Low-crystallinity tungsten disulfide construction by in-situ confinement effect enables ultrastable sodium-ion storage

• Low-crystallinity WS 2 in carbon nanofiber (WS 2 -CNF) composites are prepared through in-situ confinement effect. • The WS 2 -CNF composite presents fast electrochemical reaction kinetics and excellent structural stability. • The WS 2 -CNF electrode exhibits an ultralong cycling life in sodium-ion batteries. As a typical metal sulfide, tungsten disulfide (WS 2 ) with high theoretical capacity has attracted significant attention as the anode for sodium-ion batteries (SIBs). However, WS 2 bulk material usually displays poor rate performance and fast capacity fading in practical applications due to its low conductivity and structural instability. Herein, we propose an in-situ confinement strategy for synthesizing low-crystallinity and ultrafine WS 2 nanosheets within carbon nanofibers (WS 2 -CNF) by the simple heat treatment of electrospun polyacrylonitrile/ammonium tetrathiotungstate (PAN/(NH 4 ) 2 WS 4 ) nanofibers. The low-crystallinity structure of WS 2 with ultrasmall size and rich defects can greatly reduce the volume change and shorten the ion diffusion length. WS 2 nanosheets are confined in the CNF matrix, which is capable of effectively improving its electronic conductivity and structural stability. Based on these advantages, the WS 2 -CNF composite electrode demonstrates fast and ultrastable Na + storage performance with a high capacity of 182 mAh g –1 after 6000 cycles at 5.0 A g −1 . Therefore, this work provides a simple and facile strategy for developing high-performance WS 2 anodes for SIBs.