Synthesis Of MOFs-derived Bimetallic Selenide/carbon Materials And Their Sodium-storage Properties

In recent years,transition metal selenides derived from metal-organic frameworks(MOFs)have attracted more and more attention due to their features of hard to form sodium dendrite at low reaction voltage,conducive to conversion reaction in kinetics,high first coulomb efficiency and good conductivity of discharge product Na₂Se.However,when used as anode materials of SIBs,they still suffer from some problems,such as large volume expansion and insufficient conductivity.In this paper,transition metal selenides derived from MOFs were selected as the research object,and three parts of experiments were carefully designed.Different kinds of MOFs precursors and cation-exchange metal ions were selected,and reasonable morphology was designed to alleviate volume expansion in the process of charging and discharging.Besides,compositing with carbon materials which have good electron conductivity and high temperature heat treatment before selenizing were also used to solve the problem of insufficient conductivity.Therefore,the electrochemical performance of the materials could be further promoted.Firstly,Co(Zn)Se/CNFs nanofibers were prepared by electrospinning,in-situ growth of ZIF-67,cation exchange and selenizing.The prepared material has pearl necklace-like morphology and two-phase composition of CoSe and ZnSe,showing good sodium storage performance.The material shows a rate capacity of 340.5 mA h g^-1 at 3 A g^-1;At the current density of 0.2 A g^-1,it shows a specific capacity of 559.2 mA h g^-1 after 50cycles;Even at a high current density of 3 A g^-1,it still exhibits a specific capacity of248.7 mA h g^-1 after 800 cycles as well as an excellent long cycle stability.Then ZIF-67 precursor was synthesized by a liquid phase method,and hollow Co(Ni)Se₂@N-C nanoparticles were obtained by subsequent ion exchange,dopamine coating and selenizing process.The prepared material has hollow particle morphology and two-phase composition of CoSe₂ and NiSe₂,showing excellent sodium storage performance.The material exhibits a rate capacity of 349.7 mA h g^-1 at 3 A g^-1;At the current density of 0.2 A g^-1,it shows a specific capacity of 700.7 mA h g^-1 after 50 cycles;Even at a current density of 3 A g^-1,it still shows a specific capacity of 347.3 mA h g^-1after 800 cycles as well as an excellent long cycle stability.Finally,Ni-BTC precursor was synthesized by a solvothermal method,and Ni(Co)Se₂/C microspheres were obtained by subsequent cation exchange,heat treatment and selenizing.The prepared material has uniform microsphere morphology and two-phase composition of NiSe₂ and CoSe₂,showing the best sodium storage performance.The material exhibits a rate capacity of 424.8 mA h g^-1 at 3 A g^-1;At the current density of 0.2 A g^-1,it shows a specific capacity of 691.0 mA h g^-1 after 50 cycles;Even at a high current density of 3 A g^-1,it still shows a specific capacity of 446.4 mA h g^-1 after 800cycles as well as an excellent long cycle stability.