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.

Figure optionsDownload 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.