Electrochimica Acta, Vol.314, 115-123, 2019
Excellent cycling stability and capability of novel mixed-metal vanadate coated with V2O5 materials in an aqueous solution
Mixed metal vanadate oxide (NKVO) synthesized by hydrothermal followed by annealing was coated with an amorphous layer of V2O5 (NKVO@V2O5) by a wet-chemical method and annealed for prolong period. The amorphous state of V2O5 was suggested by X-ray diffraction predicted by the absence of a new peak of V2O5. To know the oxidation states of vanadium X-ray photon spectroscopy was carried out, to further understand the process of V2O5 deposition onto NKVO pre/post-annealing surface transmission electron microscopy was also carried out. The elemental distribution was demonstrated by Elemental dispersion spectrum. The prepared anode materials were subjected to cyclic galvanostatic charge-discharge, cyclic performance and cyclic voltammetry at multiple current rates to demonstrate the electrochemical performance. The coated NKVO@V2O5 anode material resulted in improved electrochemical performance when the anode was cycled at the current density of 3Ag(-1) with starting discharge capacity of 151.17 mAhg(-1) after 60 cycles reduced to 113.0 mAhg(-1) retaining 74.7% of initial capacity in the voltage window of -1 similar to 1V (vs SCE), in contrast, the pristine material showed only 58.5% capacity retention. The NKVO@V2O5 showed increased capacity retention i.e. 62.5, 69.8%, 80.5%, and 77.9% under current rate of 0.1Ag(-1), 0.5Ag(-1), 1Ag(-1), and 2Ag(-1) respectively, while the pristine NKVO could only retain 58.6%, 57.0%, 53.4%, and 61.4% after 60 cycles at respective current rates. The characterization methods and the results suggested that coating layer plays a key role in improving the electrochemical performance. As the V2O5 layer served as a barrier to protect from the occurrence of unwanted side reaction. However, the layer also prevented the dissolution of active material in aqueous electrolyte. Due to the high ionic conductivity of V2O5, it also promoted Li+ and electronic conductivity. The calculation of lithium ion diffusion coefficient of NKVO@V2O5 (1.07 x 10(-10), 3.96 x 10(-11) and 3.01 x 10(-12) cm(2) s(-1)) effectively suppresses that of pristine NKVO suggesting more electrode polarization during cycling. (C) 2019 Elsevier Ltd. All rights reserved.