U.S. patent application number 15/671991 was filed with the patent office on 2017-11-23 for prismatic secondary battery.
This patent application is currently assigned to HITACHI AUTOMOTIVE SYSTEMS, LTD.. The applicant listed for this patent is HITACHI AUTOMOTIVE SYSTEMS, LTD.. Invention is credited to Hiroaki EGAWA, Takeshi HIZONO, Kouichi KAJIWARA, Hayato KOGUCHI.
Application Number | 20170338448 15/671991 |
Document ID | / |
Family ID | 50182754 |
Filed Date | 2017-11-23 |
United States Patent
Application |
20170338448 |
Kind Code |
A1 |
KAJIWARA; Kouichi ; et
al. |
November 23, 2017 |
PRISMATIC SECONDARY BATTERY
Abstract
A prismatic secondary battery includes a battery case in a
prismatic shape and a battery cover which seals up an opening part
of the battery case. The battery cover has a convex part which
projects toward the inside of the battery case, faces an inner
surface of a side wall part of the battery case, and extends
continuously along the entire periphery of the side wall part.
Cover thickness of a contact part of the battery cover which is in
contact with the upper end of the side wall part of the battery
case at a position outside the convex part is greater than 1/2 of
cover thickness of a blockage part blocking up an opening part at a
position inside the convex part and is less than the cover
thickness of the blockage part.
Inventors: |
KAJIWARA; Kouichi;
(Hitachinaka-shi, JP) ; KOGUCHI; Hayato;
(Hitachinaka-shi, JP) ; HIZONO; Takeshi; (Tokyo,
JP) ; EGAWA; Hiroaki; (Hitachinaka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HITACHI AUTOMOTIVE SYSTEMS, LTD. |
Hitachinaka-shi |
|
JP |
|
|
Assignee: |
HITACHI AUTOMOTIVE SYSTEMS,
LTD.
Hitachinaka-shi
JP
|
Family ID: |
50182754 |
Appl. No.: |
15/671991 |
Filed: |
August 8, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14422938 |
Feb 20, 2015 |
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PCT/JP2012/072138 |
Aug 31, 2012 |
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15671991 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 2/024 20130101;
H01M 2220/20 20130101; H01M 2/0217 20130101; H01M 2/0439 20130101;
H01M 10/0587 20130101; H01M 2/0473 20130101; Y02E 60/10 20130101;
H01M 2/0426 20130101; H01M 10/0431 20130101 |
International
Class: |
H01M 2/02 20060101
H01M002/02; H01M 2/04 20060101 H01M002/04 |
Claims
1. A prismatic secondary battery comprising: a battery case in a
prismatic shape which includes a bottom wall part in a rectangular
shape forming a bottom, a side wall part in a prismatic tubular
shape forming a side wall, and an opening part being open upward at
an upper end of the side wall part; and a battery cover which is
welded to the upper end of the side wall part of the battery case
and seals the opening part, wherein: the battery cover includes a
blockage part which blocks the opening part, a convex part which is
positioned outside the blockage part, and a contact part which is
positioned outside the convex part; the side wall part includes a
step part on an upper end of the side wall; the step part contact
with the contact part; the convex part is arranged adjacent to the
step portion.
2. The prismatic secondary battery according claim 1, wherein the
convex part is arranged adjacent to a welding part.
Description
TECHNICAL FIELD
[0001] The present invention relates to a prismatic secondary
battery used for the purpose of vehicle installation, for
example.
BACKGROUND ART
[0002] Development of lithium-ion secondary batteries with high
energy density serving as power sources of battery electric
vehicles and other types of vehicles has been promoted
energetically in recent years. In secondary batteries for vehicle
installation, higher electric current flows through the battery in
comparison with secondary batteries for cellular phones or other
devices. Therefore, prevention of the mixing of water into the
battery and the leakage of the electrolyte is highly essential and
the sealability of the battery is a critical issue. Patent Document
1, for example, discloses a prismatic secondary battery in which a
winding electrode is stored in a battery case, the electrolyte is
injected into the battery case, and thereafter the battery housing
is hermetically sealed up with a cover welded to the battery case.
That in Patent Document 2 has a structure in which a convex part is
formed on the back side of the cover.
PRIOR ART LITERATURE
Patent Documents
[0003] Patent Document 1: JP-2010-97770-A [0004] Patent Document 2:
JP-2004-31027-A
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0005] In Patent Document 1, the battery case and the battery cover
are joined together by means of welding in order to hermetically
seal up the battery housing. The joining by means of welding
increases the reliability of the hermetic sealing. However, a
spatter caused in the welding can mix into the inside of the
battery as a metallic foreign matter and contribute to a minute
short circuit.
[0006] It is therefore an object of the present invention is to
prevent the mixing of metallic foreign matters into the battery due
to the spatter in the welding of the battery cover to the metallic
battery case and thereby provide a prismatic secondary battery with
high reliability.
Means for Solving the Problem
[0007] A prismatic secondary battery according to the present
invention achieving the above object comprises: a battery case in a
prismatic shape which includes a bottom wall part in a rectangular
shape, a side wall part in a prismatic tubular shape extending up
from the bottom wall part, and an opening part being open upward at
an upper end of the side wall part; and a battery cover which is
welded to the upper end of the side wall part of the battery case
and seals up the opening part. The battery cover has a convex part
which projects toward an inside of the battery case, faces an inner
surface of the side wall part of the battery case, and extends
continuously along an entire periphery of the side wall part. Cover
thickness at a contact part which is in contact with the upper end
of the side wall part of the battery case at a position outside the
convex part is greater than 1/2 of cover thickness at a blockage
part blocking up the opening part at a position inside the convex
part and is less than the cover thickness at the blockage part.
Effect of the Invention
[0008] According to the present invention, the mixing of metallic
foreign matters into the battery due to the spatter can be
prevented at the time of the welding of the battery cover to the
battery case and a prismatic secondary battery with high
reliability can be provided. Other objects, configurations and
advantages will be clarified in the following description of
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is an external perspective view of a prismatic
secondary battery according to a first embodiment of the present
invention.
[0010] FIG. 2 is an exploded perspective view of the prismatic
secondary battery according to the first embodiment.
[0011] FIG. 3 is an exploded perspective view showing a power
generation element of which a part is opened and extended.
[0012] FIG. 4 is a perspective view showing a cover according to
the first embodiment viewed from a lower surface's side.
[0013] FIG. 5 is a plan view showing the lower surface of the cover
according to the first embodiment.
[0014] FIG. 6 is a cross-sectional view showing a joint part where
a battery case and the cover are joined together.
[0015] FIG. 7 is a cross-sectional view showing a state in which
the battery case and the cover in FIG. 6 are separated from each
other.
[0016] FIG. 8 is a cross-sectional view showing a joint part where
a battery case and a cover of a prismatic secondary battery in
accordance with a second embodiment of the present invention are
joined together.
[0017] FIG. 9 is a cross-sectional view showing a state in which
the battery case and the cover in FIG. 8 are separated from each
other.
[0018] FIG. 10 is a cross-sectional view for explaining a
conventional example.
[0019] FIG. 11 is a cross-sectional view for explaining another
conventional example.
MODE FOR CARRYING OUT THE INVENTION
[0020] With reference to the drawings, a description will be given
in detail of preferred embodiments of the present invention.
[0021] A prismatic secondary battery according to an embodiment of
the present invention comprises: a battery case in a prismatic
shape which includes a bottom wall part in a rectangular shape, a
side wall part in a prismatic tubular shape extending up from the
bottom wall part, and an opening part being open upward at an upper
end of the side wall part; and a battery cover which is welded to
the upper end of the side wall part of the battery case and seals
up the opening part. The battery cover has a convex part which
projects toward the inside of the battery case, faces an inner
surface of the side wall part of the battery case, and extends
continuously along the entire periphery of the side wall part.
Cover thickness at a contact part which is in contact with the
upper end of the side wall part of the battery case at a position
outside the convex part is greater than 1/2 of cover thickness at a
blockage part blocking up the opening part at a position inside the
convex part and is less than the cover thickness at the blockage
part.
First Embodiment
[0022] FIG. 1 is an external perspective view of a prismatic
secondary battery according to a first embodiment of the present
invention.
[0023] The prismatic secondary battery C1 comprises a battery case
1 and a cover (battery cover) 6. A power generation element 3 (see
FIG. 2) is stored in the battery case 1 and an opening part 1a of
the battery case 1 is sealed up with the cover 6. The cover 6 is
joined to the battery case 1 by laser welding. A hermetically
sealed battery container is formed by the battery case 1 and the
cover 6. The cover 6 is equipped with a positive external terminal
8A and a negative external terminal 8B. Via the positive external
terminal 8A and the negative external terminal 8B, the power
generation element 3 (see FIG. 2) is electrically charged or
supplies electric power to an external load. The cover 6 is
integrally provided with a gas release vent 10. When the pressure
in the battery container rises, the gas release vent 10 opens,
releases gas from inside, and reduces the pressure in the battery
container, by which the safety of the prismatic secondary battery
C1 is secured.
[0024] Next, the configuration inside the battery case 1 of the
prismatic secondary battery C1 will be described below with
reference to FIG. 2.
[0025] FIG. 2 is an exploded perspective view of the prismatic
secondary battery according to the present embodiment.
[0026] The battery case 1 of the prismatic secondary battery C1 is
formed in a so-called prismatic shape. The battery case 1 includes
a bottom wall part 22 in a rectangular shape, a side wall part 21
in a prismatic tubular shape extending up from the bottom wall part
22, and an opening part 1a being open upward at the upper end of
the side wall part 21. The battery case 1 stores the power
generation element 3 via an insulating sheet 2. The power
generation element 3 is an electrode assembly that is formed by a
positive electrode body and a negative electrode body being flatly
wound while a separator is placed between the positive and negative
electrode bodies. At both edges of the power generation element 3
in the direction of the winding axis, electrode foil exposed parts
31c and 32c not coated with either a positive electrode active
material mix or a negative electrode active material mix are
formed.
[0027] Since the power generation element 3 is flatly wound, the
power generation element 3 includes a pair of curved parts having
semicircular cross-sectional shapes and facing each other and a
flat part continuously formed between the pair of curved parts. The
power generation element 3 is inserted into the battery case 1 from
one of the curved parts so that the winding axis direction of the
power generation element 3 coincides with the width direction of
the battery case 1. In this state, the other curved part of the
power generation element 3 is situated at the upper opening of the
battery case 1.
[0028] At least part of a positive electrode connection part 31d,
serving as the aforementioned flat part and electrode foil exposed
part of the power generation element 3, is bundled and formed into
a shape like a flat plate, overlaid on an end of a positive
electrode current collector plate (current collector terminal) 4A,
and connected to the end of the positive electrode current
collector plate 4A. Similarly, at least part of a negative
electrode connection part 32d, serving as the aforementioned flat
part and electrode foil exposed part of the power generation
element 3, is bundled and formed into a shape like a flat plate,
overlaid on an end of a negative electrode current collector plate
(current collector terminal) 4B, and connected to the end of the
negative electrode current collector plate 4B.
[0029] The other ends of the positive electrode current collector
plate 4A and the negative electrode current collector plate 4B are
connected to the positive external terminal 8A and the negative
external terminal 8B, respectively. The positive electrode current
collector plate 4A is equipped with current interruption means
(fuse) 44 for interrupting the electric current when excessive
current flows. For example, the current interruption means 44 is
formed by narrowing a part of the positive electrode current
collector plate 4A so that the narrowed part is blown out (melted
and disconnected) by the excessive current to separate the positive
electrode current collector plate 4A into two parts: the power
generation element 3's side and the positive external terminal 8A's
side. It should be noted while the current interruption means 44 is
arranged in the positive electrode current collector plate 4A in
the present embodiment, the current interruption means 44 may also
be arranged in the negative electrode current collector plate 4B or
in both the positive electrode current collector plate 4A and the
negative electrode current collector plate 4B. The configuration of
the current interruption means 44 is not limited to the above
example as long as the electric current can be interrupted in case
of an abnormality.
[0030] For the purpose of the electrical insulation of the positive
electrode current collector plate 4A, the negative electrode
current collector plate 4B, the positive external terminal 8A, and
the positive external terminal 8B from the cover 6, the cover 6 is
provided with gaskets 5 and insulating plates 7. An electrolyte is
filled into the battery case 1 through an injection vent 9.
Thereafter, a vent plug 11 is welded to the cover 6 by laser
welding to seal up the injection vent 9, by which the prismatic
secondary battery C1 is sealed hermetically.
[0031] Aluminum or aluminum alloy serving as metallic material is
used for the material of the battery case 1 and the cover 6.
Aluminum or aluminum alloy is used also as the material of the
positive electrode current collector plate 4A and the positive
external terminal 8A. Copper or copper alloy is used as the
material of the negative electrode current collector plate 4B and
the negative external terminal 8B.
[0032] Each of the positive external terminal 8A and the negative
external terminal 8B has a welding joint part to be joined to a bus
bar (not shown) or the like by means of welding. The welding joint
part is in a rectangular prism shape protruding upward from the
cover 6. The lower surface of the welding joint part is opposed to
the surface of the cover 6. The upper surface of the welding joint
part extends in parallel with the cover 6 at a certain height
position.
[0033] The lower surface of the welding joint part of the positive
external terminal 8A is integrally provided with a positive
electrode connection part 12A for connecting the positive external
terminal 8A to the positive electrode current collector plate 4A.
The lower surface of the welding joint part of the negative
external terminal 8B is integrally provided with a negative
electrode connection part 12B for connecting the negative external
terminal 8B to the negative electrode current collector plate
4B.
[0034] The positive electrode connection part 12A is formed in a
cylindrical shape protruding from the lower surface of the positive
external terminal 8A so that its tip end can be inserted into a
through hole 6A of the cover 6. The positive electrode connection
part 12A protrudes through the cover 6 to reach the inside of the
battery case 1 from a basal part 41A of the positive electrode
current collector plate 4A. The tip end of the positive electrode
connection part 12A is crimped, by which the positive external
terminal 8A and the positive electrode current collector plate 4A
are integrally fixed on the cover 6. The gasket 5 is arranged
between the cover 6 and the positive external terminal 8A while the
insulating plate 7 is disposed between the cover 6 and the positive
electrode current collector plate 4A. Similarly, the negative
electrode connection part 12B is formed in a cylindrical shape
protruding from the lower surface of the negative external terminal
8B so that its tip end can be inserted into a through hole 6B of
the cover 6. The negative electrode connection part 12B protrudes
through the cover 6 to reach the inside of the battery case 1 from
a basal part 41B of the negative electrode current collector plate
4B. The tip end of the negative electrode connection part 12B is
crimped, by which the negative external terminal 8B and the
negative electrode current collector plate 4B are integrally fixed
on the cover 6. The gasket 5 is arranged between the cover 6 and
the negative external terminal 8B while the insulating plate 7 is
disposed between the cover 6 and the negative electrode current
collector plate 4B.
[0035] The positive electrode current collector plate 4A has the
basal part 41A in a rectangular plate-like shape which is arranged
to face the lower surface of the cover 6 and a connection end part
42A which is bent at a lateral edge of the basal part 41A, extended
toward the bottom of the battery case 1 along a wide surface of the
battery case 1, overlaid on the positive electrode connection part
31d of the power generation element 3 to face the positive
electrode connection part 31d, and connected to the positive
electrode connection part 31d. The basal part 41A is formed to have
an opening 43A into which the positive electrode connection part
12A is inserted. Similarly, the negative electrode current
collector plate 4B has the basal part 41B in a rectangular
plate-like shape which is arranged to face the lower surface of the
cover 6 and a connection end part 42B which is bent at a lateral
edge of the basal part 41B, extended toward the bottom of the
battery case 1 along the wide surface of the battery case 1,
overlaid on the negative electrode connection part 32d of the power
generation element 3 to face the negative electrode connection part
32d, and connected to the negative electrode connection part 32d.
The basal part 41B is formed to have an opening 43B into which the
negative electrode connection part 12B is inserted.
[0036] FIG. 3 is an exploded perspective view showing the power
generation element while opening and extending a part of the power
generation element.
[0037] The power generation element 3 is an electrode assembly that
is formed by a positive electrode body 31 and a negative electrode
body 32 being flatly wound while a separator 33 is placed between
the positive and negative electrode bodies 31 and 32. The positive
electrode body 31 is formed by coating both sides of positive
electrode foil 31a with a positive electrode compound 31b. The
positive electrode body 31 has a positive electrode foil exposed
part 31c (non-coated part) at one edge of the positive electrode
foil 31a in regard to the width direction.
[0038] The negative electrode body 32 is formed by coating both
sides of negative electrode foil 32a with a negative electrode
compound 32b. The negative electrode body 32 has a negative
electrode foil exposed part 32c (non-coated part) at one edge of
the negative electrode foil 32a (opposite to the aforementioned
edge of the positive electrode foil 31a) in regard to the width
direction. The positive electrode body 31 and the negative
electrode body 32 are wound together in a way that the positive
electrode foil exposed part 31c and the negative electrode foil
exposed part 32c are situated on opposite sides in the winding axis
direction.
[0039] FIG. 4 is a perspective view showing the cover viewed from
the lower surface's side (i.e., viewed from the inside of the
secondary battery). FIG. 5 is a plan view showing the lower surface
of the cover facing the inside of the secondary battery.
[0040] The cover 6 is in a shape like a flat plate in a size big
enough to block the opening part 1a of the battery case 1. The
cover 6 is provided with the through holes 6A and 6B, the injection
vent 9 and the gas release vent 10. The cover 6 has a blockage part
54 and a contact part 52. The blockage part 54 extends at a
substantially constant cover thickness to block the opening part
1a. The contact part 52, formed outside the blockage part 54 at a
smaller cover thickness than the blockage part 54, extends along
the entire outer peripheral edge of the cover 6 so as to contact
the edge part (upper end) of the side wall part 21 of the battery
case 1.
[0041] Inside the contact part 52, a convex part 51 is formed to
project toward the inside of the battery case 1, face the inner
surface of the side wall part 21 of the battery case 1, and extend
continuously along the entire periphery of the side wall part 21.
Further, a groove 53 is formed inside the convex part 51. The
groove 53 is concavely formed in the blockage part 54.
[0042] FIG. 6 is a cross-sectional view showing a joint part where
the battery case and the cover are joined together. FIG. 7 is a
cross-sectional view showing a state in which the battery case and
the cover in FIG. 6 are separated from each other.
[0043] The contact part 52 of the cover 6, while being placed in
contact with the edge part of the side wall part 21 of the battery
case 1, is subject to laser welding from the outside of the battery
case 1, that is, from the side surface (left side in FIG. 6). A
weld part 61 is then formed between the contact part 52 of the
cover 6 and the edge part of the side wall part 21 of the battery
case 1, by which the cover 6 and the battery case 1 are joined
together. The weld part 61 is formed continuously along the entire
outer peripheral edge of the cover 6 to seal up the opening part of
the battery case 1.
[0044] The convex part 51 faces the inner surface of the side wall
part 21 of the battery case 1. In this state, a gap can occur
between the convex part 51 and the side wall part 21 of the battery
case 1 since the dimension of the convex part 51, in consideration
of the dimensional tolerance, has been set to be smaller than the
internal dimension of the side wall part 21 of the battery case 1
so that the convex part 51 can be fit in the side wall part 21
without much difficulty.
[0045] The contact part 52, the convex part 51 and the groove 53
along the entire periphery of the cover 6 can be formed with ease
by means of press work. The convex part 51 can be formed by use of
excess volume caused in the formation of the contact part 52 and
the groove 53 both having smaller cover thicknesses than the
blockage part 54. The convex part 51 is formed so that its
projection height from the contact part 52 toward the inside of the
battery case 1 equals a prescribed height L. With this
configuration, the length or distance for which the cover 6 and the
edge part of the side wall part 21 of the battery case 1 face each
other can be increased by the height L.
[0046] FIG. 10 is a cross-sectional view corresponding to FIG. 6,
showing a comparative example for explaining the operational
advantages of the present embodiment.
[0047] In the prismatic secondary battery shown in FIG. 10 as a
comparative example, a cover 106 is formed in a shape like a flat
plate having a constant thickness Tc. A contact part 152 of the
cover 106 is set on an edge part of a side wall part 121 of a
battery case 101 before laser welding is performed between the side
wall part 121 and the contact part 152 from the side. In this case,
the spatter S caused by the laser welding can pass through a gap
between the edge part of the side wall part 121 and the contact
part 152 of the cover 106 and then drop to the inside of the
battery case 101.
[0048] In particular, in a case where the end depth of a weld part
161 is increased in order to securely seal up the secondary
battery, the length H of the gap between the edge part of the side
wall part 121 and the contact part 152 of the cover 106 would
decrease along with the increase in the end depth of the weld part
161. The spatter S would easily enter the battery case 101 as a
result.
[0049] In contrast, in the present embodiment (see FIG. 6), the
cover 6 is provided with the convex part 51. Consequently, the
length of the gap formed between the cover 6 and the edge part of
the side wall part 21 of the battery case 1 is secured by the
length of the convex part 51. Therefore, if the edge part of the
side wall part 21 and the contact part 52 of the cover 6 are joined
together by laser welding from the outside of the battery case 1,
it will be possible to have the spatter actively adhere to an inner
wall surface 21a of the side wall part 21 or an opposing surface
51a of the convex part 51 and remain in the gap between the side
wall part 21 and the convex part 51. As a result, the spatter can
be effectively prevented from passing through the gap between the
edge part of the side wall part 21 and the contact part 52 of the
cover 6 and dropping to the inside of the battery case 1.
[0050] In the case of laser welding, increasing the end depth of
the weld part 61 would lead to a corresponding rise in the welding
width at the proximal end. Thus, in order to carry out the welding
deeper and seal up the secondary battery more securely, the contact
part 52 is required to have a certain cover thickness. In the
present embodiment, the cover thickness Tu of the contact part 52
is set greater than 1/2 of the cover thickness Tt of the blockage
part 54 and is less than the cover thickness Tt of the blockage
part 54 (Tt/2<Tu<Tt), allowing it to secure the welding area
of the weld part 61 as wide as possible and to increase the depth
of the weld part 61.
[0051] Increasing the depth of the weld part 61 adversely would
lead to a decrease in the length H of the gap between the edge part
of the side wall part 21 and the contact part 52 of the cover 6. In
the present embodiment, however, the cover 6 is provided with the
convex part 51. The length of the gap formed between the cover 6
and the edge part of the side wall part 21 of the battery case 1 is
secured by the height L of the convex part 51. Therefore, the
spatter caused by the laser welding can be effectively prevented
from passing through the gap between the edge part of the side wall
part 21 and the contact part 52 of the cover 6 and dropping to the
inside of the battery case 1. As described above, the mixing of
metallic foreign matters into the battery case 1 due to the spatter
can be prevented at the time of the laser welding of the cover 6 to
the battery case 1 performed from the outside of the battery case
1. Accordingly, a prismatic secondary battery C1 with high
reliability can be provided.
[0052] It should be noted that while an example in which the groove
53 is formed inside the convex part 51 has been described in the
above embodiment, the configuration of the cover 6 is not limited
to this example as long as the convex part 51 can be formed to have
a prescribed height. That is, the groove 53 is not a requisite.
Second Embodiment
[0053] Next, a second embodiment will be described below with
reference to FIGS. 8, 9 and 11.
[0054] FIG. 8 is a cross-sectional view showing a joint part where
a battery case and a cover of a prismatic secondary battery
according to a second embodiment of the present invention are
joined together. FIG. 9 is a cross-sectional view showing a state
in which the battery case and the cover in FIG. 8 are separated
from each other. Elements in FIGS. 8 and 9 equivalent to those in
the first embodiment are assigned the same reference characters as
in the first embodiment and detailed explanation thereof is omitted
for brevity.
[0055] Characteristic features of the present embodiment are as
follows: A step 23 is formed in the edge part of the side wall part
21 of the battery case 1. The battery case 1 is sealed up by
fitting the battery cover 6 in the side wall part 21 of the battery
case 1 and performing laser welding between the battery cover 6 and
the side wall part 21 from above the battery case 1.
[0056] The edge part of the side wall part 21 of the battery case 1
is formed to have the step 23. The step 23 is continuously formed
peripherally on the inner side of the edge part of the side wall
part 21. The contact part 52 of the cover 6 is placed in contact
with the step 23. The laser welding is performed between the edge
part of the side wall part 21 and the contact part 52 of the cover
6 from above (from the outside of the battery case 1). By the laser
welding, a weld part 62 is formed between the contact part 52 of
the cover 6 and the edge part of the side wall part 21 of the
battery case 1. The weld part 62 is formed continuously along the
entire outer periphery of the cover 6 to seal up the opening part
of the battery case 1.
[0057] The convex part 51 faces the inner side of the side wall
part 21 of the battery case 1 along the entire periphery. In this
state, a gap can occur between the convex part 51 and the side wall
part 21 of the battery case 1 since the dimension of the convex
part 51, in consideration of the dimensional tolerance, has been
set to be smaller than the internal dimension of the side wall part
21 of the battery case 1 so that the convex part 51 can be fit in
the side wall part 21 without much difficulty.
[0058] FIG. 11 is a cross-sectional view corresponding to FIG. 8,
showing a comparative example for explaining the advantages of the
present embodiment.
[0059] In the prismatic secondary battery shown in FIG. 11 as a
comparative example, a cover 106 is formed in a shape like a flat
plate having a constant thickness Tc. A contact part 152 of the
cover 106 is set on a step 123 in an edge part of a side wall part
121 and laser welding is performed between the side wall part 121
and the contact part 152 from above the cover 106. As a result, the
length for which the side wall part 121 and the contact part 152
face each other may not be long enough. And hence, the spatter S
caused by the laser welding can pass through a gap between the step
123 of the side wall part 121 and the contact part 152 of the cover
106 and then drop to the inside of the battery case 101.
[0060] In the laser welding, increasing the end depth of the weld
part 162 leads to a corresponding rise in the welding width at the
proximal end. Thus, the weld part 162 should be preferably situated
inward of the battery case 1 (right side in FIG. 11) in an
allowable range. This requires it to reduce the indent Ts of the
step 123 from the inner surface of the side wall part 121.
Consequently, the length of the gap between the edge part of the
side wall part 121 and the contact part 152 of the cover 6
decreases and the spatter S tends to enter the battery case 1.
[0061] In contrast, in the present embodiment, the cover 6 is
provided with the convex part 51 and because of it, the length of
the gap formed between the cover 6 and the edge part of the side
wall part 21 of the battery case 1 is ensured to be at least as
great as the length of the convex part 51 as shown in FIG. 8.
Therefore, when laser welding is performed between the edge part of
the side wall part 21 and the contact part 52 of the cover 6 from
the outside of the battery case 1, it will be possible to have the
spatter actively adhere to the side wall part 21 or the convex part
51 and remain in the gap between the side wall part 21 and the
convex part 51. Accordingly, the spatter caused by the laser
welding can be effectively prevented from passing through the gap
between the edge part of the side wall part 21 and the contact part
52 of the cover 6 and dropping to the inside of the battery case
1.
[0062] As described above, the mixing of metallic foreign matters
into the battery due to the spatter can be prevented at the time of
the laser welding of the cover 6 to the battery case 1 performed
from the outside of the battery case 1 and a prismatic secondary
battery C1 with high reliability can be provided.
[0063] The present invention is not limited to the above
embodiments and may embrace varieties of modifications without
departing from the spirit of the invention. The embodiments, for
example, have only been described in detail for a better
understanding of the invention and are therefore not necessarily
limited to the configurations containing all described constituent
elements. In addition, part of the configuration of a certain
embodiment may be replaced by the configuration of another
embodiment and the configuration of a certain embodiment may be
added to the configuration of another embodiment. Furthermore, part
of the configuration of one of the embodiments may be added to,
deleted from, and/or replaced by the other embodiments.
REFERENCE NUMERALS
[0064] 1 battery case [0065] 1a opening part [0066] 3 power
generation element (electrode assembly) [0067] 4A positive
electrode current collector plate (current collector terminal)
[0068] 4B negative electrode current collector plate [0069] 6 cover
(battery cover) [0070] 8A positive external terminal (external
terminal) [0071] 8B negative external terminal [0072] 12A positive
electrode connection part [0073] 12B negative electrode connection
part [0074] 21 side wall part [0075] 22 bottom wall part [0076] 51
convex part [0077] 52 contact part [0078] 53 groove [0079] 54
blockage part [0080] 61, 62 weld part [0081] C1 prismatic secondary
battery
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