S-Space College of Engineering/Engineering Practice School (공과대학/대학원) Dept. of Material Science and Engineering (재료공학부) Journal Papers (저널논문_재료공학부)
Phase transitions in the LiNi0.5Mn0.5O2 system with temperature
- Hinuma, Yoyo; Meng, Ying S.; Kang, Kisuk; Ceder, Gerbrand
- Issue Date
- Chemistry of Materials, Vol.19 No.7, pp.1790-1800
- We investigate the phase transformations of layered LiNi0.5Mn0.5O2 at finite temperature with a combined computational and experimental approach. The detailed changes in the ionic configurations with temperature are investigated by Monte Carlo simulations on the basis of a coupled cluster expansion that describes the dependence of the energy on the arrangement of Li+, Ni2+, and Mn4+ in the lithium layer and transition metal layer. First-principles energies in the GGA+U approximation were used to fit the Hamiltonian, as we find that GGA+U better represents magnetic interactions than standard GGA. The simulation results suggest two phase-transition temperatures at approximately 550 and 620 degrees C. Below the first phase-transition temperature, a structure with almost no Li/Ni disorder in the Li layer is energetically favorable. Between the two temperatures, a partially disordered flower structure with about 8-11% Li/Ni disorder is found. Above the second phase transition, a structure that is more disordered but still consistent with a root 3 x root 3 honeycomb model with 8-11% Li/Ni disorder is stable. The results from these simulations are corroborated with DSC, TEM, and XRD measurements on a recently synthesized LiNi0.5Mn0.5O2 with negligible Li/Ni disorder.
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