Research On Surface Modification And Electrochemical Application Of Transition Metal Based Active Materials

Transition metal based active materials are considered as promising electrode materials due to their high electrochemical reactivity and high specific capacity.However,the high reactivity leads to serious volume changes in the electrochemical reaction process,which causes serious damage to the material structure,and contact with electrolyte interface side reactions,forming unstable SEI film,resulting in poor electrochemical performance.In addition,it has been found that transition metal-based materials can be used as catalytic carriers to improve the electrochemical performance of sodium-selenium batteries,but the internal mechanism of selenium loaded by transition metal-based materials as catalytic carriers was lack of in-depth study.At present,most researchers improve the interface mainly by changing electrolyte components.It is urgent to expand other perspectives to improve the interface of transition metal-based materials,improve the interface stability of such materials,clarify the internal mechanism of selenium loading,and expand its application.In this paper,we mainly explore the surface structure control strategy of transition metal-based materials,synthesizing modified separators to improve the interfacial components of transition metal base materials,and the electrochemical performance of the materials loaded with selenium in sodium selenium batteries.Specific findings are as follows:(1)Surface structure control of transition metal-based materials:FeNCN is selected as a transition metal-based material in this chapter.By autocatalytic carbon coated with FeNCN@C,sol-gel method of alumina coated with FeNCN@Al2O3 and fluorine ion doped on FeNCN/F.It is found that the carbon coating and alumina coating mainly avoid the direct contact between the transition metal-based material and the electrolyte,improve the first cycle coulomb efficiency.At the same time,the coating can also reduce the volume expansion of the material and improve the battery life.Doping F-also alleviates the side effects of the interface and reduces the capacity loss caused by SEI film.These three methods broaden the surface structure control of transition metal-based materials,improve the properties of the interface,and obtain excellent electrochemical performance.(2)Interfacial composition regulation of transition metal-based materials:Different transition metal alloys/carbon tubes were coated on the separator to study the changes of interfacial composition during the electrochemical reaction.It was found that the modified separator had higher capacity and better rate performance,especially the modified separator coated with FeNi/CT(FeNi/CT/PP).When the current density is 0.1,0.2,0.5,1,2,5 A/g,it shows the high capacity of 603.1 mAh/g,565.3 mAh/g,526.7 mAh/g,495.7 mAh/g,440.8 mAh/g,357.3 mAh/g.Through XPS analysis,it is found that more Fe0 and Ni0 are formed at the interface,which plays a beneficial role in the formation of SEI film,makes the SEI film stable.This method can be extended to other electrode materials by modifying the separator to regulate the interfacial components,which provides ideas for improving the interfacial interface of other transition metal-based materials.(3)Study on the performance of transition metal-based materials as catalytic carriers:the final product Se@NiSe2/Ni/CTs(Se@NS-N-CT)was obtained by selenifying Ni/CT and loading selenium.It is found that the lattice distorted Ni structure can form Se-Ni3 tetrahedral bonding structure with the Se of Na2Se4.It provides high activity for catalytic electrochemical reactions in Na-Se battery.The strong adsorption and catalytic conversion of lattice distorted Ni to Na2Se4 are visually displayed by the H-type electrolytic cell.The electrode(Se@NS-N-CT)is prepared by this Ni structure can realize the rapid charge transfer and high cycle stability of the battery.The material has a performance of 345 mAh/g after 400 cycles at 1 C and 286.4 mAh/g at 10 C.This work provides further understanding of bond structure design and regulation of transition metal-based materials.