Controllable Synthesis Of Novel Silicon Oxide And Carbon Nanomaterials For Energy Storage Applications

Environmental pollution and the exhaustion of traditional fossil fuels have made the development new energy resources more urgent.In recent years,the nanomaterials based on silicon oxides and carbon have attracted extensive attentions due to the low cost,abundant reserves and excellent tenability.Herein,we systematically investigated the nanomaterials based on silicon oxides and carbon,including the optimization of synthesis routes,control of morphology and structure,characterization of electrochemical performance and analysis of energy storage mechanism.The electrochemical performances of silicon oxides lithium ion battery anode materials and carbon based supercapacitor electrode materials have been markedly improved.These main significant achievements are briefly summarized as follows:?1?In order to address the inherent defects of remarkable volume change,low conductivity and pulverization of silicon oxides based anode,we adopt one-step sol-gel reaction to realize the vinyltriethoxysilane?silicon source?and resorcinol/formaldehyde?carbon source?.And then,the non-stoichiometric SiO_x and amorphous carbon homogeneous microspheres?SiOx/C?can be obtained through the carbonizing process.With the ultrafine SiO_x nano-domains distributing uniformly in the amorphous carbon microspheres,large volume change of SiO_x was buffered effectively,and the aggregation and pulverization of SiOx were prevented.Furthermore,the electrical conductivity of whole composite was also promoted.When used as anode materials for lithium ion batteries,the obtained SiOx/C microspheres exhibited a reversible capacity of 999 mA h g^-1 can be achieved at 100 mA g^-1,retaining 85.4%of the capacity after 150 cycles.At 500 mA g^-1,the SiO_x/C delivers a specific capacity of689 mAh g^-1 and SiO_x/C//LiFePO₄ full cells are also assembled,leading to and energy density of³72 Wh kg^-11 based on the total mass of active materials.Furthermore,we also explored the influence of carbon content on the electrochemical performance of SiOx/C composite microspheres.It can be found that the initial Coulomb efficiency and reversible capacity decrease with increasing carbon content while the capacity retention increases significantly.Therefore,searching out optimum proportion of SiO_x and carbon can optimize the electrochemical performance of SiO_x/C composites.?2?In order to further optimize the electrochemical performance of silicon oxides based anode materials.The multi-layer organosilica composite microspheres are formed through multi-step sol-gel reaction.And then yolk@shell structured SiO_x/C composite microspheres can be obtained through the etching and carbonizing process.Finally,a chemical vapor deposition?CVD?process is employed to coat the yolk@shell structured SiO_x/C with semi-graphitic carbon on both the exterior and interior surfaces?SiOx/C-CVD?.The unique yolk@shell structure provides large inner voids for volume change accommodation.The semi-graphitic carbon coating layers on the exterior and interior surfaces not only promote the electrical conductivity of whole composite,but also effectively buffer the large volume variation of SiO_x and enhance the structural integrity,and induce the formation of thin and stable SEI film on the surface.When used as anode materials for lithium ion batteries,the obtained SiO_x/C-CVD composite microspheres a high reversible capacity(1165 mAh g^-1 at 100 mA g^-1)as well as outstanding durability(972 mAh g^-1 after 500 cycles at 500 mA g^-1).Furthermore,the full cells of SiO_x/C-CVD//LiCoO₂ are also assembled,delivering a high energy density of⁴28 Wh kg^-1 with a stable cycling behavior.The carbon coated yolk@shell design might be extended to other high-capacity anode materials suffering from poor electrical conductivity and large volume variations for electrochemical performance optimization.?3?In order to overcome the challenges on the fabrication of asymmetric materials and improvement of the capacity of carbon based supercapacitor.The three-layer 3-aminophenol/formaldehyde?APF?/vinyl-silica composite microspheres were fabricated through the co-condensation of VTMS?vinyltriethoxysilane?and 3-aminophenol/formaldehyde.And then,the yolk-shell carbon microspheres with well-defined hemispherical yolks?semi-yolk-shell?can be obtained through the carbonizing and etching process.When used as electrode materials for supercapacitors,the obtained semi-yolk-shell carbon microspheres exhibited excellent electrochemical performance after activation.When tested under three-electrode configuration,the specific capacitance of semi-yolk-shell carbon microspheres reaches²95 F g^-1 at a current density of 1 A g^-1,while the value remains 190 F g^-1 at a high current density of 100A g^-1.When it was measured for 10000 cycles of charge/discharge at 10 A g^-1,the capacitance(255 F g^-1)retains 99.6%of the initial value(256 F g^-1).When tested under two-electrode configuration,the specific capacitance of semi-yolk-shell carbon microspheres also reachs as high as 283 F g^-1 at a current density of 1 A g^-1,demonstrating a huge potential in practical application.Futhermore,organosilica-assisted heterogeneous contraction strategy developed in this work can provide a new idea synthesize more asymmetrical materials.