Servicenavigation

Project Details

Back

Projekt Print View

Topochemical fluorination reactions in the context of fluoride ion batteries, tailored properties and for the modification of thin films

Subject Area Solid State and Surface Chemistry, Material Synthesis
Synthesis and Properties of Functional Materials
Term from 2015 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 285249272
 
Final Report Year 2023

Final Report Abstract

In this project, topochemical fluorination reactions were investigated for the development of fluoride ion batteries based on intercalation, for the adjustment of specific properties and for the modification of thin films. In the field of fluoride ion batteries, a large number of compounds were tested for their suitability as reversible electrode materials. It has been shown that transition metal-containing compounds in the Ruddlesden-Popper structure type can reversibly intercalate and deintercalate fluoride ions, which is favoured by the layered structure and the localization of the fluoride ions within interstitial layers. Nickelates are particularly suitable for use as cathode materials, especially if the charging and discharging conditions are selected in such a way that side reactions with carbon additives are minimized. This allows solid-state fluoride ion batteries to be realized, some of which can be cycled over many months. It has been shown that the use of uniaxial pressure during the charging process can also achieve a significant improvement in the reduction of overpotentials and thus coulombic efficiency. In addition to the use of electrochemical and chemical fluorination, the project also developed selective topochemical defluorination reactions for oxyfluorides. Sodium hydride proved to be a suitable reducing agent for this purpose, which can selectively extract fluoride ions reductively due to the high lattice energy of NaF. New anode materials could be explored, e.g. based on the reductive defluorination of La2NiO3F2 or Sr2TiO3F2, whereby the defluorination can have a strong influence on the electronic and magnetic properties. Interestingly, it was shown that reductive side reactions can also occur on the carbon material during the electrochemical defluorination experiment, which can presumably be explained by the incorporation or addition of cations from solid electrolyte or electrode material to the carbon matrix. This could be avoided by elimination of the carbon as a conductive additive from the anion side. It was also shown that both ferromagnetic or superconducting properties can be reversibly switched electrochemically. The influence of topochemical fluorination on catalytic properties was investigated using barium ferrates and cobaltates. Due to the selected production method of spray pyrolysis, some new compounds were identified and characterized, and resulting powder were processed into thin films. Following further development of fluorination methods for thin films, the electrocatalytic properties of the compounds for oxygen reduction could be determined and thin films of manganates could be modified with regard to their magnetic properties.

Publications

 
 

Additional Information

© 2025 DFG Disclaimer / Copyright / Privacy Policy

Textvergrößerung und Kontrastanpassung