Due to its environmental friendliness, abundant reserves and diverse structure, organic electrode materials are attracting more and more attention. At present, most of the traditional organic electrode materials in sodium ion batteries are conjugated compounds, which can pass single and double bonds in functional groups and conjugated rings. The rearrangement mechanism realizes electronically stable storage. However, research on the mechanism of sodium storage of non-conjugated electrode materials at home and abroad is still blank. If the conjugated compound can be extended to non-conjugated compounds, not only can the types of organic electrode materials be expanded, but also the Organic electrode material activity, rich in sodium ion storage mechanism.
Recently, Liu Jianjun, a researcher at the Shanghai Institute of Ceramics, Chinese Academy of Sciences, and Wang Kaixue, a professor at Shanghai Jiaotong University, have made a breakthrough in the research on the mechanism of sodium storage of non-conjugated electrode material 1,4-cyclohexanedicarboxylic acid (CHDA). Sexual progress, related results published in the international journal "German Applied Chemistry" (Angew. Chem. Int. Ed. (DOI: 10.1002/anie.201801654)). Shanghai Jiaotong University Ph.D. student Ma Chao and Shanghai Institute of Silicate Master Zhao Xiaolin For the first author of the paper, the authors of the paper are Wang Kaixue and Liu Jianjun.
The work by density functional theory (DFT) calculation found that the non-conjugated electrode material CHDA can realize the storage of two Na+ through the H transfer between the functional group carboxyl-COOH, forming new functional groups -C(OH)2 and O=C= O, induces the transformation of π*→σ bond in CHDA, and realizes stable storage of electrons, that is, realizes sodium storage in non-conjugated system. The mechanism of non-conjugated electrode material CHDA can be used as a proton-coupled charge transfer in biological systems (PCET) ) ' An important extension of the electrochemical mechanism.
Based on the theoretical calculation of structural design, the CHDA electrode material was prepared experimentally and the reversible disappearance and formation of the reaction product O=C=O were confirmed by infrared spectroscopy. The reversible disappearance and formation of the reaction product-C(OH)2 were verified by NMR. The occurrence of H transfer was confirmed. The good electrochemical performance of CHDA was characterized by CV and charge-discharge curves. The two pairs of redox peaks in CV correspond to the two-step sodium-encapsulation reaction of CHDA, which is consistent with the calculation. The charge-discharge curve is about 249mAh. /g has a high specific capacity, close to the theoretical specific capacity.
The Liu Jianjun team has long been committed to the research of organic energy storage materials, and has obtained a series of research results, including the study of cyclooctate-based electrode materials, designing different ratios of C4/C8 series fused, including single and double bond reconstitution and aromatic The double superposition of the mechanism can produce high voltage and specific capacity. This work has been verified by relevant experiments and provides an important theoretical basis for the design of high voltage organic electrode materials (ACS Appl. Mater. Interface, 2018, 10, 2496); Molecular uric acid UA electrode material design, theoretical study of uric acid sodium storage mechanism, that is, C=C(NH-)2 strong interferential N element p orbital and carbon anion lone pair electron p orbital hybridization stabilizes carbon anion, Realization of sodium storage. The composite UA@CNT tested at the high current density of 200 mA/g can still maintain a capacity of 163 mA h/g (Appl. Mater. Interface, 2017, 9,33934).
The above research work has been supported by the national key research and development plan, the National Natural Science Foundation, and the Shanghai Materials Genome Project.
(a) Enumeration of typical conjugated and non-conjugated organic molecules, and sodium storage mechanism of conjugated organic molecules; (b) molecular structure design - electronic structural adjustment; (c) hydrogen transfer coupled electrochemical reaction characterization; (d) Electronic storage of π*→σ bond transition
(ab) Original CHDA, 1H NMR and IR spectroscopy for hydrogen transfer mechanism under discharge to 0.01 V and charge to 3.0 V; (cd) electrochemical test, CV curve (0.5 mV/s), charge and discharge curve (0.1A/g)
(a-b) Discharge curves of C8H8 and C16H12, and the number of π electrons and C-C bond length during discharge, and electron stabilization mechanism; (c-d) Organic molecular structure design and discharge voltage prediction
