Elucidating the Formation of Electrode-Electrolyte Interphases during Formation for Long-Life Na-Ion Batteries

Na-ion batteries (NIBs) have emerged as a promising alternative due to their abundant resources, low cost, and environmental friendliness. However, challenges remain in their cycling stability and electrochemical performance, particularly regarding the stability of the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI). The SEI/CEI formation mechanisms in NIBs and their influence on the electrochemical performance remain insufficiently understood. This study systematically investigates the effects of pressure and current density on the CEI/SEI formation on oxide cathodes and hard carbon anodes. Increased external pressure and current density hinder the formation of uniform and stable interphases, raising Na⁺ interfacial diffusion barriers and ultimately degrading cycling stability. Under optimized formation conditions, the Na-ion pouch cell retains 92.5% of its capacity after 650 cycles at 1 C. These findings offer new insights into optimizing the formation strategy and stabilizing the electrode-electrolyte interface, contributing to the advancement of NIBs electrochemical performance and longevity.