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-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 ).