Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-06-16
2001-06-05
Ryan, Patrick (Department: 1725)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S232000, C429S059000, C029S623500
Reexamination Certificate
active
06242133
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a hydrogen-absorbing alloy electrode for an alkaline secondary battery and a method of manufacturing a hydrogen-absorbing alloy electrode.
BACKGROUND OF THE INVENTION
An alkaline secondary battery, which uses a metal compound, for example, nickel hydroxide, for a positive electrode and a hydrogen-absorbing alloy for a negative electrode, has lately been attracting attention as a high energy density battery for replacing nickel-cadmium batteries.
A hydrogen-absorbing alloy performs absorption and desorption of hydrogen as an active material when a battery charges and discharges in an electrolyte. The alloy lattice is deformed by absorption and desorption of hydrogen and alloy particles are pulverized. The pulverized alloy drops or separates from the electrode to cause a reduction in capacity. It also causes mechanical strength of the electrode and electrical conductivity to deteriorate. It is difficult to maintain battery capacity for a long term.
A hydrogen-absorbing alloy powder has been combined with a binding agent of an alkali resistant synthetic resin and a thickening agent to manufacture a hydrogen-absorbing alloy electrode as disclosed in Japanese Patent Laid-Open Publication No. 61-66366.
Styrene-butadiene copolymer which has excellent pliability and adhesive strength is proposed for use as a binding agent for an electrode in Japanese Patent Laid-Open Publication No. 2-135665. In the hydrogen-absorbing alloy electrode disclosed in this publication, the binding agent is deformed with change of volume of the hydrogen-absorbing alloy powder to prevent separation of the pulverized alloy from the electrode. However, reduction of contact between hydrogen-absorbing alloy particles and an electrolyte prevents proper electrical reactions and high rate discharge characteristics of the battery are deteriorated.
OBJECTS OF THE INVENTION
An object of the present invention is to prevent separation of the pulverized alloy from the electrode and to inhibit reduction in capacity after repeated charge-discharge cycles.
Another object of the present invention is to increase contact between the alloy particles and the electrolyte to improve high rate discharge characteristics.
SUMMARY OF THE INVENTION
The present invention provides a hydrogen-absorbing alloy electrode for an alkaline secondary battery comprising a paste on an electrically-conductive substrate, wherein the paste comprises a hydrogen-absorbing alloy powder, binder and a transition metal salt.
The present invention also provides an alkaline secondary battery comprising the hydrogen-absorbing alloy electrode of the present invention as described above.
The present invention also provides a method of manufacturing a hydrogen-absorbing alloy electrode for an alkaline secondary battery comprising mixing a hydrogen-absorbing alloy powder, binder, a transition metal salt and water to prepare a paste, and applying the paste on an electrically-conductive substrate.
The hydrogen-absorbing alloys useful in the present invention are not particularly limited. Suitable alloys include LaNi
5
, LaNi
4
Co and LaNi
4
Cu such as described in Japanese Patent Laid-Open publication No. 59-49671, and hydrogen-absorbing alloys of an Mm-Ni type (where “Mm”, a so-called “Misch Metal” is a mixture of rare earth elements, such as La, Ce, Nd, Pr, etc.) . These alloys produce batteries that can obtain a high capacity.
As the binder, at least one of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE) and styrene-butadiene rubber (SBR) can be used. The content of the binder is preferably in a range of 0.5 wt % to 10.0 wt % based on the weight of the hydrogen-absorbing alloy powder.
As the transition metal salt, at least one salt selected from the group consisting of cobalt chloride (CoCl
2
) , nickel chloride (NiCl
2
) and copper chloride (CuCl
2
) is used. The amount of the transition metal salt is in a range of 0.3 wt % to 5.0 wt % based on the weight of said hydrogen-absorbing alloy powder.
As an electrically-conductive substrate, a punched metal, a foamed metal, and the like can be used.
The hydrogen-absorbing alloy powder can be used in the form of so-called cast alloy which is ground after casting or an atomized alloy.
A strength of electrode of the hydrogen-absorbing alloy electrode increases by manufacturing the electrode by mixing a hydrogen-absorbing alloy powder, binder, a transition metal salt and water. Therefore, reduction of capacity of a battery after repeated charge-discharge cycles for a long term can be decreased by using the electrode because of an increase in holding power of alloy. Electrical-conductivity between alloy particles or alloy and electrical collector (electrical-conductive substrate) and high rate discharge characteristics at a low temperature are improved.
High rate discharge property at a low temperature is improved because contact between the alloy and an electrolyte is not inhibited. The reason for such improvement is believed to be that the transition metal salt is dissolved and forms a metal chelate compound which polymerizes. Since impregnating ability of a binder with an electrolyte is not affected, contact between alloy and the electrolyte is maintained. Diffusion of hydroxide ion is not inhibited between an active surface of an alloy and an electrolyte. Therefore, electrical reactions can take place normally. Furthermore, binding property between alloy particles, and the alloy and electically-conductive substrate is improved and conductivity is also improved. As a result of such improvement, it is believed that high rate discharge capacity at low temperature is improved.
REFERENCES:
patent: 4140840 (1979-02-01), Ruben
patent: 4145483 (1979-03-01), Bonnemay et al.
patent: 4508799 (1985-04-01), Gopikanth et al.
patent: 4753786 (1988-06-01), Watanabe et al.
patent: 5571637 (1996-11-01), Idota
patent: 5686203 (1997-11-01), Idota et al.
patent: 5707764 (1998-01-01), Miyamoto et al.
patent: 5780184 (1998-07-01), Coco et al.
patent: 5798189 (1998-08-01), Hayashida et al.
patent: 5798190 (1998-08-01), Andrei et al.
patent: 5856044 (1999-01-01), McLin et al.
patent: 6019802 (2000-02-01), Ishizuka et al.
patent: 6040087 (2000-03-01), Kawakami
patent: 61-66366 (1986-04-01), None
patent: 2-135665 (1990-05-01), None
patent: 2-234355 (1990-09-01), None
patent: 5-13075 (1993-01-01), None
patent: 7-73874 (1995-03-01), None
Fujitani Shin
Higashiyama Nobuyuki
Hirota Yohei
Imoto Teruhiko
Kato Kikuko
Cooke Colleen P.
Kubovcik & Kubovcik
Ryan Patrick
Sanyo Electric Co,. Ltd.
LandOfFree
Hydrogen-absorbing alloy electrode for alkaline secondary... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydrogen-absorbing alloy electrode for alkaline secondary..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydrogen-absorbing alloy electrode for alkaline secondary... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2447051