The high solubility of the small organic molecule materials in organic electrolytes hinders their development in rechargeable batteries. Hence, this work designs an ultrarobust hydrogen-bonded organic–inorganic hybrid material: the small organic unit of the 1,3,6,8-tetrakis (p-benzoic acid) pyrene (TBAP) molecule connected with the hydroxylated Ti3C2T x MXene through hydrogen bonds between the terminal groups of −COOH and −OH. The robust and elastic hydrogen bonds can empower the TBAP, despite being a low-molecule organic chemical, with unusually low solubility in organic electrolytes and thermal stability. The alkali-treated Ti3C2T x MXene provides a hydroxyl-rich conductive network, and the small organic molecule of TBAP reduces the restacking of MXene layers. Therefore, the combination of these two materials complements each other well, and this organic–inorganic TBAP@D-Ti3C2T x electrode delivers large reversible capacities and long cyclic life. Notably, with the assistance of the in situ FT–IR characterization of the electrode within the fully lithiated (0.005 V) and the delithiated (3.0 V) states, it is revealed that a powerful π-Li cation effect mainly governs the lithium-storage mechanism with the highly activated benzene ring and each C6 aromatic ring, which can reversibly accept six Li-ions to form a 1:1 Li/C complex.

Covalent organic polymers are attracting more and more attention for energy storage devices due to their lightweight, molecular viable design, stable structure, and environmental benignity. However, low charge-carrier mobility of pristine covalent organic materials is the main drawback for their application in lithium-ion batteries. Herein, a yolk−shell bimetal-modified quinonyl-rich covalent organic material, Co@2AQ-MnO 2 , has been designed and synthesized by in situ loading of petal-like nanosized MnO 2 and coordinating with Co centers, with the aim to improve the charge conductivity of the covalent organic polymer and activate its Li-storage sites. As investigated by in situ FT-IR, ex situ XPS, and electrochemical probing, the quinonyl-rich structure provides abundant redox sites (carbonyl groups and π electrons from the benzene ring) for lithium reaction, and the introduction of two types of metallic species promotes the charge transfer and facilitates more efficient usage of active energy-storage sites in Co@2AQ-MnO 2 . Thus, the Co@2AQ-MnO 2 electrode exhibits good cycling performance with large reversible capacity and excellent rate performance (1534.4 mA h g −1 after 200 cycles at 100 mA g −1 and 596.0 mA h g −1 after 1000 cycles at 1000 mA g −1 ).

The rechargeable lithium/sodium-iodine battery (Li/Na-I 2 ) is a promising candidate for meeting the growing energy demand. Herein, a flexible hydrogenbonded organic framework (HOF) linked to the Ti 3 C 2 T x MXene complex (HOF@Ti 3 C 2 T x ) has been presented for iodine loading. HOF is self-assembled by organic monomers through hydrogen bonding interactions between each monomer. It leads to numerous cavities in HOF structure, which can encapsulate iodine through various adsorptive sites and intermolecular interactions. The unique structure of complex can accelerate the nucleation of iodine, achieve fast reaction kinetics, stabilize iodide and retard the shuttle effect, thus improving the cycling stability of I 2 -based batteries. The I 2 /HOF@Ti 3 C 2 T x exhibits large reversible capacities of 260.2 and 207.6 mAh g À 1 at 0.2 C after repeated cycling for Li-I 2 and Na-I 2 batteries, respectively. This work can gain insights into the HOF-related energy storage application with reversible iodine encapsulation and its related redox reaction mechanisms with Li and Na metal ions.

The poor conductivity of the pristine bulk covalent organic material is the main challenge for its application in energy storage. The mechanism of symmetric alkynyl bonds (C�C) in covalent organic materials for lithium storage is still rarely reported. Herein, a nanosized ( � 80 nm) alkynyl-linked covalent phenanthroline framework (Alkynyl-CPF) is synthesized for the first time to improve the intrinsic charge conductivity and the insolubility of the covalent organic material in lithium-ion batteries. Because of the high degree of electron conjugation along alkynyl units and N atoms from phenanthroline groups, the Alkynyl-CPF electrodes with the lowest HOMO-LUMO energy gap (ΔE = 2.629 eV) show improved intrinsic conductivity by density functional theory (DFT) calculations. As a result, the pristine Alkynyl-CPF electrode delivers superior cycling performance with a large reversible capacity and outstanding rate properties (1068.0 mAh g À 1 after 300 cycles at 100 mA g À 1 and 410.5 mAh g À 1 after 700 cycles at 1000 mA g À 1 ). Moreover, by Raman, FT-IR, XPS, EIS, and theoretical simulations, the energy-storage mechanism of C�C units and phenanthroline groups in the Alkynyl-CPF electrode has been investigated. This work provides new strategies and insights for the design and mechanism investigation of covalent organic materials in electrochemical energy storage.

The poor conductivity of the pristine bulk covalent organic material is the main challenge for its application in energy storage. The mechanism of symmetric alkynyl bonds (C�C) in covalent organic materials for lithium storage is still rarely reported. Herein, a nanosized ( � 80 nm) alkynyl-linked covalent phenanthroline framework (Alkynyl-CPF) is synthesized for the first time to improve the intrinsic charge conductivity and the insolubility of the covalent organic material in lithium-ion batteries. Because of the high degree of electron conjugation along alkynyl units and N atoms from phenanthroline groups, the Alkynyl-CPF electrodes with the lowest HOMO-LUMO energy gap (ΔE = 2.629 eV) show improved intrinsic conductivity by density functional theory (DFT) calculations. As a result, the pristine Alkynyl-CPF electrode delivers superior cycling performance with a large reversible capacity and outstanding rate properties (1068.0 mAh g À 1 after 300 cycles at 100 mA g À 1 and 410.5 mAh g À 1 after 700 cycles at 1000 mA g À 1 ). Moreover, by Raman, FT-IR, XPS, EIS, and theoretical simulations, the energy-storage mechanism of C�C units and phenanthroline groups in the Alkynyl-CPF electrode has been investigated. This work provides new strategies and insights for the design and mechanism investigation of covalent organic materials in electrochemical energy storage.