Molecular-level environments of intercalated chloroaluminate anions in rechargeable aluminum-graphite batteries revealed by solid-state NMR spectroscopy
Molecular-level environments of intercalated chloroaluminate anions in rechargeable aluminum-graphite batteries revealed by solid-state NMR spectroscopy
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DOI：
10.1039/d0ta02611e
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发表时间：
2020-08
影响因子：
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通讯作者：
Jeffrey H. Xu;A. Jadhav;D. Turney;R. Messinger
中科院分区：
文献类型：
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作者：
Jeffrey H. Xu;A. Jadhav;D. Turney;R. Messinger
可充电铝-石墨电池是一种很有前途的新兴储能技术：它们表现出高倍率性能、可循环性能和大约2V的放电电位，而两个电极都是全球性的，成本低，本质上是安全的。电池使用含氯铝酸盐的电解液，当分子AlCl4−阴离子电化学嵌入石墨电极时，电池会将电荷储存在石墨电极中。然而，关于离子插层机理仍有许多有待了解的地方，部分原因是与表征氯铝酸盐阴离子本身相关的挑战。在这里，我们使用固态27Al核磁共振(核磁共振)谱来探测不同电荷状态下插层氯铝酸盐阴离子的分子水平的电子和磁环境。结果显示，与AlCl4-−阴离子有关的广泛的27Al核磁共振信号反映了很高程度的局部无序。插层阴离子经历了不同的局部环境，其中许多远不是石墨分级模型中经常描述的理想晶状结构。用密度泛函理论(DFT)计算了27Al的各向同性位移，使化学位移、环电流效应和电四极相互作用的贡献得以定量解缠。结合固体核磁共振和密度泛函的结果，揭示了插层AlCl4−阴离子的分子几何结构和环境，并捕捉到了插层石墨电池电极中存在的显著无序。
Rechargeable aluminum–graphite batteries are an emerging energy storage technology with great promise: they exhibit high rate performance, cyclability, and a discharge potential of approximately 2 V, while both electrodes are globally abundant, low cost, and inherently safe. The batteries use chloroaluminate-containing electrolytes and store charge in the graphite electrodes when molecular AlCl4− anions electrochemically intercalate within them. However, much remains to be understood regarding the ion intercalation mechanism, in part due to challenges associated with characterizing the chloroaluminate anions themselves. Here, we use solid-state 27Al nuclear magnetic resonance (NMR) spectroscopy to probe the molecular-level electronic and magnetic environments of intercalated chloroaluminate anions at different states-of-charge. The results reveal broad 27Al NMR signals associated with intercalated AlCl4− anions, reflecting high extents of local disorder. The intercalated anions experience a diversity of local environments, many of which are far from the ideal crystalline-like structures often depicted in graphite staging models. Density functional theory (DFT) calculations of the total 27Al isotropic shifts enable the contributions of chemical shift, ring-current effects, and electric quadrupolar interactions to be disentangled quantitatively. In combination, the solid-state NMR and DFT results reveal the molecular geometries and environments of intercalated AlCl4− anions and capture the significant disorder present in intercalated graphite battery electrodes.