Redox-Active Bis-Catecholaldimine Cu(II)-Salen Complex with Hydroxyl Functionality as Cathode Material in Li-Ion...

In this paper, we report the synthesis, structure, and application of bis-catecholaldimine-based Cu^II-Salen complex as a cathode material in lithium-ion battery. [Cu(LH₂)] (1) complex was prepared using the ligand 6,6'-{[Ethane-1,2-diylbis(azanylidene)]bis(methanylidene)}-bis(3,5-di-tert-butyl-1,2-dihydroxybenzene) (LH₄). The complex 1 was characterized structurally by single-crystal X-ray diffraction technique. It was also further characterized by various techniques such as high-resolution mass spectrometry, Fourier Transform Infrared, thermogravimetric analysis, and elemental carbon, hydrogen, nitrogen (CHN) analysis. Complex 1 is a mononuclear complex that crystallizes in the triclinic P-1 Space group with a Cu⁺² ion present in a slightly distorted square planar geometry. Complex 1 [Cu(LH₂)] was further employed as a cathode material for a secondary lithium-ion battery, which shows superior cyclic and rate capability performance. The [Cu(LH₂)] (1) electrode shows an average capacity of 73.5 mAh/g at 50 mA/g after rate capability test, as compared to the 21.8 mAh/g specific capacity for the LH₄ electrode. To understand the redox chemistry of the Cu-complex, a series of Density functional theory (DFT) computations were carried out for the complex 1 and its corresponding one- and two-electron reduced species.