Stabilization of flame-retardant gel polymer electrolyte against Na anode via an additive confined MOF-based composite gel interlayer

Abstract

Flame-retardant gel polymer electrolyte (FRGPE) with high ionic conductivity and practical safety is essential for the next generation of high energy density sodium metal batteries (SMBs). However, they suffer from serious side reactions and insufficient interfacial stability against sodium metal anode, causing severe performance degradation and even safety issues. Herein, to address these challenges, a fluoroethylene carbonate (FEC) additive confined metal-organic framework (MOF)-based composite gel (AC-MCG) interlayer was constructed upon sodium anode through a facile in-situ UV-induced photopolymerization. The FEC confined in AC-MCG induces the formation of NaF-rich inorganic solid-electrolyte interphase, effectively eliminating the side reactions between the FRGPE and sodium metal anode. Moreover, the MOF with ordered nanochannels can homogenize Na⁺ flux during the plating process and also endow the AC-MCG interlayer with high mechanical strength, thus sufficiently suppressing the growth of sodium dendrites. Benefitting from these merits of the AC-MCG interlayer, a high critical current density of 2.0 mA cm⁻² and a long-term cycling life for over 4200 h at 0.1 mA cm⁻² are achieved for the Na/Na symmetric cells. Besides, the solid-state SMBs paired with the constructed AC-MCG interlayer also demonstrated considerable electrochemical performance and practical safety.