Design And Research Of Multifunctional Separator Material In Lithium Selenium Battery

Due to high electron conductivity and specific capacity,selenium is considered as a cathode material for a new generation of high energy density batteries.However,as with the lithium-sulfur battery,lithium-selenium battery has severe shuttle effect of polyselenide and slow kinetic transformation,which leads to serious overcharge phenomenon,poor rate performance and cycle performance.Developing heterostructure materials and defect-rich materials is considered to be an effective strategy to improve the performance of lithium-selenium batteries,which has the function of polyselenide adsorption and catalytic conversion.In this paper,wet chemical method and gas-phase selenium（sulfur）conversion process were used to prepare a nanorod-shaped WSe₂/WO₂heterostructure and sulfur/selenium co-doped Mo O₂ nanosphere structure.Furthermore,a multifunctional modified diaphragm was prepared using a simple coating process.The influence of the modified diaphragm on the overcharge phenomenon,rate performance and cycle performance of the lithium-selenium battery was studied.The adsorption and catalytic conversion mechanism of the above materials on the polyselenide were revealed.Specific research contents are as follows:（1）In this work,hydrothermal and gas-phase selenization methods were used to prepare nanorod-shaped WSe₂/WO₂ heterostructure,and the influence mechanism of its modified diaphragm material on the performance of lithium-selenium batteries was studied.First,W₅O₁₄-ethylenediamine nanorod precursor was synthesized by hydrothermal method and transformed into WSe₂/WO₂ heterostructure after in situ selenization（consisting of nanosheet WSe₂ and nanorods WO₂）.Secondly,visualization experiments of adsorption and permeability,Li₂Se deposition and first-principles calculation techniques were used to reveal the enhanced anchoring and catalytic transformation effects of the bridge interface structure in the WSe₂/WO₂ heterostructure on soluble Li₂Se₆ and Li₂Se₄ species.Finally,the electrochemical performance of the lithium-selenium battery with nanoflower-rod-shaped WSe₂/WO₂ heterostructure modified diaphragm was studied.The results showed that the modified separator significantly alleviated the overcharge problem(overcharge capacity was 28.3 m Ah g^–1,only 73.7%of PP-separator battery).At the same time,the cycle performance of lithium-selenium battery is improved（1.58 times the capacity of PP diaphragm）.（2）Mo O₂ nanospheres,which are co-doped with sulfur and selenium atoms,were prepared by a simple precipitation process combined with a one-step selenization/sulfuration process.And the mechanism of improving the performance of lithium-selenium batteries with the modified diaphragm was studied.Firstly,the spherical precursor structure was prepared by the co-precipitation process of pyrrolio-phosphomolybdate complex,and the Mo O₂ nanosphere structure possessing sulfur and selenium atoms was prepared by the subsequent selenization and vulcanization process.Secondly,the enhanced chemical adsorption and anchoring effect of Mo O₂ nanospheres codoped with sulfur and selenium atoms on the polyselenide and the catalytic conversion of the polyselenide were confirmed by polyselenide adsorption experiments,permeation experiments and Li₂Se electrodeposition experiments.Finally,the electrochemical performance results show that the lithium-selenium battery assembled by Mo O₂nanosphere modified separator with co-doped sulfur and selenium atoms has better cycling and rate performance.