Multifunctional Sc₂O₃@CNTs Modified Separator Improves The Performance Of Lithium Sulfur Batteries And The Mechanism

Energy storage technology is one of the key technologies to achieve efficient use of energy.At present,the Lithium-ion batteries（LIBs）have drawn great attention due to its high voltage,long cycle life and environmental friendliness.Although LIBs have been fully developed,they still cannot meet the ever-growing demand of large-volume energy field like electric vehicles,due to their limited theoretical capacities associated with commercial cathodes.Lithium sulfur（Li-S）batteries are one of the attractive candidates with energy densities of 2500 Wh kg^-1 and 2800 Wh L^-1 due to the high theoretical specific capacity(1675 m Ah g^-1).However,the practical application of Li-S batteries is severely impeded by several challenges including the low intrinsic electric conductivity of sulfur and discharged products（Li ₂S₂/Li₂S）;significant volume change（～80%）during charging-discharging process and shuttle effect of the dissolved long-chain polysulfide.In order to solve the aforementioned problems,this paper outlines the recent progress in Li-S batteries,discuss the approach for modify commercial separator.The main research contents are displayed as follows:1)The Sc₂O₃ nanoparticles was prepared by sol-gel method,then mixed with KB,the slurry was coated on one side of Celgard 2500.The micro-structure was characterized by XRD and SEM.The electrochemical performance was test with CV,EIS and GCD.As a result,homogeneous-dispersed Sc₂O₃nano-particles were prepared.The separator with Sc₂O₃ capping layer can reduce the internal resistance of the battery and accelerate the electrochemical reaction kinetics.What’more,the capping layer can effectively adsorb polysulfides and restrain shuttle phenomenon.The Li-S battery with Sc₂O₃-coated separator exhibits high reversible capacity retention of 54.5%,showing good cycle stability.2)A new multifunctional Sc₂O₃@CNTs-coated separator was developed by coating an ultrathin and lightweight capping layer of Sc ₂O₃ NPs decorated CNTs composite over one-side of the commercial PP separator using solvothermal combined with vacuum filtration approach.Both experimental studies and theoretical calculations manifest that Sc₂O₃ NPs not only chemically anchor the dissolved Li PSs,but also catalytically promote the conversion of captured Li PSs to Li₂S.The highly conductive CNTs networks not only provide fast electron pathway,but also physically blocks the transfer of polysulfide.As a result,Li-S batteries using Sc₂O₃@CNTs-coated separator show prominent electrochemical properties that are significantly superior to the batteries using the pristine separator.Specifically,it delivers a long-term cycling stability over 500 cycles with an ultralow decay rate of 0.05%per cycle at 1 C,impressive rate capacity with capability of 647.5 m Ah g^-1 at 5C.3)CMK8/S composite cathode with different sulfur loading w as prepared,and the effects of sulfur loading on the performance of Li-S batteries were investigated.CMK8 is an ordered mesoporous carbon material and a perfect host for sulfur loading.However,the pore volume of CMK8 is limited.It is important to find a suitable sulfur load for its maximum effect.The results showed that the Li-S batteries have the highest efficiency when the sulfur load in CMK8/S is 60 wt%.The modified separators with different loadings of Sc₂O₃@CNTs were prepared.The results showed that the performance of the battery was best when the area density of Sc₂O₃@CNTs on the surface of pristine separator was 0.17 mg cm^-2.