The Nature of Oxygen Vacancy and Spinel Phase Integration on Both Anionic and Cationic Redox in Li-rich Cathode Material
Tuning the anionic redox chemistry (O2-→O2n-) activity and reversibility by the crystal and/or electronic modulation is essential for Li-rich oxides cathode materials. Herein, we report a facile strategy to improve the activity and reversibility of both anionic and cationic redox by integrating oxygen vacancies and spinel phase. The initial specific capacity (216.1 mAh g-1 v.s 316.3 mAh g-1), Coulomb efficiency (80% v.s 94.8%), long-term cycling stability (1000 cycles at 5C) and voltage decay have all been greatly improved due to the largely suppressed irreversible oxygen release. The underlying modulation mechanism has been unraveled. Firstly, the introduction of oxygen vacancies decreases the covalency of TM-O and the density of the state of O 2p band, which mitigates the irreversible oxygen release during oxygen redox. Secondly, the spinel phase integration induced by oxygen vacancies not only improves the Li-ion conductivity and the rate capability due to its 3D Li+ channel and the expanded Li layer but also enhances the structure stability. Thirdly, the first-principle calculations indicate that the increase of delocalized electrons around transition metal also intensifies the MnO6 octahedral distortion and the inactive Mn-ions are partially activated during the first cycle and participate in the charge compensation. This study sheds some new light into designing the high-performance Li-rich layered oxide cathode materials by regulating the anionic and cationic redox with the incorporation of oxygen vacancies and spinel phase.