Recently, Liu Jianjun, a researcher at the Shanghai Institute of Ceramics, Chinese Academy of Sciences, and Huang Yunhui, a professor at Huazhong University of Science and Technology, designed a three-dimensional folding fan arrangement of organic conjugated molecules and coordinated metal ion coordination to construct a nano metal organic framework (MOF) material. Zinc formate (Zn-PTCA), the first breakthrough in the electrochemical activation of conjugated carbocyclic sodium storage, greatly improved the sodium storage capacity of the electrode material, providing a new idea for further design of new high specific capacity electrode materials. Related research results in Chem The magazine was published.
MOF nanomaterials with three-dimensional pore structure are mainly self-assembled by transition metal ions (or nanoclusters) and organic ligands. They are characterized by easy regulation of pore structure, high specific surface area and abundant surface functional groups in gas adsorption and separation. Nanocatalysis has been widely used. However, due to the limited specific capacity, it is greatly limited in the application of electrochemical energy storage materials. Taking sodium ion battery materials as an example, the sodium storage sites of metal organic electrode materials in sodium ion batteries are mainly concentrated. On the surface rich functional groups (C=O, C≡N), electron stable storage can be achieved by a single double bond rearrangement mechanism in the functional group and the structural framework conjugated ring. However, it is difficult to embed MOF materials due to the larger radius of sodium ions. The intercalation of the organic conjugated framework, and the destruction of the interlayer van der Waals force between the sodium ion intercalation layers and the weaker interaction between the conjugated carbocyclic rings and the like cause the sodium ions to be difficult to store in the organic structure skeleton conjugated carbocyclic ring (sp2). -C), which in turn leads to a lower reversible specific capacity of the MOF material. Therefore, the electrochemical activity of the activated conjugated carbocyclic sodium storage is essential for increasing the storage capacity of the electrode material. , but it is more challenging.
Liu Jianjun team combined with first-principles calculation of electrochemical, molecular dynamics simulation, electronic structure analysis, found that three-dimensional fan-shaped metal organic materials have the characteristics of conjugated carbon ring sp2-C storage sodium ions, to achieve conjugate carbon ring storage Theoretical design and experimental verification of sodium. It was found that the replacement of sodium ions by a stable hexacoordinate transition metal can convert the layered sodium phthalocyanate into a three-dimensional fan-like zinc phthalate, and the transition metal coordination chemical bond replaces the organic layer. Van der Waals force, the formation of open space structure not only eliminates the influence of sodium storage van der Waals force, but also increases the migration kinetics rate of Na+. The calculated electrochemical results are consistent with the experimental electrochemical characterization, which confirms Na+ in Zn-PTCA. The two-step sodium intercalation reaction with the functional group -COO-, Na+ and the conjugated carbocyclic sp2-C reached a relatively high specific capacity of 357 mAh g-1. The in-situ XRD, NMR and IR spectra of the charge and discharge process showed After the material is under low discharge voltage and repeated for many times, the structural frame still has good stability.
The research work was supported by the National Key Research and Development Program, the National Natural Science Foundation of China, and the Shanghai Materials Genome Project.
Structural design from Na-PTCA to Zn-PTCA and predicted sodium storage sites
Insertion site of sodium ion in Zn-PTCA (A), embedding voltage (B) and migration channel (C)
Electrochemical performance of Zn-PTCA: charge-discharge curve (A), cycle performance (B), rate performance (C) and CV curve
