U.S. patent application number 10/540907 was filed with the patent office on 2006-03-16 for electrical storage device and manufacturing electrical storage device.
This patent application is currently assigned to Fuji Jukogyo Kabushiki Kaisha. Invention is credited to Nobuo Ando, Yukinori Hato, Chisato Marumo, Shinichi Tasaki.
Application Number | 20060057433 10/540907 |
Document ID | / |
Family ID | 32677421 |
Filed Date | 2006-03-16 |
United States Patent
Application |
20060057433 |
Kind Code |
A1 |
Ando; Nobuo ; et
al. |
March 16, 2006 |
Electrical storage device and manufacturing electrical storage
device
Abstract
An electrical storage device of the present invention is
characterized in that a positive electrode, a negative electrode, a
lithium electrode, and an electrolyte capable of transferring
lithium ion is included, the lithium electrode is arranged to be
out of direct contact with the negative electrode, and lithium ion
can be supplied to the negative electrode by flowing a current
between the lithium electrode and the negative electrode through an
external circuit. With the above characteristic, problems such as
non-uniform carrying of lithium ion to the negative electrode,
shape-change of a cell, and temperature increase of an electrolytic
solution under incomplete sealing of a cell and the like can be
easily solved. A using method of the electrical storage device is
characterized in that, by using the lithium electrode as a
reference electrode, the positive electrode potential and negative
electrode potential can be measured, and the potential of the
positive or negative electrode can be controlled when the
electrical storage device is charged or discharged. Therefore, the
potentials of the positive electrode and negative electrode can be
monitored, thereby it can be easily determined whether
deterioration of the electrical storage device is caused by the
positive electrode or the negative electrode. Also, it is possible
to control the device with the potential difference between the
negative electrode and reference electrode, that is, the negative
potential. In addition, when characteristics deteriorate such as
the internal resistance increase, an appropriate amount of lithium
ion can be supplied to the negative electrode and/or positive
electrode by the lithium electrode.
Inventors: |
Ando; Nobuo; (Tokyo, JP)
; Tasaki; Shinichi; (Tokyo, JP) ; Hato;
Yukinori; (Tokyo, JP) ; Marumo; Chisato;
(Tokyo, JP) |
Correspondence
Address: |
DARBY & DARBY P.C.
P. O. BOX 5257
NEW YORK
NY
10150-5257
US
|
Assignee: |
Fuji Jukogyo Kabushiki
Kaisha
7-2 Nishishinjuku 1-chome, Shinjuku-ku
Tokyo
JP
JP
|
Family ID: |
32677421 |
Appl. No.: |
10/540907 |
Filed: |
December 25, 2003 |
PCT Filed: |
December 25, 2003 |
PCT NO: |
PCT/JP03/16666 |
371 Date: |
June 27, 2005 |
Current U.S.
Class: |
429/9 ; 29/623.1;
429/128; 429/231.95 |
Current CPC
Class: |
H01M 10/052 20130101;
H01M 6/5044 20130101; Y02E 60/13 20130101; H01M 6/5005 20130101;
H01M 10/0431 20130101; H01M 10/4242 20130101; Y02T 10/70 20130101;
Y10T 29/49108 20150115; H01M 10/48 20130101; H01M 4/382 20130101;
H01M 10/44 20130101; H01M 10/446 20130101; Y10T 29/4911 20150115;
H01G 9/155 20130101; H01M 10/0587 20130101; Y02E 60/10 20130101;
H01M 10/0436 20130101; H01M 4/587 20130101; H01M 2010/4292
20130101; H01M 4/13 20130101; H01M 10/058 20130101 |
Class at
Publication: |
429/009 ;
429/231.95; 429/128; 029/623.1 |
International
Class: |
H01M 14/00 20060101
H01M014/00; H01M 4/58 20060101 H01M004/58; H01M 10/04 20060101
H01M010/04 |
Claims
1. An electrical storage device comprising: a positive electrode, a
negative electrode, a lithium electrode and an electrolyte capable
of transferring lithium ions, wherein the lithium electrode is
arranged to be out of direct contact with the negative electrode
and/or the positive electrode, and lithium ion can be supplied to
the negative electrode and/or the positive electrode by flowing
current between the lithium electrode and the negative electrode
and/or the positive electrode through an external circuit.
2. The electrical storage device according to claim 1, wherein the
electrolyte is an aprotic organic solvent solution of a lithium
salt.
3. The electrical storage device according to claim 1, wherein the
positive electrode and the negative electrode are formed on a
positive electrode collector and a negative electrode collector
respectively, and each of the positive electrode collector and the
negative electrode collector has an opening that penetrates front
and rear surfaces.
4. The electrical storage device according to claim 1, wherein the
lithium electrode is formed on a lithium electrode collector made
of a conductive porous body, and at least part of the lithium
electrode is buried into a porous portion of the lithium electrode
collector.
5. The electrical storage device according to claim 1, further
comprising: an outer container made of a laminated film.
6. The electrical storage device according to claim 1, wherein the
lithium electrode is arranged to face the negative electrode and/or
the positive electrode.
7. The electrical storage device according to claim 1, further
comprising: an electrode stack unit, in which more than three
layers of electrode couple having the positive electrode and the
negative electrode are layered.
8. The electrical storage device according to claim 1, further
comprising: an electrode stack unit, in which an electrode couple
having the positive electrode and the negative electrode is
rolled.
9. The electrical storage device according to claim 1, wherein the
electrical storage device is a capacitor.
10. The electrical storage device according to claim 9, wherein the
positive electrode contains a material that can reversibly carry
lithium ion and/or anions as a positive electrode active material,
the negative electrode contains a material that can reversibly
carry lithium ion as a negative electrode active material, an
electrostatic capacitance per unit weight of the negative electrode
active material is more than three times larger than an
electrostatic capacitance per unit weight of the positive electrode
active material, and a weight of the positive electrode active
material is larger than a weight of the negative electrode active
material.
11. The electrical storage device according to claim 10, wherein
the negative electrode active material is a thermal-processed
material of an aromatic condensed polymer, and is an insoluble and
infusible base having a polyacene-based skeletal structure with a
hydrogen/carbon atomic ratio of 0.50 to 0.05.
12. The electrical storage device according to claim 1, wherein a
part of lithium electrode exists in the lithium electrode collector
after lithium ion-supplying process.
13. An electronic apparatus including the electrical storage device
according to claim 1.
14. A manufacturing method of an electrical storage device
comprising: an electrical storage device assembling step, in which
sealing a positive electrode, a negative electrode, a lithium
electrode and an electrolyte capable of transferring lithium ions,
which are arranged to be out of direct contact with one another,
are sealed; and a lithium ion supplying step, in which lithium ion
is supplied to the negative electrode and/or the positive electrode
by flowing current between the lithium electrode and the negative
electrode and/or the positive electrode through an external
circuit.
15. The manufacturing method of an electrical storage device
according to claim 14, wherein all amount of lithium ion is eluted
from the lithium electrode after lithium ion-supplying process.
16. The manufacturing method of an electrical storage device
according to claim 14, wherein a part of lithium electrode exists
in the lithium electrode collector after lithium ion-supplying
process.
17. A using method of the electrical storage device according to
claim 1, wherein by using the lithium electrode as a reference
electrode, a positive potential and a negative potential can be
measured, and the potential of the positive electrode or the
negative electrode can be controlled when the electrical storage
device is charged or discharged.
18. A using method of the electrical storage device according to
claim 1, wherein lithium ion is supplied from the lithium electrode
to the negative electrode and/or the positive electrode by flowing
current between the lithium electrode and the negative electrode
and/or the positive electrode through the external circuit after
the electrical storage device is used, or characteristics
deteriorate.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electrical storage
device and a manufacturing method of an electrical storage device
capable of readily preventing non-uniform carrying when lithium
ions are carried to a negative electrode, and shape-changing of a
negative electrode.
BACKGROUND ART
[0002] Recently, with a high energy concentration, a secondary
battery having a positive electrode such as a conductive polymer
and a transition metal oxide and a negative electrode such as a
lithium metal or a lithium alloy (hereinafter, briefly referred to
as a lithium metal) has been proposed to replace a Ni--Cd battery
and a lead battery. However, when charging and discharging are
repeatedly performed, this secondary battery is subject to large,
reduction of capacity due to degradation of the positive electrode
or the negative electrode, and thus there remains a practical
problem. In particular, degradation of the negative electrode leads
to generation a mossy lithium crystal called as a dendrite, and
with repetitive charging and discharging the dendrite penetrates a
separator to cause a short-circuit inside the battery, and in some
cases, there might have a problem in terms of safety such as
explosion of the battery.
[0003] Here, in order to solve the foregoing problems, a battery
has been proposed having a negative electrode made of a carbon
material such as graphite and a positive electrode made of a
lithium containing metal oxide such as LiCoO.sub.2. This battery is
a so-called rocking chair type battery such that, after assembling
the battery, the lithium is supplied from the lithium containing
metal oxide of the positive electrode to the negative electrode for
charging and the lithium of the negative electrode is supplied
backed to the positive electrode for discharging. This is
distinguished from the lithium battery that uses metal lithium in
that only the lithium ions are used in charging and discharging
rather than using the metal lithium at the negative electrode, so
that it is called as a lithium ion secondary battery. This battery
has characteristics such as high voltage, high capacity, and high
stability.
[0004] The lithium ion secondary battery is widely used for a
mobile phone and a notebook personal computer, and thus there is a
need for improvement of energy density. Generally, increases in
each discharging capacity of the positive electrode and the
negative electrode, improvement of charging and discharging
efficiency, and improvement of electrode density are examined. In
general, in designing a cell, a thickness and a density of each
electrode is determined such that a charging amount of the positive
electrode is identical to a charging amount of the negative
electrode. Therefore, a discharging capacity of the cell is
determined by a the lower efficiency between charging and
discharging efficiencies of the positive electrode or the negative
electrode, and thus a cell capacity grows larger as the charging
and discharging efficiency is increased.
[0005] A research and development has been made on the negative
electrode that uses an amorphous material such as tin oxide or
polyacenic semiconductor (hereinafter, referred to as PAS) as a
negative electrode for the lithium ion secondary battery. Examples
of the PAS, which can be obtained through annealing aromatic
polymer, includes insoluble and infusible base having a
polyacene-based skeletal structure as disclosed in Japanese
Examined Patent Application Publication Nos. Hei1-44212, and
Hei3-24024. In addition, the PAS having a BET specific surface area
of 600 m.sup.2/g can be obtained through a method disclosed in a
method disclosed in Japanese Examined Patent Application
Publication No. Hei3-24024. These amorphous materials have a high
capacity, and a high nonreversible capacity. For this reason, with
a typical arrangement of the typical lithium ion secondary cell,
100% of a negative electrode capacity can be used while only 60 to
80% of a positive electrode capacity can be used, which leads to
not that high capacity.
[0006] With respect to this, the inventors herein achieved a high
capacity by carrying the lithium ion to the negative PAS in
advance, according to a method disclosed in Japanese Unexamined
Patent Application Publication No. Hei8-7928. With the lithium ion
to the negative PAS, 100% of discharging capacity for both the
positive and negative electrodes can be used and thus a high
capacity can be achieved, compared to a conventional design where
only 60 to 80% of the positive electrode capacity can be used.
[0007] As described above, the lithium ion secondary battery has
been studied as a high capacity and powerful power supply and
commercialized as a primary power supply of typical notebook
computer or mobile telephone. Of these, the mobile telephone has
progressed into a small-sized and light-weighted one, and thus
there is also a need for a small sized and light weighted lithium
ion secondary ion used for the primary power supply. As a result,
an outer case of a squared battery is changed from iron to aluminum
and a weight is significantly reduced. In addition, there is a need
for a thin battery having a thickness of 4 mm or 3 mm, so that a
film battery that uses an aluminum laminated film as an outer
material has been widely used with an increasing pace. In addition,
while focusing on environmental issues, a storage system of a
regenerative energy using a solar photovoltaic or a wind power
plant, a distributed type power supply for the purpose of
regulating a power load, or an automobile power supply (main power
and auxiliary power) involved in a gasoline car have been
progressively developed. In addition, up to now, while a lead
battery is used for a power supply of electric equipment of the
automobile, apparatuses such as a power window or a stereo has
recently improved, and thus there is a need for a new power supply
in terms of an energy density and an output density. At the same
time, in terms of battery shape, there is also a need for an
arrangement of a thin frame that uses a laminated film as an outer
case, compared to the conventional rounded or squared type. This is
less restrictive to location for a case where a space is limited
such as a load conditioner installed in the household or a vehicle
trunk, and thus, examination thereof is substantially
progressed.
[0008] Like this, a film type lithium ion secondary battery has
been widely used in various fields as a high capacity and space
saving power supply.
[0009] As a method of carrying lithium ion to the negative
electrode of the lithium ion secondary battery in advance, one cell
having metal lithium in addition to the lithium ion secondary
battery is arranged to carry a predetermined amount of lithium ion
into the negative electrode, however, it is not desirable due to
its complicated manufacturing process.
[0010] Regarding this, as an industrially convenient way, a method
of electrochemically contacting the lithium metal and a negative
electrode arranged in the cell is proposed. In a given method,
carrying the lithium ion with electrochemical contact between the
lithium metal and the negative electrode can be facilitated by
using a material having an opening that penetrates a front and rear
surfaces, such as expanded metal, as a positive electrode collector
and a negative electrode collector. In addition, the lithium ion
can be readily carried with the lithium metal arranged to face the
negative or positive electrode.
[0011] However, in the method of electrochemically contacting the
lithium metal and the negative electrode, carry is non-uniformly
provided between the negative electrode arranged near the lithium
metal and the negative electrode around far from the lithium metal,
or even between a center and a corner in a sheet of the negative
electrode. In addition, it is impossible to check whether a
predetermined amount of lithium ion is carried, and thus a voltage
of the electrical storage device is just used as a reference.
[0012] Further, in the method of electrochemically contacting the
lithium metal with the negative electrode, while carry of the
lithium ion is initiated at the time of injecting the electrolyte,
the electrode is not well fixed at the time of injecting the
electrolyte solution. Therefore, a problem occurs that the negative
electrode is hardened in a rippled shape.
[0013] In particular, for a thin film type electrical storage
device that uses an aluminum laminated film as an outer case
material, a contact pressure from the outer container is weak so
that the phenomenon appears noticeably, and the strain and wrinkle
of electrode leads to cell shape-change. When the lithium ion is
carried with the electrode in the rippled shape, it will be
hardened as it is, thus leading to the distorted cell and thus
degradation of the battery performance.
[0014] In addition, when carry of the lithium ion is initiated, the
negative electrode emits a heat and thus a temperature increases.
Here, when the temperature increases while the cell is not fully
sealed, a problem such as solvent evaporation may occur. In
particular, when more than two types of solvents are mixed, a
composition of the solvents may vary, which causes non-uniform
characteristics between cells.
[0015] Therefore, an object of the present invention is to provide
an electrical storage device and a manufacturing method of an
electrical storage device, with which the electrical storage device
can be easily manufactured, it can be checked whether a
predetermined amount of lithium ion is carried, the potential of a
positive or negative electrode can be controlled at the time of
charging and discharging, and non-uniform carry of the lithium ion
and shape-change of the negative electrode can be readily
prevented.
DISCLOSURE OF THE INVENTION
[0016] In order to solve the above-mentioned problems and to
achieve the objects, an electrical storage device according to
claim 1 includes a positive electrode, a negative electrode, a
lithium electrode and an electrolyte capable of transferring
lithium ion, and the lithium electrode is arranged to be out of
direct contact with the negative electrode and/or the positive
electrode. Lithium ion can be supplied to the negative electrode
and/or the positive electrode by flowing current between the
lithium electrode and the negative electrode and/or the positive
electrode through an external circuit.
[0017] According to the invention of claim 1, problems such as
non-uniform carry of lithium ion to the negative electrode and/or
the positive electrode, shape-change of a cell, and temperature
increase of an electrolytic solution under incomplete sealing of a
cell can be easily solved.
[0018] For example, when the negative electrode lithium ion is
carried, conventionally, the lithium electrode and the negative
electrode arranged in the cell are electrochemically contact so
that the carry of lithium ion is initiated at the time of injecting
electrolyte, and thus there occurs a problem in that non-uniform of
the carry is generated between a portion that the lithium ion is
easily carried and a portion that the lithium ion is not easily
carried, or that the negative electrode is hardened in the ripple
shape. According to the present invention, the carry of lithium ion
is initiated by flowing current between the lithium electrode and
the negative electrode. Therefore, lithium ion carry timing can be
easily controlled, and thus, for example, after sealing to the
outer container, the carry of lithium ion can be initiated to the
negative electrode with planarized positive and negative electrodes
and an electrical storage device having a high surface flatness can
be easily manufactured.
[0019] In addition, in the conventional method, lithium ion is
transferred while the electrical storage device is not completely
sealed, so that there is a problem in that temperature of
electrolyte increases and a solvent is evaporated. However, in the
present invention, the lithium ion carry timing can be easily
controlled, so that a temperature increase of the electrolyte while
the electrical storage device is not completely sealed can be
easily avoided.
[0020] Further, in the conventional method, the lithium electrode
and the negative electrode arranged in the cell are
electrochemically contact, so that the potential difference between
the lithium electrode and the negative electrode becomes 0 V.
Regarding the resistance of lithium electrode, it takes a
substantial amount of time to carry lithium ion since the potential
of the negative electrode is higher than 0 V. However, according to
the present invention, the current can be flowed between the
negative electrode and the lithium electrode through the external
circuit, so that, for example, a minus voltage is applied between
the negative electrode and the lithium electrode. Thus the lithium
ion can be forcefully carried and a time to carry lithium ion can
be reduced.
[0021] In addition, in the conventional method, the lithium
electrode and the negative electrode arranged in the cell are
electrochemically contact, so that the carry of lithium ion is
initiated at the time of injecting the electrolyte. Thus, in the
beginning, a large current partially flows so that mossy metal
lithium is generated at a portion of the negative electrode, which
may cause a shirt-circuit. However, according to the present
invention, since the current flowing between the negative electrode
and the lithium electrode through the external circuit can be
controlled, the lithium ion can be carried in a current that does
not generate the mossy metal lithium.
[0022] Further, the electrical storage device of the present
invention includes cells, in which metal lithium is additionally
provided as a counter electrode, thereby a complicated
manufacturing process such as carrying a predetermined amount of
lithium ion in the negative electrode is not required, and the
electrical storage device can be easily manufactured.
[0023] In addition, when the lithium electrode can supply the
lithium ion to the negative electrode and/or the positive
electrode, the carry of lithium ion to the negative electrode is
provided by electrochemically contacting the lithium electrode and
the negative electrode arranged in the cell, as described above,
and the lithium electrode can be used as a reference electrode. At
this time, the above-mentioned problems occurs since the carry of
lithium ion is initiated before sealing, but it can be properly
determined whether the predetermined amount of lithium ion is
carried to the negative electrode, by measuring a potential
difference between the lithium electrode and the negative
electrode. In this case, it is more desirable in finding a lithium
ion carry amount that non-uniform carry of lithium ion and
shape-change of a cell are suppressed with both the lithium
electrode for supplying the negative electrode lithium ion and the
lithium electrode as a reference electrode.
[0024] In addition, in the electrical storage device claimed in
claim 2, the electrolyte may be made of a lithium salt aprotic
organic solvent solution.
[0025] With the invention claimed in claim 2, the lithium salt
aprotic organic solvent solution is used as the electrolyte, so
that, preferably, the solvent is not electrically decomposed even
in a high voltage.
[0026] In addition, in the electrical storage device claimed in
claim 3, the positive electrode and the negative electrode may be
formed on a positive electrode collector and a negative electrode
collector, respectively. Further each of the positive and negative
electrode collectors may have an opening that penetrates a front
and rear surfaces.
[0027] According to the invention claimed in claim 3, the lithium
ion can be freely transferred through the penetrating hole between
respective electrodes, so that the carry of lithium ion to the
negative electrode and/or the positive electrode from the lithium
electrode and charging and discharging can be facilitated.
[0028] In addition, according to the electrical storage device
claimed in claim 4, the lithium electrode may be formed on a
lithium electrode collector made of a conductive porous body, and
at least a part of the lithium electrode may be buried on a porous
portion of the lithium electrode collector.
[0029] According to the invention claimed in claim 4, at least the
part of the lithium electrode is buried into pores of the lithium
electrode collector, so that the lithium ion is carried to the
negative electrode and/or the positive electrode from the lithium
electrode, and even when the lithium electrode is vanished, a gap
generated between the electrodes caused by a loss of the lithium
electrode is preferably small.
[0030] In addition, according to the electrical storage device
claimed in claim 5, the electrical storage device may have an outer
container made of a laminated film.
[0031] With the invention claimed in claim 5, the laminated film is
used as an outer container, so that the electrical storage device
can be preferably small-sized and light-weighted. In addition,
while the film type electrical storage device protected with the
laminated film has a weak contact pressure from the outer
container, so that strain, shape-change and the like of the
electrode may directly lead to shape-change of a cell. However,
with the arrangement of the present invention claimed in claim 1
and the subsequent claims, the above problems can be easily
solved.
[0032] In addition, according to the electrical storage device
claimed in claim 6, the lithium electrode may be arranged to face
the negative electrode and/or the positive electrode.
[0033] With the invention claimed in claim 6, since the lithium
electrode is arranged to face the negative electrode and/or the
positive electrode, preferably, the lithium ion can be smoothly
carried to the negative electrode and/or the positive electrode
from the lithium electrode.
[0034] In addition, the electrical storage device claimed in claim
7 may further include an electrode stack unit having an electrode
couple stacked in more than three layers, in which the electrode
couple has the positive electrode and the negative electrode.
[0035] With the invention claimed in claim 7, more than three
layers are stacked to form an electrode couple that includes the
positive electrode and the negative electrode, so that a surface
area of the electrode can be increased without enlarging an area of
the electrical storage device. Thus, preferably, with a compact
size, it has a low internal resistance and a large storage
capacity.
[0036] In addition, the electrical storage device claimed in claim
8 may further include an electrode stack unit having an electrode
couple rolled, in which the electrode couple has the positive
electrode and the negative electrode.
[0037] With the invention claimed in claim 8, the electrode couple
having the positive electrode and the negative electrode is rolled,
so that the surface area of the electrode can be increased without
enlarging an area of the electrical storage device. Thus,
preferably, with a compact size, it has a low internal resistance
and a large storage capacity.
[0038] In addition, according to the electrical storage device
claimed in claim 9, the electrical storage device may be made of a
capacitor.
[0039] With the invention claimed in claim 9, the electrical
storage device of the present invention capable of carrying a
predetermined amount of lithium ion to the negative electrode in
advance is used for a capacitor, so that the potential of the
negative electrode can be reduced and preferably a capacitor having
a large storage capacity can be obtained.
[0040] In addition, according to the electrical storage device
claimed in claim 10, the positive electrode may contain a material
that can reversibly carry the lithium ion and/or anions as a
positive electrode active material. The negative electrode may
contain a material that can reversibly carry the lithium ion as a
negative electrode active material. Further, an electrostatic
capacitance per unit weight of the negative electrode active
material may be more than three times larger than an electrostatic
capacitance per unit weight of the positive electrode active
material. In addition, a weight of the positive electrode active
material may be larger than a weight of the negative electrode
active material.
[0041] With the invention claimed in claim 10, by using the
negative electrode active material having an electrostatic
capacitance per unit weight larger than an electrode capacitance
per unit weight of the positive electrode active material, and
making a weight of the positive electrode active material larger
than a weight of the negative electrode active material, an
electrostatic capacitance and a capacity of the capacitor can be
increased. In addition, by containing in the negative electrode a
material that can reversibly carry lithium ion as the negative
electrode active material, a predetermined amount of lithium ion is
carried to the negative electrode in advance to obtain a capacity
required for the negative electrode capacity. Thus, the potential
of the negative electrode can be further reduced, and density can
be improved with an increased breakdown voltage of the capacitor
energy. In addition, by reducing the potential of the negative
electrode, an amount of the potential change in discharging of the
positive electrode can be increased.
[0042] In addition, according to the electrical storage device
claimed in claim 11, the negative electrode active material is a
thermal-processed aromatic condensed polymer, and is an insoluble
and infusible base having a polyacene-based skeletal structure with
a hydrogen/carbon atomic ratio in the range of 0.50 to 0.05.
[0043] According to the invention claimed in claim 11, the
insoluble and infusible base, which has a polyacene-based skeletal
structure, and is used as the negative electrode active material,
does not vary the structure, for example, swell or contract when
lithium ion are inserted and seceded, thereby the electrical
storage device has an excellent cyclic characteristic. Also, the
electrical storage device has an isotropic molecular structure
(high-order structure) to insertion and secession of lithium ion,
thereby excellent characteristics for rapid charging and rapid
discharging can be obtained.
[0044] In addition, according to the electrical storage device
claimed in claim 12, a part of lithium electrode may exist in the
lithium electrode collector after the lithium ion supplying
process.
[0045] With the invention claimed in claim 12, it is possible to
use the lithium electrode as a reference electrode after carrying
the lithium ion to the negative electrode and/or the positive
electrode, so that the electrical storage device preferably has a
simple arrangement. Further, the existing lithium electrode can be
used for regenerating the capacity of the electrical storage
device.
[0046] In addition, an electrical apparatus claimed in claim 13 is
an electronic apparatus including the electrical storage device
according to claims 1 to 12, which is used as a typical consumer
electrical apparatus, vehicles such as an electrical automobile and
a bicycle, and an apparatus for electrical storage of a natural
energy.
[0047] In addition, a manufacturing method of an electrical storage
device claimed in claim 14 includes assembling a positive
electrode, a negative electrode, a lithium electrode and an
electrolyte capable of transferring lithium ion, through which the
positive electrode, the negative electrode and lithium electrode
are arranged to be out of direct contact with each other; and
supplying the lithium ion to the negative electrode and/or the
positive electrode by flowing a current between the lithium
electrode and the negative electrode and/or the positive electrode
through an external circuit.
[0048] With the invention claimed in claim 14, after assembling the
electrical storage device having three electrodes, i.e., the
positive electrode, the negative electrode and the lithium
electrode, the lithium ion is supplied to the negative electrode
and/or the positive electrode from the lithium electrode by flowing
a current between the lithium electrode and the negative electrode
and/or the positive electrode through the external circuit.
Therefore, problems such as non-uniform carrying of lithium ion to
the negative electrode and/or the positive electrode, shape-change
of a cell, and temperature increase of an electrolytic solution
under incomplete sealing of a cell can be easily solved.
[0049] In addition, according to the manufacturing method of the
electrical storage device claimed in claim 15, after the lithium
supplying process, a total amount of the lithium ion for the
lithium electrode may elute.
[0050] With the invention claimed in claim 15, after the lithium
supply process, the lithium that exists in the lithium electrode is
used for lithium ion, so that a highly stable electrical storage
device can be obtained. In addition, by shorting between the
lithium electrode and the negative electrode and/or the positive
electrode, the supply of lithium ion is facilitated, so that the
lithium ion supply process is simplified.
[0051] In addition, according to the manufacturing method of the
electrical storage device claimed in claim 16, after the lithium
ion supplying process, a part of the lithium electrode may exist in
the lithium electrode collector.
[0052] With the invention claimed in claim 16, since the excessive
lithium metal is prepared at the lithium electrode, a predetermined
amount of lithium ion can be smoothly supplied. Conventionally,
when a total amount of lithium ion is consumed, a resistance of the
lithium electrode is increased, since an area of the lithium metal
is gradually reduced, and thus, there needs a time to consume the
total amount. However, according to the present invention, even
when the predetermined amount of lithium ion is consumed, the area
of the lithium metal is not changed so that the lithium ion can be
smoothly supplied.
[0053] In addition, according to a method of using the electrical
storage device claimed in claim 17, the positive electrode and the
negative electrode can be measured using a lithium electrode as a
reference electrode. Further, the positive electrode or the
negative electrode can be controlled when the electrical storage
device is charged or discharged.
[0054] With the invention claimed in claim 17, by using a reference
electrode when the electrical storage device is charged and
discharged, the potentials of the positive electrode and the
negative electrode can be monitored, and thus when the electrical
storage device is deteriorated, it can be easily determined whether
deterioration is caused by the positive electrode or the negative
electrode. Furthermore, it also becomes possible to control the
device according to the potential difference between the negative
electrode and reference electrode, namely the negative potential,
rather than a voltage between the positive electrode and the
negative electrode. For example, it is possible to finish charging
before the potential of the negative electrode falls below 0 V at
the time of charging the electrical storage device.
[0055] In addition, according to a method of using the electrical
storage device claimed in claim 18, after using the electrical
storage device, or after degradation of characteristics, the
lithium ion may be supplied from the lithium electrode to the
negative electrode and/or the positive electrode by flowing a
current between the lithium electrode and the negative electrode
and/or the positive electrode through the external circuit.
[0056] With the invention claimed in claim 18, when characteristics
is degraded such as increase in an internal resistance while using
the electrical storage device, an appropriate amount of lithium ion
is supplied again to the negative electrode and/or the positive
electrode, so that internal resistance of the electrical storage
device can be improved and the capacity thereof can be
regenerated.
[0057] The electrical storage device of the present invention is
characterized to include three electrodes, i.e., a positive
electrode, a negative electrode and a lithium electrode. The
lithium ion can be carried to the negative electrode and/or the
positive electrode by flowing current between the negative
electrode and/or the positive electrode through the external
circuit, so that problems such as non-uniform carrying of lithium
ion to the negative electrode, shape-change of a cell, and
temperature increase of an electrolytic solution under incomplete
sealing of a cell can be easily solved.
[0058] When a voltage of 0 V is applied to the negative electrode
relative to the lithium electrode, current is flowed into the
lithium electrode so that the lithium ion eluted out of the lithium
electrode are transferred through the electrolyte and carried to
the negative electrode.
[0059] The `positive electrode` refers to an electrode at the side
into which the current flows at the time of charging, while the
`negative electrode` refers to an electrode at the side out of
which the current flows at the time of charging. Thus, at the time
of discharging, the lithium ion carried to the negative electrode
are emitted out, transferred through the electrolyte, and carried
to the positive electrode. In addition, at the time of charging,
the lithium ion carried to the positive ions are carried again to
the negative electrode.
[0060] Preferred embodiments of the present invention will now be
described with reference to the drawings. FIG. 1 is a perspective
view of an inner arrangement of the electrical storage device
according to the present invention. In FIG. 1, the inner
arrangement of the electrical storage device is shown in a solid
line, while an outer arrangement of the electrical storage device
is shown in a dotted line. The electrical storage device of the
present invention includes a three-electrode stack unit in which a
positive electrode 1, a negative electrode 2, a lithium electrode 7
and a separator 3 are stacked in laminated films 4 and 5. Here,
lithium ion are injected into transferable electrolyte, and then
two sheets of laminated films 4 and 5 are sealed through heat
sealing.
[0061] As shown in FIG. 1, the positive electrode 1 in which a
positive electrode laminated material 1c including a positive
electrode active material is formed on a positive electrode
collector 1a, and the negative electrode 2 in which a negative
electrode laminated material 2c including a negative electrode
active material is formed on a negative electrode collector 2a are
stacked through the separator not to directly contact with each
other, and thus to form an electrode stack unit 6. The lithium
electrode 7 attaching a lithium metal 7c on one surface of a
lithium electrode collector 7a is arranged on the electrode stack
unit 6 not to directly contact with the negative electrode 2, thus
to form a three-layered stack unit. According to the present
invention, it is important that the negative electrode 2 and the
lithium electrode 7 are arranged not to contact in the cell. When
the negative electrode 2 contacts with the lithium electrode 7, the
carry of lithium is initiated at the time of injecting electrolyte,
problems such as such as non-uniform carrying of lithium ion to the
negative electrode, shape-change of a cell, and temperature
increase of an electrolytic solution under incomplete sealing of a
cell can be undesirably generated.
[0062] FIG. 2 is a bottom view of the electrical storage device of
FIG. 1, and FIG. 3 is a cross-sectional view taken along I-I' line
of FIG. 2. In FIG. 3, the electrode stack unit 6 has a positive
electrode 1 and a negative electrode 2, each being four-layered
electrode, but the arrangement of the electrode stack unit is not
limited thereto, and once at least one positive electrode and at
least one negative electrode are provided, the number of layers for
the positive and negative electrodes are not specially limited.
[0063] In addition, in FIG. 3, for a three-electrode stack unit 8,
while the lithium electrode 7 is arranged on the electrode stack
unit 6, a position, the number of layer, and a shape of the lithium
electrode are not limited thereto. However, to facilitate carrying
lithium ion, it is desirable that the lithium electrode is arranged
to face the negative electrode or the positive electrode.
[0064] According to the electrical storage device of the present
invention, the negative electrode and the lithium electrode are
arranged not to directly contact with each other in the cell. In an
example of FIG. 1, the separators 3 are arranged among respective
electrodes, not to cause the positive electrode 1, the negative
electrode 2, and the lithium electrode 7 to directly contact with
each other. In the cell, a liquid electrolyte in which the lithium
ions can be transferred is filled, and the separator 3 that
separates each electrode is impregnated. The electrolyte is
typically a liquid phase and impregnated to the separator 3, but
when the separator 3 is not used, a gel type or a solid phase
electrolyte may be used to prevent leakage of the electrolyte and
not to cause the positive electrode 1, the negative electrode 2,
and the lithium electrode 7 to directly contact with each
other.
[0065] Each of the positive electrode collector 1a, the negative
electrode collector 2a, and the lithium electrode collector 7a has
an opening (not shown) that penetrates a front and rear surfaces,
and thus the lithium ion can be freely transferred between
respective electrodes through the given penetrating hole. For this
reason, the carry of lithium ion to the negative electrode from the
lithium electrode can be smoothly progressed. In addition, in
charging and discharging, the lithium ion can be smoothly
transferred between the positive and negative electrodes.
[0066] As shown in FIG. 2, the positive electrode collector 1a, the
negative electrode collector 2a, and the lithium electrode
collector 7a have protrusion portions having terminal connection
portions A', B', and B', respectively. The terminal welding portion
A' (two sheets) of the positive electrode collector 1a and the
positive electrode terminal 1b, the terminal welding portion B'
(three sheets) of the positive electrode collector 1b and the
negative electrode terminal 2b, and the terminal welding portion B'
(one sheet) of the lithium electrode collector 7a and the lithium
electrode terminal 7b are welded together, respectively.
[0067] The laminated films 4 and 5 are sealed with the positive
electrode terminal 1b, the negative electrode terminal 2b, and the
lithium electrode terminal electrode therebetween, and the positive
electrode terminal 1b, the negative electrode terminal 2b, and the
lithium electrode terminal 7b are heat sealed to the laminated
films 4 and 5 respectively, at heat sealing portions A, B, and B,
shown in FIG. 2. That is, in an example of FIG. 2, the electrical
storage device is sealed at the heat sealing portions A, B, and C
between the laminated films 4 and 4 and respective terminals, and
the heat sealing portion D between the laminated films 4 and 5.
Therefore, the positive electrode terminal 1b, the negative
electrode terminal 2b, and the lithium electrode terminal 7b are
protruded from between the laminated films 4 and 5 to the outer
portion of the battery, so that the positive electrode 1, the
negative electrode 2 and the lithium electrode 7 can be connected
to the external circuit through respective terminals.
[0068] While shapes and sizes of the positive electrode terminal
1b, the negative electrode terminal 2b, and the lithium electrode
terminal 7b are not specifically limited, but a thicker and larger
terminal is preferable, if possible, so long as a sufficient
airtight can be provided in a limited cell volume. It is very
appropriate that each terminal shape and size is selected in
response to target cell characteristics.
[0069] As described above, each collector 1a, 2a, and 7a has an
opening that penetrates a front and rear surfaces respectively, so
that the lithium ion can be freely transferred between respective
terminals through the given penetrating hole. For example, when a
voltage of 0 V is applied to the negative electrode 2 relative to
the lithium electrode 7 through the negative electrode terminal 2b
and the lithium electrode terminal 7b, the lithium ion eluted from
the lithium metal 6c to the electrolyte are transferred through the
penetrating hole, and carried to the negative electrode laminated
material 2c. In addition, at the time of discharging, the lithium
ion carried to the negative electrode laminated material 2c are
flowed out, transferred into the electrolyte, and carried to the
positive electrode laminated material 1c, but at this time, the
current may be flowed out through the positive electrode terminal
1b and the negative electrode terminal 2b. In addition, at the time
of charging, when a voltage is applied between the positive
electrode 1 and the negative electrode 2 through the positive
electrode terminal 1b and the negative electrode terminal 2b, the
lithium ion doped into the positive electrode laminated material 1c
are carried again to the negative electrode laminated material
2c.
[0070] When the voltage of 0 V is applied to the negative electrode
2 relative to the lithium electrode 7, the lithium metal 7c emits
lithium ions, and thus becomes reduced. An amount of the light
metal 7c (lithium ion contained in the lithium electrode) arranged
in the electrical storage device will be sufficient once the target
electrostatic capacitance of the negative electrode can be
obtained, however, when more than the amount thereof is arranged,
only a predetermined amount of the lithium metal 7c is used to
carry and then a part of the lithium metal 7c may exist in the
electrical storage device (definition of the electrostatic
capacitance will be described below.) When there exists the part of
the lithium metal 7c, it is also possible to use the lithium
electrode 7 as a reference electrode in order to determine the
potential of the positive or negative electrode. However, in terms
of safety, it is desirable that a required amount is arranged to
cause the total amount to carry the negative electrode, and it is
desirable that an amount of lithium ion be appropriately set
depending on a target.
[0071] The electrical storage device of the present invention will
now be described in detail in the following order. [A] negative
electrode, [B] positive electrode, [C] positive electrode collector
and negative electrode collector, [D] lithium electrode, [E]
lithium electrode collector, [F] electrolyte, [G] outer container,
[H] various uses of electrical storage device, [I] specific example
of an inner arrangement, and [J] electrical storage device
manufacturing method.
[A] Negative Electrode
[0072] In the electrical storage device of the present invention,
the negative electrode includes the negative electrode laminated
material and the negative electrode collector, and the negative
electrode laminated material contains a negative electrode active
material capable of reversibly carrying the lithium ion.
[0073] The negative electrode active material, which is not
specifically limited if it can be used to carry the lithium, may
include various carbon materials, for example, graphite, a
polyacenic material, tin oxide, and silicon oxide.
[0074] When an active material having a so-called amorphous
structure, in which the potential is gradually reduced as the
lithium ion is inserted and the potential is increased as the
lithium ion is emitted, such as a polyacenic organic semiconductor
(PAS), is used, the potential is reduced by as much as the lithium
ion is carried. Thus, a breakdown voltage of the capacitor
(charging voltage) that can be obtained is increased. Further, an
increase rate of the voltage (slope of the discharging curve) for
the discharging is lowered, so that the capacity is a bit
increased. Therefore, in response to the voltage of the required
capacitor, it is desirable that an amount of lithium ion be
appropriately set within a lithium ion occlusion capability of the
active material.
[0075] Since the PAS has an amorphous arrangement, it does not have
an arrangement variation such as swelling and contraction relative
to insertion and secession of the lithium ions, thus showing an
excellent cyclic characteristic, and has an isotropic molecular
structure (high-order structure) relative to insertion and
secession of the lithium ions, thus preferably obtaining excellent
characteristics for a rapid charging and a rapid discharging. Thus,
the PAS is very appropriate as a negative electrode active
material.
[0076] As the negative electrode active material of the present
invention, for a thermal-processed material of an aromatic
condensed polymer, it is desirable that an insoluble and infusible
base be used having a polyacene-based skeletal structure with a
hydrogen/carbon atomic ratio of 0.50 to 0.05.
[0077] Here, the aromatic condensed polymer refers to a condensate
of an aromatic hydrocarbon compound and an aldehyde group. The
aromatic hydrocarbon compound may use a so-called phenol group such
as phenol, cresol, and xylenol.
[0078] For example, the aromatic hydrocarbon compound can be a
methylene bisphenol group, which is represented as the following
equation, a hydroxy biphenyl group or a hydroxy naphthalene group.
Among these, a phenol group, particularly phenol is the most
preferable from a viewpoint of practical use. ##STR1## (wherein x
and y are independently from each other, in a range of 0, 1 or
2)
[0079] In addition, the aromatic condensed polymer includes a
modified aromatic condensed polymer that replaces one unit of an
aromatic hydrocarbon compound having a phenol hydroxyl radical with
an aromatic hydrocarbon compound not having the phenol hydroxyl
radical, such as xylene, toluene, and aniline, for example, a
condensate of phenol, xylene, and formaldehyde. Further, there may
be a modified aromatic polymer replaced with melanin and urea, and
a furan resin can be very appropriately used.
[0080] As the aldehyde, formaldehyde, acetaldehyde, and furfural
may be used, and among these, formaldehyde is preferable. In
addition, a phenol formaldehyde condensate may be any one of a
novolac type or a resole type, or a combination thereof.
[0081] The insoluble and infusible base, which can be obtained by
annealing the aromatic group polymer, may include any insoluble and
infusible base having the above-mentioned polyacene-based skeletal
structure.
[0082] The insoluble and infusible base for use in the present
invention can be manufactured, for example, as follows. That is,
the aromatic condensed polymer is slowly heated up to a temperature
of 400 to 800.degree. C. under a non-oxide atmosphere (including
vacuum), so that the insoluble and infusible base having a
hydrogen/carbon atomic ratio (hereinafter, referred to as H/C) of
0.5 to 0.05, and preferably, 0.35 to 0.10 can be obtained.
[0083] In addition, with the above method, the insoluble and
infusible base having a BET specific surface area of more than 600
m.sup.2/g can be obtained. For example, a solution is prepared
including an initial condensate of the aromatic condensed polymer
and inorganic salts, for example, zinc chloride, and hardened in a
frame by heating the solution so that the insoluble and infusible
base having a high specific surface area can be obtained.
[0084] The hardened body obtained in this manner is slowly heated
up to an appropriate temperature of 350 to 800.degree. C.,
preferably, 400 to 750.degree. C. under the non-oxide atmosphere
(including atmosphere), and then, is sufficiently cleansed using
water and dilute hydrochloric acid. Therefore, with the above H/C,
the insoluble and infusible base having a BET specific surface area
of more than 600 m.sup.2/g can be obtained.
[0085] For the insoluble and infusible base for use in the present
invention, with an X-ray diffraction (CuK.alpha.), a position of a
main peak is indicated as 2.theta., existing in less than
24.degree., and in addition to the main peak, there also exist
another peak that is broad in a range of 41 to 46.degree.. That is,
the insoluble and infusible base has a polyacene-based skeletal
structure in which an aromatic polycyclic structure is
appropriately developed, and takes an amorphous structure. From
this, the lithium ion can be stably doped so that it can be used as
the battery active material.
[0086] The negative electrode of the present invention contains the
negative electrode active material such as the PAS, and the
negative electrode active material that can be easily formed in a
powdered form, a grain form, and a short fiber form is preferably
formed in a binder. The binder may use, for example, a rubber type
binder such as SBR, a fluorine-based resin such as
polytetrafluoroethylene, and polyvinylidene, a thermoplastic resin
such as polypropylene and polyethylene, and among these, preferably
use a fluorine-based binder, and more preferably, a fluorine-based
binder is used having an atomic ratio of a fluoride atom to a
carbon atom (hereinafter, referred to as F/C) of preferably more
than 0.75 to less than 1.5, and more preferably more than 0.75 to
less than 1.3.
[0087] The fluorine-based binder may use, for example,
polyvinylidene, a vinylidene-trifluoroethylene copolymer, an
ethylene-tetrafluoroethylene copolymer, and a
propylene-tetrafluoroethylene copolymer. Further, a fluorine-based
polymer that replaces hydrogen of a main chain with an alkyl group
can be used.
[0088] For the polyvinylidene, the F/C is 1, and for the
vinylidene-trifluoroethylene copolymer, when a mole fraction of the
vinylidene is 50% or 80%, the F/C is 1.25 and 1.1, respectively.
Further, for the propylene-tetrafluoroethylene copolymer, when the
mole fraction of the propylene is 50%, the F/C is 0.75. Among
these, polyvinylidene, a vinylidene-trifluoro copolymer having a
mole fraction of the vinylidene of more than 50% is preferable, and
practically, polyvinylidene is preferably used.
[0089] When the above binders are used, a dope ability (capacity)
of the lithium ion that the PAS has can be sufficiently used.
[0090] In addition, the negative electrode active material may use
a conductive material such as acetylene black, graphite, and metal
power, if needed.
[B] Positive Electrode
[0091] For the electrical storage device of the present invention,
the positive electrode includes the positive electrode laminated
material and the positive electrode collector, and the positive
electrode laminated material contains a positive electrode active
material. The positive electrode active material, which can
reversibly carry lithium ion and/or negative ions such as
tetrafluoroborate, though not specifically limited thereto, may
include conductive polymer and a polyacenic material, for example.
Further, among these, the insoluble and infusible base having a
polyacene-based skeletal structure having a hydrogen/carbon atomic
ratio of 0.05 to 0.50 (hereinafter, . . . referred to as PAS),
which is a thermal-processed aromatic condensed polymer product, is
preferably used, and thus a high capacity can be obtained.
[0092] The positive electrode of the present invention is formed
with a conductive member and a binder, if required, added to the
positive electrode active material, and a type and composition of
the conductive member and the binder can be properly
determined.
[0093] The conductive member may preferably use, for example, a
carbon group such as an activated carbon, carbon black, an
acetylene black and graphite. A composition ratio of the conductive
member may vary according electrical conductivity and an electrode
shape of the active material, but it is desirable that a ratio of 2
to 40% for the active material is added.
[0094] In addition, as long as the binder is insoluble to the
following electrolyte, it may be preferably a rubber type finder
such as SBR, a fluorine-based resin such as polytetrafluoroethylene
and polyfluorovinyliden, and a thermoplastic resin such as
polypropylene and polyethylene. In addition, a composition ratio of
less than 20% for the active material is provided.
[C] Positive Electrode Collector and Negative Electrode
Collector
[0095] The positive and negative electrode collectors of the
present invention are not specifically limited, but each preferably
has an opening that penetrates a front and rear surfaces, and may
include, for example, an expanded metal, a punching metal, a net,
and a blowing agent. A type and the number of penetrating hole is
not specifically limited, but can be properly determined such that
lithium ion in the electrolyte described below can be transferred
between two faces of the electrode without binding to the electrode
collector.
[0096] In the present invention, the potentials of the negative
electrode and/or the positive electrode can be measured using the
lithium electrode, and the potential of the positive or negative
electrode can also be controlled at the time of charging and
discharging the electrical storage device. At this time, in order
to measure the potential of the positive or negative electrode more
exactly using a reference electrode, having an opening that
penetrates the front and rear surfaces in the positive electrode
collector and the negative electrode collector is more preferable
than using a foil without an opening in the collector.
[0097] A porosity of the electrode collector is defined as
{1-(collector weight/collector true specific gravity)/(collector
appearance volume)} converted into a percentile. When the porosity
is high, preferably, a time to carry the lithium ion to the
negative electrode is reduced and the non-uniformity is hardly
generated. However, it is difficult to retain the active material
in the opening, and further, since the strength of electrode is
low, a production ratio to form the electrode will be reduced. In
addition, the opening, in particular, the active material of the
edge is easily fallen off, which leads to short-circuit inside the
battery.
[0098] One the other hand, when the porosity is low, it takes a
time to carry the lithium ion to the negative electrode, but since
the strength of the electrode is strong and the active material is
difficult to be fallen off, an electrode production ratio is also
increased. Considering an arrangement (stack type or rolled type,
etc.) and productivity of the electrode, it is desirable that the
porosity of the collector and a diameter of the opening be
arbitrarily chosen.
[0099] In addition, the electrode collector can be typically made
of various materials proposed in the organic electrolyte battery,
so that the positive electrode collector may use aluminum and
stainless and the negative electrode collector may use stainless
and nickel.
[D] Lithium Electrode
[0100] For the electrical storage device of the present invention,
the lithium electrode includes lithium metal and the lithium
electrode collector. The lithium metal of the present invention
includes a material that can supply lithium ion, by including at
least lithium ion such as Li-aluminum alloy in addition to the
lithium metal.
[0101] Conventionally, one method of carrying a predetermined
amount of lithium ion to the negative electrode is to introduce
conductive materials such as nickel, copper, and stainless in the
cell or to attach the lithium metal on the negative electrode
collector. However, in this case, all negative electrodes and
lithium electrode are electrochemically contact and the carry of
lithium ion to the negative electrode active material is
undesirably initiated under a state where the positive electrode
and the negative electrode are not sufficiently fixed (contact
pressure is not given) due to injection of electrolyte. According
to the present invention, it is desirable that the lithium
electrode and the negative electrode are arranged independently
from each other, in the cell.
[0102] Depending on the target, it is desirable that an amount of
the lithium ion is properly determined. For example, a thickness of
lithium metal is 50 to 300 .mu.m, preferably 80 to 200 .mu.m, and
more preferably, 100 to 160 .mu.m.
[E] Lithium Electrode Collector
[0103] According to the present invention, the lithium electrode is
preferably arranged such that the lithium electrode is attached on
the lithium electrode collector made of a conductive porous object.
Here, the lithium electrode collector may use a conductive porous
object such as a stainless mesh.
[0104] When the conductive porous object such as the stainless mesh
is used as the lithium electrode collector, at least the part of
the lithium metal is preferably buried into a porous portion of the
lithium electrode collector. Preferably, more than 80% of the
lithium metal is filled into the porous portion of the conductive
porous object. With this, even when the lithium ion is carried, a
gap generated between the electrodes, caused by loss of the lithium
metal, is reduced and the lithium ion is smoothly carried to the
negative electrode active material.
[0105] An amount of the lithium ion carried to the negative
electrode is determined according to a negative electrode member
for use and characteristics required in the electrical storage
device.
[0106] The lithium electrode collector that forms the lithium
electrode is preferably arranged to face the negative electrode
and/or the positive electrode. With the above arrangement, the
lithium ion can be smoothly carried to the negative electrode
and/or the positive electrode. For example, it is possible to make
the negative electrode terminal and the lithium electrode terminal
to carry the lithium to the negative electrode active material by
arranging the lithium electrode in a cross sectional direction of
the electrode stack unit. However, in this case, when the negative
electrode has a long width, the non-uniform carry (non-uniform
dope) in the electrode becomes large so that a position of the
arranged lithium electrode should be selected considering a cell
arrangement and an electrode size.
[0107] For the electrical storage device of the present invention,
by locally arranging the lithium electrode carried to the negative
electrode and/or the positive electrode at the specific position, a
degree of freedom and productivity in designing the cell can be
improved, and excellent charging and discharging characteristics
can be provided.
[F] Electrolyte
[0108] An electrolyte used for the electrical storage device of the
present invention should be capable of transferring lithium ion.
The electrolyte is typically in a liquid phase, and thus
impregnated into the separator. However, when the separator is not
employed, the electrolyte may be a gel-type or solid phase to
prevent leakage and direct contact among the positive electrode,
the negative electrode and the lithium electrode. For the
separator, a porous object without an electron conductivity having
an opening durable to the electrolyte or the electrode active
material can be used.
[0109] The electrolyte in which the lithium ions can be transferred
may be preferably an aprotic organic solvent of a lithium salt,
from a viewpoint that lithium ion can stably exist without
generating electrolysis at a high voltage.
[0110] The aprotic organic solvent may be, for example, ethylene
carbonate, propylene carbonate, dimethyl carbonate, diethyl
carbonate, .gamma.-butyrolactone, acetonitrile, dimethoxyethane,
tetrahydrofulan, dioxolan, methylene chloride, and sulfolane. In
addition, a mixed solution having more than two types of these
aprotic organic solvents can be used.
[0111] The electrolyte containing the lithium ion can be obtained
by dissolving the supporting electrolyte, which is a lithium ion
source in the single or mixed solvent. The electrolyte used for the
lithium ion source may be, for example, LiI, LiClO.sub.4,
LiAsF.sub.6, LiBF.sub.4, and LiPF.sub.6.
[0112] The supporting electrolyte and the solvent are fully
dehydrated, and then mixed with each other so as to be the
electrolyte. However, a concentration of the supporting electrolyte
in the electrolyte is preferably more than 0.1 mol/l, and more
preferably, in a range of 0.5 to 1.5 mol/l to reduce the internal
resistance caused by the electrolyte.
[G] Outer Container
[0113] The outer container of the electrical storage device of the
present invention is not limited thereto, and may be made of
various types of materials generally used in the battery, including
a metal material such as Fe and aluminum, and a film material. In
addition, a shape of the outer container is not specifically
limited thereto, and can be arbitrarily selected from a rounded
type, a squared type, and the like, a according to its use. With
respect to a small-sized and light-weighted electrical storage
device, a film type outer container using an aluminum laminated
film is preferably used
[0114] A typical film battery uses a three-layered laminated film
having a nylon film arranged outside as an outer member, an
aluminum foil arranged at the center, and a modified polypropylene
adhesive layer arranged inside. The laminated film is typically
drawn depending on the size and thickness of the electrodes that is
fed into, and a unit for stacking or rolling the positive
electrode, the negative electrode and the separator is arranged,
and after injecting the electrolyte, the laminated film is sealed
by the heat sealing. At this time, the positive electrode terminal
(typically, an aluminum foil having a thickness of 100 .mu.m and
the negative electrode terminal (typically, a Ni foil having a
thickness of 100 .mu.m) are protruded out of the battery from a gap
of the laminated film. That is, the laminated film is sealed with
the positive electrode terminal and the negative electrode terminal
interposed therebetween in a simple manner. However, to have the
sufficient sealing, it is required that the terminal uses a metal
foil described above, or that a sealant film is attached in advance
on the terminal surface.
[0115] The film battery is weaker than the battery that uses a
metal case such as a rounded type or a squared type battery having
a contact pressure from the outer container, so that strain and
shape-change of the electrode directly leads to shape-change of the
cell. The negative electrode is hardened with the carried lithium
ion, but when the lithium ion is carried with a rippled electrode,
it is hardened as being rippled. Therefore, the cell is also
deformed and the performance is degraded. However, when the lithium
ion is carried to the negative electrode under a state that
flatness of the positive electrode and the negative electrode is
taken using a vice and the like, the negative electrode becomes
hardened while keeping the flatness. Thus, the cell itself is not
deformed, and the performance can be improved.
[0116] While the three-electrode stack unit 8 is rolled deep into
the laminated film 5 using the laminated films 4 and 5 as an outer
container in FIG. 1, one or both of the laminated films 4 and 5 may
be drawn. In FIG. 1, using a pair of laminated films, the outer
portion is repeatedly heat sealed to cause these to cover the
contents, and thus the contents and sealed.
[0117] According to the present invention, the film member is not
limited to a sheet type film used in FIG. 1, but it may also be
already formed in a tube type or a pouch type. When the tube type
film member is used, two sides that face each other are heat sealed
to encapsulate the contents, and when the pouch type film member is
used, one side that is opened is heat sealed to encapsulate the
contents.
[H] Various Uses of Electrical Storage Device
[0118] The electrical storage device of the present invention
refers to a device capable of charging and discharging, and
specifically, refers to a secondary battery, a capacitor, and so
on. When the electrical storage device of the present invention is
used for any kind of use, a basic arrangement, including three
electrodes such as the positive electrode, the negative electrode,
and the lithium electrode and the electrolyte in which the lithium
ion can be transferred, is identical.
[0119] The electrical storage device of the present invention will
now be described in the context that the electrical storage device
is used as a capacitor. In general, the capacitor uses almost the
same amount of active materials (typically, activated carbon) in
the positive and negative electrodes. The active material for use
in the positive and negative electrodes is charged with the
potential of about 3 V in assembling the cell, so that anions form
an electrical double layer on the positive electrode surface to
increase the potential of the positive electrode, while cations
form an electrical double layer on the negative electrode surface
to reduce the potential. On the other hand, at the time of
charging, anions are emitted from the positive electrode into the
electrolyte and cations are emitted from the negative electrode
into the electrolyte respectively, and the potentials are reduced
and increased respectively to turn back to be about 3 V. That is, a
shape of charging and discharging curve of the positive electrode
and the negative electrode is almost line symmetric with a boundary
of 3 V, and thus an amount of the potential change of the positive
electrode is almost the same as the amount of the potential change
of the negative electrode. In addition, the positive electrode
causes substantially only the anions to come in and out while the
negative electrode causes substantially only the cations to come in
and out.
[0120] Further, when the electrical storage device of the present
invention is used as a capacitor, the positive electrode preferably
uses an active material that can reversibly carry the lithium ion
and/or the anions. This also includes an activated carbon used for
the positive electrode and the negative electrode of the
conventional electrical double layer. In addition, the negative
electrode active material having an electrostatic capacitance more
than three times larger than the electrostatic capacitance per unit
weight of the positive electrode active material is used in the
negative electrode, and further, it is designed such that a weight
of the positive electrode active material is larger than a weight
of the negative electrode active material.
[0121] Here, in the present specification, an electrostatic
capacitance and a capacity are defined as follows. The
electrostatic capacitance of the cell shows a slope of charging
curve of the cell in a unit of F (farad), and an electrostatic
capacitance per unit weight of the cell is a value of the
electrostatic capacitance of the cell divided by a summation of a
weight of the positive electrode active material and a weight of
the negative electrode active material, in a unit of F/g, the
electrostatic capacitance of the positive electrode shows a cure of
the charging curve of the positive electrode in a unit of F, the
electrostatic capacitance per unit weight of the positive electrode
is a value of the electrode capacitance of the positive electrode
divided by the weight of the positive electrode active material
charged into the cell in a unit of F/g, the electrostatic
capacitance of the negative electrode shows a slope of the charging
curve of the negative electrode in a unit of F, and the
electrostatic capacitance per unit weight of the negative electrode
is a value of the electrostatic capacitance of the negative
electrode divided by the weight of the negative electrode active
material charged into the cell in a unit of F/g.
[0122] Further, a cell capacity is a difference between a
discharging initiating voltage of the cell and a discharging finish
voltage, i.e., a product between an amount of the voltage change
and the electrostatic capacitance of the cell, in a unit of C
(coulomb), and 1C refers to a quantity of charges in one second
when a current of 1A flows, indicated in mAh when converted in the
present invention. A positive electrode capacity is a difference
between the potential of the positive electrode at the time of
initiating discharging and the potential of the positive electrode
at the time of finishing discharging (i.e., an amount of positive
electrode potential change) multiplied by the electrostatic
capacitance of the positive electrode in a unit of C or mAh.
Likewise, a negative electrode capacity is a difference between the
potential of the negative electrode at the time of initiating
discharging and the potential of the negative electrode at the time
of finishing discharging (i.e., an amount of negative electrode
potential change) multiplied by the electrostatic capacitance of
the negative electrode in a unit of C or mAh. The cell capacity,
the positive electrode capacity, and the negative electrode
capacity correspond to each other.
[0123] The material having an electrostatic capacitance more than
three times larger than an electrostatic capacitance per unit
weight of the positive electrode active material may include, for
example, PAS. The inventors found that, when discharging is
conducted after 400 mAh/g of lithium ion is carried (charged) to
the PAS, the electrostatic capacitance of more than 650 F/g can be
obtained, and when more than 500 mAh/g of lithium ion is charged,
the electrostatic capacitance of more than 750 F/g can be
obtained.
[0124] The electrostatic capacitances per unit weight of the
positive electrode and the negative electrode for the typical
electrical double-layered capacitor are 60 to 200 F/g, and thus, it
will be appreciated that the PAS has a very large electrostatic
capacitance. Considering the electrostatic capacitance of the used
positive electrode, a charging amount of the negative electrode is
appropriately controlled to ensure the electrostatic storage of
more than three times of the electrostatic storage per unit weight
of the positive electrode. In addition, it is desirable that a
positive electrode active material is heavier than a negative
electrode active material, which is desirably the most advantageous
arrangement.
[0125] Here, when the electrostatic capacitance per unit weight of
the negative electrode active material is less than three times of
the electrostatic capacitance per unit weight of the positive
electrode active material, increase in the capacity is reduced
relative to the conventional double-layered capacitor using the
same amount of the active materials in the positive and negative
electrodes.
[0126] In addition, even when the electrostatic capacitance per
unit weight of the negative electrode active material is more than
three times larger than the electrostatic capacitance per unit
weight of the positive electrode active material, as in the case
that the weight of the positive electrode active material is
smaller than the weight of the negative electrode active material,
the capacity increase is undesirably reduced relative to the
conventional electrical double-layered capacitor.
[0127] The capacitor claimed in claim 10 of the present invention
achieves a high capacity through the following three effects.
[0128] In the first effect, by using the negative electrode active
material having the electrostatic capacitance per unit weight
larger than the electrostatic capacitance per unit weight of the
positive electrode active material, the weight of the negative
electrode active material can be reduced without changing an amount
of the potential change of the negative electrode. There, a
charging amount of the positive electrode active material is
increased and thus the electrostatic capacitance and the capacity
of the cell are increased. In another design, since the
electrostatic capacitance of the negative electrode active material
is large, only the potential change of the negative electrode is
reduced, and consequently, an amount of the potential change of the
positive electrode is increased so that the electrostatic
capacitance and the capacity of the cell are increased.
[0129] In the second effect, to obtain the capacity required for a
negative electrode capacity, a predetermined amount of lithium ion
is carried to the negative electrode in advance, so that the
potential of the negative electrode is lower than 3 V, compared to
a case where the potential of the positive electrode is about 3 V,
at the time that the lithium ion is carried to the negative
electrode in advance.
[0130] A voltage when the voltage of the cell is increased until
the electrolyte is oxidized and dissolved is determined almost by
the potential of the positive electrode. Compared to a capacitor
having the typical cell arrangement, the capacitor of the present
invention having the lithium ion carried in advance has a higher
breakdown voltage, but this is due to the low potential of the
negative electrode. That is, while the use voltage of the
conventional capacitor is in a range of about 2.3 to 2.7 V, the
arrangement of the present invention may be in as high as more than
3 V, thus improving energy density.
[0131] Further, as the third effect, the potential of the positive
electrode is lowered, and thus, the capacity of the positive
electrode can be increased. With a lowered potential of the
negative electrode, the amount of the potential change while
charging is conducted at the positive electrode can be further
increased. Depending on the design, the potential of the positive
electrode is lower than 3 V at the end of discharging, and thus,
for example, the discharging potential can be lowered down to 2 V
(Here, the potential is lowered largely due to anion-emission for
up to 3 V discharging, and due to doping of the lithium ion for
less than 3 V)
[0132] In the conventional electrical double-layered capacitor, the
potential of the positive electrode is lowered only down to about 3
V at the time of discharging, which is because, at this time, the
potential of the negative electrode is 3 V and thus the cell
voltage becomes 3 V. That is, the arrangement of the present
invention where the potential of the positive electrode is lowered
down to 2 V may achieve a high capacity relative to the
conventional electrical double-layered capacitor where the
potential of the positive electrode is lowered just to 3 V.
[I] Specific Example of Inner Arrangement
[0133] A specific example of the inner arrangement of the
electrical storage device according to the present invention will
now be described.
BRIEF DESCRIPTION OF THE DRAWINGS
[0134] FIG. 1 is a perspective view of a first embodiment of the
present invention;
[0135] FIG. 2 is a plan view of a first embodiment of the present
invention;
[0136] FIG. 3 is a cross-sectional view taken along I-I' of FIG.
2;
[0137] FIG. 4 is a cross-sectional view taken along II-II' of FIG.
2;
[0138] FIG. 5 is a cross-sectional view of a first example
arrangement of a three-layered stack unit according to the present
invention;
[0139] FIG. 6 is a cross-sectional view of a second example
arrangement of a three-layered stack unit according to the present
invention;
[0140] FIG. 7 is a cross-sectional view of a third example
arrangement of a three-layered stack unit according to the present
invention;
[0141] FIG. 8 is a plan view of a second embodiment of the present
invention;
[0142] FIG. 9 is a plan view of a third embodiment of the present
invention;
[0143] FIG. 10 is a cross-sectional view taken along I-I' line of
FIG. 9;
[0144] FIG. 11 is a cross-sectional view taken along II-II' line of
FIG. 9;
[0145] FIG. 12 is a plan view of a fourth embodiment of the present
invention;
[0146] FIG. 13 is a cross-sectional view taken along I-I' line of
FIG. 2;
[0147] FIG. 14 is a cross-sectional view taken along II-II' line of
FIG. 2;
[0148] FIG. 15 is an expanded perspective view of an example
electrode stack unit according to the present invention; and
[0149] FIG. 16 is an expanded perspective view of an example
electrode stack unit according to the present invention.
[0150] Hereinafter, attached numerals will be described.
[0151] The reference numeral 1 is a positive electrode, the
reference numeral 2 is a negative electrode, the reference numeral
1a is a collector (positive electrode), the reference numeral 2a is
a collector (negative electrode), the reference numeral 1b is a
positive electrode terminal, the reference numeral 2b is a negative
electrode terminal, the reference numeral 1c is a positive
electrode laminated material composed of positive electrode active
material, binder and the like, the reference numeral 2c is a
negative electrode laminated material composed of negative
electrode active material, binder and the like, the reference
numeral is a separator, the reference numeral 4 is a laminate film,
the reference numeral 5 is a laminate film (deeply drawn), the
reference numeral 6 is an electrode stack unit, the reference
numeral 7 is a lithium electrode, the reference numeral 7a is a
lithium electrode collector, the reference numeral 7b is a lithium
electrode terminal, the reference numeral 7c is a lithium metal or
lithium alloy, the reference numeral 8 is a three-electrode stack
unit, the reference numerals 9a, 9b and 9c are wirings, and the
reference numeral 10 is an electrode rolling unit. The capital
letter A is a thermal connection portion between the positive
electrode terminal and a outer film, the capital letter B is a
thermal connection portion between the negative electrode terminal
and the surface film, the capital letter C is a thermal connection
portion between the lithium electrode terminal and the surface
film, the capital letter D is a thermal connection portion of the
surface film, the capital letter A' is a welding portion between a
terminal welding portion of the positive electrode collector and
the positive electrode terminal, the capital letter B' is a welding
portion between a terminal welding portion of the negative
electrode collector and the negative electrode terminal, the
capital letter C' is a welding portion between a terminal welding
portion of the lithium electrode collector and the lithium
electrode terminal, and the symbol (*) shows a width of the widened
electrode of the second embodiment comparing with the other
Embodiments.
BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment
[0152] FIG. 1 is a perspective view of a first embodiment of the
present invention; FIG. 2 is a plan view of a first embodiment of
the present invention; FIG. 3 is a cross-sectional view taken along
I-I' of FIG. 2; and FIG. 4 is a cross-sectional view taken along
II-II' of FIG. 2.
[0153] In the first embodiment, a lithium electrode 7 is arranged
on an electrode stack unit 6, in which an electrode couple
including a positive electrode 1 and a negative electrode 2 are
stacked one after another so as to form a three-electrode stack
unit 8.
[0154] In the first embodiment, three sheets of negative electrode
collector 2a, and two sheets of positive electrode collector la are
used to form the electrode stack unit 6. The electrode stack unit 6
includes separators 3 between the positive electrodes and the
negative electrodes in order to prevent direct contact between the
positive and negative electrodes. Also, from the lower layer, there
are stacked a first negative electrode collector 2a having the
negative electrode arranged at the upper surface, a first positive
electrode collector la having the positive electrodes 1 arranged at
both surfaces, a second negative electrode collector 2a having the
negative electrodes arranged at both surfaces, a second positive
electrode collector 1a having the positive electrodes 1 arranged at
both surfaces, and a third negative electrode collector 2a having
the negative electrode arranged at the lower surface. In addition,
a lithium electrode collector 7a having the lithium electrode 7
arranged at the lower surface is arranged on the electrode stack
unit 6 with the separator 3 interposed therebetween so as to form
the three-electrode stack unit 8.
[0155] In FIG. 1, the positive electrode collector 1a, the negative
electrode collector 2a, and the lithium electrode collector 7a have
protrusions at terminal connection portions A', B', and C', and are
welded to the positive electrode terminal 1b, the negative
electrode terminal 2b, and the lithium electrode terminal 7b at the
terminal connection portions A', B', and C'. A shape of the
protrusion that becomes the terminal welding portion is not
specifically limited. It is desirable that the welding is conducted
through an ultrasonic welding by binding the protrusions of several
sheets of positive electrode collectors (or negative electrode
collectors) According to the first embodiment, the positive
electrode terminal 1b and the negative electrode terminal 2b are
protruded out to opposite sides respectively, and the positive
electrode terminal 1b and the lithium electrode terminal 7b are
protruded out to the same side, but the locations to arrange the
respective terminals are not limited thereto.
[0156] In the first embodiment, while the electrode stack unit 6
has four layers of electrode couples, each of which includes a pair
of the positive electrode and the negative electrode, the layer
number of the electrode couple for the electrode stack unit 6 is
not specifically limited, and thus either one layer or more than
two layers can be arranged. In addition, the electrode stack unit 6
may have more than two layers of electrode couple by rolling the
electrode couple including a pair of the positive electrode and the
negative electrode.
[0157] In addition, when the electrode stack unit 6 has at least
one positive electrode and one negative electrode, the electrode
stack unit 6 does not necessarily have the equal number of the
positive electrode and the negative electrode. For example, it is
possible to prepare one layer of common positive electrode to two
or more layers of negative electrode.
[0158] Further, in the first embodiment, while the three-electrode
stack unit 8 having the lithium electrode 7 arranged on a surface
of the electrode stack unit 7 is illustrated, the position of the
lithium electrode 7 is not limited thereto, and it may be arranged
on the lowermost layer, or on the lowermost and uppermost layers,
or on an intermediary layer of the electrode stack unit. For
example, instead of the three-electrode stack unit 8 of the first
embodiment, a three-electrode stack unit 8 having a different layer
arrangement shown in FIGS. 5 to 7 may be used.
[0159] FIG. 5 shows another layer arrangement of the
three-electrode stack unit 8. As shown in FIG. 5, the lithium
electrode 7 that attaches the lithium metal to the lithium
electrode collector 7a is arranged below the electrode stack unit
6, in which the positive electrode 1, the separator 3, and the
negative electrode 2 are stacked one after another so as to form
the three-electrode stack unit 8.
[0160] FIG. 6 shows another layer arrangement of the
three-electrode stack unit 8. Referring to FIG. 6, the lithium
electrode 9 that attaches the lithium metal to the lithium
electrode collector 7a is arranged on and below the electrode stack
unit 6 respectively so as to form the three-electrode stack unit
8.
[0161] In addition, in another example shown in FIG. 7, the lithium
electrode 7 is arranged in the very middle of the electrode stack
unit 6 so as to form the three-electrode stack unit 8.
[0162] Likewise, in the stack type electrode arrangement, the
arrangement position of the lithium electrode 7 can be properly
changed.
[0163] Several sheets of positive electrodes 1, negative electrodes
2, and lithium electrodes 7 stacked in the three-electrode stack
unit 8 shown in FIGS. 5 to 7 are bound to one and then connected to
wirings 9a, 9b, and 9c. The wirings 9a, 9b and 9c, for example, are
for the positive electrode terminal 1b, the negative electrode
terminal 2b, and the lithium electrode terminal 7b, respectively.
When each electrode is connected to the wiring, it is desirable
that parts of the respective electrode collectors are bound through
the ultrasonic welding.
[0164] While the lithium ions are carried to the negative electrode
from the lithium electrode, for example, when -0.05 V is applied
between the negative electrode and the lithium electrode through
the wiring 9b and 9c, a current is flowed into the lithium
electrode 7, and the lithium ions eluted out of the lithium
electrode 7 is carried (doped) to the negative electrode 2. In
addition, while the lithium ions are emitted from the negative
electrode 2 and carried to the positive electrode 1, at the time of
discharging, a current can be drawn at this time through the
wirings 9a and 9b. In addition, at the time of charging, for
example, when 3 V is applied between the positive electrode 1 and
the negative electrode 2 through the wirings 9a and 9b, i.e., when
the current is flowed into the positive electrode 1, the lithium
ion carried to the positive electrode 1 are carried again to the
negative electrode 2.
Second Embodiment
[0165] The second embodiment will now be described. FIG. 8 is a
plan view of the second embodiment. The second embodiment has the
same arrangement as in the first embodiment except that
three-electrode external terminals are protruded at the same
side.
[0166] Like numbers between the first and second embodiments refer
to like elements, so that only different portions will be described
in detail. Referring to the second embodiment, the positive
electrode terminal 1b, the negative electrode terminal 2b, and the
lithium electrode terminal 7b are protruded out of the same side.
When the laminated film has the same size, the electrode size can
be made large with the positive electrode terminal 1b, the negative
electrode terminal 2b and the lithium electrode terminal 7b, so
that a capacity is preferably increased. Comparing the first
embodiment where the positive electrode terminal 1b, the lithium
electrode terminal 7b, and the negative electrode terminal 2b are
protruded at the opposite sides as shown in FIG. 2, with the second
embodiment where three electrode terminals are protruded at the
same sides as shown in FIG. 8, a large electrode size can be taken
in the second embodiment only for a width indicated by (*).
Third Embodiment
[0167] The third embodiment will now be described. FIG. 9 is a plan
view of the third embodiment. The third embodiment involves a plan
view of a capacitor having an arrangement in which the plate type
lithium electrode is rolled into the center. FIG. 10 is a
cross-sectional view taken along an I-I' line of FIG. 9, and FIG.
11 is a cross-sectional view of II-II' line of FIG. 9. Like numbers
between the first and third embodiments refer to like elements, so
that only different portions will be described in detail.
[0168] In the third embodiment, the plate type lithium electrode 7
is rolled into the center as shown in FIG. 10. The lithium
electrode 7 is formed on both surfaces of the lithium electrode
collector 7a. The positive electrode 1 and the negative electrode 2
are formed on one surface of the ribbon type positive electrode
collector 1a and negative electrode collector 2a, respectively.
With a center of the lithium electrode collector 7a having the
lithium electrode 7 arranged on two sides, the separator 3, the
negative electrode 2, the separator 3, and the positive electrode 1
are repeatedly rolled one after another in a circular pattern, and
then formed through a press.
Fourth Embodiment
[0169] The fourth embodiment will now be described. FIG. 12 is a
plan view of the fourth embodiment. The fourth embodiment involves
a plan view of a capacitor having an arrangement in which the
lithium electrode 7 is rolled around the outermost perimeter. FIG.
13 is a cross-sectional view taken along I-I' line of FIG. 12, and
FIG. 14 is a cross-sectional view of II-II' line of FIG. 12. Like
numbers between the first and fourth embodiments refer to like
elements, so that only different portions will be described in
detail.
[0170] In the fourth embodiment, the lithium electrode 7 is
arranged around the outermost perimeter of the electrode stack unit
having a rolled arrangement. The positive electrode 1 and the
negative electrode 2 are formed on one surface of the ribbon type
positive electrode collector la and negative electrode collector
2a, respectively. In addition, the lithium electrode attaches the
lithium metal 7c at one surface of the lithium electrode collector
7a. After forming the electrode stack unit having a rolled
arrangement in which the separator 3, the positive electrode 1, the
separator 3, and the negative electrode 2 are repeatedly rolled one
after another, the lithium metal 7c side of the lithium electrode 7
that attaches the lithium metal 7c at one surface of the lithium
electrode collector 7a are arranged inside and rolled around once,
and then formed through a press.
[J] Electrical Storage Device Manufacturing Method
[0171] An example of manufacturing method of the electrical storage
device of the present invention will now be described. First, a
process of manufacturing the positive electrode, the negative
electrode and the lithium electrode is described. The positive
electrode is formed such that the positive electrode active
material is mixed with binder resin to make slurry and the slurry
is coated and dried on the positive electrode collector. In the
same manner, the negative electrode is formed such that the
negative electrode active material is mixed with binder resin to
make slurry and the slurry is coated and dried on the negative
electrode collector. The lithium electrode is formed such that the
lithium metal is attached on the lithium electrode collector made
of conductive porous objects.
[0172] While the thickness of each layer can be arbitrarily
determined according to its use, the thickness of the negative
electrode collector is, for example, 10 to 100 .mu.m, and the
thickness of the coating of the electrode active material is 50 to
300 .mu.m for one surface. Therefore, the overall thickness of (the
electrode active material+the electrode collector) things after
forming the electrode is about 100 to 500 .mu.m. In addition, the
thickness of the lithium electrode collector is about 10 to 200
.mu.m, and the thickness of the lithium metal that becomes the
lithium electrode is about 50 to 300 .mu.m.
[0173] The electrode collector that forms the electrode is dried,
and then is cut to a width corresponding to the size of the outer
container of the electrical storage device. When the electrode
stack unit in a rolled arrangement is manufactured, it is cut in a
ribbon pattern. At this time, it can be cut in a pattern having a
protrusion portion as a terminal welding portion.
[0174] Next, the electrode collector that forms the electrode has a
separator interposed between the positive electrode, the negative
electrode, and the lithium electrode not to directly contact with
each other so as to form the three-electrode stack unit. FIGS. 15
and 16 are expanded diagrams of an electrode stack unit, in which
the shape of the terminal welding portion is shown in the stacked
direction. FIG. 15 shows an example in which the terminal welding
portion of the positive electrode and the terminal welding portion
of the negative electrode are protruded out of the opposite sides
respectively, and FIG. 16 shows an example in which the terminal
welding portion of the positive electrode and the terminal welding
portion of the negative electrode are protruded out of the same
side. However, the directions of terminals of the positive and
negative electrodes are not limited to the above two types.
[0175] The terminal welding portion of the positive electrode
collector of the assembled three-electrode stack unit is welded
into the positive electrode terminal, the terminal welding portion
of the negative electrode collector to the negative electrode
terminal, and the terminal welding portion of the lithium electrode
collector to the lithium electrode terminal respectively, through
the ultrasonic welding.
[0176] The three-electrode stack unit welded to the external
terminal is arranged in the outer container, and an electrolyte
inlet is left and the outer container is closed through heat
sealing. At this time, at least the part of the external terminal
is exposed to the outside of the outer container in order to
connect with the external circuit. The electrolyte is injected from
the electrolyte inlet of the outer container, and the outer
container is filled with the electrolyte. Then, the electrolyte
inlet is closed through heat sealing to fully seal the outer
container, so that electrical storage device of the present
invention can be obtained.
[0177] In the electrical storage device of the present invention
described above, the lithium ion can be carried to the negative
electrode by flowing current between the lithium electrode and the
negative electrode through the lithium electrode terminal and the
negative electrode terminal, for example. With -0.05 V applied
between the negative electrode and the lithium electrode (a current
flowed from the external circuit to the lithium electrode), the
lithium ion is transferred from the lithium electrode through the
electrolyte, and carried to the negative electrode. At this time,
under a state where the positive and negative electrodes are
planarized due to a vice and so on, when the lithium ion is carried
to the negative electrode, the negative electrode is hardened while
keeping the flatness. Thus, there is no shape-change of a cell
itself, which preferably improves the cell performance. A timing to
carry the lithium to the negative electrode is not specifically
limited, but when the electrical storage device is charged before
carrying the lithium to ion the negative electrode, the electrolyte
may be dissolved due to a high potential of the positive electrode.
Thus, it is desirable that the negative electrode terminal and the
lithium electrode terminal are shirt-circuit before charging the
electrical storage device.
[0178] When the lithium ion is carried to the negative electrode
from the lithium electrode, the lithium metal of the lithium
electrode is gradually reduced, but when a part of the lithium
metal of the lithium electrode exists after carrying the lithium
ion to the negative electrode, it is possible to use the remaining
lithium electrode of the lithium metal in order to check the
potential of the positive or negative electrode as a reference
electrode.
[0179] That is, for example, when the potential of the negative
electrode is lower than 0 V, the lithium metal may be
electro-crystallized on the negative electrode surface. Thus, there
needs a careful attention to determine a charging condition.
Regarding this, according to the present invention, the electrical
storage device that can use the lithium electrode as a reference
electrode can determine the potential of the negative electrode at
the time of charging, so that it is possible to control the
potential of the negative electrode to be lower than 0 V for a
charging process.
[0180] In addition, according to the present invention, after
checking the potential of the negative electrode and measuring the
cell capacity, 0 V is applied between the negative electrode
terminal and the lithium electrode terminal to the lithium metal
that exists in the lithium electrode through a potentio
galvanostat, and a proper amount per unit weight of the negative
electrode active material is carried again so that the electrical
storage device can be regenerated to the capacity before testing
the electrical storage device under a high temperature load.
EXAMPLES
Examples 1 to 3
Comparative Examples 1 and 2
(Manufacturing Method of Negative Electrode)
[0181] A phenol resin formation plate having a thickness of 0.5 mm
is put into a siliconit electric furnace, and annealed up to
500.degree. C. at a rate of 50.degree. C./hr under the nitrogen
atmosphere, and further up to 650.degree. C. at a rate of
10.degree. C./hr so as to synthesize PAS. The above PAS plate is
ground with a disk mill to obtain the PAS powder. The PAS powder
has an H/C ratio of 0.22.
[0182] Next, 100 parts by weight of the PAS power is sufficiently
mixed with a solution, in which 10 parts by weight of the
polyvinylidene power is dissolved in 120 parts by weight of an
N-methyl pyrrolidone, so as to obtain slurry. The slurry is coated
and dried on both surfaces of a copper expanded metal having a
thickness of 40 .mu.m (porosity of 50%), which is pressed to obtain
a PAS negative electrode having a thickness of 200 .mu.m.
(Manufacturing Method of Positive Electrode)
[0183] A phenol resin formation plate having a thickness of 0.5 mm
is put into a Siliconit electric furnace, and annealed up to
500.degree. C. at a rate of 50.degree. C./hr under the nitrogen
atmosphere, and further up to 650.degree. C. at a rate of
10.degree. C./hr so as to synthesize PAS. The above PAS plate is
activated by water vapor, and then ground with a nylon ball mill to
obtain the PAS powder. The PAS powder has a BET specific surface
area of 1500 m.sup.2/g, and an H/C ratio of 0.10 from the element
analysis.
[0184] 100 parts by weight of the PAS power are sufficiently mixed
with a solution, in which 10 parts by weight of the polyvinylidene
power is dissolved in 100 parts by weight of an N-methyl
pyrrolidone, so as to obtain slurry. The slurry is coated and dried
on both surfaces of an aluminum expanded metal having a thickness
of 40 .mu.m (porosity of 50%), which is pressed to obtain a PAS
positive electrode having a thickness of 380 .mu.m.
(Measuring Electrostatic Capacitance per Unit Weight of Negative
Electrode)
[0185] The negative electrode is cut into four pieces having a size
of 1.5.times.2.0 cm.sup.2 to obtain sample negative electrodes. As
a counter electrode to the negative electrode, the metal lithium
having a size of 1.5.times.2.0 cm.sup.2, and a thickness of 200
.mu.m is stacked with polyethylene non-woven fabrics having a
thickness of 50 .mu.m as a separator to assemble a sample cell. The
metal lithium is used as a reference electrode. 1 mol/l LiPF.sub.6
solution, which include LiPF.sub.6 dissolved in propylene
carbonate, is used as the electrolyte. The weight of the negative
electrode active material is charged with 400 mAh/g of lithium ion
in a charging current of 1 mA, and then discharges at 1 mA until
the voltage becomes 1.5 V. The electrostatic capacitance per unit
weight of the negative electrode extracted from a discharging time
while the potential varies from that of one minute after the
beginning of the discharge to 0.2 V is 653 F/g.
(Measuring Electrostatic Capacitance per Unit Weight of Positive
Electrode)
[0186] The positive electrode is cut into three pieces having a
size of 1.5.times.2.0 cm.sup.2, and these pieces are used for the
positive electrode, the negative electrode and a reference
electrode. A sample cell of the capacitor is assembled by
interposing polyethylene non-woven fabric having a thickness of 50
.mu.m between the positive and negative electrodes as a separator.
1 mol/l triethylmethylammoniumtetrafluoroborate (TEMA BF.sub.4)
solution, which includes TEMA BF.sub.4 dissolved in propylene
carbonate, is used as a positive electrode electrolytic solution.
The sample cell is charged by a charging current of 10 mA until the
voltage becomes 2.5 V, and then a static voltage charging is
performed. After one hour of charging time, the sample cell
discharges at 1 mA until the voltage becomes 0 V. The electrostatic
capacitance per unit weight of the cell extracted from a
discharging time while the potential varies between 2.0 to 1.5 V is
21 F/g. In addition, the electrostatic capacitance per unit weight
of the positive electrode extracted in the same manner from the
potential difference between the reference and positive electrodes
is 85 F/g.
(Forming Electrode Stack Unit 1)
[0187] The PAS negative electrode having a thickness of 200 .mu.m
and the PAS positive electrode having a thickness of 380 .mu.m are
cut into pieces having sizes of 5.0.times.7.0 cm.sup.2 (not
including the area of the terminal welding portion) and the shape
of FIG. 15. A cellulose/rayon combined non-woven fabric having a
thickness of 25 .mu.m is used as a separator, the terminal welding
portions of the positive electrode collector and the negative
electrode collector are arranged at the opposite sides as shown in
FIG. 15, and the counter surfaces of the positive and negative
electrodes are stacked in 10 layers. The separators are arranged in
the uppermost and lowermost portions, and four sides are sealed
with tapes. The terminal welding portion of the positive electrode
collector (five sheets) and the terminal welding portion of the
negative electrode collector (six sheets) are ultrasonic welded to
an aluminum positive electrode terminal and a Ni negative electrode
terminal having a width of 20 mm, a length of 50 mm, and a
thickness of 0.1 mm so as to obtain the electrode stack unit 1.
Further, five sheets of the positive electrode and six sheets of
the negative electrode are used, and one of two sheets of the
negative electrode formed on both surfaces of each of the negative
electrodes at the outermost sides is removed as shown in FIG. 1.
The thickness is 120 .mu.m. The weight of the positive electrode
active material is 1.7 times larger than the weight of the negative
electrode active material.
(Forming Electrode Stack Unit 2)
[0188] The PAS negative electrode having a thickness of 200 .mu.m
and the PAS positive electrode having a thickness of 380 .mu.m are
cut into pieces having sizes of 5.0.times.8.0 cm.sup.2 (not
including the area of the terminal welding portion) and the shape
of FIG. 16. The electrode stack unit 2 is obtained in the same
manner as the electrode stack unit 1 except that the terminal
welding portion of the positive electrode collector and the
negative electrode collector are arranged at the same side.
(Forming Cell 1)
[0189] As shown in FIG. 1, a layer of lithium metal foils (160
.mu.m, 5.0.times.7.0 cm.sup.2) pressed on a stainless net having a
thickness of 80 .mu.m is used as the lithium electrode in an outer
film drawn as deep as 3.5 mm, and arranged at the opposite side of
the negative electrode on the electrode stack unit 1 so as to
obtain a three-electrode stack unit. Further, a Ni-made lithium
electrode terminal having a width of 10 mm, a length of 50 mm, and
a depth of 0.1 mm is ultrasonic welded to the terminal welding
portion (one sheet) of the lithium electrode collector, and
arranged to face the same orientation of the positive electrode
terminal as shown in FIG. 1.
[0190] The three-electrode stack unit is arranged in the drawn
outer film, and covered with the outer laminated film. Three sides
are sealed, and then 1 mol/l LiPF.sub.6 solution, which includes
LiPF.sub.6 dissolved in a mixed solvent of ethylene carbonate,
diethyl carbonate, and propylene carbonate in a weight ratio of
3:4:1, is impregnated under vacuum state into the unit as the
electrolyte. After that, the remaining side is sealed, and the film
type capacitor is assembled into eight cells. The negative
electrode terminal and the lithium electrode terminal are made
short-circuit immediately after assembling.
(Forming Cell 2)
[0191] In the same manner as the first cell, a layer of lithium
metal foils (160 .mu.m, 5.0.times.8.0 cm.sup.2) pressed on a
stainless net having a thickness of 80 .mu.m is used as the lithium
electrode, and arranged at the opposite side of the negative
electrode on the electrode stack unit 2 so as to obtain the
three-electrode stack unit. However, the positive electrode, the
negative electrode and the lithium electrode terminal face the same
directions as shown in FIG. 5. The three-electrode stack unit is
arranged in the deeply drawn outer film, and the film type
capacitor is assembled into eight cells like the forming of the
cell 1. The negative electrode terminal and the lithium electrode
terminal are made short-circuit immediately after assembling.
(Forming Cell 3)
[0192] In the same manner as the first cell, the film type
capacitor is assembled into eight cells. Immediately after
assembling, -0.05 V is applied between the negative electrode
terminal and the lithium electrode terminal through a
potentiogalvanostat.
(Forming Cell 4)
[0193] The film type capacitor is assembled into eight cells in the
same manner as the forming of the cell 1 except that the terminal
welding portion of the lithium electrode collector (one sheet) and
the terminal welding portion of the negative electrode collector
(six sheets) are ultrasonic welded to each other, the negative
electrode is short-circuited with the lithium electrode in the
cell, and the Ni negative electrode terminal having a width of 10
mm, a length of 50 mm, and a thickness of 0.1 mm is ultrasonic
welded.
(Forming Cell 5)
[0194] The film type capacitor is assembled into eight cells in the
same manner as the forming of the cell 2 except that the terminal
welding portion of the lithium electrode collector (one sheet) and
the terminal welding portion of the negative electrode collector
(six sheets) are ultrasonic welded to each other, the negative
electrode is short-circuited with the lithium electrode in the
cell, and the Ni negative electrode terminal having a width of 10
mm, a length of 50 mm, and a thickness of 0.1 mm is ultrasonic
welded.
(Initial Estimation of Cell)
[0195] On three days after assembling the cells 1 to 5, one from
the respective cells is disassembled. It is found that the lithium
metal of the cell 3 totally disappears, from which it is determined
that the lithium ion for obtaining 650 F/g of electrostatic
capacitance per unit weight of the negative electrode active
material is preliminarily charged. For the remaining cells 1, 2, 4,
and 5, the lithium metal is left.
[0196] On seven days after assembling the cells, one of the
respective cells is disassembled. It is found that the lithium
metal in all cells totally disappears, from which it is determined
that the lithium for obtaining 650 F/g of electrostatic capacitance
per unit weight of the negative electrode active material is
preliminarily charged for all cells.
[0197] When the lithium ion is carried to the negative electrode
using the external circuit, a minus voltage is applied between the
negative electrode terminal and the lithium electrode terminal,
thereby a speed to carry can be accelerated. However, when the
applied minus voltage is too high, the lithium metal may be
electro-crystallized on the negative electrode surface, thereby the
attention should be paid to.
(Cell Characteristic Estimation)
[0198] After measuring thickness of the cells 1 to 5 with
micrometer, the cells are charged by a constant current of 1000 mA
until the voltage becomes 3.3 V, and then the constant current and
constant voltage charging applying a constant voltage of 3.3 V is
performed for one hour. Next, the cell discharges at a constant
current of 100 mA until the voltage becomes 1.6 V. The cell
capacity and the energy density are estimated after repeating
3.3-1.6 v cycles three times. In addition, at the fourth time of
discharging, the cell discharges 10 A, and the direct current
resistance of the cell is measured from IR drop immediately after
discharging. The results are shown in Table 1. The data are average
values of six cells. TABLE-US-00001 TABLE 1 Cell Cell Energy DC
Example thickness Capacitance density resistance No. (mm) (mAh)
(Wh/I) (m.OMEGA.) Example 1 3.82 91 15 25.6 (Cell 1) Example 2 3.85
102 16 23.0 (Cell 2) Example 3 3.83 92 15 26.1 (Cell 3) Comparative
4.05 90 15 29.8 Example 1 (Cell 4) Comparative 4.11 101 16 28.2
Example 2 (Cell 5)
[0199] Even when the size of the film battery appearance is equal,
the filling ratio of the active material varies with how to install
the terminals, and thus differences of the capacity and energy
density are induced. It is preferable that the terminals be
arranged at the same side like the cell 2 or 5 since the terminals
can have higher capacity with the above structure.
[0200] In addition, the cells 1 to 3, which carry lithium ion
through the external circuit, have flat cell surfaces and low DC
internal resistances, however, the cells 4 and 5, in which
short-circuits are made, are warped to the cell surfaces, and
distortions are induced, thereby the average cell thickness is
higher for the cells 1 to 3. In particular, the electrode edge
portions are distorted a lot. Further, the DC internal resistance
is larger than those of the cell 1 to 3.
Comparative Example 3
[0201] Except that the lithium ion is not carried to the negative
electrode, six cells are assembled in the same manner as the first
example.
[0202] The six cells are charged by a constant current of 1000 mA
until the cell voltage becomes 3.3 V, and then the constant current
and constant voltage charging applying 3.3 V is performed for one
hour. Next, the cell discharges at a constant current of 100 mA
until the cell voltage becomes 1.6 V. After repeating the cycle of
3.3-1.6 V three times, the cell capacity is estimated to be 30 mAh
(average of six cells). The energy density of the capacitor is 4.5
Wh/l, that is, less than 10 Wh/l. When the lithium ion is not
carried to the negative electrode, a sufficient capacity cannot be
obtained.
Comparative Example 4
[0203] Except that the aluminum foil having a thickness of 20 .mu.m
is used in the positive electrode collector and that the copper
foil having a thickness of 20 .mu.m is used in the negative
electrode collector, 7 cells are assembled in the same manner as
the first example. Right after assembling, the negative electrode
terminal and the lithium electrode terminal are short-circuited.
After leaving them at the room temperature for 20 days, one cell is
disassembled, in which the most lithium metal is left.
[0204] The remaining six cells are charged by a constant current of
1000 mA until the battery voltage becomes 3.3 V, and then the
constant current and constant voltage charging applying 3.3 V is
performed for one hour. Next, the cell discharges at a constant
current of 100 mA until the cell voltage becomes 1.6 V. After
repeating the cycle of 3.3-1.6 V, the cell capacity is estimated to
be 32 mAh (average of six cells). The energy density of the
capacitor is 4.8 Wh/l, that is, less than 10 Wh/l.
[0205] When metal foils (porosity 0%) are used in the collectors,
and the lithium ion electrode is arranged to face the negative
electrode, the lithium ion cannot be carried to the negative
electrode, and sufficient capacity cannot be obtained.
Example 4
[0206] Except that the lithium metal foil of 320 .mu.m is used as a
lithium electrode, seven cells are assembled in the same manner as
the first example. After assembling, 0 V is applied between the
negative electrode terminal and the lithium electrode terminal
under a constant voltage condition by a potentiogalvanostat
(manufactured by Hokuto Denko Corporation, HA-301), a current
flowing between the negative electrode and the lithium electrode is
accumulated by a coulomb/ampere-hour meter (manufactured by Hokuto
Denko Corporation, HF-201), and the carry of lithium ion is
finished when the accumulated amount of current becomes 400 mAh/g
per unit weight of the negative electrode active material, thereby,
the lithium ion for obtaining 650 F/g of electrostatic capacitance
per unit weight of the negative electrode active material is
preliminarily charged. After finishing preliminary charging of the
lithium ion, one cell is disassembled. Here, it is found that about
a half the initial thickness of the lithium metal foil is left.
[0207] In addition, the potential difference between the negative
electrode and the lithium electrode of the remaining six cells is
measured to be around 0.25 V, therefore, it could be verified that
all of six cells are preliminarily charged with lithium ion.
[0208] When the lithium ion is carried to the negative electrode
through the external circuit, the carry amount could be controlled
to the lithium metal foil prepared in the cell by using the
coulomb/ampere-hour meter and the like. That is, the lithium ion
carry amount of the negative electrode becomes 400 mAh/g by
supplying the lithium ion from the lithium electrode to the
negative electrode.
[0209] The remaining six cells are charged by a constant current of
1000 mA until the battery voltage becomes 3.3 V, and then the
constant current and constant voltage charging applying 3.3 V is
performed for one hour. Next, the cell discharges at a constant
current of 100 mA until the cell voltage becomes 1.6 V. After
repeating the cycle of 3.3-1.6 V, the cell capacity is estimated to
be 91 mAh (average of six cells). The energy density of the
capacitor is 15 Wh/l.
[0210] For the above-mentioned charging process, it is found by
using the lithium electrode as a reference electrode that the
potential of the negative electrode is 0.18 V, that is, the
potential does not drop below 0 V. When the potential of the
negative electrode is less than 0 V, the lithium metal may be
electro-crystallized on the surface of the negative electrode.
Therefore, the attention should be paid to determine the charging
conditions. However, since the electrical storage device according
to the example is capable of using the lithium electrode as a
reference electrode, the potential of the negative electrode at the
time of charging can be verified, thereby it is preferable.
Example 5
[0211] Except that a lithium electrode such as the lithium
electrode using the lithium metal foil of 160 .mu.m is arranged at
the lower portion of the electrode stack unit 1, and used as a
reference electrode, seven cells are assembled in the same manner
as the first example. Further, contrary to the lithium electrode,
the terminal of the reference electrode is arranged in the same
side of the negative electrode terminal. Right after assembling,
the negative electrode terminal and the lithium electrode terminal
are short-circuited.
[0212] On seven days after assembling the cells, one cell is
disassembled. It is found that the lithium metal totally
disappeared, from which it is determined that the lithium ion for
obtaining 650 F/g of electrostatic capacitance per unit weight of
the negative electrode active material is preliminarily
charged.
[0213] Further, for the remaining six cells, the potential
difference between the negative electrode and the reference
electrode is measured to be 0.25 V, thereby it could be determined
that all six cells are preliminarily charged with lithium ion.
[0214] The remaining six cells are charged by a constant current of
1000 mA until the battery voltage becomes 3.3 V, and then the
constant current and constant voltage charging applying 3.3 V is
performed for one hour. Next, the cell discharges at a constant
current of 100 mA until the cell voltage becomes 1.6 V. After
repeating the cycle of 3.3-1.6 V, the cell capacity is estimated to
be 91 mAh (average of six cells) The energy density of the
capacitor is 15 Wh/l.
[0215] In the above-mentioned charging process, it is found by
using the reference electrode that the potential of the negative
electrode is 0.18 V, that is, the potential does not drop below 0
V. When the potential of the negative electrode is less than 0 V,
the lithium metal may be electro-crystallized on the surface of the
negative electrode. Therefore, the attention should be paid to
determine the charging conditions. While it is preferable to have a
reference electrode like the present example, since the potential
of the negative electrode can be checked at the time of charging,
it is also preferable to arrange more lithium metal than that
required for preliminary charging, since remaining lithium metal
after the completion of preliminary charging can be used as the
reference electrode, thereby the structure of the cell becomes
simple.
Example 6
[0216] The six cells, the capacities of which are measured in the
Example 4, are charged by a constant current of 1000 mA until the
cell voltage becomes 3.3 V, the six cells are moved to a constant
temperature tube of 60.degree. C., and then 3.3 V is continuously
applied for 2000 hours to the cells to perform a high temperature
load test. After the test, the cell capacity is estimated, the same
as the capacity measurement after assembly, to be 82 mAh (average
of six cells). After the cell capacity measurement, 0 V is applied
between the negative electrode terminal and the lithium electrode
terminal by a potentiogalvanostat, a flowing current is accumulated
with a coulomb meter, and the carry of lithium ion is finished when
the accumulated amount of current becomes 50 mAh/g per unit weight
of the negative electrode active material, and the cell capacity is
measured to be back to the capacity before the high temperature
load test, that is, 91 mAh (average of six cells).
[0217] A using method of supplying the proper lithium ion from the
lithium electrode to the electrical storage device, characteristics
of which deteriorate is preferable for long-term use of the
electrical storage device as described in the present example.
Example 7
[0218] 100 parts by weight of LiCoO.sub.2 power having a diameter
of 5 to 10 .mu.m, 5 parts by-weight of graphite, are sufficiently
mixed with a solution, in which 3.5 parts by weight of
polyvinylidene powder is dissolved in 50 parts by weight of an
N-methyl pyrrolidone in order to obtain slurry. The slurry is
coated on both surfaces of an aluminum expanded metal coated with a
carbon group conductive pigment of a thickness of 40 .mu.m
(porosity 50%) and a front and rear surfaces of the aluminum foil
of thickness of 20 .mu.m, and dried and pressed so as to obtain the
LiCoO.sub.2 positive electrodes 1 and 2 of a thickness of 285
.mu.m.
[0219] Except that a copper expanded metal having a thickness of 40
.mu.m (porosity 50%) is replaced with the copper foil of 20 .mu.m,
the PAS negative electrode is obtained in the same manner as the
manufacturing method of the negative electrode of the example
1.
(Forming Cell 6)
[0220] The same PAS negative electrode and LiCoO.sub.2 positive
electrode as the first example are cut into pieces having the shape
of FIG. 15 and a size of 5.0.times.7.0 cm.sup.2 (not including the
area of the terminal welding portion), and cellulose/rayon combined
non-woven fabrics having a thickness of 25 .mu.m are used as a
separator. As shown in FIG. 15, the terminal welding portions of
the positive electrode collector and the negative electrode
collector are arranged at the opposite sides, and the counter
surfaces of the positive and negative electrodes are stacked in ten
layers. The positive and negative electrode collectors have
openings that penetrate the front and rear surfaces of the
collectors. The separators are arranged at the uppermost and
lowermost portions, and then four sides are sealed with tapes. The
terminal welding portion of the positive electrode collector (five
sheets) and the terminal welding portion of the negative electrode
collector (six sheets) are ultrasonic welded to an aluminum
positive electrode terminal and a Ni negative electrode terminal
having a width of 20 mm, a length of 50 mm, and a thickness of 0.1
mm so as to obtain the electrode stack unit 3.
[0221] A layer including lithium metal foils (220 .mu.m,
5.0.times.7.0 cm.sup.2) pressed on a stainless net having a
thickness of 80 .mu.m is arranged on the electrode stack unit 3 as
the lithium electrode to face the negative electrode in an outer
film drawn as deep as 3.5 mm like FIG. 1 to obtain the
three-electrode stack unit. Further, a Ni-made lithium electrode
terminal having a width of 10 mm a length of 50 mm, and a depth of
0.1 mm is ultrasonic welded to the (one sheet) terminal welding
portion of the lithium electrode collector, and arranged to face
the same orientation of the positive electrode terminal as shown in
FIG. 1.
[0222] The three-electrode stack unit is arranged in the drawn
outer film, and covered with the outer laminated film. Three sides
of the film are sealed, and 1 mol/l LiPF.sub.6 solution, which
includes LiPF.sub.6 dissolved in a mixed solvent of
ethylenecarbonate, diethylencarbonate, and propylenecarbonate in a
weight ratio of 3:4:1, is impregnated in a vacuum as the
electrolyte. The remaining side is sealed, and then a cell of the
film type capacitor is assembled. After the assembly,0 V is applied
between the negative electrode terminal and the lithium electrode
terminal through a potentiogalvanostat, a flowing current is
accumulated with a coulomb/ampere hour meter, and the carry of
lithium ion is finished when the accumulated amount of current
becomes 300 mAh/g per unit weight of the negative electrode active
material, thereby a preliminary charging is made.
(Forming Cell 7)
[0223] As a counter electrode to the PAS negative electrode using
the copper foil, six sample cells, in which stainless meshes having
metal lithium of a thickness of 160 .mu.m and a size of
5.0.times.7.0 cm.sup.2 attached thereto are stacked with
polyethylene non-woven fabrics having a thickness of 50 .mu.m
interposed therebetween as separators, are assembled. The metal
lithium is used as a reference electrode. 1 mol/l LiPF.sub.6
solution, which includes LiPF.sub.6 dissolved in a mixed solvent of
ethylene carbonate, diethyl carbonate, and propylene carbonate in a
weight ratio of 3:4:1, is used as the electrolyte.
[0224] After the weight of the negative electrode active material
is charged with 300 mAh/g of lithium ion, a sample cell is
disassembled to obtain six sheets of PAS negative electrode
carrying the lithium ion.
[0225] Except that the lithium ion carrying PAS negative electrode
(six sheets) and the LiCoO.sub.2 negative electrode 2 (five sheets)
are used, the film type capacitor is assembled to one cell in the
same manner as the cell 6. However, after assembling, the
preliminary charging manipulation of the lithium ion in the
negative electrode is not performed. Further, both the positive
electrode collector and the negative electrode collector have foils
that do not have openings.
(Measuring the Potentials of Positive and Negative Electrodes in
Discharging)
[0226] Cells 6 and 7 are charged in a constant current of 150 mA
until the cell voltages become 4.2 V, and then a constant current
and constant voltage charging applying 4.2 V is performed for
twelve hours. Next, the cells are discharged in a constant current
of 150 mA until the cell voltages becomes 1.75 V. Both cells
finished the discharge after 11 hours. From the potential
differences between the lithium electrode and the positive/negative
electrodes, which are arranged in the cell, measured at every one
hour, the results of right after charging, two hours after
discharging, four hours after discharging, eight hours after
discharging, and eleven hours after discharging are shown in table.
TABLE-US-00002 TABLE 2 Cell 6 Cell 7 Negative Positive Negative
Positive electrode electrode electrode electrode Measuring
Potential Potential Potential Potential Time (V) (V) (V) (V) After
0.04 4.24 0.05 4.25 charging 2 hrs after 0.41 3.85 0.20 3.62
discharging 4 hrs after 0.82 3.82 0.21 3.21 discharging 8 hrs after
1.05 3.79 0.23 3.03 discharging 11 hrs after 2.01 3.76 0.24 1.99
discharging
[0227] Typically, the discharging potential of LiCoO.sub.2 positive
electrode is admitted to have a flat portion around 3.8 V, which
does not accompany a temporal change. While the flat portion around
3.8 V not accompanying a temporal change can be found for the cell
6, it cannot be found for the cell 7. Therefore, it is thought that
the electrical potential in the stack unit as well as the potential
around the lithium electrode can be measured by using mesh rather
than foil in the collector of the positive and negative
electrodes.
[0228] Comparing with the above, if the collectors having openings
that penetrate the front and rear surfaces of the positive and
negative electrode collectors are used, the potentials of the
positive and negative electrodes can be measured more exactly by
using a reference electrode (lithium electrode in the present
invention), therefore, it is more preferable than a case where
foils are used in the collectors.
EFFECT OF THE INVENTION
[0229] As described above, an electrical storage device according
to the present invention is an electrical storage device including
a positive electrode, a negative electrode, a lithium electrode,
all of which can be connected with a external circuits, and an
electrolyte, which charges an opening gap of each electrode, in
which the lithium electrode can supply lithium ion to the negative
electrode by flowing a current between the lithium electrode and
the negative electrode through an external circuit, thereby
problems such as non-uniform carrying of lithium ion to the
negative electrode, shape-change of a cell, and temperature
increase of an electrolytic solution under a state of incomplete
sealing of a cell can be easily solved, and the electrical storage
device can be used for a long time owing to the rebirth of cells.
In addition, the respective states of the positive and negative
electrodes can be grasped by using the lithium electrode as a
reference electrode. The electrical storage device having the above
features can be preferably used for a film-type lithium ion
secondary battery, a capacitor and the like.
* * * * *