Interface And Doping Effects On The Sodium Storage Of Two-dimensional Hetero-structures

Na ion batteries have been widely studied as the energy storage devices for replacing Li ion batteries because of their lower cost and non-toxicity.At present,Na ion battery electrode materials have problems such as low energy density and poor cycle stability.Two-dimensional materials like graphene and transition metal sulfides are expected to overcome the above problems and become potential anode materials for Na ion batteries.In addition,silicene has similar properties to graphene and is receiving more and more attention.Studies have shown that the composite materials obtained by combining these two-dimensional materials show better Na storage performance,but the microscopic mechanism of hetero-structures affecting Na storage performance is still unclear and needs to be solved.In this study,Na adsorption and diffusion on graphene,silicene and transition metal disulfide?TMD?,and at TMD/graphene,TMD/silicene composites are systematically investigated by first-principles calculation.The influence of doping on Na adsorption in the hetero-structures of Na₂S and graphene/silicene composed during charge and discharge is studied.Combined with electronic structure analysis,the interfacial and doping effects of Na storage in hetero-structures are investigated.It is found that there are two kinds of interface interactions in the hetero-structures.Considering the Na adsorption at different positions in the hetero-structures,the relationship between Na adsorption and interfacial binding characteristics is obtained by combining the analysis of the electronic structure of the system.Moreover,the contribution of the surface and interfacial Na storage of hetero-structures to electrochemical properties is also discussed.With the studies on Na diffusion considered,the synergistic effects of Na adsorption and diffusion in hetero-structures bound at different way are revealed.B,O,P and S dopants can increase the Na adsorption on graphene,and B,P and S doping have contribution to Na storage.B,N,O,P and S dopants all can increase the Na adsorption on silicene and enhance Na storage.For Na₂S/graphene and Na₂S/silicene,the interface interactions affect the adsorption position of Na in the hetero-structures.The microscopic mechanisms of Na storage in different doped Na₂S/graphene and Na₂S/silicene hetero-structures are discussed according to the doping mechanism in graphene and silicene.The results provide a theoretical basis for obtaining two-dimensional composites with excellent Na storage performance through hetero-structure and doping design.