W-doped LiW_xNi_0.5Mn_{1.5鈭?span style='font-style: italic'>x}O₄ cathodes for the improvement of high rate performances in Li ion batteries

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• 作者：S.J. Richard Prabakar ; Su Cheol Han ; Satendra Pal Singh ; Dong Kyu Lee ; Kee-Sun Sohn ; ^{kssohn@sunchon.ac.kr} ; Myoungho Pyo ; ^{mho@sunchon.ac.kr}
• 关键词：Spinel ; Cathode ; Doping ; Tungsten ; Lithium ion batteries
• 刊名：Journal of Power Sources
• 出版年：2012
• 期刊代码：58_03787753
• 类别：ce
• 出版时间：1 July, 2012
• 卷：209
• 期：Complete
• 页码：57-64
• 文件大小：1488 K

摘要

W-doped LiW_xNi_0.5Mn_1.5鈭?em>xO₄ (x = 0.00-0.10) are synthesized via a sol-gel method, and their electrochemical properties are investigated. During synthesis, W⁴⁺ is converted to W⁶⁺, the amount of which significantly affects the charge-discharge behaviors of LiW_xNi_0.5Mn_1.5鈭?em>xO₄. When limited to x 鈮?#xA0;0.005, W-doping enhances the electrochemical activity of cathodes, leading to a greater discharge capacity and less capacity fading than LiNi_0.5Mn_1.5O₄ at high C-rates. This is interesting since lowering the average valence state of Mn ions by incorporating W⁶⁺ can introduce structural instability, extending a 4 V plateau (Mn^3+/4+). The reasons for such behavior associated with W-doping are examined by electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and impedance spectroscopy. It is disclosed that the simultaneous increase in LiO bond length and decrease in transition metal-oxide bond length, while the unit cell volume is maintained almost invariant, provides LiW_0.005Ni_0.5Mn_1.495O₄ with optimal high rate performance. When W-doping exceeds x = 0.01, 3 factors (intrinsically low electronic conductivity of W⁶⁺, the presence of tungsten oxide impurities, and an increase in the inter-metallic distance) aggravates electrochemical performance of LiW_xNi_0.5Mn_1.5鈭?em>xO₄. The last factor also induces structural instability during repeated cycling because of the expansion of a unit cell volume.