Enthalpies of formation of layered LiNixMnxCo1–2xO2 (0 ≤ x ≤ 0.5) compounds as lithium ion battery cathode materials

Abstract

AbstractLayer-structured mixed transition metal oxides with the formula LiNixMnxCo1–2xO2 (0 ≤ x ≤ 0.5) are considered as important cathode materials for lithium-ion batteries. In an effort to evaluate the relative thermodynamic stabilities of individual compositions in this series, the enthalpies of formation of selected stoichiometries are determined by high temperature oxide melt drop solution calorimetry and verified by ab-initio calculations. The measured and calculated data are in good agreement with each other, and the results show that LiCoO2–LiNi0.5Mn0.5O2 solid solution approaches ideal behavior. By increasing x, i. e. by equimolar substitution of Mn4+ and Ni2+ for Co3+, the enthalpy of formation of LiNixMnxCo1–2xO2 from the elements becomes more exothermic, implying increased energetic stability. This conclusion is in agreement with the literature results showing improved structural stability and cycling performance of Ni/Mn-rich LiNixMnxCo1–2xO2 compounds cycled to higher cut-off voltages.