Single step synthesis of W-modified LiNiO2 using an ammonium tungstate flux

Abstract

LiNiO₂ has long been considered a promising cathode material owing to its high energy density. However, structural and surface instabilities, coupled with its complex synthesis, have thus far prevented its commercialisation. To address these issues, we demonstrate here the use of an ammonium tungstate flux to modify both the crystal structure and primary particle morphology of LiNiO₂. Successful synthesis was confirmed using a combination of electron microscopy and synchrotron-based X-ray diffraction (XRD). Refinement of structural models against the data suggests that tungsten dopant ions occupy the Ni site and concurrently induce migration of Ni²⁺ to Li sites. Variable temperature XRD was used to demonstrate the improved stability of the W-doped materials during calcination at high temperatures. Electrochemical characterisation shows that W-modified LiNiO₂ offers improved cycle life at the expense of little specific capacity. The structural consequences of tungsten doping on the behaviour of the material during electrochemical cycling were also investigated using operando XRD, showing reduced mechanical stress upon cycling. In conclusion, the hereby-reported LiNiO₂ modified with W via a simple route and no additional processing steps exhibits improved chemomechanics, longer cycling life and structural stability at high temperatures, offering a path towards the reliable synthesis of LiNiO₂ with controlled morphology.