| In recent years,with the development of economy and social progress,people’s demand for energy is steadily increasing.The type of energy consumption has changed from non-renewable fossil energy to sustainable renewable energy.Supercapacitors,also known as electrochemical capacitors,are new type of energy storage and supply devices,and have many advantages such as fast charging and discharging speed,high power density and long cycle life compared with traditional batteries.However,for traditional supercapacitors,there are still many problems to be solved urgently,such as low energy density,poor rate performance,and the need to use conductive agents and adhesives when making some types of devices.These problems limit the development of supercapacitors in new industries such as new electronic equipment and intelligent flexible equipment.In this thesis,we have studied the supercapacitor of nanostructured silicon carbide（Si C）materials and medium entropy alloy carbide nanowires.As a high-performance electrode material,nano-silicon carbide has good charge-discharge cycle stability,so it has broad application prospects.However,due to its low area capacitance and complex production process,the development of Si C-based micro supercapacitor（MSC）is still a huge challenge.In this thesis,Si C/C nanocomposites with hierarchical porous structure and high electrical conductivity were designed and fabricated by simple and rapid carbothermal reduction with silica sol and sucrose as silicon source and carbon source respectively.The amorphous carbon between Si C nanoparticles（NPs）is helpful to enlarge the specific surface area and provide excellent electrical conductivity,which not only ensures the close contact between electrolyte and electrode,but also provides efficient ion channels for ions in electrolyte.In this work,MSC based on Si C/C nanocomposites（Si/C mass ratio 1:1.5）has an optimal specific surface area capacitance of 11.8 m F cm-2 at 2 m V s-1,and has excellent flexibility（initial capacitance retention of 104.5%at 180°bending）and excellent integration.Most notably,after 50000 charge and discharge cycles,the capacitance keeps at 97.3%of the initial value,which is superior to the Si C-based micro supercapacitor with the best performance reported at present.Medium and high entropy alloy is different from traditional"elementary"metal materials.Because of its excellent mechanical,chemical and physical properties,it has been widely studied and concerned by various researchers in recent years,especially medium and high entropy alloy nanocomposites,which is a promising energy storage electrode material.In the present work,the highly robust and flexible micro-supercapacitors（MSCs）based on（Ta,Ti,Nb）C nanowires（NWs）and activated carbon hybrid structures（（Ta,Ti,Nb）C/C）as the electrode materials are reported,which are synthesized via carbothermal method using bamboo as both the carbon source and the natural porous template.Given to inherent advantages of（Ta,Ti,Nb）C NWs,e.g.stable electrical conductivity and mechanical flexibility under harsh low-temperature conditions and different deformational conditions,and abundant porous structure stemed from cross-linked（Ta,Ti,Nb）C NWs and bamboo-based active carbon,the as-prepared（Ta,Ti,Nb）C/C-MSCs show high electrochemical performance,mechanical stability,and temperature tolerance over a wide temperature range.It exhibits high areal capacitance of 41.6 m F cm-2,together with excellent energy density of 5.8μWh cm-2.Moreover,the（Ta,Ti,Nb）C/C composite device exhibit outstanding flexibility（97.1%retention of initial capacitance at 180°bending）and superior cycling stability（89.4%retention of initial capacitance after 20000 cycles）.Remarkably,the as-constructed（Ta,Ti,Nb）C/C-MSCs can endure the sub-ambient temperature operation down to-50°C with a capacitance retention of 82.7%and present capacitance retention up to 97.7%over one repeated cycles of cooling and heating from-50 to 25°C.Even under progressive variation in temperatures ranged between 25 and-50°C,the capacitance retentions keep higher than 92.3%for 9000 cycles,representing their promising to be serviced as highly robust MSCs against harsh low-temperature conditions for energy storage. |
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