Molecular engineering of covalent organic nanosheets for high-performance sodium-ion batteries

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 8; no. 34; pp. 1779 - 17799
• Main Authors: Kim, Min-Sung, Lee, Minseop, Kim, Min-Jae, Jeong, Young Kyu, Park, Jin Kuen, Paek, Seung-Min
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 14.09.2020
• Subjects: Anodes; Conjugation; Coupling (molecular); Cross coupling; Current carriers; Discharge; Electrochemical analysis; Electrochemistry; Electrode materials; Electrodes; Energy gap; Heat treatment; Morphology; Nanosheets; Rechargeable batteries; Self-assembly; Sodium; Sodium-ion batteries; Storage capacity
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d0ta06206e

The bandgap-dependent performance of covalent organic nanosheets (CONs) as sodium-ion battery anode materials was probed by inclusion of electron-deficient benzothiadiazole (BT) units into their network. Conjugation of BT units with electron-rich moieties afforded low-bandgap materials, and a self-assembled CON morphology with a large number of insertion sites for Na + ions was realized via solvothermal Stille cross-coupling. The bandgap dependence of Na + storage capacity was probed by the synthesis and characterization of large-bandgap CONs, which were subsequently compared to low-bandgap CONs in terms of electrochemical behavior. Four different CONs were investigated in total to reveal that the Na + storage capacity can be improved by increasing the charge carrier conductivity via the inclusion of BT units, while the surface area can be controlled by maintaining the material backbone. The electrode with a solvothermally prepared low-bandgap CON demonstrated stable rate capability and cycling performance while exhibiting highly enhanced reversible discharge capacity (∼450 mA h g −1 ) after 30 cycles at a scan rate of 100 mA g −1 . To the best of our knowledge, this discharge capacity is among the best values reported so far for organic electrodes prepared without thermal treatment. Low-bandgap covalent organic nanosheets are synthesized by combining electrically different monomers. The charge carrier conductivity resulting by lowering their bandgap is demonstrated to be important in improving the capacity of Na-ion batteries.