A Rechargeable Solid-State Sodium-Oxygen Battery with Enhanced Energy Efficiency and Cycle Life

Sodium-oxygen (Na-O 2 ) batteries offer a promising path for the advancement of high-energy-density inexpensive storage systems to replace current state of the art Li-based batteries owing to the natural abundance and low-cost Na metal. Despite numerous studies to improve the performance of liquid-based electrolyte Na-O 2 batteries, this technology suffers from poor cycle life, electrolyte stability issues, and limited choice of cell design as well as growing safety concerns associated with liquid electrolytes. Recently, solid electrolytes received a great attention to substitute traditional liquid electrolytes used in Na-O 2 batteries, due to their ability of improving safety and energy density. However, low ionic conductivity and high impedance in contact with the anode and cathode remain as major challenges for the development suitable solid-state electrolyte for Na-O 2 batteries. In addressing these challenges, we recently have established a solid-state Na-O 2 battery cell that comprises a highly conductive composite polymer-ceramic solid electrolyte with a conductivity of 0.7 mS/cm. This solid electrolyte works in synergy with vanadium phosphide (VP) nanoparticles, serving as oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts at the cathode and Na metal anode for more than 500 reversible charge-discharge cycles at a capacity of 1000 mAh/g, achieving a low polarization gap of approximately 20 mV in the first cycle. Various electrochemical and physicochemical characterization techniques, such as Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), differential electrochemical mass spectrometry (DEMS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), were employed to gain insight into the cell chemistry and solid-state electrolyte role in the formation and decomposition of sodium oxides components such as superoxide (NaO 2 ), peroxide (Na 2 O 2 ). The findings of this study underscore the significance of proper cell component design and possible mechanisms in solid-state Na-O 2 battery technologies. This research represents a promising avenue in advancing energy conversion and storage systems, showcasing the potential of solid-state batteries with enhanced safety and performance characteristics.