Amorphous Soft Carbon Coated Graphite As Anode Material for Lithium Ion Battery

The natural graphite was used without a purification process and processing step that results in the folding of the graphite fragments into small spheres. It is well known that spherically shaped anode material is preferable as a means of improving the anode characteristics due to its high tapping density [1]. To reduce movement of impurities and side reaction with electrolyte impurities [2], the amorphous soft carbon was coated on the spherical graphite surface.

In this study, we report the characteristics of anode which is made from the amorphous soft carbon coated natural graphite and charge-discharge behavior of half cells. The electrodes were prepared by pasting an aqueous slurry with styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC).

The charge–discharge tests were performed in CR2032 coin cell. Half cells consisted of the working electrode to be studied, Li metal as the counter electrode, and Celgard 2400 separator. 1 M LiPF₆in ethylene carbonate and dimethyl carbonate (1:1 by volume) was used to electrolyte. Anode half-cells were tested between 1.5 V and 5 mV at a C-rate of 0.1 C. Microstructure of the amorphous soft carbon coating layer on graphite particle  was observed using TEM to examine the cycle stability.  Fig. 1 shows structural stability of carbon layer after charge-discharge cycles and thickness of carbon layer was about 50nm. Fig. 2 shows the charge(Li insertion)-discharge(Li extraction) curves of the amorphous soft carbon coating sample versus non-coating sample for the first cycle, charged in CC-CV mode and discharged in CC mode. The discharge capacity obtained at carbon coated sample is about 330 mAh/g and the columbic efficiency is about 90 %.

This research was financially supported by the Ministry of Trade, Industry and Energy(MOTIE) and Korea Institute for Advancement of Technology(KIAT) through the Promoting Regional specialized Industry

References

[1] Y. Chen, G.X. Wang, J.P. Tian, K. Konstantinov, H.K. Liu, Electrochim. Acta 50 (2004) 435–441.

[2] C. Wang, X. Zhang, A.J. Appleby, X. Chen, F.E. Little, J. Power Sources 112 (2002) 98-104.