Study On Preparation Of Transition Metal Compounds And Performance Of Lithium-sulfur Battery

With the market demand for emerging electric vehicles and portable portable instruments,and serious environmental pollution caused by excessive consumption of non-renewable energy sources such as fossil fuels,humans are urgently required to develop non-toxic and harmless,high energy density and inexpensive electronic storage device.Although lithium-ion batteries currently occupy the vast majority of the market,their low theoretical capacity hinders their future practical applications.Therefore,the search for new energy storage devices is of great importance in the current research.Among the existing energy conversion equipment,lithium-sulfur batteries have high theoretical specific capacity(1675mAhg^-1)and high energy density(2600 Whkg^-1)is regarded as a key research object by scientific researchers.Elemental sulfur has abundant reserves in the crust,low cost,non-toxicity,and abundant resources,which can provide good basic conditions for solving these problems.However,lithium-sulfur batteries also face many problems to be solved.For example,the low conductivity of elemental sulfur and lithium sulfide results in low cycle utilization and low cycle performance,the"shuttle effect"caused by the dissolution of polysulfides in the electrolyte solution causes the battery capacity to decay faster,swelling of sulfur causes structural collapse of host material.Therefore,finding a cathode material that can accommodate the volume expansion of sulfur and also limit the dissolution of polysulfides has become the key point of this research.In this dissertation,transition metal compounds are used as strong adsorbents and dopamine is used as a carbon source.The transition metal compounds and PDA have been successfully used together as cathode materials for lithium-sulfur batteries.Using this method,the research results show that,while improving the overall material properties,composite materials can also chemically adsorb polysulfides.The main research work of this paper is as follows:?1?TiO₂ spheres were synthesized by hydrothermal method and calcination in air,then TiO₂@C was synthesized by water bath method and carbonization in N₂,and finally MoS₂ultra-thin nanosheets were synthesized outside TiO₂@C by hydrothermal method.The composition of the synthesized TiO₂@C@MoS₂ composite was analyzed using XRD,Raman,and infrared,the sulfur content of the sample was measured using TGA,and the valence state of the compound was analyzed using XPS.The morphology and lattice fringes of the compounds were characterized by SEM,TEM,and HRTEM.Finally,CV and EIS tests were performed on the composite electrode using an electrochemical workstation,and cycle performance and rate performance analysis were performed using a new Will tester.The research results show that the TiO₂@C@MoS₂/S spheres have been successfully synthesized,and their morphology uniform,sulfur content reaches 63%,and the specific capacity of charge and discharge after 99 cycles at 0.1 C current density reaches 535.8 and 535.9 mAh/g,and the capacity retention rate is about 62%.?2?NiFePBA was used as a precursor,and a layer of polydopamine was coated with tris buffer solution,followed by carbonization in a nitrogen atmosphere to generate double-shell carbon-encapsulated NiFe alloy nanoparticles.Finally,XRD,Raman,infrared and thermogravimetry were used to analyze the structure of the composite material,and the morphology of the composite material was analyzed by SEM.Electrochemical performance tests were performed using an electrochemical workstation and a new Will tester.The results show that the successfully synthesized NiFe@C/S composite has a regular morphology and high uniformity,with a sulfur load of 66.26%.At a current density of 0.1 C,the charge-discharge specific capacity can be maintained at 532 mAhg^-11 and 517 mAhg^-11 after 200cycles,in addition,the battery can maintain a coulomb efficiency of about 98%at a time.?3?CoFePBA was used as a precursor,and a layer of polydopamine was coated with tris buffer solution,followed by carbonization in a nitrogen atmosphere to generate double-shell carbon-coated CoFe alloy nanoparticles.The composition of the synthesized CoFe@C/S composite was analyzed using XRD,Raman,and infrared,the sulfur content of the sample was measured using TGA,and the valence analysis of the compound was performed using XPS.The morphology and lattice fringes of the compounds were characterized by SEM,TEM,and HRTEM.Finally,CV and EIS tests were performed on the composite electrode using an electrochemical workstation.The new Will tester was used to analyze the cycle performance and rate performance.The results show that the morphology of the successfully synthesized CoFe@C/S composites exhibits a highly uniform nanocube structure with a sulfur content of59%.After 70 cycles at 0.1 C,the specific capacity reaches more than 600 mAh/g,and after100 cycles at 2C,the capacity is as high as 140 mAh/g.Under the performance analysis of 0.1C,0.2 C,0.5 C,1 C and 2 C rates the first discharge capacity was 1106.3,873.6,679.8,438.0,and 250.6 mAhg^-1,and the coulomb efficiency remained above 97%.