battery preheating

A sodium–sulfur (NaS) battery is a type of molten-salt battery that uses liquid sodium and liquid sulfur electrodes. This type of battery has a similar energy density to lithium-ion batteries, and is fabricated from inexpensive and low-toxicity materials. Due to the high operating temperature required (usually between 300 and 350 °C), as well as the highly reactive nature of sodium and sodium polysulfides, these batteries are primarily suited for stationary energy storage applications, rather than for use in vehicles. Molten Na-S batteries are scalable in size: there is a 1 MW microgrid support system on Catalina Island CA (USA) and a 50 MW/300 MWh system in Fukuoka, Kyushu, (Japan).
Despite their very low capital cost and high energy density (300-400 Wh/L), molten sodium–sulfur batteries have not achieved a wide-scale deployment yet compared to lithium-ion batteries: there have been ca. 200 installations, with a combined energy of 5 GWh and power of 0.72 GW, worldwide. vs. 948 GWh for lithium-ion batteries. Poor market adoption of molten sodium-sulfur batteries has possibly been due to perceived safety and durability issues, such as a short cycle life of fewer than 1000 cycles on average (although there are reports of 15 year operation with 300 cycles per year). In contrast to these concerns, a recent technical data sheet indicates a cycle life of 20 years or 7300 cycles with less than 1% energy degradation per year. Also TÜV Rheinland assessed commercial NaS batteries and their safety features coming to the conclusion that "under practical conditions it is not possible to ignite an intact NGK Insulators NaS battery module (manufactured after 2011) or to trigger other dangerous scenarios from the outside or from within."
Like many high-temperature batteries, sodium–sulfur cells become more economical with increasing size. This is because of the square–cube law: large cells have less relative heat loss, so maintaining their high operating temperatures is easier. Commercially available cells are typically large with high capacities (up to 500 Ah).
A similar type of battery called the ZEBRA battery, which uses a NiCl2/AlCl3 catholyte in place of molten sodium polysulfide, has had greater commercial interest in the past, but As of 2023 there are no commercial manufacturers of ZEBRA. Room-temperature sodium–sulfur batteries are also known. They use neither liquid sodium nor liquid sulfur nor sodium beta-alumina solid electrolyte, but rather operate on entirely different principles and face different challenges than the high-temperature molten NaS batteries discussed here.

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