Preparation Of Heteroatoms Doped Carbon/Cobalt Sulfide For The Modification And Application Of Lithium Sulfur Batteries Separator

Over past decades,with the repid development of society,the growth of fossil fuels depletion is huge.As a result,the human has to face the emerging energy crisis,which is regarded as the bottleneck to society progress.Meanwhile,the using of fossil fuels has also caused serious environmental pollution,which in turn threatens ecological security.Therefore,it is of great significance to develop renewable and clean energy.Some natural power,such as wind and water,possess favorable advantages of cleanliness and cheap.However,the further utilization of these powers is seriously hindered by their inherent characters,including intermittence shortage and difficultly-carrying.At present,utilizing rechargeable batteries is considered as an effective strategy to deal with the above problems and has become a hot spot in scientific research and practical application.In recent years,the fast-growing technologies and new-energy vehicles market are driving iterations of developing green,cheap and high energy density energy system.Nevertheless,the cathode materials of LIBs and SIBs are composed of heavy metal compounds,which are detrimental to environment.Additionally,the cathode materials are costly and short in resources.On the contrary,elemental sulfur possesses the advantages of abundant reserve,cheap price and environmentally friendly.Notably,the lithium-sulfur(LSBs)batteries show extremely high energy density and high capacity(2600 Wh kg-1 and 1675 mAh g-1).In such a context,its investigation has been greatly stimulated.To achieve the commercialization of this battery,some inherent drawbacks need to be resolved efficaciously,which impair the cycling property as well as working life of battery.For instance,the shuttle behavior of soluble polysulfides often results in the loss of active materials.The side reaction between permeated polysulfides and lithium anode,continuosly destroys SEI film and aggravates the growth of dendritic lithium.Meanwhile,the mossy and overgrown lithium dentrite may pierce through the separator,causing a short circuit and thus threatening the battery safety.In order to cope with these issues,the related works have been implemented in this paper,based on the structure tailoring and separator modification strategies.(1)Deriving from the core-shell bimetal-organic-frameworks(ZIF8@ZIF67),a heteroatom doped carbon nanotube hollow architecture confining with CoS2 nanoparticles(CoS2/NSCNHF)is prepared.Firstly,compared with the micron-scale CoS2 particles,the nano-scale CoS2 particles have a shorter ion transport distance.Secondly,the hollow carbon structure can buffer the volumetric strain of CoS2 during the charge/discharge process.Consequently,this material holds excellent electrochemical performance.As LIBs anode,the electrode delivers a first discharge capacity of 1155.6 mA h g-1.Even after 100 cycles,the electrode still gives a relatively high capacity(845.0 mA h g-1).As SIBs anode,the high capacity of above 400 mA h g-1 is observed after 170 cycles.(2)Originating from the hybrid of strongly coupled metal organic frameworks on layered metallic hydroxide with sanwiched structure(CoAl-LDH@ZIF67),a heteroatom doped carbon framework with confined CoS2 nanoparticles and rooted carbon nanotubes(NSPCF@CoS2)is synthesized.heteroatom doping method can endue the carbon structure with higher conductivity and thus promote the ion electron transport.Meanwhile,carbon structure acts as robust scaffold to alleviate the serious volume changes of CoS2.The characteristics of porosity and large specific surface area of NSPCF@CoS2 also favor the electrolyte infiltration.Consequently,this material shows excellent electrochemical performance.As LIBs anode,the NSPCF@CoS2 electrode gives an inceptive discharge capacity of 921.5 mA h g-1,with Coulombic efficiency of above 97%during the 200 cycles(except for the previous 5 cycles).As SIBs anode,the NSPCF@CoS2 electrode performs a steady and relatively high capacity during 1650 cycles,and an extremely low capacity decay rate of 0.018%per cycle is obtained.(3)A facile polyacrylonitrile@metal organic framework composite fiber-derived sulfuration strategy is utilized for the preparation of heteroatom doped carbon-encapsulated CoS2 nanoparticles(NSPCFS@CoS2).The obtained NSPCFS@CoS2 shows superior electrochemical performance.After running 2095 cycles at 1 A g-1,it still presents a high discharge capacity of 546.3 mA h g-1,showing a capacity retention of 72.7%.Notably,the capacity decay ratio is as low as 0.013%per cycle.Comparison with reported CoS2-based materials firmly demonstrates its comparative or even better electrochemical property.(4)Based on evaluating the structure composition of as-prepared materials(CoS2/NSCNHF,NSPCF@CoS2 and NSPCFS@CoS2),it is deduced that these above-mentioned materials hold chemical adsorption ability to polysulfides,namely the Keesom force of heteroatom doping carbon,and the Lewis acid base action of CoS2.Also,CoS2 has excellent electrical catalytic effect on the transformation of polysulfide.In addition,the porous carbon structure also has a physical block as well as adsorption effect on polysulfides.The highly-conductive character of carbon benefits the promotion of reaction kinetics,activating the "dead sulfur and lithium" and thus reducing the loss of active material.Thus,these materials can be adopted as the modified layer of commercial separator.The modified layer can serve as a promising dam for the flooded polysulfides,avoiding the loss of active sulfur species and buffering the corrosion of lithium anode.As a result,the suppression both on shuttle effect of polysulfides and germination of lithium dentrite can be realized,leading to the promoted electrochemical property and battery safety.(5)Owing to its limited ability to inhibit the shuttle behavior of polysulfides,polyacrylonitrile membrane is not effective in improving the performance of LSBs.Here,the modification strategy with functional materials is ultiized to acquire the modified membrane with high thermal stability,as well as the function of suppressing polysulfides shuttle behavior.This work reveals that the modified membrane not only improves the electrochemical property,but also inhibits the lithium dendrite growth,thus strengthening the safety performance of batteries.