RESUMO
We present a detailed study on graphene-coated aluminum thin films for Li-ion battery anode applications. The best electrode ageing behavior is obtained for Al films encapsulated with four porous graphene layers. Graphene encapsulation prevents "crushed" Al nanoparticles from detaching from the anode, thus allowing prolonged charge-discharge cycling. Graphene also provides surface conduction paths for electrons as well as diffusion paths for Li atoms. For the first time, we report the electrochemical room temperature formation of phases such as Li3Al2 and even Li9Al4, with a higher Li content than ß-LiAl. More interestingly, we observe a progressive change of the composite thin film electrode, switching from a pure galvanic to a pseudocapacitive behavior as the size of the Al grains decreases from â¼100 to 5-10 nm due to repeated Li alloying-dealloying. The capacity values of â¼900 and 780 mAh/g are obtained after, respectively, 500 and 1000 charge-discharge cycles at 0.1C. Our results may refocus the interest of the battery community on Al-based thin film anodes, since they are potentially very simple to fabricate, particularly if porous graphene is replaced in the future by reduced graphite oxide.
RESUMO
We have studied the influence of the surface roughness of copper foils on the sheet resistance of graphene sheets grown by chemical vapor deposition. The surface roughness of the copper foils was reproducibly controlled by electropolishing. We have found that the graphene sheet resistance monotonically decreases as the surface roughness of the copper foils decreases. We show that a pre-annealing treatment combined with an optimized electropolishing process of the Cu foils and a fast CVD growth prevents the evolution of the Cu surface roughness during graphene synthesis. This combination of fabrication conditions produces small grain polycrystalline graphene films with a sheet resistance of 210 Ω â¡(-1) and carrier mobility values as high as 5450 cm(2) V(-1) s(-1) after transfer onto SiO2/Si.
