Atomistic Simulations of the Defect Chemistry and Self-Diffusion of Li-ion in LiAlO2

Abstract

Lithium aluminate, LiAlO 2 , is a material that is presently being considered as a tritium breeder material in fusion reactors and coating material in Li-conducting electrodes. Here, we employ atomistic simulation techniques to show that the lowest energy intrinsic defect process is the cation anti-site defect (1.10 eV per defect). This was followed closely by the lithium Frenkel defect (1.44 eV per defect), which ensures a high lithium content in the material and inclination for lithium diffusion from formation of vacancies. Li self-diffusion is three dimensional and exhibits a curved pathway with a migration barrier of 0.53 eV. We considered a variety of dopants with charges +1 (Na, K and Rb), +2 (Mg, Ca, Sr and Ba), +3 (Ga, Fe, Co, Ni, Mn, Sc, Y and La) and +4 (Si, Ge, Ti, Zr and Ce) on the Al site. Dopants Mg 2+ and Ge 4+ can facilitate the formation of Li interstitials and Li vacancies, respectively. Trivalent dopants Fe 3+ , Ni 3+ and Mn 3+ prefer to occupy the Al site with exoergic solution energies meaning that they are candidate dopants for the synthesis of Li (Al, M) O 2 (M = Fe, Ni and Mn) compounds.Energies 2019, 12, 2895 2 of 10 Computational MethodsThe present computational study was based on classical pair-wise potential calculations to describe LiAlO 2 via the General Utility Lattice Program (GULP) code [23,24]. In the present approach, the total energy (lattice energy) is determined by long range (i.e., Coulombic) and short range [i.e., electron-electron repulsive and attractive intermolecular forces (van der Waals forces)]. The latter were modelled using Buckingham potentials (refer to the supplementary information). The van der Waals forces arising from the spontaneous formation of instantaneous dipoles are very important as the formation energy results are sensitive to those forces. The present modelling approach takes into the account of Van der Waals forces as a function of the interatomic distance (r) [23,24]. Two-body Buckingham potential mentioned in the supplementary information consists of two parts. The first part of the equation represents the Pauli repulsion (electron-electron) and the second part denotes the van der Waals interaction. Ionic positions and lattice parameters were relaxed using the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm [24]. Convergence criteria dictated that in relaxed configurations, forces on each atom was <0.001 eV/Å. To introduce point defects in the lattice we used the Mott-Littleton methodology [25] similarly to recent work [26][27][28]. It is established that although the present methodology may overestimate the defect formation enthalpies at the dilute limit, the trends will be unchanged [29]. In a thermodynamic perspective defect parameters can be described by comparing the real (i.e., defective) crystal to an isobaric or isochoric ideal (i.e., non-defective) crystal. Defect formation parameters can be interconnected through thermodynamic relations [30,31], with the present atomistic simulations corresponding to the isobaric parameters for the mig...

Engineering Compounds for the Recovery of Critical Elements from Slags: Melt Characteristics of Li5AlO4, LiAlO2, and LiAl5O8

“…In the present study, charged particles interact via the long-range Coulomb potential supplemented by the short-range Buckingham potential (eq ) V i j = 1 4 π ε 0 q i q j r i j + [ A i j exp true( − r i j ρ i j true) − C i j r i j 6 ] here i and j denote an interacting pair of two ions among lithium, aluminum, and oxygen separated by a distance r ij , ε 0 stands for the dielectric constant. The Buckingham potential parameters are taken from Kuganathan et al and are listed in Table . Oxygen atoms’ polarizability is included using the core–shell model, in which a harmonic spring connects the positive core (charge +0.8) with the negative shell (charge −2.8).…”

“…MD studies found that networks present in TiO 2 –FeO–Na 2 O melt significantly impact viscosity and solidification processes in slags . MD simulations of lithium aluminum oxides have been used to study the defect chemistry and sophisticated potentials could be developed due to the simple crystal structures and strong ionicity among ternary lithium-containing oxides. , However, less attention was paid to transport properties, such as viscosity. Here, we study individual ion diffusivity and viscosity of Li–Al–O-compounds with different Li/Al ratios according to their thermodynamically predicted phase diagram.…”

Mg6MnO8 as a Magnesium-Ion Battery Material: Defects, Dopants and Mg-Ion Transport

“…The current simulation can provide useful information about migration paths and their activation energies. In a previous work, we used this methodology to identify diffusion paths and activation energies for a variety of Li-and Na-ion battery materials [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. Using classical potential simulation, the Li-ion migration path and activation energy were calculated in LiFePO 4 by Fisher et al [48].…”

Defects, Diffusion, and Dopants in Li2Ti6O13: Atomistic Simulation Study

“…The present study aims to examine the crystallographic defects in Li-ion diffusion paths together with activation energies and the impact of dopants in these materials, using force field methods, as reported in previous studies [22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44] for various battery materials. DFT method was applied to study the electronic structure of promising dopants substituted at the Ti site in Li 2 Ti 6 O 13 .…”