A Study Of Solid-Electrolyte-Interphases On Sn And Sn@PEO Anodes For Lithium Ion Batteries

In order to reduce this volume change and improve the stability of solid-electrolyte interphase(SEI)on the surface of tin electrodes,people have paid much attention to the polymer coating.Although the polymer shell can really improve the electrochemical performance of anode materials,few articles reported detailed studies about SEI formation and its evolution upon cycling.In this context,we synthesized Sn and Sn@PEO nanoparticles for use in a lithium-ion battery and investigated their electrochemical and morphological properties.Specifically,the formation and degradation mechanisms of SEI on bare/PEO coating Sn electrodes were investigated.We have observed that the passivation layer at the surface of the Sn electrode forms as soon as the first contact with the electrolyte,contrary to a Sn@PEO electrode.During the first cycle,the formation process of the SEI takes place in different successive stages as a function of the Sn and Sn@PEO electrode potential,which is directly linked to the voltage of the cell.Compared with the bare cycled Sn electrode,the SEI on the surface of cycled Sn@PEO electrode is thinner,smoother and more complete.Meanwhile,the Sn@PEO nanoparticles are not ruptured and they can basically keep the original appearance.Based on the results obtained from XPS,we suppose that a process of partial dissolution of organic lithium salt takes place during the following cycle of bare Sn electrodes.While the SEI formed on the Sn@PEO electrode is characterized by inorganic components(Li2CO3)-rich outer layer and organic components–rich inner which could make the SEI more stable and inhibit the electrolyte immerging into the active materials.In particular,the elastic ion-conductive PEO coating and organic components could increase the toughness of SEI and allow the SEI to bear stress change in repetitive lithium insertion and extraction process.This brings about that the Sn@PEO electrodes show significantly better capacity retention than bare Sn electrodes.