Gel Adsorbed Redox Mediators Tempo as Integrated Solid-State Cathode for Ultra-Long Life Quasi-Solid-State Na-Air Battery

In metal-air batteries, the integrated solid-state cathode is considered a promising design because it can solve the problem of high interfacial resistance of conventional solid-state cathodes. However, solid discharge products cannot be efficiently decomposed in an integrated solid-state cathode, resulting in batteries that are unable to operate for long periods of time. Herein, an integrated solid-state cathode (Gel-Tempo cathode) of sodium-air batteries (SABs) capable of promoting efficient decomposition of discharge product Na2O2 is designed. The Gel-Tempo cathode is synthesized by cationic-& pi; interaction of redox mediator 2,2,6,6-tetramethyl-1-piperidinyloxy (Tempo) and ionic liquid with carbon nanotubes. The Gel-Tempo cathode serves multiple functions as a redox mediator, flame retardancy, and high stability to air. In quasi-solid-state SABs, the Gel-Tempo cathode reduces overpotential to 1.15 V and improves coulomb efficiency to 84.5% (at a limited discharge capacity of 3000 mAh g-1) compared to gel cathodes. Experiments and density functional theory calculations indicate that Tempo significantly reduces the Gibbs free energy in the decomposition reaction of Na2O2, and high Tempo content is more conducive to enhancing the decomposition kinetics of Na2O2 and hence resulting in an ultra-long cycle life (1746 h). This work is crucial to promote practical applications of SABs, providing guidelines for functionalization design of integrated solid-state cathodes for metal-air batteries. In this study, for the first time, a strategy based on cation-& pi; interaction adsorption 2,2,6,6-tetramethyl-1-piperidinyloxy (Tempo) is applied to prepare an integrated solid-state cathode (Gel-Tempo cathode) for a sodium-air battery (SAB). Benefiting from the redox mediator and high air stability of the Gel-Tempo cathode, the fabricated quasi-solid-state SAB of the Gel-Tempo cathode achieves a state-of-the-art cycle life of more than 1746 h (72 days).image