Researchers develop fluoride-based rechargeable batteries

Based on a fluoride shuttle — the transfer of fluoride anions between the electrodes — the battery technology is reported to enhance the storage capacity reached by lithium-ion batteries by several factors. It is claimed that operational safety is also increased, as it can be done without lithium.

Metal fluorides may be applied as conversion materials in lithium-ion batteries. They also allow for lithium-free batteries with a fluoride-containing electrolyte, a metal anode, and metal fluoride cathode, which reach a much better storage capacity and possess improved safety properties.

The concept for secondary batteries based on metal fluorides was developed by Dr Maximilian Fichtner, head of the Energy Storage Systems Group, and Dr Munnangi Anji Reddy at the KIT Institute of Nanotechnology (INT). It was published in the Journal of Materials Chemistry.

’As several electrons per metal atom can be transferred, this concept allows extraordinarily high energy densities to be achieved — up to 10 times as high as those of conventional lithium-ion batteries,’ explained Fichtner.

Instead of the lithium cation, the fluoride anion takes over charge transfer. At the cathode and anode, a metal fluoride is formed or reduced.

Lithium-ion batteries are applied widely, but their storage capacity is limited. In the future, battery systems of enhanced energy density will be needed for mobile applications in particular.

The KIT researchers are now working on the further development of material design and battery architecture in order to improve the initial capacity and cyclic stability of the fluoride-ion battery.

Another challenge lies in the further development of the electrolyte. The solid electrolyte applied so far is suitable for applications at elevated temperatures only. It is therefore aimed at finding a liquid electrolyte that is suited to use at room temperature.