Controllable Preparation Of CNTs Filled With Fe And Their Application

Energy storage technology represented by lithium-ion batteries has been widely used.In particular,the rapid development of digital products and new energy vehicles in recent years has made it possible to create a green future.However,the low lithium storage capacity of the positive and negative materials of commercial lithium-ion batteries limits its application and development.Lithium-sulfur batteries have extremely high energy density(2600 Wh kg-1)and ultra-high theoretical capacity(1675 m Ah g-1)and have received researchers widespread attention.In addition,elemental sulfur has abundant reserves in the earth,has the characteristics of low cost and environmental friendliness,and has broad application prospects in electrochemical energy storage.However,the practical application of lithium-sulfur batteries has many limitations.There are problems such as poor conductivity of sulfur,the shuttle effect of the intermediate product lithium polysulfide during the cycle,and the volume expansion of battery materials during charging and discharging.It impacts electrochemical performance of Li-S batteries seriously.In this work,the controllable preparation of Fe-filled carbon nanotubes was synthesized by the method of floating catalytic chemical vapor deposition.And it as a cathode material for lithium-sulfur batteries to improve the conductivity and catalytic activity of sulfur,to improve the cycle and rate performance of lithium-sulfur batteries.The main research contents and results are as follows:1.Using anhydrous Fe trichloride as the catalyst precursor,hydrocarbons as the carbon source,nitrogen as the protective gas,and hydrogen as the reducing gas,in-situ synthesis of Fe-filled carbon nanotubes by floating catalytic chemical vapor deposition(FCCVD)in a tube furnace.Many factors that affect the morphology of carbon nanotubes are explored,such as temperature,the catalyst precursor,gas flow rate,matrix,etc.,to realize the controllable preparation of Fe-filled carbon nanotubes.The preparation process of the method is simple,environmentally friendly,and easy to be prepared on a large scale.By adjusting the quality of the catalyst precursor,high filling rate of iron-filled carbon nanotubes were synthesized.As the mass of the catalyst precursor increases,the filling rate inside the carbon nanotubes gradually increases,the highest filling rate is 32 wt% Fe in carbon nanotubes.2.Using the Fe-filled carbon nanotubes and sulfur composites as cathode materials for lithium-sulfur batteries to test their electrochemical performance.The experimental results show that when 32 wt% Fe-filled carbon nanotubes have the most excellent electrochemical performance,it initial discharge specific capacity is 528.6 m Ah g-1and remains above 389.6m Ah g-1 after 500 cycles at a current density of 1C.Capacity retention rate exceeds 73.7% and the coulombic efficiency is close to 100%,which has good long-cycle stable performance.The excellent electrochemical performance of lithium-sulfur batteries is attributed to the high conductivity of carbon nanotubes,and the introduction of transition metals can increase the catalytic activity of the material.To improve the catalytic conversion of Li PS in Li-S batteries and effectively inhibit the shuttle effect of polysulfides.This synthesis strategy opens up a new way for the controllable preparation of metal-filled carbon nanotubes,and provides new ideas for using metal-filled carbon nanotubes as cathode materials for lithium-sulfur batteries and other energy storage or catalysis.