Understanding the Effects of Cationic and Anionic Substitutions in Spinel Cathodes of Lithium-Ion Batteries

With an aim to develop a better understanding of the factors influencing the electrochemical performance of doped spinel cathodes, a series of Li1.1Mn1.8M0.1O4-δFδ and Li1+xMn2-2xMxO4-δFδ (M = Al, Ti, Cr, Fe, Co, and Ni) samples have been investigated systematically. The samples have been made by solid-state reaction followed by a low-temperature fluorination reaction and characterized by X-ray diffraction (XRD), redox titration, scanning electron microscopy (SEM), electrochemical cycling, and differential capacity measurements. Generally, LiF impurity phase begins to form at or above a fluorine content of ∼0.2. The capacity fade decreases with decreasing oxidation state of the dopant Mn+, increasing electronegativity of the dopant M, decreasing bond dissociation energy of M-O, and decreasing Mn dissolution; the capacity fade increases drastically below a Mn valence of ∼3.6+. Additionally, the charge-discharge kinetics worsen with increasing fluorine content.