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

Abstract

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 Li1.200Mn0.6065Ni0.1845Mg0.009O2 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.