Co-construction Of Carbon Nanohosts And Selenium-based Material Composite For Potassium Storage

Since the discovery of the first lithium battery in 1970,rechargeable lithium-ion batteries have been widely used in energy storage due to virtue of their high energy density and stable cycling after decades of development.However,the lack of lithium resources,high cost and uneven geographical distribution hinder the future development of LIBs.Since K and Li belong to the same main group in the periodic table and potassium elements is rich in the earth’s crust,which leads to low prices.Meanwhile,the standard redox potential of potassium ion batteries（KIBs）is very close to LIBs,which has the potential to become the next generation of rechargeable economical batteries.Due to the large radius of potassium ions affects the potassium storage process,the development of stable and suitable electrode materials is the basis for the construction of efficient KIBs systems.Among the selenium-based materials,selenium monomers have high volumetric specific capacity（3253 m A h/cm³）and excellent electrical conductivity(1×10^-3 S/m).Meanwhile metal selenides are characterized by structural stability,costless and high electrochemical activity.Selenium-based materials are suitable as KIBs electrode materials.Nevertheless,selenium-based materials face some problems in KIBs applications,such as large volume changes（about 400%）during conversion,low utilization of active materials,and slow reaction kinetics.In response to the above problems,we combined selenium-based materials with carbon materials of specific microstructures.The role played of the carbon matrix in the performance enhancement was analyzed by the corresponding characterization method.The main work is as follows:（1）In order to solve the damage of metal selenide volume expansion on cycling performance,we prepared Fe Se₂@C composites using carbon nanosphere shells as carriers.In terms of microstructure,dispersed Fe Se₂ nanoparticles are wrapped inside carbon nanospheres.Compared with pure Fe Se₂,the great improvement in structure solves the problems of structural collapse during the reaction of the transformed KIBs anode material.The Fe Se₂@C electrode maintains the reversible capacity of 286 m A h/g after long cycles at a current density of 1 A/g,providing high specific capacity and long cycle stability.The dispersed nanoparticles reduce the possibility of agglomeration,and the external flexible mesoporous carbon skeleton reduces volume expansion,which achieving stable cycling at high volumes.（2）Combined with the work of Fe Se₂@C above,we found that the choice of carbon material affects the performance of selenium-based composite electrodes.Herein,we synthesized nanosheet selenium-based composites（Se@CNS）and three-dimensional bulk selenium-based composites（Se@CB）using MOFs-based two-dimensional microporous carbon nanosheets and commercial three-dimensional bulk microporous carbon materials（YP80f）as carriers,respectively.In the study of potassium storage performance,Se@CNS electrode reached 462 m A h/g after 100 cycles at 0.2 C current density,much higher than Se@CB electrode（271 m A h/g）.By GITT characterization,the ion diffusion coefficient of Se@CNS is much higher than Se@CB.With the unique two-dimensional lamellar microporous structure,the Se@CNS material can accelerate ion/electron conduction and alleviate volume expansion,which is conducive to more efficient potassium storage performance.In addition,the conformational relationship between the SEI film of the composite electrode material and the potassium storage performance was analyzed by deep XPS.It was observed that the difference of carbon carrier affects the electrode SEI film structure.Among them,the ordered SEI film structure with organic species in the outer layer and inorganic species in the inner layer can effectively enhance the electrochemical performance of the electrode.