Residual Li Reactive Coating with Co3O4for Superior Electrochemical Properties of LiNi0.91Co0.06Mn0.03O2Cathode Material

The necessity of developing Ni-rich layered oxides cathode materials with more than 90% of Ni content is rapidly increasing for satisfying the demand of achieving the high capacity of Li-ion batteries. However, including more Ni contents results in increased formation of undesirable Li residues at the surface as well as deteriorating several types of degradation behaviors during cycling, which are the critical factors of design rules for the cathode material. In this study, the facile synthesis of an electrochemically active material, LiCoO2, is realized at the surface of LiNi0.91Co0.06Mn0.03O2 via the conventional dry coating method utilizing the Li-reactive capability of Co3O4. First-principles calculations are performed to investigate the possible formation of LiCoO2 from the phase diagram. The formation of the electrochemically active coating material considerably reduces the Li residues, increases the capacity, and exhibits a better cycle life with enhanced rate capability. The presence of LiCoO2 phase is verified from transmission electron microscopy (TEM) images, energy-dispersive X-ray spectroscopy (EDS) elemental mapping, and electron energy loss spectroscopy (EELS) spectra. Superior performance of Co3O4 is further demonstrated by comparing the results with those from conventional coating materials of Al2O3, TiO2, V2O3, and ZnO, whose electrochemical performance is worse in all of aspects.