Design,Preparation And Lithium Storage Performance Of Carbon/Metal Selenide Composites With Confined Structure

With the rapid growth of market demand for large electric vehicles and renewable power stations,a key challenge is to develop lithium-ion batteries with high energy density,good cycle stability and excellent rate performance.Because the performance of lithium-ion batteries mainly depends on electrode materials,people have led the exploration of advanced anode materials to replace the traditional anode material graphite.Recent research on advanced anode materials shows that most metal selenides are potential substitutes.Compared with commercial graphite anodes(372 m Ah g^-1),their theoretical capacities(500?1000 m Ah g^-1)are much higher.However,these materials have large volume changes during charge and discharge.And the lithium ion diffusion kinetics is slow.It leads to unsatisfactory cycle stability and rate performance.Hence the structural design and control of electrode materials are of great significance to improve the performance of the materials.So far,efficient synthesis of metal selenide nanomaterials to obtain excellent electrochemical performance is still full of challenges.In this paper,two kinds of metal selenide anode materials with confined structure are constructed.The porous carbon layer(nitrogen-doped graphene)is used to construct a confined structure,which solves the related problems of metal selenide conductivity,rate performance and cycle performance at the same time.The constructed confined structure improves not only the conductivity of the intrinsic material,but also the longitudinal mass transfer efficiency,which can effectively promote charge transfer and ion migration.Meanwhile,the structure can not only maintain the stability of the material during constant current charge and discharge cycles,but also effectively relieve stress changes during rapid charge and discharge,so that the stability of the material is further enhanced.The introduction of the confinement structure can make the anode material of the lithium ion battery exhibit good cycle stability and excellent rate performance.Firstly,a porous carbon layer confined Bi₂Se₃ nanorod composite material was constructed.The confinement structure of the porous carbon layer can effectively alleviate the volume change during charge and discharge,and improve the electrochemical performance of the intrinsic material.At a current density of 0.1 A g^-1,the specific capacity of the Bi₂Se₃@C nanorod composite material after stabilization is 288 m Ah g^-1,which is far better than that of the pure Bi₂Se₃ material.Subsequently,in order to further solve the problems of mass transfer and active site exposure,N-doped graphene confined hollow CoSe₂ nanoparticles anchored on N-doped vertical oriented graphene nanomesh arrays on carbon cloth(CC@CoSe₂-NC)has been constructed.The nanosheet arrays structure would be in favor of fast ion/electron transmission and sufficient contact between electrolyte and electrode.The unique graphene-confined structure could not only protect the active center from pulverization and aggregation,but also accelerate the charge transfer/penetration dynamics stimulated by the two-component synergistic interaction effect,as verified by density functional theory(DFT).Moreover,the electrode as anode for lithium-ion batteries also showed superior electrochemical performance with a high reversible specific capacity(3.66 m Ah cm^-2 at 0.1 m A cm^-2)and decent cycling stability(3.18 m Ah cm^-2 at 0.1 m A cm^-2 after 85 cycles).In general,the introduction of confined structures has significantly improved the electrochemical performance of intrinsic materials.This research may provide significant implications for the rational design of the appearance and structure of the integrated electrode,and it also open a new avenue for the regulation of electrochemically active species.