P2-NaxMn1/2Fe1/2O2 Phase Used as Positive Electrode in Na Batteries: Structural Changes Induced by the Electrochemical (De)intercalation Process

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• 作者：Benoit Mortemard de Boisse ; Dany Carlier ; Marie Guignard ; Lydie Bourgeois ; Claude Delmas
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：October 20, 2014
• 年：2014
• 卷：53
• 期：20
• 页码：11197-11205
• 全文大小：731K
• ISSN：1520-510X

文摘

The electrochemical properties of the P2-type Na_xMn_1/2Fe_1/2O₂ (x = 0.62) phase used as a positive electrode in Na batteries were tested in various voltage ranges at C/20. We show that, even if the highest capacity is obtained for the first cycles between 1.5 and 4.3 V, the best capacity after 50 cycles is obtained while cycling between 1.5 and 4.0 V (120 mAh g^鈥?). The structural changes occurring in the material during the (de)intercalation were studied by operando in situ X-ray powder diffraction (XRPD) and ex situ synchrotron XRPD. We show that a phase with an orthorhombic P鈥?-type structure is formed for x 鈮?1, due to the cooperative Jahn鈥揟eller effect of the Mn³⁺ ions. P2 structure type stacking is observed for 0.35 < x < 0.82, while above 4.0 V, a new phase appears. A full indexation of the XRPD pattern of this latter phase was not possible because of the broadening of the diffraction peaks. However, a much shorter interslab distance was found that may imply a gliding of the MO₂ slab occurring at high voltage. Raman spectroscopy was used as a local probe and showed that in this new phase the MO₂ layers are maintained, but the phase exhibits a strong degree of disorder.