Electrospray Synthesis of Graphene Oxide–Mixed Metal Oxide Nanocomposites for Energy Storage

Synthesis of composite materials for an improved lithium-ion battery anode with the necessary attributes for a high performance anode prompted the examination of cobalt-manganese oxide because of its high capacity for lithium ions, and graphene oxide because of its high surface-tovolume ratio and high conductivity. Mixing these materials in a controlled manner is challenging at the nanoscale. To that end, the electrospray (ES) technique is used. The ES uses an electric field to emit droplets (in which said nanomaterials are encapsulated) that have a few key characteristics: 1) they are all homopolarly charged; 2) their size can be controlled with relative ease; and 3) both size and charge level are strongly dependent on the electric conductivity of the solution that can be varied by orders of magnitude. As a result, highly controlled sprays can be established in a broad range of droplet size and charge. A twin spray setup with opposite charges on the top and bottom sprays was used, in which a cobalt manganese oxide precursor was ejected from the top spray and the graphene oxide sheets were delivered from the bottom. The aerosolized graphene oxide appeared as either flat sheets or crumpled ones, which was tentatively attributed to different levels of dryness of the aerosol at the impaction on the substrate. Coupling of the graphene oxide with the mixed oxide nanoparticles showed sparse evidence of good mixing of the two. In addition, challenges with the precipitation of the graphene solution and with its electrospraying with negative polarity, as manifested by instabilities and corona discharge, prompted the on-going search for alternative ES synthesis methods either by layer-by-layer deposition or using a different source of carbon. 1 Science, Technology, and Research Scholar, Yale College, New Haven, CT 06520 Department of Mechanical Engineering and Materials Science, Yale University