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Électrochimie et spectroscopie Raman de matériaux d’électrode positive pour batteries Li-ion

Abstract : In this work, we show the relevance of Raman spectroscopy as a useful technique to investigate the local changes induced by the electrochemical reaction of intercalation/deintercalation of lithium in positive electrode materials for rechargeable lithium ion batteries.Raman investigations concern three types of high voltage cathode materials (4-5Volts) which are layered LiCoO2 and cubic LiMn2O4 and LiNi0.4Mn1.6O4.During electrochemical deintercalation of LiCoO2, we show the existence of a two phase region where the initial hexagonal phase coexist with a second hexagonal phase with a 3% expansion of the lattice parameter indicating a weakening of the Co-O bond in the Li1-xCoO2 material.On the other hand, a new assignment of LiMn2O4 Raman spectrum was proposed. During the charge in the 4V region, a three region phase (initial LiMn2O4 phase, intermediary phase and poor lithium phase) was described using Raman spectroscopy. RX measurements can not detect this intermediary phase. Lithiated phase Raman signature shows a specific local order: Fd3m for extreme phases and F43m for partially lithiated phase. A rich Raman band spectrum is attributed to this later phase in coherence with literature calculations. Structural changes reversibility is demonstrated. Identification of this intermediary phase as a major component of a cycled electrode, underline the incomplete reduction and explain the important loss of capacity observed during cycling. Raman study of LiMn2O4 electrochemical insertion in the 3V region, has demonstrated for the first time a progressive formation of tetragonal Li2Mn2O4 phase, which is in coexistence with initial cubic phase and is pure at the end of discharge. Structural transition reversibility was also demonstrated.In the case of LiNi0.4Mn1.6O4, the assignment of the Raman spectrum of LiNi0.4Mn1.6O4 is provided for the first time. DRX study in function of the state of charge and discharge, exhibit cubic structure conservation with moderate lattice parameters variations. The Raman spectrum of the spinel oxide exhibits drastic spectral changes during Li extraction. These changes have been directly related to the Mn and Ni oxidation states in the cathode material under operation. It comes out that electrochemical reactions of LiNi0.4Mn1.6O4 are reversible and based on three redox couples of Mn3+/Mn4+, Ni2+/Ni3+, and Ni3+/Ni4+. An original and concrete Raman spectroscopy application is the study of self discharge mechanism of completely charged LiNi0.4Mn1.6O4. Raman spectra evolution exhibits a quantitative Ni4+ reduction during the first hours, and then a slower Ni3+ reduction process. Finally, LiNi0.4Mn1.6O4 lithium insertion has been explored for the first time using Raman spectroscopy, and a tetragonal Li2Ni0.4Mn1.6O4 phase has been identified.The originality of this work is the important number of experimental Raman data of 4V electrode materials. New assignment of initial compound has been proposed and original vibrationnal data of compound during charge/discharge has been presented. These Raman data has permitted to propose a quantitative explanation which must be completed with ab initio calculations to simulate vibrationnal modes frequencies/ intensities
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Yosra Dridi Zrelli. Électrochimie et spectroscopie Raman de matériaux d’électrode positive pour batteries Li-ion. Autre. Université Paris-Est, 2012. Français. ⟨NNT : 2012PEST1126⟩. ⟨tel-00807008⟩

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