Hybridizing Li@Mn6 and Sb@Ni6 superstructure units to tune the electrochemical performance of Li-rich layered oxides

Abstract

Abstract Li@Mn6 superstructure units from the model compound Li2MnO3, i.e., six MnO6 octahedra linked like a ring (Mn6) with a central LiO6 octahedron, could provide extra capacity when composited with other transition metal octahedra (TMO6) structure units in Li and Mn-rich TM layered oxides, xLi2MnO3·(1-x)LiTMO2, one of the most promising high-energy-density cathodes. Nevertheless, it suffers serious capacity and voltage fade due to the unstable local oxygen environment in the basic superstructure unit Li@Mn6. Herein, a new Li-rich layered oxide cathode, Li(Li1/6Mn1/3Ni1/3Sb1/6)O2, was designed and synthesized by compositing Li@Mn6 with a similar superstructure unit Sb@Ni6. Complementary structural/chemical analysis combining with the electronic structure calculations reveal that, the uniform mixing of these two superstructure units at the atomic level has been firstly accomplished in TM layers, which introduces a large amount of boundaries between Li@Mn6 and Sb@Ni6 super-units, thus greatly enriching the local oxygen environments, and reducing the energy barrier of Li+ diffusion. Therefore, the better electrochemical performance, especially the superb cycling stability with the larger capacity (double that of Li(Ni2/3Sb1/3)O2) is implemented. It provides another route to design new Li-rich layered oxides with the better cycling stability by modifying local oxygen environments.