First-Principles studies of Mechanical moduli and Thermodynamic Trends of R3̄m LiCoO₂ under Pressure
Rhombohedral LiCoO₂ (R3̄m) remains a benchmark layered cathode, yet its long-term cycling life is fundamentally restricted by chemo-mechanical degradation and thermal stresses. To evaluate these structural limits without electronic bias, this study provides a comprehensive first-principles evaluation of its complete elastic tensor and thermodynamic stability. Using Density Functional Theory (DFT) within the Quantum ESPRESSO package, calculations were performed using both PBE-GGA and Hubbard-corrected GGA+U frameworks (Ueff = 5.6 eV on Co 3d states) to ensure structural precision. Zero-pressure variable-cell optimizations yield stable conventional hexagonal volumes of volumes of 97.37(Å)3 for PBE and 97.80(Å)3 for PBE+U. A Birch–Murnaghan fit yields a bulk modulus of 150 -165 GPa with B’ ≈ 4.0 – 4.5. Aggregated stress–strain averages demonstrate a stiff, elastically anisotropic framework defined by a Voigt bulk modulus BH = 142.97 GPa, shear modulus GH = 44.98 GPa, and Young’s modulus (E) of 122.12 GPa. The calculated Pugh ductility index BH/GH = 3.18, and ν = 0.358) confirm high shear ductility alongside stiff intra-planar structural scaling. Utilizing these elastic parameters, the quasi-harmonic Debye model successfully projects a Debye temperature of 680.93 K, mapping out definitive baselines for temperature-dependent vibrational internal energy, heat capacity, and entropy. Ultimately, these pressure-enthalpy configurations and thermo-mechanical indices provide essential physical parameters required to simulate thermal management systems and design failure-resistant layered battery architectures.
Keywords: Density Functional Theory; LiCoO2 cathode; Quantum ESPRESSO; Thermodynamic trends; Hubbard U correction; Lithium-ion batteries.
