A Study on Long-Term Cycle Performance of Conventional Tin Anode for Sodium-Ion Batteries

Abstract

Tin has been regarded as one of the most promising anode materials owing to its high theoretical specific capacity of 847 mAh g−1, based on the full sodiation of Na15Sn4. However, the pure tin anode has a severe problem of poor cycling properties, as it loses its initial capacity within the first 10 cycles. It is believed that the pulverization of tin induced a rapid degradation of capacity during cycling. The tin anode material expands to 520% of its original volume during sodiation and contracts to its original volume during desodiation. Several approaches have been investigated to overcome this problem. One approach involves stress release by utilizing a buffer layer, decreased tin size, or a thin film. Another approach involved the suppression of volume expansion by encapsulating tin nanoparticles into carbon and coating Al2O3 onto the tin nanoparticles. For example, ultra-small (8 nm) tin nanoparticles embedded in carbon showed 415 mAh g−1 of reversible capacity for 500 cycles, and tin nano-dots (1 ~ 2 nm) encapsulated in porous nitrogen-doped carbon nanofibers showed 483 mAh g−1 for 1300 cycles. Although these previous approaches succeed in improving cycle life, most preparation methods are too complex for commercialization as compared to that of the conventional electrode using tin nanopowder, a conducting additive, and a binder. However, a conventional electrode still showed poor cycling properties. Komaba et al. reported that a conventional electrode demonstrates capacity decay from 758 mAh g−1 to 21 mAh g−1 over the course of 10 cycles, even if using tin nanopowder (< 150 nm). The cycling properties of tin anode could be improved using a conductive binder or polyacrylate binder in short-term cycling of 20 cycles, but improved long-term cycle performance of a conventional electrode has not reported yet. Previous studies indicate that the long-term cycling of tin electrode with high capacity could be improved by the release or suppression of accumulated stress in a tin due to volume change. In order to release stress of conventional electrode, the tin electrode should be designed using suitable binder, conductive additive, and its optimized structure. Therefore, we study on the long-term cycling of conventional tin anode for sodium-ion batteries by the control these components.