Abstract:

The ongoing advancements in sodium-ion battery technology necessitate an in-depth understanding of capacity fading mechanisms during high-temperature storage to enhance the calendar life of these battery systems. This study systematically investigates the high-temperature storage performance of Na₄Fe₃(PO₄)₂P₂O₇-based sodium-ion batteries. A comprehensive analysis was conducted using multiple techniques, including transmission electron microscopy (TEM), inductively coupled plasma emission spectroscopy(ICP), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy(XPS) , to assess changes in specific capacity, structural integrity, morphology, and interfacial components of both cathode and anode active materials during storage. Results reveal a slight decrease in electrode specific capacity after storage, without significant structural damage to the cathode or anode. Iron dissolution from the cathode was minimal, showing negligible crosstalk. However, the solid electrolyte interphase (SEI) on the anode thickened significantly, with the SEI layer dissolving and regenerating continuously, primarily composed of organic components. These findings indicate that side reactions at the anode interface are the primary contributors to capacity loss during high-temperature storage. This work deepens the understanding of the calendar aging process in sodium-ion batteries and provides critical scientific insights for enhancing sodium-ion battery performance.

Key words: sodium-ion batteries, storage, calendar aging, capacity fading mechanism, solid electrolyte interphase, Na₄Fe₃(PO₄)₂P₂O₇ cathode