Title: Pocketed electrode plate for use in lithium ion secondary battery, its manufacturing method and lithium ion secondary battery using the same
Abstract: A pocketed electrode plate for use in a ultra-slim lithium ion secondary battery, its manufacturing method and a lithium ion secondary battery using the same. The pocketed electrode plate comprises an electrode plate which has a coating layer of an electrode active material and a non-coated projection portion. The electrode active material can reversibly insert and extract lithium ions. The electrode plates further includes separating membranes which cover both sides of the electrode plate while exposing only the non-coated projection portion, and an insulating polymer having an adhesive component on both surfaces thereof. The insulating polymer film is placed adjacent to edges of the electrode plate but does not cover any portion of the electrode surface. The insulating polymer film is thermally bonded onto two separating membranes. A plurality of pocketed electrode plates may be produced by using a pressing roll.
Patent Number: 6,881,233 Issued on 04/19/2005 to Cho, et al.
| Inventors:
|
Cho; Su Jung (Taejon, KR);
Chung; Geun Chang (Taejon, KR);
Hwang; Sun Yoo (Taejon, KR)
|
| Assignee:
|
Korea Power Cell, Inc. (Taejon, KR)
|
| Appl. No.:
|
130931 |
| Filed:
|
May 22, 2002 |
| PCT Filed:
|
September 14, 2001
|
| PCT NO:
|
PCT/KR01/01545
|
| 371 Date:
|
May 22, 2002
|
| 102(e) Date:
|
May 22, 2002
|
| PCT PUB.NO.:
|
WO02/25758 |
| PCT PUB. Date:
|
March 28, 2002 |
| Current U.S. Class: |
29/623.4; 29/623.5; 429/136; 429/137; 429/138 |
| Intern'l Class: |
H01M 002//18; H01M 010//04 |
| Field of Search: |
429/127,144,136-139,162,246,247
29/623.4,623.5
|
References Cited [Referenced By]
U.S. Patent Documents
| 4389470 | Jun., 1983 | Plasse | 429/152.
|
| 4756717 | Jul., 1988 | Sturgis et al. | 29/623.
|
| 5296318 | Mar., 1994 | Gozdz | 429/192.
|
| 5437692 | Aug., 1995 | Dasgupta et al. | 29/623.
|
| 5478668 | Dec., 1995 | Gozdz | 429/127.
|
| 5512389 | Apr., 1996 | Dasgupta et al. | 429/192.
|
| 5741608 | Apr., 1998 | Kojima et al. | 429/94.
|
| 5741609 | Apr., 1998 | Chen et al. | 429/192.
|
| 5981107 | Nov., 1999 | Hamano et al. | 429/231.
|
| 6225010 | May., 2001 | Hamano et al. | 429/306.
|
| Foreign Patent Documents |
| 19924137 | Jun., 2003 | DE | .
|
| 09-259866 | Oct., 1997 | JP.
| |
| WO99/48162 | Sep., 1999 | WO.
| |
| WO00/04601 | Jan., 2000 | WO.
| |
Primary Examiner: Cantelmo; Gregg
Attorney, Agent or Firm: Marger Johnson & McCollom, P.C.
Claims
What is claimed is:
1. A pocketed electrode plate for use in a lithium ion secondary battery
manufactured by an electrode-stacking manner, the pocketed electrode plate
comprising:
an electrode plate which has a coating layer of an electrode active
material and a non-coated projection portion, the electrode active
material being capable of reversibly inserting and extracting lithium
ions;
separating membranes which cover both sides of the electrode plate while
exposing only the non-coated projection portion; and
an insulating polymer film having an adhesive component on both surfaces
thereof, the insulating polymer film being placed adjacent to edges of the
electrode plate but not covering any portion of the coating layer of the
electrode plate,
wherein the insulating polymer film is sandwiched between the two
separating membranes, and wherein the interface between the insulating
polymer film and separating membrane is bonded by a thermal fusion of the
adhesive component on the both surfaces of the insulating polymer film,
and wherein the separating membranes are in direct contact with the both
sides of the electrode plate.
2. The pocketed electrode plate of claim 1, wherein the insulating polymer
film is selected from the group consisting of polyolefin film, polyester
film, polystyrene film, polyimide film, polyamide film, fluorocarbon resin
film, ABS film, polyacrylic film, acetal film, and polycarbonate film.
3. The pocketed electrode plate of claim 2, wherein the adhesive component
on the insulating polymer film is comprised of a compound selected from
the high temperature melt fused adhesive group consisting of ethylene
vinyl acetate, ethylene ethyl acetate, ethylene acrylic acid,
polyethylene, poly-vinyl-acetate, and poly-vinyl-butyral.
4. The pocketed electrode plate of claim 1, wherein the electrode plate
pocketed by the separating membranes is a cathode plate.
5. The pocketed electrode plate of claim 1, wherein the separating
membranes comprise a porous polymer film.
6. The pocketed electrode plate of claim 5, wherein the porous polymer film
is made of a polyolefin material with a porous ratio of 25-60% and a width
of 10-30 microns.
7. A lithium ion secondary battery having stacked electrodes, the battery
comprising:
(a) a plurality of pocketed cathode plates, each cathode electrode
comprising,
(a-1) an electrode plate which has a coating layer of an electrode active
material and a non-coated projection portion, the electrode active
material being capable of reversibly inserting and extracting lithium
ions;
(a-2) separating membranes which cover both sides of the electrode plate
while exposing only the non-coated projection portion; and
(a-3) an insulating polymer film having an adhesive component on both
surfaces thereof, the insulating polymer film being placed adjacent to
edges of the electrode plate but not covering any portion of the coating
layer of the electrode plate,
wherein the insulating polymer film is sandwiched between the two
separating membranes, and wherein the interface between the insulating
polymer film and separating membrane is bonded by a thermal fusion of the
adhesive component on the both surfaces of the insulating polymer film;
and
(b) a plurality of anode plates, each anode plate containing a material
capable of reversibly inserting and extracting lithium ions;
wherein the separating membranes are in direct contact with the both sides
of the electrode plate.
8. The lithium ion secondary battery of claim 7, wherein the size of the
pocketed cathode plate is no smaller than that of the anode plate, and
wherein the area of the anode play is larger than that of the coating
layer of the cathode plate.
9. A method of manufacturing pocketed electrode plates for use in a lithium
ion secondary battery manufactured by an electrode-stacking manner, the
method comprising:
(a) providing a plurality of electrode plates having the same shape, each
of which has a coating layer of an electrode active material and a
non-coated projection portion, the electrode active material being capable
of reversibly inserting and extracting lithium ions;
(b) providing a tape-shaped insulating polymer film with both sides covered
with an adhesive component;
(c) blanking parts of the polymer film so that the polymer film may have
empty regions where the electrode plates are aligned and contained to a
specified spacing;
(d) aligning the electrode plates within the empty regions to a specified
spacing;
(f) locating tape-shaped separating membranes on both sides of the polymer
film with electrode plates contained therein in order to cover the
electrode plates while exposing only the non-coated projection portions of
the electrode plates;
(g) passing the polymer film covered with the separating membranes through
a pressing roll in a heated state; and
(h) stamping out the pressed polymer film to form a plurality of pocketed
electrode plates;
wherein each pocketed electrode plate is stacked in the order of a
separating membrane/ an electrode plate/ a separating membrane, and
wherein the separating membranes are bonded by the insulating polymer film
at least on the portion of external edges of the electrode plate.
10. The method of claim 9, wherein the electrode plate pocketed with the
separating membranes is a cathode plate and the size of the stamped-out
cathode plate is no smaller than that of an anode plate, and wherein the
area of the anode plate is larger than that of the coating layer of the
cathode plate.
11. The method of claim 9, wherein the insulating polymer film is selected
from the group consisting of polyolefin film, polyester film, polystyrene
film, polyimide film, polyamide film, fluorocarbon resin film, ABS film,
polyacrylic film, acetal film, and polycarbonate film.
12. The method of claim 11, wherein the adhesive component is selected from
the high temperature fused adhesive group consisting of ethylene vinyl
acetate, ethylene ethyl acetate, ethylene acrylic acid, polyethylene,
polyvinylacetate, and polyvinylbutyral.
Description
TECHNICAL FIELD
The present invention relates to a lithium ion secondary battery, and
especially to a pocketed electrode plate for use in a lithium ion
secondary battery, its manufacturing method and the lithium ion secondary
battery using the same.
The present invention is to revolutionarily improve the productivity and
energy density of a slim lithium ion secondary battery with a thickness of
5 mm or less.
BACKGROUND ART
To meet the growing and diversifying needs of markets for portable
electronic products such as mobile phones, camcorders and notebook
computers, the demand for a rechargeable battery as a portable power
supply is also increasing. As these portable electronic products become
smaller and lighter, while providing better performance and
multi-functional features, the requirement on the energy storage density
of a secondary battery is increasing very rapidly. Years of research have
yielded the current lithium ion secondary battery that adopts a pair of
electrochemically active materials, typically lithium transition metal
oxide for the cathode and carboneous material for the anode, which allows
lithium ion to be inserted into and extracted from the host structure of
the material reversibly. The lithium ion secondary battery has higher
energy density per unit volume as well as per unit weight and increased
charge and discharge lifetime compared to the existing aqueous solution
type secondary batteries such as Ni--Cd and Ni--MH batteries, and is
rapidly replacing existing batteries for portable electronic products.
However, the rapid development and diversification of portable electronic
products require batteries with higher energy density and more flexible
form factors, thus pushing the limit of the current lithium ion secondary
battery technology. In particular, the trend to manufacture slim and small
electronic products increases demands for ultra-slim prismatic lithium ion
secondary batteries however the adoption of current manufacturing methods
for cylindrical or prismatic lithium ion batteries causes drastic lowering
of energy density per volume in manufacturing slim prismatic batteries.
Therefore, when a slim prismatic battery with a thickness less than 5 mm
is used for high performance portable electronic products such as mobile
phones, camcorders and notebook computers, it is difficult to maintain
sufficient run time. Therefore, it is considered that the development of a
slim prismatic lithium ion secondary battery with higher energy density
per unit volume is essential in developing small, light and slim portable
electronic products.
FIG. 1 is a schematic diagram of a manufacturing process of a prismatic
lithium ion secondary battery described in a prior art. The anode and
cathode of a prismatic lithium ion secondary battery is integrated into
one by the so-called winding method in which an anode and a cathode are
rolled with a separator in-between them, and the integrated electrode is
called a jelly roll. FIG. 1 shows that a lithium ion secondary battery is
manufactured by inserting the jelly roll 102 into a prismatic can 104
followed by sealing the top with a cap 106 by laser welding. The anode and
the cathode are manufactured by covering a mixture of a polymer binder,
conductive powder and active material for each electrode onto copper and
aluminum thin plates, respectively. Usually, a non-covered portion remains
for the attachment of an electrode tab. An electrode tab made of nickel
and aluminum is attached to each non-covered portion of an anode and a
cathode respectively, and the two electrodes are connected to external
terminals through the tabs. One of the electrode tabs attached to the
non-covered portion is bound to either a bottom or a side of a can 104
when the jelly roll 102 is inserted into a can 104, and the other tab is
bound to a cap 106. The benefit of the manufacturing method and the
structure is that the whole electrode surface can be homogeneously
utilized when a battery is charged or discharged because the cathode and
the anode are physically and uniformly attached to each other by the
tension applied to a separator in winding and they are also physically
pressed to a wall of the can 104. Therefore, the battery thusly made has
superior performance and maintains the high performance in the long term
charging and discharging cycle. An additional benefit of a wall of a
metallic can 104 with high mechanical strength is that it can contribute
greatly to the increase in energy density per unit volume of a final
battery because the jelly roll 102 can be filled strongly inside a can 104
by physical pressing and the change in thickness by swelling resulting
from internal stress can be minimized. Furthermore, the complete fusion of
the battery can 104 and the cap 106 separates the battery inside from the
outside and the danger of a leak of battery internal material or
infiltration of external impurities can be prevented.
However, the energy density of a slim prismatic lithium ion secondary
battery with thickness below 5 mm manufactured using the same electrode
under the aforementioned assembly method will be lowered more than a
conventional cylindrical battery by around 30% as long as the constituent
material is the same. The energy density will be decreased even further
when the thickness is decreased. Furthermore, when the thickness is
decreased most of the manufacturing processes such as jelly roll and
electrolyte filling, insulation, separation of electrode terminal and
fusion using laser will be more difficult and results in the lowering of
yield and increase in manufacturing cost. The reasons for the decrease in
energy density are summarized as below.
In first, the can for a prismatic battery in prior arts is usually
manufactured by low temperature deep drawing, and the thickness of the can
is about 0.4 mm when it is made of aluminum and is 0.3 mm when it is made
of steel. The thickness of the packaging material of a cylindrical battery
is about 0.2 mm which is half or two thirds of that of an aluminum or
steel can. The volume or weight fraction of the thick packaging material
becomes bigger as the battery gets thinner especially for a battery with
thickness of 5 mm or less, and the use of a conventional can becomes a
great limit in the manufacturing of a slim prismatic battery with high
energy density.
In second, the shape of a jelly roll made by winding is not flat but is
rather elliptical and can not be inserted inside a prismatic battery
tightly, and results in a dead space. The loss of energy density of a
battery is determined by the volume fraction of unused internal space to
the whole internal space, and the loss of energy density for a slim
prismatic battery with relatively small internal space will be severe.
When the same electrodes are used, the energy density of a prismatic
battery with thickness below 4 mm is usually 30% lower than that with
thickness around 10 mm.
In third, in the winding process for a prismatic battery, an electrode has
to be wound flatly unlike a cylindrical battery, which results in the
folding of an electrode due to decreased radius of curvature at the ends
of the jelly roll. In order to prevent damages on the electrode in this
process, the thickness of an electrode has to be decreased or the amount
of non-active binder to enhance flexibility and adhesion has to be
increased. When several slim electrodes are wound more separating
membranes and current collectors has to be incorporated into a battery,
and the energy capacity of a battery decreases due to increased ratio of
non-active material to active material. On the contrary, when the amount
of non-active binder increases, the energy density of a battery decreases
as the amount of the non-active binder increases compared to active
electrode material.
The thinner the thickness of a prismatic battery is, the worse the problem
gets, and it becomes very serious in a prismatic battery with thickness
below 5 mm. So, a conventional assembly method of a prismatic battery can
not satisfy the demand for ultra slim portable electronic products.
The decrease of energy density resulting from a jelly roll can be prevented
by alternately stacking the existing slim separating membrane and
electrodes. However, since the separating membrane is very flexible,
alternate stacking of electrodes and separating membranes in a piece is
very difficult even in a manual process, and its application is close to
impossible considering productivity and yield. Furthermore, according to
the method of prior arts the matching of the edge of a cathode to the edge
of an anode is difficult and the prevention of short-circuiting of a
cathode and an anode by a separating membrane is very difficult.
Therefore, in order to prevent the problem, a method of assembling a
stacked body comprising a cathode, an anode and a separating membrane is
proposed by providing adhesion between the electrodes and a separating
membrane. The adhesion is achieved by pressing polymeric electrolyte (that
performs a dual role as a separating membrane and ion conducting
electrolyte) onto the surface of the electrode by heat and pressure or by
covering the adhesive component at the contact surface between the
electrode and the separating membrane.
In U.S. Pat. Nos. 5,296,318 and 5,478,668, a battery maintaining adhesion
without external pressure is proposed by applying ion conductive gel
polymer onto an anode, a cathode and a separating membrane followed by
heat lamination. This type of a battery is called a lithium ion polymer
battery or simply a polymer battery. This battery employs low ion
conductive gel type polymer electrolyte as an ion conductor of an
electrode and a separating membrane, so it shows insufficient charging
discharging speed and a decreased performance at low temperature compared
to the lithium ion battery. In addition, excess non-active polymer is used
for the electrode of a lithium ion polymer battery even though there are
variations in chemical composition, and the thickness of a separating
membrane has to be increased due to low mechanical strength of an ion
conductive separating membrane. Therefore, this type of a battery can not
basically excel the prismatic lithium ion battery in energy density per
unit volume.
On the other hand, in order to fully exercise benefits of the existing
lithium ion battery, U.S. Pat. No. 5,437,692 U.S. Pat. No. 5,512,389 U.S.
Pat. No. 5,741,609 and WO 9948162 disclose methods increasing adhesion
between the two electrodes and a separating membrane by placing a thin
adhesion layer between a separating membrane and an anode, and a
separating membrane and a cathode without employing polymer gel
electrolyte. In this structure, increased energy density can be obtained
and a stable battery performance is expected because the decrease of ionic
conductivity is lowered compared to the gel type polymer electrolyte and
also the amounts of non-active polymer gel can be greatly decreased.
However, in this technology discharging performance can be decreased
compared to the existing lithium ion battery due to a covering of
conductivity decreasing adhesive material on the whole active electrode
surface.
Therefore, in order to solve the problem, U.S. Pat. No. 5,981,107 discloses
a method of covering an adhesive component on the part of interface of an
electrode and a separating membrane, and additional formation of a convex
and concave surface to increase moist containing capacity of electrolyte.
Furthermore, WO 0004601 discloses a method of sticking an electrode to a
separating membrane by forming a hole at the part of an anode and a
cathode followed by filling the hole with adhesive polymer. However, the
process of forming an adhesive part is difficult in this method.
Especially, the U.S. Pat. No. 5,981,107 has a problem of performance
difference of a battery between the part covered with adhesive polymer and
the non-covered part, and the method according to WO 0004601 has a
difficulty of precise aligning of holes formed in an anode and a cathode.
Furthermore, in the aforementioned stacked body, there is an adhesion
between an electrode and an electrolyte layer without pressure applied by
a packaging material, and a method in which a slim prismatic lithium ion
secondary battery is manufactured by sealing a battery with an aluminum
laminate packaging material which is thinner and lighter than existing
metal packaging material is proposed. The aluminum laminate packaging
material comprises a polymer layer capable of heat lamination sealing, a
layer of material which is rarely penetrable by external impurities, and
an insulating cover. Such packaging material has an advantage that it is
thinner and lighter than existing metal packaging material. Accordingly,
if it is used as a substitute for the metal packaging material, the weight
of a battery can be decreased and energy density per unit thickness can be
increased because the metal packaging material contributes significantly
to the thickness and weight of a slim battery.
In addition, since the packaging material is electrically insulating, it is
easy to insert multi-layer electrode stack or jelly roll without the
danger of short-circuiting. However, the mechanical strength of the
packaging material is low in spite of the merits of thin and light
characteristics, and there can be problems resulting from mechanical
weakness of a stacked packaging material even though adhesion between an
electrode and a separating membrane can be managed by any of the
aforementioned method. Especially, the following three problems can be
fatal in the manufacturing and the use of a battery.
In first, a battery is sealed by heat lamination of innermost polymer layer
of aluminum laminated packaging material, and its sealing strength is
lower than that of laser sealing applied to existing prismatic batteries.
Especially, the sealing of a portion where an electrode tab is projected
through packaging material is determined by the adhesion between a polymer
layer and a metal layer, and there is always a gap at the edge of the
metal tab. Accordingly, the portion is prone to failure due to leakage of
electrolyte. Even in the middle of normal use, the sealing part comprising
the metal tab and polymer cover can be easily cracked due to internal
pressure increase resulting from expansion of an electrode and gas
generation, and there is a danger of leakage of electrolyte or
introduction of external impurities such as moisture. The problem gets
worse when gas is continuously generated due to impurities emanated from
the electrode and electrode active material and impurities introduced in
each battery assembly step. So the introduction of impurities should be
controlled strictly in each battery-manufacturing step but it will also
increase process cost. The danger of a leak due to cracks in adhesion
layer is severe when the possibility of gas generation due to side
reactions in a battery increases and the adhesion at the adhesion layer
gets loosened which is observed at high temperature. When there is a leak,
it will be fatal to battery performance and it may contaminate and
decrease the life span of the electronic circuit of an expensive
electronic product in which the battery is placed.
In second, the existing prismatic battery employs a metallic can with
enough mechanical strength and there is no severe increase in thickness
due to internal pressure increase, but the aluminum laminate packaging
material can not bear internal pressure and the thickness of a battery may
increase. The increase of the thickness will change the appearance of a
battery pack, make it impossible to be normally placed in a battery pack,
and bring on discontent in appearance. This problem is worsened when the
surface area of a battery is increased to enhance battery capacity, which
makes it difficult to manufacture a high capacity battery with thickness
below 5 mm.
In third, the weak mechanical strength of an aluminum laminate packaging
material lowers reliability and stability of a battery. A battery is used
from at least 6 months to several years and requires superior durability
in a wide temperature range as well as under diverse mechanical shocks.
The existing prismatic battery adopts a metal can for a packaging material
and the danger of damages due to external pressure, or local changes due
to sharp ends such as a nail is not great but the aluminum packaging
material has significantly decreased thickness and strength compared to
the existing metal packaging material and is susceptible to damages by
external shock or fire. The stability issue is critical to a high capacity
battery used for a portable computer or to a battery used without an
external plastic housing to make a slim battery pack.
The above review shows many limitations in manufacturing a durable, stable
and slim battery with high energy density and easy manufacturing steps. In
summary, the existing prismatic lithium ion battery has problems resulting
from a large portion of internal space that is not used due to a jelly
roll type electrode structure, and energy density is decreased greatly
according to the decrease of total battery thickness due to a technical
limit in decreasing thickness of a metal packaging material manufactured
by low temperature deep drawing. On the other hand, a lithium ion polymer
battery assembled by sealing a stacked electrode body with an aluminum
laminate packaging material has decreased dead space resulting from a
jelly roll, but the energy density is decreased and the battery
performance is lowered because an excess polymer binder is used for a
sealing between electrodes or an adhesive layer is coated on the
interfacial surface of the electrode and the electrolyte. Furthermore, the
aluminum laminate packaging material has problems in durability and safety
due to mechanical weakness and insufficient adhesion at adhesive surface
comprising a polymer cover and a metal tab.
DISCLOSURE OF THE INVENTION
One object of the present invention is to provide a pocketed electrode
plate which can prevent formation of wrinkles at separating membranes of a
pocketed electrode plate.
Another object of the present invention is to provide a lithium ion
secondary battery with high energy density using the pocketed electrode
plate.
A further object of the present invention is to provide a manufacturing
method of a pocketed electrode plate suitable for mass production of a
lithium ion secondary battery.
In order to achieve the above objects, the present invention provides a
pocketed electrode plate for use in a lithium ion secondary battery
manufactured by an electrode-stacking manner, the pocketed electrode plate
comprising:
an electrode plate which has a coating layer of an electrode active
material and a non-coated projection portion, the electrode active
material being capable of reversibly inserting and extracting lithium
ions;
separating membranes which cover both sides of the electrode plate while
exposing only the non-coated projection portion; and
an insulating polymer film which contains an adhesive component and is
placed between the separating membranes at least on the portion of the
external edge of the electrode plate in order to bond and fix the
separating membranes.
In order to achieve the above objects, the present invention provides a
lithium ion secondary battery having stacked electrodes, the battery
comprising:
(a) a plurality of pocketed cathode plates, each cathode electrode plate
comprising,
(a-1) an electrode plate which has a coating layer of an electrode active
material and a non-coated projection portion, the electrode active
material being capable of reversibly inserting and extracting lithium
ions;
(a-2) separating membranes which cover both sides of the electrode plate
while exposing only the non-coated projection portion; and
(a-3) an insulating polymer film which contains an adhesive component and
is placed between the separating membranes at least on the portion of the
external edge of the electrode plate in order to attach and fix the
separating membranes; and
(b) a plurality of anode plates, each anode plate containing a material
capable of reversibly inserting and extracting lithium ions; wherein the
cathode and anode plates are alternately stacked.
Preferably, the size of the pocketed cathode plate is no smaller than that
of the anode plate, and the area of the anode plate is larger than that of
the coating layer of the cathode plate.
In order to achieve the above objects, the present invention provides a
method of manufacturing pocketed electrode plates for use in a lithium ion
secondary battery manufactured by an electrode-stacking manner, the method
comprising the steps of:
(a) providing a plurality of electrode plates having the same shape, each
of which has a coating layer of an electrode active material and a
non-coated projection portion, the electrode active material being capable
of reversibly inserting and extracting lithium ions;
(b) providing a tape-shaped insulating polymer film with both sides covered
with an adhesive component;
(c) blanking parts of the polymer film so that the polymer film may have
empty regions where the electrode plates are aligned and contained to a
specified spacing;
(d) aligning the electrode plates within the empty regions to a specified
spacing;
(f) locating tape-shaped separating membranes on both sides of the polymer
film with electrode plates contained therein in order to cover the
electrode plates while exposing only the non-coated projection portions of
the electrode plates;
(g) passing the polymer film covered with the separating membranes through
a pressing roll in a heated state; and
(h) stamping out the pressed polymer film to form a plurality of pocketed
electrode plates;
wherein each pocketed electrode plate is stacked in the order of a
separating membrane/an electrode plate/a separating membrane, and
wherein the separating membranes are bonded by the insulating polymer film
at least on the portion of the external edge of the electrode plate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a manufacturing process of a prismatic
lithium ion secondary battery described in a prior art;
FIGS. 2A to 2G are diagrams of a manufacturing process of a pocketed
electrode plate according to one example of the present invention; and
FIG. 3 is a diagram comparing the size of a pocketed electrode plate and an
anode plate used in one example of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be
explained with reference to the attached drawings and the pocketed
electrode plate and its manufacturing method are explained together but
the pocketed electrode plate is limited to the cathode plate in the
example.
FIGS. 2A to 2G are diagrams of a manufacturing process of a pocketed
electrode plate according to one example of the present invention.
FIG. 2A is a diagram illustrating one example of insulating polymer film to
manufacture a pocketed electrode plate according to the present invention.
In FIG. 2A, there are multiple longitudinal perforated spaces 210 on a
continuous roll of polymer film covered with an adhesive component on both
sides. The perforated space 210 are separated at an equal distance with
the same shape, and each perforated space 210 are formed bigger than the
cathode plate to position the cathode plates at a distance as described
below. In manufacturing a pocketed electrode plate of the present
invention, the diverse shape of perforated space of an insulating polymer
film can be selected only if the cathode plates are contained within the
empty regions of the insulating polymer film to a specified spacing and
the polymer film surrounds at least edge portion of each cathode plate.
Therefore, if the cathode plate is rectangular in shape with a non-coated
projection portion, then the desirable shape of a perforated space of
polymer film is such that it surrounds at least two sides of the cathode
plate.
FIG. 2B is another example of an insulating polymer film to manufacture a
pocketed electrode plate according to the present invention. FIG. 2B shows
that there is a perforated space 210' with its shape changing periodically
on the continuous roll of polymer film 200 with an adhesive component on
both sides.
Preferably, the insulating polymer film is selected from a group consisting
of polyolefin film, polyester film, polystyrene film, polyimide film,
polyamide film, fluorocarbon resin film, ABS film, polyacrylic film,
acetal film, and polycarbonate film.
Furthermore, the adhesive component covered on both sides of the insulating
polymer film is preferably selected from a high temperature fused adhesive
group consisting of ethylene vinyl acetate, ethylene ethyl acetate,
ethylene acrylic acid type compound, ionomer type compound, polyethylene,
polyvinylacetate, and polyvinylbutyral.
FIG. 2C is a diagram showing the step of locating a cathode plate and a
separating membrane inside a perforated space of insulating polymer film
200 of FIG. 2A. FIG. 2C shows that the cathode plate comprising a coating
layer of lithium transition metal oxide, the cathode active material, and
a non-coated projection portion are located with a specified spacing in
each perforated space. The size of a cathode plate or a perforated space
is controlled to keep the spacing around the projection portion of the
cathode plate bigger than the spacing in other portions. Thereafter,
separating membranes (not drawn) with width of d is placed on both sides
of polymer film 200 which is located with the cathode plate 220, but only
the non-coated projection portion on the cathode plates 220 are exposed
while other portion of the cathode plates are covered. In FIG. 2C, the
space occupied by separating membranes is spacing in-between one-dot chain
line. In FIG. 2C, the space inside a dotted line S is a cutting line to
obtain each pocketed electrode plate after pressurizing and adhering
processes described below. According to the procedure described above, a
roll of resulting material laminated in the order of lower separating
membrane/insulating polymer film covered with adhesive component and
cathode plate located at the perforated space of the polymer film/upper
separating membrane can be obtained.
FIG. 2D is a diagram showing the step of locating a cathode plate and a
separating membrane inside a perforated space of the insulating polymer
film 200 of FIG. 2B. FIG. 2D shows that separating membranes (not drawn)
with width of d' is located on both sides of the polymer film 200 which is
located with the cathode plate 200. The size of the cathode plates 220 or
that of perforated space is determined so that the non-coated projection
portion of the cathode plate is projected outside the polymer film 200. In
FIG. 2D, the separating membrane has the same width with the polymer film
and is placed along the polymer film. In FIG. 2C, the space inside a
dotted line S is also a cutting line to obtain each pocketed electrode
plate after pressurizing and adhering processes described below.
FIG. 2E is a diagram showing a pressurizing process of a resulting material
of FIG. 2C. In FIG. 2E, the resulting material comprising an insulating
polymer film 200 covered with separating membrane 230/adhesive component
and cathode plate 220/separating membrane 230 located at the perforated
space is heated and fused in the shape of a continuous scroll by a
pressure roll 250. In FIG. 2E, the resulting material of FIG. 2C is
represented by a longitudinal cross section. By the pressurized fusing a
strong adhesion is achieved wherever the insulating polymer film is but
there is no adhesion or deformation where the cathode plate 220 is.
Desirable separating membrane used by the above example is a porous polymer
film made of a polyolefin material with a porous ratio of 25-60% and a
width of 10-30 micron. Furthermore, the desirable heated fusing
temperature for polyethylene is below 120.degree. C. and that of
polypropylene is below 150.degree. C.
FIG. 2F is a diagram showing a pocketed electrode plate manufactured by
perforating the pressurized resulting material according to the
explanation of FIG. 2E along the dotted line of FIG. 2C. In FIG. 2F, the
adhesive portion of the cathode plate 220 and the insulating polymer film
200 is drawn perspectively to clarify the drawing. In FIG. 2F, the
adhesive portion surrounds all the external edge of the cathode plate 220,
and only the non-coated projection portion of the cathode plate 220 is
exposed without being covered by the separating membrane 230.
If a pocketed electrode plate is manufactured using the resulting material
drawn in FIG. 2D, the adhesive portion will surround only the upper and
lower external edges of the cathode plate.
If a pocketed electrode plate is manufactured by the method described
above, a mass production of a pocketed electrode plate is possible.
FIG. 2G is a cross-sectional view along the A-A' line of FIG. 2F. As shown
in FIG. 2G, the difference between the thickness of a stacked portion of
separating membrane 230/cathode plate 220/separating membrane 230 and that
of separating membrane 230/insulating polymer film 200 covered with an
adhesive component/separating membrane 230 is smaller than those in prior
arts, and the generation of wrinkles in the separating membrane of the
pocketed electrode plate manufactured according to the present invention
is decreased.
FIG. 2C is a diagram comparing the size of the pocketed electrode plate and
the anode.
When a lithium ion secondary battery is manufactured by an electrode plate
stacking method, it is desirable to keep the size of the perforated
pocketed electrode plate equal to or bigger than that of the anode plate
and the size of the anode plate bigger than that of the cathode active
material covered area of the cathode plate in order to prevent edge
mismatch of active plate of an anode and a cathode and to maintain a
smooth stacking alignment. Therefore, as shown in FIG. 3, if both the
cathode plate and the anode plate are rectangular with a non-coated
projection portion, it is desirable to follow the equation 1 among the
width of the cathode plate B, the width of a separating membrane for
pocketing and the width of an anode plate C.
A.gtoreq.C.gtoreq.B+A-B/2 [Equation 1]
More desirably, if the pocketed electrode plate except for each projection
portion and the edge anode are made to coincide, the condition that all
plates facing the cathode should be covered with an anode is automatically
satisfied.
After aligning and stacking the pocketed electrode plates and the anode
plates, the non-coated projection portions of the anode plates are fused
to one another and the non-coated projection portions of the cathode
plates are fused to one another. Then, each of them is connected to an
anode tab and a cathode tab, respectively. By sealing it inside a metal
packaging material, a lithium ion secondary battery is manufactured.
The performances of the lithium ion secondary battery manufactured
according to the present invention are summarized as below.
[Prismatic Battery with Thickness of 2.4 mm]
For a prismatic battery having curved corners manufactured with thickness
of 2.4 mm, short diameter of 35 mm and long diameter of 62 mm, the
reversible capacity is 620 mAh which is 440 Wh/liter when converted to
energy density per volume.
[Prismatic Battery with Thickness of 4.0 mm]
For a prismatic battery having curved corners manufactured with thickness
of 4.0 mm, short diameter of 35 mm and long diameter of 62 mm, the
reversible capacity is 1100 mAh which is 470 Wh/liter when converted to
energy density per volume.
The pocketed electrode plate manufactured according to the present
invention has higher adhesive strength with decreased adhesion area and,
therefore, the energy density of a finished lithium ion secondary battery
can be increased. Furthermore, the pocketed electrode plate can be
manufactured in a continuous roll process, and a mass production of a
lithium ion secondary battery is made easy. Herein above the invention has
been described in reference to the preferred embodiments, but various
other modifications and variations will be apparent to those skilled in
the art without departing from the scope and spirit of the present
invention. The pocketed electrode plate is limited to a cathode plate in
the example of the present invention, but it is understood that an anode
electrode plate can be used as a pocketed electrode plate as far as the
limitation condition on the active material covering area is satisfied.
*
