Enhanced electrochemical performance of Li-rich Li1.2Mn0.52Co0.08Ni0.2O2 cathode materials for Li-ion batteries by vanadium doping

As promising cathode materials in Li-ion batteries, Li-rich layered oxides still suffer from unsatisfactory rate capability and cyclic stability during cycling. Herein, vanadium doped Li-rich cathode materials Li1.2Mn0.52-x/3Co0.08-x/3Ni0.2-x/3VxO2 were successfully prepared by using a facile low heat solid state-thermal decomposition method with the introduction of generated water-soluble vanadyl oxalate (VOC2O4) as dopant. The effects of substitution for Ni, Co and Mn with vanadium on structure, morphology, elemental valence state, rate performance and cycling stability were systematically investigated. It is concluded that a minor amount of vanadium doping (x = 0.015) expands the interslab spacing of layered oxide and facilitates the lithium-ion diffusion. The vanadium ions incorporated into crystal lattices have two valence states of +5 and +4 and elevate the conductivity via fast electron transfer between V5+ and V4+, improving the rate capability especially the high-rate performance (99.0 mAh·g−1 at 5C rate). Besides, the relatively excellent cyclic performance (a capacity retention of 90.2% is reserved after 50 cycles at 1C rate) for sample Li1.2Mn0.515Co0.075Ni0.195V0.015O2 can be also ascribed to the enhanced structure stability derived from the much more robust V-O bond in comparison with the Mn-O, Ni-O and Co-O bonds.