Construction of a Few-Layered COF@CNT Composite as an Ultrahigh Rate Cathode for Low-Cost K-Ion Batteries

Abstract

Potassium-ion batteries (PIBs) are attracting great interest for large-scale energy storage owing to the abundant resources and low redox potential of K+/K. However, the large volume changes and slow kinetics caused by the larger ionic radius of K+ for cathode materials remain a critical challenge for PIBs. Herein, we construct few-layered covalent organic frameworks integrated with carboxylated carbon nanotubes (DAAQ-COF@CNT) as cathode materials for PIBs. The synthesized DAAQ-COF@CNT features numerous active sites, a stable conductive framework, and an appropriate surface area with nanopores, which can render high electrical conductivity, shorten the ion/electron diffusion distance, and accelerate K+ diffusion. In consequence, the DAAQ-COF@CNT delivers a high reversible capacity of 157.7 mAh g–1 at 0.1 A g–1, an excellent rate capability of 111.2 mAh g–1 at 1 A g–1, and a long cycling stability of 77.6% capacity retention after 500 cycles at 0.5 A g–1. The integrated characterization of ex situ X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and theoretical simulation discloses that the storage mechanism of DAAQ-COF@CNT is based on the reversible reaction between electroactive CO groups and K+ during two successive steps. This work provides a promising high-performance cathode material for PIBs and encourages the development of new types of covalent organic frameworks for PIBs.

Schiff-Base Covalent Organic Framework/Carbon Nanotubes Composite for Advanced Potassium-Ion Batteries

“…Additionally, the CC peak in the phenyl of the original electrode is visible at 1500 cm –1 , but with the insertion of K + , the peak appears blue-shifted. The irreversible transformation of the CC peak is attributed to the partial K + intercalation into the phenyls, which is hard to extract during the charge . The K storage mechanism is also theoretically studied by DFT calculations.…”

“…The irreversible transformation of the C�C peak is attributed to the partial K + intercalation into the phenyls, which is hard to extract during the charge. 47 The K storage mechanism is also theoretically studied by DFT calculations.…”

Covalent organic frameworks as electrode materials for rechargeable metal‐ion batteries

“…In this regard, COFs demonstrate significant advantages due to their robust and porous conjugated crystalline structures. [57,113,[157][158][159][160][161] As indicated in Figure 11A, Chen and co-workers reported a boronic ester-based COF composite (COF-10@CNT) with a few-layered structure. [157] The π-cation interaction between K + and a π-electron cloud of [146] Copyright 2020, Nature Publishing Group.…”

“…Similarly, Duan and co‐workers constructed a nanofiber‐structured DAAQ‐COF@CNT as the cathode material for PIBs by integrating carboxylated CNTs with a few‐layered DAAQ‐COF. [ 160 ] As shown in Figure 11B, the 12 quinone groups in the DAAQ‐COF units could be combined with 12 K + via a two‐step multiple‐electron transfer reaction. The DAAQ‐COF@CNT as the anode for PIBs provided a high specific capacity of 157.7 mAh g −1 at 0.1 A g −1 , superior rate capability of 111.2 mAh g −1 at 1 A g −1 , and outstanding cycle performance with a capacity retention of 77.6% after 500 cycles at 0.5 A g −1 .…”

An intercalation–conversion hybrid mechanism enables covalent organic frameworks with superior Li-ion storage

“…Recently, covalent organic frameworks (COFs) have been regarded as potential electrode materials due to their designable two-dimensional frameworks, regular pore structures and abundant redox sites. [15][16][17] Besides, the utilization of a metal-free COF electrode is also expected to reduce the toxicity and the cost of LIBs. 18,19 However, current research on COF electrodes mainly focuses on two aspects: (i) ion storage behavior occurring on the framework, and its pore structure is primarily used for ion transport.…”