Redox of Dual-Radical Intermediates in a Methylene-Linked Covalent Triazine Framework for High-Performance Lithium-Ion Batteries

Abstract

Covalent triazine frameworks (CTFs) are promising electrodes for rechargeable batteries due to their adjustable structures, rich redox sites, and tunable porosity. However, the CTFs usually exhibit inferior electrochemical stability because of the inactivation of the unstable radical intermediates. Here, a methylene-linked CTF has been synthesized and evaluated as a cathode for rechargeable lithium-ion batteries. Electron paramagnetic resonance (EPR) and in situ Raman characterizations demonstrated that the redox activity and reversibility of α-C and triazine radical intermediates are essentially important for the charging/discharging process, which have been efficiently stabilized by the synergetic π conjugation and hindrance effect caused by the adjacent rigid triazine rings and benzene rings in the unique CTF-p framework. Additionally, the methylene groups provided extra redox-active sites. As a result, high capacity and cycling stability were achieved. This work inspires the rational modulation of the radical intermediates to enhance the electrochemical performance of organic electrode materials for the next-generation energy storage devices.

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

“…118 The capability of the α-C˙radicals in COF to accommodate alkali metal ions was also confirmed recently through DFT computations of MESP. 166 Therefore, harnessing the reactivity and availability of these radical intermediates is crucial to the stability and performance of the COF electrodes. For instance, Gu et al 118 demonstrated that increasing the stacking thickness of DAAQ-COF results in a higher degree of extinction and deactivation of the α-C˙radical intermediates due to increased self-discharge of the radicals during the redox process.…”

Graphitic Aza‐Fused π‐Conjugated Networks: Construction, Engineering, and Task‐Specific Applications

“…[253] Methylene group functionalized CTFs derived from ZnCl 2 -catalyzed trimerization of p-xylylene dicyanide (Figure 3) was exploited as cathode material in LIBs, displaying a specific capacity of 247 mAh g −1 at 20 mA g −1 . [254] A series of materials derived from fluorinated CQNs was prepared via the polymerization of 2,5-diamino-3,6-difluoroterephthalonitrile (DADFTN) promoted by ZnCl 2 at reaction temperatures of 400-700 °C (denoted as F-CQN-1-T, T = reaction temperature) (Figure 13A). The as-afforded materials were amorphous but possessed abundant porosity and codoped with nitrogen and fluorine moieties.…”

“…[ 253 ] Methylene group functionalized CTFs derived from ZnCl 2 ‐catalyzed trimerization of p ‐xylylene dicyanide (Figure 3) was exploited as cathode material in LIBs, displaying a specific capacity of 247 mAh g −1 at 20 mA g −1 . [ 254 ]…”

Ionic Covalent Organic Frameworks for Energy Devices

“…[ 47–51 ] In addition, the variety of COF structures and their superior electrochemical stability has led COFs to become versatile platforms for an array of engineering applications. This is aided by the functionalizability of COF backbones, which can afford COF platforms for energy devices [ 52–58 ] and a diversity of other applications, such as molecular sorption and separation, [ 59–65 ] molecular sensing, [ 66,67 ] catalysis, [ 68–73 ] optoelectronics, [ 74–78 ] piezoelectrics, [ 79 ] and low‐ k dielectric materials [ 80,81 ]…”

“…However, these membranes suffer from severe capacity fade under extreme platforms for an array of engineering applications. This is aided by the functionalizability of COF backbones, which can afford COF platforms for energy devices [52][53][54][55][56][57][58] and a diversity of other applications, such as molecular sorption and separation, [59][60][61][62][63][64][65] molecular sensing, [66,67] catalysis, [68][69][70][71][72][73] optoelectronics, [74][75][76][77][78] piezoelectrics, [79] and low-k dielectric materials [80,81] A distinct type of COFs are ionic COFs (iCOFs), [82,83] which are COFs that contain a repeating unit bearing ionic groups. In a sense, iCOFs are analogous to polyelectrolytes, as a substantial proportion of the groups on their polymer backbones are ionic or ionizable.…”