Synthesis and characterization of Li(Co0.5Ni0.5)PO4 cathode for li-ion aqueous battery applications

Abstract

Olivine-type lithium orthophosphate Li(Co0.5Ni0.5)PO4 was synthesized in a solid state reaction at 800 degrees C in air. Infra-red spectroscopy, x-ray and neutron powder diffraction were used to characterize the as-prepared compound and its electro-oxidized analogue. Rietveld analysis was used to illustrate that the synthesized compound is isostructural with LiNiPO4 and LiCoPO4 with lattice parameters larger than the former and smaller than the latter. The Rietveld-refined Ni:Co ratio was found to be 0.498(4):0.502(4) and no evidence for long-range Ni: Co ordering or mixed Li/Ni/Co cation sites was found. The electro-oxidised electrode showed a mixture of two phases i.e. parent Li(Co0.5Ni0.5)PO4 and lithium extracted Li1-x(Co0.5Ni0.5)PO4 suggesting a delithiation process in aqueous electrolytes. Reversible Li transfer between a Li(Co0.5Ni0.5)PO4 electrode and an aqueous LiOH electrolyte was demonstrated. (C) 2011 The Electrochemical Society. [doi:10.1149/1.3561764]