First-principles estimation of partition functions representing disordered lattices such as the cubic phases of Li2OHCl and Li2OHBr

Abstract

In order to develop computational methods that can simulate thermodynamic properties of disordered materials at a first principles level, we investigate the use of a random set of configurations to evaluate the canonical partition function of lattice-based disordered systems. Testing the sampling method on the one and two dimensional Ising models indicates that for the ordered system at low temperature, convergence is achieved when the number of samples S is comparable or larger than the number of configurations Ω, while for the partially disordered system at high temperature, convergence is achieved for smaller sample sizes as low as S ≈ Ω/100 or S ≈ Ω/1000. The sampling method is combined with first principles calculations to examine the ordered ↔ disordered phase transition for the Li ion electrolyte materials Li2OHCl and Li2OHBr. Static lattice internal energies and harmonic phonon free energies were incorporated into the evaluation of the partition function. The evaluation of the partition function depends on the value of Ω corresponding to the number of metastable states of the system. Accordingly, we developed a method of approximating Ω using the properties of the sampled configurations. The results of the calculations are consistent with the experimental observation that the transition temperature for the orthorhombic ↔ cubic phase transition is higher for Li2OHCl than for Li2OHBr. We expect the sampling method to be generally useful for investigating the thermodynamic properties of other disordered lattice systems. We also investigate a "disordered subspace function" which is shown to satisfy inequality relationships with respect to the Helmholtz free energy.

Theoretical insights into interfacial stability and ionic transport of Li2OHBr solid electrolyte for all-solid-state batteries

“…1(a) . Table 1 lists the optimized lattice parameters of Li 2 OHBr obtained by DFT calculations, together with the data from Howard et al 19 The lattice parameters are a = 8.015 Å, b = 8.152 Å, and c = 7.944 Å, which are agree with the experiment data (within 2% error). To obtain the electronic properties of Li 2 OHBr, the electronic band structure of Li 2 OHBr is evaluated.…”

Halide sublattice dynamics drive Li-ion transport in antiperovskites

“…8 and 16) while cooling Li 2 OHBr below −50 °C results in the transition to orthorhombic. 41 Anion substitution (Br for Cl) tunes the lattice parameter and improves the cubic stability. DFT supports this by showing that the Li–halide distances decrease.…”

“…63) as the starting configuration because this structure is reported to have the lowest energy from 0 to 300 K for the Li 2 OHX (X = Cl, Br) systems. 41 We compared the simulated XRD based on the optimized structure models with the experimental data to confirm the mixed halides' crystal structure. pLiAP phonon densities of states were calculated using density functional perturbation theory (DFPT) based on the optimized geometries.…”

“…S4 †), respectively, as expected given their Goldschmidt tolerance factors. 41 The orthorhombic phase can be considered a distortion of the Li sublattice with unequal Li + anions distances, contrary to an ideal cubic structure. For example, in the orthorhombic Li 2 OHCl the Li-Cl lengths span from 2.664 to 2.785 Å, with a $4.5% difference.…”

Lithium-Rich Anti-perovskite Li2OHBr-Based Polymer Electrolytes Enabling an Improved Interfacial Stability with a Three-Dimensional-Structured Lithium Metal Anode in All-Solid-State Batteries

“…In the search for fillers that can improve the PEO-based polymer electrolytes at low cost, we discovered lithium-rich anti-perovskite (LiRAP) Li 2 OHBr to be a strong candidate. − The idea of developing LiRAP as fillers was inspired by our previous work, in which LiRAP with high stability to lithium metal and high lithium ion conductivity was used as a protective layer between lithium metal and electrolytes to regulate lithium plating/stripping . Compared with metal oxide fillers (e.g., Al 2 O 3 or SiO 2 ) without the lithium ion conductivity property, Li 2 OHBr as a superionic conductor processes large amounts of mobile lithium ions in the crystal lattice and a low energy barrier for lithium ion transport, and therefore there is a high lithium ion conductivity. − In fact, Li 2 OHBr features easy processing and low cost and environmental impact and can be more readily adopted for practical application. Herein, Li 2 OHBr-containing PEO polymer electrolytes were facilely prepared by a mixture in solution followed by solvent evaporation.…”