Boosting lithium storage in covalent organic framework via activation of 14-electron redox chemistry

Abstract

Conjugated polymeric molecules have been heralded as promising electrode materials for the next-generation energy-storage technologies owing to their chemical flexibility at the molecular level, environmental benefit, and cost advantage. However, before any practical implementation takes place, the low capacity, poor structural stability, and sluggish ion/electron diffusion kinetics remain the obstacles that have to be overcome. Here, we report the synthesis of a few-layered two-dimensional covalent organic framework trapped by carbon nanotubes as the anode of lithium-ion batteries. Remarkably, upon activation, this organic electrode delivers a large reversible capacity of 1536 mAh g −1 and can sustain 500 cycles at 100 mA g −1 . Aided by theoretical calculations and electrochemical probing of the electrochemical behavior at different stages of cycling, the storage mechanism is revealed to be governed by 14-electron redox chemistry for a covalent organic framework monomer with one lithium ion per C=N group and six lithium ions per benzene ring. This work may pave the way to the development of high-capacity electrodes for organic rechargeable batteries.

A Redox‐Active 2D Metal–Organic Framework for Efficient Lithium Storage with Extraordinary High Capacity

“…Furthermore, both oxidized and reduced states show a peak of the C=O band at 1600 cm −1 , confirming the existence of carbonyl groups . The peak at 1530 cm −1 (attributed to C=C bond from benzene ring) almost vanished from reduced state to oxidized state, confirming the disappearance of conjugation of C 6 ring . Ex situ XPS and TEM analyses were also performed for the fully discharged and charged Cu‐THQ MOF electrodes, which also proves that PF 6 − anions are involved in the redox process of Cu‐THQ MOF (Supporting Information, Figures S13–S15).…”

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

“…The E‐TFPB‐COF and E‐TFPB‐COF/MnO 2 composite electrode in this work exhibit excellent Li‐storage performance in terms of high capacity and long cycle life compared with previous related COF‐based and MnO 2 ‐based organic–inorganic hybrid materials for Li‐ion batteries (Table S2, Supporting Information). Please note that in our previous work, the COF@CNTs composite exhibited a large capacity of 1021 mAh g −1 after 500 cycles, but more than 300 cycles are needed to activate and very small reversible capacities of ≈230–440 mAh g −1 were delivered in the first 100 cycles . There is no such long activation process for the chemically exfoliated COF electrode in this work.…”

“…The stable porous COFs structure provides an open channel for the facilitated infusion of the electrolyte and the transport of ions/electrons. Currently, few COFs have been investigated as electrode materials or electrode support for lithium storage, which usually exhibited enhanced electrochemical properties compared to common organic electrodes. The framework construction of functional organic units in COFs can largely prevent the dissolution of the organic electrode in the organic electrolyte.…”

“…The cyclic voltammetry (CV) measurement curves are shown in Figure a and Figure S12 (Supporting Information). During the first cathodic scan, a weak peak at ≈1.46 V is assigned to the lithium reaction with CN bonds, and the small broad peak observed at ≈0.68 V can be attributed to the formation of a solid electrolyte interface (SEI) layer at the electrode–electrolyte interface and the lithium insertion into the benzene (C 6 ) aromatic rings . Another obvious peak at ≈0.13 V is assigned to the initial reduction of MnO 2 to metallic Mn .…”

Kovalente organische Gerüstverbindungen: chemische Ansätze für Designerstrukturen und integrierte Funktionen

“…Kürzlich wurde ein iminverknüpftes COF für die Redoxreaktion mit Li + entwickelt, das eine ausgezeichnete Kapazität als Anode in einer Lithiumionenbatterie zeigt. Ein COF@CNT (COF=COF‐LZU1; Abbildung d) weist mehrere C=N‐ und C=C‐Bindungen an den Phenylringen zum reversiblen Binden von Li + für die Energiespeicherung auf . COF@CNT kann über einen 14‐Elektronen‐Prozess 14 Li + ‐Ionen in einem einzigen Ladevorgang binden und erreicht damit eine außergewöhnliche theoretische Kapazität von 1536 mAh g −1 bei 0.1 mAh g −1 .…”