The Preparation Of Tin-compounds/C Composites And Their K-ion Storage Mechanisms

The commercial development of electrochemical energy storage devices represented by LIBs has brought great convenience to people’s lives,it is also an important way to achieve China’s goal of carbon neutrality and emission peaking.However,LIBs are currently faced with the challenges of lithium resource shortage and uneven distribution.In order to supply the demand of different scenarios,it is particularly important to develop new and efficient secondary battery energy storage systems.PIBs has attracted close attention because that similar working principle to LIBs and abundant potassium resources.Tin based compounds are considered a promising PIBs anode,due to their high theoretical specific capacity for alloying and conversion reactions with potassium.Nevertheless,the potassium ion is much huger than that of lithium ion in PIBs,leading to Tin based compounds anode experiencing large volume changes and poor diffusion kinetics of potassium ion in the charging and discharging process.In PIBs researches,the composition and structure of anode materials determine battery performance.Considering this,in this article,high capacity,high rate and long cycle life anode materials of Sn-compounds/C nanocomposite was prepared through compounding with carbon materials and regulating micro nano structures,and its energy storage mechanism was analyzed in depth.The main contents are as follows:(1)Insights into the potassium ion storage behavior and phase evolution of SnSe@Se/N co-doped carbon anodeSnSe obtains the advantages of large layer spacing,narrow band gap and weak shuttle effect,but as potassium negative electrode,they inevitably suffer large volume expansion during potassic alteration.In this Chapter,a simple strategy for synthesizing SnSe@void@Se/N co-doped carbon(denoted as SnSe@C)in core-void-shell structure was proposed based on metal evaporation effect.The inner void can adapt to the volume change of SnSe nucleus,and the outer carbon shell could enhance the electrical conductivity.The optimized SnSe@C negative electrode exhibited a specific capacity of 443 mAh g-1 and 257 mAh g-1 at 0.1 C and 1C,respectively.Combining qualitative and quantitative electrochemical analysis,SnSe@C anode’s excellent electrochemical performance was attributed to the contribution of enhanced capacitance behavior.Moreover,first-principles calculations showed that heteroatom-doped carbon had a good affinity for potassium ion and K2Se,which improved the rate ability and capacity retention.In addition,the phase evolution of SnSe@C electrode during potassization/depotassization process was clarified by in situ X-ray diffraction characterization,and the crystal transition from the Pnma(62)point group of SnSe to the Cmcm(63)point group was discovered.(2)Preparation and study of Sn2P2Se6@Graphene composite for PIBs anodeSn,P and Se exhibit high theoretical specific capacity of potassium ion storage.ternary compound of Sn2P2Se6 was synthesized by primitive high-energy ball milling method.In view of the problems of poor electrical conductivity and severe volume expansion in potassization of Sn2P2Se6,this chapter prepared Sn2P2Se6@graphene composites(denoted as Sn2P2Se6@Gr)by particle nanosizing and 3D conductive network constructing.As the anode of potassium ion battery,it possessed excellent cycle life and rate performance.the anode exhibited a high reversible specific capacity of 389 mAh g-1 when the discharge current density was 0.05A g-1.When the current density increased to 0.5 A g-1,the anode could still show a high specific capacity of 291 mAh g-1,and with a capacity retention rate of 93%after 800 cycles.The related kinetic analysis proved that capacitive behavior dominated in charge storage process of Sn2P2Se6@Gr anode,accelerating the diffusion of potassium ions.The addition of graphene reduced the charge transfer impedance of the electrode and improved its rate performance.In addition,the micro morphology of the electrode showed Sn2P2Se6@Gr had a smoother and more complete electrode state and lower expansion rate,greatly improving the cycling performance of the electrode.In this work,the Tin-compounds/C anode was optimized based on the composition and structure designing,and its electrochemical performance and potassium storage mechanism were studied deeply,which provided new ideas for the subsequent research on PIBs anode.