Raman and X-ray photoelectron spectroscopic investigations on a new electrode material for nickel-metal hydride batteries: MgNi-graphite composites prepared by ballmilling

MgNi-graphite composites prepared by ballmilling were investigated in detail, with emphasis given to the relation between the structural characteristics and the hydrogen-absorbing properties. It was found that there was an optimal ballmilling time for the preparation of MgNi-graphite composites with enhanced electrode performance when the composite exhibited a saturation capacity of hydrogen absorption virtually identical to that of the MgNi alloy, and the modification of graphite was limited to the surface layer of the MgNi alloy. Raman and X-ray photoelectron spectroscopic investigations on the composites indicated a decline in the rr electron character of graphite and changes in the chemical states of the constituents on the alloy surface, suggesting the possibility of charge transfer between graphite and the MgNi alloy during ballmilling, which resulted in an increase in the surface Ni/Mg ratio. (C) 1999 The Electrochemical Society. S0013-4651(97)12-113-9. All rights reserved.