Structure and electrochemical behavior of lithium vanadate materials for lithium batteries

New vanadate compounds having the molecular structure Li(x)Mg(1-x)V(2-x)Mo(x)O(6) (0 <= X <= 1) were studied. Six samples were prepared by sol-gel process from precursor using the following ratios of x=0, 0.2, 0.4, 0.6, 0.8 and 1, respectively. These samples were labeled S1, S2, S3, S4, S5 and S6. The final process of firing occurred at 750 degrees C for 18 It in air. The prepared materials were characterized by XRD, SEM, IR, electron spin resonance (ESR) and magnetic measurements. The morphologies of S 1, S2, S5 and S6 are prismatic as they have monoclinic crystal structures. S3 and S4 differ in the crystal morphology from the other previous samples due to their triclinic crystal lattice structure. IR spectra revealed that the bond lengths of the vanadyl groups nu v=o, nu(sy) nu-o and sigma v-o increase in the same direction from S I to S6. The data of the ESR explain the existence of V(4+) beside V(5+) in S 1, S4 and S6 and also presence of Mo(5+) with Mo(6+), in S4 and S6. S4 exhibited better magnetic susceptibility and saturated magnetization than the other samples. The first specific discharge capacities of the samples were performed. S4 showed the maximum specific capacity of 265 mAh g(-1) in comparison with the other samples. Cyclic voltammogram, of S4 exhibited the highest current intensity in comparison with the other samples. This sample showed two peaks at 0.53 and 1.3 V versus Li/Li(+) characterizing double de-insertions of two lithium atoms from Li(1.6)Mg(0.4)V(1.4)Mo(0.6)O(6-x), and Li(0.6)Mg(0.4)V(1.4)Mu(0.6)O(6),, respectively. Also, two additional peaks were characterized for the oxidation of Mo(5+) to Mo(6+) and V(4+) to V(5+) at 3.5 and 4 V, respectively. (c) 2006 Elsevier Ltd. All fights reserved.