Synthesis, Characterization and Electrochemistry of Lithium Battery Electrodes: xLi2MnO3·(1 − x)LiMn0.333Ni0.333Co0.333O

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• 作者：Christopher S. Johnson ; Naichao Li ; Christina Lefief ; John T. Vaughey ; Michael M. Thackeray
• 刊名：Chemistry of Materials
• 出版年：2008
• 出版时间：October 14, 2008
• 年：2008
• 卷：20
• 期：19
• 页码：6095-6106
• 全文大小：559K
• 年卷期：v.20,no.19(October 14, 2008)
• ISSN：1520-5002

文摘

Lithium- and manganese-rich layered electrode materials, represented by the general formula xLi₂MnO₃·(1 − x)LiMO₂ in which M is Mn, Ni, and Co, are of interest for both high-power and high-capacity lithium ion cells. In this paper, the synthesis, structural and electrochemical characterization of xLi₂MnO₃·(1 − x)LiMn_0.333Ni_0.333Co_0.333O₂ electrodes over a wide compositional range (0 ≤ x ≤ 0.7) is explored. Changes that occur to the compositional, structural, and electrochemical properties of the electrodes as a function of x and the importance of using a relatively high manganese content and a high charging potential (>4.4 V) to generate high capacity (>200 mAh/g) electrodes are highlighted. Particular attention is given to the electrode composition 0.3Li₂MnO₃·0.7LiMn_0.333Ni_0.333Co_0.333O₂ (x = 0.3) which, if completely delithiated during charge, yields Mn_0.533Ni_0.233Co_0.233O₂, in which the manganese ions are tetravalent and, when fully discharged, LiMn_0.533Ni_0.233Co_0.233O₂, in which the average manganese oxidation state (3.44) is marginally below that expected for a potentially damaging Jahn−Teller distortion (3.5). Acid treatment of 0.3Li₂MnO₃·0.7LiMn_0.333Ni_0.333Co_0.333O₂ composite electrode structures with 0.1 M HNO₃ chemically activates the Li₂MnO₃ component and essentially eliminates the first cycle capacity loss but damages electrochemical behavior, consistent with earlier reports for Li₂MnO₃-stabilized electrodes. Differences between electrochemical and chemical activation of the Li₂MnO₃ component are discussed. Electrochemical charge/discharge profiles and cyclic voltammogram data suggest that small spinel-like regions, generated in cycled manganese-rich electrodes, serve to stabilize the electrodes, particularly at low lithium loadings (high potentials). The study emphasizes that, for high values of x, a relatively small LiMO₂ concentration stabilizes a layered Li₂MnO₃ electrode to reversible lithium insertion and extraction when charged to a high potential.