Exceptional Sodium-Ion Storage by an Aza-Covalent Organic Framework for High Energy and Power Density Sodium-Ion Batteries

Abstract

Redox-active covalent organic frameworks (COFs) are a new class of material with the potential to transform electrochemical energy storage due to the well-defined porosity and readily accessible redox-active sites of COFs. However, combining both high specific capacity and energy density in COF-based batteries remains a considerable challenge. Herein, we demonstrate the exceptional performance of Aza-COF in rechargeable sodium-ion batteries (SIBs). Aza-COF is a microporous 2D COF synthesized from hexaketocyclohexane and 1,2,4,5-benzenetetramine by a condensation reaction, which affords phenazine-decorated channels and a theoretical specific capacity of 603 mA h g −1 . The Aza-COF-based electrode exhibits an exceptional average specific capacity (550 mA h g −1 ), energy density (492 W h kg −1 ) at 0.1 C, and power density (1182 W kg −1 ) at 40 C. The high capacity and energy density are attributed to swift surface-controlled redox processes and rapid sodium-ion diffusion inside the porous electrode. Rate capability studies showed that the battery also performs well at high current rates: 1 C (363 mA h g −1 ), 5 C (232 mA h g −1 ), 10 C (161 mA h g −1 ), and 20 C (103 mA h g −1 ). In addition, the long-term cycling stability test revealed very good capacity retention (87% at 5 C) and Coulombic efficiencies near unity over 500 cycles.

Covalent Organic Framework for Rechargeable Batteries: Mechanisms and Properties of Ionic Conduction

“…[3,22,23,[44][45][46][47][48][49][120][121][122][123][124][125][126][127][128][129][130] Moreover, the emerging ion-conducting COFs with excellent ionic conductivity and high cation transfer number can reduce the battery polarization and improve the charging/discharging kinetics of electrodes. [131][132][133][134][135][136][137][138][139][140][141][142][143] The distinctive directional selectivity of ionic conduction in COFs is obviously different from the typical inorganic solid conductors and polymer conductors, so that COFs are suitable for diverse battery applications, including lithium-ion, lithiumsulfur, sodium-ion, [209][210][211][212][213][214] potassium-ion, [215][216][217][218][219] lithium-CO 2 , [220]…”

“…[ 3,22,23,44–49,120–130 ] Moreover, the emerging ion‐conducting COFs with excellent ionic conductivity and high cation transfer number can reduce the battery polarization and improve the charging/discharging kinetics of electrodes. [ 131–143 ] The distinctive directional selectivity of ionic conduction in COFs is obviously different from the typical inorganic solid conductors and polymer conductors, so that COFs are suitable for diverse battery applications, including lithium‐ion, [ 144–166 ] lithium–sulfur, [ 167–208 ] sodium‐ion, [ 209–214 ] potassium‐ion, [ 215–219 ] lithium–CO 2 , [ 220–223 ] zinc‐ion, [ 224–230 ] zinc–air batteries, [ 231–234 ] etc. In this section, the traditional classification method of battery types is replaced by the classification according to the components among the dif...…”

Covalent organic frameworks: Design and applications in electrochemical energy storage devices

“…Important findings in COFs also have been made over the studies of COF redox reactions with sodium (Na)ions. 49,57,[118][119][120] Liu and colleagues reported a crystalline 2D conjugated polymer via C C coupling reaction in 2017. 57 Prior to this study, COF linkages typically involve imine and phenazines, and the construction of crystalline organic structure using stronger covalent bonds such as C C bonds was not realized because the irreversible C C formation prevents self-correction during the growth of organic framework.…”

“…Important findings in COFs also have been made over the studies of COF redox reactions with sodium (Na)‐ions 49,57,118–120 . Liu and colleagues reported a crystalline 2D conjugated polymer via CC coupling reaction in 2017 57 .…”

Structure–Performance Relationships of Covalent Organic Framework Electrode Materials in Metal-Ion Batteries

“…redox kinetics. 46,47 However, the strong π−π interactions between COFs layers lead to dense stacking, which impairs the coordination between ions and redox active sites to some extent. 24 In this regard, regulating the micro structure and electrode structure COF electrode materials is necessary.…”