Detailed Studies of a High-Capacity Electrode Material for Rechargeable Batteries, Li2MnO3-LiCo1/3Ni1/3Mn1/3O2
Detailed Studies of a High-Capacity Electrode Material for Rechargeable Batteries, Li2MnO3-LiCo1/3Ni1/3Mn1/3O2
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DOI：
10.1021/ja108588y
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发表时间：
2011-03-30
影响因子：
15
通讯作者：
Komaba, Shinichi
中科院分区：
文献类型：
--
作者：
Yabuuchi, Naoaki;Yoshii, Kazuhiro;Komaba, Shinichi
锂过量锰层状氧化物通常由化学式ZLi(2)MnO(3)-(1-z)LiMeO2(Me=Co，Ni，Mn等)描述，是锂二次电池的重要正极材料。本文从Li1.2Ni0.13Co0.13Mn0.54O2(或0.5Li(2)MnO(3)-0.5LiCo(1/3)Ni(1/3)Mn(1/3)O(2))在电化学池中通过电化学氧化/还原过程制备了LixCo0.13Ni0.13Mn0.54O2-Delta样品，详细研究了在4.5V电压平台充电前后的反应机理对Li/Li+的影响，并用同步X射线衍射仪、X射线吸收光谱(CAS)研究了体相和表面结构的变化。X射线光电子能谱(XPS)和飞行时间二次离子质谱仪(SIMS)。SXRD数据表明，在初始充电时，在电压平台上同时去除氧和锂导致了结构重排，包括阳离子从金属层到锂层的迁移过程，这也得到了XAS的支持。这与文献中提出的有关锂过量锰层状氧化物的机理是一致的。与高压平台上的初始电荷相关的氧气去除会导致电化学电池中氧分子的产生。电池中的氧分子在随后的3.0V以下放电中被电化学还原，导致额外的容量。表面分析证实了聚积在电极表面的碳酸锂等含氧物质的形成。结果表明，除了传统的过渡金属氧化还原反应外，锂过剩锰层状氧化物的可逆容量至少有一部分来自电极表面氧分子的电化学氧化还原反应。
Lithium-excess manganese layered oxides, which are commonly described by the chemical formula zLi(2)MnO(3)-(1 - z)LiMeO2 (Me = Co, Ni, Mn, etc.), are of great importance as positive electrode materials for rechargeable lithium batteries. In this Article, LixCo0.13Ni0.13Mn0.54O2-delta samples are prepared from Li1.2Ni0.13Co0.13Mn0.54O2 (or 0.5Li(2)MnO(3)-0.5LiCo(1/3)Ni(1/3)Mn(1/3)O(2)) by an electrochemical oxidation/reduction process in an electrochemical cell to study a reaction mechanism in detail before and after charging across a voltage plateau at 4.5 V vs Li/Li+ Changes of the bulk and surface structures are examined by synchrotron X-ray diffraction (SXRD), X-ray absorption spectroscopy ()CAS), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (SIMS). SXRD data show that simultaneous oxygen and lithium removal at the voltage plateau upon initial charge causes the structural rearrangement, including a cation migration process from metal to lithium layers, which is also supported by XAS. This is consistent with the mechanism proposed in the literature related to the Li-excess manganese layered oxides. Oxygen removal associated with the initial charge on the high voltage plateau causes oxygen molecule generation in the electrochemical cells. The oxygen molecules in the cell are electrochemically reduced in the subsequent discharge below 3.0 V, leading to the extra capacity. Surface analysis confirms the formation of the oxygen containing species, such as lithium carbonate, which accumulates on the electrode surface. The oxygen containing species are electrochemically decomposed upon second charge above 4.0 V. The results suggest that, in addition to the conventional transition metal redox reactions, at least some of the reversible capacity for the Li-excess manganese layered oxides originates from the electrochemical redox reaction of the oxygen molecules at the electrode surface.