Aerosol synthesis is a versatile and economical method for the production of a broad variety of functional particles. Here we report on the synthesis of LiNi0.33Co0.33Mn0.33O2 (NCM111) and Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) particles in non-premixed flames. The objective is to investigate the effect of the solution composition on the particle morphology and electrochemical performance. Aqueous precursor solutions of metal nitrates were atomised into 3 µm droplets. The aerosol was first passed through a preheating section and then delivered to a slot burner fed with CH4/O2/N2 gases. Product particles were collected from the exhaust gas. Thermal decomposition of the precursor solutions was investigated using thermogravimetric analysis and the product materials were characterised using SEM and XRD. Cathodes were cast from the annealed materials and assembled into half-cells for electrochemical characterisation.
The results show a distinct difference in the morphology of the as-prepared Ni-rich (NCM811) and NCM111 materials. For low preheating and flame temperatures (360 K/1350 K), balanced NCM111 precursor solutions form uniform micron-sized spherical particles from single droplets. Though the formation route is the same, however, for identical synthesis conditions Ni-rich solutions lead to the formation of irregularly-shaped particles. Increasing the synthesis temperature (430 K/2200 K) improves the NCM811 particle morphology, which tend toward a spherical shape as seen for NCM111 at the same synthesis condition. TGA of the precursor solutions indicates that 1) in the early stages of thermal decomposition, at the same temperature the decomposition of Ni-rich solutions is less advanced than for balanced solutions; and 2) that decomposition completes at a higher temperature for Ni-rich solutions (930 K) than balanced solutions (770 K). Higher synthesis temperatures are required to improve the morphology of the as-prepared micron-size Ni-rich materials.
All materials were also annealed for 4 hours at 1070 K under oxygen. In terms of the particle morphology, NCM111 particles produced at either high or low temperature synthesis conditions are spherical after annealing, with a secondary particle size of 1 µm. Annealed NCM111 materials produced at the high temperature synthesis conditions have a smooth particle surface, as oppose to the NCM111 produced at lower temperatures, which after annealing have a fine primary surface structure on the scale of 100-200 nm. For the Ni-rich powders, for either synthesis condition the effect of annealing is to cause a collapse of the secondary particle structure, such that the annealed materials consist of uniformly-sized but irregularly-shaped grains with a size of 500-600 nm. XRD confirms the crystalline structure of annealed materials that were originally synthesised at higher temperatures is improved, a result that correlates with the enhanced electrochemical performance in terms of the early cycling behaviour.