Long-life Na–O2 batteries with high energy efficiency enabled by electrochemically splitting NaO2 at a low overpotential

Abstract

Metal–air batteries are thought to be the ultimate solution for energy storage systems owing to their high energy density. Here we report a long-life Na–O₂ battery with a high capacity of 750 mA h g_carbon⁻¹ by manipulating the nucleation and growth of nano-sized NaO₂ particles in a vertically aligned carbon nanotubes (VACNTs) network with a large surface area. Benefiting from the kinetically favorable formation of NaO₂ reaction with a low overpotential of ∼0.2 V, the electrical energy efficiency is as high as 90% for up to 100 cycles. A good rate performance (∼1500 mA h g_carbon⁻¹ at 667 mA g_carbon⁻¹) can be achieved through pre-deposition of a thin NaO₂ layer. This study encourages the exploration of the key factors influencing the performance of metal–air batteries, as well as Na-based batteries characterized by phase transformation or conversion reactions.