Graphene-wrapped Tin-based Composites As Anode Materials For Sodium-ion Batteries

Lithium-ion batteries?LIBs?have been the first choice for portable devices since Sony company provided its commercial product,using lithium cobaltate and graphite as the cathode and anode materials,respectively.However,considering the limited storage and the uneven distribution of the lithium resource,high price of lithium metal will be a major issue for future LIBs production.Thereout,room-temperature sodium-ion batteries?SIBs?have again aroused a great deal of interest recently because of the abundance and ubiquity of sodium resource in the Earth's crust.To develop high-performance sodium-ion energy storage system,various compounds used to be anodes for LIBs now are attempted to work in SIBs.Nevertheless,due to the bigger diameter and lower theoretical ratio capacity of sodium-ions in contrast with lithium-ions,searching for suitable materials applied to SIBs is more challenging than that for LIBs.In this work,a series of tin-based graphene-supported nanocomposites were synthesized by in situ solvothermal method and calcination in Ar/H₂ atmosphere.In the initial experiment,the SnO₂@rGO aerogel?tin oxide nano-crystals anchored on graphene sheets?was successfully prepared and characterized.Thereafter,the electrochemical performance of the composite was systematacially investigated and superior cycle stability indicated that graphene plays an essential role in restraining the expansion of tin oxide in the sodiation process.Based on the above experimental results,the SnCu@GS?SnCu nanoparticles anchored on graphene sheets?composite was self-assembled by a strategy integrating an in situ solvothermal method and a freeze-drying process with a subsequent annealing procedure.Graphene constructed a three-dimensional porous conductive framework in solvothermal reaction and led to a well dispersion of copper-coated tin nanoparticles with an average diameter of about 70 nm on graphene sheets.In contrast,SnCu alloy without graphene network obtained through the same route exhibited various diameters from 200 nm to 4?m.The electrochemical performance of nano-sized SnCu granules anchored on graphene matrix as an anode for sodium-ion batteries was also measured in detail.The statisitcs revealed that the composite showed superior cycling stability and rate capability.The specific reversible capacity of the SnCu@GS electrode can still maintain about 310 mA h g^-11 at a current density of 100 mA g^-11 after 50cycles.In the following chapter,a feasible and controllable in situ solvothermal assisted thermal reduction approach was developed to fabricate self-supporting and binder-free graphene sheets-wrapped Sn nanoparticles?Sn@GS?films.The graphene oxide?GO?,which is the original source of conductive GS network,can also serve as a surfactant to help to inhibit the secondary aggregation of nanoparticles.Accordingly,the homogeneous Sn nanoparticles?¹0 nm?can evenly distribute into the GS matrix.The as-obtained Sn@GS films,when were used as anode materials for sodium-ion batteries?SIBs?,show promising electrochemical performances.We believe that this method not only blazes a new trail for synthesizing Sn@GS nanocomposite films,but also can be extended to develop other free-standing non-noble metal?or alloy?nanoparticles@GS films for wide applications,such as catalysis,detection and the forth.