<p>Metal—organic frameworks
(MOFs) are intriguing host materials in composite electrolytes due to their
ability for tailoring host-guest interactions by chemical tuning of the MOF
backbone. Here, we introduce particularly high sodium ion conductivity into the
zeolitic imidazolate framework ZIF-8 by impregnation with the
sodium-salt-containing ionic liquid (IL) (Na0.1¬EMIM0.9)TFSI. We demonstrate an
ionic conductivity exceeding 2×10-4 S ⋅cm-1 at room
temperature, with an activation energy as low as 0.26 eV, i.e., the highest
reported performance for room temperature Na+-related ion conduction in
MOF-based composite electrolytes to date. Partial amorphization of the ZIF-backbone
by ball-milling results in significant enhancement of the composite stability,
reflecting in persistent and stable ionic conductivity during exposure to
ambient air over up to 20 days. While the introduction of network disorder
decelerates IL exudation and interactions with ambient contaminants, the ion
conductivity is only marginally affected, decreasing linearly with decreasing
crystallinity but still maintaining superionic behavior. This highlights the
general importance of 3D networks of interconnected pores for efficient ion
conduction in MOF/IL blends, whereas pore symmetry is a presumably less
stringent condition.</p>
Under Pressure: Mechanochemical Effects on Structure and Ion Conduction in the Sodium-Ion Solid Electrolyte Na3PS4