Tin and Iodine Neighbors Steer Lithium Motion in Halide Battery Material

A computational study of the halide solid electrolyte Li2ZrCl6, published in the journal Ionics, reports that the way tin and iodine substituents sit next to each other in the crystal lattice changes both the stability of the structure and the mobility of lithium ions. Xinyuan Zhang and Yuyang Chen used density-functional theory together with an adapted machine-learning interatomic potential to compare several substitution patterns in the material.

The team constructed models in which tin alone, iodine alone, or both elements together replace atoms in the LZC lattice. In the co-substituted cases, two charge-compensating lithium configurations were considered, and the iodine either sat near the tin or far from it. The configuration labeled Sn/I-near-A, in which iodine initially sits near the tin atom, came out approximately 435 meV per cell lower in energy than the distant arrangement, Sn/I-far-A. This preference held for the second compensating-lithium arrangement as well.

To probe how these local arrangements affect ion transport, the researchers ran molecular-dynamics production trajectories of 2000 picoseconds for five representative models at 600 and 700 K, in both the canonical (NVT) and microcanonical (NVE) ensembles. From these trajectories they extracted finite-time estimates of the whole-cell lithium tracer diffusivity. The facial iodine-only model, called I-fac, produced the highest whole-cell finite-time lithium tracer estimate among the models examined.

The comparison between the two co-substituted structures depended on temperature. At a nominal 600 K, Sn/I-near-A exceeded Sn/I-far-A in its lithium tracer estimate. At 700 K, the two models gave similar estimates over the 40 to 80 picosecond fitting interval.

In the first 50 picoseconds of the NVT trajectories at 600 K, Sn/I-near-A showed lower tin-centered lithium occupation and a faster continuous decay of that occupation than both the tin-only model, Sn-A, and Sn/I-far-A. Lithium ions left the neighborhood of the tin atom more quickly when iodine was nearby.

Atom-resolved path analysis from these records showed tin displacement and the exchange of halide neighbors around the tin, while the three tin-iodine separations in Sn/I-far-A shortened asynchronously rather than all at once.

For a more precise measure of the energy cost of lithium hopping, the researchers used the climbing-image nudged elastic band method on a local path. For a lattice lithium ion in the Sn/I-near-A configuration, the forward migration barrier came out at 425 meV and the reverse barrier at 183 meV.

The authors describe the work as a combined comparison that relates configurational stabilization to local lithium exchange and whole-cell motion. The study is computational throughout, so the reported barriers and diffusivity estimates are model predictions rather than measurements on physical battery cells, and the temperature range examined lies well above room temperature. Because halide solid electrolytes are investigated for their ionic conductivity, understanding how co-substitution reshapes the local environment gives researchers a specific structural lever to consider when tuning compositions of Li2ZrCl6 and related compounds. The work also illustrates how machine-learning interatomic potentials, trained within a density-functional framework, allow nanosecond-scale molecular dynamics at temperatures where direct first-principles molecular dynamics would be prohibitively expensive.

Subject of Research: Computational study of how tin-iodine local arrangement affects structural stability and lithium ion mobility in the halide solid electrolyte Li2ZrCl6

Article Title: First-principles investigation of Sn–I local arrangement and lithium mobility in Li2ZrCl6

Article References: Zhang, X., & Chen, Y. (2026). First-principles investigation of Sn–I local arrangement and lithium mobility in Li2ZrCl6. Ionics. https://doi.org/10.1007/s11581-026-07626-5

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07626-5

Keywords: Li2ZrCl6, halide solid electrolyte, density-functional theory, machine-learning interatomic potential, molecular dynamics, lithium ion mobility, tin-iodine co-substitution, migration barrier, nudged elastic band, solid-state batteries, First-principles, investigation