A Metal–Organic Framework of Organic Vertices and Polyoxometalate Linkers as a Solid-State Electrolyte

A new three-dimensional
metal–organic framework (MOF) was
synthesized by linking ditopic amino functionalized polyoxometalate
[N­(C4H9)4]3[MnMo6O18­{(OCH2)3CNH2}2] with 4-connected tetrahedral tetrakis­(4-formyl­phenyl)­methane
building units through imine condensation. The structure of this MOF,
termed MOF-688, was solved by single crystal X-ray diffraction and
found to be triply interpenetrated diamond-based dia topology.
Tetrabutylammonium cations fill the pores and balance the charge of
the anionic framework. They can be exchanged with lithium ions to
give high ionic conductivity (3.4 × 10–4 S
cm–1 at 20 °C), a high lithium ion transference
number (tLi+ = 0.87), and low interfacial
resistance (353 Ω) against metallic lithiumproperties
that make it ideally suited as a solid-state electrolyte. Indeed,
a prototype lithium metal battery constructed using MOF-688 as the
solid electrolyte can be cycled at room temperature with a practical
current density of ∼0.2 C.