| In recent years,batteries can be seen everywhere in our daily life,with the widespread application of electronic devices.Due to their advantages of low cost and abundant resources,sodium ion batteries have become the most competitive and promising energy storage equipment after lithium ion batteries.The anode materials of sodium ion battery include tin,antimony,germanium and their alloy and other transition metals,which have been widely studied because of their advantages such as large theoretical capacity,high electrical conductivity,low price and strong reversibility.However,these materials suffer from severe volume expansion and pulverization during charging and discharging,which seriously hinder their further application as anode materials.In order to solve these problems,nanocrystallization of materials or composites with other materials are commonly used to solve the problem.In this paper,tin-based materials were selected as the main body,which were respectively combined with polypyrrole,graphene and nitrogen-doped three-dimensional graphene as sodium ion battery anode materials to optimize its electrochemical performance.Specific research contents are as follows:（1）The elemental Sn metal was prepared by ice water bath method,and the Sn@PPy composite with core-shell structure was coated with pyrrole monomer.The electrochemical properties of Sn and Sn@PPy were tested under the same conditions.The first specific discharge capacities are 785.5 and 873.4 mAh g-1,respectively,and the retention capacity of Sn@PPy anode after 200 cycles is 192.5 mAh g-1.Impedance curve fitting analysis shows that Sn@PPy has a higher diffusion coefficient of sodium ions than that of Sn.The results show that the Sn@PPy anode formed by the polymerization of Sn elemental and pyrrole monomer has better cyclic stability.The reason is that the PPy shell can effectively buffer the volume expansion of Sn in the process of charge and discharge,and alleviate the powder of the electrode material.（2）Sn Sb nanoparticles were synthesized by ice-water bath co-precipitation method,and then Sn Sb and reduced graphene oxide were combined by hydrothermal method to form Sn Sb/r GO.At the charge/discharge rate of 0.1 C,the first specific discharge capacities of Sn Sb and Sn Sb/r GO anode are 844.2 mAh g-1 and 946.2 mAh g-1.In addition,the retention capacity of Sn Sb/r GO anode after 200 cycles is 200.4 mAh g-1,and its cycling performance is obviously better than that of Sn Sb anode.The kinetic analysis ofAbstractthe electrode shows that the Sn Sb/r GO electrode not only has a faster diffusion rate of sodium ions,but also has a capacitive contribution in the process of charge and discharge due to the presence of r GO,so the Sn Sb/r GO electrode has better cyclic and rate performance.（3）Furthermore,Sn Sb/3D-r NGO composites with three-dimensional network structure were prepared by freeze-drying and high-temperature reduction method.The network structure played a key role in inhibiting the agglomeration of Sn Sb nanoparticles and promoted the surface-driven capacittivity contribution.Through a series of electrochemical performance test,the results show that under the same test conditions,the Sn Sb/3D-r NGO as sodium ion battery anode material has more excellent performance,it is because the three-dimensional structure of high specific surface area and activity area can contact and more sodium ion adsorption.The Sn Sb/3D-r NGO anode not only contributes capacity through diffusion process,but also provides a surface-driven capacity contribution mechanism.The results of electrochemical analysis showed that Sn Sb/3D-r NGO,as the anode of sodium ion battery,exhibited a specific capacity of 1169.6 mAh g-1 at 0.1 C,a reversible specific capacity of 55%,and retained a specific capacity of 479.3 mAh g-1 after200 cycles. |
PDF Full Text Request