Potential-Dependent Electric Double Layer Structures in Aqueous Batteries and Dynamic Local Structure in Crystalline Superionic Conductors: Insight from X-ray Scattering

Abstract: Technologically important functional properties in energy storage materials have often been measured and reported without intimate knowledge of interfacial or dynamic local structure. However, the success of new liquid and solid-state battery chemistries with improved transport increasingly depends on understanding dynamic local structures at interfaces and in the bulk at relevant length and time scales.

This talk will address the lack of direct experimental insight on these two fronts and showcase advanced X-ray scattering methods for structural characterization in energy storage materials. First, a strong dependence on applied potential is revealed in the structure of the electric double layer (EDL) formed at liquid/solid interfaces from operando resonant and non-resonant X-ray reflectivity measurements. We determine potential-dependent ion distributions at buried electrolyte/electrode interfaces in aqueous electrolytes and observe hysteretic switching behavior in the EDL structure when the polarity of the potential is reversed.

On the second front, I will discuss a novel approach to understanding atomic-scale ion diffusion mechanisms in crystalline ion conductors using ultrafast X-ray total scattering. The time-resolved atomic pair- distribution function measured during coherently triggered ion hops will be used to map the structural origin of superionic conductivity in fast sodium ion conductors. These approaches bring direct insight of the potential-dependent structural motifs adopted at liquid electrolyte/solid electrode interfaces and deviations in local order in crystalline electrolytes that are crucial for understanding and predicting interface and bulk ionic transport.