| Tin-based anode materials have been one of the most popular materials for sodium ion battery anode materials.Due to the high theoretical capacity(the capacity of the formed Na15Sn4 can reach 845 mAh·g-1),the low potential of sodium insertion and environment friendly,it has been sought after by researchers.However,tin-based materials are prone to large volume expansion during the sodium insertion process,it causes the structure demage of the electrode and rapidly decreasing of the material's reversible capacity.In addition,its poor conductivity also makes the rate performance unstable at large current densities.Therefore,how to improve the stable reversible capacity during the charge and discharge process has become the main research hotspots.This research chooses commercial carbon cloth as one of the flexible current collectors and carbon sources.Utilizing the good conductivity of carbon cloth and using as self-assembled substrate and building tin-based materials with various morphologies on its surface.In order to better study the volume expansion problem of tin-based materials,this thesis is mainly divided into the following four parts for research:(1)The Sn/CC electrode material was successfully synthesized by liquid-phase reduction method,and the effects of heat treatment on its morphology and electrochemical performance were researched in different solvent media.The Sn/CC electrode material has the best electrochemical performance after heat treatment at 400? when using glycerol as the solvent media.The first discharge capacity of the sample during charging and discharging was 877.6 mAh·g-1 and the first coulombic efficiency was 62.2%.After 500 cycles,the reversible capacity still remained 441.2 mAh ·g-1.After the third cycle,the coulombic efficiency remained above 96%.In addition,the reversible capacities of the samples under current densities of 500 mA·g-1 and 1A·g-1 were 585.8 mAh·g-1 and 445.3 mAh·g-1,respectively.It is mainly due to the influence of-OH functional groups during the preparation process which leads to inconsistent reaction kinetics and structural inconsistency.The heat treatment process further optimized the surface structure of Sn particles distributed on the carbon cloth and pyrolyzed large-sized spheric carbon.The Sn particles was remained and redistributed uniformly on the surface of the carbon cloth.This microstructure has a small size and a large specific surface area,which can provide more chemical reaction sites,thereby improving the cycle performance and rate performance of the anode material.(2)The C@gray-Sn/Sn/CC anode materials were successfully synthesized at low temperature.The effect of different phase compositions and structure sizes of the material on the electrochemical performance were researched.As an anode material for sodium ion batteries,this electrode exhibits excellent electrochemical performance.After 500 cycles of stable cycling at a current density of 1 A·g-1,it can still maintain a reversible capacity of 387.2 mAh·g-1.The phase transition of Sn was controlled at low temperature to change the nanosphere diameter of Sn particles,and the particle diameter of Sn particles was reduced from?180 nm to~ 25 nm.When the particle size was reduced,the charge and discharge stability of the material was significantly improved.Moreover,after a long-cycle charge and discharge process,the surface structure and morphology of the electrode material can remain stable.It indicated that the volume expansion of Sn under this structure was suppressed.The above results illustrate the effect of the material structure size on maintaining the structural stability in the Sn anode material,and its excellent electrochemical performance and stable structure are attributed to the appropriate material structure size.(3)The influence of stress on the electrochemical performance and structural stability of the material were researched.The C@Sn@SnO2/CC electrode material with a controlled stress state was synthesized by adjusting the temperature of the calcination process.As an anode material for sodium ion batteries,the electrode has excellent electrochemical performance(after 800 cycles at a current density of 1 A·g-1,it still has a capacity close to 400 mAh·g-1 and a capacity retention rate of 86.9%).The volume expansion of Sn during charge and discharge process was suppressed by controlling the stress of Sn in the carbon structure.When the heat treatment temperature was 700 degrees,the existence of compressive stress can significantly improve the charge and discharge stability of the material.At the same time,it can stabilize the structure and surface morphology of the material,and maintain a stable charge transfer process between Sn and carbon structures.These results reveal the effect of stress on the sodium storage behavior in Sn anode materials.It provides a reference for the practical application of other materials with alloy reaction mechanism as anode materials for high-performance sodium ion batteries.(4)The C@CuSn/SnO2/CC composite material was successfully prepared by two consecutive steps of hydrothermal method and carbonization pyrolysis method.The composite material has good cycle stability and high rate when it was used as anode material for sodium ion batteries.Coulombic efficiency of the first cycle has reached 87.1%and the reversible capacity has maintained at 354.5 mAh·g-1 after 200 cycles.On the one hand,the introduction of Cu improved the first coulombic efficiency of electrode;on the other hand,the external carbon layer alleviates the stress caused by the volume change of the electrode material during the charge and discharge process.Therefore,the electrode has better structural stability. |
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