Simultaneous Reduction of Co3+ and Mn4+ in P2-Na2/3Co2/3Mn1/3O2 As Evidenced by X-ray Absorption Spectroscopy during Electrochemical S

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• 作者：Ju-Hsiang Cheng ; Chun-Jern Pan ; Jyh-Fu Lee ; Jin-Ming Chen ; Marie Guignard ; C. Delmas ; Dany Carlier ; Bing-Joe Hwang
• 刊名：Chemistry of Materials
• 出版年：2014
• 出版时间：January 28, 2014
• 年：2014
• 卷：26
• 期：2
• 页码：1219-1225
• 全文大小：413K
• ISSN：1520-5002

文摘

Sodium intercalation in P2-Na_2/3Co_2/3Mn_1/3O₂ (obtained by a coprecipitation method) was investigated by ex situ and in situ X-ray absorption spectroscopy. The electronic transitions at the O K-edge and the charge compensation mechanism, during the sodium intercalation process, were elucidated by combining Density Function Theory (DFT) calculations and X-ray absorption spectroscopy (XAS) data. The pre-edge of the oxygen K-edge moves to higher energy while the integrated intensity dramatically decreases, indicating that the population of holes in O 2p states is reduced with increasing numbers of sodium ions. From the K-edge and L-edge observations, the oxidation states of pristine Co and Mn were determined to be +III and +IV, respectively. The absorption energy shifts to lower positions during the discharging process for both the Co and the Mn edges, suggesting that the redox pairs, that is, Co³⁺/Co²⁺ and Mn⁴⁺/Mn³⁺, are both involved in the reaction.