Tin-nitrogen coordination boosted lithium-storage sites and electrochemical properties in covalent-organic framework with layer-assembled hollow structure.

A small amount of tin ions modified covalent organic framework hollow microsphere (Sn@COF-hollow) is designed and demonstrated with more active sites, facilitated lithium-storage kinetic and highly reversible large capacities. [Display omitted] • Sn-doped COF layer-assembled hollow microspherical composite is fabricated via the Sn-N coordination. • The Sn@COF-hollow is adopted as the electrode for lithium-ion battery for the first time. • Enhanced electrochemical performances can be achieved for the Sn@COF-hollow electrode. • Lithium-reaction activation on Sn centers, C C and C N groups can be boosted for the Sn@COF-hollow electrode. Covalent-organic frameworks (COFs) and related composites show an enormous potential in next-generation high energy-density lithium-ion batteries. However, the strategy to design functional covalent organic framework materials with nanoscale structure and controllable morphology faces serious challenges. In this work, a layer-assembled hollow microspherical structure (Sn@COF-hollow) based on the tin-nitrogen (Sn-N) coordination interaction is designed. Such carefully-crafted hollow structure with large exposed surface area and metal center decoration endows the Sn@COF-hollow electrode with more activated lithium-reaction sites, including Sn ions, carbon-nitrogen double bond (C N) groups and carbon-carbon double bond (C C) units from aromatic benzene rings. Besides, the layer-assembled hollow structure of the Sn@COF-hollow electrode can also alleviate the volume expansion of electrode during repeated cycling, and achieve fast electrons/ions transmission and capacitance-dominated lithium-reaction kinetics, further leading to enhanced cycling performance and rate properties. In addition, the effective combination of the inorganic metal and organic framework components in the Sn@COF-hollow electrode can promote its improved conductivity and further enhance lithium-storage properties. Benefited from these merits, the Sn@COF-hollow electrode delivers highly reversible large capacities of 1080 mAh g−1 after 100 cycles at 100 mA g−1 and 685 mAh g−1 after 300 cycles at 1000 mA g−1. This work provides an interesting and effective way to design COF-based anodes of lithium-ion battery with improved electrochemical performances. [ABSTRACT FROM AUTHOR]