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Abstract The interface between cathode and electrolyte is a significant source of large interfacial resistance in solid‐state batteries (SSBs). Spark plasma sintering (SPS) allows densifying electrolyte and electrodes in one step, which can improve the interfacial contact in SSBs and significantly shorten the processing time. In this work, we proposed a two‐step joining process to prepare cathode (LiCoO₂, LCO)/electrolyte (Li_0.33La_0.57TiO₃, LLTO) half cells via SPS. Interdiffusion between Ti^4+/Co³⁺was observed at the interface by SEM/STEM, resulting in the formation of the Li−Ti−La−Co−O and Li−Ti−Co−O phases in LLTO and the Li−Co−Ti−O phase in LCO. Computational modeling was performed to verify that the Li−Ti−Co−O phase has a LiTi₂O₄host lattice. In a study of interfacial electrical properties, the resistance of this interdiffusion layer was found to be 10⁵ Ω, which is 40 times higher than the resistance of the individual LLTO phase. The formation of an interdiffusion layer is identified as the origin of the high interface resistance in the LLTO/LCO half‐cell. 

The microstructural optimization of porous lithium ion battery electrodes has traditionally been driven by experimental trial and error efforts, based on anecdotal understanding and intuition, leading to the development of useful but qualitative rules of thumb to guide the design of porous energy storage technology. In this paper, an advanced data-driven framework is presented wherein the effect of experimentally accessible microstructural parameters such as active particle morphology and spacial arrangement, underlying porosity, cell thickness, etc. , on the corresponding macroscopic power and energy density is systematically assessed. For the Li x C 6 | LMO chemistry, an analysis performed on 53 356 battery architectures reported in the literature revealed that for commercial microstructures based on oblate-shaped particles, lightly textured samples deliver higher power and energy density responses as compared to highly textured samples, which suffer from large polarization losses. In contrast, high aspect ratio prolate-shaped particles deliver the highest energy and power density, particularly in the limit of wire-like morphologies. Polyhedra-based colloidal microstructures demonstrate high area densities, and low tortuosities, but provide no appreciable power and energy density benefit over currently manufactured particle morphologies. The developed framework enables to establish general microstructure design guidelines and propose optimal electrode microstructures based on the intended application, given an anode and cathode chemistry. 

In this study, fabrication processes of solid electrolyte/cathode interfaces for their use in next‐generation all‐solid‐state lithium‐ion battery (LIB) applications are described. Standard lithium–aluminum–titanium–phosphate (LATP) solid electrolyte and lithium–manganese oxide (LMO) spinel cathode ceramic half cells are assembled using two all‐solid‐state methods: a) co‐sintering the cathode and electrolyte materials via field‐assisted sintering and b) field‐assisted high‐temperature bonding. The morphology and composition of the interfaces are analyzed by scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectroscopy (EDS). This study reveals that the formation of interphases can be significantly decreased by separately performing the densification and joining procedures. Electrochemical impedance spectroscopy (EIS) is applied to understand and determine the effect of the manufactured interfaces on the system conductivity. Based on the results, it is concluded that the high‐temperature bonding technique appears to be a suitable technique for future production of all‐solid‐state LIBs.