High‐Lithium‐Affinity Chemically Exfoliated 2D Covalent Organic Frameworks

Abstract

Covalent organic frameworks (COFs) with reversible redox behaviors are potential electrode materials for lithium‐ion batteries (LIBs). However, the sluggish lithium diffusion kinetics, poor electronic conductivity, low reversible capacities, and poor rate performance for most reported COF materials limit their further application. Herein, a new 2D COF (TFPB‐COF) with six unsaturated benzene rings per repeating unit and ordered mesoporous pores (≈2.1 nm) is designed. A chemical stripping strategy is developed to obtain exfoliated few‐layered COF nanosheets (E‐TFPB‐COF), whose restacking is prevented by the in situ formed MnO2 nanoparticles. Compared with the bulk TFPB‐COF, the exfoliated TFPB‐COF exhibits new active Li‐storage sites associated with conjugated aromatic π electrons by facilitating faster ion/electron kinetics. The E‐TFPB‐COF/MnO2 and E‐TFPB‐COF electrodes exhibit large reversible capacities of 1359 and 968 mAh g−1 after 300 cycles with good high‐rate capability.

Acid Exfoliation of Imine‐linked Covalent Organic Frameworks Enables Solution Processing into Crystalline Thin Films

“…Although Tsuru and co‐workers demonstrated that thin films can be prepared from a dilute suspension (0.15 mg mL −1 ) of COF‐1 powder prepared through sonication in dichloromethane, the fabrication process required repeated drop‐casting/drying cycles to form a continuous film, and therefore lacks scalability and practicality . More recently, charge‐mediated and chemical exfoliation strategies have been developed, which produce more concentrated suspensions (≥0.5 mg mL −1 ) that can be drop‐cast to produce large‐area films . However, these strategies have thus far made use of intentionally incorporated functional groups that are not generalizable across broad classes of COF networks .…”

Construction of 1D conductive Ni-MOF nanorods with fast Li+ kinetic diffusion and stable high-rate capacities as an anode for lithium ion batteries

“…S4b †), it is easy to nd a weak peak appearing at 289.8 eV, which corresponds to the C-Li groups and can be ascribed to the lithiation reaction with C]C groups. 20 Therefore, lithium storage in Ni-CAT mainly relies on the reversible insertion/de-insertion in its organic ligands and pores (Fig. S5, ESI †).…”

Two‐Dimensional MOF and COF Nanosheets: Synthesis and Applications in Electrochemistry

“…This is due to their strong covalent framework with open channels in π conjugate porous structure, which is used for reversible and smooth electrochemical insertion/extraction of Na ions. Chen et al. successfully exfoliated layered TFPB‐COF with the method of chemical exfoliation and obtained TFPB‐COF (E‐TFPBCOF) and E‐TFPB‐COF/MnO 2 composite nanosheets (Figure a).…”