Calcium battery technology promises low-cost production and high energy density. However, the electrolytes available so far have not been able to charge calcium batteries at ambient temperature. Researchers at the Karlsruhe Institute of Technology (KIT) have now presented a promising electrolyte class that makes this possible for the first time. If the breakthrough is successful, efficient, large and cost-effective energy storage systems could come within reach, and the comprehensive transition to emission-free mobility and power supply would no longer be a distant vision of the future.
Today’s predominant lithium-ion technology cannot fulfil this task on a global scale, says Professor Maximilian Fichtner from KIT, Director of the CELEST research platform (Center for Electrochemical Energy Storage Ulm & Karlsruhe, Germany), which explores calcium batteries and other storage technologies. “Lithium-ion batteries will reach their limits in the medium term 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 turnaround.”
One of the most important reasons why lithium-ion technology offers only dim prospects for the future: The earth has only limited reserves of crucial raw materials such as cobalt, nickel and lithium. Fichtner and his team at the Helmholtz Institute Ulm (HIU), which was founded by KIT in cooperation with Ulm University, are therefore focusing on alternative battery technologies. These are based on raw materials that occur much more frequently on earth. He considers calcium to be a promising candidate because it is the fifth most abundant element in the earth’s crust. It is also evenly available on earth and has the advantage of being safe, non-toxic and cost effective.
In contrast to lithium, calcium can take up and take up two electrons per atom, which is reflected in a higher current density. At the same time, it delivers a voltage similar to lithium.
However, there has been a major hurdle in the development work on the calcium battery so far: 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 existed at all,” explain Dr. Zhenyou Li, first author of the study, and Dr. Zhirong Zhao-Karger, project manager, both working in the POLiS (Post Lithium Storage Cluster of Excellence) excellence cluster at KIT, which is further developing the calcium battery as part of CELEST. However, these experimental materials only allow charging at temperatures above 75 degrees Celsius and are still susceptible to undesired side reactions.”
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 example of the new electrolyte calciumtetrakis[hexafluoroisopropyloxy]borate, 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 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 has dominated the market to date.
However, this will not be the case already tomorrow. “The new electrolytes are a first important step,” emphasizes Fichtner. “We still have a long way to go before we have a calcium battery that is ready for the market. It is not impossible that someday the KIT team will receive the Nobel Prize for this achievement – in a few decades’ time.
Original publication: https://pubs.rsc.org/en/content/articlelanding/2019/EE/C9EE01699F#!divAbstract
KIT Energy Center: https://www.energy.kit.edu/index.php
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