Rational Construction of Yolk–Shell Bimetal-Modified Quinonyl-Rich Covalent Organic Polymers with Ultralong Lithium-Storage Mechanism

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-MnO2, has been designed and synthesized by in situ loading of petal-like nanosized MnO2 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-MnO2. Thus, the Co@2AQ-MnO2 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)

Boosted π‑Li Cation Effect in the Stabilized Small Organic Molecule Electrode via Hydrogen Bonding with MXene

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 Ti3C2Tx 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 Ti3C2Tx 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-Ti3C2Tx 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