Truncated Octahedral High-Voltage Spinel LiNi_0.5Mn_1.5O₄Cathode Materials for Lithium Ion Batteries: Positive Influences of Ni/Mn Disordering and Oxygen Vacancies

Micron-sized truncated octahedral LiNi 0.5 Mn 1.5 O 4 (LNMO) samples with different degrees of Ni/Mn disordering have been obtained by controlling the synthesis conditions, such as calcination atmosphere (O 2 and air), cooling rate or additional annealing step. The influences of Ni/Mn disordering on the physical properties and electrochemical performance of the truncated octahedral LNMO samples have been systematically investigated. The analyses of thermogravimetry, X-ray photoelectron spectroscopy, X-ray diffraction, powder neutron diffraction, Raman spectroscopy and X-ray absorption spectroscopy reveal that the occurrence and degree of Ni/Mn disordering are closely related with the formation of oxygen vacancies and presence of Mn 3+ . Slow cooling rate and post-annealing can result in low degrees of Ni/Mn disordering and oxygen vacancies. Electrochemical measurements show that Ni/Mn disordering and oxygen vacancies have no obvious effect on the rate capability since all LNMO samples share a truncated octahedral morphology with the exposed {100} surfaces. However, they play significant roles in improving long-term cycling stability, especially at the elevated temperature of 60°C. This work suggests that the electrochemical performance of LNMO with optimized truncated morphology can be further enhanced through tuning the degrees of Ni/Mn disordering and oxygen vacancies.