Sealed rechargeable battery

Details Sealed rechargeable battery Sealed rechargeable battery

2003-04-24

2004-05-11

Maples, John S. (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Plural concentric or single coiled electrode

C429S057000, C429S176000, C429S185000

Reexamination Certificate

active

06733918

ABSTRACT:

The present disclosure relates to subject matter contained in priority Japanese Patent Application No. 2002-121571, filed on Apr. 24, 2002, the contents of which is herein expressly incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sealed rechargeable battery. More particularly, it relates to a battery having an electrode plate group constructed with a positive electrode plate and a negative electrode plate wound around with a separator interposed therebetween and accommodated in a case having an oval or rectangular cross section.
2. Description of Related Art
Demands have been growing for electric vehicles or gasoline-electric hybrid vehicles in light of global environmental issues. Rechargeable batteries used as power sources for such vehicles are required to be small and lightweight as well as to have high capacity and high power output. Lithium ion rechargeable batteries and nickel metal hydride batteries are known to satisfy these requirements and have actually found practical applications.
FIG. 6
shows one such conventional sealed rechargeable battery. It accommodates an electrode plate group
24
in a cylindrical metal case
25
together with liquid electrolyte. The electrode plate group
24
consists of a strip of positive electrode plate
21
and a strip of negative electrode plate
22
wound around with a separator
23
interposed therebetween. Positive and negative electrode tabs
26
and
27
are extended from given locations of the positive electrode plate
21
and negative electrode plate
22
in opposite directions. The negative electrode tab
27
extended to the lower side is welded to a bottom face of the case
25
, and the positive electrode tab
26
extended to the upper side is welded to a sealing plate
28
for sealing the open end of the case
25
. The sealing plate
28
is fixed to the case
25
with a gasket
29
fitted therebetween to provide a seal.
In the construction shown in
FIG. 6
, because the positive electrode plate
21
is connected to the sealing plate
28
via the positive electrode tab
26
and the negative electrode plate
22
is connected to the case
25
via the negative electrode tab
27
, the connection resistance is large. The battery internal resistance is accordingly large, because of which the output characteristics and large current discharge characteristics are not satisfactory. There is also the problem of high costs because of large numbers of components and assembling steps.
Japanese Patent Laid-Open Publication No. 2000-243433 discloses a construction for a rechargeable battery, which is shown in
FIG. 7A. A
positive electrode plate
31
and a negative electrode plate
32
are wound around with a separator
33
interposed therebetween to form an electrode plate group
34
such that one lateral edge of the positive electrode plate
31
and one lateral edge of the negative electrode plate
32
are respectively protruded. These projecting portions
31
a
and
32
a
of the positive and negative electrode plates are directly bonded to a sealing plate
36
and the bottom face of a case
35
, respectively, by laser beam welding. To achieve high bonding strength in the welding between the positive electrode projecting portion
31
a
and the sealing plate
36
and between the negative electrode projecting portion
32
a
and the bottom face of the case
35
, radial ribs
37
are provided on the sealing plate
36
or on the bottom face of the case
35
so as to form protruding bonding surfaces as shown in
FIGS. 7B and 7C
.
The battery shown in
FIGS. 7A
to
7
C, however, has the following problems: When constructing a battery pack by connecting a plurality of such batteries as battery modules, the number of the batteries that can be accommodated in a confined space is limited because they are cylindrical. The volume efficiency will be further reduced if cooling passages are to be formed between the batteries to prevent battery temperature rise. Each battery will exhibit poor cooling properties particularly in the central portion because its cross section is circular. That is, this battery has poor volume efficiency per power output.
Another problem is that, because the electrode plate group
34
is welded to the case
35
and the sealing plate
36
at the radial ribs
37
as shown in FIG.
7
B and
FIG. 7C
, welds are gathered in high density in the central portion of the electrode plate group
34
while the welds are sparse in the outer peripheral portion. This makes the current distribution in the positive and negative electrode plates
31
and
32
uneven, which increases battery internal resistance and makes the chemical reactions of active materials uneven. The output characteristics and large current discharge characteristics are thereby reduced, adversely affecting the battery life.
Japanese Patents Nos. 2692533 and 2697565 show a construction for a sealed prismatic rechargeable battery, in which an electrode plate group formed by winding around a positive electrode plate and a negative electrode plate with a separator therebetween is accommodated in a prismatic case such that its winding axis is in parallel to the open end of the case. The open end of the case is sealed by a lid provided with a positive terminal, to which one end of the positive electrode plate is connected. The negative electrode plate which is located at the outermost side of the electrode plate group is connected to the case. With this construction, because one end of the positive and negative electrode plates is connected to the positive terminal and the case which forms the opposite terminal, the current path from each electrode plate is relatively long, so that the battery internal resistance is large because of the large current resistance inside the battery, and therefore the output characteristics and large current discharge characteristics are not satisfactory. Moreover, while a cylindrical battery can retain its electrode plate group securely in position within the case, the prismatic battery cannot hold its rolled electrode plate group securely inside the rectangular tube case. Thus, there is a risk that active material mixtures may come off the positive or negative electrode plates when vibration is applied to the battery, whereupon the battery characteristics are suddenly deteriorated because of the damaged electrode plate group.
SUMMARY OF THE INVENTION
In light of the problems of the conventional batteries, an object of the present invention is to provide a sealed rechargeable battery having high volume efficiency per power output and favorable output characteristics and large current discharge characteristics.
The present invention provides a sealed rechargeable battery including: a metal case having any of an oval cross section and a rectangular cross section; a metal sealing plate for sealing an open end of the case; an insulation gasket interposed between the case and the sealing plate; and an electrode plate group including a positive electrode plate and a negative electrode plate wound around with a separator interposed therebetween. Core materials of the positive electrode plate and the negative electrode plate are protruded to opposite sides to form a positive electrode end face and a negative electrode end face at either end of the electrode plate group. The electrode plate group is accommodated in the case with liquid electrolyte with its winding axis vertical relative to the open end of the case. The positive electrode end face is connected to either one of a bottom face of the case and the sealing plate in direct surface contact therewith or indirectly coupled thereto, and the negative electrode end face is connected to the other one of the bottom face of the case and the sealing plate in direct surface contact therewith or indirectly coupled thereto.
With this construction, because the battery case has an oval or rectangular cross section, its volume efficiency per power output is higher than that of a cylindrical battery. A plurality of such batt

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