High redox potential transition metals incorporated olivine structure: LiFe 0.7 (Mn 1/3 Co 1/3 Ni 1/3 ) 3x−y V y PO 4 ( x = 0.1, 0.0 ≤ y ≤ 0.10) cathode for Li-ion battery

A series of LiFe 0.7 (Mn 1/3 Co 1/3 Ni 1/3 ) 3 x − y V y PO 4 ( x = 0.1, y = 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, and 0.10) compositions doped with high concentration (30 mol%) of transition metals having higher redox potential are synthesized by sol-gel process. In the composition, assumption is made that equal contents of Mn, Co, and Ni are replaced simultaneously by vanadium (V), and changes in structural and electrochemical characteristics are systematically investigated. The X-ray diffraction analysis confirms that for y > 0.04, a secondary phase Li 3 V 2 (PO 4 ) 3 formation takes place. The Rietveld refinement performed on XRD data shows continuous change in lattice parameters and cell volume with increasing y . X-ray photoelectron spectroscopy study confirms the oxidation state of Fe, Mn, Co, and Ni in + 2, whereas V in + 4 state. The electrochemical characteristics show the positive contribution of Li 3 V 2 (PO 4 ) 3 in capacity as well as cycle life among doped samples. Graphical abstract