Correlating Local Structure with Electrochemical Activity in Li2MnO3

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• 作者：Rose E. Ruther ; Hemant Dixit ; Alan M. Pezeshki ; Robert L. Sacci ; Valentino R. Cooper ; Jagjit Nanda ; Gabriel M. Veith
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：August 13, 2015
• 年：2015
• 卷：119
• 期：32
• 页码：18022-18029
• 全文大小：531K
• ISSN：1932-7455

文摘

Li₂MnO₃ is believed to be a critical component of the high capacity Li-rich鈥搈anganese-rich oxide materials; however, the mechanism of its electrochemical activity remains controversial. Here, Raman spectroscopy and mapping are used to follow the chemical and structural changes that occur in Li₂MnO₃ during electrochemical cycling. Conventional composite electrodes cast from a slurry and thin films are studied as a function of the state of charge (voltage) and cycle number. Thin films have similar electrochemical properties as electrodes prepared from slurries but enable spectroscopy of uniform samples without carbon additives and binder. First-principles density functional theory is used to calculate the phonon spectra and identify the Raman-active modes. On the basis of the calculations of phonon spectra for pristine Li₂MnO₃ and structures with Li vacancies, we discuss the origin of Raman-active peaks observed during the electrochemical cycling. The spectral changes correlate well with the electrochemical behavior and support a mechanism whereby capacity is lost upon extended cycling due to the formation of new manganese oxide phases.