| Sodium-ion batteries(SIBs)have attracted lots of interest as potential applications in large scale stationary energy storage.However,commercial graphite,which is mostly used as anode materials in lithium-ion batteries,has little ability of sodium storage.So,it is vital to explore new anode materials with high electrochemical performance in order to realize the successful application of SIBs.Among various anode materials,tin-based materials are considered as one of the most promising candidates due to their high theoretical capacity,low cost,large abundant,and low average reaction voltage.Specifically,tin dioxides and tin sulfides are widely explored because of their lower toxicity and easier preparation process.However,for tin dioxides and tin sulfides anode materials,large volume expansion and intrinsic poor conductivity limit their practical application in SIBs.To fabricate tin dioxides/tin sulfides anode materials with long-term stability,high rate capability and low cost for SIBs,we conduct some researches by rational microstructure design,novel energy storage mechanism exploration and materials fabrication process modification,which are listed in detail as followed:1.In order to improve the cycling performance of tin dioxides as anode materials for SIBs,we successfully prepared tin dioxides/carbon composites with hierarchical microstructures by combing hydrothermal method and annealing process,which can be descried as porous carbon sphere@Sn O2@nano-scale carbon layer(PCS@Sn O2@C).The PCS@Sn O2@C composite exhibits superior cycling stability.At a current density of 50 m A g-1,the PCS@Sn O2@C electrode can deliver a capacity of 326 m Ah g-1 after80 cycles.At a high current density of 1600 m Ah g-1,the capacity retention can reach to as high as 99.1%after 550 cycles.By comparing the microstructure changes of the PCS@Sn O2@C before and after sodium storage and analyzing the sodium storage mechanism,we conclude that it is this unique microstructure that facilitates the electrochemical performance,which means that the synergistic effect of porous carbon sphere and nano-scale carbon layer helps to accommodate the volume expansion and maintain the stability of the electrode.2.In order to improve the rate capability of tin dioxides as anode materials for SIBs,we try to explore novel mechanism to improve the charge transfer in electrode materials.We prepared Sn O2/Co3O4/graphene oxide(GSC)composite with heterostructures through one-step hydrothermal.The GSC composite exhibits excellent electrochemical performance.Specifically,at a current density of 0.1 A g-1,the GSC electrode can deliver a reversible capacity of 461 m Ah g-1 after 80 cycles.At a high current density of 1 A g-1,the GSC electrode can still deliver a reversible capacity of241 m Ah g-1after 500 cycles.By using various characterization methods and electrochemical calculations,we conclude that it is the synergistic effect of heterostructures and pseudocapacitance that facilitates the rate capability.3.In order to simplify the preparation process of Sn S2/graphene composite and lower the cost of production,we design a one-pot synthesis approach with features of low-temperature,short-time,low-energy consumption to successfully prepare Sn S2/graphene composite.By modulating the amount of added graphene,we analyze the effect of graphene amount on the microstructure of the composite and the electrochemical performance.And we get to know the most suitable amount of added graphene.Therefore,this Sn S2/graphene composite prepared by this simple one-pot method exhibits great sodium storage performance.Specifically,at a current density of0.1 A g-1,the Sn S2/graphene composite can deliver a capacity of 702 m Ah g-1 after 50cycles.At a high current density of 1 A g-1,the Sn S2/graphene composite can still deliver a reversible capacity of 330 m Ah g-1after 600 cycles. |
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