Rational Design of Cell Configurations for High-Performance Na-O2 Batteries

Abstract

Growing environmental concerns and continuously surging demand for energy have stimulated extensive interests in exploring advanced energy storage systems. Na-O2 batteries have recently attracted an extensive amount of attention due to their high theoretical energy density, which is 6-9 folds higher than that of the conventional Li-ion batteries [1]. Moreover, the high round-trip energy efficiency, as well as the natural abundance and low cost of sodium resources make Na-O2 batteries promising for large-scale application [2]. However, the practical application of Na-O2 batteries has been hindered by their poor cycling performance [3]. Parasitic reactions and continuous consumption of the metallic Na anode caused by O2/O2 - crossover are one of the main causes of Na-O2 battery failure [4]. Except for the Na degradation, the implementation of metallic Na anode in Na-O2 battery is associated with dendrite formation [5].To address these issues, we successfully designed novel Na-O2 cell configurations. Firstly, a novel Na-O2 cell using electrically connected carbon paper (CP) with Na metal as a protected anode is developed. The CP demonstrates great effectiveness in addressing the fatal issue of cell short circuit by facilitating the dense Na deposition within the 3D CP skeleton. On the other hand, the CP acts as a protective layer to alleviate the Na corrosion caused by O2/O2- crossover. Consequently, a significantly enhanced Na-O2 cell cycling performance with a low charge overpotential can be achieved. Since the diffusion of O2/O2 - from the cathode to anode mainly through the electrolyte, and a physical barrier to retain the O2/O2 - on the cathode side would also be effective. Therefore, for the first time, we successfully developed a hybrid solid-electrolyte Na-O2 battery based on solid-state electrolyte (SSE) and a protected Na anode. The dense structure of SSE effectively suppressed the O2/O2 - crossing over, which simultaneously mitigate the Na corrosion and decrease the reversible capacity loss. More importantly, the SSE is chemical stable against the O2 - radical, benefiting to achieving high-performance Na-O2 batteries with high capacities and long cycle lives.In conclusion, the importance of addressing issues of Na dendrite growth and O2/O2 - crossover were presented. Although more future work is needed to make Na-O2 battery system commercially viable, the strategies developed here provide guidance to achieve Na-O2 cells with longer lifespans and better cycling performance. Reference [1] H. Yadegari, et al., Advanced Materials, 28 (2016) 7065-7093.[2] X. Li, et al. Carbon Energy, 2019, 1:141-164.[3] X. Lin, et al. Chemistry of Materials, 2020, 32, 7, 3018-3027.[4] S. Wu, et al. Advanced Functional Materials, 2018, 28, 1706374.[5] X. Bi, et al., Chemical Communications, 51 (2015) 7665-7668.