Boosting Na-O2 battery performance by regulating the morphology of NaO2

Abstract

Na-O2 batteries, as one of the most promising advanced battery technologies, have attracted attention due to their low cost and high energy density. The formation mechanism of discharge products in Na-O2 batteries directly relates to their electrochemical performance, yet our understanding of it is still meagre. In this work, the growth pattern of NaO2 is investigated by in-situ X-ray diffraction and the morphologies of discharge products have been linked to their corresponding electrochemical performance. Furthermore, the ratio between the rates of solvation and desolvation is proposed for the first time as a descriptor (denoted as α) for predicting the morphological variation of NaO2 by tuning the ratio of 1, 2-dimethoxyethane (DME): tetraethylene glycol dimethyl ether (TEGDME) in electrolyte (from 0:5 to 5:0). As a result, combined with the optimized electrolyte (DME: TEGDME of 4:1) and an efficient cathode (N-doped porous carbon), easy-to-decompose thick sheet-like NaO2 could be produced during discharge, achieving highly efficient Na-O2 batteries performance (excellent rate capability, high discharge capacity of 5812 mAh g−1, the highest reported Coulombic efficiency of 91.1%, and superior cycling performance over 100 cycles at a current density of 1000 mA g−1). This work provides new insight into the growth patterns of discharge products and paves the way to a deeper understanding of the reaction mechanism as well as improving battery performance.