Functional surface modifications of a high capacity layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode

Abstract

With an aim to enhance the electrochemical performances of the high capacity layered oxide solid solution Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ cathode, its surface has been modified with 2 wt.% Al₂O₃, 2 wt.% RuO₂, and 1 wt.% Al₂O₃ + 1 wt.% RuO₂. The bare samples and the surface-modified samples have been characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (TEM), charge–discharge measurements in lithium cells, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The surface-modified samples exhibit much improved electrochemical performances, particularly the 1 wt.% Al₂O₃ + 1 wt.% RuO₂ coated sample exhibiting the highest discharge capacity and rate capability. Specifically, the Al₂O₃ + RuO₂ coated sample delivers ∼280 mAh g⁻¹ at C/20 rate with a capacity retention of 94.3% in 30 cycles and ∼ 160 mAh g⁻¹ at 5 C rate. The superior electrochemical performances of the Al₂O₃ + RuO₂ coated sample are attributed to the suppression of SEI layer formation and the facilitation of fast electron transfer and lithium ion diffusion channels as evident from the EIS and XPS data.