Preparation And Lithium Storage Properties Of Tin-based Metal-organic Framework And Its Derivative

The rapid development of electric vehicles places higher demands on the specific capacity of lithium-ion batteries.Tin-based materials are expected to be the anodes of next-generation lithium-ion batteries due to their high specific capacity.However,tin anodes have huge volume change during lithiation/delithiation,which can seriously affect the cycling stability.To solve this problem,a lot of research has been done on the modification of tin-based anodes.In recent years,there have been many reports on the use of tin-based metal-organic frameworks（Sn-MOFs）and their derivatives as anode materials for lithium-ion batteries.These materials have greatly improved the problem of poor cycle stability of common tin-based anode materials,showing great application prospects.In this paper,the recent lithium storage applications of Sn-MOFs and their derivatives are reviewed,a new Sn-MOF and a Sn-MOF-derived material were designed and synthesized,and their structures and properties were characterized.In this work,Sn-DCTP metal-organic framework was synthesized by a hydrothermal method using 2,5-dichloroterephthalic acid（H₂DCTP）as the organic ligand.When used as anode material for lithium-ion battery,Sn-DCTP exhibits a high specific capacity of 1021.6 m A hg^-1 at a current density of 200 m A g^-1 after 100cycles and 475.2 m A hg^-1 at 800 m A g^-1 after 1000 cycles.The X-ray photoelectron spectroscopy and the cyclic voltammetry preliminarily revealed the lithium storage mechanism of Sn-DCTP.The Sn²⁺center and Cl atoms of organic ligands may be the main lithium storage sites.Kinetic analysis shows that pseudocapacitive behavior plays an important role in the electrode reaction process.Compared with the currently known Sn-MOFs anodes,Sn-DCTP is highly competitive due to its low-cost organic ligands and excellent performance.In this work,Sn-PMA metal-organic framework was synthesized by hydrothermal method using pyromellitic acid（PMA）as the organic ligand,and the Sn/Sn O_x@NC composite was synthesized by co-calcination of Sn-PMA and dicyandiamide.The composites are composed of numerous Sn/Sn O_x core-shell microspheres encapsulated in 3D porous nitrogen-doped carbon frameworks.This unique structure not only has a large number of active sites for lithium storage,but also effectively buffers the volume expansion of tin and promote the transmission of electrons and lithium ions.When used as anode material for lithium-ion batteries,Sn/Sn O_x@NC exhibites high initial Coulombic efficiency,long cycling stability,and excellent rate capability.It remains a high reversible capacity of 817.8 m A h g^-1 at100 m A g^-1 after 200 cycles.Even at a large current density of 1 A g^-1,it still remains a high capacity of 525.7 m A h g^-1 after 800 cycles.