Influence of Mn2+ and Fe2+ doping in LiNi0.8M0.2PO4·3H2O on H-bond strength in crystalline hydrates and thermal transformation mechanism
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The LiNi0.8M0.2PO4·3H2O (M = Mn2+, Fe2+) were successfully synthesized with a simple co-precipitation route to obtain the lithium binary transition metal phosphate hydrates, in which the corresponding calcined products can be used as cathode materials in Li-ion batteries. The hydrates and their calcined products were characterized using FTIR/FT Raman spectrophotometer, atomic absorption/atomic emission spectrophotometer, X-ray powder diffraction and TG/DTG/DTA. The morphologies of the synthesized compounds were investigated by using scanning electron microscope technique and found to be the thick-plate particles, which were changed to small-bead particles after the thermal treatment. The influence of the transition metal doping on the strength of hydrogen bonding in the structure of the studied compounds was investigated by using the FTIR and TG/DTG/DTA techniques. Moreover, the decomposition mechanism and vibrational properties of the products were studied and it was found that the H-bond strength and transformation mechanisms of three studied hydrates, namely LiNiPO4·3H2O, LiNi0.8Mn0.2PO4·3H2O and LiNi0.8Fe0.2PO4·3H2O, were significantly different. In addition, based on the results from both vibrational and kinetic properties, the strength of H-bonding of the title compounds was obtained in order of magnitude as LiNiPO4·3H2O > LiNi0.8Fe0.2PO4·3H2O > LiNi0.8Mn0.2PO4·3H2O.
KeywordsHydrogen bond Kinetic study Ni0.8M0.2PO4·3H2O Transformation mechanism Vibrational spectroscopy
We thank the Department of Chemistry, Faculty of Science, Khon Kaen University, for providing research facilities. The financial support from the Center of Excellence for Innovation in Chemistry (PERCH-CIC) and Materials Chemistry Research Center, Department of Chemistry, Faculty of Science, Khon Kaen University, is gratefully acknowledged.
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