A hydrogen storage alloy contains Mm, Ni, Mn, Al, and Co and has a main phase having a CaCu.sub.5-type crystal structure. La and Ce together account for 95 mass % or more of Mm. When the mole ratios of Ni, Mn, Al, and Co with respect to 1 mol of Mm are represented by a, b, c, and d, respectively, d is 0.00 or more and less than 0.15, d/b is 0.00 or more and 0.35 or less, and the sum of a+b+c+d is 5.22 or more and 5.44 or less. The ratio H/E of hardness H (GPa) to composite elastic modulus E (GPa) as measured using a nanoindentation technique is 0.08 or more and 0.15 or less.

Provided is an electrode alloy powder that is useful to obtain a nickel-metal hydride storage battery having a high battery capacity and a reduced self-discharge. The alloy powder is: a mixture including particles of a first hydrogen storage alloy having an AB.sub.5-type crystal structure, and particles of at least one second hydrogen storage alloy selected from the group consisting of a hydrogen storage alloy a having an AB.sub.2-type crystal structure and a hydrogen storage alloy b having an AB.sub.3-type crystal structure, wherein an amount of the first hydrogen storage alloy included in the mixture is greater than 50 mass %.

Provided are a composition including a hydrogen-selective porous composite, a hydrogen gas sensor device including the hydrogen-selective porous composite, a kit for detecting hydrogen including the hydrogen gas sensor device, and a method for detecting hydrogen including contacting a hydrogen-comprising gas to the hydrogen selective porous composite. The method may include, for example: providing a hydrogen-comprising gas; providing a hydrogen-selective porous composite, the hydrogen-selective porous composite comprising cerium oxide; contacting the hydrogen-comprising gas to the hydrogen-selective porous composite; and selectively detecting hydrogen in the hydrogen-comprising gas according to a decrease in an electrical resistance of the hydrogen-selective porous composite.

A nickel hydrogen secondary battery 2 has an electrode group 22 including a separator 28, a positive electrode 24, and a negative electrode 26. The negative electrode 26 has a negative electrode core, and a negative electrode mixture held on the negative electrode core. The negative electrode mixture contains a hydrogen absorbing alloy and a water repellent. The hydrogen absorbing alloy has a composition represented by the general formula: Ln.sub.1-xMg.sub.xNi.sub.y-a-bAl.sub.aM.sub.b, where Ln represents at least one element selected from rare earth elements, Ti and Zr; M represents at least one element selected from V, Nb, Ta, and the like, and the subscripts a, b, x and y satisfy relations represented by 0.05a0.30, 0b0.50, 0x<0.05 and 2.8y3.9, respectively. The hydrogen absorbing alloy has a structure of an A.sub.2B.sub.7 type. The water repellent comprises a perfluoroalkoxyalkane.

A battery negative electrode includes a hydrogen storage alloy as a negative electrode active material, wherein the hydrogen storage alloy has a mean volume diameter within a range from 4 m to 12 m, and is disposed to be capable of being in contact with hydrogen in a hydrogen containing part in which hydrogen is contained.

This disclosure provides a hydrogen storing alloy and a production method thereof. The hydrogen storing alloy has a chemical composition of a general formula R.sub.(1-x)Mg.sub.xNi.sub.y, wherein R is one or more elements selected from rare earth elements comprising Y, x satisfies 0.05x0.3, and y satisfies 2.8y3.8. The ratio of the maximal peak intensity present in a range of 2=31-33 to the maximal peak intensity present in a range of 2=41-44 is 0.1 or less (including 0), as measured by X-ray diffraction in which a CuK ray is set as an X-ray source.

A method for regenerating a nickel metal hydride battery is provided. The nickel metal hydride battery includes a hydrogen absorbing alloy that serves as a negative electrode material and a safety valve that opens when an internal pressure of a battery case is greater than or equal to a predetermined pressure. The method includes connecting a plurality of nickel metal hydride batteries in parallel. Each nickel metal hydride battery is formed by integrating one or more battery cells. The method further includes overcharging the nickel metal hydride batteries by supplying current from a charge unit that is connected in parallel to the nickel metal hydride batteries. The method further includes, when each nickel metal hydride battery is overcharged, restoring a discharge reserve of a negative electrode by releasing at least some of an oxygen gas generated at a positive electrode out of the battery case through the safety valve.

Methods of preparing improved metal hydride alloy materials are provided. The alloys include a mixture of at least four of vanadium, titanium, nickel, chromium, and iron. The alloy is processed by at least one of thermal and physical treatment to generate a refined microstructure exhibiting improved kinetics when used as electrodes in MH batteries (e.g., higher discharge current). The thermal treatment includes rapid cooling of the alloy at greater than 10.sup.4 K/s. The physical treatment includes mechanical pulverization of the alloy after cooling. The microstructure is a single phase (body centered cubic) with a heterogeneous composition including a plurality of primary regions having a lattice parameter selected from the range of 3.02 to 3.22 and a plurality of secondary regions having a lattice parameter selected from the range of 3.00 to 3.22 and at least one physical dimension having a maximum average value less than 1 m.

A conventional bipolar battery is constituted of a combination of cells hermetically sealed for preventing a liquid junction and preventing corrosion of a peripheral device due to a liquid leakage. Therefore, electrolytic solution injecting processes are carried out as many as the number of cells, so that much times and costs have been required for manufacturing a large-scale battery. In addition, a wiring space has been required since the cells are connected to one another with wires. The use of a current collector formed of a one-end closed tubular conductor, the current collector having a bottom protruding outward to form a protrusion, eliminates the wiring space and achieves a reduction in ohmic loss due to the wires. In addition, an electrolytic solution in one cell is separated by a water-repellent sheet from an electrolytic solution in another cell, so that a liquid junction is prevented.

In an aspect, an electrochemical cell comprises: a positive electrode; a negative electrode, said negative electrode having an alloy having a composition comprising V; and an electrolyte; wherein an additive is provided in said electrolyte to form primary vanadate ions upon dissociation of said additive in said electrolyte; and wherein the electrochemical cell is a metal hydride battery. In some embodiments of this aspect, the alloy is configured to sorb hydrogen during charging of said electrochemical cell and desorb hydrogen during discharging of said electrochemical cell. In some embodiments of this aspect, the electrolyte has a pH selected from the range of 13 to 15.