Electrochemical characterization of high performance Al2O3 (MEA) coated LiNiVO4 cathode materials for secondary lithium batteries

Inverse spinel structured LiNiVO4 has been prepared by a citric acid polymeric process in addition with urea. Al2O3 derived from (methoxyethoxy) acetate-alumoxane (MEA) has been used to coat the LiNiVO4 cathode and it has established sustainable extended cycle stability. The (MEA)-alumoxane was prepared by reacting pseudo-boehmite with (methoxyethoxy) acetic acid. XRD patterns showed that the formation of a crystalline phase occurred at 723 and 873 K and for the coated material with no indication of new peaks. TEM micrographs of the pristine LiNiVO4 and coated powder revealed that particle size ranged from 50 to 70 nm and the coating was compact with an average thickness of about 15 nm. ESCA depth profiles of the constituent elements in the coated particle confirmed a layer of Al2O3 formed on the surface of the LiNiVO4. The galvanostatic cycling studies suggest that 0.5 wt.% coating resultant from a (methoxyethoxy) acetate-alumoxane enhanced the cycle stability two times compared with the pristine LiNiVO4. The improved performance is attributed to the ability of the Al2O3 resultant (MEA) precursor layer on the core material to suppress the side reaction and dissolution of 3d metals in LiPF6 based liquid electrolytes during charge–discharge processes. A comparison of the electrochemical impedance behavior of the pristine and coated materials suggested that the coated material was resistant to the impedance growth of the LiNiVO4 cathode upon cycling.