Research On Preparation And Performances Of SiO_x-based Anode Materials

SiO_x material is considered as one of the next generation lithium battery anode materials because of its suitable high specific capacity,lower volume expansion than that of Simaterial,suitable working potential,rich natural resources and low cost.However,its low conductivity,low initial coulomb efficiency（ICE）and nonnegligible volume effect still need to be solved.In this paper,disproportionated SiO_x,nano SiO_x and SiO_x/lithium silicate（Li_aSi_bO_c）-based composites were prepared;and single-walled carbon nanotubes（SWCNT）was used to improve their conductivity,structure stability and electrochemical properties.Disproportionated SiO_x and nano SiO_x were prepared by high temperature sintering and high energy ball milling method.The effects of ball milling time and sintering temperature on the material properties were investigated.As temperature increasing,the oxygen content on the surface of SiO_x particles increased gradually.The SiO_x material was disproportionated and the diffraction peak of crystalline silicon appeared.As milling time increasing,particles size was decreased.When the milling time reached 6 h,SiO_x particles agglomerated.SiO_x/SWCNT composite electrode was prepared by adding SWCNT and graphite（C）.The effects of SWCNT and graphite on the composite electrode were studied.After cycling,SWCNT wrapped SiO_x particles to ensure the electrochemical activity of SiO_x.The optimal addition amount of SWCNT is 0.8%.When the addition amount of graphite was 30%,the SiO_x/C/SWCNT composites displayed a reversible specific capacity of1117.7 m Ah g^-1 at 0.8 A g^-1 with no capacity fading after 100 cycles and the reversible specific capacity of 858.3 m Ah g^-1 at 4 A g^-1。SiO_x/Li_aSi_bO_c-based composites were prepared by using different SiO_x materials and different lithium sources under high temperature sintering conditions.The effects of SiO_x materials and lithium sources on the properties of SiO_x/Li_aSi_bO_c-based composites were studied.The optimal combination obtained was ball milling&disproportionated SiO_x-1h-900 and LiH.The effects of the proportion of SiO_x materials and LiH on SiO_x/Li_aSi_bO_c-based composites were investigated.There are three forms of lithium silicate in SiO_x/Li_aSi_bO_c-based composites:Li₂Si₂O₅,Li₂SiO₃ and Li₄SiO₄.With the increase of Li/Siratio,the morphology of lithium silicate changes from Li₂Si₂O₅to Li₂SiO₃ and then to Li₄SiO₄.SWCNT was added in SiO_x/Li_aSi_bO_c-based composites to prepare the electrode.The optimized conditions were as follows:the molar ratio of SiO_x materials to LiH is 3:1 and the content of SWCNT is 0.8%.The resulting material has a reversible capacity of 680.9 m Ah g^-1,with the ICE of 76.3%and a capacity retention of 87.6%at 0.8 A g^-1 after 200 cycles,a reversible capacity of 506.1 m Ah g^-1 at 4 A g^-1,and returns to 1115.0 m Ah g^-1 at 0.1 A g^-1.