Iron-air batteries can be very durable and withstand 10,000 charge-discharge cycles, significantly more than lithium-ion batteries. That sounds good, but the system has some serious disadvantages. The iron-air battery has an unfavorable relationship between performance and capacity. A lithium battery can typically build up or release its charge in one to two hours. The iron-air battery takes about 100 hours.
It is therefore only suitable to a very limited extent to compensate for the daily cycle, but is very good for bridging longer power shortage situations. The efficiency is not specified on the website, however, is usually very low for metal-air batteries . When asked by “Spektrum.de”, Form Energy named a typical value of 40 percent for the first commercial systems. This makes it roughly comparable to hydrogen technology. Nevertheless, the approach is promising, Form Energy has already booked the first major orders, and improvements are certainly still possible.
The American company ESS Inc. has brought a third approach to market maturity. She builds a so-called flow battery. Two liquid electrolytes are pumped along either side of a semi-permeable membrane. The potential difference between the electrolytes generates a voltage at the electrodes. As soon as the circuit is closed, current flows, similar to all other electrochemical wet cells. If an external voltage is applied to the cell, the reaction is reversed and the electrolyte is recharged. The size of the membrane determines the performance, the size of the electrolyte tank determines the capacity of the battery. Performance and capacity are therefore separate in the flow battery, although not always completely.
The first systems go into operation
ESS Inc. uses a liquid iron salt – ferric chloride – as an electrolyte. It is cheap and available in almost unlimited quantities. The devil is in the details here, too. It took the company from 2011 to 2019 to turn a plausible functional principle into a ready-to-sell battery. The first commercial system was delivered in 2022. In an interview with »Spektrum.de«, Alan Greenfields, head of the European business, stated that the system’s efficiency was around 60 to 70 percent. ESS Inc. primarily wants to serve the area of load shifting over periods of six to twelve hours.
The price of the system is a matter of negotiation, but at least according to Greenfield it is very reasonable “if you take into account a service life of 25 years”. On the other hand, redox flow batteries have a comparatively low power density. The “Energy Warehouse” from ESS Inc. is housed in a twelve meter long shipping container and stores 400 kWh. Tesla’s Megapack accommodates 3.9 MWh of lithium-ion batteries, almost ten times as much, in a container nine meters long.
In Europe, ESS Inc. will deploy a first system at Amsterdam’s Shiphol Airport. So far there are no locations in Germany, but there is cooperation with German companies for projects in other European countries. Form Energy’s and ESS’s systems aren’t critically dependent on Chinese components either, which could certainly be an advantage in negotiations in the US, Australia and Europe.
The systems from ESS Inc., Form Energy and Tesla are also suitable for relieving the load on the distribution grids, i.e. the low-voltage grids for which municipal utilities are responsible. Mobile, container-sized units can temporarily store the electricity produced by the many photovoltaic systems on house roofs during the day, so that it can be released again in the evening. The energy supplier EnBW already offers such systems at, and the competitor E.ON sees it as “a necessary addition to efficient grid expansion”.
Maybe Chinese companies will get into the large battery business after all. CATL, one of the world’s largest suppliers of lithium ion batteries, plans to start mass production of sodium ion batteries this year. The construction principle is very similar, but the energy density is somewhat lower. For this, the production costs are at least 20 percent, according to other estimates 30 to 50 percent less. The Chinese company HiNa is apparently already delivering. Their sodium batteries are in the Hua Xianzi small electric car, which has just been presented by JAC Motors and VW for the Chinese market.
The technology is still new and little is known about service life, self-discharge or efficiency. If the sodium ion batteries achieve values similar to those of lithium ion batteries, it will certainly be a bit more difficult for the competitors to attack the market dominance of Chinese companies.