Application Of Multifunctional Carbon-based Composites In Lithium-sulfur Battery Separators

Due to its theoretical capacity of 1675 m Ah/g,and the characteristics of large reserve,wide distribution and low price of sulfur materials,lithium-sulfur batteries have attracted great attention and extensive research.However,many scientific issues,such as the dissolving and shuttling of polysulfide ions and the erosion of lithium metal anode,still need to be solved.Carbon-based material modified separator is an effective strategy to solve the problem of polysulfide ions dissolution shuttle in lithium-sulfur batteries.In this paper,the multifunctional carbon materials derived from biomass and MOF materials modified separator is used to solve the polysulfide ions shuttle issue of lithium sulfur batteries.Thus,the electrochemical performance of lithium sulfur batteries has been significantly improved.The main research contents are as follows:(1)Carbon materials derived from hazelnut-based biomass are applied in modification of separator for lithium sulfur battery.Hazelnut shells with high carbon yield can be prepared into biomass derived carbon materials with large specific surface area and multiple pore channels by secondary carbonization activation method.The surface morphology of the material is cheese structure due to chemical etching of activation process.The activated hazelnut shell showed a micromesoporous multi-level pore structure with a specific surface area of 2147.7 m~2/g.The multistage pore structure can not only adsorb the polysulfide ions,but also improve the wettability of the separator to the electrolyte.At the same time,there are abundant oxygen-containing functional groups on the surface of carbon derived from hazelshell biomass,which also has the effect of chemisorption on polysulfide ions.The electrochemical test results show that the initial capacity of the lithium-sulfur battery can be increased from 782.3m Ah/g to 1318.8 m Ah/g at 0.2 C by modification of the separator with hazelshell biomass derived carbon.Even at the current density of 1 C,the reversible capacity can still reach 611.2 m Ah/g after 500 cycles.Through comparison,it is found that the modified separator has better wettability to the electrolyte,higher lithium ion migration number,inhibition of multi-sulfur ion shuttle effect and safety thermal stability of the separator are improved.(2)Metal/carbon composites derived from MOF are applied in modification of separator for lithium sulfur battery.In this paper,a simple and rapid liquid phase synthesis method was used to obtain the columnar Ni-Co binary MOF,and then the bimetallic MOF derived carbon composites were prepared by high temperature carbonization.MOF derived carbon has abundant polar functional groups on its surface,which makes it have higher electrolyte absorption rate and wettability.The higher graphitization degree of the carbon frame generated by(Ni,Co)/C in situ can improve the ion mobility coefficient and lithium ion conductivity of the lithium-sulfur battery,and accelerate the lithium ion reaction kinetics process.At the same time,bimetallic particles will form metallic bonds with polysulfide ions,which can effectively inhibit the shuttle effect of polysulfide ions and improve the utilization rate of active substances.Therefore,at the current density of 1 C,the capacity of(Ni,Co)/C modified separator can reach 1035.6m Ah/g in first cycle,and it still has a reversible capacity of662.2 m Ah/g after 500 cycles.