Preparation Of Tin-based Metal-organic Frameworks Derived Materials And Their Electrochemical Performance

The new energy vehicle industry has developed rapidly in recent years.However,commercial graphite anodes have the problem of poor capacity and poor rate performance at present,these limitations make it difficult to meet the key requirements of endurance,fast charging and discharging,and safety,which is a major bottleneck that restricts industrial development.In addition,it cannot meet the rapid growth demand in new energy industry because of the scarcity of lithium resources.Sodium is expected to be an alternative to lithium as a much more abundant resource.Accordingly,the development of new lithium/sodium ion battery shared anode electrode materials with high energy density has important scientific and practical application significance.Lithium and sodium can form alloys with stannum.Tin-based oxides,sulfides,and phosphides have high theoretical capacity in lithium/sodium-ion batteries with both conversion and alloying mechanisms of energy storage,which is an ideal shared anode material.But there are still many problems with tin-based materials from large-scale commercial applications,such as low initial coulombic efficiency,rapid decay and short lifetime caused by drastic volume expansion,poor rate performance and conductivity.To address these issues,tin oxide/carbon composites with multi-level structure and tin selenide/carbon composites with heterogeneous structure were prepared using tin-based metal-organic frameworks as precursors in the paper,electrochemical energy storage performance and mechanisms were carried out,as follows:(1)In response to the problem of short battery cycle life due to mechanical failure caused by the large volume change of oxide.In this study,a dual-nanoconfinement strategy of MOF-derived carbon network and titanium dioxide in situ wrapped tinbased oxide particles was proposed,and the carbon/titanium dioxide co-covered SnO2@TiO2/C-SN electrode materials were successfully prepared.The lithium-ion battery with its anode maintains a specific capacity of 461.5 mAh g-1 at a current density of 0.1 A g-1 for 100 cycles.In the sodium ion battery,the specific capacities of 487.0 mAh g-1 and 847.4 mAh g-1 for the first charge and discharge at a current density of 0.1 A g-1,respectively,demonstrating good sodium storage capacity.It is shown that tinbased materials embedded in conductive carbon networks not only provide space for volume changes but also improve the rate of charge transfer,while the introduction of nickel in tin-based MOFs can effectively increase the number of active sites and improve the reaction kinetic performance.(2)In this study,tin-based selenide/carbon composites with heterogeneous structures were prepared by regulating the selenization temperature using tin-based MOF as the precursor.In sodium ion batteries,the composite materials integrate three energy storage mechanisms,intercalation,conversion and alloying,exhibiting good sodium ion battery performance.The capacity retention of the SnSex/NiSey@C-500 after rate testing is 91.80%,and the reversible capacity after 200 cycles at a high current density of 1.0 A g-1 is about 184.3 mAh g-1.Full-cell NVP|SnSex/NiSey@C-500 based on sodium vanadium phosphate cathode exhibited an energy density of 141.1 w h kg-1 at 0.78C with energy efficiency up to 72.31%.Studies have shown that the larger layer spacing and conductive carbon network of tin-based selenide/carbon composites can promote Na+ diffusion and charge transfer,while the space charge layer brought by the heterogeneous structure can accelerate the carrier directional movement and provide good kinetic conditions for fast charging and discharging;meanwhile,the rich interface of the heterogeneous structure increases the density of active sites,which is conducive to improving the utilization of active materials.