Etching Preparation Of Silicon-Based Anode Materials And Its Electrochemical Property

The rapid development of new energy vehicle industry is advancing the power battery technology.High capacity anode materials are required for the high energy density power batteries,and silicon anode materials received extensive attraction owing to its high theoretical lithium capacity(4200 mAh·g-1).However,the huge volume expansion in silicon-lithium alloying reaction is 400%,which results in silicon pulverization,unstable solid electrolyte interface film(SEI)in the electrolyte,and thus inferior cycle performance of the battery.The previous reports showed that a reasonable nano-microstructure can effectively improve the electrochemical performance of Si materials.In this paper,nano-microstucture silicon anode materials were prepared by etching Al-Si alloy,and the influences of etching temperature and amount of hydrochloric acid on the final Si anode microstructure and electrochemical performance were studied.Finally,the preparation and electrochemical performance of nanoporous silicon/graphene composites were also discussed.The main research contents and results are shown as follows:(1)Si anode materials were prepared by HCl etching of micrometer-sized A160Si40 alloy at 0,20,40,60 ?,respectively.X-ray diffraction(XRD),inductively coupled plasma emission spectroscopy(ICP),scanning electron microscope(SEM)and specific surface characterization were used to study the material structure and morphology.It shows that the prepared nano-microstructured silicon is characteristic of nanoporous structure and high crystallinity.The diameter of silicon nanoparticles increases with the increase of reaction temperature.When preparation temperature is set to be 20 ?,the prepared Si exhibits the residual aluminum content of 0.95%and a low specific surface area of 15 m2/g.The Si prepared at 20 ? shows a superior electrochemical performance with the first charge and discharge capacity of 3311 mAh·g-1 and 3783 mAh·g-1,respectively,the initial coulomb efficiency(ICE)of 87.52%,and the residual capacity is 769.2 mAh·g-1 after 100 cycle.(2)Si anode materials were prepared by HCl etching with the various molar ratios of aluminum and hydrochloric acid of 1:1.6,1:2.2,1:3.0,1:3.8 and 1:4.4,respectively.The Si structure and morphology were characterized by XRD,ICP,SEM,TEM and specific surface instrument.It shows that the particle size i.e.D50 of the nano-microstructured Si ranges from 3.0 to 9.0 ?m.With increasing HCl content,the residual aluminum content decreases and the specific surface area of Si increases.Note that the Si prepared with the molar ratio of 1:4.4 shows an low aluminum content of 0.02%and high specific surface area of 32 m2/g.Electrochemical measurement results exhibit that the Si prepared with molar ratio of 1:2.2 has the best performance,with the first delithiation and lithiation capacities of 3342 mAh·g-1 and 3771 mAh·g-1,ICE of 88.63%,and the residual capacity of 825 mAh ·g-1 after 100 cycles.Thus,the remaining aluminum content and the nano-micro structure of the Si anode material can be regulated by varying the addition amount of hydrochloric acid.Moreover,appropriate aluminum amount and reasonable specific surface ares can improve the electrical conductivity and cycling performance of the Si material.(3)On the basis of the previous,etching A160Si40 and graphene in situ preparation of nano porous silicon/graphene composites at 20 ?,molar ratio of aluminum and hydrochloric acid is 1:4.4 and 1:2.2,respectively.It is found that graphene does not improve the capacity and cycling performance of the Si anode material,showing the initial charge and discharge capacities of 1:2.2-Si+5%G is 2704 mAh·g-1 and 3202 mAh·g-1,ICE of 84.46%,and the residual capacity after 100 cycles of 504.9 mAh g-1,for the silicon/graphene composite with the graphene content of 5%.This simple and facile in-situ preparation of Si-based composite provides useful experience for the future research on the preparation of Si/C composites.