Research On Phosphorus-doped Carbon In Sulfur And Selenium-based Batteries

With the increase of energy demand and people's awareness of environmental protection increases.The lead-acid batteries with low energy density and traditional lithium-ion batteries are no longer sufficient for human needs.Therefore,it is urgent to research and develop a new high-energy storage system.Due to the high theoretical specific capacity of sulfur and the high electrical conductivity of selenium,sulfur and selenium-based lithium secondary batteries stand out.However,whether it is lithium-sulfur battery,lithium-selenium battery or selenium sulfide battery,it will face the problem of volume expansion during charging and discharging,and the shuttle effect of lithium polysulfide and lithium polyselenide dissolved in the electrolyte make the fast capacity decay and the low coulombic efficiency.In this study,the prepared phosphorus-doped porous carbon?P-C?was applied as a carrier of sulfur and selenium to positive electrode modification,and the surface of the pristine celgard separator was coated with phosphorus-doped porous carbon to prepare a P-C coated separator.The research is carried out from the positive electrode and the separator,the sandwich structure of positive electrode,coating and separator is used to intercept the polysulfide/selenide before passing through the separator to achieve the purpose of secondary utilization to improve the utilization rate of active substances and the electrochemical performance of the battery.The main research contents include:?1?The P-C/S electrode material was prepared by heating and melting to inject the sulfur into the pores of phosphorus-doped porous carbon,and the lithium-sulfur battery was assembled using p-c coated separator.Porous structure can not only serve as the conductive skeleton of sulfur,but also limit the intermediate of polysulfide.Physical adsorption and chemical bond cooperation exist between phosphorus doped porous carbon and polysulfide,which can not only effectively inhibit the shuttle effect,but also improve the utilization rate of active substances.Assembled with p-c coated separator,the as-constructed Li-S batteries deliver an initial capacity of 1430 mAh g^-1 at 0.1 C and 650 mAh g^-1 at 5 C,achieving outstanding cyclability with negligible capacity fading rate of 0.09%per cycle at 1 C for 500cycles.?2?The phosphorus-doped porous carbon was used to load Se to prepare P-C/Se composite material as the electrode material of lithium selenium battery.The electrochemical performance was tested by assembling lithium selenium battery with pristine celgard separator,Super P coated separator and P-C coated separator,the results show that the P-C coated separator can effectively improve the cycle reversible capacity and cycle stability of the battery.the as-constructed Li-S batteries deliver an initial capacity of 580 m Ah g^-1 at 0.2 C and 220 mAh g^-1 at 5 C,achieving outstanding cyclability with negligible capacity fading rate of 0.06%per cycle at 1 C for 310 cycles.?3?Nano SeS₂ was synthesized in aqueous solution at room temperature,and polythiophene was coated on the outer layer at low temperature,finally graphene oxide is wrapped outside to form double protection layer through electrostatic interactions between GO and PEDOT to form SeS₂@PEDOT/GO.The electrochemical performance of the composite electrode material is greatly improved compared to the SeS₂ and SeS₂@PEDOT electrode materials,and the P-C coated separator is applied to the selenium sulfide battery,which shows stable cycle performance and rate performance.The initial discharge specific capacity can be as high as 1030 mAh g^-1 at a current density of 100 mA g^-1,and the specific capacity can be maintained at 700 mAh g^-1 after 100 cycles,the capacity retention rate is68%.When the battery is discharged from a large current density to a small current density,the capacity retention rate is 92%.The coulombic efficiency of the battery is maintained at about 100%during charge and discharge.