An induced recrystallization self-healing separator for stabilizing ultra-long cycles of aqueous sodium ion batteries

Captured by attractive theoretical specific capacity (170 mAh g⁻¹), 3D open framework and adjustable structure/chemical-composition, Mn, Co, and Fe based Prussian blue analogues (PBAs) have been considered as the promising cathode materials for aqueous sodium-ion batteries (ASIBs). However, their large-scale energy storage applications were seriously restricted by the rapid capacity decay behaviors and Jahn-Teller distortions. To solving these issues, a fiberglass separator modified by Na₄Fe(CN)₆ was utilized herein to release Fe(CN)₆^4‒ in full-cell system. Serving as functional groups, Fe(CN)₆^4‒ could fill the surface Mn/Co vacancies formed in MnCo-substituted Prussian blue Na_1.74Mn_0.88Co_0.12Fe(CN)₆·2·37H₂O (MnCO-PBA) positive electrode materials during cycling. With the assistance of Na₄Fe(CN)₆ additives introducing, the self-decomposition effect of free water in the high concentration electrolyte could be effectively reduced. When the engineered separator and the MnCo-PBA-based positive electrode are tested in combination with NaTi₂(PO₄)₃@C-based negative electrode in the coin cell configuration, a specific energy of 101.35 Wh kg^‒1 at 0.05 A g^‒1 (specific energy based on the active material mass of both electrodes) and a specific discharge capacity retention of 85.8% after 5000 cycles at 0.2 A g^‒1 are achieved. This work was expected to probe the large-scale development of ASIBs.