|Budget Amount *help
¥1,600,000 (Direct Cost : ¥1,600,000)
Fiscal Year 1997 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 1996 : ¥1,200,000 (Direct Cost : ¥1,200,000)
Highly efficient AB_5-type Hydrogen Storage Alloys for Ni-MH Battery Ternary LaNi_<5-X>M_X hydrogen storage alloys, partially substituted Ni by Co or Al, react with the alkaline electrolyte in Ni-MH battery to form La(OH)_3 whiskers and inductively precipitate metallic Ni or Ni-Co microcrystals around the surface of the alloys. Hydrogen storage alloy electrode performances were largely dependent on the electrochemical properties of these new microcrystals.
So the LaNi_<5-(a+b)>Co_aAl_b alloys were designed and synthesized accordingly to following course, determinations of (1) Al contents which induce the growth of La(OH)_3 whiskers and the precipitations of microcrystals effectively and (2) Co contents which dominate the electrochemical characteristics of alloy electrodes, and comfirmatively evaluated the electrode performances in Ni-MH battery.
With increase of Al contents, the maximum discharge capacities of alloy electrodes decreased, while the capacity decays of them during charge-discharge cycles were suppressed. Moreover, electrochemically nonactive Al_2O_3 formed and dispersed on ths surface of the alloys by an excess of Al substitutions (b>0.4), and difficulties of utilization of charged hydrogens increased. On the other hand, Ni-Co microcrystals of almost same compositions as mother alloys were induced and those of composition Co/Ni*3, which have a homogeneous structure of substitutional solid solutions, were superiorly resistant to corrosion.
LaNi_<3.5>Co_<1.1>Al_<0.4> alloys synthesized accordingly to the electrochemical data mentioned above were verified to be haigh capacity and long life (maximum discharge capacity : 320 Ah/kg, degradation : 0.01 Ah・kg^<-1>・cycle^<-1>).