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To buffer the unavoidable volume expansion and structure collapse problems of transitional metal sulfides during lithiation process, herein, nanosized α-MnS homogenously embedded in axial multichannel carbon nanofibers was well designed and directly used as freestanding anodes for lithium-ion batteries (LIBs). The obtained carbon nanofibers were interwoven into a flexible and cross-linked film, which offered a 3D successive conductive networks and guaranteed sufficient contact interface for electrode/electrolyte. The nanosized α-MnS was homogenously embedded into the carbon nanofiber framework and surrounded with a thin protective carbon layer, which effectively maintained the structural integrity for a satisfied cycling performance. The high aspect ratio carbon nanofibers with axial open channels supplied sufficient active sites and formed long-range electronic pathways along the axial carbon wall. Meanwhile, the radial voids provided enormous accommodation space to alleviate volume expansion and shortened diffusion paths for faster ionic transfer. Benefitting from the above unique merits, the freestanding electrodes delivered excellent lithium storage performances and remarkable long-term cycling stability, including a high initial reversible capacity of 772 mAh g−1 and excellent cycling capacity retention of 93.4% after 100 cycles at a current density of 0.5 A g−1. [ABSTRACT FROM AUTHOR]

The thermosetting polyimide PI nano -fibers based nonwoven membrane is prepared by electrospinning technique and followed by thermal imidization. The physical and mechanical properties of PI nano-fibers based nonwoven separators are tested and the electrochemical performance of the PI membrane for lithium ion battery at different charge cut-off voltage herein common voltage 4.2 V and higher 4.4 V is investigated. The results show that the average diameter of PI nano-fibers is as fine as 276 nm the porosity of PI nano-fibers based nonwoven separators is up to 92% and they exhibit better wettability for the polar electrolyte compared to the commercial Celgard 2400 membrane After 50 cycles at 0.2C/0.2C charge and discharge rate the capacity retention ratio of the cell assembled with PI nano-fibers based nonwoven separators at both voltage range is higher than 80% especially that of 4.4 V charge is up to 91.6% which are obviously superior to commercial Celgard 2400 membrane moreover the special capacity of PI separators fades slower than Celgard 2400 membrane with the increase of discharge rate at both situation. [ABSTRACT FROM AUTHOR]

• The metal sulfide nanoparticles are strongly bridged to fiber skeleton. • The interconnected porous structure offers enough elastic space for volume change. • The protective macro-porous skin prevents the shedding of active nanoparticles. 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. [ABSTRACT FROM AUTHOR]