Heterolayered Li+鈥揗nO2鈥揫Mn1/3Co1/3Ni1/3]O2 Nanocomposites with Improved Electrode Functionality: Effects of Heat Treatment and Layer D

详细信息    查看全文

• 作者：Kyung Min Lee ; Yu Ri Lee ; In Young Kim ; Tae Woo Kim ; Song Yi Han ; Seong-Ju Hwang
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：February 9, 2012
• 年：2012
• 卷：116
• 期：5
• 页码：3311-3319
• 全文大小：589K
• 年卷期：v.116,no.5(February 9, 2012)
• ISSN：1932-7455

文摘

Novel heterolayered nanocomposites consisting of interstratified MnO₂ and [Mn_1/3Co_1/3Ni_1/3]O₂ nanosheets are synthesized by a layer-by-layer self-assembly between negatively charged metal oxide nanosheets and lithium cations. According to powder X-ray diffraction and micro-Raman analysis, all of the as-prepared Li⁺鈥?i>xMnO₂鈥?1鈥?i>x)[Mn_1/3Co_1/3Ni_1/3]O₂ nanocomposites with x = 1, 0.7, and 0.4 have a lamella structure with similar basal spacing of 7.1 脜, indicating the formation of lithium intercalation structure with cointercalated water bilayers. The nanoscale mixing of MnO₂ and [Mn_1/3Co_1/3Ni_1/3]O₂ nanosheets is confirmed by energy-dispersive spectrometry鈥揺lemental mapping analysis. Upon a self-assembly with Li⁺ ions, there occur no marked changes in the octahedral symmetry and mixed oxidation state of M³⁺/M⁴⁺ ions (M = Mn, Co, and Ni) in the precursor metal oxide nanosheets. All of the as-prepared nanocomposites commonly experience a structural transformation from hydrated layered structure to dehydrated layered structure at 200 掳C, which is followed by the second-phase transition to cubic spinel structure at 600 掳C. Despite distinct structural changes of the nanocomposites at elevated temperatures, their porous stacking structure is well-maintained up to 400 掳C. The heat-treatment at 400 掳C leads to a significant improvement of the discharge capacity of the present nanocomposites because of the dehydration of as-prepared materials and the enhancement of crystallinity. The doping of [Mn_1/3Co_1/3Ni_1/3]O₂ layers enables us not only to increase the discharge capacity of the Li鈥揗nO₂ nanocomposite but also to prevent the phase transition of layered manganese oxide to spinel structure during electrochemical cycling. The present study clearly demonstrates that a postcalcination process as well as a partial doping of [Mn_1/3Co_1/3Ni_1/3]O₂ layer is effective in improving the electrode performance of reassembled Li鈥揗nO₂ nanocomposites.