Effect Of Electrodepositing Coatings On Electrochemical Properties Of La-Mg-Ni-Based Hydrogen Storage Alloy

In order to improve the electrochemical properties of La-Mg-Ni-based alloy electrodes, especially the cycle stability, a novel electroplating treatment was applied onto La_0.88Mg_0.12Ni_2.95Mn_0.10Co_0.55Al_0.10 alloy powders using the self-made electroplating facility. The surface morphologies were analyzed by FESEM and EDS. The electrochemical properties were tested by the methods of galvanostatic charge-discharge, linear polarization, Electrochemical Impedance Spectroscopy (EIS) and cyclic voltammetry.FESEM and EDS results showed that a dense layer of spherical cobalt particles with uniform radius (¹30 nm) and an undulate layer of lamellar nickel formed on the surface of the Co- and Ni-coated alloys, respectively. These metallic coatings enhanced the conductivity and the catalytic activity, besides acting as a protective layer, thereby improving the electrochemical properties. For Co- and Ni-coated alloys, the maximum discharge capacity increased from original 316 mAh/g to 335 mAh/g and 336 mAh/g, and the charge retention was improved from 83% to 87% and 93%, respectively. The cycling stability was enhanced and the high rate dischargeability (HRD) was ameliorated remarkably.The spherical nickel-cobalt alloy particles and layered nickel-copper coating were deposited on the hydrogen storage alloy surface after the alloy powders were microencapsulated with nickel-cobalt and nickel-copper alloy. After 200 charge/discharge cycles, the capacity retention rosed by 20% and 10%, the high rate dischargeability (HRD) rosed by 23% and 11%, for nickel-cobalt and nickel-copper coated alloy electrodes, respectively. The exchange current density I0 increased from 265.8 mA/g (bare) to 363.5 mA/g (Ni-Co coated) and 319.3 mA/g (Ni-Cu coated).