No abstract

Hard carbon anodes are the most promising candidates for sodium-ion batteries due to lower sodium-embedded platform and higher specific capacity. However, pure hard carbon carbons usually show very low initial coulombic efficiency, low electronic conductance, et al. Herein, hard carbon-soft carbon (HC-SC) composites composed of carbon nanotubes (CNTs) blooming on porous hard carbon, which were synthesized through thermal decomposition of zeolitic imidazolate framework-67 (ZIF-67) and polyvinyl alcohol (PVA) composite. This unique structure could greatly promote the sodium-ion diffusion and electron transport due to the increased electrode/ electrolyte contact area and enlarged pores. As expected, the HC-SC delivers a high capacity (306.8 mAh g À 1 at 500 mA g À 1), impressive cycling stability (256.8 mAh g À 1 after 1000 cycles) and enhanced rate performance (144.9 mAh g À 1 at 20 C), which are far superior to those of both individual hard carbon and soft carbon. This encouraging performance may benefit from the synergistic effect of the modified defect concentration and interlayer distance in hard carbon by soft carbon, as well as the unique hierarchical structure. This work provides an exemplary strategy to develop optimized carbon materials for sodium-ion batteries.

Developing suitable electrode materials for electrochemical energy storage devices by biomorph assisted design has become a fascinating topic due to the fantastic properties derived from bio-architectures. Herein, zephyranthes-like Co 2 NiSe 4 arrays grown on butterfly wings derived three-dimensional (3D) carbon framework (Z-Co 2 NiSe 4 /BWC) is fabricated via hydrothermal assembly and further conversion method. Benefiting from its unique structure and multi-components, the obtained Z-Co 2 NiSe 4 /BWC electrode for supercapacitor delivers an excellent specific capacitance of 2,280 F•g −1 at 1 A•g −1 . Impressively, the constructed asymmetric supercapacitor using Co 2 NiSe 4 /BWC as positive electrode and activated butterfly wings carbon as negative electrode acquires a high energy density of 42.9 Wh•kg −1 at a power density of 800 W•kg −1 with robust stability of 94.6% capacitance retention at 10 A•g −1 after 5,000 cycles. Moreover, the Z-Co 2 NiSe 4 /BWC as anode for sodium-ion batteries exhibits a high specific capacity of 568 mAh•g −1 at 0.1 A•g −1 and high cycling stability (maintaining 80.1% of the second cycle after 100 cycles). The outstanding electrochemical performances are ascribed to that the synergistic effect of bimetallic selenides and N-doped carbon improves electrochemical activities and conductivity. One-dimensional (1D) nanoneedles grown on 3D porous framework increase the exposure of redox-active sites, endow adequate transmission channels of electrons/ions, and guarantee stability of the electrode during charge/discharge processes. This study will shed light on the avenue towards extending such nanohybrids to excellent energy storage applications.

To address low electrical conductivity of sulfur and “poly‐sulfide shuttle” for constructing sulfur hosts with excellent cyclic stability, CoSnO3/CNTs composites are successfully synthesized by combining CoSnO3 cubes and carbon nanotubes (CNTs) via coprecipitation and annealing process. CoSnO3 cubes are bound by continuous carbon nanotube networks, with high specific surface area and vast mesoporous. CoSnO3 with multiple polar active sites has a strong chemical adsorption effect on lithium polysulfide, suppressing the shuttle effect. The carbon nanotubes have continuous conductive networks, which can provide physical confinement with polysulfides and good electrical conductivity. Through the effective combination of advantages of CoSnO3 and carbon nanotubes, CoSnO3/CNTs/S exhibits excellent sulfur storage performance. The maximum discharge capacity of CoSnO3/CNTs/S is 453.3 mAh g−1 at a current density of 0.2 C. After 500 cycles, the discharge specific capacity is still 377.7 mAh g−1. The simple synthesis of CoSnO3/CNTs/S with long cycle life provides a new direction for the future LSBs cathode material research.

A (Ni0.6Fe0.4)65B18Si10Nb4C3 amorphous composite coating has been fabricated on a mild steel substrate by a laser cladding process under different heat inputs. Observation of the structure and phase showed that the thickness of the coating decreased and the amorphous fraction increased when the laser cladding heat input was lower. The cooling rate increases when the heat input decreases, which favours the formation of amorphous phase. Microhardness and wear resistance test results indicated that a lower heat input led to higher microhardness and better wear resistance of the coating. An average microhardness of 1187.0 HV0.2 was obtained with a heat input of 69 J mm–1.