Room temperature sodium-ion batteries are of great interest for high-energy-density energy storage systems because of low-cost and natural abundance of sodium. Here, we report a novel phosphorus/graphene nanosheet hybrid as a high performance anode for sodium-ion batteries through facile ball milling of red phosphorus and graphene stacks. The graphene stacks are mechanically exfoliated to nanosheets that chemically bond with the surfaces of phosphorus particles. This chemical bonding can facilitate robust and intimate contact between phosphorus and graphene nanosheets, and the graphene at the particle surfaces can help maintain electrical contact and stabilize the solid electrolyte interphase upon the large volume change of phosphorus during cycling. As a result, the phosphorus/graphene nanosheet hybrid nanostructured anode delivers a high reversible capacity of 2077 mAh/g with excellent cycling stability (1700 mAh/g after 60 cycles) and high Coulombic efficiency (>98%). This simple synthesis approach and unique nanostructure can potentially be applied to other phosphorus-based alloy anode materials for sodium-ion batteries.

Understanding oxidation of layered chalcogenide semiconductors is important for device processing, as oxidation can be both an intentional and unintentional result of processing steps. Here, the authors investigate chemical and morphological changes in mechanically exfoliated few-layer MoS2 in oxidizing and inert environments using different microscopies (optical, scanning electron, and atomic force) and spectroscopy (Raman, x-ray photoelectron, and Auger electron) techniques. The environments studied were oxygen, oxygen and water vapor, argon, argon and water vapor, and ultraviolet-generated ozone at temperatures from 25 to 550 °C. Oxidation at low temperatures resulted in the formation of a condensed molybdenum oxide phase and sulfur trioxide gas. At sufficiently elevated temperatures, all the products of oxidation volatilize, resulting in a vapor-phase etch. The kinetics of oxidation and etching depended upon the annealing gas, temperature, time, and the number of layers of MoS2. Conditions can be selected to create isolated etch pits, smooth oxide layers, oxide islands, or flakes of reduced lateral dimensions (etching from the flakes' edges). These results can provide useful guidance for MoS2 device processing.

Physical vapour deposition of Mn metal followed by annealing in air is a promising route to prepare MnOx-anodes for water-oxidation.