Revealing the Role of Ammonia in the Rapid Crystallization Kinetics for Ni-Rich Hydroxide Precursors via Microreactors

The morphology and microstructure of precursors are the key to the preparation of high-quality NCM cathodes due to their inheritance relationship. However, a large amount of sulfate exists in the precursors, to the detriment of the electrochemical performance of the Ni-rich cathode materials. Herein, an effective method for sulfate reduction was proposed for the synthesis of Ni0.90Co0.05Mn0.05(OH)2 precursor by adding 0.24 M ammonia in the microreactor. The less sulfate in the Ni(OH)2 with ammonia system is attributed to the higher formation energy of sulfate adsorption (ENi(OH)2-am-SO42– = 7.483 eV vs ENi(OH)2-SO42– = 3.451 eV). The results demonstrated that ammonia can promote the growth of primary particles (81.5 nm) and reduce the content of impurity sulfate from 0.80 to 0.28% in the precursors. Moreover, the prepared cathode materials exhibit a high specific capacity of 190.4 mAh g–1 at 1C and superior Li+ diffusion coefficients. This study sheds light on the role of ammonia in rapid coprecipitation and provides guidance for the rapid synthesis process of Ni-rich cathodes.