Thermodynamics, Kinetics and Structural Evolution of ε-LiVOPO4 over Multiple Lithium Intercalation

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• 作者：Yuh-Chieh Lin ; Bohua Wen ; Kamila M. Wiaderek ; Shawn Sallis ; Hao Liu ; Saul H. Lapidus ; Olaf J. Borkiewicz ; Nicholas F. Quackenbush ; Natasha A. Chernova ; Khim Karki ; Fredrick Omenya ; Peter J. Chupas ; Louis F. J. Piper ; M. Stanley Whittingham ; Karena W. Chapman ; Shyue Ping Ong
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：March 22, 2016
• 年：2016
• 卷：28
• 期：6
• 页码：1794-1805
• 全文大小：878K
• ISSN：1520-5002

文摘

In this work, we demonstrate the stable cycling of more than one Li in solid-state-synthesized ε-LiVOPO₄ over more than 20 cycles for the first time. Using a combination of density functional theory (DFT) calculations, X-ray pair distribution function (PDF) analysis and X-ray absorption near edge structure (XANES) measurements, we present a comprehensive analysis of the thermodynamics, kinetics, and structural evolution of ε-Li_xVOPO₄ over the entire lithiation range. We identify two intermediate phases at x = 1.5 and 1.75 in the low-voltage regime using DFT calculations, and the computed and electrochemical voltage profiles are in excellent agreement. Operando PDF and EXAFS techniques show a reversible hysteretic change in the short (<2 Å) V—O bond lengths coupled with an irreversible extension of the long V—O bond (>2.4 Å) during low-voltage cycling. Hydrogen intercalation from electrolyte decomposition is a possible explanation for the ∼2.4 Å V—O bond and its irreversible extension. Finally, we show that ε-Li_xVOPO₄ is likely a pseudo-1D ionic diffuser with low electronic conductivity using DFT calculations, which suggests that nanosizing and carbon coating is necessary to achieve good electrochemical performance in this material.