Kinetics and electrochemical characteristics of Mg_2NiH_4-x wt.% MmNi_(3.8)Go_(0.75)Mn_(0.4)Al_(0.2) (x = 5,10, 20, 40) composites for Ni-MH battery

摘要

The structure, kinetics and electrochemical characteristics of Mg_2NiH_4-x wt.% MmNi_(3.8)-Co_(0.75)Mn_(0.4)Alo_(0.2) (x = 5, 10, 20, 40) composites prepared by mechanical milling have been investigated in this paper. XRD results indicate that the as-milled Mg_2NiH_4 shows nano-crystalline or amorphous-like structure, and it does not react with MmNi_(3.8)Co_(0.75)Mn_(0.4)Al_(0.2) during mechanical milling. As the amount of MmNi_(3.8)CO_(0.75)Mn_(0.4)Al_(0.2) increases, the maximum discharge capacity decreases initially from 508 mAh/g (x = 5) to 440 mAh/g (x = 10) and then increases to 509 mAh/g (x = 40). Meanwhile, the capacity retention (R_(10)) increases from 12.8% (x = 5) to 23.4% (x = 40), and the corrosion potential of electrode (E_(corr)) increases from -0.930 V to -0.884 V (us. Hg/HgO). Especially, the more MmNi_(3.8)Co_(0.75)M-n_(0.4)Al_(0.2) content the composite contains, the higher high rate dischargeability (HRD) the electrode exhibits, which could be attributed to the catalytic reaction and reduction of the Mg_2NiH_4 grain size brought by MmNi_(38)Co_(0.75)Mn_(0.4)Al_(0.2)- The improvement in electrode kinetics has been depicted from the bulk hydrogen diffusion coefficient (D), the exchange current density (I_o) and the charge transfer resistance (R_(ct)) on the alloy surface.