Preparation And Electrochemical Properties Of Si Nanowires Anode For Lithium Ion Battery

Lithium ion battery as a green energy storage device,having the advantages of high energy density,low self discharge,no memory effect,and long life,is widely used in portable electronic products,and has a wide application prospect in the field of electric vehicles and other energy.Currently commercial lithium-ion battery carbon anode material has a low theoretical specific capacity,only 372 mAh g^-1,which can not meet the demand of high performance lithium ion batteries.Si is abundant in nature and and have the high theoretical specific capacities of 4200 m Ah g^-1,respectively.However,in the process of intercalation/deintercalation of lithium ions Si will produce a huge volume expansion,which results in the destruction of electrode's structure and rapid decline in capacity.In this paper,the electrochemical performances of Si electrodes have been improved by a strategy of nanostructuring and further pickling.Using micron-sized Si and Fe powders as the raw materials,the novel Si nanowires?NWs?were synthesized by a transient VLS mechanism through DC arc discharge plasma.Characterization on the powders were carried out by means of XRD and TEM.It was indicated that the disordered network of Si NWs are formed with small Fe Si2 particles at their tips and amorphous a-SiO_x coating on the surface.The Si NWs have uniform morphology with about 10-20 nm in diameter and hundreds of nanometers in length.The electrochemical performance of silicon nanowires can be improved by selecting suitable binder and increasing the content of conductive agent.The Si nanowires of sample b has the smallest diameter and the highest first discharge capacities(3309.2 mAh g^-1).The Si nanowires of sample c has the longest length and the most excellent cycle performance.It's first discharge capacities was 2165.2 mAh g^-1.After 100 cycles,the reversible capacity is 539.7 mAh g^-1.To further improve the cycling performance of Si nanowires electrode,the active component of nanopowders?Si:Fe=1:1 in mass ratio?was treated with 8 wt.%dilute hydrochloric acid to remove of the metal Fe phase.It was confirmed by XRD and TEM analysis that the metallic Fe was completely removed and a little?-Fe was persisted.After etching,the material is still intertwined nanowires,but the distance between nanowires decreases.The Si nanowires was used to fabricate an composite electrode,which exhibited the first discharge capacity of 1334 mAh g^-1at 300 mAh g^-11 current density.After 10 cycles,the capacity reduced to 400 mAh g^-1,but the columbic efficiency can always be kept above 94%.After 140 cycles,the reversible capacity is 700 mAh g^-1,which is 1.8 times of the traditional carbon materials.