Effect of impeller type on preparing spherical and dense Ni1−x−yCoxMny(OH)2 precursor via continuous co-precipitation in pilot scale: A case of Ni0·6Co0·2Mn0·2(OH)2

Abstract

The spherical and dense Li[Ni1−x−yCoxMny]O2 particles work excellently as the cathode material for Li-ion secondary batteries. The key to their preparation lies in synthesizing the spherical and dense Ni1−x−yCoxMny(OH)2 precursor via co-precipitation in a mechanically stirred tank reactor. The effect of impeller type on the precursor property was investigated by taking Ni0·6Co0·2Mn0·2(OH)2 as an example. Four different types of impellers were tested and compared, which were the propeller turbine (PT), pitched blade turbine (PBT), flat blade turbine (FBT) and Rushton turbine (RT). Only with the PT could the spherical and dense precursor be prepared, whose tap density exceeded 2.0 g/mL. As expected, the LiNi0·6Co0·2Mn0·2O2 obtained in this case exhibited the best electrochemical property, which delivered a discharge capacity of 182.3 mAh/g at 0.2C rate between 2.7 and 4.3 V. The capacity retention was 97.9% after 200 cycles at 2C rate. The different properties of the precursors resulted from the different flow fields in the reactor. The single-loop flow field excited by the PT caused the nuclei to grow into flat and thick flaky primary particles, which then could assemble tightly to form the dense secondary particles. Additionally, the circulation of secondary particles in the whole reactor further enabled them to grow, consolidate, become spherical and smooth by adsorbing the free nuclei and primary particles. On the other hand, the double-loop flow field generated by the FBT or RT caused the primary particles to be thin and curve, which could only pile up loosely to form the secondary particles. What's worse, the secondary particles were entrapped in the lower loop, having little chance to grow and consolidate by adsorbing the nuclei and primary particles that were mainly formed in the upper loop.