Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-04-14
2001-12-25
Griffin, Steven P. (Department: 1754)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S224000, C429S229000
Reexamination Certificate
active
06333125
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a non-sintered nickel electrode for use in an alkaline storage cell such as a nickel-hydrogen storage cell, a nickel-cadmium storage cell. The present invention also relates to an alkaline storage cell utilzing the electrode.
(2) Description of the Prior Art
In impregnating an active material into a substrate, a non-sintered substrate generally makes it possible to achieve a higher impregnating density, in comparison with a sintered substrate. However, when a porosity of the substrate is raised in order to increase the impregnating density, the proportion of the active material being not immediately in contact with the substrate is increased, and therefore the current collection efficiency of the substrate is degraded, inducing the decrease of an active material utilization rate. Thus, even if the impregnating density is increased in impregnating an active material using a substrate with a large porosity, an actual capacity of a cell cannot be sufficiently increased. In view of such a problem, Japanese Unexamined Patent Publication No. 3-147258 discloses such a technique that, for a non-sintered nickel electrode, a plated layer of cobalt is formed on the surface of an active material consisting of nickel hydroxide. According to this technique, since the cobalt layer formed on the surface of nickel hydroxide enhances the conductivity between the active material particles, the active material utilization rate of the electrode is improved, resulting in an increase of a discharge capacity.
However, in course of the rapid development of mobile electronic devices and the like, there is a growing need for a cell having a higher energy density and a longer cycle life. In consideration of such circumstances, there is still an ample room for improvement in the technique described above. In particular, a short cycle life of the cell still lies as a problem.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the problems as described above. It is therefore an object of the present invention to provide a non-sintered nickel electrode for an alkaline storage cell in which an active material utilization rate is rendered high and a deterioration of a discharge capacity is suppressed.
It is another object of the present invention to provide a high-performance alkaline storage cell utilizing such a non-sintered nickel electrode.
These and other objects are accomplished, in one aspect of the invention, by the provision of a non-sintered nickel electrode for use in an alkaline storage cell comprising a porous substrate and coated nickel active material particles impregnated in the porous substrate, each of the coated nickel particles comprising,
a base particle comprising nickel hydroxide, and
a Co—P—A layer coated on a surface of the base particle, the Co—P—A layer consisting of Co, P, and an element A, where A is at least one element selected from the group consisting of Mn, Zn, Ni, Y, and Bi.
According to this construction, the discharge capacity of a non-sintered nickel electrode is increased and the cycle life is remarkably improved. The reasons are considered to be as follows.
Firstly, in a cell according to the above construction, Co (cobalt) in the Co—P—A layer serves to increase the electrical conductivity between the coated nickel active material particles. As a result, an active material utilization rate is increased along with a current collection efficiency in the electrode. Secondly, P (phosphorus) serves to prevent the coating layer (the Co—P—A layer) from becoming a crystalline layer which is dense. If the coating layer is a dense and crystalline layer, the permeation of the electrolyte solution is hindered and thereby the electrochemical reaction of the nickel hydroxide in the base particle is hindered. On the other hand, when the coating layer is an amorphous layer, such hindrance of the electrochemical reaction does not occur. Moreover, since the Co—P—A layer shows an excellent electrical conductivity, a charge-discharge reaction is smoothly proceeded and as a result a discharge capacity is remarkably increased.
Thirdly, the element A (at least one element selected from the group consisting of Mn, Zn, Ni, Y, and Bi) serves to suppress the expansion of the nickel active material. Therefore, a capacity decrease caused by a dryout of a separator (i.e., a phenomenon in which an electrolyte solution permeates into the expanded crystal lattices of nickel hydroxide) is suppressed, and thereby the degradation of a cycle life is suppressed.
Hence, according to the construction described above, a non-sintered nickel electrode having a high discharge capacity and a long cycle life is achieved.
In addition, in the above-described construction, the element A in the Co—P—A layer may be at least one element selected from the group consisting of Zn (zinc) and Mn (manganese). That is, the Co—P—A layer may be a Co—P—Zn layer, or a Co—P—Mn layer, or a Co—P—Zn—Mn layer. According to this construction, the discharge capacity and the cycle life of the electrode are further improved, although the cause is not yet fully understood.
In addition, in the above-described construction, the amount of the formed Co—P—A layer may be 1-20 wt % based on the weight of the coated nickel particles. When the amount of the formed coating layer is within the above range, the effect of improving the electrical conductivity by the formation of the Co—P—A layer (which is an advantageous effect) surpasses the effect by the relative decrease of the amount of nickel hydroxide serving as an active material (which is an adverse effect), and therefore, the discharge capacity and the cycle life are both improved.
In addition, in the above-described construction, the Co—P—A layer may be a sodium-containing Co—P—A layer in which sodium is contained. According to this construction, the electrical conductivity of the coated nickel active material particle is further improved, and thereby the discharge capacity is remarkably increased, although the cause is not yet identified.
In addition, in the above-described construction, the Co—P—A layer may be formed by an electroless plating. The Co—P—A layer formed by an electroless plating is made to be appropriately dense and uniform to such a degree that the layer does not hinder the permeation of an electrolyte solution, and therefore, the electrochemical reaction of nickel hydroxide as an active material is smoothly proceeded.
In addition, in the above-described construction, the Co—P—A layer may be an amorphous layer. When the Co—P—A layer is an amorphous layer, the electrochemical reaction of nickel hydroxide constituting the base particle is smoothly proceeded because a contact of nickel hydroxide and an electrolyte solution is not hindered.
A non-sintered nickel electrode for an alkaline storage cell in accordance with the construction described above may be produced, in accordance with another aspect on the invention, by a method of producing a non-sintered nickel electrode for an alkaline storage cell, the non-sintered nickel electrode comprising a porous substrate and coated nickel active material particles impregnated in the substrate, the method comprising at least the steps of:
producing a base particle comprising nickel hydroxide, and
electroless-plating to form a Co—P—A layer on a surface of the base particle by using an electroless plating bath, the Co-P-A layer comprising Co, P, and an element A, where the element A is at least one element selected from the group consisting of Mn, Zn, Ni, Y, and Bi.
The above producing method may comprise a step of adding sodium in the Co—P—A layer to form sodium-containing nickel particles, by adding sodium hydroxide to the coated nickel particles produced in the step of electroless-plating and thereafter heating the coated nickel particles. According to this construction, sodium can be readily added in the coating layer, and thereby the electrical conductivity of the coated particle is further increased.
In the method de
Maeda Reizo
Matsuura Yoshinori
Nishio Koji
Shinyama Katsuhiko
Yonezu Ikuo
Armstrong Westerman Hattori McLeland & Naughton LLP
Griffin Steven P.
Sanyo Electric Co,. Ltd.
Strickland Jonas N.
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