The Research On The Sodium-ion Storage Performance And Synthesis Of Sulfur-modified Molybdenum-based Composites By Electrospinning

To achieve the high-quality development in the new era,traditional car companies have gradually transformed into a electric and intelligent one.For new energy vehicles,only the long battery life,cost-effective and high cycle life of power batteries could diversified and personalized of the market.At present,lithium-ion batteries as energy storage batteries is almost at the critical point of cost.Affected by this,the researchers turned their attention to the field of sodium-ion batteries.In order to meet the requirements of rapid charging and long stability of the power battery,we mainly use the role of sulfur modification to study the sodium storage performance of molybdenum-based material.The modification of carbon by sulfur further enhances the ion/electron conductivity,accelerates the diffusion and transportation of Na⁺,thereby achieving charge and discharge rapidly.In addition,it can provides additional active sites to store Na⁺,which improve the electrochemical activity of the material.The works carried out in this thesis are as follows:Firstly,we prepared MoO₂@C nanofiber material by uniaxial electrospinning method using ammonium molybdate and polyvinyl alcohol as raw materials,and then double-modifying the material by vulcanization to successfully prepare sulfur-doped carbon and replace MoO₂（S-MoO₂@CNFs）.The S-MoO₂@CNFs was used as the negative electrode for sodium-ion battery,the composition and morphology of the materials were characterized by a series of characterizations.FT-IR and XPS results show that S-doped C and a small amount of S replaced MoO₂ to generate trace MoS₂.The test data of S-MoO₂@CNFs electrode at 1 and 5 A g^-1 high magnification are considerable,showing long cycle stability.Among them,the discharge specific capacity remained at 86 mA h g^-1 after 1200^th cycle at 5 A g^-1.Based on the idea that MoO₂ can be further reduced by C to form Mo₂C at high temperature,we successfully synthesized Mo₂C/C materials based on the previous work.Using sulfur to dope cardon to obtain our final materials（Mo₂C/S-CNFs）and study its electrochemical properties.The experimental data show that the Mo₂C/S-CNFs electrode exhibits batter rate performance,and the stable discharge specific capacities at current densities of 0.1,0.2,0.5,1,2 and 5 A g^-1 are 242,210,188,169 and 96 mA h g^-1,respectively.Even with excellent high-rate and long-term performance,the reversible specific capacity after 1000^th remained at 102.7 mA h g^-1at a high current density of 5 A g^-1.Sulfur-doped carbon materials not only provides more additional active sites for storing Na⁺,but also enhances electrons transport and ions diffusion rates to improve its sodium storage performance.