Molten Salt-Based Batteries for Safe, Reliable Long-Duration Energy Storage

Long-duration energy storage (LDES) continues to emerge as a critical necessity in the evolving sustainable, carbon-free global energy infrastructure. While batteries are expected to play key roles in meeting select LDES demands, both current and developing technologies will be challenged to safely and reliable store energy at unprecedented levels. The required increases in battery scale, durability, and longevity needed for these very large systems introduces new issues associated with safety and reliability that must be considered. Here, we describe how molten salt-based batteries, formulated from earth-abundant reagents, may offer promise for safe and reliable storage from several different perspectives including long discharge duration (e.g., &gt;6-10 hours), long storage duration between charge and discharge (long shelf-life), or long battery lifetime (&gt;10-15 years). We will describe here the structure and chemistry of emerging molten-salt based batteries and highlight why they may be well-suited for LDES. For example, we will consider emerging low temperature (near 100°C) molten sodium-halide batteries, comprising a molten sodium anode, a fully inorganic, molten sodium iodide-based metal halide salt catholyte, and an efficient solid state sodium ion-conducting separator. These batteries show high voltage (&gt;3.5V) and promising cycle life at 110°C. Importantly, in simulated failures, these molten salt-based batteries do not exhibit thermal runaway or generate hazardous gas overpressure. For LDES applications, these fully inorganic systems are projected to be scalable for long-duration discharge, they have historically long lifetimes, and they can be utilized for long shelf-life storage and seasonal storage, as charged batteries can be “frozen,” providing reliable energy storage with extremely low self-discharge. Continued advances in this class of batteries will further open the door to additional, low-cost battery chemistries. <br/> <br/>Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & 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.