Studies On Interfacial Layer Constructing Of Lithium Anode And Its Application In Lithium-sulfur Batteries

Lithium-sulfur（Li-S）battery has become the research focus recently due to the advantages of high theoretical mass energy density,abundant sulfur resources and low price.However,the commercialization process of Li-S batteries has been limited by the shuttle effect and instability of metal lithium anode.The stable interfacial layer of metal Li anode can effectively restrain the dendrite growth and suppress the shuttle effect.In this paper,the interfacial modification strategies were carried out on Li anode,aiming to inhibit the dendrite growth,alleviate the volume effect,regulate the lithium ion depositing behavior and thus achieve the high interfacial stability of Li anode.Besides,the action mechanism of interfacial modification on Li anode for longer cycling lifespan was studied by testing in Li-S battery system and using various physical/chemical characterizations.A natural agar polymer layer was successfully constructed on Li surface through a simple pretreatment coating.The elastic modulus of the coating layer reaches to 1.6GPa,which can effectively alleviate the volume effect of Li anode during repeated depositing/stripping processes.The excellent chemical stability of the agar layer can effectively maintain the electrode/electrolyte interfacial stability.As a physical barrier,agar layer can separate Li anode from electrolyte corrosion,thus reducing side reactions and restraining shuttle effect.The electrochemical measurements exhibit that the Li/Li symmetric cells with agar-coating pretreatment realize the long cycling life of 500 h and 300 h under the current density of 1.0 m A cm^-2 and 3.0 m A cm^-2,respectively.Also,the Li-Cu half cells with agar-coated Li anodes achieve cycling life twice as the non-modified Li-Cu cells under different current densities.The Li-S batteries with agar-coated Li anodes maintain the discharge capacity of 651m Ah g^-1 and 500 m Ah g^-1 after 100 cycles at 0.5 C and 1.0 C,respectively.An interfacial layer composed of 4-chlorophenylboronic acid was constructed on Li surface by solution-soaking method.The theoretical calculation shows that the strong chemical adsorption happens between the molecules of the modified layer and metal Li.X-ray photoelectron spectroscopy（XPS）analysis demonstrates that 4-chlorophenylboronic acid can successfully modify the interfacial layer on Li anode.The polar functional groups of modified layer can effectively regulate the lithium ion depositing and inhibit the dendrite growth.The Li/Li symmetric cells using modified Li electrodes can obtain stable cycling performance over 600 h and 500 h at 0.5 m A cm^-2 and 1.0 m A cm^-2,respectively.During the cycling,the voltage polarization keeps low and stable,and the morphology of modified Li anode after cycling is smooth and compact without any dendrite or dead Li.The Li-S batteries using modified Li anodes can achieve stable and long cycling performance under different test conditions,maintaining the discharge capacity of 605 m Ah g^-1 and high Coulomb efficiency（>99.97%）after 200 cycles at 0.5 C.Under the condition of no Li NO₃ additive in electrolyte,the modified Li-S batteries can still achieve stable 120 cycles.An interfacial layer consisting of hybrid phases of lithium fluoride and lithium-antimony alloy was constructed on Li surface by the metal replacement reaction and alloying reaction.During the depositing process,the lithium ions are reduced and then deposit on the modified interfacial layer because of the excellent electrical conductivity of lithium-antimony alloy component.The formed uniform convex structure ensures the same probability of lithium ions depositing on the surface.In ether-electrolyte system,the modified Li/Li symmetric cells realize stable cycling more than 700 h at 1.0 m A cm^-2 and over 400 h at 3.0 m A cm^-2.The modified Li-S batteries also exhibit excellent cycling properties under different test conditions and maintain the discharge capacity of 640 m Ah g^-1 after 200 cycles at 0.5 C.In carbonate-based electrolyte system,the modified Li/Li symmetric cell achieves stable cycling over 500 h at 1.0 m A cm^-2.Matching with lithium cobalt oxide（LCO）cathodes,the modified Li metal batteries show better cycling stability under various test conditions（high LCO areal capacity,thin Li anode,lean electrolyte and thin Li anode+lean electrolyte）.