High-performance quasi-solid-state flexible sodium metal battery: Substrate-free FeS2–C composite fibers cathode and polyimide film-stuck sodium metal anode

Abstract

A substrate-free carbon-coated FeS2-fiber-based cathode for quasi-solid-state rechargeable flexible sodium metal batteries is reported for the first time. A facile electrospinning technique followed by carbonization is employed for the synthesis of a novel cathode for a flexible sodium metal batteries. For fabrication of the solid-state flexible battery, a Na3Zr2Si2PO12-based hybrid solid electrolyte is utilized as the separator and electrolyte. A discharge capacity of about 808.26 mAh g−1 is obtained in the first charge–discharge cycle, which is greater than that of any previously reported Na/FeS2-based battery. The carbon coating on the FeS2 fiber allows the flexible battery to have an enhanced discharge capacity of 633.43 mAh g−1, even after undergoing five charge–discharge cycles at a 0.1 C rate. At a 2 C rate, a high specific capacity of 393.5 mAh g−1 is maintained, and the value increases on the return from 2 C to 0.1 C until it reaches a value similar to the initial 0.1 C rate. A superior rate capability with enhanced electrochemical stability of the quasi-solid-state sodium metal battery is also demonstrated due to the substrate-free flexible carbon-coated FeS2-fiber-based cathode. Owing to its high flexibility and electrochemical properties, the flexible solid-state sodium metal battery has considerable potential for high-performance sodium batteries.