Locking metal sulfide nanoparticles in interconnected porous carbon nanofibers with protective macro-porous skin as freestanding anodes for lithium ion batteries

An innovative structure of metal sulfide nanoparticles locked in interconnected porous carbon nanofiber with protective macro-porous skin (M x S y @MPCNF) is successfully prepared by electro-blowing spinning technique and subsequent one-step sulfurization/carbonization process. The obtained film is directly used as freestanding anodes for lithium ion batteries (LIBs), which provides a three-dimensional (3D) crosslinked conductive network and ensures the fast penetration of electrolyte. Meanwhile, the interconnected porous structure of fibers provides enough active sites for Li + storage and shortens the pathways for Li + transport. Moreover, the protective skin with macro-porous structure endows a fast access pathway for electrolyte and prevents the active nanoparticles from shedding. Most importantly, the metal sulfide nanoparticles are locked in a carbon cage which immobilized by the interconnected porous structure, and strongly bridged to the fiber skeleton through a carbon coating layer. Such a well-designed structure offers enough space for volume change and makes the metal sulfide nanoparticles difficult to detach from the carbon nanofiber support. Benefiting from the above advantages, the optimized freestanding Fe 7 S 8 @MPCNF -15 anodes deliver a high reversible capacity of 776 mAh g −1 at 0.2 A g −1 after 200 cycles, and exhibits an excellent cycling stability after 500 cycles with 86% capacity retention at a high current density of 1 A g −1 . Extraordinarily, the synthetic method is very versatile and can be easily extended to fabricate Co 9 S 8 @MPCNF and Ni 9 S 8 @MPCNF composites with excellent electrochemical performances, which will shed some lights on the development of flexible anodes for various energy conversion and storage systems.