyses showed the structure of SBP-BF₄. The as-obtained SBP-BF₄ was dissolved in AN and used as the electrolyte for supercapacitor. Electrochemical measurements demonstrate that, compared with commercial electrolyte TEMA-BF₄/AN, SBP-BF₄/AN exhibits high ionic conductivity, lower resistance and improved cycling performance, which is due to its smaller ion size and stable symmetry structure.

Key words:spiro-type quaternary ammonium salt; synthesis; electrolyte; electric double-layer capacitor