A rechargeable all-solid-state sodium peroxide (Na2O2) battery with low overpotential

Abstract

Na–O2 batteries have been attracting attention owing to their intrinsically high theoretical energy density. Several Na–O2 systems can produce various discharge products with different electrochemical performances. For example, sodium superoxide (NaO2) batteries have a low overpotential, and sodium peroxide (Na2O2) batteries have a high capacity. Studies of Na2O2 batteries are relatively scarce, owing to the difficulty of forming pure Na2O2 discharge products. A pure Na2O2 battery system is highly desirable for fully exploring the formation and decomposition of Na2O2 in Na–O2 batteries and evaluating their potential. This model of a Na2O2 battery should also be compatible with in situ characterization. To this end, we constructed a simple rechargeable all-solid-state Na2O2 battery. Using a nanoporous gold film as the cathode and Na–β″-Al2O3 as a solid electrolyte, we assembled a Na–O2 battery that can produce and decompose Na2O2. The all-solid-state Na–O2 battery is a simple model for conducting in situ ambient-pressure x-ray photoelectron spectroscopy (APXPS) investigations. The battery can be cycled at a low overpotential (≈450 mV). Qualitative and quantitative analyses of the APXPS and Raman results demonstrated that Na2O2 was the main discharge product and its transformation occurred during the charge and discharge periods. The operando investigation of this type of all-solid-state Na2O2 battery can help in the comprehensive exploration of the potential of Na–O2 batteries.