| Sn features a theoretical capacity of 847 mAh g-1,high electronic conductivity,low toxicity and low potential of～0.3 V(vs.Na+/Na)forsodium storage.However,the combination with multiple Na+causes a large volume expansion of Sn electrode,resulting in a decrease in the adhesion of Sn electrode to current collector,and the continuous evolution of solid-electrolyte interface.Therefore,solving this issue is an importent way to improve the electrochemical performance of Sn for stable sodium storage.In this thesis,we apply an alloy "glue" strategy to robustly connnect the Sn array(SnNA)electrode and the current collector.The electrochemical performance and the mechmism of SnNA upon sodium storage have been explored.The main context is given as follows:(1)We prepared SnNA by template-free electrodeposition and showed a new strategy to strengthen the connection between electrode and current collector by Cu-Sn alloy at the electrode interface by annealing treatment.The locally formed Cu-Sn alloys are electron-conductive and meanwhile electrochemically inactive,working as an ideal"glue" robustly bridging Sn and Cu to survive harsh cycling conditions in sodium ion batteries.Therefore,SnNA exhibits reversible capacity of 801 mAh g-1 at 0.2 C,and maintains 501 mAh g-1 after 300 cycles at 5 C.The working mechanism of the alloy "glue"is further revealed through a combination of electrochemical impedance spectroscopy,atomic structural analysis and in situ X-ray diffraction.(2)In order to understand the kinetic characteristics of SnNA upon sodium storage,we also conducted a series of electrochemical studies.Alternating current impedance and galvanostatic intermittent titration technology were used to measure the diffusion coefficient of Na+in SnNA.In addition,cyclic voltammetry was used to distinguish the capacity from surface contribution and diffusion-controlled contribution.Finally,Arrhenius’s law was utilized to calculate the activation energy of Na+ at half sodiation and full sodiation. |
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