Electrochemo-Mechanical Coupled Behaviors in Sodium-Ion Batteries Upon Stack Pressure

Abstract

Owing to their low cost, environmental friendliness, and high safety, sodium-ion batteries (SIBs) are considered promising alternatives to lithium-ion batteries (LIBs). However, the electro-chemo-mechanical coupled behaviors of sodium-ion batteries, which represent a typical and critical operational scenario, remain largely unexplored. In this study, a unique bimodal swelling behavior specific to sodium-ion batteries is revealed through operando swelling-force measurements upon stack pressure. Meanwhile, a detailed, multiscale electrochemical-mechanical computational framework, rigorously validated by experiments, is developed to quantitatively assess the contributions of individual cell components to the overall swelling behavior. The results show that swelling is primarily driven by anode expansion at low State-of-Charge (SOC), whereas cathode-driven shrinkage governs swelling at high SOC, with the separator serving mainly as a load-transfer and mechanical-buffering layer. In addition, an SOC-dependent, electrodedominated swelling mechanism for sodium-ion batteries is systematically established and elucidated. Finally, higher C-rates lead to higher swelling force at full charge and an earlier peak force during discharge. Overall, this study provides fundamental insights into electro-chemomechanical coupling in sodium-ion batteries and offers important guidance for the development of safer next-generation sodium-ion battery systems.