Optimized Particle Porosity to Alleviate Diffusion-Induced Stresses in High-Capacity Electrodes

Electrode materials like silicon offer the potential to increase the capacity of lithium-ion batteries by an order of magnitude. However, their widespread adoption is hindered by substantial volume changes during lithium insertion and extraction, which leads to mechanical degradation and capacity fade. Experimental studies suggest that replacing solid silicon particles with their porous counterparts might reduce the volume expansion. To explain this phenomenon, we develop a chemo-mechanical model for porous silicon-anode particles. The model utilizes the theory of mixtures and finite-deformation theory to capture the diffusion-strain coupling behavior of porous particles. It demonstrates the effects of porosity on reducing stress evolution and volume changes over time. Specifically, a particle with initial radius of 500 nm and porosity of 0.2 would reduce stress by 30% and volume expansion by 13%; initial porosity of 0.5 would reduce stress and volume expansion by 70% and 36%, respectively. Our investigation of the parameter space under galvanostatic and potentiostatic operating conditions predicts the existence of a critical porosity value, about 68%, above which silicon particles of all sizes are mechanically stable. These findings suggest that our model can be deployed in optimal design of porous silicon structures for next-generation lithium-ion battery electrodes.