AMaSiS 2021 - Abstract

Latz, Arnulf

Modeling of batteries from nanometer to cell scale: Beyond concentrated solution and porous electrode theory

DLR/Helmholtz Institut Ulm, Germany

Improving the design of batteries to achieve higher power density, energy density, safety and longevity is a complex task, which requires not only optimizing materials but equally important optimizing function and interplay of materials as well as reducing side reactions during the operation of the battery. The function of the material during operation is determined by electrode and cell design. The interplay of the materials influences structure of double layers and emergence of interphases (e.g. the solid electrolyte interphase or SEI) which may affect dramatically reaction kinetics and overpotentials as in ionic liquids or water in salt concepts or when using multivalent ions in Post Lithium batteries. Side reactions as e.g. plating are initiated on a very local nanometer to micrometer scale and therefore strongly depends on the local overpotential distribution, which is influenced by the design of the active particle shape or morphology and local fluctuations in the SEI thickness. To capture all these phenomena within a rational design approach for batteries using modelling and simulations, it is not sufficient to rely on the traditional concentrated solution theory for electrolytes or the porous electrode theory used in the Doyle-Fuller-Newman battery models. In the presentation an overview is given about our recent theoretical developments which are extending electrolyte transport theories including double layer predictions, interface degradation modeling (SEI formation and impact on plating) and the Doyle- Fuller-Newman (DFN) upscaling paradigm for Lithium ion batteries. Our systematic Free Energy based theory for electrolytes captures complex correlated structure formation phenomena in highly concentrated electrolytes as e.g. ionic liquids or water in salt electrolytes. Our new models for SEI formation identifies thickness fluctuations on electrode scale and different growth regimes depending on the operating conditions. Finally it is shown how local overpotential fluctuations relevant for local plating conditions and for the first time observed in microstructure resolved battery simulations can be explained by local anisotropies of active particle properties which can also be captured on the macroscopic cell scale via an improved DFN approach.