History of the Molten Salt Batteries
The first molten salt batteries actually weren't intended to operate for very long periods of time at all, but were instead used as single activation primary batteries for bombs and rockets. Invented by German WWII era scientist Georg Otto Erb, the first practical cells were called thermal batteries and while they were never used during the war, the United States Ordnance Development Division would eventually acquire the technology and use it to power rockets, bombs, and even nuclear weapons. These early batteries could last indefinitely (over 50 years) in the solid state while supplying a huge burst of power. Today thermal batteries are still used as the primary source of power for missiles like the AIM-9 Sidewinder, BGM-109 Tomahawk and the MIM-104 Patriot.
In 1966 Ford Motor Company invented the Sodium-Sulfur (NaS) liquid metal battery for electric vehicle application. The high power density and high energy capacity looked promising but the high operating temperature of 290-390 °C caused Ford to drop research and development. In 1983, Tokyo Electric Power Company (TEPCO) and Nippon Gaishi Kaisha (NGK) realized the potential for NaS battery system as a solution for grid storage and began research and development of the technology. In 1993 the first large-scale prototype of such a system was field tested at TEPCO’s Tsunashima substation. The system consisted of three 2 MW, 6.6 KV battery banks. This laid the groundwork for NGK/TEPCO consortium’s current line of grid storage NaS batteries, which produce 90 MW of storage capacity every year.
Meanwhile in Pretoria, South Africa, 1985, the Zeolite Battery Research Africa Project (ZEBRA) led by Dr. Johan Coetzer at the Council for Scientific and Industrial Research, invented the first sodium nickel chloride battery. It had a specific energy of 90 Wh/kg, a notably stable beta alumina solid electrolyte, and enhanced corrosion resistance over NaS. This design, while novel, has yet to see large scale commercial grid storage applications and remains a hot topic in battery research and development. They have however been deployed by FIAMM Sonick and used in the Modec Electric Van.