Effect of the synthesis procedure on the electrochemical properties of Na2/3Ni1/2Mn1/2O2 used as an electrode material in lithium-ion batteries

In this contribution, we study in details the effect of synthesis procedure on the electrochemical properties of NaxNi1/2Mn1/2O2 with x=2/3 when it is used as an electrode in lithium cells. For the preparation of oxides Na0.67Ni0.5Mn0.5O2, the precursor-based method was chosen. The method of synthesis is based on the formation of homogeneous precursor phases, which are easily transformed to the target product by a sequence of low-temperature reactions. The precursors are obtained by freeze-drying of aqueous solutions of Li(I), Ni(II) and Mn(II) salts. Two types of soluble salts are selected: acetate and nitrates. Thermal treatment of freeze-dried acetate-nitrate precursors at temperatures above 400 degrees C yields layered Na0.67Ni0.5Mn0.5O2 with a P3-type of structure. Thermal properties of acetate-nitrate precursors are studied by DTA/TG analysis. The crystal structure and morphology of NaxNi1/2Mn1/2O2 are analyzed by means of X-ray powder diffraction and SEM analysis. The electrochemical properties of Na0.67Ni0.5Mn0.5O2 are examined in model lithium cells. The oxide Na0.67Ni0.5Mn0.5O2 obtained from freeze-dried acetate precursors displays a better electrochemical performance in terms of reversible capacity and cycling stability.