Solvent‐Free Ultrafast Construction of Se‐Deficient Heterojunctions of Bimetallic Selenides toward Flexible Sodium‐Ion Full Batteries

Abstract Flexible quasi‐solid‐state sodium ion batteries featuring their low‐cost, high safety and excellent mechanical strength have attracted widespread interest in the field of wearable electronic devices. However, the development of such batteries faces great challenges including the construction of interfacial compatible flexible electrode materials and addressing the high safety demands of electrolyte. Here selenium‐vacancies regulated bimetallic selenide heterojunctions anchored on waste cotton cloth‐derived flexible carbon cloth (FCC) with robust interfacial C‐Se‐Co/Fe chemical bonds as a flexible anode material (CCFSF) is proposed by ultrafast microwave pyrolysis method. Rich selenium vacancies and CoSe₂/FeSe_2−x heterostructures are synchronously formed that can significantly improve ionic and electronic diffusion kinetics. Additionally, a uniform carbon layer coating on the surface of Se‐deficient heterostructures endows it with outstanding structural stability. The flexible cathode (PB@FCC) is also fabricated by directly growing Prussian blue nanoparticles on the FCC. Furthermore, an advanced flexible quasi‐solid‐state Na‐ion pouch cell is assembled by coupling CCFSF anode, PB@FCC cathode with P(VDF‐HFP)‐based gel polymer electrolyte. The full cell not only demonstrates excellent energy storage performance but also robust mechanical flexibility and safety. The present work offers an effective avenue to achieve high safety flexible energy storage device, promoting the development of flexible wearable electronic devices.