Quantitative MAS NMR characterization of the LiMn_1/2Ni_1/2O₂ electrode/electrolyte interphase

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• 作者：M. Cuisinier^a ; J.-F. Martin^a ; ^b ; ^d ; P. Moreau^a ; T. Epicier^c ; R. Kanno^b ; D. Guyomard^a ; N. Dupré ; ^a ; ^{nicolas.dupre@cnrs-imn.fr}
• 关键词：Lithium Batteries ; Electrode/electrolyte interface ; 7Li ; 19F and 31P MAS NMR ; Surface analysis
• 刊名：Solid State Nuclear Magnetic Resonance
• 出版年：2012
• 期刊代码：83_09262040
• 类别：ce
• 出版时间：April, 2012
• 卷：42
• 期：Complete
• 页码：51-61
• 文件大小：1579 K

摘要

The conditions in which degradation processes at the positive electrode/electrolyte interface occur are still incompletely understood and traditional surface analytical techniques struggle to characterize and depict accurately interfacial films. In the present work, information on the growth and evolution of the interphases upon storage and cycling as well as their electrochemical consequences are gathered in the case of LiNi_1/2Mn_1/2O₂ with commonly used LiPF₆ (1 M in EC/DMC) electrolyte.

The use of ⁷Li, ¹⁹F and ³¹P MAS NMR, made quantitative through the implementation of empirical calibration, is combined with transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) to probe the elements involved in surface species and to unravel the inhomogenous architecture of the interphase. At room temperature, contact with the electrolyte leads to a covering of the oxide surface first by LiF and lithiated organic species are found on the outer part of the interphase. At 55 掳C, not only the interphase proceeds in further covering of the surface but also thickens resulting in an increase of 240%of lithiated species and the presence of -POF₂ fluorophosphates. The composition gradient within the interphase depth is also strongly affected by the temperature.

In agreement with the electrochemical performance, quantitative NMR surface analyses show that the use of LiBOB-modified electrolyte results in a Li-enriched interphase, intrinsically less resistive than the standard LiPF₆-based interphase, comprised of a mixture of resistive LiF with non lithiated species.