Molecular design and post-synthetic vulcanization on two-dimensional covalent organic framework@rGO hybrids towards high-performance sodium-ion battery cathode

Abstract

Covalent organic frameworks (COFs) with stable porous structure are considered as promising electrode materials for next-generation sustainable sodium-ion batteries (SIBs). However, how to enhance their surface activity and utilize more superficial active sites remains great challenge to satisfy the potential applications. Herein, a “three-in-one” structure regulation strategy including morphology control, molecular design and post-synthetic vulcanization is proposed to design an enhanced polyimide COFs cathode. Through morphology control, two-dimensional COFs nanosheets can be easily controlled due to the directing effect of the π-π interactions between rGO and the structure units of COFs, which leads to short channels to make more active sites available for sodium storage; Through molecular design, COFs with more active atoms can be acquired by simply replacing N atom with triazine ring in monomer, resulting in more active sites in the COFs skeleton; Through post-synthetic modification, the transformation of CO bonds to CS bonds can be facilely realized via Lawesson reagent, leading to the activity enhancement of the COF surface due to the higher activity of CS to sodium. With these triplex structural enhancements, the resulting S@TAPT-COFs (sulfuretted 2,4,6-Tris(4-aminophenyl)-1,3,5-triazine) nanosheets cathode exhibits excellent SIBs performances with a high specific capacity of 109.3 mAh g−1 at 0.1 A g−1 and a long-term stability with 68.6 mAh/g specific capacity remaining after 2000 cycles of charge/discharge process at 2.0 A g−1. This three-in-one strategy integrating morphology control, molecular design and post-synthetic modification provides an effective route to inspire the development of novel organic electrodes especially COFs for sustainable and durable rechargeable batteries.