10-Li[Li13–2x3NixMn23–x3]O2-AM

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Crystal Habit-Tuned Nanoplate Material of Li[Li1/3–2x/3NixMn2/3–x/3]O2 for High-Rate Performance Lithium-Ion BatteriesBy Guo-Zhen Wei, Xia Lu, Fu-Sheng Ke, Ling Huang, Jun-Tao Li, Zhao-Xiang Wang, Zhi-You Zhou, and Shi-Gang Sun*The increasing demand for high-energy and high-power batteries, especially in the development of electric vehicles (EVs), has stimulated great research interest focused on lithium ion batteries (LIBs).[1–5] Olivine LiFePO4 has recently attracted particular attention as high-power batteries for EVs. In spite of the material’s low electronic conductivity, its fabrication as a battery cathode has been engineered to give quite high power levels.[6] However, its low theoretical capacity and low volume energy density compared with layered LiMO2 (M= Co, Ni, Mn, or/and Cr) composite materials make it less attractive for high-energy LIBs. Lithium Mn-rich metal oxides such as Li[Li1/3–2x/3MxMn2/3–x/3]O2 (M= Ni, Co, or/and Cr) are currently receiving signi cant attention for use as modern cathode materials for LIBs, owing to their high capacity of over 200 mA h g 1 when charged to 4.5 V or higher.[5,7–14] Because of the rapidly fading capacity and the poor rate-capability of Li[Li1/3–2x/3MxMn2/3–x/3]O2 materials,[15] extensive efforts have been made in recent years to improve their rate-capability,[16–20] such as fabrication of nanoparticles, nanowires, and nanoplates, which possess a short Li+ transportation path due to their reduced dimensions. Although the move to nanometer-sized materials can improve performance to a certain extent,[16–23] the structure of the materials, especially the surface structure, is a crucial factor that determines the rate for Li+ deintercalation/intercalation. Our research group has recently demonstrated that the catalytic properties of Pt nanoparticles can be signi cantly enhanced by tuning the surface of Pt nanoparticles from closest-packed to an open structure, such as from{111} or{100} to{730} and vicinal high-index facets.[24,25] During our research into nanomaterials applied in LIBs,[21,22] we further noticed that the nanomaterials are generally bounded by closest-packing facets, which intrinsically present dif culties in furnishing suitable channels for fast Li+ transportation. Recent reports have also evidenced that the surface structure for Li+ transportation is critical to the rate capability.[6,26–30] Li+ can only intercalate into the bulk of a crystal along the direction parallel to the Li+ layers in a layered cathode material with anα-NaFeO2 structure, such as Li[Li1/3–2x/3NixMn2/3–x/3]O2. As illustrated in Figure 1, each layer perpendicular to the c-axis is indexed as a (001) plane; the planes perpendicular to a (001) plane and parallel to the a- (or b-) axis are indexed as (010) planes (or (100) planes). The (010) plane is equivalent to the (100) plane in a typical perfect crystal. When a Li[

Li1/3–2x/3NixMn2/3–x/3]O2 nanoplate grows perpendicular to the[001] direction (c-axis of the crystal), its surface is preferentially dominated by (001) planes ((001) nanoplates), which are not electrochemically active for Li+ transportation because they cannot provide an appropriate path for Li+ transportation.[26] In contrast, the (010) (or (100)) plane that is perpendicular to the (001) plane is an active plane for Li+ deintercalation/intercalation.[31] If a Li[Li1/3–2x/3NixMn2/3–x/3]O2 nanoplate grows perpendicular to the[010] (or[100]) direction, its surface will be consequently dominated by the (010) (or (100)) planes ((010) nanoplates). Therefore, the rate-capability of LIBs employing Li[Li1/3–2x/3NixMn2/3–x/3]O2 nanoplates as cathode materials can be signi cantly improved by tuning the crystal habit to obtain (010)-nanoplate material. To the best of our knowledge, such a (010)-nanoplate material of Li[Li1/3–2x/3NixMn2/3–x/3]O2 has not been reported before. Based on the structural analysis above, we calculated the surface energy of the (001) and (010) planes of Li(Li0.17Ni0.25Mn0.58)O2 materials withα-NaFeO2 structure to quantify their stability (see Supporting Information, Figure S1). The result indicates that the surface energy of the (001) plane is lower than that of the (010) plane. As the crystal growth rate of a high-energy plane is faster than that of a low-energy plane, the high-energy planes have the tendency to disappear during growth and the surface of the grown crystal will be dominated by low-energy planes. As a consequence, the (001) nanoplates are thermodynamic equilibrium products in most synthesis route when the synthesis reaction is under hydrothermal conditions for a long enough time.[19,20,23] Therefore, the nanoplates were always less attractive in terms of rate-performance in previous reports. In the present Communication, we report a crystal habit-tuned nanoplate material of Li(Li0.17Ni0.25Mn0.58)O2 (HTN-LNMO), in

[ ] Dr. G.-Z. Wei, F.-S. Ke, L. Huang, Z.-Y. Zhou, Prof. S.-G. Sun State Key Laboratory of Physical Chemistry of Solid Surfaces Department of Chemistry College of Chemistry and Chemical Engineering Xiamen University Xiamen, 361005 (China) E-mail: sgsun@ Dr. X. Lu, Prof. Z.-X. Wang Laboratory for Solid State Ionics Institute of Physics Chinese Academy of Sciences Beijing, 100190 (China) Dr. J.-T. Li School of Energy Research Xiamen University, Xiamen, 361005 (China)

DOI: 10.1002/adma.201001578

4364

© 2010 WILEY-VCH Verlag GmbH& Co. KGaA, Weinheim

Adv. Mater. 2010, 22, 4364–4367

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Figure 1. Schematic illustration of two kinds of nanoplates and the microstructure of their surfaces.

which the number of (010) nanoplates has been signi cantly increased in comparison with the conventional thermodynamic equilibrium nanoplate material of Li(Li0.15Ni0.25Mn0.6)O2 (CN-LNMO). In our synthesis route,

the precursor, which is different from …… 此处隐藏：6229字，全部文档内容请下载后查看。喜欢就下载吧 ……