A Redox-Active 2-D Covalent Organic Framework as a Cathode in an Aqueous Mixed-Ion Electrolyte Zn-Ion Battery: Experimental and Theoretical Investigations

Abstract

We demonstrate here a simple alternative strategy of developing a stable and long-lived aqueous Zn-ion battery. The battery comprises a redox-active anthraquinone-based covalent organic framework (COF) and a graphene oxide composite (COF-GOPH) as the cathode, zinc metal as the anode, and a mixed-ion electrolyte with varying proportions of zinc and lithium ions. This cell configuration contrasts with those of conventional organic batteries with aqueous electrolytes having a single type of cation. Our findings convincingly show that an optimal Li + to Zn 2+ ion ratio is beneficial for Zn 2+ -ion diffusion into the COF. The energy storage mechanism is found to be due to the Zn 2+ -ion intercalation/ deintercalation into the COF with simultaneous reversible redox activity of the framework carbonyl and imine moieties. Additionally, a theoretical analysis of the radial distribution function reveals the preferential insertion of Zn 2+ -ions along with its partial solvation shell into the framework, leading to an optimal coordination of Zn 2+ with oxygen and nitrogen moieties of the COF network. On the other hand, the Li + ions preferentially reside in solution. Irrespective of the electrolyte composition, the composite electrode COF-GOPH performs better than the COF. The best battery performance is obtained with the COF-GOPH in the presence of 0.5 M ZnSO 4 and 0.5 M Li 2 SO 4 electrolyte. The cell shows excellent cyclability and superior capacity with 82% retention even after 500 cycles (from the second cycle onwards). Our studies also reveal a Li + -ion-assisted pseudocapacitance mechanism that is partially responsible for the enhancement in the electrochemical performance in the mixed-ion electrolytes.

Made to Measure Squaramide COF Cathode for Zinc Dual‐Ion Battery with Enriched Storage via Redox Electrolyte

“…[41] We are reporting for the first time such stable charge-discharge performance at such high current densities with such large specific capacities for a COF-derived ZIB cathode. [21][22][23][24][25][26][27][28] We attribute this to the high degree of crystallinity leading to the uniform exposure of the welldefined chelating squarate units for the favorable binding with the guest ions. A comparison with some of the top-performing ZIB cathodes shows that this high specific capacity at this discharge voltage plateau (1.3 V) is record-breaking (Table S4, Supporting Information).…”

“…Previously, only a few COFs, such as HqTq-COF, PA-COF, and PI-COF, have been reported as electrode materials in aqueous ZIBs. [21][22][23][24][25] Recently, Alshareef and co-workers engineered COF with and without a quinone-functional group to achieve a peak specific capacity of 344 mAh g −1 at 0.1 A g −1 for the latter. [26] Meanwhile, Tao and co-workers reported another carbonyl-decorated COF with a storage capacity of 225 mAh g −1 at 0.1 A g −1 , attributed to a synergistic co-insertion of Zn 2+ and protons.…”

Covalent Organic Frameworks as Model Materials for Fundamental and Mechanistic Understanding of Organic Battery Design Principles

“…Interestingly, the nanoporous channels of COF improve the diffusion kinetics of the charges that flow in and out of it . Furthermore, due to the modular construction principle and the vast variety of organic reactions to construct COFs, the molecular building blocks are precisely assembled into a crystalline framework, align donor–acceptor moieties, control the planarity, and retain the conjugation of the framework, which all tune the polymeric band structure and electronically activate the redox functionalities of the framework. − Owing to these fascinating properties and additionally the controllable pore structure, large surface area, simple surface/structural modification, and high thermal and chemical stability, COFs have been investigated as intriguing electrode materials in reversible energy storage, especially in secondary ion batteries (Li + , Na + , K + , Mg 2+ , Ca 2+ , Zn 2+ , , , Al 3+ , etc.) (Figure A) …”

Revealing the Self-Generated Heterointerface of NaV2O5 in Zn Storage via a Scalable Production Method

“…Lithium-ion batteries (LIBs) are frequently employed in our daily life including portable electronic devices, electric vehicles, etc. − However, most of the electrolytes utilized in commercial LIBs are organic with serious safety risks, such as being toxic and flammable. − Aqueous secondary batteries are regarded as potential energy storage devices because of their high level of safety, low cost, simple assembly, and environmental friendliness. − In various aqueous battery systems, zinc anode has a wide range of applications because of its low redox potential (−0.762 V vs SHE) and high specific capacity (820 mAh g –1 ) . Therefore, among the numerous secondary batteries, aqueous zinc-ion batteries (AZIBs) are becoming more appealing and attracting more attention. , …”