Flame Aerosol Synthesis and Electrochemical Characterization of Ni-Rich Layered Cathode Materials for Li-Ion Batteries

We report on the synthesis of LiNi0.8Co0.1Mn0.1O2 (NCM811) Li-ion battery cathode materials using an aerosol of micron-size aqueous metal nitrate solution droplets delivered to non-premixed flames. The objective is to investigate the effect of Ni mole fraction and the aerosol preheating and flame synthesis temperatures on the particle properties and electrochemistry by comparing NCM811 with LiNi0.33Co0.33Mn0.33O2 (NCM111). It is found that the solution composition strongly influences precursor precipitation and oxidation and the resultant particle morphology. NCM111 solutions form predominantly spherical particles from single droplets, whereas Ni-rich solutions form irregularly shaped particles because the lower solubility of Ni nitrate and its high concentration causes rapid precipitation at the droplet surface and subsequent formation and collapse of shell-like structures in the flame. After annealing, NCM111 retains the secondary particle structure, but NCM811 forms irregular shapes with a broad size distribution of primary features because the higher decomposition temperature of NCM811 precursor solutions limits the oxidation and particle formation in the aerosol phase. It is also found that aerosol preheating and flame temperatures play critical roles in determining the electrochemical properties of the final annealed product. The best NCM811 cycling performance was achieved using higher aerosol preheating temperatures (450 K) and lower synthesis temperatures (1350 K). These conditions promote single-mode solid particle formation which increases the size of the primary particles and enhances the uniformity of the primary particle size distribution, thereby improving structural stability without using high synthesis temperatures that damage the ordering of the layered crystal structure.