Electrolytes with high-efficiency lithium-ion transfer and reliable safety are of great importance for lithium battery. Although having superior ionic conductivity (10−3–10−2 S·cm−1), traditional liquid-state electrolytes always suffer from low lithium-ion transference number (
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Solid polymer electrolytes (SPEs) hold great application potential for solid-state lithium metal battery because of the excellent interfacial contact and processibility, but being hampered by the poor room-temperature conductivity (~ 10−7 S·cm−1) and low lithium-ion transference number (
As a new class of porous material, polymer-metal-organic framework (polyMOF) has attracted tremendous interests owing to their combined advantages of polymer and crystalline MOF. However, the poor film-forming ability of polyMOF limits its widespread application, especially in membrane separation area. Herein, for the first time, we demonstrate the fabrication of free-standing polyMOF membrane. The polyMOF nanosheets are synthesized by a polymer-assisted self-inhibition crystal growth strategy. Followed by self-assembly through vacuum filtration, a 20 μm-thick free-standing polyMOF membrane is constructed. Benefiting from the inclusion of polymer with hydrophobic backbone and the continuously distributed non-coordinated hydrophilic groups along polymer chain, the polyMOF membrane attains excellent structure stability against water, as well as superior proton transfer property. Proton conductivity as high as 112 and 25.6 mS·cm–1 is obtained by this polyMOF membrane at 100% and 20% relative humidity (RH), respectively, which are two orders of magnitude higher than those of pristine MOF. The conductivity under low humidity (20% RH) is even over 8 times higher than that of commercial Nafion membrane (3 mS·cm–1). This study may provide some guidance on the development of polyMOF membranes.
Porous laminar membranes hold great promise to realize ultrafast ion transfer if efficient and stable transfer channels are constructed in vertical direction. Here, metal-organic framework (MOF) nanosheets bearing imidazole molecules in the pores were designed as building blocks to assemble free-standing MOF laminar membrane. Then, Nafion chains were threaded into the pores induced by electrostatic attraction from imidazole molecules by slowly filtering dilute Nafion solution. We demonstrate that the threaded Nafion chains lock adjacent MOF nanosheets, affording highly enhanced structural stability to the resultant laminar membrane with almost no water swelling. Significantly, abundant acid-base pairs are formed in the pores along Nafion chains, working as efficient, continuous conduction pathways in vertical direction. Proton conductivities as high as 110 and 46 mS·cm–1 are obtained by this membrane under 100% and 40% relative humidity (RH), respectively, which are two orders of magnitude higher than that of pristine MOF membrane. The conductivity under low humidity (40% RH) is even over 2 times higher than that of commercial Nafion membrane, generating the maximum power density of 1,100 mW·cm–2 in hydrogen fuel cell (vs. 291 mW·cm–2 of Nafion membrane). Besides, the influence of water state on proton transfer in confined space is investigated in detail.