Analysis of Electrochemical Reactions of Natural Graphite Electrode in Chloroaluminate Type Room-temperature Ionic Liquid Electrolyte Containing Lithium Ion

Abstract

We have reported that the electrochemical characteristics of a natural graphite (NG-3) electrode in the chloroaluminate type room-temperature ionic liquid containing lithium ion as the electrolyte for non-flammable lithium-ion batteries were improved by employing polyacrylic acid (PAA) as the binder. Therefore, we have analyzed the influence of the binder types on the electrochemical reaction (charge-discharge reaction) of the natural graphite electrode in more detail. The FE-SEM observations showed that the surface morphology of the NG-3 electrode coated with the PAA binder was smooth, whereas that of the NG-3 electrode using poly(vinylidene difluoride) as a binder was rough. The EDX mappings showed that the reduction of SOCl2 and the deposition of Al would be suppressed to some extent during charging by employing the PAA binder; the deposit from the surface of the NG-3 electrode coated with the PAA binder would be exfoliated or disappeared during discharging. Based on the XPS results, it was clarified that Al would be deposited on the surface of the NG-3 electrode during charging. These results clarified that the deposition reaction that was a side reaction was different according to the binder types during initial charging; the exfoliation or the disappearance of the deposit occurred during discharging.