The Investigation Of SiO_x-TiO_y-CNT Anode Materials

Silicon material have a high theoretical specific capacity of 4200 mAh/g,but the volume effect of the material during charging/discharging process are too drastic,resulting in short cycling life and low coulombic efficiency.Titanium oxide is known as"zero strain"material due to no evident volume expansion can be observed upon the repeated cycling process,which contributes to an exceptional cycle stability.However,that electrode material is formidably plagued with poor conductivity and low theoretical specific capacity.In this investigation,SiO_x-TiO_y-CNT composites based on the principle of complementary advantages are designed as the anode materials for new-generation lithium ion batteries.The introduction of SiO_x raises the specific capacity of the material.Additionally,the introduction of TiO_y greatly buffers the volume expansion of SiO_x material in cycling,prolongs the life of the material,and promotes the cycle stability of materials.Furthermore,CNT is utilized to form aelectric conductive network inside the material.Among this compoites,SiO_x-TiO_y is bonded by-Si-O-Ti-O-bonds to form a uniformly distributed material.SiO_x-TiO_y-CNT composites were prepared by a simple and facile solvothermal synthesis method.And then the properties of SiO_x-CNT,TiO_y-CNT,and SiO_x-TiO_y-CNT materials were parallelly compared.Moreover,the effects of different CNT contents in SiO_x-TiO_y-CNT materials,calcination temperature in SiO_x-TiO_y-CNT synthesis,and different Si sources used in the synthesis procedure were investigated.(1)Comparing the properties of SiO_x-CNT,TiO_y-CNT,and SiO_x-TiO_y-CNT materials,the synergistic effect of SiO_x and TiO_y on SiO_x-TiO_y-CNT materials can be obtained.SiO_x-TiO_y-CNT displayed a significant improvement with respect to electrochemical properties compared to SiO_x-CNT and TiO_y-CNT materials.Consequently,it can deliver a reversibly stable specific capacity at 270 mAh/g after 200 cycles.And its rate performance is also noteworthy,specific capacity of 170 mAh/g and 154 mAh/g can be maintained at current densities of 3000 mA/g and 4000 mA/g,respectively.(2)The effect of CNT on the properties of SiO_x-TiO_y-CNT materials was investigated by varying the content of CNTs in SiO_x-TiO_y-CNT materials.Four groups of materials with CNT contents of 0,15 wt%and 25 wt%were tested,respectively.The electrode material without CNT showed poor conductivity,which caused unsatisfactory cycle stability,drastic capacity decay,and unacceptable rate performance.When the CNT content reaches 25 wt%,the specific capacity of the material decreases.15 wt%of CNT is a good composition.(3)The preparation temperature is an important factor that influence the properties of the material.With the increase of calcination temperature,thematerial convert to crystalized material from the amorphous material,and the crystal grows bigger at elevated temperature.The lithium ion conductivity of amorphous materials is significantly higher than that of crystalline materials.When the calcination temperature is raised to 500℃,a platform appears on the charge/discharge curves,thereby,causing a loss of specific capacity of the material.(4)Different silicon sources were tested in the synthesis of SiO_x-TiO_y-CNT to look for a suitable silicon source for the topical material synthesis.It turns out that tetrapropoxysilane was proved to be the best.