Stacking-Fault Defects Modulate Ion Transport in Ternary Halide Solid Electrolytes

Li, Y.; Huang, W.-F.; Deng, Z.; Grabow, L.; Canepa, P.

doi:10.26434/chemrxiv.15007134/v1

Stacking-Fault Defects Modulate Ion Transport in Ternary Halide Solid Electrolytes

Y. Li, W.-F. Huang, Z. Deng, L. Grabow, and P. Canepa; ChemRxiv (2026).

BibTeX

@misc{Li2026stacking,
  author        = {Li, Y. and Huang, W.-F. and Deng, Z. and Grabow, L. and Canepa, P.},
  title         = {{Stacking-Fault Defects Modulate Ion Transport in Ternary Halide Solid Electrolytes}},
  howpublished  = {ChemRxiv},
  year          = {2026},
  doi           = {10.26434/chemrxiv.15007134/v1}
}

Brief summary

Stacking faults are common flat defects in crystals, but their effect on halide solid electrolytes was unknown. Combining cluster expansions, Monte Carlo and machine-learned potentials, we show that stacking faults raise lithium conductivity in Li₃YCl₆ tenfold, lowering the migration barrier from 0.33 to 0.21 eV by breaking up the ordered lithium sublattice.

Full abstract

Despite the prevalence of stacking faults (SFs) as planar defects in crystalline materials used for energy applications, their thermodynamic stability and influence on Li-ion transport in ternary halide solid electrolytes (SEs) for all-solid-state batteries (ASSBs) remain poorly understood. Here, we combine first-principles-trained cluster-expansion Hamiltonians and Monte Carlo simulations with machine-learned interatomic potentials to investigate SFs in trigonal Li₃YCl₆ (LYC) and monoclinic Li₃YBr₆ (LYB), two promising SEs compatible with high-voltage positive-electrode materials. SFs in LYC are metastable. In LYB, SFs are nearly energetically degenerate with the pristine phase. Nanosecond-scale molecular dynamics simulations of thermodynamically accessible faulted structures show that SFs increase Li-ion conductivity in LYC by an order of magnitude while lowering the Li-ion migration activation energy from 0.33 (in the bulk) to 0.21 eV. The analysis suggests that this enhancement arises from the disruption of the rigid Li sublattice ordering and the activation of three-dimensional diffusion pathways by SFs at low temperatures. Our approach provides a general protocol for screening SFs in layered materials, including ion conductors. We show that defect-transport coupling is strongly framework dependent, highlighting synthesis-controlled defect engineering as a route to tune ionic conductivity in halide SEs and potentially other ion conductors.