从联合宽带同位体固态MAS NMR光谱学和DFT计算中对磁性过渡金属酸盐中的旋转转移途径
Raphaële J Clément1, Andrew J Pell, Derek S Middlemiss
1Centre de RMN à Très Hauts Champs, UMR 5280 CNRS/Ecole Normale Supérieure de Lyon/UCB, Lyon 1, 69100 Villeurbanne, France.
Journal of the American Chemical Society
|September 26, 2012
概括
研究人员开发了一个新的NMR实验和DFT计算来描述铁酸电池材料中的原子结构. 这为先进的电池设计提供了对电子结构和超精细参数的详细见解.
科学领域:
- 材料科学 材料科学 材料科学
- 固态化学 固态化学
- 电化学 电化学 电化学
背景情况:
- 过渡金属 (TM) 酸盐,如LiFe{x}Mn{1-x}PO{4),是下一代离子电池的有希望的阴极材料.
- 目前缺乏对这些混合TM酸盐相的全面原子层结构描述.
- 了解原子结构对于优化电池性能至关重要.
研究的目的:
- 开发和应用一个结合实验和理论方法,详细分配 (31) P NMR光谱在LiFe(x) Mn(1-x) PO(4) 材料.
- 阐明LiFe(x) Mn(1-x) PO(4) 组成范围内的原子层结构和电子差异.
- 提供对超精度参数和Mn/Fe替代效应的见解.
主要方法:
- 开发了一种新的核磁共振 (NMR) 实验,称为aMAT (adiabatic磁化转移),利用短,高功率的adiabatic脉冲 (SHAP).
- 应用固态混合密度函数理论 (DFT) 计算来确定不同Mn-O-P和Fe-O-P键路径的超细贡献.
- 在LiFe{x}Mn{1-x}PO{4}系列 (x = 0, 0.25, 0.5, 0.75, 1) 中纯和混合TM酸盐的表征.
主要成果:
- 对所有LiFe(x) Mn(1-x) PO(4) 组合物,包括混合相,成功分配了 (31) P的NMR光谱.
- 分离同位素化学转移,并详细分析单个Mn/Fe位点的高精度贡献.
- 洞察电子结构的变化以及/铁替代对超细度参数和结构扭曲的影响.
结论:
- 结合的NMR和DFT方法提供了前所未有的替代过渡金属酸盐的原子层次描述.
- 这种方法提供了对电子结构差异的详细见解,这些差异导致电池阴极材料的超细参数变化.
- 该方法广泛适用于其他TM轴承阴极相和复杂的偏磁材料.
相关概念视频
02:42Valence Bond Theory
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
01:08NMR Spectroscopy: Spin–Spin Coupling
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...
03:02Colors and Magnetism
Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
01:08Spin–Spin Coupling Constant: Overview
In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...