Identifying limiting factors on the cell performance of all-solid-state batteries by microstructural resolved simulations

Abstract

All-solid-state batteries (ASSBs) are predicted to play an important role in future battery applications, because they potentially provide high energy densities and an enhanced safety in operation. The ceramic electrolyte LLZO is a promising choice for the solid electrolyte (SE), as it is stable against Li-metal and shows a high ionic conductivity which is essential for a high cell performance. However, experimental results still show low capacities for garnet-based ASSBs at room temperature and a severe capacity fade after the cycling of the cells. In this contribution we explore the reasons for the observed limitations and show possible optimization strategies by continuum modelling and simulations. First, we perform microstructural-resolved simulations on a set of virtual composite cathodes to identify the limitations of the underlying microstructure. In doing so we want to provide advantageous target values for the cell production regarding active material content, sinter density and particle sizes. Furthermore, we focus on the role of secondary phases in the composite cathode that can form as a result of degradation phenomena at the interface between the SE and cathode active material (CAM). By extending our simulation environment with an interface model, we show that a resistive layer at the interface SE/CAM resulting from secondary phase formation is a plausible explanation for the low measured capacities at room temperature. An increase in layer thickness when cycling the cell due to electrochemical degradation is a possible mechanism for the observed capacity fade.