Hydrogen Absorbing Electrode and Nickel Metal-Hydridge Battery

Abstract

The object of the present invention is to provide a nickel metal-hydride battery excellent in cycle performance, high-rate discharging ability, and output power performance, by utilizing a hydrogen absorbing electrode comprising a hydrogen absorbing alloy powder as an active material, which is excellent in resistance to corrosion and high-rate discharging performance. Provided are a hydrogen absorbing electrode comprising 100 parts by weight of a hydrogen absorbing alloy powder which contains, as a main component, a rare earth element and a transition metal element, and has a saturation mass susceptibility of 1.0 to 6.5 emu/g, and 0.3 to 1.5 part by weight of an oxide or hydroxide of a rare earth element, the oxide or hydroxide has as a main component one or two or more rare earth elements selected from a group consisting of Dy, Ho, Er, Tm, Yb, and Lu and is in the form of powder whose average diameter is equal to or less than 5 μm, and a nickel metal-hydride battery comprising a nickel electrode as a positive electrode and a hydrogen absorbing electrode as a negative electrode.

1 . A hydrogen absorbing electrode comprising 100 parts by weight of a hydrogen absorbing alloy powder which contains, as a main component, a rare earth element and a transition metal element and has a saturation mass susceptibility of 1.0 to 6.5 emu/g, and 0.3 to 1.5 parts by weight of an oxide or hydroxide of a rare earth element wherein said oxide or hydroxide has as a main component one or two or more rare earth elements selected from a group consisting of Dy, Ho, Er, Tm, Yb, and Lu and is in the form of powder whose average diameter is equal to or less than 5 μm.  
   
   
       2 . The hydrogen absorbing electrode as described in  claim 1  wherein 80 wt % or more of a rare earth element contained in said oxide or hydroxide of a rare earth element is one or two or more selected from a group consisting of Dy, Ho, Er, Tm, Yb, and Lu.  
   
   
       3 . The hydrogen absorbing electrode as described in  claim 2  wherein 80 wt % or more of the rare earth element contained in said oxide or hydroxide of a rare earth element is Er.  
   
   
       4 . The hydrogen absorbing electrode as described in  claim 2  wherein 80 wt % or more of the rare earth element contained in said oxide or hydroxide of a rare earth element is Yb.  
   
   
       5 . The hydrogen absorbing electrode as described in  claim 1  wherein said hydrogen absorbing alloy powder is obtained by immersing a hydrogen absorbing alloy powder containing, as a main component, a rare earth element and a transition metal element, in an aqueous alkaline solution at a high temperature so that its saturation mass susceptibility is 1.0 to 6.5 emu/g.  
   
   
       6 . The hydrogen absorbing electrode as described in  claim 5  wherein said hydrogen absorbing alloy powder is obtained by immersing a hydrogen absorbing alloy powder in an aqueous sodium hydroxide solution containing sodium hydroxide at a concentration of 28 to 50 wt % and at 90 to 110° C.  
   
   
       7 . The hydrogen absorbing electrode as described in  claim 1  wherein said hydrogen absorbing alloy powder has an average diameter of 10 to 30 μm.  
   
   
       8 . The hydrogen absorbing electrode as described in  claim 1  wherein said oxide or hydroxide of a rare earth element in the form of powder has an average diameter equal to or less than 3.5 μm.  
   
   
       9 . The hydrogen absorbing electrode as described in  claim 8  wherein said oxide or hydroxide of a rare earth element in the form of powder has an average diameter of 0.1 to 3 μm.  
   
   
       10 . A nickel metal-hydride battery comprising a nickel electrode as a positive electrode and a hydrogen absorbing electrode as a negative electrode, wherein said hydrogen absorbing electrode comprises a mixture of 100 parts by weight of a hydrogen absorbing alloy powder containing, as a main component, a rare earth element and a transition metal element and having a saturation mass susceptibility of 1.0 to 6.5 emu/g, and 0.3 to 1.5 parts by weight of a powder of an oxide or hydroxide of a rare earth element which has as a main component one or two or more rare earth elements selected from a group consisting of Dy, Ho, Er, Tm, Yb, and Lu, and has an average diameter equal to or less than 5 μm.  
   
   
       11 . The nickel metal-hydride battery as described in  claim 10  wherein said powder of said oxide or hydroxide of a rare earth element is a powder of an oxide or hydroxide of a rare earth element which has as a main component at least one of Er and Yb.  
   
   
       12 . The nickel metal-hydride battery as described in  claim 11  wherein said powder of said oxide or hydroxide of element which has as a main component at least one of Er and Yb has an average diameter equal to or less than 3.5 μm.  
   
   
       13 . The nickel metal-hydride battery as described in  claim 10  wherein said hydrogen absorbing alloy powder has a saturation mass susceptibility of 2 to 6 emu/g.  
   
   
       14 . The nickel metal-hydride battery as described in  claim 10  wherein 80 wt % or more of a rare earth element contained in said oxide or hydroxide of a rare earth element is accounted for by Er or Yb.  
   
   
       15 . The sealed nickel metal-hydride battery as described in  claim 10  obtained by inserting a rolled electrode assembly having an upper current collecting plate attached thereon into a cylindrical container with a bottom, closing an open end of said cylindrical container by means of a lid, and connecting a sealing plate composing said lid and said upper current collecting plate via a current collecting lead whose one end is attached to the internal surface of said sealing plate and the other end to the upper surface of said upper current collecting plate, wherein, at least one out of a welded point between said internal surface of said sealing plate and one end of current collecting lead and a welded point between the other end of current collecting lead and said upper surface of said upper current collecting plate has been welded by applying current through an interior of said battery by an external power source between the positive and negative terminals of said battery after the sealing.