Direct Evidence of a Chemical Conversion Mechanism of Atomic-Layer-Deposited TiO2 Anodes During Lithiation Using LiPF6 Salt

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• 作者：Matthew R. Charlton ; Anthony G. Dylla ; Keith J. Stevenson
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：December 24, 2015
• 年：2015
• 卷：119
• 期：51
• 页码：28285-28291
• 全文大小：368K
• ISSN：1932-7455

文摘

Titanium dioxide has been identified as a prospective anode material for use in lithium ion batteries. The higher lithiation potential of TiO₂ versus other common anodes is more electrochemically compatible with most organic electrolytes, thus leading to reduced solid electrolyte interphase formation and overall more stable battery systems. However, in this study TiO₂ has exhibited poor cycling stability with common electrolytes containing lithium hexafluorophosphate (LiPF₆) salt. Combined electrochemical and spectroscopic analyses have revealed this to be due to the onset of reversible fluorination of the anode and chemical conversion of TiO₂ to TiOF₂ during lithiation. Comparison of electrochemical cycling of atomic-layer-deposited TiO₂ anodes using LiPF₆ with and without a hydrofluoric acid scavenger, tributylamine, to cycling using a nonfluorinated lithium perchlorate (LiClO₄) salt indicates that the in situ formation of hydrofluoric acid in the electrolyte from decomposition of the PF₆^– anion alters the lithiation electrochemistry. X-ray photoelectron spectroscopy (XPS) analysis and time-of-flight secondary-ion mass spectrometry (ToF SIMS) depth profiling measurements confirmed the presence of TiF₂ and TiOF surface and bulk phases, respectively, in the electrode upon lithiation.