Electrochemical properties of vanadium-substituted lithium silicate materials Li2+xFe0.5−x/2Mn0.5−x/2Si1−xVxO4 (x = 0, 0.1, 0.2, 0.3 and 0.4) for lithium-ion battery cathodes

Abstract Vanadium-substituted LiFe 0.5 Mn 0.5 SiO 4 cathode material for Li-ion batteries is synthesized by solid state reaction, and the effect of V-substitution on the material is investigated by X-ray diffraction and charge–discharge tests. X-ray diffraction patterns seem to indicate that V +5 is substituted for Si 4+ in Li 2+x Fe 0.5−x/2 Mn 0.5−x/2 Si 1−x V x O 4 (x = 0, 0.1, 0.2, 0.3, 0.4) by maintaining electroneutrality. The substitution of V for Si in Li 2 Fe 0.5 Mn 0.5 SiO 4 increases the charge and discharge capacities as a cathode material of Li-ion batteries; Li 2.2 Fe 0.4 Mn 0.4 Si 0.8 V 0.2 O 4 delivers an initial discharge capacity of 197 A h/kg, while Li 2 Fe 0.5 Mn 0.5 SiO 4 delivers that of 134 A h/kg. The main reason for the high capacity with the V substitution for Si in Li 2 Fe 0.5 Mn 0.5 SiO 4 is considered not due to the redox capacity of V but due to the lowering of the charge voltage, while, substituting a higher amount of V, with x over 0.2 in Li 2+x Fe 0.5−x/2 Mn 0.5−x/2 Si 1−x V x O 4 , reduces capacity in accordance with theoretical capacity calculation. In order to confirm the V-substitution site exactly, however, strong evidence by Rietveld refinement is necessary, which is left as our urgent future work.