Lithium loss mechanisms during synthesis of layered LixNi2 − xO2 for lithium ion batteries

Abstract

Solution based combinatorial samples of lithium nickel oxide were synthesized and studied by X-ray diffraction in order to develop a method that limits the amount of lithium lost during synthesis. Variables tested were the substrate used (alumina, magnesia or alumina treated with LiOH), heating temperature, the atmosphere during heating (air or oxygen) and the chemical used to precipitate the metals (ammonium bicarbonate or ammonium hydroxide). Two distinct mechanisms for lithium loss were identified. The first is the thermal decomposition of lithium nickel oxide, which was studied using thermogravimetric analysis. XRD scans taken after heating the combinatorial samples to various temperatures from 200 to 900°C revealed a second means of losing lithium: the decomposition of lithium carbonate before the lithium could enter the nickel oxide structure. Both decomposition reactions were followed by conversion of lithium oxide to lithium peroxide vapor. The conditions required to minimize the lithium loss were found and LixNi2−xO2 samples up to x=0.95 were made at 800°C. Size/strain analysis of the XRD scans showed that heating to this temperature was sufficient to eliminate any defects and in-homogeneities that arose during synthesis. Since these samples and LiNixMn2−xO4 (0<x<0.5) spinel samples can be made under the same conditions, it is now possible to simultaneously synthesize samples with the correct metal stoichiometry over the entire Li–Mn–Ni oxide pseudo-ternary system using a solution dispensing robot.