Low Temperature Molten Sodium-Based Batteries for Large Scale Electrical Energy Storage

Abstract

Despite the tremendous advances in batteries for portable electronics and vehicle electrification, truly effective battery technologies for large scale energy storage remain relatively underdeveloped. These systems have distinct requirements as safe, low-cost, reliable systems, critical to robust and agile energy distribution, integration of renewable energy, effective emergency response, and even emerging national defense initiatives. Here, we describe a promising new class of molten sodium-halide batteries that show exciting potential as safe, cost-effective, long-lived batteries for large-scale applications. These Na-NaI batteries comprise a molten sodium anode and a molten NaI-based halide salt catholyte, separated by highly conductive solid-state sodium-ion conducting membrane. This NaI-based system offers a higher voltage (>3V) than traditional molten sodium batteries and enables the use of fully molten catholytes desired for long cycle life. By engineering the materials chemistry of these batteries, we have driven down operating temperature to near 100°C, utilizing chemistries that avoid potential problems with thermal runaway or flammable organic electrolytes that often plague other battery technologies. This dramatic reduction of operating temperature (compared to ~300°C typical of traditional molten sodium batteries) opens the door to valuable reduction in costs and extension of battery life. This presentation will discuss specific advances in molten catholyte composition and electrochemistry, the performance of the solid-state separators at these reduced temperatures, and the efficient cycling behavior of laboratory-scale prototypes. The encouraging performance of these innovative “low” temperature molten salt batteries promises new opportunities to address the widespread need for safe, reliable, and cost-effective large scale energy storage solutions. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.