Nickel Metal-Hydride Battery and Method of Manufacturing the Same
An object of the present invention is to provide a sealed nickel metal-hydride that shows an excellent output power performance, while maintaining an excellent charge/discharge cycle performance, and a method of manufacturing the same. A hydrogen absorbing electrode is made of hydrogen absorbing alloy powder containing rare earth elements and Ni and other metal elements other than rare earth elements and the hydrogen absorbing alloy powder shows a specific saturation mass susceptibility and a specific content ratio of the rare earth elements to the non-rare earth elements. A nickel metal-hydride battery is formed by using such a hydrogen absorbing electrode and welding at least the welded points of the inner surface of a sealing plate and a current collecting lead or the welded points of the current collecting lead and an upper current collecting plate by causing an electric current to flow between the positive electrode terminal and the negative electrode terminal of the battery from an external power source after sealing the battery.
1 . A nickel metal-hydride battery including a nickel electrode operating as positive electrode and a hydrogen absorbing electrode containing hydrogen absorbing alloy powder and operating as negative electrode, characterized in that
said hydrogen absorbing alloy powder contains a rare earth element and a non-rare earth metal element including nickel (Ni),
when the atomic ratio (H/M) of the hydrogen absorbed in said hydrogen absorbing alloy powder to the total metal elements contained in the hydrogen absorbing alloy powder is 0.5, the equilibrium hydrogen dissociation pressure of the hydrogen absorbing alloy powder is not less than 0.04 mega pascals (Mpa) and not more than 0.12 MPa at 40° C. and,
the saturation mass susceptibility of said hydrogen absorbing alloy powder is not less than 2 emu/g and not more than 6 emu/g, while
the component ratio of said non-rare earth metal element to said rare earth element is not less than 5.10 and not more than 5.25 in terms of mole ratio.
2 . The nickel metal-hydride battery according to claim 1 , characterized in that, when the atomic ratio (H/M) of the hydrogen absorbed in said hydrogen absorbing alloy powder to the total metal elements contained in the hydrogen absorbing alloy powder is 0.5, the equilibrium hydrogen dissociation pressure of the hydrogen absorbing alloy powder is not less than 0.06 MPa and not more than 0.10 MPa at 40° C.
3 . The nickel metal-hydride battery according to claim 1 , characterized in that said saturation mass susceptibility is not less than 3 emu/g and not more than 6 emu/g.
4 . The nickel metal-hydride battery according to claim 2 , characterized in that said saturation mass susceptibility is not less than 3 emu/g and not more than 6 emu/g.
5 . The nickel metal-hydride battery according to claim 1 , characterized in that a hydrogen absorbing electrode contains said hydrogen absorbing alloy powder and oxide or oxides or hydroxide or hydroxides of Er and/or Yb added to and mixed with the hydrogen absorbing alloy powder.
6 . A method of manufacturing a nickel metal-hydride battery according to claim 1 , characterized in that hydrogen absorbing alloy powder containing said rare earth element and non-rare earth metal element including nickel (Ni) is immersed in a caustic alkali aqueous solution at high temperature to make the saturation mass susceptibility thereof not less than 2 emu/g and not more than 6 emu/g.
7 . The method of manufacturing a nickel metal-hydride battery according to claim 3 , characterized in that hydrogen absorbing alloy powder containing said rare earth element and non-rare earth metal element including nickel (Ni) is immersed in a caustic alkali aqueous solution at high temperature to make the saturation mass susceptibility thereof not less than 3 emu/g and not more than 6 emu/g.
8 . The nickel metal-hydride battery according to claim 1 , including a rolled electrode assembly and a cylindrical bottomed container having its open end sealed by a lid, the inner surface of the sealing plate of said lid and the upper surface of the upper current collecting plate fitted to the upper rolled end of said electrode assembly being connected to each other by way of a current collecting lead, characterized in that at least either the welded point of the inner surface of said sealing plate and the current collecting lead or the welded point of the current collecting lead and the upper current collecting plate is welded by causing an electric current to flow between the positive electrode terminal and the negative electrode terminal of the battery from an external power source by way of the inside of the battery after sealing the open end of the container.
9 . The nickel metal-hydride battery according to claim 5 , including a rolled electrode assembly and a cylindrical bottomed container having its open end sealed by a lid, the inner surface of the sealing plate of said lid and the upper surface of the upper current collecting plate fitted to the upper rolled end of said electrode assembly being connected to each other by way of a current collecting lead, characterized in that at least either the welded point of the inner surface of the sealing plate and the current collecting lead or the welded point of the current collecting lead and the upper current collecting plate is welded by causing an electric current to flow between the positive electrode terminal and the negative electrode terminal of the battery from an external power source by way of the inside of the battery after sealing the open end of the container.
10 . The nickel metal-hydride battery according to claim 8 , characterized in that said current collecting lead and upper current collecting plate are welded at a plurality of welded points, the ratio of the distance from the center of the upper current collecting plate to the welded points to the radius of said rolled electrode assembly is 0.4 to 0.7, a disk-shaped lower current collecting plate is fitted to the lower rolled end of said rolled electrode assembly and the lower current collecting plate and the inner surface of the bottom of the container are welded at a plurality of welded points including one located at the center of the lower current collecting plate and ones located off the center of the lower current collecting plate, and the ratio of the distance from the plurality of welded points other than the one located at the center to the center of said lower current collecting plate to the radius of said rolled electrode assembly is 0.5 to 0.8.
11 . The nickel metal-hydride battery according to claim 9 , characterized in that said current collecting lead and upper current collecting plate are welded at a plurality of welded points, the ratio of the distance from the center of the upper current collecting plate to the welded points to the radius of said rolled electrode assembly is 0.4 to 0.7, a disk-shaped lower current collecting plate is fitted to the lower rolled end of said rolled electrode assembly, the lower current collecting plate and the inner surface of the bottom of the container are welded at a plurality of welded points including one located at the center of the lower current collecting plate and ones located off the center of the lower current collecting plate, and the ratio of the distance from the plurality of welded point other than the one located at the center to the center of the lower current collecting plate to the radius of said rolled electrode assembly is 0.5 to 0.8.