Improving damage resistance of solid-state battery cathodes with block copolymers: A non-linear diffusion-mechanics study at the microscale

Abstract

Minimizing interfacial failure in the composite cathode remains a crucial challenge to unravel the full potential of all solid-state batteries (ASSBs). Polymer-based ASSBs offer promising means of minimizing those damage effects due to their high ductility. However, multicomponent polymers such as block copolymers (BCPs) are needed to meet requirements for both ionic conductivity and mechanical resistance. This study aims to provide a new insight into the combined effects of block copolymer composition (soft-to-hard phase ratio) and interfacial strength on the coupled diffusion-mechanics response of an ASSB cathode, achieved by proposing a non-linear computational micromechanics approach. The approach combines a pressure-dependent diffusion process, interfacial gap-dependent diffusivity, and advanced elasto-viscoplastic constitutive model for a BCP, and it is implemented numerically within a non-linear finite element framework. Two cathode design concepts are explored here, with and without the BCP coating. Results from these case studies suggest that there is a strong interplay between the interface strength (between active particles and the BCP matrix), the BCP material composition, and the interfacial diffusivity. It is found that interfacial damage can be minimized by increasing both the interfacial strength and the amount of the soft component in the BCP system. If the diffusivity across the interface is damage-dependent, the latter is reduced when the BCP is predominantly made of the hard phase. Ultimately, a simple sensitivity analysis reveals that interfacial strength plays a vital role in minimizing interfacial damage, while the coating thickness is the least influential design parameter.