The importance of developing new low-cost and safe cathodes for large-scale sodium batteries has led to recent interest in silicate compounds. A novel cobalt orthosilicate, NaCoSiO, shows promise as a high voltage (3.3 V vs. Na/Na) cathode material for sodium-ion batteries. Here, the synthesis and room temperature electrochemical performance of NaCoSiO have been investigated with the compound found to yield a reversible capacity greater than 100 mA h g at a rate of 5 mA g. Insights into the crystal structures of NaCoSiO were obtained through refinement of structural models for its two polymorphs, Pn and Pbca. Atomistic modelling results indicate that intrinsic defect levels are not significant and that Na diffusion follows 3D pathways with low activation barriers, which suggest favourable electrode kinetics. The new findings presented here provide a platform on which future optimisation of NaCoSiO as a cathode for Na-ion batteries can be based.

which has been optimized for capacity and voltage, against a pristine hard carbon anode. The development of a full sodium ion cell and the optimization for energy density is discussed, and we report a 3.3 Ah cell with a demonstrated cell energy density of 211 Wh/L with 94% capacity retention after 150 cycles, and a 4.2 Ah cell with a demonstrated cell energy density of 252 Wh/L. The hard carbon is not pre-cycled and therefore the cells exhibit a 20% loss during the formation stage. These results represent realistic values for larger scale sodium ion battery manufacture as a drop-in technology for lithium ion batteries.

The large-scale utilisation of renewable energy technologies depends on solving the intermittency of energy production with large scale energy-storage solutions. The Lithium-ion battery has been widely considered as the technology of choice to meet the future energy challenge. However, increasing demand for Li based energy storage technologies is likely to tax current Li production. There is growing research and commercial interest in other metal ion battery technologies that could be developed to meet the needs of large scale energy storage applications. As such, the room temperature Na-ion secondary battery has been the subject of increasing research and development due to its feasibility to compete with the already well-established Li-ion secondary battery.1 Although, there are many technical barriers to overcome before Na-ion technology becomes competitive with current metal ion batteries. However, recent research into Na-ion systems has shown that some of the known Na-ion battery materials have advantages over the current Li-ion counterparts.2  In this publication, we present detailed characterisation of novel sodium ion cathode materials based on a layered oxide framework as strong candidates for Na-ion battery cathode materials. We will present a review of layered oxides (Na Nix TMyO2, TM = Ti, V, Cr, Mn, Fe, Co, Ni, and a mixture of 2 or 3 elements). Single TM layered oxide systems are well characterised not only for their electrochemical performance but also for their structural transitions during electrochemical cycling.1 Binary TM systems are often favoured as modifications through doping seem to address issues of low reversible capacity, capacity retention, operating voltage, and structural stability when compared to the single TM analogues.2 As a consequence, some materials already have reached a specific energy density of 578 mW h g−1 comparable to that of LiFePO4.3 Furthermore, some binary and ternary TM systems have shown exceptional stability and rate capability.4 Herein, we present development work of Na Nix Mny TM1TM2 O2 quaternary and higher substituted sodium layered oxides.5 We demonstrate that further substitution within the layered oxide structure is beneficial to improving reversible capacity, capacity retention and operating voltage of these materials. These higher order substitutions leading to materials which show comparable electrochemical properties to simple Li ion technologies. We have begun development of Full cell technology based on some of the best performing layered oxides.   N. Yabuuchi, et al. Chem. Rev., 2014, 114 (23), pp 11636–11682 L. Yuechuan, et al. Chem. Mater. 2014, 26, 5288−5296 X. Li et al.  Electrochemistry Communications 49 (2014) 51–54 H. Yoshida, N. Yabuuchi and  S. Komaba Electrochem. Commun., 34 (2013), pp. 60–6 J. Barker, et al. Doped Nickelate Compounds WO 2014/009710A1