In Situ Preparation Of Metal Fe,Co,Ni/KB Composite Nanomaterials And Their Applications In Lithium-sulfur Batteries

Due to its high theoretical energy density and environmentally friendly characteristics,lithium-sulfur batteries are more in line with the energy requirements of electric vehicles and portable electronic products,and have become a new research hotspot to replace lithium-ion batteries.Therefore,from the perspective of practicality,this article uses Ketjen Black（KB）,which has the advantages of large specific surface area and high conductivity,as the carbon support material,and transition metal Fe,Co,and Ni as additives,respectively.Through the in-situ synthesis method,the metal Fe,Co,and Ni were embedded into the micropores and mesopores of KB to obtain Fe/KB,Co/KB and Ni/KB composite nanomaterials with high purity,thin particle size,low cost,good dispersibility and tightly bonded to the matrix,and used them as sulfur carriers to prepare Fe/KB/S,Co/KB/S and Ni/KB/S composite cathode materials.Through microstructure analysis and electrochemical performance detection,the mechanism of Fe,Co,Ni nanoparticles as cathode modification additives on the electrochemical performance of lithium-sulfur batteries is studied.The main research contents and results are as follows:（1）On the basis of wet impregnation,introducing a mixed atmosphere of nitrogen and hydrogen under high temperature conditions,some nano-metal Fe particles were successfully embedded in the hierarchical pore structure of KB,with a size between 3-30 nm.The adsorption-catalytic effect of nano-metal Fe is confirmed by UV-vis absorption spectra,XPS spectrum and Li₂S deposition experiments.While forming Fe-S bonds to enhance the trapping capacity of Li PSs,it can increase active sites and enhance intrinsic activity,and catalyze electrochemical reaction kinetics.And in the electrochemical performance analysis,it is proved that the Fe/KB/S cathode has higher conductivity,faster Li⁺migration,less polarization and more effective electrochemical catalytic ability.When the cathode S load is 3.0 mg cm^-2,the initial discharge specific capacity at 0.05 C reaches 1219.0 m Ah g^-1,and the initial discharge specific capacity at 0.5 C reaches 826.6 m Ah g^-1.The stable cycle exceeds400 times,the remaining specific capacity is 426.6 m Ah g^-1,and the coulomb efficiency remains above 95%.（2）Co/KB composite nanomaterials were prepared based on wet impregnation and carbothermic reduction methods.The visible diameter of nano metal Co particles is about 3-30 nm,and the specific surface area reaches 905.5 m²g^-1.It is proved that the uniformly distributed nano-metal Co particles in the composite material increase the active sites for adsorption and catalytic Li PSs,which can not only prevent the migration of Li PSs from the KB structure through strong chemical interactions,but also provide power for the nucleation of Li₂S through its catalytic effect.When the cathode S load is 3.0 mg cm^-2,the initial discharge specific capacity of the Co/KB/S cathode at 0.05 C reaches 1249.0 m Ah g^-1,and an initial specific capacity of 785.5m Ah g^-1at 0.5 C,and stable cycle more than 500 times.At the same time,it has a higher discharge capacity at different discharge rates of 0.1-2 C.（3）Nano-metal Ni nanospheres with a diameter of 3-30 nm were prepared in Ni/KB composite nanomaterials,which originate from the penetration of Ni²⁺into the micropores and mesopores of KB to form highly dispersed nano Ni particles,and the physical confining of KB pore structure inhibits its growth.It is proved that the uniformly distributed Ni nanoparticles can be used as the active site of the catalytic reaction to accelerate the reaction kinetics,and effectively adsorb Li PSs generated during the reaction process,thereby reducing the influence of the shuttle effect.In the electrochemical test,the Ni/KB/S cathode shows super high conductivity and surface activity,and has good chemical stability and reversibility.When the S load is 3.1 mg cm^-2,the initial discharge capacity of the Ni/KB/S cathode at 0.05 C increases from1035 m Ah g^-1to 1253 m Ah g^-1,and the initial discharge specific capacity at 0.5 C increases more than 20%reaches 818.4 m Ah g^-1.At the same time,the specific capacity of the KB/S cathode decays rapidly after 270 cycles,while the capacity decay rate of the Ni/KB/S cathode slows down a little,and the stable cycle exceeds 500 times.