Journal of Power Sources Modelling electro-chemical induced stresses in all-solid-state batteries: Anisotropy effects in cathodes and cell design optimisation

Abstract All-solid-state lithium batteries offer promising advantages in energy density and safety compared to conventional lithium ion batteries. However, the majority of this type of batteries suffers from a low cycling stability, which might originate from mechanical fatigue caused by mechanical stresses and strains in the rigid structure. We introduce a general approach to model and analyse the stresses in rigid cathode/electrolyte electrodes on a cell level, which enables to develop optimised cell designs with an improved mechanical stability. We apply this approach on composite cathodes with a Li7La3Zr2O12 (LLZO) ceramic electrolyte and LiCoO2 (LCO) active material. Using the 3D microstructure of a real cathode, the stresses inside a free-standing electrode and model cells with a thin and a thick LLZO separator are calculated for the charging cycle considering isotropic and anisotropic material properties of LCO as well as non-textured and textured crystallographic alignment. Compared to randomly oriented crystals, the textured crystallographic alignment of LCO grains, introduced by the manufacturing process, has a significant effect and yields considerably better stress distributions in all cell configurations investigated. The design of optimised all-solid-state cells with reduced separator thickness leads to a significantly more favourable stress state than a typical lab scale separator-supported cell.