Regulating The Status And Transport Behavior Of Ions For High-performance Li-S Batteries

The exhaustion of traditional resources and the rising demand of energy are calling for the alternatives of lithium ions batteries(LIBs).In this regard,Li-S batteries are triggering booming attention due to its ultrahigh energy density(2600 Wh kg^-1)and advantages of resource abundance,environmental benignity and low cost of S cathode.However,there are still some problems hinder broad application of Li-S batteries.On the one hand,the forth and back shuttle of polysulfide leads to irreversible capacity loss and poor cycling stability.On the other hand,the formation and propagation of lithium dendrites would induce poor cycling stability and even safety hazard.After a comprehensive review on the recent progress in the sulfur cathode and lithium anode of Li-S battery,firstly,depending on the 2D COFs based separator,we successfully regulate the transport behavior of Li⁺ions and polysulfide,as a result,the cycling stability of Li-S battery is enhanced significantly.Then,by adding certain amounts of additives,we successfully regulate the status of Li⁺ions and polysulfide.The changes of status of Li⁺ions and polysulfide lead to high-performance Li-S battery.Main results of this dissertation are presented below:First of all,depending on the?-?interaction between the graphene and the 2D COFs,we achieve large-area anisotropic ordering of 2D COFs by only filtration process.And when the resulted graphene-COFs double-layer membrane is fabricated as the ionic sieve in the Li-S batteries,the uniform nanopores impressively suppress the shuttle of larger sized polysulfide while allow the transport of Li ions thoroughly.As a result,depending on the regulation the transport behavior of polysulfide,the cycling performance of Li-S batteries is improved significantly.Then,we design a double-layer membrane,in which the first PEO based polymer layer enable the effective desolvation and the second COFs layer facilitate the exclusive transport and homogeneous deposition of Li ions.As a result,by regulating the transport behavior of Li ions,the formation and propagation of lithium dendrites is suppressed effectively,and the cycling stability of anode of Li-S batteries was improved.Thirdly,we propose a novel strategy to regulate the solvation sheath,through introducing intermolecular hydrogen bonds with both anions of Li salts and the solvent molecules by small amount of additives.The presence of such kind of hydrogen bonds promoted the formation of high-quality SEI,reduced the amount of free solvent molecules and therefore widened the electrochemical window of electrolyte.As a result,by regulating the status of Li⁺ions,the cycling stability of anode of Li-S batteries was enhanced significantly.Fourthly,we proposed a novel strategy to suppress the shuttle effect of polysulfide,through introducing insoluble organopolysulfide by certain amount of additive.The in-situ synthesized organopolysulfide can also effectively facilitate the deposition of Li₂S?dissolution of Li₂S and the conversion between soluble polysulfides.As a result,by regulating the status of polysulfide,the cycling stability of cathode of Li-S battery was improved significantly.Finally,we summarize our works in the last chapter,and give a perspective for the future research.