Structural and mechanistic revelations on high capacity cation-disordered Li-rich oxides for rechargeable Li-ion batteries

High capacity cation-disordered Li-rich oxides not only enlarge the chemical design space of cathode materials, but also play an important role in promoting the development of high energy density Li-ion batteries. However, there are still some issues, such as capacity degradation, that impede their practical applications. In-depth understanding of the structure and mechanisms in cation-disordered Li-rich oxides is favorable for their further performance optimization. Herein, taking the new designed high capacity (~ 280 mA h/g) disordered Li1.2Ti0.35Ni0.35Nb0.1O1.8F0.2 as a model compound, we meticulously study its structure evolution and electrochemical reaction mechanisms upon cycling by combination of first principles calculation, synchrony X-ray diffraction (SXRD), X-ray pair distribution function (XPDF), X-ray absorption spectroscopy (XAS), in situ XRD, and Neutron powder diffraction (NPD) et al. The excellent structure stability and robust anions framework of cation-disordered Li-rich oxides are experimentally demonstrated. Meanwhile, the high capacity mechanisms rely on the simultaneous cations and anions redox reactions and the capacity degradation mechanism induced by oxygen loss upon cycling are also proposed. Based on these revelations, the optimization strategy and potential applications of cation-disordered Li-rich oxides are further proposed.