Investigating the Removal of Layered Double Hydroxides in [Ni0.80Co0.15]0.95-xAl0.05+x(OH)2 (x = 0, 0.05) Prepared by Coprecipitation

Abstract

Nickel-rich materials such as LiNi1-x-yCoxAlyO2 (NCA) are prepared starting with Ni1-x-yCoxAly(OH)2 precursors. In Ni1-x-yCoxAly(OH)2, the oxidation states cannot balance because Al takes the 3+ oxidation state, so these precursors also incorporate undesired anions, like CO32− or NO3−, into the structure and forming what is known as a layered double hydroxide (LDH) phase to balance the excess charge on Al. The incorporation of anions leads to a large expansion of the M(OH)2 c-axis layer spacing leading to undesired low density materials. [Ni0.80Co0.15]0.95-xAl0.05+x(OH)2 (x = 0, 0.05) precursors were prepared by the coprecipitation method. The materials contained appreciable amounts of undesired LDH phase, with increasing LDH phase presence as Al content increased. The LDH phase can be removed by subjecting the hydroxide precursor materials to a washing treatment with hot NaOH. NaOH concentration, temperature, and stirring time were varied to study their impact on LDH removal. Unwashed and washed samples were characterized to monitor crystal structure, LDH content, metal ratios, LDH anions, and morphological changes. The oxidation state balance in the materials containing Al and without corresponding anions is discussed.