Two-dimensional covalent organic frameworks with p- and bipolar-type redox-active centers for organic high-performance Li-ion battery cathodes

Abstract

A bipolar-type 2D COF has been fabricated through the condensation of TPPDA and Cu-TFPP. The COF cathode with p- and bipolar-type redox-active centers exhibits good performance for Li-ion batteries.

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

“…Bipolar-type organic materials possess the properties of both n-type and p-type materials, that is, they can utilize their negatively or positively charged states to combine with cations or anions, which extends their applications to not only rechargeable metal-ion batteries but also dual-ion batteries. [34,35,[70][71][72] Nitroxyl radical compounds, with bipolar-type features, have been widely investigated for energy storage. [73,74] As displayed in Scheme 1, they can be reversibly reduced to N-O − anions or oxidized to O=N + cations, along with the incorporation of cations or anions.…”

“…Besides, porphyrin and phthalocyanine (Pc) derivatives have also been reported as bipolar-type redox-active moieties for energy storage. [70,[75][76][77][78][79] As can be seen from Scheme 1, the 18 π-electrons of Pc-Cu can be oxidized or reduced into 16 π-electrons or 20 π-electrons, respectively. The bipolar feature renders them with a wide working potential window, even suitable for all-organic symmetric batteries.…”

“…[68,[100][101][102][103][104][105] Therefore, introducing p-type active moieties into COFs structures, such as N,N′-substituted phenazine, triphenylamine derivatives, and 2,2,6,6-tetramethylpiperdinyloxyl (TEMPO), has also emerged as an effective strategy to obtain COF-based electrode materials with high redox potentials. [68][69][70]106] As shown in Figure 4A, Meng and co-workers designed and synthesized two p-type phenoxazine-based COFs (DAPO-COFs) as cathode materials for LIBs, which can afford high redox potentials (~3.6 V vs. Li/Li + ). [69] The pristine DAPO-TpOMe-COF provided the first discharge capacity of 81.9 mAh g −1 at 100 mA g −1 .…”

“…[76,[107][108][109] In consequence, constructing COFs with a bipolar feature by molecular design has become an efficient strategy to pursue satisfying capacity and redox potential simultaneously. [62,[70][71][72]77,110] For instance, Yang and co-workers synthesized a series of nanoporous fluorinated covalent quinazoline networks (F-CQNs in Figure 4E) with the bipolar feature as cathode materials for LIBs. [71] As shown in Figure 4F, F-CQNs cathode materials were capable of operating in a large working potential window of 1.5-4.5 V versus Li/Li + , with 1.2 M LiPF 6 in ethyl methyl carbonate and ethylene carbonate as the electrolyte, the p-doping process of F-CQNs occurred in the high potential range of 3.0−4.5 V versus Li/Li + , accompanied by the combination between TCQ cores and PF 6 − anions, whereas the n-doping process was performed in the low potential region of 1.5-3.0 V Li/Li + , involving in the adsorption of Li + into benzene rings.…”

Sulfonated covalent organic framework packed Nafion membrane with high proton conductivity for H2/O2fuel cell applications

“…Covalent organic frameworks (COFs) are a new kind of crystalline porous polymers connected by strong covalent bonds, which have the advantages of high specic surface area, adjustable periodic pores, and ordered structure. [22][23][24][25][26][27][28][29][30][31][32][33][34] Ordered nanopore channels can provide an orderly proton transport path and increase proton carrier quantity in the nanopore, thus obtaining high proton conductivity. Compared with other porous llers, COFs have excellent thermal and chemical stability due to the relatively stable covalent bonding.…”