Liquid phase exfoliation of MoO₂ nanosheets for lithium ion battery applications

Molybdenum dioxide (MoO₂) is a layered material which shows promise for a number of applications in the electrochemical energy storage arena. Mostly studied as a bulk layered material, MoO₂ has not previously been exfoliated in large quantities. Here we demonstrate the liquid phase exfoliation of MoO₂ in the solvent isopropanol, yielding reasonable amounts of good quality nanosheets. However, we found that, when dispersed in isopropanol under ambient conditions, MoO₂ nanosheets are gradually oxidized to higher oxides such as MoO₃ over a period of days. Conversely, if the nanosheets are processed into dried films immediately after exfoliation, and before oxidation has had a chance to progress, the nanosheets are relatively stable under ambient conditions, remaining unoxidised unless the films are heated. We also found that MoO₂ nanosheets can be size selected by controlled centrifugation and show size-dependent optical properties. This allows us to propose spectroscopic metrics which allow concentration- and size-estimation from extinction spectra. Finally, we found that liquid-exfoliated MoO₂ nanosheets could be used to produce lithium ion battery anodes with capacities of up to 1140 mA h g^-1.