Engineering the Site-Disorder and Lithium Distribution in the Lithium Superionic Argyrodite Li6PS5Br

Lithium argyrodite superionic conductors, of the form Li6PS5X (X = Cl, Br, and I), have shown great promise as electrolytes for all-solid-state batteries because of their high ionic conductivity and processability. The ionic conductivity of these materials is highly influenced by the structural disorder of S2-/X- anions; however, it is unclear if and how this affects the Li distribution and how it relates to transport, which is critical for improving conductivities. Here it is shown that the site-disorder once thought to be inherent to given compositions can be carefully controlled in Li6PS5Br by tuning synthesis conditions. The site-disorder increases with temperature and can be frozen in. Neutron diffraction shows this phenomenon to affect the Li+ substructure by decreasing the jump distance between so-called cages of clustered Li+ ions; expansion of these cages makes a more interconnected pathway for Li+ diffusion, thereby increasing ionic conductivity. Additionally, ab initio molecular dynamics simulations provide Li+ diffusion coefficients and time-averaged radial distribution functions as a function of the site-disorder, corroborating the experimental results on Li+ distribution and transport. These approaches of modulating the Li+ substructure can be considered essential for the design and optimization of argyrodites and may be extended to other lithium superionic conductors.

Automated summary

The study shows that controlling site-disorder in Li6PS5Br by adjusting synthesis conditions can enhance lithium ion diffusion pathways and increase ionic conductivity. Experimental results and ab initio molecular dynamics simulations corroborate each other, highlighting the importance of this modulation method for design and optimization of argyrodites.