Placement student research focused on improving models that predict fluoride ion movement in next-generation batteries
06 Mar 2026 - Rohini Gupta
As the world looks for alternatives to lithium batteries, researchers are exploring fluoride ion batteries, which could store large amounts of energy and offer high efficiency. However, one major challenge is finding solid materials that allow fluoride ions (F⁻) to move easily at room temperature.
During Robbie Shaw’s Industrial Placement at the ISIS Neutron and Muon Source, he developed a new computational approach to address this challenge. Working with ISIS crystallographers Gabriel Pérez, Helen Playford and Stephen Hull, he improved an established computational screening method known as the bond valence sum (BVS) approach. The traditional method assumes atoms are spherical and does not properly account for lone pair electrons found in certain cations such as Sn²⁺, Pb²⁺, Sb³⁺, Tl⁺ and Bi³⁺. These lone pairs change the shape of crystal structure and can strongly influence how fluoride ions move through a material.
To solve this limitation, the team introduced a simple but powerful modification by adding a ‘dummy’ lone pair site into the crystal structure model, which prevented unrealistic ion placements and more accurately represented fluoride ion movement pathways. The method was implemented in a fast Python-based program capable of screening large materials databases in seconds.
Robbie tested the method on the well-known high-conductivity fluoride conductor PbSnF₄. The new model successfully reproduced experimentally observed fluoride ion distributions and conduction pathways determined by neutron diffraction and molecular dynamics simulations, something conventional methods failed to achieve.
To further test its reliability, the researchers used the model to make predictions, and compared these with reported experimental conductivity results. They checked whether materials that were predicted to let fluoride ions move easily actually showed good conductivity in lab experiments. The predicted values matched trends in the experimental data, testing the reliability of the method.
Using this improved screening tool, the researchers analysed 136 fluoride compounds from the Inorganic Crystal Structure Database (ICSD). Several promising new materials were identified, particularly tin-based compounds, which showed low predicted energy barriers for fluoride ion diffusion.
One of the key strengths of this research is its speed and accessibility. Compared to advanced simulation techniques like molecular dynamics, which require significant computational power and time, this modified bond valence approach can screen materials in seconds. This makes it highly effective for rapidly narrowing down candidate materials before applying more detailed experimental or computational studies.
A key question for future research is whether the predictions made by this modified bond valence approach will hold across a broader range of materials, and how experimental validation could further refine its accuracy in guiding the discovery of novel solid electrolytes.
Overall, this work provided a practical and efficient pathway to accelerate the discovery of solid electrolytes for next-generation fluoride-ion batteries. It not only advances computational materials screening but also demonstrates the valuable and meaningful contributions that placement students can make to cutting-edge scientific research.
The full paper is available to read here:
A bond valence sum method to identify potential new fluoride ion conductors
