Structural Evolution of a Na/NaFePO_4 Sodium-ion Battery during Discharge Determined by in-situ Synchrotron X-ray Diffraction

使用即時同步輻射解析Na/NaFePO_4鈉離子電池放電時的結構變化

黃爾文(E-Wen Huang) ； 張仍奎(Jeng-Kuei Chang) ； 李岱洲(Tai-Chou Lee) ； 廖孜康(Tzu-Kang Liao) ； 洪意鈞(Yi-Chun Hung) ； 吳采羚(Tsai-Ling Wu) ； 廖揚鴻(Yang-Hung Liao) ； 王誼珍(Yi-Chen Wang) ； 黃斌源(Ping-Yuan Huang)

《中國機械工程學刊》 36卷3期 (2015/06) Pp. 271-274

摘要

本論文研究一個新型的Na/NaFePO4電池。在實驗之初，先將電池充電至2.4V。緊接著使用即時同步輻射觀察放電過程中電池結構的變化。我們發現在充電之後，電池的繞射強度主要來自於NaxFePO4相。在放電的過程中，依據NaxFePO4相各繞射峰的變化所估算的晶格應變顯示晶格皆隨著電壓的下降而伸長。可能的機制是來自於鈉的嵌入。除此之外，透過繞射峰形的分析，在放電的過程中，這些繞射峰的強度增加且同時峰寬下降。這樣的現象可能來自於放電時NaxFePO4相持續地形成更有序地排列。上述的觀察總結出放電的機制不只純粹來自化學反應，同時也伴隨著因晶格變化引進的機械能與結晶程度的轉變。時間解析的晶格應變更顯示了在放電的過程中個晶面的不同調行為。

並列摘要

In this study, a newly-developed Na/NaFePO_4 cell is studied. We charge the cell up to 2.4V and then apply in-situ synchrotron x-ray diffraction to resolve structural evolution during discharge. An intermediate of NaxFePO_4 diffracts strongest x-ray intensity among all the components of the cell. During discharging, several (hkl) planes of the NaxFePO_4 phase of the cathode are found to expand. The expansion of the cathode-lattice size suggests a Na-insertion mechanism. Upon the lattice expansion, a peak-profile analysis shows a correlation between the increase of the peak-intensity and the decrease of the peak-width evolution. The correlation suggests that there is more well-defined NaxFePO_4 formed during the discharge. Coupled with the Na insertion, the discharge of the Na/NaFePO_4 cell shows a convolution of mechano-chemical reaction. Moreover, the time-resolved measurements reveal an asynchronous lattice-strain fluctuations within a stepwise discharge plateau.

並列關鍵字

Na/NaFePO_4 ； Sodium-ion Battery ； in-situ Synchrotron X-ray Diffraction ； Discharge