The structural conversion from α-AgVO to β-AgVO: Ag nanoparticle decorated nanowires with application as cathode materials for Li-ion batteries.

The majority of electrode materials in batteries and related electrochemical energy storage devices are fashioned into slurries via the addition of a conductive additive and a binder. However, aggregation of smaller diameter nanoparticles in current generation electrode compositions can result in non-homogeneous active materials. Inconsistent slurry formulation may lead to inconsistent electrical conductivity throughout the material, local variations in electrochemical response, and the overall cell performance. Here we demonstrate the hydrothermal preparation of Ag nanoparticle (NP) decorated α-AgVO nanowires (NWs) and their conversion to tunnel structured β-AgVO NWs by annealing to form a uniform blend of intercalation materials that are well connected electrically. The synthesis of nanostructures with chemically bound conductive nanoparticles is an elegant means to overcome the intrinsic issues associated with electrode slurry production, as wire-to-wire conductive pathways are formed within the overall electrode active mass of NWs. The conversion from α-AgVO to β-AgVO is explained in detail through a comprehensive structural characterization. Meticulous EELS analysis of β-AgVO NWs offers insight into the true β-AgVO structure and how the annealing process facilitates a higher surface coverage of Ag NPs directly from ionic Ag content within the α-AgVO NWs. Variations in vanadium oxidation state across the surface of the nanowires indicate that the β-AgVO NWs have a core-shell oxidation state structure, and that the vanadium oxidation state under the Ag NP confirms a chemically bound NP from reduction of diffused ionic silver from the α-AgVO NWs core material. Electrochemical comparison of α-AgVO and β-AgVO NWs confirms that β-AgVO offers improved electrochemical performance. An ex situ structural characterization of β-AgVO NWs after the first galvanostatic discharge and charge offers new insight into the Li reaction mechanism for β-AgVO. Ag between the van der Waals layers of the vanadium oxide is reduced during discharge and deposited as metallic Ag, the vacant sites are then occupied by Li.