The role of oxygen vacancies in the performance of LiMn₂O₄ spinel cathodes for lithium-ion batteries

Oxygen vacancies, known to have unavoidable existence in a spinel LiMn₂O₄ material, play an essential role in its physicochemical and electrochemical properties. However, the function mechanism of oxygen vacancies and its influence on electrochemical properties have been poorly understood so far. Hence, we investigate the role of oxygen vacancies in the spinel LiMn₂O₄ material by controlling the annealing atmosphere. The relative amount of oxygen deficiency in the samples prepared under oxygen and air atmospheres is 0.098 and 0.112, respectively. Impressively, the relative oxygen deficiency of the sample increased from 0.112 to 0.196 after re-annealing with nitrogen. However, the conductivity of the material changes from 2.39 to 10.3 mS m⁻¹, but the ion diffusion coefficient is significantly reduced from ∼10⁻¹² to ∼10⁻¹³ cm² s⁻¹, resulting in a decrease in the initial discharge capacity from 136.8 to 85.2 mA h g⁻¹. In addition, we attempted to use the nitrogen-sample annealing again under oxygen, which can significantly reduce the conductivity (from 10.3 to 6.89 mS m⁻¹), and the discharge capacity also increased by 40% of the original. Therefore, the effect of the mechanism of the interaction of the oxygen vacancies on the material electronic conductivity, lithium-ion diffusion coefficient and electrochemical properties provides a basis for the objective treatment of oxygen vacancies in spinel structured materials.