Metal-ion-coordinated cross-linked quasi-solid-state polymer electrolyte for a high energy-density and long-life Prussian blue analogs cathode

Abstract

As one of the most promising cathode materials for sodium-ion batteries, Prussian blue analogs (PBAs) cathodes face challenges in terms of poor cycling stability owing to their poor interfacial stability. Poor interfacial stability often leads to irreversible behaviors such as dissolution of cathode transition metals and catalytic decomposition of solvents. Herein, a novel metal ion-coordinated cross-linked quasi-solid-state polymer electrolyte was prepared via an in situ method using a four-armed cross-linker, where the denser and more efficient three-dimensional network renders the electrolyte with excellent chemical and electrochemical stabilities, minimizes catalytic decomposition side reactions and improves the interfacial stability of high-voltage PBAs cathodes. Moreover, the combination of in situ technology with Ti-MOFs fillers affords a highly compatible electrode/electrolyte interphase and an organic/inorganic composite Na⁺ conduction pathway, which accelerates Na⁺ transport and enhances interfacial stability. Thus, the as-designed polymer electrolyte exhibits an ionic conductivity of 3.85 mS cm⁻¹ and extended oxidation stability of 5.1 V, coupled with improved mechanical strength and safety. The CFM-PBAs‖Na battery demonstrates excellent rate performance and cycling stability (with an average coulombic efficiency of nearly 100% over 2000 cycles). Furthermore, the high-capacity FM-PBAs‖Na battery achieves an ultra-high energy density of 445 Wh kg⁻¹, showcasing significant potential for high energy-density and long-life PBAs cathodes.