LAUSR

Two major strategies are currently pursued to improve the energy density of lithium-ion batteries using LiNixCoyMnzO2 (NCM) cathode materials. One is to increase the fraction of redox active Ni (≥80%), which allows larger amounts of Li to be extracted at a given cutoff voltage (Umax). The other is to increase Umax, in particular for medium-Ni content NCM materials. However, the accompanying lattice changes ultimately lead to capacity fading in both cases. Here the structural changes occurring in Li1.02NixCoyMnzO2 (with x = 1/3, 0.5, 0.6, 0.7, 0.8 and 0.85) during cycling operation in the voltage range between 3.0 and 4.6 V vs Li are quantified by means of operando X-ray diffraction combined with detailed Rietveld analysis. All samples show a large decrease in unit cell volume upon charging, ranging from 2.4% for NCM111 (33% Ni) to 8.0% for NCM851005 (85% Ni). To make a fair comparison of the structural stability of the different NCM materials, energy densities as a function of Umax are estimated and corre...