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

• An enhanced imide COFs cathode is designed by a “three-in-one” structure regulation strategy. • Morphology control results in COFs nanosheets with more active sites available for sodium storage. • Molecular design leads to more active sites in the COF’s skeleton. • Post synthetic vulcanization of C=O sites to C=S bring more active surface for COF material. • The triplex structural regulation endows the S@TAPT-COFs cathode excellent SIBs performances. 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 C=O bonds to C=S bonds can be facilely realized via Lawesson reagent, leading to the activity enhancement of the COF surface due to the higher activity of C=S 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 -1 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.