Why Substitution Enhances the Reactivity of LiFePO4

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• 作者：Fredrick Omenya ; Natasha A. Chernova ; Ruibo Zhang ; Jin Fang ; Yiqing Huang ; Fred Cohen ; Nathaniel Dobrzynski ; Sanjaya Senanayake ; Wenqian Xu ; M. Stanley Whittingham
• 刊名：Chemistry of Materials
• 出版年：2013
• 出版时间：January 8, 2013
• 年：2013
• 卷：25
• 期：1
• 页码：85-89
• 全文大小：403K
• 年卷期：v.25,no.1(January 8, 2013)
• ISSN：1520-5002

文摘

The impact of substitution at the Fe site in LiFePO₄ on reaction pathway, kinetics, and crystallographic changes upon electrochemical delithiation has been determined. Substitution was found by X-ray diffraction to reduce the lattice mismatch between the Li-rich and the Li-poor phases of the substituted samples as compared to the unsubstituted one. Substitution was also found, by monitoring the 200 reflection peaks of both the triphylite and heterosite phases, to increase the composition width of the single phase formed on lithium removal, Li_{1聽鈥撀?i>x}FePO₄. A single phase was observed as high as x = 0.15 in Li_{1聽鈥撀?i>x}Fe_0.85V_0.1PO₄, whereas LiFePO₄ at the same state of charge and of similar particle size show the existence of two phases. In addition, the temperature at which a single phase is observed for the composition range 0 鈮?x 鈮?1 is decreased from slightly above 300 掳C to ca. 200 掳C. This increased single-phase-like behavior explains the enhanced kinetics of substituted LiFePO₄ and is consistent with a pseudosingle-phase reaction mechanism.

Keywords:

Olivine; lithium battery; vanadium substitution; reaction mechanism