U.S. patent application number 12/155093 was filed with the patent office on 2008-12-04 for battery module.
Invention is credited to Masayuki Fujiwara, Atsuhiro Funahashi, Hitoshi Maeda, Yoshitaka Shinyashiki.
Application Number | 20080299453 12/155093 |
Document ID | / |
Family ID | 40088635 |
Filed Date | 2008-12-04 |
United States Patent
Application |
20080299453 |
Kind Code |
A1 |
Shinyashiki; Yoshitaka ; et
al. |
December 4, 2008 |
Battery module
Abstract
A battery module has a plurality of prismatic batteries (2)
stacked in a thickness direction. Two plates (3, 4) are provided
between each of the batteries (2), and each of the batteries (2) is
compressed by shifting the two plates (3, 4) in directions away
from each other. A pair of frame members (10, 20) having opposing
surfaces (11, 21) extending along the stacking direction of the
batteries (2) are disposed face to face so as to sandwich the
batteries (2) in a direction perpendicular to the stacking
direction of the batteries. Wedge-shaped spacers (12, 22) inserted
between the two plates (3, 4) are provided respectively on the
opposing surfaces. By narrowing the gap between the pair of frame
members (10, 20), the spacers (12, 22) are allowed to advance
inwardly between the two plates (3, 4) so that the two plates are
shifted in directions away from each other, whereby the batteries
are compressed.
Inventors: |
Shinyashiki; Yoshitaka;
(Osaka, JP) ; Fujiwara; Masayuki; (Osaka, JP)
; Maeda; Hitoshi; (Osaka, JP) ; Funahashi;
Atsuhiro; (Osaka, JP) |
Correspondence
Address: |
KUBOVCIK & KUBOVCIK
SUITE 1105, 1215 SOUTH CLARK STREET
ARLINGTON
VA
22202
US
|
Family ID: |
40088635 |
Appl. No.: |
12/155093 |
Filed: |
May 29, 2008 |
Current U.S.
Class: |
429/152 |
Current CPC
Class: |
H01M 50/103 20210101;
Y02E 60/10 20130101; H01M 50/209 20210101; H01M 6/46 20130101; Y10T
29/49108 20150115; H01M 50/20 20210101; H01M 10/0525 20130101 |
Class at
Publication: |
429/152 |
International
Class: |
H01M 10/36 20060101
H01M010/36 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 1, 2007 |
JP |
2007-147116 |
Claims
1. A battery module comprising a plurality of prismatic batteries
stacked in a thickness direction, wherein two plates are provided
between each of the batteries, and each of the batteries is
compressed by shifting the two plates in directions away from each
other.
2. The battery module according to claim 1, wherein each of the
prismatic batteries is a lithium-ion battery having a battery case
made of a laminate film.
3. The battery module according to claim 1, wherein: a pair of
frame members having opposing surfaces extending along a stacking
direction of the batteries are disposed face to face so as to
sandwich the batteries in a direction perpendicular to the stacking
direction of the batteries; wedge-shaped spacers, each being
inserted between the two plates, are provided on the opposing
surfaces respectively; and by narrowing a gap between the pair of
frame members, the spacers are allowed to advance inwardly between
the two plates, whereby the two plates are shifted in directions
away from each other so that each of the batteries is
compressed.
4. The battery module according to claim 3, wherein the two plates
are shifted in directions away from each other, whereby each of the
batteries is compressed and each of the batteries is sandwiched and
held between adjacent ones of the plates.
5. The battery module according to claim 3, wherein a plurality of
connecting rods are provided between the pair of frame members, and
the gap between the pair of frame members is narrowed by tightening
a threaded fastener provided on at least one end of each of the
connecting rods.
6. The battery module according to claim 1, wherein the plates are
made of metal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a battery module in which a
plurality of prismatic batteries are retained in a compressed
state.
[0003] 2. Description of Related Art
[0004] A battery module has a laminate type casing member and
incorporates a plurality of prismatic lithium-ion batteries
accommodated in the casing member, each having a plurality of
electrode plates laminated with separators sandwiched between them.
This type of battery module has a large capacity and shows good
performance at high rate current. For this reason, the battery has
been used for robots, electric vehicles, and backup power sources,
for example.
[0005] In the laminate type prismatic lithium-ion batteries such as
described above, expansion and shrinkage of the electrode plates
occur during charge and discharge. When the distance between the
electrode plates increases, electron conductivity lowers in the
positive electrode active material layer and the negative electrode
active material layer, and as a consequence, the internal
resistance increases, causing battery capacity loss and cycle
performance deterioration. In view of this, in the battery module
in which the prismatic lithium-ion batteries are stacked, it is
desirable that each of the batteries is compressed so that the
distance between the electrode plates cannot increase.
[0006] In Japanese Published Unexamined Patent Application Nos.
2003-323874, 2005-259500, and 2006-196222, the laminate type
prismatic lithium-ion batteries as described above are stacked in a
thickness direction with plates or spacers interposed therebetween.
Constraining plates are provided at both ends of the stacked
batteries, and the constraining plates are clamped with a belt or
connecting rods so that each of the batteries is compressed.
[0007] A problem with such methods of compressing the batteries is
that it is difficult to apply a uniform pressure to each of the
batteries. In particular, when the number of the stacked batteries
is large, the problem arises that the pressure applied tends to
vary between the batteries positioned at both ends and those
positioned in the vicinity of the center. Thus, the internal
resistance rises in some of the batteries, and consequently,
battery capacity loss and cycle performance deterioration tend to
occur easily.
[0008] During high rate discharge, each of the batteries generates
heat, but in the conventional battery module structures, the heat
cannot be dissipated sufficiently. In some cases, the battery
temperature rises to the upper limit of the operating temperature
range, causing the battery to fail to discharge.
[0009] In Japanese Published Unexamined Patent Application No.
2006-40696, a plurality of flat-shaped batteries is stacked in a
thickness direction, and a set of heat sinks are provided at both
ends along the stacking direction. By bringing a set of fastening
plates provided at side faces close to each other, the heat sinks
are shifted so that they are brought close to each other, whereby
the batteries are compressed.
[0010] This type of battery module also has the problem that it is
difficult to apply a uniformly pressure to each of the batteries
because the batteries are pressed by the heat sinks disposed at
both ends. Moreover, heat dissipation from each of the batteries is
not sufficient, so the problem of the battery temperature elevation
also remains unresolved.
BRIEF SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to provide a
battery module of prismatic batteries in which each of the
batteries can be compressed uniformly and moreover heat can be
dissipated efficiently from each of the batteries.
[0012] In order to accomplished the foregoing and other object, the
present invention provides a battery module comprising a plurality
of prismatic batteries stacked in a thickness direction, wherein
two plates are provided between each of the batteries, and each of
the batteries is compressed by shifting the two plates in
directions away from each other.
[0013] In the present invention, two plates are disposed between
each of the stacked batteries, and each of the batteries is
compressed by shifting the two plates in directions away from each
other. As a result, each of the batteries can be compressed
substantially uniformly, and the effect of preventing the distance
between the electrodes from increasing can be obtained to
substantially the same degree among the batteries. Thus, battery
capacity loss and cycle performance deterioration can be
minimized.
[0014] Moreover, since the two plates disposed between each of the
batteries are shifted in directions away from each other, a space
is formed between the two plates. According to the present
invention, heat generated in the battery can be released from this
space. As a result, the heat generated from each of the batteries
during high rate discharge can be released outside efficiently, and
high rate charge-discharge becomes possible.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a side view of a battery module of Example 1
according to the present invention;
[0016] FIG. 2 is a perspective view illustrating the battery module
of Example 1 according to the present invention;
[0017] FIG. 3 is a perspective view illustrating a frame member and
spacers used in the battery module of Example 1 according to the
present invention;
[0018] FIG. 4 is a perspective view illustrating a stack electrode
battery of Example 1 according to the present invention; and
[0019] FIG. 5 is a side view illustrating a battery module of
Comparative Example.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The battery module according to the present invention
comprises a plurality of prismatic batteries stacked in a thickness
direction. Two plates are provided between each of the batteries.
Each of the batteries is compressed by shifting the two plates in
directions away from each other.
[0021] In the present invention, two plates are provided between
each of the batteries, and each of the batteries is compressed by
shifting the two plates in directions away from each other.
Therefore, each of the batteries can be compressed under
substantially the same conditions, and each of the batteries can be
compressed uniformly. Moreover, since the two plates disposed
between each of the batteries are shifted in directions away from
each other, a space can be formed between the two plates. As a
result, heat can be dissipated from the space, so it becomes
possible to dissipate heat from each of the batteries
efficiently.
[0022] In a preferred embodiment according to the present
invention, a pair of frame members having opposing surfaces
extending along a stacking direction of the batteries are disposed
face to face so as to sandwich the batteries in a direction
perpendicular to the stacking direction of the batteries;
wedge-shaped spacers, each being inserted between the two plates,
are provided on the opposing surfaces respectively; and by
narrowing a gap between the pair of frame members, the spacers are
allowed to advance inwardly between the two plates, whereby the two
plates are shifted in directions away from each other so that each
of the batteries is compressed.
[0023] The wedge-shaped spacers are not particularly limited as
long as they have a shape that allows an edge of each of the
spacers to advance inwardly between the two plates so that the two
plates can be shifted in directions away from each other. An
example of the wedge-shaped spacer includes a triangular
prismatic-shaped spacer.
[0024] By making the battery module according to the present
invention using the above-described pair of frame members, it
becomes possible to compress each of the batteries and also to hold
each of the batteries by sandwiching them therebetween.
Specifically, by shifting the two plates in directions away from
each other, each of the batteries can be compressed, and also each
of the batteries can be sandwiched and held between adjacent ones
of the plates.
[0025] In a preferred embodiment according to the present
invention, each of the spacers is allowed to advance inwardly
between the two plates by narrowing the gap between the pair of
frame members. An example of the method for narrowing the gap
between the pair of frame members is as follows. A plurality of
connecting rods may be provided between the pair of frame members,
and the gap between the pair of frame members is narrowed by
tightening a threaded fastener provided on at least one end of each
connecting rod.
[0026] According to the present invention, two plates are provided
between each of the batteries, and the two plates are shifted in
directions away from each other, as described above. Therefore, a
space is formed between the two plates, so that utilizing this
space, heat can be dissipated outside. For this reason, it is
preferable that the plates be formed of a material that has a high
thermal conductivity. For example, it is preferable that the plates
be formed of a metal, such as stainless steel, aluminum, and
copper. In addition, the spacers are inserted between the two
plates, and heat can be released also through the spacers.
Therefore, it is preferable that the spacers also be formed of a
material that has a high thermal conductivity. For example, it is
preferable that the spacers be formed of the same metal as that of
the plates. Nevertheless, the materials for the plates and spacers
in the present invention are not limited to metal, and the plates
and spacers may be formed of a resin or the like.
[0027] Moreover, the spacers may either be formed integrally with
the frame members or be formed separately and attached to the frame
members.
[0028] It is preferable that the plates in the present invention
have a flat surface portion that is substantially the same area or
wider than the side surface of the prismatic battery that is to be
compressed. When the plates have such a flat surface portion, the
side surfaces of the batteries can be compressed uniformly.
[0029] It is preferable that the prismatic battery in the present
invention be a battery in which a plurality of layers of the
positive electrode and the negative electrode are laminated
alternately with separators sandwiched therebetween. In such a
laminate type battery, the positive electrode tabs connected to the
positive electrodes and the negative electrode tabs connected to
the negative electrodes are bundled respectively and taken out, and
the positive electrode tabs are connected to a positive electrode
terminal while the negative electrode tabs are connected to a
negative electrode terminal.
[0030] It is preferable that the prismatic battery in the present
invention be a battery in which an electrode assembly comprising a
positive electrode, a negative electrode, and a separator, which
are laminated on top of each other, is inserted in a battery case
made of a flexible film such as a laminate film and an electrolyte
solution is filled in the battery case.
[0031] Alternatively, the prismatic battery in the present
invention may be a battery prepared in the following manner. A
positive electrode and a negative electrode are overlapped and
wound in a spiral state with a separator interposed therebetween to
form a wound electrode assembly. The electrode-assembly is pressed
into a flat shape and inserted into a battery case made of a
laminate film or the like.
[0032] The shape of the prismatic battery in the present invention
is not particularly limited as long as it has opposing side
surfaces that are to be compressed by the plates.
[0033] It is expected that the effect of the present invention can
become most significant when a lithium-ion battery employing a
battery case made of a laminate film is used as the prismatic
battery in the present invention. The effect of preventing the
distance between the electrodes from increasing by compressing the
battery can be obtained most noticeably since the lithium-ion
battery employing a battery case made of a laminate film tends to
expand by charge-discharge particularly easily. For this reason, it
is expected that the effect of the present invention can become
most significant in the lithium-ion battery employing a battery
case made of a laminate film. The present invention is, however,
not limited as such, and it is possible to use other battery cases,
such as those made of a metal can or a resin case, and other
battery systems, such as nickel-cadmium storage batteries and
nickel-metal hydride batteries.
EXAMPLES
[0034] Hereinbelow, the present invention is described in further
detail based on examples thereof. It should be construed, however,
that the present invention is not limited to the following
examples.
[0035] Preparation of Multi-layered Laminate Type Prismatic
battery
Preparation of Positive Electrode
[0036] 90 weight % of LiCoO.sub.2 as a positive electrode active
material, 5 weight % of carbon black as a conductive agent, and 5
weight % of polyvinylidene fluoride as a binder agent were mixed
with N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a
positive electrode mixture slurry. Thereafter, the resultant
positive electrode mixture slurry was applied onto both sides of an
aluminum foil serving as a positive electrode current collector.
Then, the material was dried to remove the solvent and compressed
with rollers to a thickness of 0.1 mm, and thereafter, it was cut
into a sheet having dimensions of 95 mm in width and 95 mm in
height. Thus, a positive electrode was prepared.
[0037] It should be noted that LiNiO.sub.2, LiMn.sub.2O.sub.4, and
composite materials thereof may be used as a positive electrode
active material other than the LiCoO.sub.2 mentioned above.
[0038] Preparation of Negative Electrode
[0039] 95 weight % of graphite powder as a negative electrode
active material and 5 weight % of polyvinylidene fluoride as a
binder agent were mixed with a NMP solution as a solvent to prepare
a negative electrode mixture slurry. Thereafter, the resultant
slurry was applied onto both sides of a copper foil serving as a
negative electrode current collector. Then, the material was dried
to remove the solvent and compressed with rollers to a thickness of
0.08 mm, and thereafter, it was cut into a sheet having dimensions
of 100 mm in width and 100 mm in height. Thus, a negative electrode
was prepared.
[0040] Although artificial graphite was used as the negative
electrode active material, natural graphite and other carbon
materials may also be used suitably.
[0041] Attaching Current Collector Tabs
[0042] A positive electrode tab made of an aluminum foil and a
negative electrode tab made of a copper foil were attached to the
positive electrode and the negative electrode, respectively, by
ultrasonic welding.
[0043] Preparation of Stacked Electrode Assembly
[0044] 50 sheets of the above-described positive electrode with the
positive electrode tab and 51 sheets of the above-described
negative electrode with the negative electrode tab were laminated
with polypropylene separators (100 mm.times.100 mm, thickness 30
.mu.m) so that the positive electrode tabs and the negative
electrode tabs were located on the same side. It should be noted
that the positive and negative electrodes were laminated so that
the negative electrodes were located at the outermost portions. An
insulating tape was wound around the resultant laminate, and a
stacked electrode assembly was thus completed.
[0045] Preparation of Electrolyte Solution
[0046] Ethylene carbonate (EC) and methyl ethyl carbonate (MEC)
were mixed at a volume ratio of 30:70, and LiPF.sub.6 was dissolved
into the resultant mixed solvent at a concentration of 1 M
(mole/liter) Thus, an electrolyte solution was prepared.
[0047] Preparation of Multi-Layered Laminate Type Battery
[0048] The above-described stacked electrode assembly was inserted
into a battery case made of a laminate film. A side of the battery
case on which the positive electrode tabs and the negative
electrode tabs were attached was thermally bonded, and further, two
sides of the remaining three sides were also thermally bonded.
Next, the above-described electrolyte solution was filled into the
battery case from the one side that was not yet thermally bonded.
After filling the electrolyte solution, the one side that was not
yet bonded was thermally bonded to thereby hermetically seal the
battery case. Thus, a stack electrode battery was completed.
[0049] FIG. 4 is a perspective view illustrating the stack
electrode battery. As illustrated in FIG. 4, a positive electrode
terminal 5 and a negative electrode terminal 6 are attached to the
stack electrode battery 2. A bent portion 5a is formed at an end of
the positive electrode terminal 5. Likewise, a bent portion 6a is
formed at an end of the negative electrode terminal 6. The bent
portion 5a and the bent portion 6a are bent in opposite directions
to each other. The positive electrode terminal 5 is attached, by
ultrasonic welding, to the positive electrode tabs of the positive
electrodes that are laminated in the battery. Likewise, the
negative electrode terminal 6 is attached, by ultrasonic welding,
to the negative electrode tabs of the negative electrodes that are
laminated in the battery.
[0050] The stack electrode battery has a width of 100 mm, a height
of 110 mm, and a thickness of 12 mm.
[0051] Preparation of Battery Module
[0052] Using the stack electrode battery prepared in the
above-described manner, a battery module was prepared in the
following manner.
Example 1
[0053] FIG. 1 is a side view of the battery module prepared in
Example 1, and FIG. 2 is a perspective view thereof.
[0054] As illustrated in FIGS. 1 and 2, the battery module of the
present example comprises stack electrode batteries 2 stacked in a
thickness direction, and two plates 3 and 4 are inserted between
each of the batteries 2. Each of the plates 3 and 4 is formed of
stainless steel and has a width of 100 mm, a height of 115 mm, and
a thickness of 2 mm.
[0055] A pair of frame members 10 and 20 are provided so as to
sandwich the batteries 2 along a direction perpendicular to the
stacking direction of the batteries 2. The frame members 10 and 20
have respective opposing surfaces 11 and 21 opposed to each other,
and the frame members 10 and 20 are disposed so that the opposing
surfaces 11 and 21 face each other. Wedge-shaped spacers 12 and 22
are provided on the opposing surfaces 11 and 21, respectively. The
wedge-shaped spacers 12 and 22 have a triangular prismatic shape.
Each of the wedge-shaped spacers 12 and 22 is disposed so that its
edge is inserted between the plates 3 and 4.
[0056] The width of the frame members 10 and 20 is 80 mm. The
length thereof along the stacking direction of the batteries 2 is
300 mm, and the thickness thereof is 2 mm. Support portions 13 and
23 are provided at both widthwise ends of the frame members 10 and
20. The height of the support portions 13 and 23 is 8 mm, and the
thickness of the frame member is 2 mm. Thus, the total height is 10
mm.
[0057] The spacers 12 and 22 have a triangular prismatic shape, as
described above, and the base of the triangular prism is 4 mm and
the height thereof is 10 mm. Each of the spacers 12 and 22 has an
isosceles triangular cross section. The length thereof along the
battery width is 80 mm. The spacers are provided in such a manner
that the interval between the vertexes of the triangular prisms of
the adjacent spacers is 18 mm.
[0058] The frame members 10 and 20 are formed of stainless steel.
The spacers 12 and 22 are also formed of stainless steel.
[0059] As illustrated in FIG. 2, a battery 2 is electrically
connected in series with an adjacent battery 2 by connecting a
positive electrode terminal 5 and a negative electrode terminal 6.
In the adjacent battery 2, the bent portion 5a of the positive
electrode terminal 5 and the bent portion 6a of the negative
electrode terminal 6 are bent in opposite directions. Thus, the
bent portion 5a of the positive electrode terminal 5 is connected
to the bent portion 6a of the negative electrode terminal 6 of the
adjacent battery 2 so that they overlap with each other. The
connecting of the positive electrode terminal 5 and the negative
electrode terminal 6 may be effected by ultrasonic welding,
resistance welding, screw fastening, and the like. In the case that
screw-fastening is carried out, a hole through which a bolt is
pierced may be formed in each of the terminals so that the
terminals may be secured to each other with a bolt and a nut.
Electric current of the batteries 2 connected in series is taken
out from the positive electrode terminal 5 of the battery 2 that is
positioned at one end and the negative electrode terminal 6 of the
battery 2 that is positioned at the other end. In the present
example, the stacked batteries 2 are electrically connected in
series, but it is also possible to electrically connect the
batteries 2 in parallel. It should be noted that in FIG. 1, the
positive electrode terminals 5 and the negative electrode terminals
6 are not shown.
[0060] FIG. 3 is a perspective view illustrating a frame member 20.
It should be noted that a frame member 10 is also configured in the
same manner. As illustrated in FIG. 3, holes 20a are formed in end
portions of the frame member 20 along the battery stacking
direction. Two holes are formed in each end portion, so in both end
portions, four holes are formed in total. As illustrated in FIGS. 1
and 2, a connecting rod 30 is pierced through each of the holes,
and as illustrated in FIG. 1, threaded fasteners 31 are attached to
both ends of each connecting rod 30. By tightening the threaded
fasteners 31, the distance between the frame member 10 and the
frame member 20 can be narrowed. It should be noted that in FIG. 2,
the threaded fasteners 31 are not shown. The connecting rod 30 has
a diameter of 8 mm and a length of 133 mm. The connecting rods 30
are also made of stainless steel. By mounting the threaded
fasteners 31 and narrowing the gap between the frame member 10 and
the frame member 20, the wedge-shaped spacers 12 of the frame
member 10 and the wedge-shaped spacers 22 of the frame member 20
are allowed to advance inwardly between the plates 3 and the plates
4. By allowing the spacers 12 and 22 to advance toward the center
in this way, the two plates 3 and 4 can be shifted in directions
away from each other, and by allowing the plates 3 and 4 to shift
in directions away from each other, each of the batteries 2 can be
compressed between adjacent ones of the plates.
[0061] Each battery 2 is compressed by being pressed and sandwiched
between the plates 3 and 4 that are shifted in the above-described
manner. Almost the same compression state can be achieved in each
of the batteries 2. Therefore, a uniform pressure can be applied to
each of the batteries 2 in the battery module of the present
example, and as a result, for example, the problem of varying
compression states between the batteries positioned at end portions
and the batteries positioned at the center portion, as observed in
the conventional batteries, does not arise.
[0062] In addition, by allowing the spacers 12 and 22 to advance, a
space is formed between the plate 3 and the plate 4, so heat can be
dissipated from this space. Thus, according to the present example,
the heat generated in the batteries 2 can be released efficiently.
For this reason, high rate charge-discharge becomes possible.
Moreover, in the present example, since the plate 3 and the plate 4
are formed of a metal, the heat generated in the batteries 2 can be
transmitted and released outside efficiently. Furthermore, since
the spacers 12 and 22 as well as the frame members 10 and 20 are
also made of a metal, the heat from the plate 3 and the plate 4 can
be transmitted and released outside efficiently.
[0063] In the present example, the spacers 12 and 22 are made in
the same dimensions and shapes. However, they may have different
dimensions and shapes depending on the locations at which the
spacers are to be provided. By varying the dimensions and shapes of
the spacers, the compression state of the batteries 2 can be
varied. In addition, the space volume between the plates may be
varied. Thus, it is possible to vary the dimensions and shapes of
the plates so that the gap between the plates becomes wider for a
location in which better heat dissipation is desired.
[0064] In addition, because the dimensions and shapes of the
spacers affect the compressed state of the batteries as described
above, it is also possible to adjust the compressed state to the
batteries by varying the dimensions and shapes of the spacers.
[0065] In the present example, the number of the batteries 2
stacked in the battery is 15.
Comparative Example 1
[0066] A battery module of Comparative Example, shown in FIG. 5,
was prepared using the same stack electrode battery 2 described
above. FIG. 5 shows a side view thereof. A plate 7 (width 100 mm,
height 115 mm, thickness 5 mm) formed of a polyether ether ketone
(PEEK) resin is disposed between each of the batteries 2.
Compressing plates 41 and 42 (width 130 mm, height 140 mm,
thickness 5 mm) formed of stainless steel are provided on both ends
of the stacked batteries 2. Holes are formed at the four corners of
the compressing plates 41 and 42, which are connected by four
connecting rods 40 guided through the holes. By tightening threaded
fasteners 43 provided on both ends of each of the connecting rods
40, the batteries 2 are compressed. The connecting rod 40 has a
diameter of 8 mm and a length of 290 mm, and it is formed of
stainless steel.
[0067] In Comparative Example 1 as well, the number of the
batteries 2 stacked in the battery is 15.
[0068] Evaluation of Compression State of the Batteries
[0069] In order to evaluate the state of the pressure applied to
each of the batteries 2 in Example 1, a pressure sensitive paper (a
pressure sensitive paper that shows a response at 0.2 MPa and shows
a change in color at the area in which pressure is applied) was
inserted between each of the plates 3 or 4 and each side surface of
the batteries 2, and the compression state in the battery module
was thus evaluated. Likewise, in order to evaluate the state of the
pressure applied to each of the batteries 2 in Comparative Example
1, a pressure sensitive paper was inserted between each plate 7 and
each of the batteries 2, and the compression state was
evaluated.
[0070] As a result, it was observed in Comparative Example 1 that
there was a large difference in the applied pressure between a
stack electrode battery positioned at a central portion of the
battery module and a battery positioned at a peripheral portion
thereof. In contrast, it was confirmed in the battery of Example 1
that substantially the same level of pressure was applied to each
of the batteries, and that each of the batteries was compressed
uniformly.
[0071] Evaluation of Heat Dissipation Capability
Evaluation for Stack Electrode Battery
[0072] Heat dissipation capability of the stack electrode battery
before assembled into the battery module was evaluated. First, the
battery was charged at a constant current of 1 C (12 A) and
thereafter charged at a constant voltage of 4.2 V. Thereafter, the
battery was discharged at 1 C (12 A), and in this discharge, the
discharge capacity was found to be 12 Ah. When the battery was
discharged at 10 C (120 A), the discharge capacity was found to be
10.8 Ah.
[0073] Assuming a hermetically sealed condition in a battery, the
battery was thermally insulated with a 20 mm thick thermal
insulating material (glass wool). When discharged at 10 C, the
temperature of the battery increased from 20.degree. C. to
60.degree. C. (at the end of discharge).
[0074] Evaluation for the Battery module of Example 1
[0075] The battery module of Example 1 was placed in a hermetically
closed space. The battery was charged at 1 C and thereafter
discharged at 10 C, to measure the temperature increase. As a
result, it was found that the battery temperature increased from
20.degree. C. to 50.degree. C. (immediately after the discharge).
The temperature variation between the batteries in the battery
module was within
[0076] As described above, the temperature increase in the battery
module of Example 1 proved to be less than that of the battery in
the thermally insulated condition. Even when the battery module was
placed in a hermetically closed space, the battery temperature did
not rise to an abnormal temperature of 70.degree. C. Thus, it is
demonstrated that according to the present invention, heat can be
dissipated from each of the batteries efficiently.
[0077] The number of the batteries stacked is 15 in the foregoing
example. However, the number of batteries stacked in the battery
module according to the present invention is not limited by the
foregoing example as long as a plurality of batteries is contained
therein.
[0078] Moreover, in the foregoing example, two plates are shifted
in directions away from each other by using a pair of frame
members, providing wedge-shaped spacers on opposing surfaces of the
frame members, and inserting the spacers between the two plates;
however, the present invention is not limited to the foregoing
example, and the two plates may be shifted in directions away from
each other by other means.
[0079] Furthermore, the dimensions, shapes, and materials of the
plates and spacers in the present invention are not limited to
those described in the foregoing example, and various dimensions,
shapes, and materials may be employed.
[0080] Only selected embodiments have been chosen to illustrate the
present invention. To those skilled in the art, however, it will be
apparent from the foregoing disclosure that various changes and
modifications can be made herein without departing from the scope
of the invention as defined in the appended claims. Furthermore,
the foregoing description of the embodiments according to the
present invention is provided for illustration only, and not for
limiting the invention as defined by the appended claims and their
equivalents.
[0081] This application claims priority of Japanese patent
application No. 2007-147116 filed Jun. 1, 2007, which is
incorporated herein by reference.
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