Influence of the binder types on the electrochemical characteristics of natural graphite electrode in room-temperature ionic liquid

To improve the electrochemical characteristics of the natural graphite (NG-3) negative electrode in the LiCl saturated AlCl3-1-ethyl-3-methylimizadolium chloride + thionyl chloride (SOCl2) melt as the electrolyte for non-flammable lithium-ion batteries, we examined the influence of the binder types on its electrochemical characteristics. The cyclic voltammograms showed that the reduction current at 1.2–3.2 V vs. Li/Li(I) was repressed using polyacrylic acid (PAA) as the binder. The charge–discharge tests showed that the discharge capacity and the charge–discharge efficiency of the NG-3 electrode coated with the PAA binder at the 1st cycle were 322.8 mAh g−1 and 65.6%, respectively. Compared with the NG-3 electrode using the conventional poly(vinylidene fluoride) binder, it showed considerably a better cyclability with the discharge capacity of 302.1 mAh g−1 at the 50th cycle. Li(I) ion intercalation into the graphite layers could be improved because the NG-3 electrode coated with the PAA binder changed to a golden-yellow color after the 1st charging, and the formation of first stage LiC6 was demonstrated by X-ray diffraction (XRD) measurement. In addition, the XRD and X-ray photoelectron spectroscopy indicated that one of the side reactions during charging was the formation of LiCl on the graphite surface regardless of the binder types.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights▶ The cycling curves of the NG-3 electrode using the PVdF binder are shown in Fig. (a). ▶ The cycling curves of the NG-3 electrode using the PAA binder are shown in Fig. (b). ▶ The use of the PAA binder improved the initial cycling efficiency of it. ▶ The use of the PAA binder repressed the reduction reaction of SOCl2.