Ultra-Stable Sodium-Ion Battery Enabled by All-Solid-State Ferroelectric-Engineered Composite Electrolytes

Symmetric Na-ion cells using the NASICON-structured electrodes could simplify the manufacturing process, reduce the cost, facilitate the recycling post-process, and thus attractive in the field of large-scale stationary energy storage. However, the long-term cycling performance of such batteries is usually poor. This investigation reveals the unavoidable side reactions between the NASICON-type Na₃V₂(PO₄)₃ (NVP) anode and the commercial liquid electrolyte, leading to serious capacity fading in the symmetric NVP//NVP cells. To resolve this issue, an all-solid-state composite electrolyte is used to replace the liquid electrolyte so that to overcome the side reaction and achieve high anode/electrolyte interfacial stability. The ferroelectric engineering could further improve the interfacial ion conduction, effectively reducing the electrode/electrolyte interfacial resistances. The NVP//NVP cell using the ferroelectric-engineered composite electrolyte can achieve a capacity retention of 86.4% after 650 cycles. Furthermore, the electrolyte can also be used to match the Prussian-blue cathode Na_xFe_yFe(CN)_6-z·nH₂O (NFFCN). Outstanding long-term cycling stability has been obtained in the all-solid-state NVP//NFFCN cell over 9000 cycles at a current density of 500 mA g^-1, with a fading rate as low as 0.005% per cycle.