A₃V₂(PO₄)₃ (A?=?Na or Li) probed by in situ X-ray absorption spectroscopy

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• 作者：Maja Pivko ; Iztok Arcon ; Marjan Bele ; Robert Dominko ; Miran Gaberscek
• 关键词：Li3V2(PO4)3 ; Na3V2(PO4)3 ; XAS ; Li-ion batteries ; Sodium batteries ; NASICON
• 刊名：Journal of Power Sources
• 出版年：2012
• 出版时间：15 October, 2012
• 年：2012
• 卷：216
• 期：Complete
• 页码：145-151
• 全文大小：715 K

文摘

Two stable modifications of A₃V₂(PO₄)₃ (A?=?Na or Li) were synthesized by citric acid assisted modified sol-gel synthesis. The obtained samples were phase pure Li₃V₂(PO₄)₃ and Na₃V₂(PO₄)₃ materials embedded in a carbon matrix. The samples were tested as half cells against lithium or sodium metal. Both samples delivered about 90?mAh?g^?1 at a C/10 cycling rate. The change of vanadium oxidation state and changes in the local environment of redox center for both materials were probed by in-situ X-ray absorption spectroscopy. Oxidation state of vanadium was determined by energy shift of the absorption edge. The reversible change of valence from trivalent to tetravalent oxidation state was determined in the potential window used in our experiments. Small reversible changes in the interatomic distances due to the relaxation of the structure in the process of alkali metal extraction and insertion were observed. Local environment (vanadium-oxygen bond distances) after 1st cycle were found to be the same as in the starting material. Both structures have been found very rigid without significant changes during alkali metal extraction.