Preparation Of Cobalt-Copper Bimetallic Compounds And Their Applications In Lithium-Sulfur Batteries

With the advantages of ultra-high theoretical specific capacity,low cost,and environmental friendliness,lithium-sulfur batteries are considered as one of the most promising next-generation energy storage devices.However,the commercial application of lithium-sulfur batteries still faces key problems such as shuttle effect,poor conductivity of singlet sulfur,and volume expansion.At present,polar bimetallic compounds with abundant empty d orbitals and active sites,form strong chemical bonds with negatively charged lithium polysulfide,which can effectively promote the conversion between long-chain lithium polysulfide and short-chain polysulfide,and can effectively promote the catalytic conversion of lithium polysulfide and suppress the shuttle effect.In this thesis,CuCo-based compounds loaded with sulfur are used as sulfur host materials for lithium-sulfur batteries using a combination of catalytic conversion and physical and chemical domain-limiting means,and their structural characteristics,physicochemical properties and performance of lithium-sulfur batteries are investigated separately.The specific studies in this thesis are as follows:（1）Bimetallic oxide CuCo₂O₄ with cube structure was loaded on carbon cloth（CuCo₂O₄/CC for short）by solution method and heat treatment process as sulfur host material for lithium sulfur batteries.Among them,Co₃O₄/CC was used as a single metal oxide comparison sample to assemble two kinds of cathode materials into lithium sulfur batteries,and the performance was tested.The results show that CuCo₂O₄/CC has strong adsorption and catalytic conversion ability for polysulfide lithium.In addition,the three-dimensional self-supporting structure is beneficial to alleviate the volume expansion during the reaction process and promote the rapid transfer of electrons and ions.The S@CuCo₂O₄/CC cathode lithium-sulfur battery with sulfur load of 3.5 mg cm^-2 has a high specific discharge capacity of 1141 m Ah g^-1 when the current density is 0.2 C,and can still maintain a high specific discharge capacity of 918 m Ah g^-1 after100 cycles.（2）CuCoN_0.6 nanoparticles loaded with nitrogen-doped carbon nanofibers(here referred to as CuCo N_0.6/NC)with necklace-like structure were prepared by electrostatic spinning technique and nitriding process,and used as sulfur host material for lithium-sulfur batteries.Through electrochemical performance tests and theoretical calculations,it can be concluded that CuCo N_0.6/NC bimetallic nitride is beneficial to promote chemisorption and improve catalytic activity.In addition,the three-dimensional necklace-like framework provides abundant cavities for high sulfur utilization and rapid lithium ion diffusion and electron transfer,and alleviates the volume expansion during charging and discharging.