Exploring organo-palladium(II) complexes as novel organometallic materials for Li-ion batteries

Three novel trans-halogeno(4-acetoxyphenyl)bis(triphenylphosphine)palladium(II) complexes (XPd(4-AcOC6H4)(PPh3)2, with X = I (3), Br (4) and Cl (5)) were synthesized and characterized by spectroscopic techniques and by X-ray diffraction analysis. The SEM images of the particles obtained after synthesis and microwave treatment show uniform morphology and particle size lower than 1 μm for the iodo-palladium complex (3). The electrochemical performance of the palladium-based anode materials was evaluated by cyclic voltammetry and galvanostatic cycling. The results show that the nature of the halogen ligand (X = I, Br and Cl) has a high impact on the reaction mechanism during the first discharge and cycling performance. Thus, the three materials IPd(4-AcOC6H4)(PPh3)2 (3), BrPd(4-AcOC6H4)(PPh3)2 (4) and ClPd(4-AcOC6H4)(PPh3)2 (5) deliver high initial irreversible capacities of 1089, 444 and 684 mAh g−1, respectively, during the first discharge at 20 mA g−1 at a voltage window between 0.01 and 3.0 V. In addition, the iodo-palladium-based anode material shows the highest specific capacity and a high capacity retention after 200 cycles at a current density of 50 mA g−1 with an average discharge capacity of about 170 mAh g−1.