Low Temperature Sodium-Sulfur Battery Enabled By Superior Molten Na Wettability

Abstract

Sodium based batteries are inexpensive and widely available, making it a promising candidate grid energy storage application. Particularly, high temperature molten sodium batteries, such as sodium–sulfur (NaS) and sodium–metal halide (ZEBRA) batteries, have received increasing attentions, where the enormous capacity demand of grid storage will require the natural abundance of raw materials and a reasonable footprint of the facility. NaS batteries use molten sulfur/polysulfides as the cathode material and operate typically at 350 °C.Although operating at higher temperatures, the state-of-art high-temperature NaS batteries offer high system level energy and long-life expectancy (over 10 years) all at a low cost of materials.In fact, conventional high-temperature molten NaS batteries have already been in production and widely implemented as test units for grid storage or for supplementing wind and solar installations. Despite of its longevity and high energy density, NaS battery technology still faces tremendous challenges for further the market penetration due to their safety concerns and high cost. Reducing the operating temperatures of molten NaS batteries would retard the severity of discharge from cell failures and make them safer. Moreover, lower temperatures allow the integration of cost-effective polymer materials as seals, replacing more expensive techniques used for NaS batteries in the past. Improving sodium wetting by engineering the β"-Al2O3 solid-state electrolytes (BASE)-anode interface is one of the most important topics for lowering the operating temperature of NaS battery. In here, we present a new surface treatment method to greatly improve the Na wettability on surface of BASE, and report that the performance of low-temperature (<150 °C) NaS battery is drastically improved in both capacity and stability. Innovations in surface modification boost the interfacial activity of BASE even further at lower operating temperature and make NaS battery more competitive in the upcoming challenges in grid energy storage applications.