Intrinsic linker flexibility in an anionic metal-organic framework electrolyte for selective lithium-ion conduction.

Although solid-state batteries promise improved safety and higher energy density, their performance is fundamentally constrained by solid electrolytes that fail to reconcile fast, selective Li+ transport with conformal interfacial contact. Here, we report ZnBTCA, an anionic zinc-based metal-organic framework constructed from the flexible aliphatic linker 1,2,3,4-butanetetracarboxylic acid, introducing intrinsic framework compliance. Ion exchange converts Na+-ZnBTCA to its Li+ form, enabling highly Li+-selective ionic conduction within a mechanically soft framework (Young's modulus ≈ 4.6 GPa) that promotes conformal Li|electrolyte contact and reduces interfacial impedance. ZnBTCA exhibits Li+ conductivities of 3.53 × 10-5 S cm-1 at 20 °C and 1.87 × 10-4 S cm-1 at 60 °C (E a = 0.36 eV), together with a high Li+ transference number (t Li+ = 0.79). This combination of structural compliance and selective Li+ conduction enables stable interfacial behavior, demonstrated by ∼300 h of Li|ZnBTCA@5-PEO|Li cycling at 0.2-1.0 mA cm-2 with stable voltage polarization. To our knowledge, this represents the first aliphatic-based MOF electrolyte and establishes linker flexibility coupled with framework anionicity as a general design strategy for mechanically adaptive, high Li+ transport MOF electrolytes in next-generation solid-state batteries.