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.

Functioning bulk-type all-solid-state batteries in a practical form factor with composite positive electrodes, using Al-substituted Li7La3Zr2O12 (LLZO) as the solid electrolyte, have been demonstrated for the first time. The devices incorporate bilayers composed of dense LLZO membranes and porous LLZO scaffolds infiltrated with LiNi0.6Mn0.2Co0.2O2 and other components as positive electrodes, combined with lithium anodes. The porous scaffolds are prepared using an easily scaled freeze-tape-casting method. The unidirectional pores of the scaffold facilitate infiltration of cathode components and shorten lithium ion diffusion path lengths, while the addition of a soft ionically conductive solid to the scaffold ensures good contact among the components.