Controls Stack Pressure Induced Fracture Using Microstructural Modulation in Solid-State Batteries

TL;DR: High-energy-density cathode materials in solid-state batteries require high stack pressure to achieve intimate contact between the active material and the solid-state electrolyte. However, high stack pressure can induce fracture in the active material. This study utilizes microstructural modulation to alleviate stack pressure-induced fracture and develops a thermodynamically consistent computational framework to understand the interplay between stack pressure, microstructural modulation, and fracture behavior.

Abstract: All-solid-state batteries (ASSBs) provide higher energy densities and safer alternatives to Li-ion batteries by incorporating Li-metal anode and inflammable solid electrolytes. To match the increased capacity of metallic anodes, ASSBs require high-energy-density cathode materials such as LiNixCoyMn1-x-yO2 (also known as NMC cathode) blended with a solid-state electrolyte (SSE). However, a key challenge is resolving the interfacial incompatibility between the active particulate material and the solid-state electrolyte within these composite cathodes. To obtain intimate contact between SSE and the active material, an external load (or stack pressure) needs to be applied during the processing and service life of cell. Nevertheless, such densification of cathode composites can lead to grain boundary fracture and/or complete particle disintegration. Therefore, the present work utilizes a microstructural modulation procedure to alleviate stack pressure-induced fracture in a polycrystalline cathode. Accordingly, a thermodynamically consistent computational framework is developed to understand the interplay between the stack pressure, microstructural modulation, and fracture behavior for polycrystalline NMC secondary particles embedded in a sulfide-based solid electrolyte. A phase-field fracture variable is employed to consider the initiation and propagation of cracks in the active material and SSE. This modeling framework is implemented in the open-source finite element package (MOOSE) to solve three state variables: concentration, displacement, and the phase-field damage parameter. A systematic parametric study is performed to explore the effects of stack pressure, aspect ratio, and the crystal orientation of grains on the chemo-mechanical performance of the composite electrode. We also quantitatively validate the numerical model with experimental investigation using state-of-the-art Nano-CT (Compact tomography) technique. The findings of this study offer predictive insights for designing solid-state batteries with reduced fracture evolution and stable performance. Figure 1