Shanghai Key Laboratory of Green Chemistry and Chemical Processes, College of Chemistry and Molecular Engineering, East China Normal University , Shanghai 200062, China.
Shanghai Key Laboratory of Magnetic Resonance, School of Physics and Materials Science, East China Normal University , Shanghai 200062, China.
ACS Appl Mater Interfaces. 2017 Jul 5;9(26):21839-21847. doi: 10.1021/acsami.7b05889. Epub 2017 Jun 23.
Recently, more and more metal-organic frameworks (MOFs) have been directly used as anodic materials in lithium-ion batteries, but judicious design or choice of MOFs is still challenging for lack of structural-property knowledge. In this article we propose a pillared-layer strategy to achieve improved Li-storage performance. Four Mn(II) and Co(II) MOFs with mixed azide and carboxylate ligands were studied to illustrate the strategy. In these 3D MOFs, layers (1, 3, and 4) or chains (2) with short bridges are linked by long organic spacers. All the MOFs show very high lithiation capacity (1170-1400 mA h g at 100 mA g) in the first cycle owing to the rich insertion sites arising from the azide ion and the aromatic ligands. After the formation cycles, the reversible capacities of the anodes from 1, 3, and 4 are kept at a high level (580-595 mA h g) with good rate and cycling performance, while the anode from 2 undergoes a dramatic drop in capacity. All the MOFs lose the crystallinity after the first cycle. While the amorphization of the chain-based framework of 2 leads to major irreversible deposit of Li ions, the amorphous phases derived from the pillared-layer frameworks of 1, 3, and 4 still retain rich accessible space for reversible insertion and diffusion of active Li ions. Consistent with the analysis, electrochemical impedance spectra revealed that the pillared-layer MOFs led to significantly smaller charge-transfer resistances than 2. Soft X-ray absorption spectroscopy suggested that no metal conversion is involved in the lithiation process, consistent with the fact that the isomorphous Co(II) (3) and Mn(II) (4) MOFs are quite similar in anodic performance.
最近，越来越多的金属-有机骨架（MOFs）被直接用作锂离子电池的阳极材料，但由于缺乏结构-性能知识，明智地设计或选择 MOFs 仍然具有挑战性。在本文中，我们提出了一种支柱层策略来实现改善的锂存储性能。研究了四种具有混合叠氮化物和羧酸盐配体的 Mn(II)和 Co(II) MOFs 来说明该策略。在这些 3D MOFs 中，层（1、3 和 4）或链（2）通过长有机间隔物连接短桥。所有 MOFs 在第一个循环中都表现出非常高的锂化容量（1170-1400 mA h g 在 100 mA g 下），这是由于叠氮化物离子和芳族配体产生的丰富插入位点。在形成循环之后，来自 1、3 和 4 的阳极的可逆容量保持在较高水平（580-595 mA h g），具有良好的倍率和循环性能，而来自 2 的阳极的容量急剧下降。所有 MOFs 在第一个循环后失去了结晶度。虽然链状框架 2 的非晶化导致大量不可逆的 Li 离子沉积，但来自支柱层框架 1、3 和 4 的非晶相仍然保留了丰富的可用于可逆插入和扩散活性 Li 离子的空间。与分析一致，电化学阻抗谱表明，与 2 相比，支柱层 MOFs 导致的电荷转移电阻显著减小。软 X 射线吸收光谱表明，锂化过程中不涉及金属转化，这与同晶 Co(II)（3）和 Mn(II)（4）MOFs 在阳极性能上非常相似的事实一致。
