Extended Application of the Couette-Taylor Flow for the Continuous Synthesis of Spherical Shaped Ni-Rich Cathode Materials for Lithium Ion Batteries

摘要

The electrochemical performance of transition metal oxide (NCM)-based cathodes depends strongly on the physical properties of the applied materials. Recently, an increase of capacity was achieved through the optimization of the chemical composition, leading to the development of Ni-rich layered oxide cathode materials. However, the poor rate capability and capacity retention as well as the high first cycle irreversible capacity loss (ICL) and the low volumetric energy density have to be improved by specific design of the particle shape. The realization of a spherical morphology with a narrow size distribution is the preferred particle shape and can only be synthesized during the co-precipitation of transition metal hydroxides or carbonates by a continuously stirred tank reactor (CSTR). The CSTR-process allows a further improvement of the cathode materials during the synthesis of core-shell and full concentration-gradient particles. Here, we present the design and the operating principle of a novel Couette-Taylor-Flow-Reactor (CTFR) that offers a continuous process for the synthesis of spherical shaped transition metal hydroxide particles as precursors for cathode materials for lithium ion batteries. The CTFR is composed of two co-axial arranged cylinders which have a small gap and a low working volume between the cylinders. The rotational motion of the inner cylinder induces a turbulent Taylor-vortex flow. Above the critical Taylor number (Ta), a periodic and stable turbulent fluid motion is formed which increases the fluid shear and promotes the agglomeration of precipitates to uniform spherical particles with narrow particle size distribution. The unique operating principle of the CTFR is studied by the co-precipitation of spherical Ni-rich transition metal hydroxides. Here, we investigate the influence of rotation speed, mean residence time, temperature and pH value on the growth behavior of the particles. The morphology, particle size distribution, tap density and chemical composition of the Ni-rich precursors and lithiated cathode materials are investigated. The electrochemical properties of the corresponding cathode materials with their unique particle morphology in dependence of the co-precipitation conditions are evaluated.