| As a major energy storage device of portable electronic devices, lithium-ion batteries are getting more and more attention. Because its practical applications mainly depend on the cycle performance and rate performance of electrode materials, how to improve the performances of electrode materials has become an important topic of the chemistry and materials science. Mo S2 is a typical member of inorganic graphene analogues with high theoretical capacity(670 m Ah·g-1), which allows easy Li+ ion intercalation and deintercalation among the layers. Mo S2 is emerging as a fascinating anode candidate for next-generation, high power lithium-ion batteries(LIBs). In this paper, we designed and constructed a 3D Mo S2 nanotubes@Fe3O4 nanoparticles hybrid structure due to its advantages of easily stack, aggregation and volume change in the charge and discharge cycles of layered Mo S2 structure, and it showed excellent electrochemical performances of lithium storage by lightening the synergies.Herein, Mo S2 tubes with hollow structure were synthesized by means of solvothermal reaction. Through the research on the key parameters including ethanol content and the reaction temperature, the best technology of synthesis of Mo S2 tubes was determined, and the mechanism of the formation of Mo S2 tubes was proposed, that is, the increase of temperature and ethanol content decreased the stability of the intermediates formed in the layered Mo S2, making the forces between Mo S2 layers weaken gradually from the edge to the middle layer, so the layers were getting curly until the formation of tubular structure. Electrochemical tests show that, it delivers a reversible capacity of 721 m Ah·g-1 after 50 cycles under the current density of 100 m A·g-1, showing a good cycle performance. The reason is that the hollow internal structures offer more free volume, relieving the stress in the process of charging and discharging, and shortening the Li+ diffusion path. At the same time, large specific surface area has increased the electrode/electrolyte contact area, providing more lithium storage sites, which makes the cycle performance of the material greatly increased.However, due to a certain degree of aggregation of Mo S2 tubes after several cycles, the insertion and extraction of lithium ions have been hampered, resulting in the decay of discharge capacity. Based on this, we expect to suppress the aggregation of Mo S2 tubes by introducing a second component, which is Fe3O4. So we designed a three-dimensional Mo S2 nanotubes@Fe3O4 nanoparticle hybrid structure, through the study of Hansen solubility parameters, the most suitable solvent, THF, was determined, in which the Fe3O4 nanoparticles self-assembled uniformly and densely at the surface of Mo S2 nanotubes with the van der Waals force, which exhibited excellent electrochemical properties of lithium storage by an impressive synergistic interplay. By means of TEM, XRD, XPS characterization, it proves that it has not changed the structures and properties of the two components during the assembly process. Electrochemical tests show that under the current density of 100 m A·g-1, it delivers a capacity of 1113 m Ah·g-1 after 100 cycles, and when the current density increased to 2000 m A·g-1, there is still a reversible capacity of 800 m Ah·g-1, showing a good cycle performance and rate performance. The ultra-high electrochemical properties benefit from the following aspects:(1) In the composite materials, tubular Mo S2 itself has high specific surface area and unique porous, which greatly benefits to the storage and transportation of Li+, providing more attachment points for the particulate Fe3O4 at the same time, restraining the reunion effectively between Fe3O4 nanoparticles and buffering the stress among Mo S2 nanotubes in the process of charging and discharging.(2) Fe3O4 nanoparticles have played an important role as mechanical isolation, preventing Mo S2 tubes from restacking in the charging and discharging process, it functions through an impressive synergistic interplay between the two active materials.(3) Compared with carbon materials and precious metals, Fe3O4 has high theoretical specific capacity, which contributes a part to the capacity for composite materials. Thus, after decorated with Fe3O4 nanoparticles, tubular Mo S2 behaves with higher cycle performance and rate performance.In short, in this paper, Mo S2 nanotubes and Fe3O4 nanoparticles were successfully self-assembled together in a simple and effective method, which improved the electrochemical properties of the materials. This novel hybrid structure design and self-assembly method provide the beneficial reference for new lithium ion batteries and even for the development of other nano-functioned materials. |
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