A Room‐Temperature All‐Solid‐State Na‐Ag Battery with a Long Cycle Life and Low Overpotential

Aqueous Zn‐Ag batteries have been developed and commercialized for nearly a century, offering stable discharge and high specific energies. Sodium, with its lower redox potential, smaller charge‐to‐mass ratio, and abundant resources, presents a promising alternative to zinc. In this study, we successfully developed an all‐solid‐state Na‐Ag battery system. This battery demonstrates stable discharge and charge voltages, low overpotential (0.27 V), high energy efficiency (>91%), and long cycle life under moderate humidity at room temperature. The reaction mechanism was elucidated through combined analyses using differential electrochemical mass spectrometry (DEMS), X‐ray diffraction (XRD), Raman spectroscopy, and X‐ray photoelectron spectroscopy (XPS). Our findings indicate that metallic Ag in the cathode materials acts as an effective catalyst for the oxygen reduction reaction during the initial discharge process, forming NaOH as the discharge product. Ag is then oxidized during the charging process and recovered during discharge, serving as an active reactant in the Na‐Ag battery. This work demonstrates superior performance of all‐solid‐state Na‐Ag battery over aqueous Zn‐Ag battery. Na‐Ag battery may be of interest in applications with stringent requirements on stable discharge voltage and high specific energy.