Study On The Synthesis Of Cobalt (nickel) Sulfide@fiber Composite And Its Sodium Storage Performance

Sodium-ion batteries?SIBs?,as potential large-scale energy storage systems,have recently attracted large attention because of the low cost and the high abundance of sodium.However,the large size and high ionization potential of Na⁺ions hinder its diffusion in the electrode during the discharge/charge process,thus leading to the defect in practical utilization.Accordingly,alternative anode materials with high theoretical capacity including transition metal sulfides?TMSs?have been developed as feasible candidates for electrochemical Na⁺storage.When serving as anodes for SIBs,TMSs normally undergo a plural electron-involved conversion reaction of nTMS+2ne^-+2nNa⁺=TM⁰+nNa₂S,which is the main reason of the high theoretical specific capacity of TMSs.However,their practical application is still limited by the inferior electro-conductibility,severe volume changes,and slow kinetics of the conversion reactions,which results in unsatisfactory actual specific capacity,rate performance,and cycling stability.The compound of TMSs and carbon materials is the better solution,which can not only overcome the volume expansion,but also greatly improve the electrochemical conductivity.We chose sustainable alginate fibers as the precursor because of the abundant,renewable,and nontoxic properties of biomass.M²⁺?M=Ni,Co?are immobilized into a unique“egg-box”framework via coordination with?-L-guluronate?G?blocks of the alginate macromolecule,following the high temperature treatment to obtain composite materials with different morphologies.In the composite material,the carbonaceous fibers?CFs?not only increase the electrical conductivity of electrodes by providing the paths for charge transport but also serve as the physical support of the TMSs.This results in improved rate and cycling performance of the SIBs.In this work,we use biomass materials calcium alginate fibers as carbon source and compound with TMSs on the following aspects:?1?The transition metal is complexed into the calcium alginate fiber by ion-exchange,and after carbonization and sulfuration treatment in a tube furnace,the anode material with hollow structure of transition metal sulfide and carbon fiber composite is obtained,and the stability of the sodium ion battery can be effectively improved compared with pure transition metal sulfide.?2?The transition metal is complexed into alginate fiber by ion-exchange,and after oxidation and sulfuration treatment in the tube furnace.Then the transition metal oxide and the sublimed sulfur are packaged into the quartz tube at a molar ratio of 1:1,a composite material in which the transition metal sulfide is supported on the carbon fiber is obtained.which was applied to the anode material and shows high performance in SIBs.