Single-Ion Li⁺, Na⁺, and Mg²⁺ Solid Electrolytes Supported by a Mesoporous Anionic Cu–Azolate Metal–Organic Framework

Abstract

A novel Cu(II)-azolate metal-organic framework (MOF) with tubular pores undergoes a reversible single crystal to single crystal transition between neutral and anionic phases upon reaction with stoichiometric amounts of halide or pseudohalide salts. The stoichiometric transformation between the two phases allows loading of record amounts of charge-balancing Li, Na, and Mg ions for MOFs. Whereas the halide/pseudohalide anions are bound to the metal centers and thus stationary, the cations move freely within the one-dimensional pores, giving rise to single-ion solid electrolytes. The respective Li-, Na-, and Mg-loaded materials exhibit high ionic conductivity values of 4.4 × 10, 1.8 × 10, and 8.8 × 10 S/cm. With addition of LiBF, the Li conductivity improves to 4.8 × 10 S/cm. These are the highest values yet observed for MOF solid electrolytes.

Nanostructured Metal–Organic Framework (MOF)‐Derived Solid Electrolytes Realizing Fast Lithium Ion Transportation Kinetics in Solid‐State Batteries

“…The solid electrolyte pellet with a composition of UIO/Li‐IL (15/16) was used for further studies, it shows a high conductivity of 3.2 × 10 −4 S cm −1 at 25 °C, and the activation energy calculated from the Arrhenius plot is about 0.4 eV, demonstrating a solid‐state conduction behavior. The conductivities of UIO/Li‐IL SEs are comparable to inorganic SEs (10 −4 S cm −1 ), while higher than those of polymer electrolytes (10 −6 –10 −4 S cm −1 ), other MOF‐derived SEs (10 −5 –10 −4 S cm −1 ), and covalent organic framework–derived SEs (10 −6 –10 −4 S cm −1 at 60 °C) …”

“…Kitagawa and co‐workers focused on the ionic conductivity of another MOF‐derived solid conductors, ZIF‐8 with inclusion of lithium‐containing ionic liquid (Li‐IL), whose conductivity reaches 0.1 mS cm −1 at room temperature. Dincă and co‐workers reported MIT‐20 (a Cu 2+ ‐containing MOF) derived SEs with metal salts of LiCl, NaSCN, or MgBr 2 in propylene carbonate. In the case of LiCl, the lithium ion conductivity is 1.3 × 10 −5 S cm −1 ; in the case of NaSCN, the sodium ion conductivity is 1.8 × 10 −5 S cm −1 ; while in the case of MgBr 2 , the magnesium ion conductivity is 8.8 × 10 −7 S cm −1 .…”

Recent Progress of Hybrid Solid‐State Electrolytes for Lithium Batteries

“…[63] As displayed in Figure 6c,t he structure of MIT-20 ((CH 3 ) 2 NH 2 )[Cu 2 Cl 3 BTDD]·(DMF) 4 (H 2 O) 4.5 )i sc omposed of alternate pair of Cu atoms connected either by BTDD 2À or by BTDD 2À and m 2 -Cl, which shows anionic framework balanced by free dimethylammonium (DMA). [63] As displayed in Figure 6c,t he structure of MIT-20 ((CH 3 ) 2 NH 2 )[Cu 2 Cl 3 BTDD]·(DMF) 4 (H 2 O) 4.5 )i sc omposed of alternate pair of Cu atoms connected either by BTDD 2À or by BTDD 2À and m 2 -Cl, which shows anionic framework balanced by free dimethylammonium (DMA).…”

A Metal–Organic Framework with Tetrahedral Aluminate Sites as a Single‐Ion Li+ Solid Electrolyte

“…Thefilms were prepared by mixing the solid electrolytes with polyvinylidene fluoride in a1:1 weight ratio in anhydrous N-methyl-2-pyrrolidone.T he slurries were cast on aluminum foils and carefully dried to ensure complete removal of the solvent. [3,5,7] Ionic conductivity was found to scale with temperature ( Figure 4b)a nd showed Arrhenius character (Figure 4c)i ndicating that ah opping mechanism is responsible for lithium transport whereby coordinated lithium diffuses to the nearest vacant site. Room-temperature Nyquist plots (normalized by the ratio of area to thickness) along with an equivalent circuit model are shown in Figure 4a.V alues of R1 were used to calculate the ionic conductivity and will include both bulk and grain boundary resistance.T he plots indicated room-temperature Li + conductivity values of s = 5.7 AE 1.9 10 À5 and 0.7 AE 0.2 10 À5 Scm À1 for Al-Td-MOF-1 and the amorphous aluminate framework, respectively.T hose values are in the same range than the best values reported for MOFs and borate COFs and MPNs.…”

“…[1] Twoa lternatives are currently proposed to circumvent those limitations:s olid-state or mechanically robust electrolytes that prevent dendrites to cross the cell and create short circuits,and single-ion electrolytes where only the lithium cations are mobile while the anions are immobilized within am atrix to prevent sidereactions at the electrodes.T he larger electrochemical window of solid electrolytes in comparison to carbonate electrolytes will also allow for the development and implementation of high voltage cathode (> 4.8 V) and low voltage anode (< 1.0 V) materials. [5] Stoichiometric incorporation of negatively charged building blocks was recently developed for purely organic microporous polymer networks (MPNs) and covalent organic frameworks (COFs) by introducing tetracoordinate borate, [6,7] tetra-and hexacoordinate phosphate, [8] and hexacoordinate silicon [9] ionic functionalities.A lthough only evaluated for the borate frameworks,t his approach also proved to be promising for the synthesis of single-ion solid electrolytes. MOFs with unidirectional pore systems are of interest due to their potential to provide highly anisotropic lithium ion conduction paths if they can be crystallographically oriented.…”