Promoting reversible reaction of oxygen anions in cobalt-free lithium-rich layered oxides to improve their electrochemical performance

Highlights: • The influence of magnesium doping on the structure of lithium-rich layered oxides were studied. • The electrochemical test with gradually opening the voltage window shows that the high-capacity voltage range is consistent with the oxygen anion reaction. • The XPS curve fitting before and after charging quantitatively proves that more oxygen anions participate in the redox reaction. Lithium-rich layered oxides, which have a unique anion redox result in outstanding specific capacity, are perceived as the most valuable cathode materials for Li-ion batteries in the next generation. Here, the cobalt-free Li_1.200Mn_0.6065Ni_0.1845Mg_0.009O₂ has a high first cycle discharge capacity of 293.6 mA h g⁻¹, which is 33.8 mA h g⁻¹ higher than the pristine sample. This biased Mg²⁺ doping mitigates voltage decay by stabilizing the crystal lattice, and reduces the diffusion length of lithium ions and increases the electronic conductivity to improve the rate performance of lithium-rich layered oxides. In addition, using the method of gradually opening the voltage window and comparing before and after charging of XPS, the influence of Mg²⁺ on the cation/anion redox reaction was systematically studied. XPS shows that a small amount of Mg²⁺ increases the degree of oxygen anion reaction from 27.4% to 32.7%, giving a new explanation for the increase in capacity.