What is a sodium sulfur battery?

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.

Why are sodium sulfur batteries more economical?

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).

What is a sodium polysulfide battery?

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.

Are molten sodium-sulfur batteries more energy efficient than lithium-ion batteries?

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.

Why are molten sodium-sulfur batteries so bad?

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).

What happens if a battery holds molten sodium?

Sodium has a lower melting point, around 98 °C, so a battery that holds molten sulfur holds molten sodium by default. This presents a serious safety concern; sodium can spontaneously ignite in air, and sulfur is highly flammable.