New stoichiometric Li-rich layered oxides (xLi(2)MnO(3)center dot(1-x)LiMn0.5Ni0.25Co0.25O2 or Li[LiyMn1-y-2zNizCoz]O-2) were proposed as high-energy density cathode materials for Li-ion batteries. The correlation between chemical composition of the materials and their structural as well as electrochemical performances is discussed. It was found that all synthesized materials crystalize within C2/m space group with existence of superstructure and possess nanometric spherical-shaped morphology. The analysis of the charge/discharge tests shows that Li[Li0.2Mn0.6Ni0.1Co0.1]O-2 electrode delivers nearly 350 mAh . g(-1) for the first discharge process and 250 mAh . g(-1) for following cycles. The investigation of the kinetics of the electrode reactions by means of CV and EIS methods confirmed that Li[Li0.2Mn0.6Ni0.1Co0.1]O-2 exhibits highest lithium diffusion coefficients, whatwith obtained electrochemical cycling tests suggest optimal chemical composition of this material ensuring high energy density along with long-term endurance. (C) The Author(s) 2019. Published by ECS.