Do Increased Ni Contents in LiNi<i>_<i>x</i></i>Mn<i>_<i>y</i></i>Co<i>_<i>z</i></i>O₂ (NMC) Electrodes Decrease Structural and Thermal Stability of Li Ion Batteries? A Thorough Look by Consideration of the Li⁺ Extraction Ratio

Abstract

Apparently, high nickel content in LiNixMnyCozO2 (NMC) is beneficial in terms of specific capacity but detrimental in terms of structural and thermal stabilities. Such conclusions are conventionally drawn from experiments where NMCs have been charged to an equal cutoff potential, which suggests an unequal Li+ extraction ratio. Therefore, the validity of those conclusions must be questioned, because the latter dictates structural stability. This study shows that the order of structural stability significantly differs when Li+ extraction ratio rather than charge cutoff potential is considered while the thermal stability indeed correlates with the nickel content, and is thus rather unaffected by the Li+ extraction ratio.