Construction Of Cathode Materials For Lithium-sulfur, Lithium-selenium, And Sodium-selenium Batteries Based On Low-dimensional Materials And Their Electrochemical Research

Rechargeable lithium-ion batteries(LIBs)are key for portable electronic products and large-scale electricity storage.LIBs based on traditional metal oxides(e.g.,Li Co O₂,Li Mn₂O₄,Li Fe O₄,etc.)cathode and graphite anode with low theoretical specific energy density cannot meet the demand of electric vehicle(EVs)and grid energy.Lithium-sulfur batteries(LSBs)have attracted great interest because of their high theoretical specific capacity(1675 m A h g^-1)and high energy density(2600 W h kg^-1),and are considered as one of the most promising next-generation rechargeable batteries.In addition,sulfur has the advantages of cheap,plentiful,and environmentally friendly.However,the practical application of LSBs has been hampered by two overarching problems:(1)Low conductivity of sulfur(5×10^-30 S cm^-1 at 25?),which results in low utilization of sulfur in the electrode.(2)Soluble polysulfides(Li PSs)intermediates formed during charge and discharge can be dissolved in the ether electrolyte,causing shuttle effect,resulting in a rapid reduction in capacity.A variety of strategies have been proposed to address these problems,including construction of high efficiency sulfur anode,optimization of electrolyte,introduction of functional layer and protection of lithium anode.Here,we report a novel Janus electrode as a self-supporting cathode material for LSBs,with Fe₃C nanoparticles modified one-dimensional nitrogen-doped carbon nanofibers(Fe₃C/N-CNF)on one side and 2D reduced graphene oxide(RGO)on the other the Fe₃C/N-CNF@RGO integrated electrode combines physical confinement,chemisorption,and catalysis.Polar Fe₃C accelerates the reaction process of Li-S by capturing soluble Li PSs and catalyzing its in situ redox conversion.The 2D RGO layer physically blocks the active Li PSs on the positive side.This enhances the role of the anchored Li PSs,improves the redox kinetics,and greatly inhibits the shuttle effect of Li PSs.At the same time,one-dimensional N-CNF's interconnected conductive network structure expedites the transfer of electrons and ions,and also ensures the sulfur carrying and adaptation to sulfur volume changes during the cycle.Therefore,excellent electrochemical performance was achieved:the reversible capacity of Fe₃C/N-CNF@RGO/S cathode reached 1154.5 m A h g^-1 after 100 cycles of 0.2 C.The specific capacity at 2.0 C is 821.7 m A h g^-1.At 0.5 C,the single-turn decay rate is only 0.0089%after 300 cycles.The high area capacity of 4.96 m A h cm^-2 was obtained at 6.29 mg cm^-2.In recent years,people have devoted themselves to exploring new electrode materials.Selenium is considered as the most promising electrode material for lithium-selenium batteries(LSe B)due to its similar chemical properties with sulfur,high electron conductivity(1×10^-3 S m^-1)and theoretical capacity(3253 Ah L^-1).In addition,the sodium selenium battery(Na Se B)has recently gained widespread attention due to its high sodium content,cost-effective,and environmentally friendly advantages.However,similar to S,Se cathode also suffers from poor cycling performance and low Coulomb efficiency,which is similar to that of higher order polyselenides(M2Sen,M=Li,Na;3?n?8).Here,we present a simple and scalable strategy for the design of PNCNF/Se@MXene.The superior electrochemical performance is derived from the following advantages of the electrode:(i)The porous three-dimensional interconnected PNCNF framework significantly improves electron and Na⁺transport,resulting in a high power density;(ii)Interwoven CNF with optimized micropores and mesopores that allow for high Se loading;(iii)MXene can provide anchoring of polyselenide sites,inhibiting their shuttle,and achieving high specific capacity.