Promoting the Electrochemical Performance of Li-Rich Layered Li<sub>1.2</sub>(Ni<sub>1/6</sub>Co<sub>1/6</sub>Mn<sub>4/6</sub>)<sub>0.8</sub>O<sub>2</sub> with the In Situ Transformed Allogenic Spinel Phase
Jianyu He, Hongyun Ma, Hongzhou Zhang, Dawei Song, Xixi Shi, Qibo Deng, Chunliang Li, Lifang Jiao, Lianqi Zhang
Abstract
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.