Structure Design And Lithium Storage Performance Of Bismuth Selenide-based Composites

Bismuth selenide has emerged as a promising anode material for lithium-ion batteries（LIBs）,owning to its high theoretical specific capacity derived from the conversion-alloying reaction mechanism.However,there are still some challenges,such as severe volume expansion,inherent low conductivity,unclear energy storage mechanism and limited material type,which seriously hinder further application.Thus,in this work,various strategies including morphology design,interface regulation and composition optimization are adopted,combined with advanced techniques and theoretical calculation,to comprehensively investigate the optimization and lithium storage mechanism,so as to establish an overall relationship between structural features and electrochemical performance.Herein,the main research contents are listed as following:（1）Carbon dots（CDs）are proposed as“structure-directing agent”to induce the self-assembly of ultra-thin Bi₂Se₃ nanosheets into three-dimensional rod-like structures,which could ensure sufficient buffer space to improve structural stability and also provide efficient channels for electron/ion transport to accelerate reaction kinetics.On the other hand,Rich surface oxygen-containing functional groups of CDs are employed to promote the formation of stable interface Bi-O-C bonds,which could regulate the electronic structure and strengthen the interface coupling,giving rise to the significant improvement of intrinsic low conductivity and sluggish ion diffusion.As a result,when applied as an anode in LIBs,the as-built Bi₂Se₃-based composite exhibits durable long cycling life(502m Ah g^-1 at 1 A g^-1 after 950 cycles)and superfast-charging capability(165m Ah g^-1 at 20 A g^-1,corresponding to charge in≈27 s).Such a facile and efficient CDs-tailored method provides some guidance for the design of self-assembly electrode materials with adjustable structure,morphology and heterogeneous interface properties for improving the electrochemical energy storage capability.（2）A new kind of Bi₃Se₄-based electrode material is successfully developed by adjusting the selenization temperature to control the Bi:Se atomic ratios of Bi_xSe_y.Followed with the comprehensive evaluation of detailed morphology,lithium storage mechanism and electrochemical performance.Surprisingly,the Bi₃Se₄-based composite exhibits a uniform structure with Bi₃Se₄ nanodots embedded within a sheet-like carbon framework.The nanosized structure ensures a fast kinetics and efficient alleviation of stress/strain caused by the volume change.On the other hand,the resilient and conductive carbon matrix provides an interconnected electron transportation pathway.More importantly,robust interfacial C-Se bond is well existed,which is proved to significantly enhance structural stability and improve charge transfer kinetics.As expected,Bi₃Se₄-based electrode delivers outstanding lithium-storage performance with an ultralong cycle life of 1500 cycles at a high current density of 2 A g^-1 and an excellent rate capability of 211 m Ah g^-1 at an ultrahigh current rate of20 A g^-1.Such exceptional performance fully proves the huge potential of Bi₃Se₄ electrode and also provides some guidance for the lithium storage application of other Bi_xSe_y-based anodes.