Hydrogen occluding alloy for battery cathode

Abstract

Disclosed is a hydrogen occluding alloy used for a cathode of battery which enables to provide for a high discharge capacity at small number of charge/discharge cycles by a high-rate initial activation treatment and to increase a high-rate discharge capacity at low temperature. The hydrogen occluding alloy comprises; 32 to 38% of rare earth elements mainly comprising La and/or Ce, 0.1 to 17% of Co, 0.1 to 3.5 % of Al, 0.5 to 10 % of Mn and 0.005% to 0.2% of hydrogen, with the balance being Ni and inevitable impurities, and has a microstructure obtained by X-ray diffraction and microstructure observation with scanning electron microscope, the microstructure comprising a continuous phase and dispersed phase wherein the continuous phase is composed of CaCu 5 -type crystal structure and the dispersed phase is composed of three phases comprising Ce 2 Ni 7 -type crystal structure, rare earth element hydride which is a reaction product produced by the hydrogen heat treatment of the Ce 2 Ni 7 -type crystal structure and CaCu 5 -type crystal structure, and the dispersed phase of the CaCu 5 -type crystal structure is interposed in between the Ce 2 Ni 7 -type crystal structure and rare earth element hydride both of which are dispersed phases, A hydrogen occluding alloy used as a cathode of a battery provides for a high discharge capacity at a small number of charge/discharge cycles by a high-rate initial activation treatment and increases a high-rate discharge capacity at low temperatures. The hydrogen occluding alloy comprises 32 to 38% of rare earth elements mainly comprising La and/or Ce, 0.1 to 17% of Co, 0.1 to 3.5% of Al, 0.5 to 10% of Mn and 0.005% to 0.2% of hydrogen, with the balance being Ni and inevitable impurities. The alloy has a microstructure comprising a continuous phase and a dispersed phase including three phases.

What is claimed is:  
     
         1 . A hydrogen occluding alloy used for a cathode of battery which comprises; 
 32 to 38% of rare earth elements mainly comprising La and/or Ce,    0.1 to 17% of Co,    0.1 to 3.5% of Al,    0.5 to 10% of Mn and    0.005% to 0.2% of hydrogen, with the balance being Ni and inevitable impurities,    and has a microstructure obtained by X-ray diffraction and microstructure observation with scanning electron microscope, said microstructure comprising a continuous phase and dispersed phase wherein the continuous phase is composed of CaCu 5 -type crystal structure and the dispersed phase is composed of three phases comprising Ce 2 Ni 7 -type crystal structure, rare earth element hydride which is a reaction product produced by the hydrogen heat treatment of the Ce 2 Ni 7 -type crystal structure and CaCu 5 -type crystal structure, and the dispersed phase of the CaCu 5 -type crystal structure is interposed in between the Ce 2 Ni 7 -type crystal structure and rare earth element hydride both of which are dispersed phases, wherein the hydrogen occluding alloy enables to provide to the battery a high discharge capacity at small number of charge/discharge cycles by a high-rate initial activation treatment and to increase a high-rate discharge capacity at low temperature.