Keggin-type Polyoxometalates as Bidirectional Redox Mediators for Rechargeable Batteries

Abstract

Keggin-type polyoxometalates (POMs), which possess multiple redox centers, were investigated as bidirectional redox mediators in rechargeable batteries. A series of POMs have been synthesized and employed in sulfur electrodes where neither the active material nor the discharge product were electrically conductive. POMs were found to have multiple redox potentials covering the range of the equilibrium potentials of the redox reactions of sulfur, which consequently facilitated both charge and discharge reactions. In particular, [SiMo 12 O 40 ] 4− offered a large discharge capacity of 1270 mAh g −1 by accelerating the reduction of shorter, less soluble polysulfides, leading to a higher cycling performance. The mediator role was confirmed via an X-ray photoelectron spectroscopy study on the cycled cathodes. Density functional theory calculations showed that the redox potentials of POMs are tunable, allowing selective design of suitable POM molecules for specific battery electrodes.

Bifunctional K3PW12O40/Graphene Oxide-Modified Separator for Inhibiting Polysulfide Diffusion and Stabilizing Lithium Anode

“…Moreover, each tungsten (W) atom of Keggin-type KPW is in the highest valence state (VI), which endows phosphotungstate with a unique multielectron storage capacity and robust redox ability. The KPW cluster and its corresponding reduced KPW species can reversibly store or transfer multiple electrons during reactions. , Subsequently, X-ray photoelectron spectroscopy (XPS) was further employed to investigate the interaction between Li 2 S 4 and KPW clusters (Figure S5c). Comparing the pristine KPW cluster, we observed a slight broadening of the W 6+ 4f doublet and a shift toward lower binding energies (BEs) of 37.1 and 34.8 eV for the W 5+ 4f 5/2 and W 5+ 4f 7/2 peaks, respectively, upon the adsorption of Li 2 S 4 .…”

“…The KPW cluster and its corresponding reduced KPW species can reversibly store or transfer multiple electrons during reactions. 50,55 Subsequently, X-ray photoelectron spectroscopy (XPS) was further employed to investigate the interaction between Li 2 S 4 and KPW clusters (Figure S5c). Comparing the pristine KPW cluster, we observed a slight broadening of the This indicates the oxidation of Li 2 S 4 into long-chain polysulfide (Figure S5d).…”

Graphene-supported polyoxometalate entrapped in a MIL-88A network with highly efficient conversion of polysulfides in Li–S batteries

“…15–19 In recent years, the application of POMs has been extended to LSB systems to conquer the shuttle effect. According to previous reports, 20,21 it can be concluded that W-containing POMs present appropriate redox potentials that cover the range of equilibrium potentials of sulfur redox reactions, and thus are more conducive to enhancing the electrochemical property of LSBs. Notably, when bulk POMs are utilized as the sulfur-fixing materials, the inevitable agglomeration will bury the effective active sites of POMs so as to limit their adsorption or catalysis function for LiPSs.…”

Ion-channel aligned gas-blocking membrane for lithium-air batteries

“…This ceramic membrane also completely separates the anode and cathode sides, allowing the use of different electrolyte compositions on each side 6 . Carefully selected electrolytes can suppress excessive reactions on the metal, and this allows the uses of mediators 8–10 and aqueous electrolytes on the cathode 11–23 . However, thick ceramic plates are needed to compensate for their mechanical fragility, which adds significant volume and mass to the cell and lowers the specific energy of the Li-air batteries.…”