Superior electrochemical properties of Li[Li0.2Ni0.18Mn0.6Mg0.02]O2 cathode material with hierarchical micro−nanostructure for lithium ion batteries

Abstract

Li[Li0.2Ni0.18Mn0.6Mg0.02]O2 electrode material with hierarchical micro‒nanostructure is prepared via a porous polypropylene membrane as the hard template. The X‒ray diffraction (XRD) spectrum shows that the doping of Mg2+ does not affect the crystal structure of the sample, and there is no diffraction peaks related to any impurities. The scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) mapping deliver that the sample composed of nanoparticles has a porous sheet‒like structure, and the elements (i.e., Mn, Ni, Mg and O) are uniformly distributed in the viewed regions. The X‒ray photoelectron spectroscopy (XPS) shows that the valence states of the Mg, Mn and Ni elements in the sample are +2, +4 and + 2, respectively, and a small amount of Mn3+ and Ni3+ is also present for the valence degeneracy effect. Electrochemical properties show that the Mg2+‒doped electrode material compared with pristine sample has lower initial irreversible capacity loss, higher charge/discharge specific capacity, better rate performance and capacity retention. The outstanding electrochemical performance of the Li[Li0.2Ni0.18Mn0.6Mg0.02]O2 could be attributed to the enhanced structure stability, improved the purity for the decrease of valence degeneracy, reduced the charge transfer resistance and improved the diffusion coefficient of lithium ions during prolonged cycling.