Structure And Composition Design Of Hollow Carbon Microspheres And Research Of Their Electrochemical Performance

Nowadays,climate change and the limited availability of fossil fuels have greatly affected the development of world ecology and economy,developing sustainable clean energy and advanced energy storage technology are the great challenges.Therefore,the development of clean energy storage devices for much-higher-performance are essential.Currently,lithium–sulfur?Li–S?batteries are considered as next generation efficient energy storage systems due to their high theoretical energy densities and low cost.Constructing uniform hybrid structure of metallic oxide by coating carbonaceous have been turned out to be an effective way of provide efficient retention of Li₂S_x via a synergistic strategy of structure restriction and chemical encapsulation and realize the structural stability of the whole electrode improving in Li–S batteries.While supercapacitors have also attracted much attention because of their pulse power supply,long cycle life and high dynamic of charge propagation.Hollow porous carbon materials are the most ideal material for energy storage as the electrode material for supercapacitors owing to their extraordinarily conductivity,adjustable pore structure,high surface areas and large pore volumes.In this paper,we synthesized a kind of novel sandwich-type C@TiO₂@C hollow microspheres and a kind of uniform discrete cage-like nitrogen-doped hollow porous carbon spheres?CN–HPCSs?with tunable direct large mesoporous?18–30 nm?,respectively.We present an ingenious design and synthesis of a sandwich-type C@TiO₂@C configuration with a TiO₂ layer protected by carbon on both sides to prepare the C@TiO₂@C–S composite,when being used as cathode for Li–S batteries,which exhibit excellent electrochemical performance.In addition,we also used these CN–HPCSs as the electrode material of supercapacitors,and then investigated by electrochemical performance test.The influences of the pore size and carbonization temperature on electrochemical properties are discussed in the two aspects works.The main research work includes the follows:?1?In this work,novel sandwich-type carbon/titanium dioxide/carbon?C@TiO₂@C?hollow microspheres as a new kind of molecularly designed physical and chemical trap for lithium polysulfides?Li₂S_x?x=4–8??are reported.In such a unique architecture,an interlay TiO₂ layer as the carrier for sulfur could effectively confine polysulfides by chemical binding between TiO₂ and polysulfides,while the sandwich–type hollow carbon structure could buffer the volume change during the charge–discharge process by means of physical force.Moreover,the inner and outmost carbon layers provide an effective conductive network to improve the electronic conductivity of sulfur cathodes,and at the same time further suppress the dissolution of polysulfides,leading to structural and interfacial stabilization of the TiO₂ interlay.Benefiting from the synergistic encapsulation,the developed C@TiO₂@C–S hybrid hollow microspheres with 76.4 wt%sulfur content deliver a high specific capacity of 1247.3 mA h g^-1 at 0.2 C with higher coulombic efficiency??96%?,and retain a discharge capacity of 741.3 mA h g^-1 after 300 cycles at 0.5 C and511 mA h g^-1 after 500 cycles at 2 C,which are much better than those of the contrast TiO₂–S and C@C–S electrodes.?2?Uniform discrete cage-like nitrogen-doped hollow porous carbon spheres?CN–HPCS?with tunable direct large mesoporous?18–30 nm?have been successfully synthesized for the first time by using the carboxylated polystyrene spheres and silica particles as a dual-template and dopamine as the carbon and nitrogen sources.The CN–HPCS integrate the advantages of large specific surface area,multiscale porous structure,and good conductivity,which provide the sufficient space for charge storage and fast transport for ions and electrons when they are used as electrode for supercapacitors and endow the sample of CN–HPCS700–2 with a much higher specific capacitance of 257 F g^-1 at 1 A g^-1 and194 F g^-1 at 10 A g^-1 with excellent rate capability and cycling stability after 20000 cycles at 10 A g^-1.Simultaneously,the introduced nitrogen could improve the surface wettability,which was also favorable to the permeation of electrolyte solution into the pores of the material.