Investigating All-Solid-State Battery Cell Interfaces By Multi-Scale Continuum Modelling and Simulation
Authors: Becker-Steinberger Katharina , Neumann Anton , Hein Simon , Horstmann Birger , Urban Karsten , Latz Arnulf 
Published: February 2020

Driven by all-solid-state battery (ASSB) applications there is an increased interest in understanding the dynamics of solid electrolytes (SEs) and ASSBs. Particularly, the large charge transfer resistances at the various ASSB interfaces are still subject to scientific discussions requiring further investigations. To advance ASSB design, fundamental knowledge of the underlying processes at both the heterogeneous SE-electrode-interfaces and the homogeneous SE-SE-interfaces, i.e., grain boundaries, are essential.
In this contribution, we explore transport and interfacial processes in ASSB cells by a continuum modelling framework and numerical simulations. Special attention is paid to the coupled multi-physics at heterogeneous SE-electrode-interfaces and their feedback to bulk properties. Local balancing processes lead to charge accumulation at the solid-solid interface and the formation of charged zones, i.e., space charge layers (SCL), in the near interface regions. These local charge distributions cause locally strong electric fields, induce large changes in the mechanical field sizes, and lead to local changes in the energy states. The numerical investigation of these boundary layers on the nanometer scale in a continuum approach requires suitably refined models. Therefore, previous approaches either resolve the SCLs [1] or consider scales beyond the SCL width and use less intense bulk type models to examine the interaction of physical processes and numerically demanding microstructures in composite electrodes [2, 3].
We combine the advantages of both approaches yielding a multi-scale model, which is based upon a free energy model, extending earlier work [1] by including mechanical and configurational contributions of detailed lattice structural properties on the atomic scale. The resulting improved transport model is combined with a new active interface model including the electrode SCL. The interfaces are active in the sense that they carry dynamical responding interfacial species. This enables the description of charge transfer and intercalation as a multi-step process and to split the electrical current crossing the interfaces into charge transferred by a defect reaction mechanism and a polarization induced contribution. In the quasi-static regime, we deduce material dependent, non-linear, differential capacities characterizing the SCLs without spatial resolution. These capacities serve as theory-based input in 3D microstructure-resolved simulations and bridge the scales.
This model is used to simulate charge/discharge, cyclic voltammetry and impedance measurements for ASSBs; it is validated with experimental data. Furthermore, we study and identify individual contributions of the interface processes as well as time scales. Particularly, we show that the phase-interface processes are affected by bulk properties such as grain boundaries.
[1] S. Braun, C. Yada, A. Latz, J. Phys. Chem. C., 2015, 19, 22249.
[2] A. Latz, J. Zausch, Beilstein Journal of Nanotechnology, 2015, 6, 987-1007.
[3] M. Finsterbusch, T. Danner, C.-L. Tsai, S. Uhlenbruck, A. Latz and O. Guillion, ACS
Applied Materials & Interfaces, 2018, 10, 22329.