A rechargeable all-solid-state sodium peroxide (Na 2 O 2 ) battery with low overpotential

Abstract Na–O 2 batteries have been attracting attention owing to their intrinsically high theoretical energy density. Several Na–O 2 systems can produce various discharge products with different electrochemical performances. For example, sodium superoxide (NaO 2 ) batteries have a low overpotential, and sodium peroxide (Na 2 O 2 ) batteries have a high capacity. Studies of Na 2 O 2 batteries are relatively scarce, owing to the difficulty of forming pure Na 2 O 2 discharge products. A pure Na 2 O 2 battery system is highly desirable for fully exploring the formation and decomposition of Na 2 O 2 in Na–O 2 batteries and evaluating their potential. This model of a Na 2 O 2 battery should also be compatible with in situ characterization. To this end, we constructed a simple rechargeable all-solid-state Na 2 O 2 battery. Using a nanoporous gold film as the cathode and Na–β″-Al 2 O 3 as a solid electrolyte, we assembled a Na–O 2 battery that can produce and decompose Na 2 O 2 . The all-solid-state Na–O 2 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 Na 2 O 2 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 Na 2 O 2 battery can help in the comprehensive exploration of the potential of Na–O 2 batteries.