Layered Ni-rich LiNi0.6Co0.2Mn0.2O2 (LNCMO) materials are prepared by calcining the mixture of Ni0.6Co0.2Mn0.2(OH)2 precursor (co-precipitation method) and Li salts (Li2CO3). Two different caicination atmosphere (air and oxygen) are adopted to obtain final two samples of LNCMO-A (air) and LNCMO-O (oxygen) to individually investigate the influence of oxygen instead of air atmosphere on the structure and electrochemical behavior of the LNCMO materials. Both two samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical charge/discharge tests including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). XRD and SEM results show the LNCMO-O sample possesses relatively smaller Li+/Ni2+ cation mixing, better layer-structure ordering and smaller primary particle size. The electrochemical charge/discharge test results show the LNCMO-O sample exhibits superior discharge capacity (184.6mAhg−1 at 0.1C), higher cycling retention (91.4% after 100 cycles at 0.5C) and promoted rate performance. Further XPS, CV and EIS analyses on the promotion mechanism demonstrate that the oxygen-atmosphere calcination is important and beneficial to improve the electrochemical performance for Ni-rich LiNi0.6Co0.2Mn0.2O2 material.