(Digital Presentation) Modifying LiNiO2 with W Via a Single Step Synthesis Route

Abstract

LiNiO2 has been long considered as a promising cathode material owing to its high practical energy density. However, structural and surface instabilities, coupled with complexities in the LiNiO2 synthesis, have thus far prevented its commercialisation. To address issues with the material’s stability during synthesis and cycling, the use of an ammonium tungstate flux is demonstrated here to modify both the LiNiO2 crystal structure and primary particle morphology without introducing additional steps into the synthesis. The successful preparation of LiNiO2 modified with an industrially relevant amount of W (< 5 mol %) was confirmed using a combination of electron microscopy and synchrotron-based X-ray diffraction (XRD). Refinement of structural models against the data suggests tungsten dopant ions occupy the Ni site and concurrently induce migration of Ni2+ to the Li sites. Moreover, W enrichment at grain boundaries has been observed under some of the synthesis conditions. Variable temperature XRD was used to highlight the improved stability of the W-doped materials during the calcination at high temperatures. Electrochemical characterisation shows that W-doped 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 was also investigated using operando XRD, showing reduced mechanical stress upon cycling. In conclusion, we will show that LiNiO2 modified by W with a simple route and no additional processing steps exhibits structural stability at high temperatures, offering a path towards the reliable synthesis of LiNiO2 with controlled morphology, improved chemomechanics and longer cycling life.