Design of slurry processed electrodes and separators for the integration in sulfide-based all-solid-state batteries

This thesis focuses on a first principal study of manufacturing and operating All-Solid-State Batteries (ASSB) using sulfide-based solid electrolyte Li6PS5Cl (Argyrodite). The main goal is the part design of cathode, separator and anode inspired by commercial Lithium-Ion Battery (LIB) production, which rely on castable slurries. The investigated reference consists of LiNi0.6Mn0.2Co0.2O2 (NMC622) as cathode active material and silicon as anode active material. The chemical and structural investigation of parts as well as starting materials was conducted via X-Ray Diffraction analysis (XRD), Infrared (IR) and Raman spectroscopy as well as Scanning Electron Microscopy (SEM). The latter was particularly used to study cryogenically ion-polished cross-section of assembled ASSB. The electrochemical evaluation on ASSBs was conducted via galvanostatic cycling (incl. rapid aging testing), C-rate capability testing as well as impedance spectroscopy. The development of a thin separator (25 – 35 μm) focused on two approaches: self-standing and bilayer casting. In the bilayer casting approach, a layer of solid electrolyte slurry was directly cast onto a pre-cast anode. In contrast, the self-standing design utilized a polyethylene terephthalate (PET)-based nonwoven as a scaffold structure, which was infiltrated by the slurry. The comparison of both separator designs revealed the superiority of the self-standing approach in terms of cycle stability, while maintaining similar C-rate capability. Additionally, a reduction in mass of lithium per kWh of approx. 15 % can be achieved when using the self-standing design. For anode development two topics were explored. One study was conducted on electrolyte-blended and -free silicon anodes. The direct comparison showed that while cells with electrolyte-blended anodes demonstrated superior cycle stability and C-rate capability, the cells with electrolyte-free anodes still managed to undergo hundreds of cycles, when using an appropriate binder system. To gain deeper insights into the lithiation pathway of electrolyte-free silicon anodes, charged ASSB were investigated. This investigation was conducted at the cross-section using a combination of SEM and Soft X-ray Emission Spectroscopy (SXES) as well as at interface of the current collector using X-ray Photon Spectroscopy (XPS). The findings revealed that even though no electrolyte was present continuous through-plane lithiation occurred inside the silicon anode during the first charge. To further enhance the concept of electrolyte-free silicon anodes, the second topic focused on the chemical prelithiation of silicon powder using a Lithium-Arene-Complex (LAC) as mediator. The successful prelithiation was proven via the combination of various methods (IR, Raman, SEM-SXES, ICP-OES), but was found to be inhomogeneous. The incorporation of prelithiated silicon as electrolyte-free anode in ASSB revealed an increased cycle stability at 2 C compared to the pristine silicon counterpart. However, the formation of internal resistances at higher C-rates affected the cell with prelithiated silicon negatively, resulting in a loss of cycle stability and C-rate capability. The last topic revolved around the possible increase in energy density by investigating the electrochemical performance of different variations of LiNixMnyCozO2 (NMC-X) at the same mass loading. NMC-83 exhibited the best overall performance (cycle stability, energy density and C-rate capability) and was chosen for investigation at a higher mass loading (50 % increase). However, at this dimension the cell experienced an increase in overpotential, which limited the energy density to ~295 Wh·kgcell−1. In summary the presented findings of this thesis demonstrate the feasibility of manufacturing ASSB using LIB production standards as a role model. The integration of silicon on the anode side and a thin separator layer allowed for the ASSB cell to reach energy densities, which matches or even surpasses those of commercial LIB. Thus, paving the way for a new generation of high-energy battery cells with exciting discoveries to be made.