Synergistic enhancement of Li-ion and electron transport in thick electrodes via tailored microstructural gradients

Abstract

The global transition to decarbonization and the rapid rise of electric mobility demand lithium-ion (Li-ion) batteries with higher energy density. Thick electrodes offer a viable pathway but introduce microstructural complexity that impedes Li-ion and electron transport. In this study, a heterogeneous particle-packing model with active material-binder gradients is developed to investigate how gradients in particle size, particle diffusion coefficient, porosity, electronic conductivity, and conductive binder content enhance electrode performance from the perspectives of Li-ion and electron transport. The results reveal that: (1) particle-size gradients combine lower tortuosity from large particles with shorter diffusion paths from small particles; (2) diffusion-coefficient gradients facilitate Li-ion insertion near the separator; (3) porosity gradients enhance Li-ion transport in the electrolyte while maintaining energy density; and (4) conductivity and binder gradients improve electronic pathways. At higher discharge rates and greater electrode thickness, Li⁺ accumulation intensifies near the separator, while overpotential rises markedly adjacent to the current collector. Consequently, an effective strategy for thick electrode design is to enhance ionic transport at the separator side in combination with enhanced electronic conductivity at the current collector side. These insights provide guiding principles for the rational design of high-performance thick electrode architectures.