Preparation Of Transition Metal-based Electrode Materials And Its Application In Lithium Sulfur Batteries

The rapidly growing market for electric vehicles and electronics has placed strict demands on advanced electrochemical energy storage systems.Lithium-sulfur batteries have become one of the most promising next-generation energy storage devices due to their high theoretical specific capacity(1675 m Ah g^-1)and high energy density(2600 Wh kg^-1).However,due to the poor electrical conductivity of sulfur,the insulation of discharge products,the shuttle effect of lithium polysulfide and the volume expansion of sulfur,the commercialization of lithium-sulfur batteries is hindered.For the above problems,this paper mainly focuses on the two aspects of current collector and transition metal oxide to design the cathode material,design conducive to the storage of sulfur structure,accelerate the catalytic conversion of polysulfide,and improve the conductivity of cathode materials.The mian research work of this paper is as follows:（1）A new cathode material in the form of current collector,cobalt nickel layered double hydroxide（LDH）grown on nickel foam（NF）was designed and synthesized（Co Ni LDH@NF for short）.Nickel foam has a three-dimensional pore structure,which can provide enough space for sulfur storage and inhibit its volume effect during charge and discharge.Co Ni LDH also provides a large number of hydroxyl active sites,which can enhance the enhanced adsorption capacity of polysulfide.Co Ni LDH@NF not only has a large specific surface area,but also has many transition metals cobalt and nickel active centers,which promotes the rapid conversion of lithium polysulfide,and the metal skeleton improves the conductivity of the material,which is more conducive to improving the electrochemical performance of the battery.Thus,S/Co Ni LDH@NF showed excellent cycling stability after 100 cycles with a capacity of 793 m Ah g^-1at 0.2 C.（2）This work a three-dimensional ordered microporous（3DOM）titania composite cathode material doped with Ta,loaded Co nanoparticles was prepared by template method,referred to as 3DOM Co Ta@Ti O₂.Three-dimensional ordered macropores structure has abundant pores,which can store a large number of active substances,and have a certain buffer effect on the volume expansion of sulfur,and can speed up the mass transfer.There is a strong electrostatic attraction between Ti-O bond and polysulfide in the transition metal titanium dioxide,which can enhance the adsorption of polysulfide.In addition,doping Ta improves the conductivity of Ti O₂by narrowing the energy band gap,while supporting Co can accelerate the catalytic conversion of polysulfide.Thanks to the advanced structural design,the lithium-sulfur battery with 3DOM Co Ta@Ti O₂/S as the cathode electrode has an initial discharge specific capacity of 1192 m Ah g^-1at 0.2 C,and a discharge specific capacity of 916 m Ah g^-1after 100 charge and discharge tests.In the long cycle test at 1 C,the initial specific discharge capacity is 865 m Ah g^-1,and the capacity loss rate per cycle is only 0.037%after 500 charge and discharge tests.In this paper,metal layered double hydroxide and metal oxide with strong adsorption to polysulfide are proposed as composite cathode materials for lithium-sulfur batteries,which provides suggestions for their development and enlightenment for the application engineering of related energy storage materials.