Operando evolution of battery materials and functional solid-solid interfaces
Our work focuses on the understanding of functional solid-solid interfaces at the atomistic level.
Electrochemical solid state devices beyond single-crystalline model systems contain many solid-solid interfaces between grains of the same or of different materials. The systems of relevance for energy storage and conversion processes comprise such different classes as solid state batteries and high temperature solid oxide electrolyzers. The function of all these devices requires control over charge carrier transport across the internal interfaces on the one hand and sufficient long-term stability, i.e. robustness against parasitic migration processes which potentially change the materials' structure and composition, on the other hand.
Experimentally, such interfaces are not easily accessible as they are buried deeply inside the typically sintered solid materials. A comparatively small interface to volume ratio and partial amorphization at the interfaces adds to the complications faced by purely experimental approaches. We therefore develop closely linked theoretical/experimental workflows, where large scale simulations provide the basis for the interpretation of indirect spectroscopic and microscopic observations in terms of atomistic structure and mechanisms and experimental data is used to validate the theoretical approaches and approximations necessitated by the complexity of the systems under study.
For these simulations we combine DFT to compute observables that require access to the systems' electronic structure with molecular dynamics and accelerated sampling methods in a multi-scale and -modal approach. Potential energy surfaces are based on a range of low-cost methods such as classical and machine-learned force-fields and semi-empirial models which are parametrized from first-principles calculations and allow for simulations of ensembles of large-scale atomistic structural models.