Construction Of Carbon Nanotubes Embedded Transition Metal Sulfide Microspheres And Sodium Storage Performance

With the growing demand for energy,fossil fuels are being consumed.Environmental pollution is becoming more and more serious.Therefore,it is urgent to develop clean,free-pollution,efficient,convenient,renewable energy storage devices.In recent years,lithium-ion batteries?LIBs?have been widely used in energy vehicles,mobile phones,computers and other fields.However,the limitation of lithium resources will become the bottleneck of lithium ion battery development.The resource-rich and low-cost SIBs is expected to become the next generation of high-performance large-scale energy storage devices.It's an urgent task for us to develop SIBs to seek new high specific capacity and long life sodium storage anode materials.Transition metal sulfide?TMS?storage sodium-ion anode materials have the advantages of high theoretical ratio,low cost,simple preparation and so on.But they still have the problem of poor multiplier performance and sharp capacity attenuation caused by volume effect.Based on this,this paper constructs a transition metal sulfide microsphere structure embedded in carbon nanotubes,and studies its sodium storage electrochemical properties and charging and discharging mechanism.?1?Preparation of hierarchical microstructure of CNTs interwoven ultrathin Co₃S₄ nanosheets and sodium storage performance.The precursor of Co₃O₄/CNTs was obtained by ultrasound-assisted precipitation and subsequent combined with heat-treatment.Carbon nanotube embedded in Co₃S₄ nanosheets microspheres were obtained by hydrothermal vulcanization of Co₃O₄/CNTs with thioacetamide as the sulfur source.The optimized Co₃S₄/CNTs-9 composite material is composed of CNTs interwoven Co₃S₄ microspheres.The thickness of the nanosheets composed of the microsphere is about 10 nm.The nanosheets comprises nanoparticles and has rich mesoporous structures.The specific surface area of the nanocomposites is 11.7 m² g^-1,and the pore diameter is mainly distributed between 7-50 nm.After 100 cycles,the Co₃S₄/CNTs-9 electrode delivered 355.90 mA h g^-1 capacity at 0.5 A g^-1,with 67.78%retention of the initial one.It displays a charge capacity of 508.50 mA h g^-1 at 1 A g^-1with the 76.22%retention of the capacity at 0.05 A g^-1.?2?Preparation of CNTs embedded Ni₃S₂ microspheres and its sodium storage performance.Porous and hollow NiO/CNTs precursors were obtained by ultrasonic precipitation combined with heat treatment.The structure of Ni₃S₂/CNTs microspheres was obtained by high-temperature vulcanization of NiO/CNTs with sulfur powde r as sulfur source.The structure of Ni₃S₂/CNTs microspheres was obtained by high-temperature vulcanization of NiO/CNTs with sulfur powder as sulfur source.With the increase of CNTs content,the agglomeration phenomenon of microsphere structure was weakened and showed porosity.The specific surface area of Ni₃S₂/CNTs-10 is 14.769m² g^-1,and the pore diameter distribution is mainly micropores less than 2 nm.The discharge capacity of the Ni₃S₂/CNTs-10 electrode at 0.5 A g^-1 was 343.0 mA h g^-1after200 cycles.The capacity retention was 78.8%and the initial coulomb efficiency was80.5%.Its discharge capacity at 5 A g^-1 is 417.8 mA h g^-1,with 76.4%capacity retention compared with 0.05 A g^-1.?3?The high initial coulomb efficiency,excellent cycling,and sodium storage performance of carbon nanotubes embedded in transition metal sulfide microstructures are mainly attributed to as follows:?a?the three-dimensional conductive network formed by CNTs in the composite system makes the whole composite electrode display excellent conductivity;?b?nano-particle size within the microstructure reduces the transmission distance of sodium ions;?c?the gaps within the microstructure relieve the stress caused by volume effect and improve the cycling stability;?d?the microstructure reduces the formation of SEI film,thus improving the first coulomb efficiency.This paper provides a feasible scheme for the preparation of transition metal sulfide embedded carbon nanotube micro/nano structure,and also provi des a kind of thought for improving the electrochemical performance of the transition metal sulfide sodium ion battery anode material,especially improving the initial coulombic efficiency and rate performance.We also has laid a good foundation for further research on sodium storage anode materials.