Factors influencing the crystal chemistry of chemically delithiated layered HxNi1-y-zMnyCozO2

Layered HxNi1-y-zMnyCozO2 oxides have been synthesized by chemically extracting lithium from the corresponding LiNi1-y-zMnyCozO2 with the oxidizer NO2BF4 in acetonitrile. Rietveld analysis of the X-ray diffraction data reveals that the structure of the delithiated HxNi0.5-yMn0.5-yCo2yO2 phases obtained from LiNi0.5-yMn0.5-yCo2yO2 synthesized at 900 degrees C changes from P3 type (in HxCoO2) to O1 type (in HxNi0.33Mn0.33Co0.33O2) to O3 type (in HxNi0.5Mn0.5O2) with decreasing Co content. In addition, the tendency to form the P3 type phase instead of the O1 type phase in the case of HxNi0.33Mn0.33Co0.33O2 increases as the synthesis temperature of the parent LiNi0.33Mn0.33Co0.33O2 decreases from 900 to 600 degrees C. A similar tendency to form the P3 type phase instead of the O3 type phase is also seen with the HxNi0.5Co0.5O2 system with decreasing synthesis temperature of LiN(i0.)5Co(0.5)O(2). These observed variations in the type of phases formed are explained on the basis of (i) the differences in the chemical lithium extraction rate caused by the differences in the degree of cation disorder and surface area, and (ii) the proton content inserted during chemical lithium extraction.