Laser micro-structuring of magnetron-sputtered SnOx thin films as anode material for lithium ion batteries

SnOx electrode thin films for lithium ion batteries were deposited by reactive and non-reactive rf magnetron sputtering of a SnO2 target in an argon-oxygen atmosphere. Amorphous and nano-crystalline SnOx films could be synthesized, with regard to the O-2:Ar volume ratio in the sputter gas which was adjusted to 0, 3.5 or 10%. Laser micro-structuring using a KrF excimer laser operating at a wavelength of lambda = 248 nm was applied to create free-standing microstructures. Thus, the active surface of the anode material was significantly increased. Furthermore, it was expected that the large volume changes during electrochemical cycling of SnOx could be better compensated by a microstructured surface. The laser parameters were optimized in a way which leads to structures without any defects and little debris. Depending on the laser fluence and pulse number, free-standing conical structures could be formed with a horizontal spacing of < 0.5 mu m up to 2 mu m. The structured and unstructured thin films were cycled in a battery tester against metallic lithium. The structured SnOx thin films exhibited significantly better battery performance with respect to cycling stability.