Study on Electrochemical Performance of Thin Film C60 As an Anode Material for Lithium Secondary Batteries

Lithium ion batteries are gaining more attention these days since it is being used in many application, ranging from portable devices to electric vehicles due to their superior energy density and cycleability over the other energy storage technologies. Among those applications, microrobotics is also getting more attention since it can be used for exploration in small and/or dangerous environment, finding survivor in the disaster site, and defense department needs. However, there is crucial shortage from these microrobotics, which are its power source limitation. In order to overcome this limitation, special attempts should be done by designing the energy storage cell as small as possible. In order to achieve this, carbon based thin film might be one of the plausible alternative. To this end, we made a carbon based thin film using the plasma enhanced thermal evaporation deposition. Since the available commercial graphite and graphene have extremely high melting point (ca. 3600 ^oC and ca. 3900 ^oC for graphite and graphene, respectively), these materials are not applicable when used as the precursor for thin film deposition process [1]. It has been already investigated that carbon with the structure of C₇₀ and C₆₀ has significantly low sublimation point of ca. 850 ^oC and 600 ^oC, respectively [2]. In our experiment scope, we made the carbon based thin film electrode using C₆₀powder.

The deposition of C₆₀ thin films were deposited by plasma enhanced thermal evaporation. The samples were prepared under following conditions: a working pressure of 25 mTorr and deposition time of 1 min. The film thickness and RF power were varied. The film thickness was varied by introducing different amount of C₆₀powder of 0.01 g, 0.02 g, and 0.04 g. The RF power variation was 100 W, 200 W, and 300 W.

The results show that thicker C₆₀ thin film would result in lower volumetric capacity. This might be related to the characteristic of C₆₀ that intrinsically high resistance. Thus, increasing the thickness might increase the resistance of the film and might also lead to longer distance for lithium to diffuse into the C₆₀electrode. Meanwhile, the investigation of plasma power variation shows that lower plasma power results in higher volumetric capacity. These phenomena would be the focus of our detail discussion.

Reference

1. J. H. Los, K. V. Zakharchenko, M. I. Katsnelson, and A. Fasolino, Physical Review B 91, 045415 (2015).

2. Eiji Osawa (2002). Perspective of fullerene nanotechnology. Springer. pp. 275.