The Research On Transition Metal Sulfides Materials For Energy Storage Performance

Compared with transition metal oxidation,transition metal sulfides?TMSs?have higher electrical conductivity,good electrocatalytic activity,stronger mechanical and thermodynamic stability,and more excellent electrochemical performance.Thus,TMSs have become one of the hot topics in the field of energy materials research.In particular,the use of TMSs in the field of anode materials for sodium ion batteries and high-efficiency electrocatalysis has gradually attracted wide attention from researchers.Among the many TMSs,Fe S₂ has high theoretical sodium storage capacity(894 m Ah g^-1),abundant reserves,simple preparation and low cost,so it has become a potential anode material for sodium ion batteries.However,due to the semiconductor characteristics and the morphology pulverization during the charge-discharge process of the Fe S₂ bulk material,it suffers from severe capacity decay and poor rate performance.In addition,TMSs also show good catalytic activity in the field of electrocatalysis due to the advantages of higher conductivity and lower reaction energy barrier.For zinc-air batteries,the catalyst of air electrode has always been one of the main factors restricting its development.If we can assemble a high-efficiency bifunctional electrocatalyst on the basis of low-cost TMSs,it will promote the development of secondary zinc-air batteries.Based on the above ideas,we researched application of TMSs in the fields of sodium storage,electrocatalysis and zinc-air batteries,and we achieved some research results as follow:1. Fe S₂ nanosheets encapsulated in 3D porous carbon spheres?Fe S₂@C?were fabricated by a series of treatments and structural regulation using Fe₂O₃ hollow nanospheres as starting materials.The preparation process is as follows:first fabricated Fe₂O₃ hollow nanospheres were prepared by the solvothermal process,and then a conductive polymer PPy was coated on the surface to form Fe₂O₃@PPy.Fe₂O₃@PPy was annealed treatment?400??under an Ar atmosphere.With the carbonization of PPy and the reduction reaction of carbon with Fe₂O₃ at high temperature,the product was converted into Fe₃O₄@C.Fe₃O₄@C composites were etched in 2 M HCl for 2 h,and the Fe₃O₄ in the porous hollow carbon spheres partially dissolved to form dispersed nanoparticles.Finally,the obtained product was further sulfidation to form Fe S₂@C-2h,and Fe₃O₄ nanoparticles dispersed in the porous carbon shell were transformed into Fe S₂.Experimental results show that Fe S₂@C-2h exhibit a significantly improved sodium storage performance compared with Fe S₂ bulk material.At a current density of 0.5 A g^-1,the Fe S₂@C-2h electrode delivered a high capacity of 514.9 m Ah g^-1 after 100 cycles.The capacity of 420.1,410.5 and 396.6 m Ah g^-1 can be achieved at high current densities of 1,2 and 3 A g^-1after 200 cycles,respectively.The capacity is still as high as 272.4 m Ah g^-1 after 500cycles at a higher current density of 5 A g^-1.2. Hollow Fe S₂ nanospheres were successfully synthesized via a simple precursor sulfidation process.These nanospheres have diameters of approximately range from 300 to 400 nm and shells about 50 nm thick.Due to the unique hollow structures,these hollow Fe S₂ nanospheres show excellent sodium storage performance.At a current density of 1 A g^-1,the Fe S₂ anode delivered a high capacity of 541.5 m Ah g^-1 after 100 cycles.In addtion,these Fe S₂ could retain a capacity of313.5 m Ah g^-1 after 500 cycles at a high current density of 5 A g^-1,and still achieve a capacity of 147.2 m Ah g^-1 after 400 cycles at a higher current density of 10 A g^-1.We explored the sodium storage mechanism of Fe S₂ hollow spheres.It was found that its hollow structure can increase the proportion of pseudocapacitance in charge storage,thus hollow Fe S₂ nanospheres exhibit excellent cycle stability performance.3. The one-dimensional Mn₃O₄/Ni Co₂S₄ nanorod structure was designed by diffusion mechanism.First,using?-Mn O₂ nanorods as templates,Ni Co₂O₄ is grown on the surface to form?-Mn O₂/Ni Co₂O₄ composite nanorods.1D Mn₃O₄/Ni Co₂S₄nanorod is obtained by sulfdation of?-Mn O₂/Ni Co₂O₄.During the sulfdation process,the outer layer of Ni Co₂O₄ was transformed into Ni Co₂S₄,the inner?-Mn O₂ was reduced to Mn₃O₄.An interlaced region is formed at the interface of the dual phases by the Kirkendall effect,where lots of Mn₃O₄/Ni Co₂S₄ nanocrystals and amorphous regions co-exist.Moreover,the sulfdation process also resulted in a large number of defects and oxygen vacancies in the mixed region.Thus exhibiting a rather high bifunctional catalytic activity??E=0.74 V?and durability toward ORR/OER.The Mn₃O₄/Ni Co₂S₄ exhibits an onset potential of 0.92 V and a half-wave potential of0.81 V,and the OER potential is only 1.55 V at 10 m A cm^-2.When using this catalyst in rechargeable ZABs,the batteries show a high power density(106.26 m W cm^-2),superior rate stability,small charge-discharge voltage gap?0.86 V?and long-term cycles(650 cycles over 216 h at 5 m A cm^-2).We have also designed the flexible soft-pack ZABs based on the catalyst material,the flexible battery exhibits a high open-circuit voltage of 1.427 V,can be normally charged and discharged at any bending angle,and can maintain a small charge-discharge voltage gap?0.5 V?and cycle stabilityat 1 m A cm^-2.