Low Temperature Niobium Tungsten Oxides as Anodes for Fast Charging Li-Ion Batteries

Abstract

The development of fast-charging Li-ion batteries is one of the important steps in building electric vehicles that need high power and fast charging. The reduction in the particle size to the nanometre length scale drastically improves the charging rate by increasing the surface area but lowers the volumetric energy density and can potentially result in more rapid degradation of the electrolyte via electrode-catalysed reactions. Recent reports show that niobium tungsten oxides (NbWOs) with µm sized particles serve as good anode materials for Li-ion batteries having high volumetric capacity with good cyclability at high rates while avoiding solid electrolyte interphase formation (SEI). The high rate performance of NbWOs is attributed to the topochemical charge storage mechanism that exhibits (i) minimal, highly reversible structural changes during the charge-discharge cycles, (ii) high Li-ion diffusion coefficients due to the presence of fast conducting tunnels, and (iii) high electronic conductivity upon lithiation.1,2 The NbWOs are known to crystallize into two families of different crystal structures depending on the composition and synthesis conditions. The NbWOs phases can either have tungsten bronze-type structures or block-type structures (commonly referred to as Wadsley-Roth phases). Different NbWO phases are reported in the literature3 which could serve as potential anode materials with better performance.In this work, a series of new NbWO phases have been synthesized at reduced annealing temperatures and the structure of these phases has been established using X-ray and neutron diffraction data. The electrochemical properties of NbWO/Li half cells were examined through a series of galvanostatic (dis)charge tests at varying current rates ranging from 0.2 C to 20 C. The NbWO phases delivers a high reversible capacity of 200 and 130 mAh/g at 0.2C and 10 C respectively vs. Li metal. Here we use operando powder X-ray diffraction to investigate the structural changes occurring at the anode during the charge-discharge process in the newly synthesised NbWO phases. Reference s : 1 K. J. Griffith, K. M. Wiaderek, G. Cibin, L. E. Marbella and C. P. Grey, Nature, 2018, 559, 556–563.2 C. P. Koçer, K. J. Griffith, C. P. Grey and A. J. Morris, Chem. Mater., 2020, 32, 3980–3989.3 N. C. Stephenson, Acta Crystallogr. Sect. B Struct. Crystallogr. Cryst. Chem., 1968, 24, 637–653. Figure 1