A photochromic zinc-based coordination polymer for a Li-ion battery anode with high capacity and stable cycling...

Rechargeable Li-ion batteries (LIBs) are currently the dominant power source for electric vehicles and portable electronic devices, and for small-scale stationary energy storage. However, one bottleneck of the anode materials for LIBs is the poor cycling performance caused by the fact that the anodes cannot maintain their integrity over several charge-discharge cycles. In this article, a zinc-based two-dimensional coordination polymer [Zn(bcbpy)_0.5(PTA)(H₂O)] (Zn-BCP) has been synthesized (H₂bcbpy·2Cl = 1,1'-bis(3-carboxylatobenzyl)-(4,4'-bipyridinium) dichloride, PTA = terephthalic acid), which was characterized by single-crystal X-ray diffraction, powder X-ray diffraction, infrared spectroscopy and thermogravimetric analysis. Because of the presence of electron-deficient bipyridinium moieties, Zn-BCP can easily undergo photoinduced electron transfer and eye-detectable photochromic behavior. Moreover, its luminescence can be switched by UV-Vis light irradiation. When Zn-BCP acts as an anode material for lithium ion batteries, it can deliver a high reversible capacity of 386.2 mA h g^-1 at 100 mA g^-1 after 100 cycles and a high capacity retention of 93.1% after 1000 cycles at a high rate of 200 mA g^-1, which is supposed to be due to the flexible structure characteristic of the proposed anode. The high capacity may be mainly ascribed to rich insertion sites arising from the aromatic ligands and all of the aromatic ligands are taking part in lithium storage.