Electrocatalysis To Improve The Electrochemical Performance Of Lithium-Selenium Batteries

Lithium-selenium batteries are widely regarded as one of the most promising new energy storage systems,due to their high volumetric energy density.However,the capacity fading caused by the slow redox reaction and"shuttle effect"of polyselenides is the main problem of current lithium-selenium batteries.Therefore,this work made reasonable modifications to improve the electrochemical performance of lithium-selenium batteries.By selecting metal ion compounds with high conductivity(?-MoO₃,Li_0.5La_0.5TiO₃,CoSe₂),and using their efficient adsorption to reduce the solubility of polyselenide in the electrolyte,to suppress the shuttle effect.Secondly,as a host,it can also effectively enhance the kinetics of polyselenide conversion reaction and improve the electrochemical performance.Moreover,the above materials as hosts have stable molecular structures under the operating voltage platform of lithium-selenium batteries,and it can be used in the charging and discharging process lasting effect.In the first chapter,hollow spherical?-MoO₃ was synthesized by a simple solvothermal method.During the charging and discharging,the hollow structure and rough surface can effectively alleviate the volume expansion problem.?-MoO₃ can adsorb polyselenide and reduce its dissolution in the electrolyte.The CV results of symmetrical cells showed that?-MoO₃ significantly accelerates the conversion reaction of polyselenides.Due to the synergistic effect of electrocatalysis and adsorption,the electrochemical performance of Se was significant improved.Electrochemical test results showed that the Se/?-MoO₃ electrode can still provide a discharge capacity of 355.3 m Ah g^-1 after 200 cycles at 0.5 C,which far exceeding that of the Pristine Se electrode.Moreover,at the high rate of 2 C,the Se/?-MoO₃electrode still has better cycling stability,indicating that?-MoO₃ can effectively improve the reaction kinetics of the battery.While the Pristine Se electrode has serious problems about the shuttle effect,resulting in a rapid capacity decay during cycling.The test results of electrochemical impedance spectroscopy and Li⁺diffusivity both showed that?-MoO₃ can reduce the electron transport impedance of the electrochemical reaction interface,and improve the Li⁺diffusivity.The above results indicate that?-MoO₃ can improve the electrochemical performance of Lithium-selenium batteries by adsorbing and promoting the conversion of polyselenides.In the next chapter,the fast Li⁺conductor Li_0.5La_0.5TiO₃(LLTO)with rod-like structure was prepared by electrospinning technology and template method.In this chapter,LLTO was used as the host of Se to improve the diffusion rate of Li⁺,and added carbon nanotubes(CNTs)to enhance the electron-side transport rate.SEM result showed that LLTO has a relatively uniform morphology.After selenium was loaded,it can be dispersed uniformly,so that Li⁺can be effectively conducted.In addition,the rod-like structure of CNTs can realize the rapid directional transport of electrons,and the synergistic work can further improve the polyselenide conversion reaction.The test results showed that LLTO can effectively adsorb polyselenide and catalyze its conversion reaction.Moreover,the LC-Se electrode exhibits excellent rate performance,indicating that the LC-Se electrode has fast reaction kinetics.Which can regulate the rapid conversion of polyselenide to reduce the shuttle effect and improve the cycling stability of the battery.This chapter proved that improve the rapid conduction of electrons/ions,it is a feasible solution to accelerate the conversion reaction and improve the shuttle effect of lithium-selenium batteries.In the last chapter,CoSe₂@CNF was prepared by in-situ growth of CoSe₂ nanoparticles on carbon nanofibers(CNF)by electrospinning technology and calcination process.Experiments results demonstrated that CoSe₂ nanoparticles have effective chemisorption and efficient catalytic function for polyselenides.This unique structure provides a 3D conductive framework and buffer layer for electron/ion transfer,which can effectively improve the utilization of active Se,alleviate the volume change of active Se during cycling and the shuttle effect.Moreover,the electrochemical test results showed that CoSe₂ nanoparticles can improve the kinetics of polyselenide conversion reaction,reduce the overpotential required for Li₂Se deposition/dissolution.And then greatly improve the capacity contribution of solid/liquid phase conversion reaction.The prepared Se/CoSe₂@CNF freestanding electrode without adhesives and conductive agents,which increases the proportion of active selenium in the electrode,thereby improving the overall energy density of the electrode.The results showed that the catalytic effect of CoSe₂ can realize the rapid deposition and dissolution of Li₂Se to improve the cycling performance of lithium-selenium batteries.