Multifunctional Fe-S bonds assist poly(3,4-ethylenedioxythiophene) to enhance iron diselenide for ultra-long sodium storage lifetime

Transition metal selenides (TMS) have been used to prepare hundreds of electrode materials for ion batteries due to their superior theoretical capacity, but have been repeatedly limited by the sluggish reaction kinetics and the enormous volume change during the repeated charge/discharge process. Here, we report a facile strategy to fabricate organic-inorganic composites by engineering a unique chemical bonding interface between TMS and conductive polymers. For the first time, poly(3,4-ethylenedioxythiophene) (PEDOT) is utilized to encapsulate iron diselenide (FeSe2) nanoparticles by in situ polymerization, and the Fe-S bonds are meanwhile formed at the interface of FeSe2 and PEDOT. The experimental analysis demonstrates the stability of Fe-S bonds during the sodiation/desodiation process and after long cycling, which can serve as a "bridge" for fast charge transfer and also serve as a "rivet" to stabilize the composite structure. When used for sodium ion storage, the composite offers an exceptionally long lifetime of up to 17,000 loops at 10 A/g without capacity degradation. In addition, it delivers a high specific capacity of 490.4 mAh/g and retains 60 % when the current density is amplified 150 times. The assembled full cell also exhibits excellent cycling stability. This work will provide a feasible way to improve the metal oxide/sulfide/selenides for long-life ion batteries.