Atomic layer deposition of crystalline epitaxial MoS₂ nanowall networks exhibiting superior performance in thin-film rechargeable Na-ion batteries

We have grown ultrathin crystalline epitaxial thin films of MoS₂ on c-sapphire by employing atomic layer deposition, without the need for post-annealing. The films have been characterized by using various microscopic and spectroscopic techniques. The crystallographic epitaxial relationships between the films and the substrate are 〈01-10〉 Al₂O₃∥〈11-20〉 MoS₂ and 〈0001〉Al₂O₃∥〈0001〉 MoS₂. Interestingly, the films show a high density of nanowalls and exhibit a high surface to volume ratio. The high surface area of the nanowall network results in excellent electrochemical characteristics as demonstrated by the performance of the Na-ion battery with MoS₂ as the active electrode. The battery exhibits high capacity, remarkable stability, cyclability and high rate capability over a wide range of operating currents, even in the absence of conducting and binder additives. The MoS₂ Li-ion battery also exhibits similar features.