Molten-salt battery
Traditional non-rechargeable thermal batteries can be stored in their solid state at room temperature for long periods of time before being activated by heating.
[1][2] Thermal batteries originated during World War II when German scientist Georg Otto Erb developed the first practical cells using a salt mixture as an electrolyte.
Erb developed batteries for military applications, including the V-1 flying bomb and the V-2 rocket, and artillery fuzing systems.
This information was subsequently passed on to the United States Ordnance Development Division of the National Bureau of Standards.
[3] When the technology reached the United States in 1946, it was immediately applied to replacing the troublesome liquid-based systems that had previously been used to power artillery proximity fuzes.
[10] A consortium formed by Tokyo Electric Power Co. (TEPCO) and NGK Insulators Ltd. declared their interest in researching the NaS battery in 1983, and became the primary drivers behind the development of this type ever since.
TEPCO chose the NaS battery because its component elements (sodium, sulfur and ceramics) are abundant in Japan.
The first large-scale field testing took place at TEPCO's Tsunashima substation between 1993 and 1996, using 3 × 2 MW, 6.6 kV battery banks.
The positive electrode is composed mostly of materials in the solid state, which reduces the likelihood of corrosion, improving safety.
[16] ZEBRA batteries are currently manufactured by FZSoNick[18] and used as a power backup in the telecommunication industries, Oil&Gas and Railways.
After shutdown a fully charged battery pack loses enough energy to cool and solidify in five-to-seven days depending on the amount of insulation.
The lower operating temperature allowed the use of a less-expensive polymer external casing instead of steel, offsetting some of the increased cost of cesium.
[28] Innovenergy in Meiringen, Switzerland has further optimised this technology with the use of domestically sourced raw materials, except for the nickel powder component.
Despite the reduced capacity compared with lithium-ion batteries, the ZEBRA technology is applicable for stationary energy storage from solar power.
In 2022, the company operated a 540 kWh storage facility for solar cells on the roof of a shopping center, and currently produces over a million battery units per year from sustainable, non-toxic materials (table salt).
[29] Professor Donald Sadoway at the Massachusetts Institute of Technology has pioneered the research of liquid-metal rechargeable batteries, using both magnesium–antimony and more recently lead–antimony.
In 2011, the researchers demonstrated a cell with a lithium anode and a lead–antimony cathode, which had higher ionic conductivity and lower melting points (350–430 °C).
Once activated, they provide a burst of high power for a short period (a few tens of seconds to 60 minutes or more), with output ranging from watts to kilowatts.
One design uses a fuze strip (containing barium chromate and powdered zirconium metal in a ceramic paper) along the edge of the heat pellets to initiate the electrochemical reaction.
Another design uses a central hole in the middle of the battery stack, into which the high-energy electrical igniter fires a mixture of hot gases and incandescent particles.
The standard heat source typically consists of mixtures of iron powder and potassium perchlorate in weight ratios of 88/12, 86/14, or 84/16.
A radioisotope thermal generator, such as in the form of pellets of 90SrTiO4, can be used for long-term delivery of heat for the battery after activation, keeping it in a molten state.
In these batteries the electrolyte is immobilized when molten by a special grade of magnesium oxide that holds it in place by capillary action.
This powdered mixture is pressed into pellets to form a separator between the anode and cathode of each cell in the battery stack.
