• A size effect in mechanical properties of thick electrodes due to through-thickness gradient in porosity is revealed. • A robust method is developed to fabricate damage-free, free-standing LIB active layers for mechanical testing. • A mesostructure-based modeling framework is constructed to establish a direct causal link between structural heterogeneity and macroscopic weakening. The pursuit of higher energy density through thick lithium-ion battery electrodes is fundamentally challenged by their increased susceptibility to cracking during fabrication. This work reveals that this failure stems from a pronounced size effect. As the active layer thickens, drying-induced binder migration creates a steeper gradient in porosity from top to bottom. This amplified mesostructural heterogeneity directly governs the macroscopic mechanical weakening. We developed a robust method using a soft substrate to fabricate damage-free, free-standing thick active layers for accurate tensile testing, which confirmed the systematic reduction in both modulus and strength with increasing thickness. Mesostructure-based finite element simulations establish a direct causal link, showing that the porosity gradient elevates local stress concentrations and reduces the effective load-bearing capacity. By establishing a mechanistic link between mesostructure and macroscopic performance, this study provides a critical foundation for designing high-energy-density thick electrodes.
Huang et al. (Sun,) studied this question.