Construction And Sodium Storage Properties Investigation Of Hierarchical Metal Sulfides

With rapid population growth and economic development,the energy issue has become one of the major problems limiting the development and progress of human society.As a viable alternative to large-scale energy systems,sodium-ion batteries have been attracted great interest owing to the low-cost price and the abundance of Na,as well as their similar electrochemical energy storage mechanism of lithium-ion battery.However,the larger ionic radius of Na⁺ion results in slow reaction kinetics and low capacity of graphite.There for,it is crucial to develop new anode materials for sodium-ion batteries with high-performanc and simple preparation proecss.Due to the higher electronic conductivity,high theoretical capacities and remarkable electrochemical reversibility compared with corresponding metal oxides,this thesis focuses on metal sulfides as anode materials for sodium-ion batteries.The main challenge for practical application of metal sulfides as anode materials is their severe volume expansion causes structural collapse and unsatisfactory cycling stability.To solve these problems,two types of Mo S₂-Ni S anode materials with high capacity,stable cycle,and superior rate performance were fabricated by various strategies of morphology modifications,composition control,interfacial engineering,and electrolyte optimization.It provides a new experimental basis reference and theoretical guidance.The main contents of this thesis are as follows:（1）In this chapter,a template-assistant hydrothermal and sulfuration approach has been successfully developed.Firstly,weakly crosslinked MF microspheres were prepared as templates.Subsequently,Ni Mo O₄nanosheets were produced on the MF surface during hydrothermal.After that,dopamine was employed as a carbon source.Finally,H₂S gas generated by thermal decomposition of thiourea was used to remove the MF templates.The hierarchical hollow spherical structure Ni S-Mo S₂bimetallic sulfide combined with heterojunction and carbon coating was obtained.Mixed metal sulfides have richer redox reactions and higher electron conductivity.The heterostructure greatly enhanced the interfacial reaction kinetics due to abundant active sites and shorten the electrons/ions transport pathway.Mixed metal sulfides show an intrinsic synergistic effect for enhancing sodium storage avoids the aggregation of metal nanoparticles.As an anode electrode for sodium-ion batteries,a reversible capacity as high as 311 m Ah·g^-1after 700 cycles at 1 A·g^-1can be achieved.Furthermore,it shows a superior rate capability of 377 m Ah·g^-1at 8 A·g^-1,indicating that rational structural design can effectively improve the electrochemical properties of electrode materials.（2）Combining the strategies of structural design and heterostructures,Mo S₂-Ni S@NC hollow nanotubes was fabricated by template-assisted hydrothermal treatment and post-sulfidation strategy.Mo O₃nanowires were used asself-sacrificial template and Mo source to form Ni/Mo precursor during hydrothermal treatment.Afterward,Ni/Mo precursors were coated with dopamine with sulfidation under high temperature.This strategy combines the high capacity of metal sulfides,the large specific surface area of ultrathin nanosheets,the hollow tubular shape to shorten ion transport paths,and carbon protection to improve cycling stability and multiplicative performance.The use of ether-based electrolytes facilitates to form thin solid electrolyte（SEI）films,Improving interfacial reaction kinetics.As anode for SIBs,the Mo S₂-Ni S@NC has stable long-term cycling stability(391 m Ah·g^-1maintained after 700 cycles at 2 A·g^-1)and superior rate performance(342 m Ah·g^-1at 10A·g^-1).The as-fabricated pouch battery can power a LED array,indicating its potential for practical application.