The recent upsurge of interest in all solid-state lithium batteries for electric vehicles is driven by a need for improved safety and higher energy densities than what are currently available from conventional lithium-ion batteries. Replacement of flammable liquid electrolytic solutions with solid electrolytes allows the use of higher energy lithium metal anodes instead of graphite, and lessens the probability of catastrophic failure, which can result in fire. Most solid-state batteries available today, however, are fabricated in small, thin film formats requiring costly vacuum deposition technologies, and suffer from low practical energy densities due to low areal capacities that restrict their use to specialty applications. In this article, we discuss the current status of solid electrolytes for solid-state lithium batteries and what is needed from a cell design and fabrication viewpoint to develop large format devices for traction applications.

All solid-state lithium batteries are, potentially, higher energy density and safer alternatives to conventional lithium-ion batteries (LIBs). These are particularly attractive characteristics for large-scale applications such as electric vehicles and grid energy storage systems. However, the thin film deposition techniques used to make current devices are not readily scalable, and result in low areal capacities, which translate to low practical energy densities. To overcome these deficiencies, it is necessary to design thicker electrodes similar to what are used in LIBs (30-100 μm), in which the active material is composited with an ionic conductor and an electronically conducting additive, to overcome transport limitations. In this paper, we propose a method for making such an electrode, starting with a porous scaffold, i.e. Li7La3Zr2O12 (LLZO), made by freeze casting, which is then infiltrated with the active material LiNi0.6Mn0.2Co0.2O2 (NMC-622) and other components. The freeze casting technique results in the formation of oriented channels with low tortuosity, which run roughly parallel to the direction of the current. The scaffolds were characterized with synchrotron X-ray micro-tomography for structural analysis, as well as synchrotron X-ray fluorescence to map the elemental distribution in the infiltrated composite. A hybrid half-cell was constructed and cycled as proof of principle, and it showed good stability. In addition, a bilayer structure consisting of a porous layer combined with a dense LLZO film was successfully made as a prototype of an all solid-state battery. A mathematical model was established to propose optimized scaffold structures for battery performance.