Preparation Of Silicon And Carbon Nanofibers And Their Electrochemical Performance

There is a harsh demand on advanced lithium-ion batter ies with the development of large-scale energy storage,such as electrical vehicles.To solve these problems,one of critical factors is to develop an anode materials with higher performance.In this work,we have studied the most promising anode materials of SiO2/C composites.Their electrochemical properties have been improved through in-situ compositing,annealing conditions optimizating,nitrogen-doping and porous-structural preparation,the internal reasons of the promoted electrochemical performance were also revealed.In this work,solid SiO2 powders and liquid TEOS were used as the silicon sources,self-standing SiO2/C composite nanofibers were prepared by electrospining and carbonization.Compared with the ex-situ composite nanofibers,the in-situ composite SiO2/C nanof ibers carbonized at 800 °C exhibited no agglomeration,uniform size and amorphous structurer.And as free-standing anode materials in lithium-ion batteries,the in-situ SiO2/C composite nanofibers showed capacity of 405 m Ah/g after cycled 1000 times.Furthermore,as free-standing anode materials in sodium-ion batteries,the composite showed ultrahigh capacity of 429 mAh/g at the first discharge,and 150 mAh/g maintained after cycled 250 times.Importantly,this is the first research result of SiO2/C composite as anode materials in sodium-ion batteries.The superior electrochemical performance can be ascribed to their uniform distribution of carbon and silicon atoms,amorphous structure,nitrogen doping,exc ellent flexibility and mechanical strength,and self-standing electrode.Nitrogen doping of carbon materials is an efficient way to improve their electrochemical performance.The nitrogen-doped carbon nanofibers with different nitrogen content have been prepared through adding different proportions of urea in the precursor.It is found that the nitrogen-doped carbon nanofibers with a ratio of 1:0.75(m:m)by carbon and nitrogen,exhibited good cycle and capacitance stability in low and high current density,respectively.The good electrochemical performance can be rationalized by the appropriate doping amount and the form of nitrogen.The nitrogen-dopedporous carbon nanofibers can further improve its performance.The porous nitrogen-doped carbon nanofibers were successfully prepared by adding different proportions of template in the precursor followed by etching processing.It is found that the porous nitrogen-doped carbon anodes exhibited mesh structure,excellent flexibility and electrochemical performance.After cycled 500 times at a current density of 1000 m A/g,the porous nitrogen-doped carbon anodes showed excellent capacity of 473 m Ah/g.Outstanding rate capability was also realized with capacity of 120 m Ah/g at a rate of 3000 m A/g.The superior electrochemical performance of porous nitrogen-doped carbon nanofibers were expected to be applied in large-scale energy storage.