Interatomic Potential of Li–Mn–O and Molecular Dynamics Simulations on Li Diffusion in Spinel Li_1–xMn₂O₄

Abstract

An interatomic potential of the Li−Mn−O ternary system has been developed on the basis of the second-nearest-neighbor modified embedded-atom method (2NN MEAM) formalism combined with a charge equilibration (Qeq) concept. The potential reproduces fundamental physical properties (structural, elastic, thermodynamic and migration properties) of various compounds well, including lithium oxides, manganese oxides, and lithium manganese ternary oxides. Through molecular dynamics (MD) simulations using the developed potential, lithium diffusion properties (activation energy for lithium migration and diffusion coefficient) in spinel Li 1−x Mn 2 O 4 are also reproduced in good agreement with experiments. We have found that the effect of the lithium vacancy concentration is marginal on the activation energy for lithium diffusion in the Li 1−x Mn 2 O 4 cathode, but it is significant in the lithium diffusion coefficient. The potential can be further utilized for atomistic simulations of various materials phenomena (phase transitions, defect formation, lithiation/delithiation, etc.) in LIB cathode materials.

Beyond Coherent Oxide Heterostructures: Atomic‐Scale Structure of Misfit Dislocations

“…Furthermore, noticeable charge transfer and intermixing at oxide heterointerfaces result in the occurrence of a variety of point defects [129,130] in conjunction with structural defects, [13,14,101] which further convolutes the interface structure. Development of charge transfer ionic potentials for oxides, [131][132][133] reactive force-fields, [134] bond-valence interatomic potentials, [135,136] and second-nearestneighbor modified embedded-atom method [137] are prospective approaches that could address the complex charge transfer and related atomic-scale processes at semi-coherent oxide heterointerfaces, further assisting in comprehending the actual atomic and chemical structure of the interface. As recently demonstrated by Uberuaga and co-workers, [138][139][140] albeit for a heterointerface between metal and metal oxide, one promising strategy to investigate the structure of misfit dislocations at oxide heterostructures is to strain the film and the substrate so as to keep the supercell size tractable, while still incorporating the full misfit dislocation structure in the DFT supercell.…”

Tracer Diffusion Coefficients of Li Ions in LixMn2O4 Thin Films Observed by Isotope Exchange Secondary Ion Mass Spectrometry

“…These values of D* agree well with the results of recent MD simulations, which suggest that D* ranges from 10 −15 to 10 −12 cm 2 s −1 at 1.0 ≤ x ≤ 0.5. 17 Chemical Diffusion Coefficient of the Li x Mn 2 O 4 Film. The chemical diffusion coefficient (D ̃) of the Li x Mn 2 O 4 thin film was determined by PITT.…”

“…The D* determined at each temperature and the corresponding activation energies are summarized in Table 3 Whereas the value of D* varies by 4 orders of magnitude depending on x, the activation energy is almost constant, consistent with the vacancy diffusion mechanism. The relationship between Li composition and activation energy in Li x Mn 2 O 4 has been investigated by theoretical calculations, including DFT, 2,14 MD, 17 and kinetic Monte Carlo simulations. 18 The DFT calculations by Xu and Meng 2 predicted that E a = 0.8 eV when the numbers of Mn 4+ ions and Mn 3+ ions are equal, whereas 0.2 ≤ E a ≤ 0.4 in the case of Mn 4+rich rings.…”

“…Other self-diffusion measurements have been reported using 2D exchange nuclear magnetic resonance, 11 quasielastic neutron scattering, 12 and muon spin relaxation. 13 Computational studies have predicted many important physical properties relating the ionic diffusion, including activation barriers for site hopping, 2,3,14 diffusion pathways, 15 vacancy formation energies, 14,16 tracer diffusion coefficients from the mean square displacement, 17 and the thermodynamic factor from the fluctuation of the number of particles. 18 In particular, the tracer diffusion coefficient is directly related to the mean square displacements obtained in molecular dynamics (MD) simulations, 19−21 making the D* an ideal parameter for comparing with calculations.…”

Implementation of the coupled two‐mode phase field crystal model with Cahn–Hilliard for phase‐separation in battery electrode particles

“…This intercalation process is highly complex and can structurally transform the electrode material, 5 resulting in defect formation, 6 lattice expansion, 7 grain boundary migration 8 and fracture 9 . One can potentially use molecular dynamics (MD) 10 to model the electrode and simulate the diffusion of Li‐ions or use density function theory (DFT) 11 to study local preferential sites of Li‐atoms. Although MD and DFT can capture certain effects in great detail, both cannot completely model the phase‐separation process in a electrode particle.…”