Abstract
The ordering effects in anthraquinone (AQ) stacking forced by thin-film application and its influence on dimer solubility and current collector adhesion are investigated. The structural characteristics of AQ and its chemical environment are found to have a substantial influence on its electrochemical performance. Computational investigation for different charged states of AQ on a carbon substrate obtained via basin hopping global minimization provides important insights into the physicochemical thin-film properties. The results reveal the ideal stacking configurations of the individual AQ-carrier systems and show ordering effects in a periodic supercell environment. The latter reveals the transition from intermolecular hydrogen bonding toward the formation of salt bridges between the reduced AQ units and a stabilizing effect upon the dimerlike rearrangement, while the strong surface–molecular interactions in the thin-film geometries are found to be crucial for the formed dimers to remain electronically active. Both characteristics, the improved current collector adhesion and the stabilization due to dimerization, are mutual benefits of thin-film electrodes over powder-based systems. This hypothesis has been further investigated for its potential application in sodium ion batteries. Our results show that AQ thin-film electrodes exhibit significantly better specific capacities (233 vs 87 mAh g–1 in the first cycle), Coulombic efficiencies, and long-term cycling performance (80 vs 4 mAh g–1 after 100 cycles) over the AQ powder electrodes. By augmenting the experimental findings via computational investigations, we are able to suggest design strategies that may foster the performance of industrially desirable powder-based electrode materials.
Highlights
Organic semiconducting materials based on small molecules like quinones, which build the core semiconductor element, have gained increasing interest as novel candidates for naturederived organic electrodes.[1]
We found that the structural characteristics and the chemical environment of the AQ molecules have a substantial influence on their electrochemical performance
IR analysis reveals significantly stronger π−π interactions and a lower degree of disorder in the AQ thin-film over the AQ powder electrodes. This has been further augmented by computational investigations of different charged states of AQ on a carbon carrier substrate obtained via basin hopping global minimization at the SCC DFTB/3ob level
Summary
Organic semiconducting materials based on small molecules like quinones, which build the core semiconductor element, have gained increasing interest as novel candidates for naturederived organic electrodes.[1] Such molecules are found in the bark and roots of certain plants and have previously been utilized as centuries-old natural dyes.[2] More recently, other useful commercial applications, such as organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), and organic solar cells (OPVs), have been added, owing to their high conductivity and minimum footprint in nature.[3−6] These low-molecular-weight carbonyl compounds are processable into thin films that demonstrate a long-range order due to extensive intermolecular π−π interactions, resulting in a decent charge carrier transport and current collector adhesion.[1,7−9] carbonyl compounds are capable of reversible charge storage via an enolization-type reduction reaction and a reverse oxidation reaction of the carbonyl group, leading to energy densities and power-rate performances that are comparable or superior to state-of-the-art lithium (Li) ion batteries (LIBs).[6,10−12] Especially anthraquinone (AQ) and its derivatives[13] have been previously investigated as promising cathode materials for various organic metal ion batteries,[5,14−16] due to their high theoretical capacity of 257 mAh g−1.17−24 Since their redox potential fits well within the voltage stability window of most battery electrolytes, AQ-based electrodes may serve as model compounds for the study of low-cost and energy-efficient electrodes. The choice for Na as the central metal ion is mainly driven by its high natural abundance, being about ten thousand times higher than that for Li.[26−28] In recent years, Received: December 2, 2020 Revised: January 11, 2021 Published: February 10, 2021
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