Coprecipitation-Gel Synthesis and Degradation Mechanism of Octahedral Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ as High-Performance Cathode Materials for Lithium-Ion Batteries

Abstract

The octahedral core-shell Li-rich layered cathode material of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ can be synthesized via an ingenious coprecipitation-gel method without subsequent annealing. On the basis of detailed X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and electron energy loss spectroscopy characterizations, it is suggested that the as-prepared material consists of an octahedral morphology and a new type of core-shell structure with a spinel-layered heterostructure inside, which is the result of overgrowth of the spinel structure with {111} facets on {001} facets of the layered structure in a single orientation. The surface area of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ crystals where the spinel phase is located possesses sufficient Li and O vacancies, resulting in the reinsertion of Li into position after the first charge and maintenance of the interface stability via the replenishment of oxygen from the bulk region. Compared to that synthesized by the traditional coprecipitation method, the Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ synthesized by the coprecipitation-gel method exhibits higher discharge capacity and Coulombic efficiency, from 73.9% and 251.5 mAh g^-1 for the spherical polycrystal material to 86.2% and 291.4 mAh g^-1.