Molecular-Scale Elucidation of Ionic Charge Storage Mechanisms in Rechargeable Aluminum–Quinone Batteries

Abstract

Rechargeable aluminum–organic batteries are of great interest as a next-generation energy storage technology because of the earth abundance, high theoretical capacity, and inherent safety of aluminum metal, coupled with the sustainability, availability, and tunabilty of organic molecules. However, the ionic charge storage mechanisms occurring in aluminum–organic batteries are currently not well understood, in part because of the diversity of possible charge-balancing cations, coupled with a wide array of possible binding modes. For the first time, we use multidimensional solid-state NMR spectroscopy in conjunction with electrochemical methods to elucidate experimentally the ionic and electronic charge storage mechanism in an aluminum–organic battery up from the atomic length scale. In doing so, we present indanthrone quinone (INDQ) as a positive electrode material for rechargeable aluminum batteries, capable of reversibly achieving specific capacities of ca. 200 mAh g–1 at 0.12 A g–1 and 100 mAh g–1 at 2.4 A g–1. We demonstrate that INDQ stores charge via reversible electrochemical enolization reactions, which are charge compensated in chloroaluminate ionic liquid electrolytes by cationic chloroaluminous (AlCl2 +) species in tetrahedral geometries. The results are generalizable to the charge storage mechanisms underpinning anthraquinone-based aluminum batteries. Lastly, the solid-state dipolar-mediated NMR experiments used here establish molecular-level interactions between electroactive ions and organic frameworks while filtering mobile electrolyte species, a methodology applicable to many multiphase host–guest systems.

Redox‐Bipolar Polyimide Two‐Dimensional Covalent Organic Framework Cathodes for Durable Aluminium Batteries

“…The apparent line broadening of the imide C=O 13 C signal could originate from the heteronuclear 13 C‐ 27 Al dipole‐dipole interaction, as the interaction with quadrupole nuclei (like 27 Al) normally induces the line broadening of spin‐1/2 nuclei (like 13 C) even under MAS (Figure 5a). [42, 45] Additionally, the reduction of the imide C=O bond was manifested by the O 1s XPS spectrum of the fully discharged 2D‐NT‐COF30 electrode (Figure 5b), in which an additional C−O peak at 534.8 eV associated with the formed enolate species was detected [46, 37] . Figure 5c compares the N 1s XPS spectra of the pristine, fully charged, and fully discharged 2D‐NT‐COF30 electrodes.…”

“…82 ppm was detected, suggesting the appearance of cationic AlCl 2 + (Figure 4b). [42] 27 Al spin‐spin relaxation ( T 2 relaxation, correlated to the dephasing of spin coherence) analysis (Figure 4c) was also carried out for the fully discharged 2D‐NT‐COF30 electrode based on the spin‐echo experiment. Since the immobilization degree of the Al species increases along with the strengthening binding between Al species and the 2D‐COF, the shorter T 2 relaxation is normally indicative of the stronger binding of the Al species to 2D‐COF.…”

“…(Figure 5a). [42,45] Additionally, the reduction of the imide C=O bond was manifested by the O 1s XPS spectrum of the fully discharged 2D-NT-COF30 electrode (Figure 5b), in which an additional CÀ O peak at 534.8 eV associated with the formed enolate species was detected. [46,37] Figure 5c compares the N 1s XPS spectra of the pristine, fully charged, and fully discharged 2D-NT-COF30 electrodes.…”

Redox‐Bipolare Polyimid Zweidimensionale Covalent Organic Framework Kathoden für langlebige Aluminum‐Akkumulatoren

“…82 ppm beobachtet, was auf das Auftreten von kationischem AlCl 2 + hindeutet (Abbildung 4b). [42] Die 27 Al‐Spin‐Spin‐Relaxation ( T 2 ‐Relaxation, korreliert mit der Dephasierung der Spin‐Kohärenz) (Abbildung 4c) wurde auch für die vollständig entladene 2D‐NT‐COF30‐Elektrode auf der Grundlage des Spin‐Echo‐Experiments durchgeführt. Da der Immobilisierungsgrad der Al‐Spezies mit der stärkeren Bindung zwischen Al‐Spezies und 2D‐COF zunimmt, ist die kürzere T 2 ‐Relaxation normalerweise ein Hinweis auf die stärkere Bindung der Al‐Spezies an 2D‐COF.…”

“…Die offensichtliche Linienverbreiterung des Imid‐C=O− 13 C‐Signals könnte von der heteronuklearen 13 C‐ 27 Al‐Dipol‐Dipol‐Wechselwirkung herrühren, da die Wechselwirkung mit Quadrupolkernen (wie 27 Al) normalerweise die Linienverbreiterung von Spin‐1/2‐Kernen (wie 13 C) selbst unter MAS hervorruft (Abbildung 5a). [42, 45] Zusätzlich wurde die Reduktion der Imid‐C=O‐Bindung durch das O 1s‐XPS‐Spektrum der vollständig entladenen 2D‐NT‐COF30‐Elektrode (Abbildung 5b) deutlich, in dem ein zusätzlicher C‐O‐Peak bei 534.8 eV, der mit der gebildeten Enolat‐Spezies assoziiert ist, entdeckt wurde [46, 37] . Abbildung 5c vergleicht die N 1s XPS‐Spektren der unberührten, vollständig geladenen und vollständig entladenen 2D‐NT‐COF30‐Elektroden.…”