Co-precipitation preparation of LiNi0.5Mn1.5O4 hollow hierarchical microspheres with superior electrochemical performance for 5 V Li-ion batteries

Abstract

In this work, a NH4HCO3 co-precipitation method was used to prepare the precursor of LiNi0.5Mn1.5O4 (LNMO). An orthogonal experiment method was applied to analyze the effects of synthetic conditions such as concentration and molar ratio of Mn2+ and Ni2+ in initial solution, reaction temperature, concentration of NH4HCO3, addition speed of NH4HCO3 on the molar ratio of Mn/Ni in the sediments, through which the co-precipitation process was also optimized. It was found that both Mn and Ni are not completely precipitated from the NH4HCO3 solution, and the precipitation rate of Ni2+ is much lower than that of Mn2+. Among these synthetic conditions, the molar ratio of Ni/Mn in the mixed metal ion solution has the greatest impact on the molar ratio of Mn/Ni in the precursor. A LNMO spinel with precise stoichiometric Ni/Mn and classic Fd3¯m structure was obtained by using a precursor prepared under the optimal synthesis conditions. Additionally, the prepared LNMO has a spherical hierarchical morphology, composed of submicron primary particles with a chamfered polyhedral structure. This LNMO shows superior electrochemical performance. It delivers a high reversible capacity of ∼110 mAh/g and superior capacity retention of 68.2% after 900 cycles at 1 C. Even at a higher discharge rate of 10 C, the LNMO material still shows a reversible capacity of 84 mAh/g.