Authors: S. Vivekanandhan, M. Venkateswarlu and N. Satyanarayana
Affilation: Pondicherry University, India
Pages: 406 - 409
Keywords: nano - crystalline LiNiVO4, glycerol, polymeric gel, DSC, FTIR, SEM, XRD
Inverse spinel LiNiVO4 has been used as a cathode material for high voltage lithium battery applications. Better performance of the cathode material is due to its physical and chemical properties, which are mainly depending on the synthesis process. Wet chemistry (sol- gel, gel combustion etc.) methods are more suitable for the synthesis of multi-component oxide powders in nano - scale. In the present work, nano - crystalline inverse spinel LiNiVO4 powders were prepared by the gel combustion route with citric acid and glycerol under three different fuel conditions as total metal ion to citric acid to glycerol ratio of (i) M/CA/G = 1:1:1 (ii) M/CA/G = 1:1:2 and (iii) M/CA/G = 1:2:1. Required stoechiometric amounts of the lithium nitrate, nickel nitrate and ammonium vanadate solutions were prepared with three different total metal ions to citric acid to glycerol ratio (M/CA/G) of 1:1:1, 1:1:2 and 1:2:1 and the resulting solutions were evaporated at 75oC under constant stirring. The evaporation lead to the formation of gel and it was further heated at 175oC for 12 hours to obtained polymeric intermediates. Thermal decomposition of the polymeric intermediates led to the formation of nano - crystalline LiNiVO4 powders, which were investigated using DSC, FTIR, SEM and XRD measurements. Fig 1 shows the DSC curves of the polymeric intermediates. From fig 1, the observed exothermic peaks showed that the combustion reaction completes at 400oC, which may caused the formation of LiNiVO4, further it is confirmed by SEM, FTIR and XRD results. Fig. 2a, 2b and 2c show the microstructures of the three polymeric intermediates obtained by SEM. Fig 3 shows the FTIR spectra of polymeric intermediates and the observed IR peaks (3392cm-1, 1570cm-1 and 1255cm-1) confirm the formation of the organic derivatives. The organic derivatives were disappeared when the intermediates were heated at 450oC and above, shown by fig.4. From fig 4, the observed new peaks at 811 cm-1 and 690 cm-1 are attributed to the stretching vibrations of V-O bonds of VO4 tetrahedra, which may be due to the formation of the LiNiVO4 structure. Fig.5 shows the XRD spectra of the as prepared and also calcined polymeric intermediate (M/CA/G = 1:1:1) at different temperatures. From fig.5, the crystalline LiNiVO4 phase was confirmed, for the polymeric intermediate calcined at 450oC and above, by comparing the observed XRD spectra with the JCPDS standard. The crystallite size for the LiNiVO4 powders, obtained from the dried gels calcined at 450oC, prepared with three different fuel conditions as M/CA/G = 1:1:1, 1:1:2 and 1:2:1, shown in fig.6, are respectively found to be 39, 55 and 40 nm. Detailed results will be presented and discussed.