U.S. patent application number 15/626757 was filed with the patent office on 2017-12-28 for battery and manufacturing method of the same.
The applicant listed for this patent is SEMICONDUCTOR ENERGY LABORATORY CO., LTD.. Invention is credited to Ryota TAJIMA, Kensuke YOSHIZUMI.
Application Number | 20170373285 15/626757 |
Document ID | / |
Family ID | 60677947 |
Filed Date | 2017-12-28 |
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United States Patent
Application |
20170373285 |
Kind Code |
A1 |
TAJIMA; Ryota ; et
al. |
December 28, 2017 |
BATTERY AND MANUFACTURING METHOD OF THE SAME
Abstract
To provide a battery capable of changing in shape safely. To
provide a battery capable of repeatedly bent. The battery includes
a first lead, a second lead, a first current collector, and a
second current collector. The first current collector includes a
first portion bonded to the first lead and a second portion coated
with a first active material. The second current collector includes
a third portion bonded to the second lead and a fourth portion
coated with a second active material. The first lead, the second
portion, and the fourth portion overlap with each other in a
portion. The second lead, the second portion, and the fourth
portion overlap with each other in a portion.
Inventors: |
TAJIMA; Ryota; (Isehara,
JP) ; YOSHIZUMI; Kensuke; (Isehara, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEMICONDUCTOR ENERGY LABORATORY CO., LTD. |
Atsugi-shi |
|
JP |
|
|
Family ID: |
60677947 |
Appl. No.: |
15/626757 |
Filed: |
June 19, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 2/266 20130101;
H01M 2/0275 20130101; Y02E 60/10 20130101; H01M 10/0525 20130101;
H01M 4/661 20130101; H01M 10/0585 20130101; H01M 2/0207 20130101;
H01M 2220/30 20130101 |
International
Class: |
H01M 2/02 20060101
H01M002/02; H01M 10/0525 20100101 H01M010/0525; H01M 10/0585
20100101 H01M010/0585 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 2016 |
JP |
2016-123209 |
Claims
1. A battery comprising: a first lead; a second lead; a first
current collector; and a second current collector, wherein the
first current collector includes a first portion bonded to the
first lead and a second portion coated with a first active
material, wherein the second current collector includes a third
portion bonded to the second lead and a fourth portion coated with
a second active material, wherein the first lead, the second
portion, and the fourth portion overlap with each other in a
portion, and wherein the second lead, the second portion, and the
fourth portion overlap with each other in a portion.
2. The battery according to claim 1, further comprising: an
insulating fixing member, wherein the first lead, the first current
collector, and the second current collector are fixed by the
insulating fixing member in a portion where the first lead, the
first current collector, and the second current collector overlap
with each other, and wherein the second lead, the first current
collector, and the second current collector are fixed by the
insulating fixing member in a portion where the second lead, the
first current collector, and the second current collector overlap
with each other.
3. The battery according to claim 1, wherein the first current
collector is folded back between the first portion and the second
portion, wherein the first lead, the first portion, and the second
portion overlap with each other in a portion, wherein the second
current collector is folded back between the third portion and the
fourth portion, and wherein the second lead, the third portion, and
the fourth portion overlap with each other in a portion.
4. The battery according to claim 3, wherein the first current
collector is folded back such that a surface of the first current
collector faces outward, the surface of the first current collector
being bonded to the first lead, and wherein the second current
collector is folded back such that a surface of the second current
collector faces outward, the surface of the second current
collector being bonded to the second lead.
5. The battery according to claim 3, further comprising: a first
insulating member; and a second insulating member, wherein the
first portion and the second portion overlap with each other with
the first insulating member positioned therebetween, and wherein
the third portion and the fourth portion overlap with each other
with the second insulating member positioned therebetween.
6. The battery according to claim 5, wherein the first insulating
member covers the first portion and the first lead, and wherein the
second insulating member covers the third portion and the second
lead.
7. The battery according to claim 1, further comprising: an
exterior body, wherein the exterior body has a film-like shape and
is folded in two such that the first current collector and the
second current collector are sandwiched by the exterior body,
wherein the exterior body includes a pair of first seal portions by
which the first current collector and the second current collector
are sandwiched and a second seal portion overlapping with the first
lead and the second lead, and wherein the exterior body has a wave
shape almost parallel to the second seal portion in a region
overlapping with the first current collector and the second current
collector.
8. The battery according to claim 7, wherein the first seal
portions and the second seal portion are flat without the wave
shape.
9. The battery according to claim 7, wherein a distance between
each of the first seal portions and an end portion of the first
current collector or an end portion of the second current collector
is 0.8 times or more and 3.0 times or less as large as a thickness
of a stack including the first current collector and the second
current collector.
10. The battery according to claim 7, wherein a difference between
a distance between the pair of first seal portions and a width of
the first current collector or a width of the second current
collector is 1.6 times or more and 6.0 times or less as large as a
thickness of a stack including the first current collector and the
second current collector.
11. A method for manufacturing a battery including a first current
collector, a second current collector, a first lead, and a second
lead, comprising: a first step of stacking the first current
collector and the second current collector, a second step of
bonding the first lead to the first current collector and bonding
the second lead to the second current collector, and a third step
of fixing the first current collector, the second current
collector, the first lead, and the second lead by a fixing
member.
12. The method for manufacturing a battery according to claim 11,
further comprising: a fourth step of folding back a part of the
first current collector and a part of the second current collector
between the second step and the third step.
13. The method for manufacturing a battery according to claim 12,
further comprising: a fifth step of stacking a plurality of first
current collectors and a plurality of second current collectors
instead of the first step, wherein, in the fifth step, the
plurality of first current collectors are stacked such that
positions of the plurality of first current collectors are shifted
from each other, and the plurality of second current collectors are
stacked such that positions of the plurality of second current
collectors are shifted from each other.
14. A battery comprising: a current collector including: a first
portion bonded to a lead in a bonding portion; and a second portion
coated with an active material, wherein the first portion is bent
such that the bonding portion overlaps with the second portion.
15. The battery according to claim 14, wherein the battery is a
secondary battery.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] One embodiment of the present invention relates to a
battery. One embodiment of the present invention relates to a
bendable battery. One embodiment of the present invention relates
to an inside structure of a battery.
[0002] Note that one embodiment of the present invention is not
limited to the above technical field. Examples of the technical
field of one embodiment of the present invention disclosed in this
specification and the like include a semiconductor device, a
display device, a light-emitting device, a power storage device, a
memory device, an electronic device, a lighting device, an input
device, an input/output device, a driving method thereof, and a
manufacturing method thereof.
2. Description of the Related Art
[0003] Portable information terminal devices typified by
smartphones and tablet terminals have been actively developed. Such
electronic devices are required to be lightweight and compact, for
example.
[0004] In recent years, wearable electronic devices (also referred
to as wearable devices) especially have been under active
development. Examples of wearable devices include a watch-type
device worn on an arm, a glasses-like or a goggle-type device worn
on a head, and a necklace-type device worn on a neck. For example,
a watch-type device includes a small-sized display instead of a
conventional watch dial to provide the user with various
information in addition to the time. Such wearable devices have
attracted attention to the medical use, the use for self-health
management, or the like and have been increasingly put into
practical use.
[0005] Mobile devices include secondary batteries that are capable
of being repeatedly charged and discharged, in many cases. Wearable
devices particularly include small-sized secondary batteries; thus,
secondary batteries should be lightweight and compact and should be
capable of being used for a long time.
[0006] Patent Document 1 discloses a highly flexible battery using
a thin, pliant film-like material as an exterior body.
REFERENCE
Patent Document
[0007] [Patent Document 1] PCT International Publication No.
2012/140709
SUMMARY OF THE INVENTION
[0008] A battery occupies a large volume in a mobile device. When a
battery is capable of changing in shape, for example, is bendable,
the battery can be disposed in limited space in a housing, leading
to downsizing of a device. Furthermore, in a conventional wearable
device, it has been difficult to dispose a battery in a movable
portion. When a battery is capable of repeatedly changing in shape,
a device with a more sophisticated design can be obtained.
[0009] A secondary battery is generally covered with a hard
exterior body even in the case where a film is used for the
exterior body because a secondary battery might cause heat
generation or catch fire when its exterior body is damaged.
However, this structure has a problem in that change in shape of
the secondary battery such as bending is not assumed and the place
where the secondary battery is provided is limited in the case of
being mounted on an electronic device.
[0010] In addition, there has been a safety problem with a
conventional secondary battery. That is, there is a concern that,
when a conventional secondary battery is bent repeatedly, a short
circuit between electrodes in its exterior body, damage to the
electrodes themselves, or the like may be caused as well as damage
to the exterior body.
[0011] An object of one embodiment of the present invention is to
provide a battery that is capable of changing in shape safely. An
object of one embodiment of the present invention is to provide a
battery that can be bent repeatedly.
[0012] An object of one embodiment of the present invention is to
provide a battery with high capacity per unit volume. An object of
one embodiment of the present invention is to provide a highly
reliable battery.
[0013] Note that the descriptions of these objects do not disturb
the existence of other objects. In one embodiment of the present
invention, there is no need to achieve all the objects. Other
objects can be derived from the description of the specification
and the like.
[0014] One embodiment of the present invention is a battery
including a first lead, a second lead, a first current collector,
and a second current collector. The first current collector
includes a first portion bonded to the first lead and a second
portion coated with a first active material. The second current
collector includes a third portion bonded to the second lead and a
fourth portion coated with a second active material. The first
lead, the second portion, and the fourth portion overlap with each
other in a portion. The second lead, the second portion, and the
fourth portion overlap with each other in a portion.
[0015] In the above embodiment, it is preferable that an insulating
fixing member be included. In this case, it is preferable that the
first lead, the first current collector, and the second current
collector be fixed by the fixing member in a portion where the
first lead, the first current collector, and the second current
collector overlap with each other and the second lead, the first
current collector, and the second current collector be fixed by the
fixing member in a portion where the second lead, the first current
collector, and the second current collector overlap with each
other.
[0016] In the above embodiment, it is preferable that the first
current collector be folded back between the first portion and the
second portion and the first lead, the first portion, and the
second portion overlap with each other in a portion. It is
preferable that the second current collector be folded back between
the third portion and the fourth portion and the second lead, the
third portion, and the fourth portion overlap with each other in a
portion.
[0017] In the above embodiment, it is preferable that the first
current collector be folded back such that a surface of the first
current collector that is bonded to the first lead faces outward
and the second current collector be folded back such that a surface
of the second current collector that is bonded to the second lead
faces outward.
[0018] In the above embodiment, it is preferable that a first
insulating member and a second insulating member be included. In
this case, it is preferable that the first portion and the second
portion overlap with each other with the first insulating member
positioned therebetween and the third portion and the fourth
portion overlap with each other with the second insulating member
positioned therebetween. In this case, it is preferable that the
first insulating member cover the first portion and the first lead
and the second insulating member cover the third portion and the
second lead.
[0019] In the above embodiment, it is preferable that an exterior
body be included. In this case, it is preferable that the exterior
body have a film-like shape and be folded in two such that the
first current collector and the second current collector are
sandwiched by the exterior body. It is preferable that the exterior
body include a pair of first seal portions by which the first
current collector and the second current collector are sandwiched
and a second seal portion overlapping with the first lead and the
second lead. It is preferable that the exterior body have a wave
shape almost parallel to the second seal portion in a region
overlapping with the first current collector and the second current
collector.
[0020] In the above embodiment, it is preferable that the first
seal portions and the second seal portion be flat without the wave
shape.
[0021] In the above embodiment, it is preferable that a distance
between the first seal portion and an end portion of the first
current collector or an end portion of the second current collector
be 0.8 times or more and 3.0 times or less as large as a thickness
of a stack including the first current collector and the second
current collector.
[0022] In the above embodiment, it is preferable that a difference
between a distance between the pair of first seal portions and a
width of the first current collector or a width of the second
current collector be 1.6 times or more and 6.0 times or less as
large as a thickness of a stack including the first current
collector and the second current collector.
[0023] Another embodiment of the present invention is a method for
manufacturing a battery including a first current collector, a
second current collector, a first lead, and a second lead. The
method includes a first step of stacking the first current
collector and the second current collector, a second step of
bonding the first lead to the first current collector and bonding
the second lead to the second current collector, and a third step
of fixing the first current collector, the second current
collector, the first lead, and the second lead by a fixing
member.
[0024] In the above embodiment, it is preferable that a fourth step
of folding back a part of the first current collector and a part of
the second current collector be included between the second step
and the third step.
[0025] In the above embodiment, it is preferable that a fifth step
of stacking a plurality of first current collectors and a plurality
of second current collectors be included instead of the first step.
In the fifth step, the plurality of first current collectors are
stacked such that positions of the plurality of first current
collectors are shifted from each other, and the plurality of second
current collectors are stacked such that positions of the plurality
of second current collectors are shifted from each other.
[0026] According to one embodiment of the present invention, a
battery that is capable of changing its shape safely can be
provided. Furthermore, a battery that can be bent repeatedly can be
provided. Furthermore, a battery with high capacity per unit volume
can be provided. Furthermore, a highly reliable battery can be
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a flow chart of a manufacturing method of a
battery according to one embodiment.
[0028] FIGS. 2A and 2B show current collectors according to one
embodiment.
[0029] FIGS. 3A to 3C illustrate a manufacturing method of a
battery according to one embodiment.
[0030] FIGS. 4A to 4D illustrate a manufacturing method of a
battery according to one embodiment.
[0031] FIGS. 5A to 5C illustrate a manufacturing method of a
battery according to one embodiment.
[0032] FIGS. 6A to 6C illustrate a manufacturing method of a
battery according to one embodiment.
[0033] FIGS. 7A and 7B illustrate a manufacturing method of a
battery according to one embodiment.
[0034] FIGS. 8A and 8B illustrate a manufacturing method of a
battery according to one embodiment.
[0035] FIG. 9 is a flow chart of a manufacturing method of a
battery according to one embodiment.
[0036] FIGS. 10A and 10B illustrate a manufacturing method of a
battery according to one embodiment.
[0037] FIGS. 11A and 11B illustrate a manufacturing method of a
battery according to one embodiment.
[0038] FIGS. 12A to 12C illustrate a manufacturing method of a
battery according to one embodiment.
[0039] FIGS. 13A, 13B1, 13B2, 13C, and 13D illustrate structure
examples of a battery according to one embodiment.
[0040] FIG. 14 illustrates a structure example of a battery
according to one embodiment.
[0041] FIGS. 15A to 15H illustrate electronic devices according to
one embodiment.
[0042] FIGS. 16A and 16B illustrate electronic devices according to
one embodiment.
[0043] FIGS. 17A to 17C are photographs showing the appearance
according to Example 1.
[0044] FIGS. 18A to 18C are photographs showing the appearance
according to Example 1.
[0045] FIGS. 19A to 19C are photographs showing the appearance
according to Example 1.
[0046] FIGS. 20A and 20B are photographs showing the appearance of
a battery according to Example 1.
[0047] FIGS. 21A to 21C are transmission X-ray images of a battery
according to Example 2.
[0048] FIGS. 22A to 22C are transmission X-ray images of a battery
according to Example 2.
[0049] FIGS. 23A to 23C are X-ray CT images of batteries according
to Example 2.
[0050] FIGS. 24A and 24B show charge and discharge characteristics
of a battery according to Example 2.
[0051] FIGS. 25A and 25B show charge and discharge characteristics
of a battery according to Example 2.
[0052] FIGS. 26A and 26B show charge and discharge characteristics
of a battery according to Example 2.
[0053] FIGS. 27A and 27B are transmission X-ray images of batteries
according to Example 2.
DETAILED DESCRIPTION OF THE INVENTION
[0054] Embodiment will be described in detail with reference to the
drawings. Note that the present invention is not limited to the
following description. It will be readily appreciated by those
skilled in the art that modes and details of the present invention
can be modified in various ways without departing from the spirit
and scope of the present invention. Thus, the present invention
should not be construed as being limited to the description in the
following embodiments.
[0055] Note that in structures of the present invention described
below, the same portions or portions having similar functions are
denoted by the same reference numerals in different drawings, and a
description thereof is not repeated. Further, the same hatching
pattern is applied to portions having similar functions, and the
portions are not especially denoted by reference numerals in some
cases.
[0056] Note that in each drawing described in this specification,
the size, the layer thickness, or the region of each component is
exaggerated for clarity in some cases. Therefore, the size, the
layer thickness, or the region is not limited to the illustrated
scale.
[0057] Note that in this specification and the like, ordinal
numbers such as "first," "second," and the like are used in order
to avoid confusion among components and do not limit the
number.
Embodiment 1
[0058] In this embodiment, a structure example of a battery of one
embodiment of the present invention and examples of a manufacturing
method thereof will be described.
[0059] A battery of one embodiment of the present invention has a
structure in which a first current collector and a second current
collector are stacked in a film-like exterior body. The first
current collector is one of a positive electrode current collector
and a negative electrode current collector, and the second current
collector is the other of the positive electrode current collector
and the negative electrode current collector. The battery includes
a pair of leads extending from the inside to the outside of the
exterior body. The leads are bonded to the first current collector
and the second current collector in the exterior body.
[0060] The first current collector and the second current collector
each include a projected portion (also referred to as a tab
portion) in a plan view. The tab portion includes a bonding portion
to which the lead is bonded (also referred to as a first portion).
The first current collector and the second current collector each
include a portion coated with an active material or the like (also
referred to as an electrode portion or a second portion).
[0061] In this specification and the like, a structure included in
the exterior body is also referred to as an electrode stack, a
stack, an electrode member, or the like. The electrode stack
includes at least the first current collector and the second
current collector. In some cases, the electrode stack includes the
lead bonded to the first current collector and the lead bonded to
the second current collector. The electrode stack may include a
separator and an electrolyte solution between the first current
collector and the second current collector. Note that the separator
is not necessarily provided in the case where a solid electrolyte
is used as the electrolyte solution.
[0062] The battery may include a plurality of first current
collectors and a plurality of second current collectors. The larger
the number of stacked current collectors is, the higher the
capacity of the battery can be.
[0063] In one embodiment of the present invention, the lead, the
second portion of the first current collector, and the second
portion of the second current collector include a portion fixed by
a fixing member. That is, the lead and the first current collector
are not only bonded to each other at a portion overlapping with the
tab portion but also fixed at a portion other than the tab portion.
Similarly, the lead and the second current collector are fixed at a
portion other than the tab portion.
[0064] Here, description is given of the case where the lead and
the first current collector are fixed only at the tab portion and
the lead and the second current collector are fixed only at the tab
portion. When the shape of the battery is changed, for example,
when the battery is bent repeatedly, the shapes of the first
current collector and the second current collector are also changed
repeatedly. In the first current collector and the second current
collector, the tab portions are not coated with an active material
layer and are thinner than the other portions. Furthermore, the
widths of the tab portions are narrower than the widths of the
second portions coated with active material layers. Therefore, the
tab portions have lower mechanical strength than the other portions
of the current collectors. In addition, portions at the root of the
projected tab portions also have comparatively lower mechanical
strength. Thus, by repeatedly changing the shape of the first
current collector and the second current collector, a crack is
likely to be formed in the tab portions of the first current
collector and the second current collector and the portions at the
root of the tab portions. In the worst case, fractures might be
formed in the tab portions.
[0065] In one embodiment of the present invention, the first
current collector or the second current collector is bonded to the
lead through the tab portion, and, in addition, the lead and the
second portion of the current collector are fixed by the fixing
portion, achieving a structure in which the tab portion hardly
changes in shape. Thus, a highly reliable battery can be obtained
in which a problem is hardly caused by change in shape such as
repeated bending.
[0066] It is preferable that the first current collector and the
second current collector not be fixed to each other in a portion
other than the portion fixed by the fixing member. In such a
structure, when the battery is bent, the positions of the current
collectors are shifted from each other while the portion fixed by
the fixing member serves as a fulcrum, thereby relieving stress
applied to the current collectors and preventing damage to the
current collectors. Furthermore, in such a structure, the battery
can be bent with weaker force.
[0067] In an example of a preferred structure, the tab portions of
the first current collector and the second current collector are
each folded back in a region between the bonding portion to which
the lead is bonded and the electrode portion coated with the active
material or the like. Furthermore, the parts of the tab portions
including the bonding portions (the first portions), the parts of
the leads, and the electrode portions (the second portions) of the
first current collector and the second current collector are fixed
by the fixing member.
[0068] It is preferable that each of the tab portions not be bent
sharply but be folded back in a curved state. For example, the tab
portion is preferably curved with a curvature radius that is 5
times or more, preferably 10 times or more, further preferably 20
times or more and less than 50 times as large as the thickness of
the tab portion. If the curvature radius in the folded-back portion
is less than 5 times as large as the thickness of the tab portion,
a fracture might be formed in the tab portion, depending on a
material of the current collector, when the tab portion is folded
back. If the curvature radius is too large (e.g., 50 times or
more), the thickness of the battery is increased.
[0069] In the case where the tab portion is folded back, there is a
concern that an electrical short circuit may be caused by contact
between the tab portion of one of the current collectors and the
other current collector of opposite polarity. Thus, it is
preferable that a surface of the part of the tab portion be
insulated. Specifically, it is preferable that an insulating member
be provided between the folded-back tab portion and the current
collector. In this case, it is further preferable that the part of
the tab portion be covered with the insulating member.
[0070] In the case where the tab portion is folded back, the tab
portion is preferably folded back such that the surface bonded to
the lead faces outward.
[0071] In another example of a preferred structure, the lead has a
shape extending from the portion bonded to the tab portion to the
electrode portion. The part of the lead and the electrode portion
may be fixed by the fixing member in a region where the part of the
lead and the electrode portion overlap with each other.
[0072] For the exterior body covering the first current collector
and the second current collector, a film in the shape of a periodic
wave in one direction is preferably used. The use of the wave shape
for the exterior body relieves stress when the exterior body is
bent because the form of the exterior body changes such that the
period and amplitude of the wave are changed, preventing the
exterior body from being damaged.
[0073] Furthermore, it is preferable that, in the exterior body,
one side is folded such that the first current collector and the
second current collector are sandwiched and portions (the other
three sides) surrounding the first current collector and the second
current collector are crimped to form seal portions. In this
structure, the part of the seal portions that overlaps with the
part of the lead can be referred to as a top seal portion, and the
other parts can be referred to as side seal portions.
[0074] In this structure, in the case where space is provided
between an end portion of the first current collector or the second
current collector in the width direction (the direction parallel to
the top seal portion) and the side seal portion, it is possible to
inhibit rubbing of the first current collector or the second
current collector against the exterior body at the time when the
battery is bent repeatedly. For example, the distance between the
first current collector or the second current collector and the
side seal portion is preferably 0.8 times or more, further
preferably 0.9 times or more, still further preferably 1.0 times or
more and preferably 3 times or less, further preferably 2 times or
less as large as the thickness of the stack in which the first
current collector and the second current collector are stacked.
Furthermore, for example, the difference between the distance
between the pair of side seal portions and the width of the first
current collector or the second current collector is preferably 1.6
times or more, further preferably 1.8 times or more, still further
preferably 2.0 times or more and preferably 4 times or less as
large as the thickness of the stack in which the first current
collector and the second current collector are stacked.
[0075] The exterior body is preferably shaped in advance (or
pre-shaped) to provide space between the end portion of the first
current collector or the second current collector in the width
direction and the side seal of the exterior body. The pre-shaping
is performed as follows, for example: before the side seal is
formed, the exterior body is shaped by pressing so that a gently
curved shape is formed between the position overlapping with the
end portion of the first current collector or the second current
collector of the exterior body in the width direction and the
portion in which the side seal is formed in a later step.
[0076] In the case where the pre-shaping is not performed, when the
side seal is formed, for example, a sharply bent portion might be
formed in the exterior body while the end portion of the first
current collector or the second current collector in the width
direction serves as a fulcrum. In contrast, in the case where the
above-described pre-shaping is performed on the exterior body, such
a sharply bent portion is hardly formed when the side seal is
formed. Thus, it is possible to inhibit rubbing of the first
current collector or the second current collector against the
exterior body more effectively at the time when the battery is bent
repeatedly, whereby the battery can be highly resistant to change
in shape such as repeated bending.
[0077] A more specific example is described below with reference to
drawings.
MANUFACTURING METHOD EXAMPLE 1
[0078] A manufacturing method example of a battery of one
embodiment of the present invention will be described below. FIG. 1
is a flow chart of a manufacturing method example of a battery
described below.
[Current Collector]
[0079] First, a current collector included in a battery of one
embodiment of the present invention is described. FIGS. 2A and 2B
are schematic top views of a current collector 11a and a current
collector 11b.
[0080] One of the current collector 11a and the current collector
11b serves as a positive electrode current collector, and the other
of the current collector 11a and the current collector 11b serves
as a negative electrode current collector. In this embodiment, the
current collector 11a is used as a negative electrode current
collector, and the current collector 11b is used as a positive
electrode current collector.
[0081] The current collector 11a includes a tab portion 21a and an
electrode portion 22a that serves as an electrode of the battery.
The tab portion 21a is a projected portion of the current collector
11a and has a narrower width than the electrode portion 22a. The
electrode portion 22a is coated with an active material layer
13a.
[0082] The current collector 11b includes a tab portion 21b and an
electrode portion 22b that serves as an electrode of the battery.
The tab portion 21b is a projected portion of the current collector
11b and has a narrower width than the electrode portion 22b. The
electrode portion 22b is coated with an active material layer
13b.
[0083] It is preferable that only one surface of each of the
current collectors 11a and 11b be coated with the active material
layer 13a or the active material layer 13b and the other surface
not be coated with the active material layer 13a or the active
material layer 13b.
[0084] It is preferable that a width Wa of the current collector
11a be different from a width Wb of the current collector 11b. In
FIGS. 2A and 2B, an example of the case where the width Wa of the
current collector 11a is wider than the width Wb of the current
collector 11b is shown.
[0085] The above is the description of the current collector.
[0086] Next, a method for manufacturing a battery is described with
reference to the flow chart shown in FIG. 1 and FIGS. 3A to 3C,
FIGS. 4A to 4D, FIGS. 5A to 5C, FIGS. 6A to 6C, FIGS. 7A and 7B,
and FIGS. 8A and 8B.
[Step S01]
[0087] First, a plurality of current collectors 11a and a plurality
of current collectors 11b are prepared and stacked such that their
positions are shifted from each other in the length direction.
[0088] FIG. 3A is a schematic perspective view showing the
stacked-layer structure. Note that the active material layer 13a
and the active material layer 13b are not shown below for
clarity.
[0089] In FIG. 3A, an example of the case where four current
collectors 11a and four current collectors 11b are used is shown.
Two current collectors 11a are provided on the outer side. On the
inner side of the two current collectors 11a, a pair of current
collectors 11b and a pair of current collectors 11a are alternately
provided. The pair of current collectors 11a is provided such that
the surfaces of the pair of current collectors 11a that are
opposite to the surfaces coated with the active material layers 13a
(not shown) are in contact with each other. Similarly, the pair of
current collectors 11b is provided such that the surfaces of the
pair of current collectors 11b that are opposite to the surfaces
coated with the active material layers 13b (not shown) are in
contact with each other. That is, a structure is obtained in which
the active material layer 13a and the active material layer 13b are
positioned between the current collector 11a and the current
collector 11b and an active material layer is not provided between
two adjacent current collectors 11a and between two adjacent
current collectors 11b. In the structure, the positions of the pair
of current collectors 11a can be easily shifted from each other and
the positions of the pair of current collectors 11b can be easily
shifted from each other when the battery is bent. As described
later, by sliding current collectors of the same polarity, stress
applied to the current collectors themselves at the time of bending
the battery can be reduced.
[0090] As shown in FIG. 3A, a separator 14 indicated by a dashed
line may be provided between the current collector 11a and the
current collector 11b. The separator 14 is preferably wider than
the current collector 11b.
[0091] The stacked-layer structure is not limited to that shown in
FIG. 3A. For example, the separator 14 may be provided on the outer
side of each of the two outermost current collectors 11a as shown
in FIG. 4A. Thus, the contact between an exterior body to be
described later and the current collector 11a can be prevented,
whereby damage to the exterior body due to rubbing of the exterior
body and the current collector 11a against each other can be
prevented. In this case, the separator 14 is preferably wider than
the current collector 11a.
[0092] In FIG. 4B, an example in which one current collector 11b is
positioned between two current collectors 11a is shown. In this
example, it is preferable that opposite surfaces of the current
collector 11b be coated with the active material layers 13b. Owing
to such a structure, the battery can be thinned, and the capacity
per unit volume and the capacity per unit weight can be increased.
Since the battery can be thinned, the battery can be bent with weak
force. Moreover, the pair of current collectors 11a is slid on each
other easily because the pair of current collectors 11a is provided
such that the surfaces of the pair of current collectors 11a that
are opposite to the surfaces coated with the active material layers
13a (not shown) are in contact with each other. Thus, the battery
can be bent with weaker force.
[0093] In FIG. 4C, a structure in which the pair of current
collectors 11b is sandwiched by one separator 14a is shown. In this
structure, the separator 14a is preferably shaped into a bag-like
form by bonding the surrounding portion after the separator 14a is
folded back. The use of the separator 14a having such a shape can
inhibit an electrical short circuit between a positive electrode
and a negative electrode even when the positions of the pair of
current collectors 11b are shifted.
[0094] In FIG. 4D, each of two outermost current collectors 11a is
also sandwiched by the separator 14a in comparison with FIG. 4C.
Owing to such a structure, damage to the exterior body due to
rubbing of the exterior body and the current collector 11a against
each other can be prevented.
[0095] FIG. 3B shows a state where the current collectors 11a and
the current collectors 11b overlap with each other. Note that the
separator 14 is not shown below for clarity.
[0096] As shown in FIG. 3B, the current collectors 11a and the
current collectors 11b are preferably stacked such that the
relative positions of the current collectors 11a and the current
collectors 11b are shifted in a direction in which the tab portions
21a or the tab portions 21b are provided (in a direction indicated
by an arrow). In the case where the positions thereof are shifted
in advance, positional shift that occurs at the time of folding the
parts of the current collectors 11a and the parts of the current
collectors 11b can be offset as described below. Specifically, the
alignment of the plurality of electrode portions 22a and 22b can be
uniform. Note that at this time, the plurality of current
collectors 11a are preferably stacked such that a portion where the
tab portions 21a of all of the current collectors 11a overlap with
each other is formed. Similarly, the plurality of current
collectors 11b are preferably stacked such that a portion where the
tab portions 21b of all of the current collectors 11b overlap with
each other is formed.
[0097] Note that as shown in FIG. 3B, the positions of the pair of
current collectors 11a and the pair of current collectors 11b that
are provided on the inner side are not necessarily shifted from
each other.
[Step S02]
[0098] Then, as shown in FIG. 3C, a lead 12a and a lead 12b are
bonded to the tab portion 21a of the current collector 11a and the
tab portion 21b of the current collector 11b, respectively. The
bonding can be performed by ultrasonic welding, for example.
[0099] The positions of the tab portions 21a of the current
collectors 11a are shifted, and therefore, it is important that a
bonding portion 15a where the tab portion 21a of the current
collector 11a and the lead 12a are bonded to each other is formed
so as to include areas of all of the tab portions 21a of the
current collectors 11a. The same applies to a bonding portion 15b
where the tab portion 21b of the current collector 11b and the lead
12b are bonded to each other.
[0100] Note that in FIGS. 3A to 3C, the plurality of current
collectors 11a and 11b have the same shape, but the plurality of
current collectors 11a and 11b may differ in length. FIGS. 5A and
5B show an example of the case of using the current collectors 11a
and the current collectors 11b that are longer in the length
direction as they are closer to the bonding surface. Owing to such
a structure, the positions of the tab portions 21a and the tab
portions 21b are not shifted in the length direction, so that the
lead 12a and the lead 12b are bonded to each other easily. In FIGS.
5A and 5B, the current collectors 11a and the current collectors
11b are equal in the length of the tab portion 21a or the tab
portion 21b and differ in the length of the electrode portion 22a
or the electrode portion 22b. As shown in FIG. 5C, the plurality of
current collectors 11a and 11b may be equal in the length of the
electrode portion 22a or the electrode portion 22b and differ in
the length of the tab portion 21a or the tab portion 21b.
[Step S03]
[0101] Then, the part of the tab portion 21a and the part of the
lead 12a are insulated, and the part of the tab portion 21b and the
part of the lead 12b are insulated.
[0102] FIG. 6A is a perspective view showing a state of bonding the
lead 12a and the lead 12b to the plurality of current collectors
11a and the plurality of current collectors 11b, respectively.
[0103] As shown in FIG. 6B, the part of the tab portion 21a of the
current collector 11a and the part of the lead 12a are covered with
an insulating member 16a, whereby surfaces thereof can be
insulated. At this time, the bonding portion 15a is preferably
covered with the insulating member 16a. Similarly, the part of the
tab portion 21b of the current collector 11b and the part of the
lead 12b are covered with an insulating member 16b.
[0104] The insulating member 16a and the insulating member 16b are
provided in portions of the current collectors 11a and the current
collectors 11b that are to be folded back later. This can prevent
contact and an electrical short circuit between a folded-back
portion of the current collector 11b and the surface of the current
collector 11a. Note that in the case where two current collectors
11a are positioned on the outermost side as shown in FIG. 6A and
other drawings, the insulating member 16a on the current collector
11a side need not be necessarily provided. This is because the
current collector 11a and the lead 12a are already electrically
connected to each other and a problem is thus not caused even when
they come into contact with each other.
[0105] As shown in FIG. 6C, one insulating member 16 may be
provided covering the part of the tab portion 21a of the current
collector 11a, the part of the lead 12a, the part of the tab
portion 21b of the current collector 11b, and the part of the lead
12b.
[0106] As each of the insulating member 16a, the insulating member
16b, and the insulating member 16, an insulating tape such as a
polyimide tape can be suitably used. The insulating members having
a sticking property can prevent positional shift when the battery
changes in shape. Note that the insulating members are not limited
thereto, and various modes such as a bag-like shape and a
sheet-like shape can be employed. Alternatively, an insulating
member formed by curing a liquid resin material applied to a
surface of a portion to be insulated may be used.
[0107] The insulating member is provided to prevent an electrical
short circuit at the time of folding back the tab portion 21a and
the tab portion 21b, and the position of the insulating member is
not limited to the positions described above. For example, the
insulating member can cover the electrode portion 22a and the
electrode portion 22b or can be attached to the parts of surfaces
thereof. Alternatively, the insulating member can be provided
between the current collector 11a and the folded-back portion of
the tab portion 21b that is formed when the tab portion 21b is
folded back.
[Step S04]
[0108] Then, the tab portion 21a and the tab portion 21b are each
folded back.
[0109] The tab portion 21a and the tab portion 21b are preferably
folded back such that the surfaces of the tab portion 21a and the
tab portion 21b that are bonded to the lead 12a and the lead 12b,
respectively, are positioned on the outer side.
[0110] FIG. 7A is a perspective view on the bonding portion 15a
side at the time when the tab portion 21a and the tab portion 21b
are folded back. FIG. 7B is a perspective view obtained by rotating
FIG. 7A by 180 degrees. Note that the insulating member 16a, the
insulating member 16b, or the insulating member 16 is not shown
below for clarity.
[0111] As shown in FIG. 7A, the tab portion 21a and the tab portion
21b are preferably folded such that the part of the lead 12a and
the part of the lead 12b overlap with the electrode portion 22a of
the current collector 11a and the electrode portion 22b of the
current collector 11b. Furthermore, the tab portion 21a and the tab
portion 21b are preferably folded such that the tab portion 21a and
the tab portion 21b also overlap with the electrode portion 22a and
the electrode portion 22b.
[Step S05]
[0112] Then, the lead 12a, the lead 12b, the electrode portion 22a,
and the electrode portion 22b are fixed by a fixing member 17.
[0113] FIG. 8A is a perspective view on the bonding portion 15a
side at the time when the fixing member 17 is provided. FIG. 8B is
a perspective view obtained by rotating FIG. 8A by 180 degrees.
[0114] As the fixing member 17, an insulating tape such as a
polyimide tape can be suitably used. Note that the fixing member 17
is not limited thereto; a ring rubber (a rubber band) may be used
or an insulating material such as a resin material formed into an
appropriate shape may be used.
[0115] In the above-described manner, an electrode member 10 can be
formed.
[0116] As shown in FIG. 8A and other drawings, the electrode member
10 has a structure in which the tab portion 21a and the tab portion
21b are folded back and the bonding portion 15a and the bonding
portion 15b overlap with the part of the electrode portion 22a and
the part of the electrode portion 22b. The electrode member 10
having the structure can therefore have a shorter length in the
length direction than that having a structure in which the tab
portion 21a and the tab portion 21b are not folded back. Thus, the
battery including the electrode member 10 can be more compact and
can have higher capacity per unit volume.
[Step S06]
[0117] Then, the electrode member 10 and an electrolyte solution
are covered with the exterior body, and the periphery of the
exterior body is sealed.
[0118] Through the above-described process, the battery of one
embodiment of the present invention can be manufactured.
MANUFACTURING METHOD EXAMPLE 2
[0119] A manufacturing method example of a battery, which is partly
different from the above-described manufacturing method example 1,
is described below with reference to drawings. Note that
description of the same part as the above description may be
skipped.
[0120] FIG. 9 is a flow chart of the manufacturing method example
described below.
[Step S11]
[0121] First, as shown in FIG. 10A, the plurality of current
collectors 11a and the plurality of current collectors 11b are
prepared and stacked. In this example, the positions of the
plurality of current collectors 11a and the plurality of current
collectors 11b are not shifted from each other unlike in the
manufacturing method example 1.
[Step S12]
[0122] Then, as shown in FIG. 10B, the lead 12a and the lead 12b
are bonded to the tab portion 21a of the current collector 11a and
the tab portion 21b of the current collector 11b, respectively.
[0123] At this time, the lead 12a and the lead 12b have shapes in
which the part of the lead 12a and the part of the lead 12b overlap
with the electrode portion 22a and the electrode portion 22b.
[Step S13]
[0124] Then, in order to prevent the lead 12b and the current
collector 11a from being electrically short-circuited, an
insulating member 18 is provided therebetween; thus, the lead 12b
and the current collector 11a are insulated.
[0125] FIG. 11A shows an example in which the insulating member 18
is wound around the part of the current collector 11a and the part
of the current collector 11b.
[0126] Note that the structure of the insulating member 18 is not
limited thereto and can have any of a variety of structures as long
as the lead and the current collector that are of opposite
polarities can be insulated. FIG. 12A shows an example of the case
where an insulating member 18a is positioned only between the
current collector 11a and the lead 12b. FIG. 12B shows an example
of the case where a portion of the lead 12b that overlaps with the
current collector 11a is covered with an insulating member 18b.
FIG. 12C shows an example of the case where a portion of the lead
12a that overlaps with the current collector 11a and the portion of
the lead 12b that overlaps with the current collector 11a are
sandwiched by an insulating member 18c.
[0127] For the insulating member 18, the insulating member 18a, and
the insulating member 18b, a material similar to that used for
forming the insulating member 16 and the like can be used.
[Step S14]
[0128] Then, as shown in FIG. 11B, the lead 12a, the lead 12b, the
electrode portion 22a, and the electrode portion 22b are fixed by
the fixing member 17.
[0129] In the above-described manner, an electrode member 10a can
be formed.
[0130] In this manufacturing method example, a step of folding back
the tab portion 21a and the tab portion 21b is not performed, which
further increases the productivity.
[Step S15]
[0131] Then, the electrode member 10a and the electrolyte solution
are covered with the exterior body, and the periphery of the
exterior body is sealed.
[0132] Through the above-described process, the battery of one
embodiment of the present invention can be manufactured.
[0133] The above is the description of the battery manufacturing
method example.
[Structure Example of Battery]
[0134] A structure example of a battery including the electrode
member described in the manufacturing method example is described
below with reference to drawings. In particular, a structure
example of a battery suitable for repeated bending is
described.
[0135] FIG. 13A is a schematic top view of a battery 50. FIGS.
13B1, 13B2, and 13C are schematic cross-sectional views taken along
the cutting line C1-C2, the cutting line C3-C4, and the cutting
line A1-A2, respectively, in FIG. 13A.
[0136] The battery 50 includes an exterior body 51 and the
electrode member 10 held in the exterior body 51. The lead 12a and
the lead 12b that the electrode member 10 has are extended to the
outside of the exterior body 51. In addition to the electrode
member 10, the electrolyte solution (not shown) is enclosed in the
exterior body 51.
[0137] The exterior body 51 has a film-like shape and is folded in
two so as to sandwich the electrode member 10. The exterior body 51
includes a folded portion 61, a pair of seal portions 62, and a
seal portion 63. The pair of seal portions 62 is provided with the
electrode member 10 positioned therebetween and therefore can also
be referred to as side seals. The seal portion 63 has portions
overlapping with the lead 12a and the lead 12b and can also be
referred to as a top seal.
[0138] The part of the exterior body 51 that overlaps with the
electrode member 10 preferably has a wave shape in which crest
lines 71 and trough lines 72 are alternately arranged. The seal
portions 62 and the seal portion 63 of the exterior body 51 are
preferably flat without a wave shape. Note that in some cases, the
seal portion 63 includes a step in a portion overlapping with the
lead 12a and the lead 12b.
[0139] The above description can be referred to for the structure
of the electrode member 10.
[0140] FIG. 13B1 shows a cross section cut along the part
overlapping with the crest line 71. FIG. 13B2 shows a cross section
cut along the part overlapping with the trough line 72. FIGS. 13B1
and 13B2 correspond to cross sections of the battery 50 and the
electrode member 10 in the width direction.
[0141] The distance between an end portion of the electrode member
10 in the width direction, i.e., an end portion of the current
collector 11a or the current collector 11b, and the seal portion 62
is referred to as a distance La. When the battery 50 changes in
shape, for example, is bent, the current collector 11a and the
current collector 11b change in shape such that the positions
thereof are shifted from each other in the length direction as
described later. At the time, if the distance La is too short, the
exterior body 51 and the current collector 11a or the current
collector 11b are rubbed hard against each other, so that the
exterior body 51 is damaged in some cases. In particular, when a
metal film of the exterior body 51 is exposed, there is a concern
that the metal film may be corroded by the electrolyte solution.
Therefore, the distance La is preferably set as long as possible.
However, if the distance La is too long, the volume of the battery
50 is increased.
[0142] The distance La between the end portion of the current
collector 11a or the current collector 11b and the seal portion 62
is preferably increased as the thickness of the electrode member 10
is increased.
[0143] Specifically, when a thickness of the electrode member 10 is
regarded as a thickness t, the distance La is preferably 0.8 times
or more and 3.0 times or less, further preferably 0.9 times or more
and 2.5 times or less, still further preferably 1.0 times or more
and 2.0 times or less as large as the thickness t. When the
distance La is in the above-described range, a compact battery
highly reliable for bending can be obtained.
[0144] Furthermore, when a distance between the pair of seal
portions 62 is regarded as a distance Lb, it is preferable that the
distance Lb be sufficiently longer than a width of the electrode
member 10 (in this example, the width Wa of the current collector
11a ). In this case, even when the electrode member 10 comes into
contact with the exterior body 51 by change in the shape of the
battery 50 such as repeated bending, the position of the part of
the electrode member 10 can be shifted in the width direction;
thus, the electrode member 10 and the exterior body 51 can be
effectively prevented from being rubbed against each other.
[0145] For example, the difference between the distance La (i.e.,
the distance between the pair of seal portions 62) and the width Wa
of the current collector 11a (or the width Wb of the current
collector 11b ) is preferably 1.6 times or more and 6.0 times or
less, further preferably 1.8 times or more and 5.0 times or less,
still further preferably 2.0 times or more and 4.0 times or less as
large as the thickness t of the electrode member 10.
[0146] In other words, the distance Lb, the width Wa, and the
thickness t preferably satisfy the following relation.
[ Formula 1 ] Lb - Wa 2 t .gtoreq. a ( 1 ) ##EQU00001##
[0147] In the formula, a is 0.8 or more and 3.0 or less, preferably
0.9 or more and 2.5 or less, further preferably 1.0 or more and 2.0
or less.
[0148] FIG. 13C shows a cross section including the lead 12a and
corresponds to a cross section of the battery 50 and the electrode
member 10 in the length direction.
[0149] FIG. 13D is a schematic cross-sectional view of a structure
in which the electrode member 10a is used instead of the electrode
member 10.
[0150] As shown in FIG. 13C, space 73 is preferably provided
between an end portion of the electrode member 10 in the length
direction, i.e., the end portion of the current collector 11a or
the current collector 11b, and the exterior body 51 in the folded
portion 61.
[0151] FIG. 14 is a schematic cross-sectional view of the battery
50 in a state of being bent. FIG. 14 corresponds to a cross section
along the cutting line B1-B2 in FIG. 13A.
[0152] When the battery 50 is bent, the part of the exterior body
51 positioned on the outer side in bending is unbent and the other
part positioned on the inner side changes its shape as it shrinks.
More specifically, the part of the exterior body 51 positioned on
the outer side in bending changes its shape such that the wave
amplitude becomes smaller and the length of the wave period becomes
larger. In contrast, the part of the exterior body 51 positioned on
the inner side in bending changes its shape such that the wave
amplitude becomes larger and the length of the wave period becomes
smaller. When the exterior body 51 changes its shape in this
manner, stress applied to the exterior body 51 due to bending is
relieved, so that a material itself that forms the exterior body 51
does not need to expand and contract. As a result, the battery 50
can be bent with weak force without damage to the exterior body
51.
[0153] Furthermore, as shown in FIG. 14, the electrode member 10
changes its shape such that the positions of the current collector
11a and the current collector 11b are shifted relatively. At this
time, one end on the seal portion 63 side of each of the current
collectors 11a and 11b of the electrode member 10 is fixed by the
fixing member 17. Thus, the plurality of current collectors 11a and
the plurality of current collectors 11b of the electrode member 10
change their shapes such that the relative positions of the
plurality of current collectors 11a and the plurality of current
collectors 11b are more shifted at a position closer to the folded
portion 61. Therefore, stress applied to the electrode member 10 is
relieved, and the current collectors 11a and 11b themselves do not
need to expand and contract. As a result, the battery 50 can be
bent without damage to the electrode member 10.
[0154] Note that in the case where a battery including a solid
electrolyte or a gel electrolyte with high viscosity is provided,
when the entire electrode member 10 is covered with the
electrolyte, the relative positions of the current collector 11a
and the current collector 11b are less likely to be shifted, and
therefore, relief of stress cannot be expected. Therefore, a
plurality of stacks each including an electrolyte layer between a
pair of current collectors 11a and 11b are preferably prepared and
stacked. Thus, a structure can be obtained in which the relative
positions of the current collectors 11a and 11b are shifted even in
the case of using a solid electrolyte or a gel electrolyte with
high viscosity.
[0155] Furthermore, when the space 73 is provided between the
electrode member 10 and the exterior body 51, the relative
positions of the current collectors 11a and 11b located inward from
a neutral plane of the electrode member 10 can be shifted while the
current collectors 11a and 11b do not contact the exterior body
51.
[0156] In the battery exemplified in this structure example, the
exterior body and the electrode member are less likely to be
damaged and the battery characteristics are less likely to
deteriorate even when the battery is repeatedly bent and
unbent.
[0157] The above is the description of the battery structure
example.
[Components]
[0158] Each component of the electrode member and the battery of
one embodiment of the present invention is described below.
[Positive Electrode]
[0159] The positive electrode includes, for example, the positive
electrode current collector and a positive electrode active
material layer formed over the positive electrode current
collector. The positive electrode active material layer can be
formed on one surface or opposite surfaces of the positive
electrode current collector.
[0160] The positive electrode current collector can be formed using
a material that has high conductivity and does not dissolve at the
potential of the positive electrode, such as a metal typified by
stainless steel, gold, platinum, aluminum, or titanium, or an alloy
thereof. Alternatively, an aluminum alloy to which an element which
improves heat resistance, such as silicon, titanium, neodymium,
scandium, or molybdenum, is added can be used. Still alternatively,
a metal element which forms silicide by reacting with silicon can
be used. Examples of the metal element which forms silicide by
reacting with silicon are zirconium, titanium, hafnium, vanadium,
niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel,
and the like. The positive electrode current collector can have a
foil-like shape, a plate-like shape (a sheet-like shape), a
net-like shape, a punching-metal shape, an expanded-metal shape, or
the like as appropriate. The positive electrode current collector
preferably has a thickness of greater than or equal to 5 .mu.m and
less than or equal to 30 .mu.m. The surface of the positive
electrode current collector may be provided with an undercoat layer
using graphite or the like.
[0161] The positive electrode active material layer may further
include, in addition to a positive electrode active material, a
binder for increasing adhesion of the positive electrode active
material, a conductive additive for increasing the conductivity of
the positive electrode active material layer, and the like.
[0162] Examples of the positive electrode active material that can
be used for the positive electrode active material layer include a
composite oxide with an olivine crystal structure, a composite
oxide with a layered rock-salt crystal structure, and a composite
oxide with a spinel crystal structure. For example, a compound such
as LiFeO.sub.2, LiCoO.sub.2, LiNiO.sub.2, LiMn.sub.2O.sub.4,
V.sub.2O.sub.5, Cr.sub.2O.sub.5, or MnO.sub.2 can be used as the
positive electrode active material.
[0163] In particular, LiCoO.sub.2 is preferable because it has high
capacity and higher stability in the air and higher thermal
stability than LiNiO.sub.2, for example.
[0164] It is preferable to add a small amount of lithium nickel
oxide (LiNiO.sub.2 or LiNi.sub.1-xM.sub.xO.sub.2 (0<x<1)
(M=Co, Al, or the like)) to a lithium-containing material with a
spinel crystal structure which contains manganese such as
LiMn.sub.2O.sub.4 because characteristics of the secondary battery
using such a material can be improved.
[0165] Alternatively, a complex material (LiMPO.sub.4 (general
formula) (M is one or more of Fe(II), Mn(II), Co(II), and Ni(II)))
can be used. Typical examples of the general formula LiMPO.sub.4
which can be used as a material are lithium compounds such as
LiFePO.sub.4, LiNiPO.sub.4, LiCoPO.sub.4, LiMnPO.sub.4,
LiFe.sub.aNi.sub.bPO.sub.4, LiFe.sub.aCo.sub.bPO.sub.4,
LiFe.sub.aMn.sub.bPO.sub.4, LiNi.sub.aCo.sub.bPO.sub.4,
LiNi.sub.aMn.sub.bPO.sub.4 (a+b.ltoreq.1, 0<a<1, and
0<b<1), LiFe.sub.cNi.sub.dCo.sub.ePO.sub.4,
LiFe.sub.cNi.sub.dMn.sub.ePO.sub.4,
LiNi.sub.cCo.sub.dMn.sub.ePO.sub.4 (c+d+e.ltoreq.1, 0<c<1,
0<d<1, and 0<e<1), and
LiFe.sub.fNi.sub.gCo.sub.hMn.sub.iPO.sub.4 (f+g+h+1, 0<f<1,
0<g<1, 0<h<1, and 0<i<1).
[0166] LiFePO.sub.4 is particularly preferable because it meets
requirements for the positive electrode active material in a
balanced manner, such as safety, stability, high capacity density,
and the existence of lithium ions that can be extracted in initial
oxidation (charging).
[0167] Alternatively, a complex material such as
Li.sub.(2-j)MSiO.sub.4 (general formula) (M is one or more of
Fe(II), Mn(II), Co(II), and Ni(II); 0.ltoreq.j.ltoreq.2) can be
used. Typical examples of the general formula
Li.sub.(2-j)MSiO.sub.4 which can be used as a material are lithium
compounds such as Li.sub.(2-j)FeSiO.sub.4, Li.sub.(2-j)NiSiO.sub.4,
Li.sub.(2-j)CoSiO.sub.4, Li.sub.(2-j)MnSiO.sub.4,
Li.sub.(2-j)Fe.sub.kNi.sub.lSiO.sub.4,
Li.sub.(2-j)Fe.sub.kCo.sub.lSiO.sub.4,
Li.sub.(2-j)Fe.sub.kMn.sub.lSiO.sub.4,
Li.sub.(2-j)Ni.sub.kCo.sub.lSiO.sub.4,
Li.sub.(2-j)Ni.sub.kMn.sub.lSiO.sub.4 (k+l.ltoreq.1, 0<k<1,
and 0<l<1), Li.sub.(2-j)Fe.sub.mNi.sub.nCo.sub.qSiO.sub.4,
Li.sub.(2-j)Fe.sub.mNi.sub.nMn.sub.qSiO.sub.4,
Li.sub.(2-j)Ni.sub.mCo.sub.nMn.sub.qSiO.sub.4 (m+n+q.ltoreq.1,
0<m<1, 0<n<1, and 0<q<1), and
Li.sub.(2-j)Fe.sub.rNi.sub.sCo.sub.tMn.sub.uSiO.sub.4
(r+s+t+u.ltoreq.1, 0<r<1, 0<s<1, 0<t<1, and
0<u<1).
[0168] Still alternatively, a nasicon compound expressed by
A.sub.xM.sub.2(XO.sub.4).sub.3 (general formula) (A=Li, Na, or Mg,
M=Fe, Mn, Ti, V, or Nb, X.dbd.S, P, Mo, W, As, or Si) can be used
for the positive electrode active material. Examples of the nasicon
compound are Fe.sub.2(MnO.sub.4).sub.3, Fe.sub.2(SO.sub.4).sub.3,
and Li.sub.3Fe.sub.2(PO.sub.4).sub.3. Further alternatively, a
compound expressed by Li.sub.2MPO.sub.4F, Li.sub.2MP.sub.2O.sub.7,
or Li.sub.5MO.sub.4 (general formula) (M=Fe or Mn), a perovskite
fluoride such as NaFeF.sub.3 and FeF.sub.3, a metal chalcogenide (a
sulfide, a selenide, or a telluride) such as TiS.sub.2 and
MoS.sub.2, an oxide with an inverse spinel crystal structure such
as LiMVO.sub.4, a vanadium oxide (V.sub.2O.sub.5, V.sub.6O.sub.13,
LiV.sub.3O.sub.8, or the like), a manganese oxide, an organic
sulfur compound, or the like can be used as the positive electrode
active material.
[0169] In the case where carrier ions are alkali metal ions other
than lithium ions, or alkaline-earth metal ions, a material
containing an alkali metal (e.g., sodium or potassium) or an
alkaline-earth metal (e.g., calcium, strontium, barium, beryllium,
or magnesium) instead of lithium may be used as the positive
electrode active material. For example, the positive electrode
active material may be a layered oxide containing sodium such as
NaFeO.sub.2 or Na.sub.2/3[Fe.sub.1/2Mn.sub.1/2]O.sub.2.
[0170] Further alternatively, any of the above materials may be
combined to be used as the positive electrode active material. For
example, a solid solution obtained by combining two or more of the
above materials can be used as the positive electrode active
material. For example, a solid solution of
LiCo.sub.1/3Mn.sub.1/3Ni.sub.1/3O.sub.2 and Li.sub.2MnO.sub.3 can
be used as the positive electrode active material.
[0171] Note that a conductive material such as a carbon layer may
be provided on a surface of the positive electrode active material
layer. With the conductive material such as the carbon layer,
conductivity of the electrode can be increased. For example, the
positive electrode active material layer can be coated with the
carbon layer by mixing a carbohydrate such as glucose at the time
of baking the positive electrode active material.
[0172] The average particle diameter of the primary particle of the
positive electrode active material layer is preferably greater than
or equal to 50 nm and less than or equal to 100 .mu.m.
[0173] Examples of the conductive additive include acetylene black
(AB), graphite (black lead) particles, carbon nanotubes, graphene,
and fullerene.
[0174] A network for electron conduction can be formed in the
positive electrode by the conductive additive. The conductive
additive also allows maintaining of a path for electric conduction
between the particles of the positive electrode active material
layer. The addition of the conductive additive to the positive
electrode active material layer increases the electron conductivity
of the positive electrode active material layer.
[0175] As the binder, instead of polyvinylidene fluoride (PVDF) as
a typical one, polyimide, polytetrafluoroethylene, polyvinyl
chloride, ethylene-propylene-diene polymer, styrene-butadiene
rubber, acrylonitrile-butadiene rubber, fluorine rubber, polyvinyl
acetate, polymethyl methacrylate, polyethylene, nitrocellulose or
the like can be used.
[0176] A favorable range of the content of the binder in the
positive electrode active material layer may be determined as
appropriate in accordance with the particle diameter of the active
material, and can be preferably greater than or equal to 1 wt % and
less than or equal to 10 wt %. For example, the favorable range can
be greater than or equal to 2 wt % and less than or equal to 8 wt %
or greater than or equal to 3 wt % and less than or equal to 5 wt
%. The content of the conductive additive in the positive electrode
active material layer is preferably greater than or equal to 1 wt %
and less than or equal to 10 wt %, further preferably greater than
or equal to 1 wt % and less than or equal to 5 wt %.
[0177] In the case where the positive electrode active material
layer is formed by a coating method, the positive electrode active
material, the binder, and the conductive additive are mixed to form
a positive electrode paste (slurry), and the positive electrode
paste is applied to the positive electrode current collector and
dried.
[Negative Electrode]
[0178] The negative electrode includes, for example, the negative
electrode current collector and a negative electrode active
material layer formed over the negative electrode current
collector. The negative electrode active material layer can be
formed on one surface or opposite surfaces of the negative
electrode current collector.
[0179] The negative electrode current collector can be formed using
a material that has high conductivity and is not alloyed with a
carrier ion of lithium or the like, such as stainless steel, gold,
platinum, iron, copper, titanium, or an alloy thereof
Alternatively, an aluminum alloy to which an element which improves
heat resistance, such as silicon, titanium, neodymium, scandium, or
molybdenum, is added can be used. The negative electrode current
collector can have a foil-like shape, a plate-like shape (a
sheet-like shape), a net-like shape, a punching-metal shape, an
expanded-metal shape, or the like as appropriate. The negative
electrode current collector preferably has a thickness greater than
or equal to 5 .mu.m and less than or equal to 30 .mu.m. The surface
of the negative electrode current collector may be provided with an
undercoat layer using graphite or the like.
[0180] The negative electrode active material layer may further
include, in addition to a negative electrode active material, a
binder for increasing adhesion of the negative electrode active
material, a conductive additive for increasing the conductivity of
the negative electrode active material layer, and the like.
[0181] There is no particular limitation on the negative electrode
active material as long as it is a material with which lithium can
be dissolved and precipitated or a material into/from which lithium
ions can be inserted and extracted. Other than a lithium metal or
lithium titanate, a carbon-based material generally used in the
field of power storage, an alloy-based material, or the like can
also be used for the negative electrode active material layer.
[0182] The lithium metal is preferable because of its low redox
potential (3.045 V lower than that of a standard hydrogen
electrode) and high specific capacity per unit weight and per unit
volume (3860 mAh/g and 2062 mAh/cm.sup.3).
[0183] Examples of the carbon-based material include graphite,
graphitizing carbon (soft carbon), non-graphitizing carbon (hard
carbon), a carbon nanotube, graphene, carbon black, and the
like.
[0184] Examples of the graphite include artificial graphite such as
meso-carbon microbeads (MCMB), coke-based artificial graphite, or
pitch-based artificial graphite and natural graphite such as
spherical natural graphite.
[0185] Graphite has a low potential substantially equal to that of
a lithium metal (0.1 V to 0.3 V vs. Li/Li.sup.+) when lithium ions
are inserted into the graphite (when a lithium-graphite
intercalation compound is formed). For this reason, a lithium ion
battery can have a high operating voltage. In addition, graphite is
preferable because of its advantages such as relatively high
capacity per unit volume, small volume expansion, low cost, and
safety greater than that of a lithium metal.
[0186] For the negative electrode active material, an alloy-based
material or an oxide which enables charge-discharge reaction by an
alloying reaction and a dealloying reaction with lithium can be
used. In the case where lithium ions are carrier ions, the
alloy-based material is, for example, a material containing at
least one of Mg, Ca, Al, Si, Ge, Sn, Pb, Sb, Bi, Ag, Au, Zn, Cd,
Hg, In, and the like. Such elements have higher capacity than
carbon. In particular, silicon has a significantly high theoretical
capacity of 4200 mAh/g. For this reason, silicon is preferably used
as the negative electrode active material. Examples of the
alloy-based material using such elements include Mg.sub.2Si,
Mg.sub.2Ge, Mg.sub.2Sn, SnS.sub.2, V.sub.2Sn.sub.3, FeSn.sub.2,
CoSn.sub.2, Ni.sub.3Sn.sub.2, Cu.sub.6Sn.sub.5, Ag.sub.3Sn,
Ag.sub.3Sb, Ni.sub.2MnSb, CeSb.sub.3, LaSn.sub.3,
La.sub.3Co.sub.2Sn.sub.7, CoSb.sub.3, InSb, SbSn, and the like.
[0187] Alternatively, for the negative electrode active material,
an oxide such as SiO, SnO, SnO.sub.2, titanium oxide (TiO.sub.2),
lithium titanium oxide (Li.sub.4Ti.sub.5O.sub.12), lithium-graphite
intercalation compound (Li.sub.xC.sub.6), niobium oxide
(Nb.sub.2O.sub.5), tungsten oxide (WO.sub.2), or molybdenum oxide
(MoO.sub.2) can be used.
[0188] Still alternatively, for the negative electrode active
material, Li.sub.3-xM.sub.xN (M is Co, Ni, or Cu) with a Li.sub.3N
structure, which is a nitride containing lithium and a transition
metal, can be used. For example, Li.sub.26Co.sub.0.4N.sub.3 is
preferable because of high charge and discharge capacity (900 mAh/g
and 1890 mAh/cm.sup.3).
[0189] A nitride containing lithium and a transition metal is
preferably used, in which case lithium ions are contained in the
negative electrode active materials and thus the negative electrode
active materials can be used in combination with a material for a
positive electrode active material that does not contain lithium
ions, such as V.sub.2O.sub.5 or Cr.sub.3O.sub.8. Note that in the
case of using a material containing lithium ions as a positive
electrode active material, the nitride containing lithium and a
transition metal can be used as the negative electrode active
material by extracting the lithium ions contained in the positive
electrode active material in advance.
[0190] Alternatively, a material which causes a conversion reaction
can be used as the negative electrode active material. For example,
a transition metal oxide with which an alloying reaction with
lithium is not caused, such as cobalt oxide (CoO), nickel oxide
(NiO), or iron oxide (FeO), may be used for the negative electrode
active material. Other examples of the material which causes a
conversion reaction include oxides such as Fe.sub.2O.sub.3, CuO,
Cu.sub.2O, RuO.sub.2, and Cr.sub.2O.sub.3, sulfides such as
CoS.sub.0.89, NiS, or CuS, nitrides such as Zn.sub.3N.sub.2,
Cu.sub.3N, and Ge.sub.3N.sub.4, phosphides such as NiP.sub.2,
FeP.sub.2, and CoP.sub.3, and fluorides such as FeF.sub.3 and
BiF.sub.3. Note that any of the fluorides can be used as a positive
electrode active material because of its high potential.
[0191] In the case where the negative electrode active material
layer is formed by a coating method, the negative electrode active
material and the binder are mixed to form a negative electrode
paste (slurry), and the negative electrode paste is applied to the
negative electrode current collector and dried. Note that a
conductive additive may be added to the negative electrode
paste.
[0192] Graphene may be formed on a surface of the negative
electrode active material layer. In the case of using silicon as
the negative electrode active material, the volume of silicon is
greatly changed due to occlusion and release of carrier ions in
charge-discharge cycles. Therefore, adhesion between the negative
electrode current collector and the negative electrode active
material layer is decreased, resulting in degradation of battery
characteristics caused by charge and discharge. Thus, graphene is
preferably formed on a surface of the negative electrode active
material layer containing silicon because even when the volume of
silicon is changed in charge-discharge cycles, decrease in the
adhesion between the negative electrode current collector and the
negative electrode active material layer can be inhibited, which
makes it possible to reduce degradation of battery
characteristics.
[0193] Alternatively, a coating film of an oxide or the like may be
formed on the surface of the negative electrode active material
layer. A coating film formed by decomposition or the like of an
electrolyte solution or the like in charging cannot release
electric charges used at the formation, and therefore forms
irreversible capacity. In contrast, the film of an oxide or the
like provided on the surface of the negative electrode active
material layer in advance can reduce or prevent generation of
irreversible capacity.
[0194] As the coating film coating the negative electrode active
material layer, an oxide film of any one of niobium, titanium,
vanadium, tantalum, tungsten, zirconium, molybdenum, hafnium,
chromium, aluminum, and silicon or an oxide film containing any one
of these elements and lithium can be used. Such a coating film is
denser than a conventional coating film formed on a surface of a
negative electrode due to a decomposition product of an electrolyte
solution.
[0195] For example, niobium oxide (Nb.sub.2O.sub.5) has a low
electric conductivity of 10.sup.-9 S/cm and a high insulating
property. For this reason, a niobium oxide film inhibits
electrochemical decomposition reaction between the negative
electrode active material and the electrolyte solution. On the
other hand, niobium oxide has a lithium diffusion coefficient of
10.sup.-9 cm.sup.2/sec and high lithium ion conductivity.
Therefore, niobium oxide can transmit lithium ions. Alternatively,
silicon oxide or aluminum oxide may be used.
[0196] A sol-gel method can be used to coat the negative electrode
active material layer with the coating film, for example. The
sol-gel method is a method for forming a thin film in such a manner
that a solution of metal alkoxide, a metal salt, or the like is
changed into a gel, which has lost its fluidity, by hydrolysis
reaction and polycondensation reaction and the gel is baked. Since
a thin film is formed from a liquid phase in the sol-gel method,
raw materials can be mixed uniformly on the molecular scale. For
this reason, by adding a negative electrode active material such as
graphite to a raw material of the metal oxide film which is a
solvent, the active material can be easily dispersed into the gel.
In such a manner, the coating film can be formed on the surface of
the negative electrode active material layer. A decrease in the
capacity of the battery can be prevented by using the coating
film.
[Separator]
[0197] As a material of the separator, a porous insulator such as
cellulose, polypropylene (PP), polyethylene (PE), polybutene,
nylon, polyester, polysulfone, polyacrylonitrile, polyvinylidene
fluoride, tetrafluoroethylene, or polyphenylene sulfide can be
used. Alternatively, nonwoven fabric of a glass fiber or the like,
or a diaphragm in which a glass fiber and a polymer fiber are mixed
may be used.
[Electrolyte Solution]
[0198] As an electrolyte in the electrolyte solution, a material
having carrier ion mobility and containing lithium ions serving as
carrier ions is used. Typical examples of the electrolyte are
lithium salts such as LiPF.sub.6, LiClO.sub.4, LiAsF.sub.6,
LiBF.sub.4, LiCF.sub.3SO.sub.3, Li(CF.sub.3SO.sub.2).sub.2N,
Li(C.sub.2F.sub.5SO.sub.2).sub.2N, and Li(SO.sub.2F).sub.2N. One of
these electrolytes may be used alone, or two or more of them may be
used in an appropriate combination and in an appropriate ratio.
[0199] It is particularly preferable that the electrolyte have high
heat resistance in the case where treatment is performed at high
temperature in molding rubber or the like. It is preferable to use
imide salt having high thermal decomposition temperature, for
example.
[0200] As a solvent of the electrolyte solution, a material having
carrier ion mobility is used. As the solvent of the electrolyte
solution, an aprotic organic solvent is preferably used. Typical
examples of aprotic organic solvents include ethylene carbonate
(EC), propylene carbonate (PC), dimethyl carbonate, diethyl
carbonate (DEC), ethylmethyl carbonate (EMC),
.gamma.-butyrolactone, acetonitrile, dimethoxyethane,
tetrahydrofuran, and the like, and one or more of these materials
can be used. When a gelled high-molecular material is used as the
solvent of the electrolytic solution or a high-molecular material
for gelling is added to the electrolytic solution, for example,
safety against liquid leakage and the like is improved.
Furthermore, a thinner storage battery having lighter weight can be
provided. Typical examples of gelled high-molecular materials
include a silicone gel, an acrylic gel, an acrylonitrile gel, a
polyethylene oxide-based gel, a polypropylene oxide-based gel, a
gel of a fluorine-based polymer, and the like. Alternatively, the
use of one or more kinds of ionic liquids (room temperature molten
salts) which have features of non-flammability and non-volatility
as the solvent of the electrolyte solution can prevent the storage
battery from exploding or catching fire even when the storage
battery internally shorts out or the internal temperature increases
owing to overcharging or the like. An ionic liquid is a salt in the
fluid state and has high ion mobility (conductivity). An ionic
liquid contains a cation and an anion. Examples of ionic liquids
include an ionic liquid containing an ethylmethylimidazolium (EMI)
cation and an ionic liquid containing an
N-methyl-N-propylpiperidinium (PP.sub.13) cation.
[0201] It is particularly preferable to use a material having high
boiling temperature as the solvent of the electrolyte solution in
the case where treatment is performed at high temperature. It is
preferable to use propylene carbonate (PC), for example.
[Exterior Body]
[0202] There are a variety of structures of a secondary battery,
and a film is used as the exterior body in this embodiment. Note
that the film used for the exterior body is a single-layer film
selected from a metal film (e.g., an aluminum film, a stainless
steel film, and a nickel steel film), a plastic film made of an
organic material, a hybrid material film including an organic
material (e.g., an organic resin or fiber) and an inorganic
material (e.g., ceramic), and a carbon-containing inorganic film
(e.g., a carbon film or a graphite film); or a stacked-layer film
including two or more of the above films. Forming depressions or
projections on a surface of a metal film by embossing increases the
surface area of the exterior body exposed to outside air, achieving
efficient heat dissipation.
[0203] In the case where the secondary battery is changed in form
by externally applying force, bending stress is externally applied
to the exterior body of the secondary battery. This might partly
deform or damage the exterior body. Projections or depressions
formed on the exterior body can relieve a strain caused by stress
applied to the exterior body. Therefore, the secondary battery can
be more reliable. Note that a "strain" is the scale of change in
form indicating the displacement of a point of an object relative
to the reference (initial) length of the object. The exterior body
having depressions or projections can reduce the influence of a
strain caused by application of external force to the battery to an
acceptable level. Thus, the battery having high reliability can be
provided.
[0204] The above is the description of the components.
[0205] At least part of this embodiment can be implemented in
combination with any of the other embodiments described in this
specification as appropriate.
Embodiment 2
[0206] In this embodiment, examples of electronic devices
incorporating a battery obtained using Embodiment 1, in particular,
a secondary battery will be described.
[0207] The secondary battery that can be fabricated according to
Embodiment 1 includes a thin and flexible film as an exterior body
and thus can flexibly change its form.
[0208] A part of an electronic device like a watch is brought into
contact with a part of the body (wrist or arm) of a user, that is,
the user wears the electronic device, whereby the user can feel
like the electronic device is lighter than the actual weight. A
flexible secondary battery can be provided in an electronic device
having a form with a curved surface that fits a part of the body of
a user so that the secondary battery can be fixed in a suitable
form.
[0209] When a user moves a part of the body where an electronic
device is on, the user might feel uncomfortable regarding the
electronic device as a distraction, and feel stress even in the
case where the electronic device has a curved surface that fits the
part of the body. An electronic device provided with a flexible
secondary battery in a portion whose form can be changed can change
its form at least partly according to movement of the body of a
user; thus, an electronic device with which the user does not feel
uncomfortable can be obtained.
[0210] An electronic device does not necessarily have a form with a
curved surface or a complicated form; an electronic device may have
a simple form. The number or size of components that can be
incorporated in an electronic device with a simple form, for
example, is determined depending on the volume of a space formed by
a housing of the electronic device in many cases. Providing a
flexible secondary battery in a small space between components
other than the secondary battery enables a space formed by a
housing of an electronic device to be efficiently used; thus, the
electronic device can be reduced in size.
[0211] Examples of wearable devices include wearable input
terminals such as a wearable camera, a wearable microphone, and a
wearable sensor; wearable output terminals such as a wearable
display and a wearable speaker; and wearable input/output terminals
having the functions of any of the input terminals and any of the
output terminals. Another example of a wearable device is a
wearable computer including a CPU, which is a typical example of a
device that controls each device and calculates or processes data.
Other examples of wearable devices include devices that store data,
send data, and receive data, typically, a portable information
terminal and a memory.
[0212] Examples of electronic devices each using a flexible
secondary battery are as follows: display devices such as
head-mounted displays and goggle-type displays, televisions (also
referred to as television receivers), desktop personal computers,
laptop personal computers, monitors for computers or the like,
digital cameras, digital video cameras, digital photo frames,
electronic notebooks, e-book readers, electronic translators, toys,
audio input devices such as microphones, electric shavers, electric
toothbrushes, high-frequency heating appliances such as microwave
ovens, electric rice cookers, electric washing machines, electric
vacuum cleaners, water heaters, electric fans, hair dryers,
air-conditioning systems such as humidifiers, dehumidifiers, and
air conditioners, dishwashers, dish dryers, clothes dryers, futon
dryers, electric refrigerators, electric freezers, electric
refrigerator-freezers, freezers for preserving DNA, flashlights,
electric power tools, alarm devices such as smoke detectors, gas
alarm devices, and security alarm devices, industrial robots,
health equipment and medical equipment such as hearing aids,
cardiac pacemakers, X-ray equipment, radiation counters, electric
massagers, and dialyzers, mobile phones (also referred to as mobile
phone devices or cell phones), portable game machines, portable
information terminals, lighting devices, headphone stereos,
stereos, remote controls, clocks such as table clocks and wall
clocks, cordless phone handsets, transceivers, pedometers,
calculators, portable or stationary music reproduction devices such
as digital audio players, and large game machines such as pachinko
machines.
[0213] In addition, a flexible secondary battery can be
incorporated along a curved inside/outside wall surface of a house
or a building or a curved interior/exterior surface of an
automobile.
[0214] FIG. 15A illustrates an example of a mobile phone. A mobile
phone 7400 includes a display portion 7402 incorporated in a
housing 7401, an operation button 7403, an external connection port
7404, a speaker 7405, a microphone 7406, and the like. Note that
the mobile phone 7400 includes a secondary battery 7407.
[0215] FIG. 15B illustrates the mobile phone 7400 that is curved.
When the whole mobile phone 7400 is curved by external force, the
secondary battery 7407 included in the mobile phone 7400 is also
curved. FIG. 15C illustrates the bent secondary battery 7407. The
secondary battery 7407 is a laminated storage battery (also
referred to as a layered battery or a film-covered battery). The
secondary battery 7407 is fixed while being bent. Note that the
secondary battery 7407 includes a lead electrode 7408 electrically
connected to a current collector 7409. A film serving as an
exterior body of the secondary battery 7407 is embossed, so that
the secondary battery 7407 has high reliability even when bent, for
example. The mobile phone 7400 may further be provided with a slot
for insertion of a SIM card, a connector portion for connecting a
USB device such as a USB memory.
[0216] FIG. 15D illustrates an example of a mobile phone that can
be bent. When bent to be put around a forearm, the mobile phone can
be used as a bangle-type mobile phone as in FIG. 15E. A mobile
phone 7100 includes a housing 7101, a display portion 7102, an
operation button 7103, and a secondary battery 7104. FIG. 15F
illustrates the secondary battery 7104 in the state of being bent.
When the mobile phone is worn on a user's arm while the secondary
battery 7104 is bent, the housing changes its form and the
curvature of a part or the whole of the secondary battery 7104 is
changed. Specifically, a part or the whole of the housing or the
main surface of the secondary battery 7104 is changed in the range
of radius of curvature from 10 mm to 150 mm inclusive. Note that
the secondary battery 7104 includes a lead electrode 7105 that is
electrically connected to a current collector 7106. Pressing is
performed to form a plurality of projections and depressions on a
surface of a film serving as an exterior body of the secondary
battery 7104, for example; thus, reliability is retained even when
the secondary battery 7104 is bent many times with different
curvatures. The mobile phone 7100 may further be provided with a
slot for insertion of a SIM card, a connector portion for
connecting a USB device such as a USB memory. When a center portion
of the mobile phone illustrated in FIG. 15D is bent, a form
illustrated in FIG. 15G can be obtained. When the center portion of
the mobile phone is folded so that end portions of the mobile phone
overlap with each other as illustrated in FIG. 15H, the mobile
phone can be reduced in size so as to be put in, for example, a
pocket of clothes a user wears. As described above, the mobile
phone illustrated in FIG. 15D can change its form in more than one
way, and it is desirable that at least the housing 7101, the
display portion 7102, and the secondary battery 7104 have
flexibility in order to change the form of the mobile phone.
[0217] A power storage device described in Embodiment 1 can be
provided in wearable devices like those illustrated in FIG.
16A.
[0218] For example, the power storage device can be provided in a
glasses-type device 400 illustrated in FIG. 16A. The glasses-type
device 400 includes a frame 400a and a display part 400b. The power
storage device is provided in a temple of the frame 400a having a
curved shape, whereby the glasses-type device 400 can have a
well-balanced weight and can be used continuously for a long
time.
[0219] The power storage device can be provided in a headset-type
device 401. The headset-type device 401 includes at least a
microphone part 401a, a flexible pipe 401b, and an earphone part
401c. The power storage device can be provided in the flexible pipe
401b and the earphone part 401c.
[0220] The power storage device can be provided in a device 402
that can be attached directly to a body. A power storage device
402b can be provided in a thin housing 402a of the device 402.
[0221] The power storage device can be provided in a device 403
that can be attached to clothes. A power storage device 403b can be
provided in a thin housing 403a of the device 403.
[0222] The power storage device can be provided in a watch-type
device 405. The watch-type device 405 includes a display part 405a
and a belt part 405b, and the power storage device can be provided
in the display part 405a or the belt part 405b.
[0223] The display part 405a can display various kinds of
information such as time and reception information of an e-mail or
an incoming call.
[0224] The watch-type device 405 is a wearable device that is wound
around an arm directly; thus, a sensor that measures the pulse, the
blood pressure, or the like of the user may be incorporated
therein. Data on the exercise quantity and health of the user can
be stored to be used for health maintenance.
[0225] The power storage device can be provided in a belt-type
device 406. The belt-type device 406 includes a belt part 406a and
a wireless power feeding and receiving part 406b, and the power
storage device can be provided inside the belt part 406a.
[0226] FIG. 16B is a projection view illustrating an example of an
external view of an information processing device 200. The
information processing device 200 described in this embodiment
includes an arithmetic device 210, an input/output device 220, a
display portion 230, and a power storage device 250.
[0227] The information processing device 200 includes a
communication portion having a function of supplying data to a
network and acquiring data from the network. Image information may
be generated in accordance with received information distributed
among a specific space using a communication portion 290. For
example, educational materials can be distributed among a classroom
and displayed to be used as a school book. Alternatively, materials
transmitted among a conference room in a company can be received
and displayed.
[0228] At least part of this embodiment can be implemented in
combination with any of the other embodiments described in this
specification as appropriate.
EXAMPLE 1
[0229] In this example, a battery of one embodiment of the present
invention was fabricated. Here, the method exemplified in the
manufacturing method example 1 of Embodiment 1 was employed.
[0230] Six positive electrode current collectors each made of
aluminum foil including one surface provided with a layer of a
positive electrode active material and six negative electrode
current collectors each made of copper foil including one surface
provided with a layer of a negative electrode active material were
prepared. LiCoO.sub.2 and graphite were used as the positive
electrode active material and the negative electrode active
material, respectively.
[0231] The positive electrode current collector was obtained such
that, after a pair of positive electrode current collectors was
made to overlap with each other with surfaces opposite to the
coated surfaces facing each other, the pair of positive electrode
current collectors was covered with a bag-like separator.
[0232] Then, as shown in FIG. 17A, the positive electrode current
collectors each covered with the separator and the negative
electrode current collectors were stacked such that the positions
of the positive electrode current collectors and the negative
electrode current collectors were shifted in the length direction.
After that, as shown in FIG. 17B, a lead was bonded to each of tab
portions of the positive electrode current collectors and the
negative electrode current collectors by ultrasonic welding. FIG.
17C is an enlarged view of FIG. 17B.
[0233] Then, as shown in FIG. 18A, a polyimide tape was wound as an
insulating member to cover a pair of bonding portions. FIG. 18B is
a photograph of the reverse side, and FIG. 18C is an enlarged view
of FIG. 18A.
[0234] Then, the tab portions of the positive electrode current
collectors and the negative electrode current collectors were
folded back. Then, as a fixing member, a polyimide tape was wound
to fix the pair of tab portions including the bonding portions, the
positive electrode current collectors, and the negative electrode
current collectors. FIG. 19B is a photograph of the bonding portion
side, FIG. 19A is a photograph of the reverse side, and FIG. 19C is
an enlarged view of FIG. 19B.
[0235] In this manner, the electrode member was completed.
[0236] Then, the electrode member was sandwiched by an exterior
body, and side seals and a top seal were formed; thus, the battery
was fabricated.
[0237] As the exterior body, an aluminum laminated film with a
thickness of approximately 70 .mu.m in which polypropylene,
aluminum foil, and nylon are stacked in this order was used. The
film was obtained by being processed to have a wave pitch of 2 mm
and a height difference between a crest and a trough of 0.5 mm.
[0238] Bonding for formation of seal portions of the film was
performed using a mold (heat bar) with a flat surface. For the side
seals, a heat bar with a width of 1 mm was used. For the top seal,
a heat bar with a width of 2 mm provided with a groove at the
position facing a lead portion was used.
[0239] FIGS. 20A and 20B are photographs showing the appearance of
the fabricated battery. As shown in FIGS. 20A and 20B, it is
confirmed that the top seal and the side seals are extremely flat,
and the part of the film changes in shape such that the wave period
of a portion close to an end portion of the film is longer than
that of a center portion thereof and the wave amplitude of the
portion close to the end portion of the film is smaller than that
of the center portion thereof.
[0240] The above description thus far is Example 1.
[0241] At least part of this example can be implemented in
combination with any of the embodiments or the other example
described in this specification as appropriate.
EXAMPLE 2
[0242] A battery of one embodiment of the present invention and
batteries for reference were fabricated, and the results of taking
images of inside structures of the batteries and the evaluation
results of electrical characteristics of the batteries before and
after a repeated bending test are described below.
[Fabrication of Samples]
[0243] First, three kinds of samples (Reference sample 1, Reference
sample 2, and Sample 1) were fabricated.
[0244] Aluminum foil with a width of 9 mm and copper foil with a
width of 10 mm were used as a positive electrode current collector
and a negative electrode current collector, respectively. In this
example, six positive electrode current collectors and six negative
electrode current collectors that each include one surface provided
with an active material layer were stacked.
[0245] Sample 1 was fabricated by a method similar to that
described in Example 1. A 16-mm-width aluminum laminated film
embossed in advance was used as an exterior body of Sample 1.
[0246] Reference sample 1 and Reference sample 2 were each
fabricated under conditions where a lead and a current collector
were fixed to each other only at a bonding portion. In Reference
sample 1 and Reference sample 2, as in Sample 1, aluminum laminated
films embossed in advance were used as exterior bodies. As the
exterior body of Reference sample 1, a 15-mm-width aluminum
laminated film was used. As the exterior body of Reference sample
2, a 16-mm-width aluminum laminated film similar to that of Sample
1 was used.
[Observation of Inside Structure]
[0247] The inside of each of the batteries of fabricated Reference
sample 2 and Sample 1 was observed by X-ray computed tomography
(X-ray CT).
[0248] FIGS. 21A to 21C are transmission X-ray photographs of
Reference sample 2. FIG. 21A is a photograph in the horizontal
direction, FIG. 21B is a photograph in a plan view, and FIG. 21C is
an enlarged photograph of a region in the vicinity of a tab portion
in FIG. 21A.
[0249] In these photographs, the exterior body, the positive
electrode current collectors, and the like that are formed of
aluminum foil appear transparent because a lighter element
transmits X-rays more easily.
[0250] As shown in FIG. 21C, a bonding portion where a lead and a
tab are bonded to each other is provided in the position apart from
a portion where regions provided with the active material layers of
the current collectors are stacked.
[0251] FIGS. 22A to 22C are transmission X-ray photographs of
Sample 1. As shown in FIG. 22C, tab portions of the current
collectors are folded back. Furthermore, it is confirmed that the
bonding portion where the current collector and the lead are bonded
to each other overlaps with a portion where the current collectors
are stacked.
[0252] Note that the drawing of Reference sample 1 is not shown
because Reference sample 1 is different from Reference sample 2
only in the width of the exterior body.
[Bending and Unbending Test]
[0253] The bending and unbending test was repeatedly performed on
Reference sample 1, Reference sample 2, and Sample 1. As the
bending and unbending test, bending with a curvature radius of 25
mm and unbending were repeated.
[0254] In Reference sample 1, damage to the exterior body and
leakage of the electrolyte solution were observed after the bending
and unbending test was performed 6000 times. The damaged part of
the exterior body of Reference sample 1 was positioned in a portion
where the exterior body was in contact with the end portion of the
negative electrode current collector.
[0255] In contrast, in Reference sample 2 and Sample 1, damage to
the exterior body and leakage of the electrolyte solution were not
observed even after the bending and unbending test was performed
10000 times.
[Observation 1 of Inside Structure]
[0256] FIGS. 23A to 23C are X-ray CT images of cross sections of
the samples before the bending and unbending test. FIG. 23A shows
the cross section along the trough line of the exterior body of
Reference sample 1; FIG. 23B, Reference sample 2; and FIG. 23C,
Sample 1.
[0257] At this time, the value of a in Formula (2) was estimated.
In Formula (2), L represents the distance between the pair of side
seals, W represents the width of the negative electrode current
collector, and t represents the thickness of the electrode member
(the distance between two negative electrode current collectors
positioned on the outer side).
[ Formula 2 ] a = L - W 2 t ( 2 ) ##EQU00002##
[0258] The estimated value of a of Reference sample 1 was 0.66. The
estimated value of a of Reference sample 2 was 1.04. The estimated
value of a of Sample 1 was 1.03.
[0259] The above results show that, in Reference sample 1, the
width of space between each of the end portions of the negative
electrode current collector and the side seal was less than 0.7
times as large as the thickness. The bending and unbending test
results show that, in Reference sample 1, the end portion of the
negative electrode current collector came in contact with the
exterior body and the exterior body was damaged; accordingly, it is
revealed that space with such a width is not enough.
[0260] In Reference sample 2 and Sample 1, the width of space
between each of the end portions of the negative electrode current
collector and the side seal was 0.8 times or more as large as the
thickness. In the bending and unbending test results, damage was
not observed even after the test was repeated 10000 times;
accordingly, it is shown that the space therebetween is
sufficiently ensured.
[Charge and Discharge Characteristics]
[0261] Charge and discharge characteristics of the samples before
and after the bending and unbending test were measured.
[0262] The characteristics of Reference sample 1 are shown in FIGS.
24A and 24B. FIG. 24A shows the characteristics before the bending
and unbending test is performed, and FIG. 24B shows the
characteristics after the bending and unbending test is performed
3000 times. In each of the drawings, the vertical axis represents
voltage and the horizontal axis represents capacity per unit weight
of the positive electrode active material. As shown in FIGS. 24A
and 24B, a decrease in the capacity by the bending and unbending
test was confirmed.
[0263] The characteristics of Reference sample 2 are shown in FIGS.
25A and 25B. FIG. 25B shows the characteristics after the bending
and unbending test is performed 10000 times. As shown in FIGS. 25A
and 25B, a decrease in the capacity by the bending and unbending
test was confirmed, though damage to the exterior body was not
observed.
[0264] The characteristics of Sample 1 are shown in FIGS. 26A and
26B. FIG. 26B shows the characteristics after the bending and
unbending test is performed 10000 times. In Sample 1, a decrease in
the capacity was hardly observed when the characteristics before
and after the bending and unbending test were compared. The
discharge capacity before the bending and unbending test was 134.0
[mAh/g], whereas the discharge capacity after the bending and
unbending test was 133.3 [mAh/g].
[0265] [Observation 2 of Inside Structure]
[0266] Transmission X-ray photographs of Reference sample 2 and
Sample 1 were taken again after the bending and unbending test was
performed 10000 times, and the inside structures were observed.
[0267] FIG. 27A is a transmission X-ray photograph of a region in
the vicinity of the tab portions of Reference sample 2 in the
horizontal direction. As shown in the portion surrounded by the
dashed line in the drawing, a fracture was observed in the part of
the negative electrode current collector. This suggests that the
decrease in capacity is due to the fracture of the tab portion.
[0268] FIG. 27B is a transmission X-ray photograph of a region in
the vicinity of the tab portion of Sample 1 in the horizontal
direction. It is shown that little change was observed when the
transmission X-ray photograph is compared with the
transmission-X-ray photograph before the bending and unbending test
(FIG. 22C).
[0269] The above results show that the battery of one embodiment of
the present invention is a highly reliable battery in which a
decrease in capacity is hardly observed even after bending and
unbending are repeated.
[0270] The above description thus far is Example 2.
[0271] At least part of this example can be implemented in
combination with any of the embodiments and the other example
described in this specification as appropriate.
[0272] This application is based on Japanese Patent Application
serial no. 2016-123209 filed with Japan Patent Office on Jun. 22,
2016, the entire contents of which are hereby incorporated by
reference.
* * * * *