文章基本信息

标题：Fast discharge process of layered cobalt oxides due to high Na⁺ diffusion
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作者：Takayuki Shibata ; Yuya Fukuzumi ; Wataru Kobayashi 等
期刊名称：Scientific Reports
电子版ISSN：2045-2322
出版年度：2015
卷号：5
DOI：10.1038/srep09006
出版社：Springer Nature
摘要：Sodium ion secondary battery (SIB) is a low-cost and ubiquitous secondary battery for next-generation large-scale energy storage. The diffusion process of large Na⁺ (ionic radius is 1.12 Å), however, is considered to be slower than that of small Li⁺ (0.76 Å). This would be a serious disadvantage of SIB as compared with the Lithium ion secondary battery (LIB). By means of the electrochemical impedance spectroscopy (EIS), we determined the diffusion constant ( D ) of Na⁺ in thin films of O3- and P2-type NaCoO₂with layered structures. We found that the D values (~ 0.5–1.5 × 10⁻¹⁰ cm²/s) of Na⁺are higher than those ( −11 cm²/s) of Li⁺ in layered LiCoO₂. Especially, the D values of O3-NaCoO₂are even higher than those of P2-NaCoO_2, probably because O3-NaCoO₂shows successive structural phase transitions from the O3, O’3, P’3, to P3 phases with Na⁺ deintercalation. We further found that the activation energy ( E_D ~ 0.4 eV) for the Na⁺ diffusion is significantly low in these layered cobalt oxides. We found a close relation between the relative capacity and the renormalized discharge rate ( = L ²/ DT , where L and T are the film thickness and discharge time, respectively).