High-Entropy Lithium Argyrodite Superionic Conductors

Solid-state batteries (SSBs) are a potentially safe, next-generation energy storage technology. For SSBs to be commercially viable, the development of solid electrolytes with high ionic conductivity, high (electro)chemical stability, and good processability is imperative. A new strategy for modifying materials, potentially leading to improved properties, is the high-entropy (HEMs) concept, referring to compounds having five or more elements occupying a single crystallographic site (resulting in a configurational entropy ΔS_conf ≥ 1.5<i>R</i>).<br/>Our recent research has shown that high-entropy argyrodites (HEAs) can be synthesized both by multianionic and/or -cationic substitution. Especially, multication substituted HEA shows a low activation energy (<i>E</i>_A ≈ 0.20 eV) for lithium transport and a high r.t. ionic conductivity (≈10 mS/cm) as shown by ⁷Li pulsed field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy and electrochemical impedance spectroscopy (EIS). These findings were rationalized from a structural point of view via neutron powder diffraction in combination with magic angle spinning (MAS) NMR spectroscopy. For the multication substituted HEA, high S^2-/I^- anion site disorder (up to ~11%) and Li⁺ redistribution led to shortened jump distances and therefore facilitated long-range ion diffusion. Conversely, multianionic substitution resulted in increased intercage jump distances. Overall, our results emphasize the potential of high-entropy lithium argyrodites (large compositional space) for developing novel superionic conductors with enhanced properties.