Defect-Engineered β-MnO Precursors Control the Structure-Property Relationships in High-Voltage Spinel LiMnNiO.

This study examines the role of defects in structure-property relationships in spinel LiMnNiO (LMNO) cathode materials, especially in terms of Mn content, degree of disorder, and impurity phase, without the use of the traditional high-temperature annealing (≥700 °C used for making disordered LMNO). Two different phases of LMNO (i.e., highly 432-ordered and highly 3̅-disordered) have been prepared from two different β-MnO precursors obtained from an argon-rich atmosphere (β-MnO (Ar)) and a hydrogen-rich atmosphere [β-MnO (H)]. The LMNO samples and their corresponding β-MnO precursors are thoroughly characterized using different techniques including high-resolution transmission electron microscopy, field-emission scanning electron microscopy, Raman spectroscopy, powder neutron diffraction, X-ray photoelectron spectroscopy, synchrotron X-ray diffraction, X-ray absorption near-edge spectroscopy, and electrochemistry. LMNO from β-MnO (H) exhibits higher defects (oxygen vacancy content) than the one from the β-MnO (Ar). For the first time, defective β-MnO has been adopted as precursors for LMNO cathode materials with controlled oxygen vacancy, disordered phase, Mn content, and impurity contents without the need for conventional methods of doping with metal ions, high synthetic temperature, use of organic compounds, postannealing, microwave, or modification of the temperature-cooling profiles. The results show that the oxygen vacancy changes concurrently with the degree of disorder and Mn content, and the best electrochemical performance is only obtained at 850 °C for LMNO-(Ar). The findings in this work present unique opportunities that allow the use of β-MnO as viable precursors for manipulating the structure-property relationships in LMNO spinel materials for potential development of high-performance high-voltage lithium-ion batteries.