| With the application of new energy electric vehicles and various types of portable electronic devices,people put forward of new requirements to energy storage devices?like battery?.In secondary batteries,lithium-sulfur batteries have the highest energy density(2600 Wh kg-1)and specific capacity(1675 m Ah g-1).However,because the sulfur is easy to fall off from the cathode frame,and the intermediate polysulfide is easy to dissolve and diffuse in the electrolyte to produce shuttle effect,resulting in poor cycle life,lithium sulfide battery failed to large-scale commercial production and application.Because the active material in lithium-sulfur battery underwent a transition from nonpolarity to polarity during the discharge process,it is necessary to adopt different methodes to effectively bind the active material according to the characteristics of the active material in different stages.In order to improve the binding effect of carbonbased materials on active material at different stages,this paper studies the composition and structure of carbon-based materials?namely the selection of carbon sources?,the regulation of pore structure of non-polar carbon-based materials,the nonpolar carbonpolar carbon composites and their optimization,as follows:?1?Using waste cotton fabric as non-polar carbon source,the mesoporous proportion of carbon material is regulated by different activators to study the electrochemical properties of waste cotton fabric based carbon cathode material.It is found that the specific surface area(2835.47 m2 g-1)and mesoporous volume(1.631 cm3 g-1)of KOH actived carbon are the highest and the mesoporous proportion is moderate?57.85%?.Electrochemical tests show that too high or too low mesoporous ratio will make the battery maintain fast capacity attenuation of mesoporous structure or has the low discharge platform of microporous structure.The higher the total hole volume,the better the battery stability.Specifically,the specific capacity of KOH actived carbon/sulfur battery can reach 1577 m Ah g-1 at 0.1C,and only attenuate from 650.5 m Ah g-1 to 477.6 m Ah g-1 after 220 cycles at 1C.?2?The ionic liquid Emim-dca is used as carbon source of polar N-doped carbon,and the ionic liquid based carbon is compounded with the above nonpolar carbon to construct the cathode of the nonpolar carbon-polar carbon composite material.Then the influence of the composite mode on the electrochemical properties is studied.Compared with the mechanical mixing method,direct coating and pore-making coating can reduce the pore volume and specific surface area of the material and reduce the utilization rate of sulfur.Electrochemical tests show that the specific capacity of the battery after composited with ionic liquid based carbon is improved comparing with KOH actived carbon/sulfur.Since the mechanical mixing method can anchor polysulfide by N-doped carbon without damaging the hole structure of KOH actived carbon,and the active materials can be bound regionally.So the specific capacity(1C 768.3 m Ah g-1)and cyclic stability?0.116% attenuation per cycle?of this material are better than the other two composites.?3?The intertwined multi-wall carbon nanotubes?MWCNTS?are used as the frame of ionic liquid-based carbon to optimize the combination methode of non-polar carbon-polar carbon.The results of characterization and microscopic morphology analysis show that the amorphous Emim-dca carbon is mainly filled in the intertwined gap of MWCNT after carbonization,and the microporous and low-diameter mesopores are the main porous structure.The nitrogen content of the composite is up to 7.42 At.%.Electrochemical tests show that the specific capacity and cycling stability of the filled battery are better than those of the coated and mechanically mixed batteries.The specific capacity of the battery is 1558.6 m Ah g-1 at the rate of 0.1C.After 300 cycles at 1C,the specific capacity only decreases from the initial 655.77 m Ah g-1 to 614.34 m Ah g-1,and the attenuation per cycle is only 0.021%. |
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