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Sodium-ion batteries (SIBs) have attracted widespread attention as future energy storage systems. However, the development of advanced anodes for SIBs still lags far behind. Metal sulfides exhibit high theoretical capacity yet suffer from low rate-capability and limited life span, resulted from their poor electric conductivity, volumetric fluctuation, and polysulfide dissolution and shuttling. Herein, a two-dimensional (2D) vertical aligned nickel sulfide nanosheets grown uniformly on reduced graphene oxide (rGO) is designed. The unique 2D on 2D structure enhances the electrolyte/electrode contact and reduces the migration/diffusion path of electrons/Na+, thereby greatly improving the rate-performance. Besides, the rGO provides sufficient surface area to absorb polysulfides, which effectively mitigates the shuttling of the intermediates. The NiS@rGO composite delivers 360 mAh/g after 800 cycles at 5 A/g, and a capacity of 540 mAh/g is maintained after 100 cycles at 0.1 A/g. In-situ XRD diffraction confirmed the reversible transformation between NiS and Ni during cycling. Furthermore, when coupled with the well-developed Na 3 V 2 (PO 4) 3 @C (NVP@C) cathode, the NiS@rGO/NVP@C full cell achieves a stable discharge capacity of around 200 mAh/g. [Display omitted] [ABSTRACT FROM AUTHOR]

Acrylic fiber is one of three important synthetic fibers in the world. The disposal and reuse of large number of waste acrylic fibers from fabric manufacturers or waste recovery is an urgent economic and environmental issue. Here, a porous carbon was derived from waste acrylic fibers via pre-oxidized, carbonization and KOH activation. Furthermore, we adopted melamine as nitrogen source to dope the porous carbon materials. When used as the anode of lithium ion batteries, this nitrogen-doped porous carbon shows high reversible capacity of ca. 1200 mA h g −1 after 50 cycles at 0.1 A g −1 . Reversible capacities of 550 and 370 mA h g −1 are obtained at higher current densities of 1 and 5 A g −1 after 500 cycles, respectively. The outstanding electrochemical performance are a result of its large mesopore volume, high-level N-doping (especially, pyridinic-N), large quantity of edge defects, and three-dimensional hierarchical porous architecture. This paper demonstrates that the reuse of waste industrial acrylic fibers as energy storage materials is a promising method for both energy and environmental fields. [ABSTRACT FROM AUTHOR]

• A 2D MXene wrapped Ni-Fe oxide nanocube based flexible electrode was synthesized. • The composite film functioned like a mixed analogous heterostructure. • The film successfully combined the advantages of different components. • The film demonstrated satisfied electrochemical performance and flexibility. In this work, we addresses the fabrication of a flexible film electrode based on 2D MXene wrapped 3D Ni-Fe oxide nanocube mixed analogous heterostructure. The resulted composite film electrode successfully inherits the merit of different building blocks: MXene layers works as binders and conductive additives that can connect cubic Ni-Fe oxide nanoparticals, facilitate the charge transfer and avoid a significant conductivity decrease in the resulting electrode. While cubic Ni-Fe oxide serves as an active spacer inside the adjacent MXene layers to increase the interlayer space, facilitate the electrolyte diffusion and enhance the electrochemical activity of the composite film. As a result, the optimized composite film manifests excellent specific capacitance of 1038.43 mF cm−2 at current density 0.5 mA cm−2. Meanwhile by assembling into all-solid-state flexible supercapacitor, an excellent specific areal capacitance of 328.35 mF cm−2 at 0.2 mA cm−2 was achieved. Additionally, the excellent energy storage performance is well maintained with a capacitance retention of 90.9% during 10,000 charging-discharging long cycles. Furthermore, a high mechanical robustness with 88.9% capacitance remained after subjected to bending at 90° for 50 cycles, suggesting great potentials for the applications in future flexible and wearable devices. [ABSTRACT FROM AUTHOR]