Influence of pressure on structure, stability and ionic conductivity of lithium argyrodite solid electrolytes

Whilst the importance of external pressure in the manufacturing and operation of practical solid-state batteries has been clearly recognised, its impact on the fundamental properties of solid electrolytes remains underexplored. Here, we combine density functional theory and molecular dynamics simulations to investigate the effect of pressure (0-10 GPa) on the structural, electronic and ion transport properties of lithium argyrodite solid electrolytes, Li₆PS₅X (X = Cl and/or Br), with different levels of halide mixing and anion site (S^2-/X^-) disorder. We show that increased pressure induces systematic decreases in lattice volume and thermodynamic stability for both ordered and disordered systems. Anion disorder narrows the bandgap, which can change dramatically as a function of pressure. The Li-ion conductivities ( ~ 0.54-1.05 S cm^-1 at 600 K) and activation energies ( < 0.16 eV), remain high and low, respectively, up to ~2 GPa, with particularly pressure-resilient conduction networks observed in the mixed halide and disordered structures. At higher pressures ( > 2 GPa), most compositions show a clear increase in activation energy (0.15-0.42 eV) accompanied by reduced conductivity ( ~ 0.12-0.59 S cm^-1 at 600 K). These findings establish external pressure, site disorder and halide mixing as interdependent parameters that can be used to tune argyrodite solid electrolytes for high-performance solid-state batteries.