Ionic covalent organic frameworks (ICOFs) have recently emerged as promising candidates for solid-state electrolytes. Herein, we report the first example of a series of crystalline imidazolate-containing ICOFs as single-ion conducting COF solid electrolyte materials, where lithium cations freely travel through the intrinsic channels with outstanding ion conductivity (up to 7.2 × 10–3 S cm–1) and impressively low activation energy (as low as 0.10 eV). These properties are attributed to the weak Li ion–imidazolate binding interactions and well-defined porous 2D framework structures of such ICOFs. We also investigated the structure–property relationship by varying the electronic properties of substituents (electron donating/withdrawing) that covalently attached to the imidazolate groups. We found electron-withdrawing substituents significantly improve the ion-conducting ability of imidazolate-ICOF by weakening ion-pair interactions. Our study provides a convenient bottom-up approach toward a novel class of highly efficient single-ion conducting ICOFs which could be used in all solid-state electrolytic devices.

All-solid-state lithium ion batteries (LIBs) are ideal for energy storage given their safety and long-term stability. However, there is a limited availability of viable electrode active materials. Herein, we report a truxenone-based covalent organic framework (COF-TRO) as cathode materials for allsolid-state LIBs. The high-density carbonyl groups combined with the ordered crystalline COF structure greatly facilitate lithium ion storage via reversible redox reactions. As a result, a high specific capacity of 268 mAh g À1 , almost 97.5 % of the calculated theoretical capacity was achieved. To the best of our knowledge, this is the highest capacity among all COF-based cathode materials for all-solid-state LIBs reported so far. Moreover, the excellent cycling stability (99.9 % capacity retention after 100 cycles at 0.1 C rate) shown by COF-TRO suggests such truxenone-based COFs have great potential in energy storage applications.

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A nonlinear and nonadditive composition-dependent change of the ionic conductivity in mixed glass-former (MGF) glasses when one glass former, such as PS(5/2), is replaced by a second glass former, such as GeS2, at constant alkali modifier concentrations, such as Na2S, is known as the mixed glass-former effect (MGFE). Alkali ion conducting glasses are of particular interest for use as solid electrolytes in alkali-based all-solid-state batteries because sulfide amorphous materials have significantly higher alkali ion conductivities than their oxide glass counterparts. In this study of the ternary MGF system Na2S + GeS2 + PS(5/2), we report the careful structural characterization of these glasses using a combination of vibrational, infrared (IR), Raman, and nuclear magnetic resonance (NMR) spectroscopies. Our measurements of the 0.5Na2S + 0.5[xGeS2 + (1-x)PS(5/2)] MGF system show that this glass system exhibits a strongly negative MGFE and non-Arrhenius ionic conductivities. While this negative MGFE in the Na(+) ion conductivity makes these glasses less attractive for use in solid-state Na batteries, the structural origin of this effect is important to better understand the mechanisms of ion conduction in the glassy state. For these reasons, we have examined the structures of ternary 0.5Na2S + 0.5[xGeS2 + (1-x)PS(5/2)] glasses using Raman, IR, and (31)P MAS NMR spectroscopies. In these studies, it is found that the substitution of PS(5/2) by GeS2, that is, increasing x, leads to unequal sharing of the Na(+) in these glasses. Thus, in all MGF compositions, phosphorus groups are associated with a disproportionately larger fraction, f(Na(P)) > 0.5(1 - x), of the Na(+) ions while the germanium groups are found to be Na(+)-deficient relative to the total amount of Na(+) present in the glass, that is, f(Na(Ge)) < 0.5x. From the spectroscopic study of these glasses, a short-range order (SRO) structural model is developed for these glasses and is based on the germanium and phosphorus SRO groups in these glasses as a first step in understanding the unique negative MGFE and non-Arrhenius behavior in the Na(+) ion conductivity in these glasses.

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