Reactive crystallization regulation for synthesizing NCM811 precursor by different impellers

Abstract

The spherical and dense precursors with a narrow particle size distribution are essential to achieve high electrochemical performance in cathode materials. Four newly designed impellers, including the punched-flow turbine (PFT), punched-flow disc turbine (PFDT), curved-inclined-blade disc turbine (CIBDT), and 6-folded-pitched turbine (FPT-6), are applied to prepare the precursors to investigate the interplay among the fluid flow state, precursors’ morphology and growth, and physicochemical properties of cathodes. The flow and mixing features of double impellers are predicted using computational fluid dynamics, indicating that the FPT-6 plays a crucial role in crystal nucleation while PFDT facilitates crystal growth. This concurrence can be corroborated by examining the performance of precursors synthesized using these four impellers. It is first found that the electrochemical performance is distinctly enhanced by utilizing different impellers to regulate the specified nucleation and growth stage. By increasing the nucleation rate with double impellers of FPT-6, the tap density and sphericity of the precursor and cathode materials are significantly improved. The discharge capacity of cooperative agitators (FPT-6+PT) is 2.1 times that of the only propeller turbine at a high current density (10 C). The later growth stage is suitably regulated by FPT-6 or PFDT; properly extended reactive time can enhance the sphericity and electrochemical performance. The dual mixed-impeller (PT/CIBDT) combines intense mixing and shear ability, attaining a dense spheroid with a highly smooth surface. The cycle retention of this cathode is increased by 10.35% after 200 cycles at 1 C compared to a commercial counterpart. A regulatory strategy for the reactive co-precipitation process to enhance precursor stability is proposed here. Furthermore, the optimal operation parameters derived from this strategy can be effectively applied to commercial cathode materials.