Thermal stability of Li1−ΔM0.5Mn1.5O4 (M = Fe, Co, Ni) cathodes in different states of delithiation Δ

Abstract

The thermal stability of sol–gel synthesized Li_1−ΔM_0.5Mn_1.5O₄ (M = Fe, Co, Ni) electrodes with different degrees of delithiation were analyzed with TG-DSC and in situ synchrotron diffraction under an Ar atmosphere and compared. The onset temperatures for structural degradation are dependent on the amount of lithium 1−Δ in the sample. The Li_1−ΔFe_0.5Mn_1.5O₄ electrode exhibited the highest thermal stability among the three materials with different dopant M. The reason for this difference is discussed with respect to the oxidation states of the transition metals. The mechanism of degradation for M = Fe, Co was found to be through gas evolution, mainly CO₂ and O₂, and the carbon conductive additive was found to play a major role in the thermal degradation process. For delithiated Li_1−ΔNi_0.5Mn_1.5O₄ the temperature induced degradation includes phase separation into Mn₃O₄ with spinel structure and Li_xNi_1−xO with rock-salt structure together with oxygen and carbon dioxide release.