Changes in electronic structure upon Li-ion extraction of LiMPO_4 (M=Fe,Co) using X-ray absorption spectroscopy and First Principle calculation

使用 X 射线吸收光谱和第一原理计算锂离子萃取 LiMPO_4 (M=Fe,Co) 时电子结构的变化

• 批准号: 16350109
• 负责人: UCHIMOTO Yoshiharu
• 金额: $ 9.47万
• 依托单位: Kyoto University (2005-2006)Tokyo Institute of Technology (2004)
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2004
• 资助国家: 日本
• 起止时间: 2004 至 2006
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-16350109/
• 关键词: Electronic structure; Lithium-ion batteries; First Principle calculation; Topochemical; Polyanion compounds; olivine type structure; リチウム電池; X線吸収; セラミックス; エネルギー効率化; 表面・界面物性; 正極活物質; オリビン; 局所構造

Li-ion secondary batteries have widely been utilized as consumers' electronic devices such as cellular phones, personal computers, etc. because of their high electrical density. A phosphate system, LiMPO_4 (M = Fe,Ni,Co) with the olivine-related structure, has recently been intensively studied as a candidate for positive electrodes. In the Olivine-type phosphate, it has been generally recognized that PO_4 polyanion units form their valence and conduction bands far from the Fermi level where an electronic exchange mainly occurs because of its closed shell electronic configuration. As a result, the transition-metal valence electrons tend to be isolated from those of polyanions, leading to the fact that the electronic exchange arising from Li removal/uptake mainly occurs at transition metal ions. The isolated transition-metal electronic structure would be the reason for the observed high voltage properties, and it simultaneously leads to the low electronic conductivities, causing technica … More l difficulties in fabrication of batteries. Thus, an understanding of their unique electronic structure is important to apply to rechargeable lithium-ion batteries.Co,P, and 0 K-edge XAS measurements were carried out using synchrotron radiation at beam lines BL-7C,BL-11B, and BL-11A. In Co K-edge XANES around the threshold energy for electrochemically prepared samples, Li_<1-x>,CoPO_4, the threshold energy of LiCoPO_4 is close to that of a divalent reference sample, CoCO_3, the Co ions could be almost divalent in LiCoPO_4. The threshold energy gradually shifted to higher energy with charge reaction, indicating that Co ions are oxidized for the charge compensation over an entire region of the charge reaction (from x = 0.0 to 1.0). A absorption peak in P K-edge XANES gradually shifted with electrochemical Li removal, resulting an 0.2 eV shift at a composition of x = 1.0. This indicates that phosphate ions also contribute to the variation of the electronic structure and become less negative with charging. The results of 0 K-edge XANES of Li_<1-x>CoPO_4 indicate Ssarp absorption peaks appeared at the lower energy region. Since they are caused by the transition to hybridized unoccupied orbitals between the Co 3d and 0 2p orbitals, peak A is attributed to an absorption associated with the Co 3d-0 2p hybridized orbital. Peak A gradually shifted to lower energy at small x values (0 5_x approx. 0.5). The intensity of peak A increased with composition x, indicating an increase of holes at oxygen sites. Namely, the observed peak shift and the intensity increase of peak A indicate a decrease in d electron donation from the transition metal ions to hybridized orbitals. In addition, only a little variation was observed at the 0 K-edge XAS in the region of x 【approximately equal】0.5 which is a one-to-one correspondence to that observed in the Co K-edge XANES. Therefore, the oxide ions only contribute to charge compensation process at an early stage of lithium extraction, while the cobalt ions contribute to it at a later stage of the reaction.The analysis of XANES for Li_<1-x>CoPO_4 shows that two effects would be responsible for the modification of the electronic structure of PO_4 polyanion, (1) the hybridization effect between the Co 3d and 0 2p orbitals, and (2) the polarization effect induced by strong ionic character of Li ions. The variation of the Co-, P-and 0 K-edge XANES reveals the important role of the hybridization between the Co and 0 ions and of the polarization in Li-O-P sequences. Less

锂离子二次电池由于其高电密度而被广泛用作消费者的电子设备，例如蜂窝电话、个人计算机等。LiMPO_4（M = Fe，Ni，Co）是一种具有橄榄石型结构的磷酸盐体系，近年来被广泛研究。在橄榄石型磷酸盐中，由于PO_4的闭壳层电子构型，PO_4聚阴离子单元在远离费米能级的位置形成价带和导带，而费米能级主要发生电子交换。结果，过渡金属价电子倾向于与聚阴离子的价电子隔离，导致由Li去除/吸收引起的电子交换主要发生在过渡金属离子处的事实。孤立的过渡金属电子结构可能是观察到的高电压特性的原因，同时它导致低的电子电导率，导致技术缺陷。 ...更多信息 l制造电池的困难。因此，了解其独特的电子结构是很重要的，适用于可充电的锂离子battery.Co，P，和0 K边XAS测量进行了使用同步辐射在光束线BL-7 C，BL-11B，和BL-11 A。在电化学制备的样品Li_2，CoPO_4的阈值能量附近的Co K边XANES中<1-x>，LiCoPO_4的阈值能量接近于二价参考样品CoCO_3的阈值能量，在LiCoPO_4中Co离子几乎可以是二价的。阈值能量随着电荷反应逐渐向更高的能量移动，表明Co离子在整个电荷反应区域（从x = 0.0到1.0）上被氧化用于电荷补偿。随着电化学Li的去除，P K边XANES中的吸收峰逐渐偏移，导致在x = 1.0的组成处偏移0.2 eV。这表明磷酸根离子也有助于电子结构的变化，并且随着充电而变得不那么负。0 K边XANES结果表明Li_ CoPO_4<1-x>的Ssarp吸收峰出现在低能区。由于它们是由跃迁到Co 3d和0 2 p轨道之间的杂化未占轨道引起的，因此峰A归因于与Co 3d-0 2 p杂化轨道相关的吸收。峰A在小的x值（约0 5_x）处逐渐移动到较低的能量。0.5）。峰A的强度随着组成x而增加，表明氧位点处的空穴增加。即，观察到的峰位移和峰A的强度增加表明从过渡金属离子到杂化轨道的d电子捐赠减少。此外，在0 K边缘XAS处在x [约等于]0.5的区域中仅观察到很小的变化，这与Co K边缘XANES中观察到的变化一一对应。对Li_ CoPO_4的XANES分析<1-x>表明，两种效应对PO_4聚阴离子的电子结构有影响：（1）Co 3d和02 p轨道间的杂化效应;（2）Li离子的强离子性引起的极化效应。Co-、P-和0 K边XANES的变化揭示了Co和0离子之间的杂化以及极化在Li-O-P序列中的重要作用。少

项目成果

Changes in electronic structure upon lithium insertion into Fe2(SO4)3 and Fe2(MoO4)3 investigated by X-ray absorption spectroscopy

• DOI: 10.1021/jp065802g
• 发表时间: 2007-02-15
• 期刊: JOURNAL OF PHYSICAL CHEMISTRY B
• 影响因子: 3.3
• 作者: Shirakawa, Junichi;Nakayama, Masanobu;Uchimoto, Yoshiharu
• 通讯作者: Uchimoto, Yoshiharu

X-Ray Absorption Spectroscopic Study on Electron Exchange in Li1-xCoPO4 Electrodes as 4.8 V Positive Electrodes for Rechargeable Lithium Ion Batteries

X 射线吸收光谱研究 Li1-xCoPO4 电极作为可充电锂离子电池 4.8 V 正极的电子交换

• 发表时间: 2005
• 期刊: Phys.Chem.B 109
• 作者: M.Nakayama;S.Goto;Y.Uchimoto;M.Wakihara;Y.Kitajima;T.Miyanaga;I.Watanabe
• 通讯作者: I.Watanabe

Changes in Electronic Structure of Li_<1-x>CoPO_4 as 4.8 V Material using X-ray Absoprtion Spectroscopy

X 射线吸收光谱法研究 4.8 V 材料 Li_<1-x>CoPO_4 电子结构的变化

• 发表时间: 2004
• 期刊: Chemistry of Materials 16
• 作者: M.Nakayama;S.Goto;Y.Uchimoto;M.Wakihara;Y.Kitajima;T.Miyanaga;I.Watanabe;Yoshiharu Uchimoto 他
• 通讯作者: Yoshiharu Uchimoto 他