Study On Construction And Electrochemical Performance Of Cathode,Anode And Separator For Lithium Sulfur Battery

Lithium sulfur battery is considered as the next generation of new energy storage secondary battery with great potential due to its high theoretical capacity and high energy.However,the practical development of lithium sulfur battery is faced with the challenges of the shuttle of polysulfide,slow electrochemical reaction kinetics and the safety of lithium anode.In this paper,the design and construction engineering of sulfur host materials,separator modification engineering and lithium anode protection engineering strategies are adopted to effectively suppress the"shuttle effect",improve the cycling ability of lithium-sulfur batteries under high sulfur load,and promote the development of high areal specific capacity.Furthermore,the mechanism of inhibiting the"shuttle effect"and the basic principle of constructing lithiophilic current collector are systematically revealed by first principles calculations.The specific research contents are as follows:（1）Through the self-assembly property of graphene oxide（GO）,we designed and prepared the three-dimensional graphene-supported Ti N nanowires（3DNG/Ti N）composite structure.The highly conductive porous 3DNG and the polar compound Ti N nanowires effectively inhibit the dissolution of polysulfides in the electrolyte,and promote the conversion of polysulfides adsorbed on the surface of Ti N nanowires,so as to improve the utilization rate of active substances.Under the sulfur loadings of7.2 mg cm^-2and 9.6 mg cm^-2respectively,the 3DNG/Ti N showed an area specific capacity as high as 10.9 m Ah cm^-2and 12 m Ah cm^-2,which meets the requirements of4 m Ah cm^-2for commercial application.First principles calculations revealed that the solid chemisorption of Ti N to long-chain polysulfides is the fundamental reason for inhibiting the"shuttle effect"of lithium-sulfur batteries.（2）In combination with oxygen vacancies（OVs）engineering and separator modification engineering,a functional OVs-Ti O₂modified layer OVs-Ti O₂@PP separator with a thickness of 500 nm is designed and constructed.Benifits to OVs,the ability of OVs-Ti O₂modified layer to chemisorption and catalytic conversion capacity of polysulfide has been enhanced,and the low utilization rate of active substances and slow electrochemical reaction of lithium-sulfur battery have been effectively solved.The lithium sulfur battery was assembled with r GO/S cathode and OVs-Ti O₂@PP membrane,and the sulfur loading of the battery reached 7.1 mg cm^-2and the specific areal capacity of the battery remained 5.83 m Ah cm^-2after 100 cycles.The first principles calculations revealed that the introduction of OVs promoted the change of electron cloud density on the surface of OVs-Ti O₂,and the distribution was more uneven,so that the polarity of OVs-Ti O₂was enhanced,and then the adsorption of polysulfide was enhanced.（3）In order to solve the problem of lithium anode failure in lithium-sulfur batteries,a three-dimensional conductive framework（M@Cu₃N）as lithium metal anode current collector was prepared by constructing a"lithophilic"layer on the framework surface.The lithiophilic Cu₃N layer can spontaneously react with the deposited lithium to form a Li₃N layer with excellent ion conduction ability.The Li₃N layer can promote the rapid transfer of lithium ions and induce uniform lithium deposition on the conductive Cu skeleton,so as to obtain dendrite-free lithium anode.Coulomb efficiency and symmetrical cell tests show that the as-prepared Cu@Cu₃N current collector can promote both the reversibility of lithium deposition and stripping as well as the cycling stability.The electrochemical performance of the full cell paired Cu@Cu₃N/Li anode with sulfur,LFP and NMC811 cathodes,the enhanced cycling stability indicates that the improvement of anode is an effective approach to optimize the performance of LMB.First principles calculations revealed that the reaction of Cu₃N and Li to form a new Li-N chemical bond is the fundamental reason for the realization of"lithiophilic",which provides a clear instruction for the design and construction of"lithiophilic"current collector.