PAANa-induced ductile SEI of bare micro-sized FeS enables high sodium-ion storage performance

High-capacity metal chalcogenides often suffer from low initial coulombic efficiency (ICE) and serious capacity fading owing to the shuttle effect and volumetric expansion. Various carbon-coating and fixing methods were used to improve the above-mentioned performance. However, the synthesis processes of them are complex and time-consuming, limiting their engineering applications. Herein, polar polymer binder sodium polyacrylate (PAANa) is selected as an example to solve the problems of metal chalcogenides (bare micro-sized FeS) without any modification of the active materials. The special function of the polymer binder in the interface between the active material particles and the electrolytes demonstrates that a PAANa-induced network structure on the surface of ion sulfide microparticles not only buffers the mechanical stress of particles during discharging-charging, but also participates in forming a ductile solid electrolyte interphase (SEI) with high interfacial ion transportation and enhanced ICE. The cyclic stability and rate performance can be simultaneously improved. This work not only provides a new understanding of the binder on electrode, but also introduces a new way to improve the performance of batteries.