Liquid phase exfoliation of MoO 2 nanosheets for lithium ion battery applications.

Molybdenum dioxide (MoO 2 ) 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, MoO 2 has not previously been exfoliated in large quantities. Here we demonstrate the liquid phase exfoliation of MoO 2 in the solvent isopropanol, yielding reasonable amounts of good quality nanosheets. However, we found that, when dispersed in isopropanol under ambient conditions, MoO 2 nanosheets are gradually oxidized to higher oxides such as MoO 3 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 MoO 2 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 MoO 2 nanosheets could be used to produce lithium ion battery anodes with capacities of up to 1140 mA h g -1 .