Double additive electrolyte solvation engineering to achieve long cycle and high capacity sodium-ion battery

Sodium-ion batteries are a promising energy storage system due to their rich sodium resources and many other advantages. However, its development is severely hampered by the electrolyte's low compatibility with the electrode contact. Herein, we propose a solvation control strategy with ethoxy (pentafluoro) cyclotriphosphazene (PFPN) and NaClO4 double additives to reconstruct the solvation structure of sodium ions in electrolytes. This enables the electrolyte to form a dense and stable solid electrolyte interlayer (SEI) and double-layer cathode electrolyte interphase (CEI) on the surface of the electrode material to achieve long-cycle and high-capacity sodium-ion batteries. PFPN can form a stable SEI rich in inorganic components at the anode interface. ClO4- can first reach the cathode surface to create a NaCl and polymer-like chain CEI with sodium ions and solvents, and then the PFPN derivatives are migrated to the cathode surface to open the ring and decompose, thus forming a double-layer stable CEI. Therefore, the PEDN electrolyte can simultaneously improve the interface stability of the battery's cathode and anode solid electrolyte. Hence, the capacity retention rate of the 4.5 Ah Na3Fe2(PO4)P2O7 (NFP)||hard carbon (HC) pouch cell after 2500 cycles at 1C is 88.26%.