Growing demand for electric vehicles and more sustainable forms of transport means finding new forms of energy storage such as batteries, supercapacitors, and fuel cells. Currently, a major challenge facing the industry is the poor performance quality of rechargeable batteries, which often lose energy and power too quickly over time.
A novel and affordable rechargeable iron-oxygen battery containing a biphase electrolyte of molten carbonate and solid oxide was developed that merges the merits of a solid-oxide fuel cell and molten metal-air battery, offering significantly improved battery reaction kinetics and power capability without compromising the energy capacity. Since the major challenge to rechargeable metal-oxygen batteries resides in the sluggish kinetics of electrode reactions, resulting in low energy and power densities, activation of the reactions of both the negative and positive electrodes is crucial for high-performance rechargeable metal-oxygen batteries.
Researchers elevated the working temperature of the metal-oxygen battery using metals such as iron as a base, as this can be activated at a high temperature and keeps the cost low. Solid oxide fuel cells use tin or bismuth as negative electrode materials, but one issue was metal oxides forming between the metal and solid electrolyte and impeding the ion conductivity. One type of high-temperature metal-oxygen battery is the molten air battery that can use base metals for fast multiple electron charge transfer in molten salts. The molten salts have the capability to dissolve metal oxides. The resulting molten salt iron-oxygen battery with a bi-phase electrolyte of molten carbonate and solid oxide merges the merits of both types of battery.
The new battery has potential application in the area of grid-scale and renewable energy storage; molten salts are the ideal storage fluid for solar heat at high temperatures. Therefore, the molten salt iron-oxygen battery is, in principle, capable of storing both the solar heat and electricity, which is desirable for both domestic and industrial energy needs.