Effect of oxidizer in the synthesis of NiO anchored nanostructure nickel molybdate for sodium-ion battery Manickam Minakshi a, b, * , Maryam Barmi a , David R.G. Mitchell c , Anders J. Barlow d , Maximilian Fichtner b, ** a Engineering and InformationTechnology, Murdoch University, WA 6150, Australia b Helmholtz Institute Ulm for Electrochemical Energy Storage (HIU), Ulm 89081, Germany c Electron Microscopy Centre, Innovation Campus, University of Wollongong, North Wollongong, NSW 2500, Australia d Centre for Materials and Surface Science, La Trobe University, Bundoora, VIC 3086, Australia article info Article history: Received 19 June 2018 Received in revised form 6 August 2018 Accepted 14 August 2018 abstract Sodium-ion batteries are an excellent candidate to meet the challenge of grid-level storage because of the abundance and low cost of sodium resources. It is crucial to identify suitable anode material for such batteries in order to replace the current technology involving metallic sodium- or carbon-based anodes. Anodes of metal-ion batteries determine key characteristics, such as safety issues and cyclability. Nickel molybdate (NiMoO 4 ) is an alternative candidate material for anode applications, possessing a number of useful characteristics. In this work, we have produced the phase by solution combustion synthesis. We have investigated the influence of oxidant (NH 4 NO 3 ) concentration and optimised it to produce desirable material characteristics. The oxidant has a central role in the synthesis, being able to influence the properties of NiMoO 4 including the electrochemical performance. At a low concentration of oxidiser (NH 4 NO 3 ) the product obtained is partly crystalline and contains carbonaceous impurities while at a higher concentration of oxidiser, the reaction is incomplete forming secondary phases. The optimised fuel-to-oxidiser ratio is found to be around 1:1 whereby the oxidant is able to interact and chelate metal cations. This optimised material produces a high initial discharge capacity of NiMoO 4 vs. Na of 550 mAh g 1 at a current density of 0.05 A g 1 . However, the reversible capacity is found to be 245 mAh g 1 but resulted in good capacity retention of 82% after 50 cycles and higher rate capability performance. This anode material is comparable to the capacity and outperforms by the voltage of classical carbon anodes used in sodium-ion battery. In the case of material produced with the lowest and highest concentrations, capacity retention is 45% and 75%, respectively. The electrochemical intercalation of Na ions into nickel molybdate produces a new type of intercalation compound (Na 2 MoO 3 ) and this is discussed. These results provide insight regarding a versatile methodology based on solution combustion synthesis and an alternative insertion-type anode to metallic sodium or carbon. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction With growing concerns of the need for low carbon emissions and the depletion of fossil energy, there is an increasing demand for renewable energy sources [1]. Clean energy sources such as solar and wind are being integrated into power systems, but they are non-dispatchable and have variable output. Therefore, the search for cost-effective storage technology is of great importance to store the excess energy and to supply it during high demand [2]. Sec- ondary batteries are among the most successful energy storage technologies that can be used to provide an efficient storage/release of renewable energy over many cycles [3]. Extensive research has been focussed on energy storage materials for such batteries and supercapacitors [3e5]. Currently, lithium-ion batteries are widely used, this has resulted in rapid rises in global lithium prices and growing demand may not be sustainable in terms of both avail- ability and cost. Therefore, sodium-ion batteries, which do not suffer from such constraints, have been the focus of recent research * Corresponding author. Engineering and Information Technology, Murdoch University, WA 6150, Australia. ** Corresponding author. E-mail addresses: minakshi@murdoch.edu.au (M. Minakshi), m.fichtner@kit.edu (M. Fichtner). Contents lists available at ScienceDirect Materials Today Energy journal homepage: www.journals.elsevier.com/materials-today-energy/ https://doi.org/10.1016/j.mtener.2018.08.004 2468-6069/© 2018 Elsevier Ltd. All rights reserved. Materials Today Energy 10 (2018) 1e14