Investigating Limiting Processes for the Electrochemical Performance of Sulfidic All-Solid-State Batteries

Kurzfassung

All-solid-state batteries (ASSB) are candidates for the next-generation of safe and high energy density storage systems. However, energy and power density are currently limited by microscopic processes at the interfaces as well as macroscopic processes on the cell level. As part of the FestBatt Cluster, we explore the working principle of sulfidic ASSBs through a cross-platform approach combination of theoretical and experimental methods. In order to gain insight on the limiting processes and give directions for the development of future ASSBs, we develop a numerical framework to capture the electrochemical processes by combining thermodynamic consistent modelling [1] and microstructure resolved 3D simulations [2,3]. This approach enables us to include virtual electrode reconstructions based on experimental measurements to improve the simulation accuracy and account for additional material features. The investigated sulfidic cell systems consist of the solid electrolyte ß-LiPS4 and the nickel-rich layered oxide NMC622 as active material. To account for the material inherent transport limitations in the electrode, our model is further expanded through the introduction of state-of-charge dependent transport parameters for conductivity and diffusivity. Furthermore, we account for percolating ion transport pathways in the polycrystalline electrolyte by resolving the grain particles in the solid matter. By introducing a modified interface flux at the grain particle interfaces the lithium ion hopping probability between two neighbouring grains is captured. The introduced simulation framework allows us a precise time resolved mapping of the cell performance for different cell designs, operation conditions and material modifications. We present a detailed study on the capacity density, the microscopic lithiation behaviour of sulfidic cells under structural, and interfacial modification through conductive agents, solid electrolyte delamination and current collector decontacting. The comparison against the experimental work identifies various performance limiting processes e.g. discontinuous material properties and restricted intercalation processes. Especially, the grain flux model allows to reproduce and identify the experimentally observed impedance characteristics connected to solid electrolyte grain size and grain surface effects. Our simulation based approach allows for a more economical and efficient testing of new battery designs in order to enable high performance future ASSBs.