Defect-Engineered β-MnO(2−δ) Precursors Control the Structure–Property Relationships in High-Voltage Spinel LiMn(1.5)Ni(0.5)O(4−δ)

[Image: see text] This study examines the role of defects in structure–property relationships in spinel LiMn(1.5)Ni(0.5)O(4) (LMNO) cathode materials, especially in terms of Mn(3+) 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 P4(3)32-ordered and highly Fd3̅m-disordered) have been prepared from two different β-MnO(2−δ) precursors obtained from an argon-rich atmosphere (β-MnO(2−δ) (Ar)) and a hydrogen-rich atmosphere [β-MnO(2−δ) (H(2))]. The LMNO samples and their corresponding β-MnO(2−δ) 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(2−δ) (H(2)) exhibits higher defects (oxygen vacancy content) than the one from the β-MnO(2−δ) (Ar). For the first time, defective β-MnO(2−δ) has been adopted as precursors for LMNO cathode materials with controlled oxygen vacancy, disordered phase, Mn(3+) 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(3+) 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(2−δ) as viable precursors for manipulating the structure–property relationships in LMNO spinel materials for potential development of high-performance high-voltage lithium-ion batteries.