Accurate estimation of Li/Ni mixing degree of lithium nickel oxide cathode materials

Abstract

Li/Ni mixing negatively influences the discharge capacity of lithium nickel oxide and high-nickel ternary cathode materials. However, accurately measuring the Li/Ni mixing degree is difficult due to the preferred orientation of lab-based XRD measurements using Bragg–Brentano geometry. Here, we find that employing spherical harmonics in Rietveld refinement to eliminate the preferred orientation can significantly decrease the measurement error of the Li/Ni mixing ratio. The Li/Ni mixing ratio obtained from Rietveld refinement with spherical harmonics shows a strong correlation with discharge capacity, which means the electrochemical capacity of lithium nickel oxide and high-nickel ternary cathode can be estimated by the Li/Ni mixing degree. Our findings provide a simple and accurate method to estimate the Li/Ni mixing degree, which is valuable to the structural analysis and screening of the synthesis conditions of lithium nickel oxide and high-nickel ternary cathode materials.