Systematic Optimization and Characterization of All-Solid-State Batteries with Slurry-Cast Cathode

To address the ever-increasing demands for driving range and safety in electric vehicles, solid-state batteries (SSBs) have emerged as one of the most promising next-generation energy-storage technologies. Among various material configurations, the combination of sulfide solid electrolytes (SSEs), featuring high ionic conductivity and favorable processability, with layered Ni-rich oxide cathodes has demonstrated significant commercial potential. Furthermore, the adoption of slurry-casting processes for cathode fabrication provides a viable pathway toward the scalable manufacturing of SSBs. Nevertheless, complex interfacial reactions and the progressive emergence of electro-chemo-mechanical degradation during operation continue to severely limit the cycling stability and practical performance of such systems. This dissertation focuses on polycrystalline LiNi0.85Co0.10Mn0.05O2 (PC NCM85) as the cathode active material (CAM) coupled with argyrodite Li6PS5Cl (LPSCl) as the SSE. Through three complementary research directions, this work advances the mechanistic understanding of degradation phenomena in the cathode and develops systematic optimization strategies for SSBs. The first section investigates interfacial (physicochemical) characteristics and associated degradation mechanisms. Using cryogenic transmission electron microscopy (cryo-TEM) combined with electron energy-loss spectroscopy (EELS), electrochemically induced reduction of transition-metal species and their dissolution from the CAM into the SSE are identified, leading to pronounced electrolyte poisoning. In parallel, a nanoparticle coating strategy is systematically investigated, resulting in substantial improvements in electrochemical performance. By designing a reliable three-electrode (3E) setup for SSBs, the second section focuses on interfacial kinetics between the working electrode (WE) and the counter electrode (CE). Emphasis is placed on the overlap of characteristic kinetic processes across relevant timescale regimes, as well as on the evolution of state-of-charge (SOC)-dependent overpotentials and interface-related kinetic responses from different CEs and their influence on cell performance. The third section addresses mechanical degradation of the cathode by employing Li4Ti5O12 (LTO) as the anode/CE in conjunction with a low negative-to-positive (n/p) capacity ratio design. By leveraging the lithiation profile of LTO near its terminal region, the volume changes in the cathode are effectively mitigated. Upon cycling, the capacity loss resulting from the incremental growth of cathode polarization can be partially mitigated through adaptive compensation. As a result, an optimal balance between attainable capacity and long-term capacity retention is achieved. Collectively, the findings provide a comprehensive understanding of electro-chemo-mechanically induced degradation in the SSBs under investigation. The proposed strategies demonstrate pronounced performance improvements and strong transferability, offering effective methodologies and analytical perspectives for the rational design of high-performance SSBs.

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Systematic Optimization and Characterization of All-Solid-State Batteries with Slurry-Cast Cathode

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