Hydrogen storage alloy, production method therefor and ickel-hydrogen secondary battery- use cathode

Abstract

The present invention relates to hydrogen storage alloys, methods for producing the same, and anodes produced with such alloys for nickel-hydrogen rechargeable batteries. The alloys are useful as electrode materials for nickel-hydrogen rechargeable batteries, excellent, when used as anode materials, in corrosion resistance or activity such as initial activity and high rate discharge performance, of low cost compared to the conventional alloys with a higher Co content, and recyclable. The alloys are of a composition represented by the formula (1), and has a substantially single phase structure, and the crystals thereof have an average long axis diameter of 30 to 160 μm, or not smaller than 5 μm and smaller than 30 μm. The present anodes for rechargeable batteries contain at least one of these hydrogen storage alloys. RNi x Co y M z   (1) (R: rare earth elements etc., M: Mg, Al, etc., 3.7≦x≦5.3, 0.1≦y≦0.5, 0.1≦z≦1.0, 5.1≦x+y+z≦5.5)

What is claimed is:  
     
         1 . A hydrogen storage alloy of a composition represented by the formula (1), wherein said alloy has a substantially single phase structure, and crystals of said alloy has an average long axis diameter of 30 to 160 μm:  
       RNi x Co y M z    (1)  
       wherein R stands for one or a mixture of rare earth elements including yttrium, M stands for Mg, Al, Mn, Fe, Cu, Zr, Ti, Mo, W, B, or mixtures thereof, x satisfies 3.7≦x≦5.3, y satisfies 0.1≦y≦0.5, z satisfies 0.1≦z≦1.0, and 5.1≦x+y+z≦5.5.  
     
     
         2 . A hydrogen storage alloy of a composition represented by the formula (1), wherein said alloy has a substantially single phase structure, and crystals of said alloy have an average long axis diameter of not smaller than 5 μm and smaller than 30 μm.  
     
     
         3 . The hydrogen storage alloy of  claim 1  or  2 , wherein said R in the formula (1) is selected from the group consisting of La, Ce, Pr, Nd, and mixtures thereof.  
     
     
         4 . The hydrogen storage alloy of  claim 3 , wherein a composition of said R in the formula (1) is 50 to 100 at % La, 0 to 50 at % Ce, 0 to 50 at % Pr, and 0 to 50 at % Nd.  
     
     
         5 . The hydrogen storage alloy of  claim 1 , wherein said average long axis diameter is 30 to 120 μm.  
     
     
         6 . The hydrogen storage alloy of  claim 2 , wherein said average long axis diameter is 10 to 20 μm.  
     
     
         7 . A method for producing an alloy of  claim 1  comprising the steps of: 
 (A) melting materials for an alloy of a composition represented by the formula (1) to prepare an alloy melt;  
 (B-1) cooling and solidifying said alloy melt into alloy flakes having an average thickness of 0.1 to 0.5 mm; and  
 (C-1) heat-treating said alloy flakes at 950 to 1100° C. for 30 minutes to 10 hours.  
 
     
     
         8 . A method for producing an alloy of  claim 2  comprising the steps of: 
 (A) melting materials for an alloy of a composition represented by the formula (1) to prepare an alloy melt;  
 (B-2) cooling and solidifying said alloy melt into alloy flakes having an average thickness of 0.05 to 0.2 mm; and  
 (C-2) heat-treating said alloy flakes at 900 to 1000° C. for 1 to 10 hours.  
 
     
     
         9 . An anode for a nickel-hydrogen rechargeable battery comprising a hydrogen storage alloy of  claim 1  and an electrically conductive material as anode materials.  
     
     
         10 . An anode for a nickel-hydrogen rechargeable battery comprising a hydrogen storage alloy of  claim 1 , a hydrogen storage alloy of  claim 2 , and an electrically conductive material as anode materials.  
     
     
         11 . The anode for a nickel-hydrogen rechargeable battery of  claim 10 , wherein a ratio of said hydrogen storage alloy of  claim 1  to said hydrogen storage alloy of  claim 2  existing in said anode materials is 99:1 to 90:10.