Sanyo Electric Co., Ltd.

Yohei Hirota

Teruhiko Imoto

Shin Fujitani

Koji Nishio

Mamoru Kimoto

Nobuyuki Higashiyama

Kikuko Kato

Masutaka Ouchi

Tadashi Ise

Tetsuyuki Murata

Takuya Hashimoto

Koji Miki

Takayuki Murakami

A method of producing a hydrogen storage alloy, for use in alkaline storage batteries, includes two steps. A first step involves preparing alloy particles having a CaCu-type crystal structure and the compositional formula MmNiCoMnM, wherein M represents at least one element selected from the group consisting of aluminum (Al) and copper (Cu), 3.0&#x2266;x&#x2266;5.2, 0&#x2266;y&#x2266;1.2, 0.1&#x2266;z&#x2266;0.9, and 4.4&#x2266;x+y+z&#x2266;5.4. A second step involves immersing the alloy particles in an acid treating solution containing a cobalt compound and a copper compound, each in the amount of 0.1 to 5.0% by weight based on the weight of the alloy particles, and an organic additive to remove oxide films from and to reductively deposit cobalt and copper on a surface of each alloy particle to form a surface region surrounding a bulk region and having a graded composition. When the sum in percentage of numbers of cobalt (Co) atoms and copper (Cu) atoms present in the surface region is given by a and that in the bulk region by b, the relationship a/b&#x2267;1.3 is satisfied.

Method for production of hydrogen storage alloy for use in alkaline storage batteries

A hydrogen storage alloy, for use in alkaline storage batteries, having a CaCu -type crystal structure and represented by the compositional formula MmNi Co Mn M (wherein M represents at least one element selected from the group consisting of aluminum (Al) and copper (Cu); x is a nickel (Ni) stoichiometry and satisfies 3.0&lE;x&lE;5.2; y is a cobalt (Co) stoichiometry and satisfies 0&lE;y&lE;1.2; z is a manganese (Mn) stoichiometry and satisfies 0.1&lE;z&lE;0.9; and the sum of x, y and z satisfies 4.4&lE;x&plus;y&plus;z&lE;5.4). The hydrogen storage alloy includes a bulk region having a CaCu -type crystal structure and a substantially uniform composition and a surface region surrounding said bulk region and having a graded composition. When the sum in percentage of numbers of cobalt (Co) atoms and copper (Cu) atoms present in the surface region is given by a and that in the bulk region by b, the relationship a/b&gE;1.3 is satisfied.

Hydrogen storage alloy for use in alkaline storage batteries and method for production thereof

The method of manufacturing a hydrogen-absorbing alloy electrode according to this invention comprises the steps of: dissolving a particle surface of said hydrogen-absorbing alloy by a surface-treatment solution; and washing the hydrogen-absorbing alloy with the particle surface dissolved using an alkaline solution at a temperature of 30&deg; C.&tilde;40&deg; C. The metal ions dissolved by the surface-treatment solution can be completely washed away by the alkaline solution so that they will not be precipitated onto the surface of the hydrogen-absorbing alloy again as the hydroxide.

Method of manufacturing hydrogen-absorbing alloy electrode

A hydrogen-absorbing alloy electrode is prepared by reducing an oxide or hydroxide residing on the surface of a hydrogen-absorbing alloy particle while the alloy particle is held in an atmosphere of a hydrogen gas maintained at a temperature where absorbing of a hydrogen gas does not substantially occur; cooling the atmosphere from a temperature where absorbing of the hydrogen gas does not substantially occur to a temperature where the equilibrium hydrogen pressure of the hyrogen-absorbing alloy is equal to the hydrogen pressure in the atmosphere of the hydrogen gas and thereafter vacuum-evacuating and removing the hydrogen gas so that the hydrogen-absorbing alloy particle is cooled to room temperature while the hydrogen gas is exhausted; and thereafter introducing argon, nitrogen or carbon dioxide gas into the atmosphere, thereby returning the atmosphere to normal atmospheric pressure; and immersing the hydrogen-absorbing alloy particle so prepared in a solution containing an oxidation inhibiting agent.

In the present invention, a hydrogen absorbing alloy obtained by sintering hydrogen absorbing alloy powder containing not less than 50% by weight of particles having a particle diameter of not more than 25 &mgr;m at a temperature of not more than 850&deg; C. is used for a hydrogen absorbing alloy electrode for an alkali storage battery, and the hydrogen absorbing alloy electrode for an alkali storage battery is used as a negative electrode of the alkali storage battery.

Hydrogen absorbing alloy for alkali storage battery, hydrogen absorbing alloy electrode for alkali storage battery, and alkali storage battery

A hydrogen absorbing alloy electrode is provided which has an excellent oxygen gas absorbing capacity and further improved in charge-discharge cycle characteristics and high-rate discharge characteristics. The electrode contains a powder prepared by mixing a hydrogen absorbing alloy powder with a powder of at least one complex oxide selected from the group consisting of a ZrO &mdash;Y O solid solution, ZrO &mdash;CaO solid solution, CeO &mdash;Gd O solid solution, CeO &mdash;La O solid solution, ThO &mdash;Y O solid solution, Bi O &mdash;Y O solid solution, Bi O &mdash;Gd O solid solution, Bi O &mdash;Nb O solid solution and Bi O &mdash;WO solid solution. Preferably the electrode contains 0.1 to 10 wt. % of the complex oxide powder based on the combined amount of the two powders.

Hydrogen absorbing alloy electrode and process for producing same

A hydrogen absorbing alloy electrode is provided which is improved in hydrogen gas absorbing ability and in low-temperature discharge characteristics. The electrode contains a hydrogen absorbing alloy having a crystal structure of the CaCu5 type and represented by the stoichiometric ratio ABx, the hydrogen absorbing alloy being represented by MmNiaCobAlcMd wherein Mm is a misch metal, M is Mn and/or Cu, the atomic ratios a, b, c and d are in the respective ranges of 3.0&lE;a&lE;5.2, 0&lE;b&lE;1.2, 0.1&lE;c&lE;0.9, 0.1&lE;d&lE;0.8, wherein X is the sum of the atomic ratios a, b, c, and d, such that, X&equals;a&plus;b&plus;c&plus;d and, is in the range of 4.4&lE;X&lE;5.4. More specifically, the electrode contains a hydrogen absorbing alloy powder at least 5.0 in X, and a hydrogen absorbing alloy powder less than 5.0 in X.

A hydrogen absorbing alloy electrode characterized in that the electrode consists mainly of a mixture of a first hydrogen absorbing alloy powder A formed on surfaces of particles thereof with a surface layer,containing metallic copper or a copper oxide and a second hydrogen absorbing alloy powder B formed on surfaces of particles thereof with a surface layer,containing metallic cobalt or a cobalt oxide. The copper-coated hydrogen absorbing alloy powder A affords improved electric conductivity, and the cobalt-coated hydrogen absorbing alloy powder B gives improved ability to absorb and desorb hydrogen, whereby the electrode is improved in different battery characteristics, such as cycle characteristics, high-rate discharge characteristics and infernal pressure characteristics, at the same time.

Hydrogen absorbing alloy electrode and process for fabricating same

A hydrogen-absorbing alloy electrode for an alkaline secondary battery. The electrode is prepared by adding a transition metal salt to a paste comprising a hydrogen-absorbing alloy powder and binder. The electrode improves charge-discharge cycle performance and high rate discharge capacity at low temperature of an alkaline secondary battery.

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Itano-gun, Japan

Yohei Hirota