The Synthesis And Lithium Storage Performance Of Silicon-Nano Composites

The research focused on Lithium-ion batteries(LIBs)with high energy density is critical for achieving the development gole of high capacity,long life rechargeble power batteries.Silicon resents an exceptionally high specific capacity of around 4200 mAh·g-1 upon full lithiation with the formation of Li22Si5,with environmentally friendly properties,elemental abundance and a slightly higher voltage platform(0.5 V vs.Li+/Li)than graphite anodes.Especially,under various working conditions such as low temperature and fast charging,Si anodes can avoid the formation of dendritic lithium existed in the traditional anode(graphite or metal lithium).Those characteristics make Si become the most promising anode material for the next generation batteries into the electric vehicles and beyond.The main disadvantages that restrict the application of Si include the large volume changes during lithiation,the continuous growth of the unstable SEI layer,and poor intrinsic conductivity.In this thesis,we firstly synthesized coral-shaped Si nanocrystals via a selective-dealloying method,and then bulit a conductive polymer buffer to combine "nano porous silicon" and "conductive composites" advantages.Besides,a Si/Cu hierarchical porous structure was created as a binder-free 3D continuous integrated anode for lithium-ion batteries.The main contents and results are as follows:(1)The preparation and characterization of coral-shaped nano porous Si via selective dealloying methods.Upon dealloying the carefully selected A192Si8 binary alloy in a HCl solution at room temperature,the obtained Si materials have a uniform continuous porous structure in three dimensions with nano pore size distribution.To analysis the structure evolution mechanism during the dealloying process,we studied the effects of the acid concentration and the reaction time to Si products' structures,morphologies,and the resulted components,by testings of XRD,SEM,HRTEM and XRF.These results indicate that the synthesized coral-shaped nano porous Si materials own good electrochemical properties.By dealloying Al92Si8 alloy in 3 M HC1 solution for 8 h at room temperature,the obtained materials(containing 7.96%Al)demonstrates a high capacity of 2337.5 mAh·g-1 and a high combic efficiency of?86.82%in first charge-discharge cycle at a current desity of 100 mA·g-1,and a stable cycling perfomance with a remained capacity of 1105.1 mAh·g-1 over 100 cycles at a current desity of 500 mA·g-1.(2)The synthesis and characterization of coral-shaped nano porous Si-conducting polymer composite.The interfacial modification of coral-shaped nano porous Si was achieved by surface coating polyaniline in oxalic acid ambient.The conducting polymer combines both continuous electrically network and buffer layer for volume expansion of Si,resulting in excellent long cycle life.Without additional conductive agent,the DS-OP electrode can deliver a capacity of 1897.4 mAh·g-1 and a combic efficiency of 85.48%in the first charge-discharge cycle at a current desity of 200 mA·g-1,and a reversible specific capacity of 547.9 mAh·g-1 at the current density of 1000 mA·g-1 after 1000 cycles.The uniform PANi coating on the Si particles enables a deformable and stable SEI on the coral-shaped nanoporous Si surface and provides fast electronic and ionic transfer channels,which ensure the Si anode with excellent cycle stability.(3)The preparation and structure optimization of high-rate Si/Cu integrated anode.In this work,we designed a binder-free Si/Cu integrated electrode based on in-situ decomposition of Si/CuC2O4 nanocomposites within the pores of Cu foam,and further the Si/Cu/Ag integrated electrode was prepared by simple Ag-mirror reaction.The Si/Cu/Ag integrated electrode resulting in a good rate performance(over 5000 mAh g 'at 1421.97 mA·g-1).