Multi-component precursor droplet evaporation in spray synthesis of cathode materials

Spray synthesis methods are highly attractive for manufacturing materials for energy storage and conversion owing to their scalability and controllability. The key to achieving high controllability in spray synthesis is understanding the complex relationship between the precursor spray droplet evaporation process and the final product structure. Although several studies on precursor droplet evaporation have been reported, very few consider multi-component droplets, which are relevant in practical applications. In this study, we analysed the evaporation of multi-component single precursor droplets used in flame-assisted spray pyrolysis (FASP) of Li(Ni0.8Co0.1Mn0.1)O2 (NCM811) cathode materials. The product particles of FASP were characterized using SEM, EDS and EELS to determine the structure and morphology of particles obtained from precursors with and without urea additives. The qualitative and quantitative changes during evaporation were analysed using high-speed visualization of suspended single droplets on cross-wires. An in-house developed numerical model was used to track the trajectory of the solutes within the evaporating droplet and elucidate the connection between the evaporation process and the final product structure. It was found that evaporating droplets with multiple precursor solutes (Li, Ni, Co, and Mn) formed product particles with gradient element distribution in the radial direction. However, the addition of a small amount of urea (2.5 wt%) caused significant disturbances in the droplet evaporation process triggered by the urea decomposition reaction leading to uniformly distributed elements in the final product particle. The study contributes towards enhancing fundamental knowledge on multi-component droplet evaporation leading to improved design of spray drying and synthesis processes.