Data-driven unlocking volume conservation in single-crystal Ni-rich layered oxides

Abstract

Our study redefines anisotropic lattice variation through volume conservation (VC) in single-crystal (SC) Ni-rich layered oxides to facilitate long-term cycling stability. Data-driven analysis of the correlation heatmap of the five covariate variables and cycling retention enables precise cut-off voltage modulation for high-energy-density Ni-rich cathodes. We establish the anisotropic variation between a and c lattice constants as critical, leading to interfacial microcracks formation in degrading cycling retention. A balanced use of this variation, verified through computational models, Li1−x[Ni10/12Co1/12Mn1/12]O2 (NCM) and Li1−x[Ni10/12Co1/12Ti1/12]O2 (NCT), creates a volumetric stress free state at the inflection point. Unfortunately, two-scale challenges, namely macroscopic and local structure lattice misfits, which trigger intragranular microcracks, remain unresolved. Formation energy diagrams show biphasic reaction causing macroscopic lattice misfit based on the lattice direction occurring below x = 0.75 in both cathode models. Its effect can be mitigated by doping Ti into the Ni-rich material. Atomistic misfits of in-plane and out-of-plane directions are observed. Furthermore, MO2 and LiO2 slabs anisotropically vary in the complexes for NCM and NCT. Moreover, Ti-doped layered oxide clearly reduces local structural misfits and anisotropy. The proposed VC holds potential as a universal parameter for durable Ni-rich layered oxide fabrication for lithium-ion batteries.