Calcium-based batteries promise low-cost production and high energy density. This technology from the laboratory has the potential to replace lithium-ion technology as the energy store of the future. However, the electrolytes available to date have not been able to charge calcium batteries at room temperature.
"In the medium term, lithium-ion batteries will reach their limits due to their performance and some of the raw materials used in them and could then not be used wherever energy storage would make sense in the context of the energy revolution. We only have limited deposits of raw materials such as cobalt, nickel and lithium that are necessary for production," says Professor Maximilian Fichtner, spokesman for the Cluster of Excellence. He considers calcium to be a promising candidate because, in contrast to lithium, calcium can take up and take up two electrons per atom and because it delivers a voltage similar to that of lithium: "Calcium is the fifth most abundant element in the earth's crust. It is available evenly throughout the earth and has the advantage of being safe, non-toxic and inexpensive."
However, there has so far been a major hurdle in the development of the calcium battery: In contrast to the established lithium-ion technology or the more recent sodium or magnesium technology, no practicable electrolytes existed to date to produce rechargeable calcium batteries. "It is only a few years since experimental electrolytes and thus prototypes of the calcium battery have been available," explain Dr. Zhenyou Li, first author of the study, and Dr. Zhirong Zhao-Karger, project manager, who both work in the POLiS (Post Lithium Storage Cluster of Excellence) excellence cluster at KIT.
The researchers have now succeeded in synthesizing a class of new electrolytes based on special organic calcium salts that enable charging processes even at room temperature. Using the new electrolyte as an example, the researchers have now been able to demonstrate that calcium batteries with high energy density, storage capacity and rapid charging capability are possible. They presented their results in the trade journal Energy & Environmental Science.
The new electrolyte class now creates an important basis for transferring calcium batteries from the laboratory to the application. In electric cars, mobile electronic devices and stationary network storage devices, they could one day replace the lithium-ion battery that had previously dominated the market. The new electrolytes are a first important step," emphasizes Fichtner. "We still have a long way to go before we have a market-ready calcium battery.
Zhenyou Li, Olaf Fuhr, Maximilian Fichtner, Zhiron Zhao-Karger: Towards stable and efficient electrolytes for room-temperature rechargeable calcium batteries. Energy & Environmental Science, 2019 DOI: 10.1039/c9ee01699f.