Promoting the Electrochemical Performance of Li-Rich Layered Li1.2(Ni1/6Co1/6Mn4/6)0.8O2 with the In Situ Transformed Allogenic Spinel Phase

To promote the electrochemical performance of a Li-rich layered cathode material Li1.2(Ni1/6Co1/6Mn4/6)0.8O2, the allogenic spinel@Li-rich (1 – y)[Li1.2(Ni1/6Co1/6Mn4/6)0.8O2]core·y[Lix(Ni1/6Co1/6Mn4/6)2O4]shell composite is developed by the in situ phase transformation method. The allogenic structure of the composite was characterized by X-ray powder diffraction, Raman spectroscopy, high-resolution transmission electron microscopy, and selected area electron diffraction. The obtained allogenic electrodes exhibit better initial Coulombic efficiency, higher reversible capacity, and good capacity retention than the pristine Li-rich layered oxide. Electrochemical tests show that the electrochemical properties of the cathode material are excellent when the ratio of the spinel component is 3%. After 120 cycles at a rate of 0.2 C, excellent reversible capacity (246 mA h g–1) and good capacity retention (94%) were obtained. Moreover, the rate performance of the allogenic spinel@Li-rich composites has also been greatly improved. In particular, the sample with 3% spinel composition maintained a high discharge capacity of 120 mA h g–1 even at a high power rate of 10 C. The better electrochemical performance of the allogenic composites is owing to the three-dimensional paths of the in situ transformed spinel phase, which offers the possibility of accelerating the Li+ diffusion and decreasing the charge-transfer resistances illustrated by galvanostatic intermittent titration technique and electrochemical impedance spectroscopy in this work.