Iodide substituted halide-rich lithium argyrodite solid electrolytes with improved performance for all solid-state batteries†

Halogen substitution has been a widely accepted strategy to boost ionic conductivity of lithium argyrodites. Mixed halide argyrodites containing Cl and Br have been shown to be promising candidates as solid electrolytes, featuring high room temperature ionic conductivities >10 mS cm⁻¹. This study focuses on the less explored halide-rich Cl–I mixed halide argyrodites as solid-state electrolytes, comparing them to their Cl–Br analogues. DFT calculations reveal that Cl–I argyrodites possess enhanced phase stability and electrode compatibility. Despite differences in the type of halogen used, Cl–I and Cl–Br argyrodites exhibit similar ionic conductivities at equivalent Cl/X (X = Br, I) ratios. AIMD simulations of Li_5.5PS_4.5Cl_1.5−xI_x systems identify an optimal I and Cl content of 0.75 each, yielding a maximum conductivity of 23.5 mS cm⁻¹, attributed to enlarged Li⁺ migration channels.