Research On The Construction Of Silicon-based Materials With Diverse Structure For The Anodes Of Lithium Ion Batteries

Nowadays,Li-ion secondary batteries have become the main energy storage devices,and the energy density has been increasing during the past three decades.The anode materials are widely studied as the key component of Li-ion batteries.Currently,the commercial anode material is graphite,but the theoretical capacity of graphite is inferior,and it can no longer meet the needs of high-capacity battery.Therefore,new promising anode materials are expected to replace graphite.The theoretical capacity of Si can reach about 4200 mAh g-1,which is more than 10 times that of graphite.However,the huge volume expansion(over 300%)impedes commercialization application of silicon during the charge/discharge process,which would cause the active material to peel off and detach from the collector.Constructing nanoporous Si-based composites can effectively buffer the volume expansion and shorten the Li+transmission distance,and these methods can improve the electrochemical performance effectively.Firstly,preparation of nanoporous silicon-antimony alloy(np-SimSb)was completed by chemical dealloying method.Firstly,the precursor alloy was prepared by rapid solidification technology.By adjusting the composition of the three alloys of the precursor(Al70(SixSb)30 and Al80(SiySb)20(at.%)alloy(x=0.6,0.8,1;y=0.6,0.8,1)),np-SimSb alloys with different structures and morphologies were prepared.Among them,the sponge-like np-Si15Sb15(corresponding precursor is Al70(SiSb)30)exhibits the most uniform pore structure and the largest specific surface area.The np-Si15Sb15 was used as the negative electrode of Li-ion battery at a current density of 100 mA g-1 for 90 cycles and the reversible specific capacity was 647.4 mAh g-1.Moreover,the np-Si1Sb15 showed excellent rate performance(at 500 mA g-1 and 1000 mA g-1,the reversible capacity were 551.31 and 453.96 mAh g-1).Nanopores can not only effectively buffer the volume expansion,but also increase the contact area between the electrode material and the electrolyte,which can shorten the migration and diffusion distance of Li+.Finally,utilizing Si@RF and ZIF-67 as precursors,the composite material(Si@C-Co9S8/C)with spherical Si@C and dodecahedron Co9S8/C with hollow core-shell structure was prepared.It can exhibit the excellent electrochemical performance.The electrochemical tests show that the Si@C-Co9S8/C anode can maintain the reversible capacity for 1399 mAh g-1 after 200 cycles at 100 mA g-1,and the coulombic efficiency keeps at 99%.When the current density increased into 1000 mA g1,the reversible specific capacity could maintain 840.46 mAh g-1 after 500 cycles.It also represents excellent rate performance.When the current densities are set at 200,400,1000,2000 mA g-1,the reversible specific capacities are about 1365,1170,943,and 630 mA h g-1.The core-shell Co9S8/C has the adsorption effect on Si@C,which can effectively inhibit the agglomeration of Si@C during the cycling,in addition,coating Si with carbon and compounding with Co9S8/C is effective to buffer the volume changes during the cycles.The carbon shell on the surface of composites can form a dense conductive network,which can speed up charge transport and Li+diffusion.