U.S. patent application number 11/242010 was filed with the patent office on 2006-04-13 for nonaqueous electrolyte secondary battery.
Invention is credited to Hirotaka Hayashida, Kengou Kurata, Yuuichi Sato.
Application Number | 20060078787 11/242010 |
Document ID | / |
Family ID | 33156787 |
Filed Date | 2006-04-13 |
United States Patent
Application |
20060078787 |
Kind Code |
A1 |
Sato; Yuuichi ; et
al. |
April 13, 2006 |
Nonaqueous electrolyte secondary battery
Abstract
The invention provides a nonaqueous electrolyte secondary
battery excellent in output characteristic such as large current
discharge or pulse discharge in ordinary use, high in safety by
preventing destruction due to suppression of current in an
abnormality such as external short-circuiting, and further large in
capacity. The nonaqueous electrolyte secondary battery comprises an
external can opened at one end thereof, an electrode assembly
contained in the external can, and comprising a negative electrode,
a separator and a positive electrode, a nonaqueous electrolyte
contained in the external can, and a sealing lid group tightly
sealed at the opening of the external can by way of an insulating
member, wherein the sealing lid group includes an intact plate-like
PTC element having a fragile portion to be easily broken due to
elevation of internal pressure by gas generation.
Inventors: |
Sato; Yuuichi; (Tokyo,
JP) ; Kurata; Kengou; (Kumagaya-shi, JP) ;
Hayashida; Hirotaka; (Fujisawa-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
33156787 |
Appl. No.: |
11/242010 |
Filed: |
October 4, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP04/04846 |
Apr 2, 2004 |
|
|
|
11242010 |
Oct 4, 2005 |
|
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Current U.S.
Class: |
429/62 ; 429/161;
429/174; 429/56 |
Current CPC
Class: |
H01M 10/0525 20130101;
Y02E 60/10 20130101; H01M 50/581 20210101; H01M 50/572 20210101;
H01M 50/171 20210101; H01M 50/3425 20210101; H01M 2200/106
20130101; H01M 50/166 20210101 |
Class at
Publication: |
429/062 ;
429/174; 429/056; 429/161 |
International
Class: |
H01M 10/50 20060101
H01M010/50; H01M 2/08 20060101 H01M002/08; H01M 2/12 20060101
H01M002/12; H01M 2/26 20060101 H01M002/26 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 4, 2003 |
JP |
2003-102021 |
Claims
1. A nonaqueous electrolyte secondary battery comprising: an
external can opened at one end thereof; an electrode assembly
contained in the external can, and comprising a negative electrode,
a separator and a positive electrode; a nonaqueous electrolyte
contained in the external can; and a sealing lid group tightly
sealed at the opening of the external can by way of an insulating
member, wherein the sealing lid group comprises an intact
plate-like PTC element having a fragile portion to be easily broken
due to elevation of internal pressure by gas generation.
2. The nonaqueous electrolyte secondary battery according to claim
1, wherein the PTC element has a structure in which a resin sheet
containing conductive carbon is interposed between a pair of
electrodes composed of a metal thin film.
3. The nonaqueous electrolyte secondary battery according to claim
2, wherein the fragile portion is a notch formed at least in one of
the pair of electrodes in the PTC element.
4. The nonaqueous electrolyte secondary battery according to claim
3, wherein the notch has a depth of 4% or more of the electrode
thickness, and not more than the total of the electrode thickness
and 20% of the thickness of the resin sheet.
5. The nonaqueous electrolyte secondary battery according to claim
3, wherein the notch has a width of 5 .mu.m or more.
6. The nonaqueous electrolyte secondary battery according to claim
3, wherein the notch has an opening area of 1 mm.sup.2 or more.
7. The nonaqueous electrolyte secondary battery according to claim
1, wherein the fragile portion is a recess formed in the PTC
element.
8. The nonaqueous electrolyte secondary battery according to claim
7, wherein the recess has a depth of 20 .mu.m or more.
9. The nonaqueous electrolyte secondary battery according to claim
1, wherein the sealing lid group further comprises a rupture plate
whose outer periphery is fixed to the insulating member, the
rupture plate having a fragile portion to be broken easily by
elevation of internal pressure by gas generation.
10. The nonaqueous electrolyte secondary battery according to claim
9, wherein the fragile portion is a notch formed at least in one
side of the rupture plate.
11. The nonaqueous electrolyte secondary battery according to claim
1, wherein the sealing lid group further comprises a battery
breaking member.
12. The nonaqueous electrolyte secondary battery according to claim
1, wherein the sealing lid group further comprises a conductive
support plate positioned at one side of the PTC element and fixed
in the insulating member at a peripheral edge thereof.
13. The nonaqueous electrolyte secondary battery according to claim
12, wherein the support plate has an intact fragile portion to be
broken easily by elevation of internal pressure by gas
generation.
14. The nonaqueous electrolyte secondary battery according to claim
13, wherein the support plate is a ring.
15. The nonaqueous electrolyte secondary battery according to claim
12, wherein the support plate is composed of a ring plate to be
fixed by the insulating member, a thin plate fixed to cover a
hollow space at least at one side of the ring plate excluding the
fixed portion by the insulating member, and a fragile portion to be
broken easily by elevation of internal pressure by gas generation,
the fragile portion being formed in the thin plate.
16. The nonaqueous electrolyte secondary battery according to claim
12, wherein the support plate is composed of a ring plate, and a
circular high molecular resin layer disposed in tight contact with
the inner side of a hollow space of the ring plate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a Continuation Application of PCT Application No.
PCT/JP2004/004846, filed Apr. 2, 2004, which was published under
PCT Article 21(2) in Japanese.
[0002] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2003-102021,
filed Apr. 4, 2003, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to a nonaqueous electrolyte
secondary battery.
[0005] 2. Description of the Related Art
[0006] Recently, along with a downsizing trend of electronic
appliances such as cellular phones and portable personal computers
and an increase in demand for them, there is a mounting demand for
higher performance in secondary batteries used as a power source of
these electronic appliances. To meet such a demand, nonaqueous
electrolyte batteries using a material, such as a carbon material,
capable of intercalating and deintercalating lithium ions as a
negative electrode material have been developed, and are used
widely as a power source for portable electronic appliances. The
nonaqueous electrolyte secondary battery is, unlike the
conventional battery, characterized by light weight and high
electromotive force, and its excellent performance has been
noticed. In particular, the portable personal computer has varied
functions, including Web browsing, electronic mail exchange, and
video viewing. Accordingly, the battery used as a power source is
required to have not only larger capacity, but also higher output,
that is, excellent large current discharge characteristic and pulse
discharge characteristic.
[0007] For higher output of a secondary battery, it is needed to
decrease the output resistance (internal resistance) of the
battery. It is hence extremely important to lower the resistance of
electrodes and battery constituent members.
[0008] For this purpose, various secondary batteries have been
proposed, including a cylindrical lithium ion secondary battery or
square lithium ion secondary battery having plural current
collecting leads attached to electrodes thereof, as disclosed in
Jpn. Pat. Appln. KOKAI Publication Nos. 11-317218 and 11-339758.
Such secondary batteries are improved in current collection
efficiency and lowered in output resistance, so that enhancement of
the output characteristic is achieved.
[0009] Jpn. Pat. Appln. KOKAI Publication No. 2002-110254 discloses
enhancement of the output characteristic of a lithium ion secondary
battery by reducing the thickness of the electrodes. In these
electrodes, in particular, by reducing the thickness of the
positive electrode, diffusion of lithium ions in the electrodes is
accelerated, and a lithium ion secondary battery of high output can
be obtained.
[0010] However, when plural current collecting leads are connected
to the electrodes as disclosed in Jpn. Pat. Appln. KOKAI
Publication Nos. 11-317218 and 11-339758, the assembly procedure is
complicated, and consequently, productivity of batteries is
lowered.
[0011] In addition, when the battery is designed by reducing the
thickness of the electrodes as in Jpn. Pat. Appln. KOKAI
Publication No. 2002-110254, the occupying rate of current
collectors in electrodes is larger, and the quantity of reaction
substances such as active materials of electrodes is inevitably
decreased. This is significantly disadvantageous in terms of
advance of larger capacity of the secondary battery. Therefore, to
achieve both larger capacity and higher output of the secondary
battery, it is further required to lower the resistance of battery
constituent members without reducing the thickness of electrodes
more than necessary.
[0012] On the other hand, the lithium ion secondary battery has
other problems, that is, overcurrent flows in the battery in the
event of an abnormality such as overcharge or short-circuiting, a
nonaqueous electrolysis solution is decomposed, and a decomposition
reaction of the electrolysis solution causes heat generation to
raise the battery temperature, or liquid leaks or causes a rupture.
As a countermeasure, the lithium ion secondary battery
incorporates, as one of battery constituent members, a ring-shaped
PTC element for limiting the flow of current due to elevation of
resistance when the battery temperature rises by overcharge or the
like. The PTC element has a structure in which an element main body
showing a sharp resistance increase along with temperature
elevation caused by overcurrent or the like is disposed between a
pair of electrodes.
[0013] By forming the PTC element in a ring shape, a sufficient gas
passage can be provided. That is, a rupture plate which is broken
by elevation of internal pressure due to gas generation is
separately assembled in an external can to the inner side from the
PTC element so as to be connected to the PTC element. The rupture
plate breaks to release gas when the battery internal pressure is
raised due to heat generation or another abnormality. At this time,
by forming the PTC element in a ring shape, a gas passage is
maintained in the hollow space, so that gas can be smoothly
discharged and released outside.
[0014] In the PTC element, however, since its material
configuration and shape, especially shape aspects, function as
relatively large resistance components, elevation of output of the
secondary battery may be hindered.
BRIEF SUMMARY OF THE INVENTION
[0015] It is hence an object of the invention to provide a
nonaqueous electrolyte secondary battery excellent in output
characteristic such as large current discharge or pulse discharge
in ordinary use, and effective in current suppression at an
abnormal time such as external short-circuiting.
[0016] According to the present invention, there is provided a
nonaqueous electrolyte secondary battery comprising:
[0017] an external can opened at one end thereof;
[0018] an electrode assembly contained in the external can, and
comprising a negative electrode, a separator and a positive
electrode;
[0019] a nonaqueous electrolyte contained in the external can;
and
[0020] a sealing lid group tightly sealed at the opening of the
external can by way of an insulating member,
[0021] wherein the sealing lid group comprises an intact plate-like
PTC element having a fragile portion to be easily broken due to
elevation of internal pressure by gas generation.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0022] FIG. 1 is a partial sectional view showing a cylindrical
nonaqueous electrolyte secondary battery according to a first
embodiment of the invention.
[0023] FIG. 2 is an exploded perspective view showing essential
parts of a sealing lid group assembled in the cylindrical
nonaqueous electrolyte secondary battery in FIG. 1.
[0024] FIG. 3 is a plan view showing a PTC element assembled in the
cylindrical nonaqueous electrolyte secondary battery in FIG. 1.
[0025] FIG. 4 is a sectional view taken along line IV-IV in FIG.
3.
[0026] FIG. 5A is a plan view showing another mode of the PTC
element assembled in the nonaqueous electrolyte secondary battery
of the invention.
[0027] FIG. 5B is a plan view showing another mode of the PTC
element assembled in the nonaqueous electrolyte secondary battery
of the invention.
[0028] FIG. 5C is a plan view showing another mode of the PTC
element assembled in the nonaqueous electrolyte secondary battery
of the invention.
[0029] FIG. 5D is a plan view showing another mode of the PTC
element assembled in the nonaqueous electrolyte secondary battery
of the invention.
[0030] FIG. 6 is a sectional view showing another mode of the PTC
element assembled in the nonaqueous electrolyte secondary battery
of the invention.
[0031] FIG. 7 is an exploded perspective view showing another mode
of essential parts of the sealing lid group assembled in the
cylindrical nonaqueous electrolyte secondary battery.
[0032] FIG. 8 is an exploded perspective view showing another mode
of essential parts of the sealing lid group assembled in the
cylindrical nonaqueous electrolyte secondary battery.
[0033] FIG. 9 is an exploded perspective view showing another mode
of essential parts of the sealing lid group assembled in the
cylindrical nonaqueous electrolyte secondary battery.
[0034] FIG. 10 is an exploded perspective view showing another mode
of essential parts of the sealing lid group assembled in the
cylindrical nonaqueous electrolyte secondary battery.
[0035] FIG. 11 is a partial sectional view showing a cylindrical
nonaqueous electrolyte secondary battery according to a second
embodiment of the invention.
[0036] FIG. 12 is an exploded perspective view showing essential
parts of a sealing lid group assembled in the cylindrical
nonaqueous electrolyte secondary battery in FIG. 11.
[0037] FIG. 13 is a partial sectional view showing a cylindrical
nonaqueous electrolyte secondary battery according to a third
embodiment of the invention.
[0038] FIG. 14 is an exploded perspective view showing essential
parts of a sealing lid group assembled in the cylindrical
nonaqueous electrolyte secondary battery in FIG. 13.
DETAILED DESCRIPTION OF THE INVENTION
[0039] The present invention will be specifically described
below.
First Embodiment
[0040] FIG. 1 is a partial sectional view showing a cylindrical
nonaqueous electrolyte secondary battery according to a first
embodiment of the invention; FIG. 2 is an exploded perspective view
showing essential parts of a sealing lid group assembled in the
cylindrical nonaqueous electrolyte secondary battery in FIG. 1;
FIG. 3 is a plan view showing a PTC element assembled in the
cylindrical nonaqueous electrolyte secondary battery in FIG. 1; and
FIG. 4 is a sectional view taken along line IV-IV in FIG. 3.
[0041] As shown in FIG. 1, an external can 1 of cylindrical shape
with a bottom is made of, for example, stainless steel or iron, and
also functions as one polar terminal (for example, negative
electrode terminal). In the bottom of the external can 1, an
insulator (not shown) is disposed. An electrode assembly 2 is
contained in the external can 1. The electrode assembly 2 is
constituted of a positive electrode 3, a negative electrode 4, and
a separator 5 interposed therebetween to wind up spirally. An
insulated presser plate 8 having two semicircular holes 6 and a
small hole 7 near the center is disposed on the electrode assembly
2 in the external can 1.
[0042] A sealing lid group 9 is insulated and closed in the upper
end opening of the external can 1 by way of, for example, an
insulating gasket 10. The sealing lid group 9 is electrically
connected to one electrode (for example, positive electrode 3) of
the electrode assembly 2 by way of, for example, a folding type
lead wire 11 made of a metal such as aluminum. The sealing lid
group 9 has a current breaking member 12 for conducting and cutting
off current, the current breaking member having a open valve which
is cut off when internal pressure elevates due to gas generation, a
PTC element 13, and a hat-shaped terminal plate 15 having gas vents
14 opened and serving as the other polar terminal (for example,
positive electrode terminal), which are disposed sequentially in
this order from the electrode assembly 2 side by crimping and
fixing the peripheral edges by the insulating gasket 10.
[0043] The current breaking member 12 is not particularly limited
in structure or composition. Specifically, as shown in FIGS. 1 and
2, the current breaking member 12 comprises a metallic stripper 16,
and a metallic rupture plate 18 overlaid on the stripper 16 by way
of an insulating sheet 17. The stripper 16, insulating sheet 17,
and rupture plate 18 are formed like a dish, and the peripheral
edges are crimped and fixed by the insulating gasket 10. The
insulating sheet 17 is opened at the central side from near the
riser part, and forms a gas passage.
[0044] The stripper 16, as shown in FIG. 2, has three sector holes
19 as gas passages at a position thereof corresponding to the
opening of the insulating sheet 17, and also has a small hole 20
near the center thereof. A conductive thin film 21 is bonded to the
side of the stripper 16 opposite to the electrode assembly 2 so as
to seal the small hole 20. At the side of the conductive thin film
21 opposite to the electrode assembly 2, the lead 11 is connected.
The stripper 16 is made of stainless steel or aluminum, and is
formed in a thickness of 0.1 to 1.0 mm. The conductive thin film 21
is made of, for example, aluminum, and is formed in a thickness of
0.05 to 0.2 mm. The conductive thin film may be omitted.
[0045] The rupture plate 18 has a protrusion 22 projecting toward
the stripper 16 in the central part so as to operate also as
current breaking means as shown in FIG. 2, and the leading end of
the protrusion 22 is connected to the conductive thin film 21
through the opening of the insulating sheet 17 and the small hole
20 of the stripper 16. In order that the rupture plate 18 also
functions as an open valve, notches, for example, a circular notch
23 surrounding the protrusion 22 and eight linear notches 24 formed
to extend radially to the peripheral edges from the circular notch
23, are formed at the side of the PTC element 13. The rupture plate
18 is made of, for example, stainless steel or aluminum, and is
formed in a thickness of 0.1 to 0.5 mm.
[0046] The terminal plate 15 serving as the other polar terminal
(for example, positive electrode terminal) having the gas vent 14
opened is made of, for example, stainless steel or aluminum, and is
formed in a thickness of 0.2 to 1.0 mm.
[0047] The PTC element 13 is interposed between the rupture plate
18 of the current breaking member 12 and the terminal plate 15,
that is, in a current passage of the positive electrode, and limits
current by increase of resistance when the temperature rises due to
flow of overcurrent, and prevents abnormal heat generation caused
by a large current. The PTC element 13 is in a disk shape as shown
in FIGS. 1 and 2, and is crimped and fixed to the insulating gasket
10 so as to cover the entire rupture plate 18.
[0048] The PTC element 13 has a structure as shown in FIG. 4, for
example, in which a resin sheet 26 of polyethylene or polypropylene
containing conductive carbon is interposed between a pair of
electrodes 25 composed of a metal thin film such as a nickel thin
film.
[0049] The PTC element 13 has a notch, which is a fragile portion
to be easily broken by elevation of internal pressure due to gas
generation, formed at least at the side of the terminal plate 15.
For example, as shown in FIGS. 2 to 4, four sector notches 28
(blade type notches) including the circular notch 27 are formed
symmetrically on the pair of electrodes 25 on both sides of the
resin sheet 26. These notches formed in the PTC element 13 are
broken when the gas generated in the battery reaches a
predetermined pressure, and act to open a gas passage in the
disk-shaped PTC element 13.
[0050] Notches to be formed in the PTC element 13 are preferably
formed in a closed loop shape (for example, circular shape) at
least near the center as shown in FIGS. 2 to 4 described above.
However, the notches are not limited to the closed loop shape, but
may be formed, for example, in a cross shape having two linear
notches intersected, or in a C shape obtained by partly cutting off
the loop. The intersecting linear notches may be three or more.
[0051] Aside from the shape in FIGS. 2 to 4 described above,
notches having a closed loop shape at least near the center (for
example, circular shape, quadrangular shape, triangular shape, or
another polygonal shape) will be explained below with reference to
FIGS. 5A to 5D. The notches may be formed at the side of the PTC
element 13 opposite to the terminal plate 15 or at both sides.
[0052] (1) The PTC element 13 shown in FIG. 5A has a small circular
notch 29 formed in the electrode 25.
[0053] (2) The PTC element 13 shown in FIG. 5B has a small square
notch 30 formed in the electrode 25.
[0054] (3) In the electrode 25 of the PTC element 13 shown in FIG.
5C, a small circular notch 29 and, for example, four linear notches
31 extending radially from the notch 29 to the peripheral edge of
the electrode 25 are formed. The number of linear notches 31 is not
limited to four, but may be two, three, five or more.
[0055] (4) In the electrode 25 of the PTC element 13 shown in FIG.
5D, small circular and large circular notches 29, 32 are
concentrically formed, and also, for example, four linear notches
31 crossing with these small circular and large circular notches
29, 32, and extending radially are formed. The number of linear
notches 30 is not limited to four, but may be two, three, five or
more. The circular notches may be also formed in three or four
circles concentrically.
[0056] In the notches formed in a closed loop shape at least near
the center, the notch in the shape of FIG. 5C has an intersection
of notches as compared with FIGS. 5A and 5B. Thus, when the gas
generated in the battery reaches a predetermined pressure, the PTC
element can be easily broken. The notch in the shape of FIG. 5D has
more intersections than that in FIG. 5C, and therefore, the PTC
element can be broken more easily when the gas generated in the
battery reaches a predetermined pressure. Further, the notches in
the shape of FIGS. 2 to 4 described above can break the PTC element
yet more easily when the gas generated in the battery reaches a
predetermined pressure because of layout of notches as compared
with FIG. 5D, or the like.
[0057] The depth of the notch formed in the PTC element is
preferably 4% or more of the electrode thickness (t1), and not more
than the total thickness (t1+t2.times.0.2) of the electrode
thickness (t1) and 20% of the resin sheet thickness (t2). If the
depth is less than 4% of the electrode thickness, the PTC element
may be hardly broken with the notch being a starting point when the
gas generated in the battery tears the rupture plate and reaches
the PTC element. On the other hand, if the depth of the notch
exceeds the total thickness of the electrode thickness and 20% of
the resin sheet thickness, the function of the PTC element may be
broken.
[0058] The width of the notch formed in the PTC element is not
particularly specified, but is preferably 5 .mu.m or more. More
preferably, the width of the notch is 50 .mu.m or more. If the
width of the notch is less than 5 .mu.m, the PTC element may hardly
be broken with the notch being a starting point when the gas
generated in the battery tears the rupture plate and reaches the
PTC element. The upper limit of the width of the notch is
preferably 5 mm.
[0059] The opening area of the notch formed in the PTC element is 1
mm.sup.2 or more, more preferably 5 mm.sup.2 or more. If the
opening area of the notch is less than 1 mm.sup.2, the PTC element
may hardly be broken with the notch being a starting point when the
gas generated in the battery tears the rupture plate and reaches
the PTC element. The upper limit of the opening area of the notch
is preferably 120 mm.sup.2.
[0060] The fragile portion to be easily broken by elevation of
internal pressure due to gas generation formed in the PTC element
may be, for example, a circular recess 33 as shown in FIG. 6. The
recess is not limited to circular, but may be polygonal such as
quadrangular or pentagonal.
[0061] The depth (step) of the recess is preferably 20 .mu.m or
more.
[0062] The electrode assembly, the positive electrode, negative
electrode and separator configuring the electrode assembly, and the
nonaqueous electrolyte will be specifically explained below.
1) Electrode Assembly
[0063] The electrode assembly is composed by interposing a
separator between a positive electrode and a negative electrode.
Specifically, the electrode assembly is manufactured by (i) winding
the positive electrode and negative electrode flatly or spirally
together with the separator interposed therebetween; (ii) winding
the positive electrode and negative electrode spirally together
with the separator interposed therebetween, and then compressing in
a radial direction; (iii) folding the positive electrode and
negative electrode one or more together with the separator
interposed therebetween; or (iv) laminating the positive electrode
and negative electrode together with the separator interposed
therebetween.
[0064] The electrode assembly may not be pressed, but may be
pressed to reinforce the integrating strength of the positive
electrode, negative electrode and separator. It may be also heated
at the time of pressing.
2) Positive Electrode
[0065] The positive electrode has a structure in which a positive
electrode layer containing an active material is carried on one
side or both sides of a current collector.
[0066] The positive electrode layer comprises a positive electrode
active material, a binder, and a conductive agent.
[0067] Preferable examples of the positive electrode active
material include various oxides, for example, manganese dioxide,
lithium-manganese composite oxide, lithium-containing nickel oxide,
lithium-containing cobalt oxide (for example, LiCoO.sub.2),
lithium-containing nickel cobalt oxide (for example,
LiNi.sub.0..sub.8Co.sub.0..sub.2O.sub.2), and lithium-manganese
composite oxide (for example, LiMn.sub.2O.sub.4, LiMnO.sub.2)
because a high voltage can be obtained from these materials.
[0068] Examples of the conductive agent include acetylene black,
carbon black, and graphite.
[0069] Examples of the binder include polytetrafluoroethylene,
polyvinylidene fluoride, ethylene-propylene-diene copolymer, and
styrene-butadiene rubber.
[0070] The blending rate of the positive electrode active material,
conductive agent, and binder is preferably in a range of 80 to 95
wt. % of the positive electrode active material, 3 to 20 wt. % of
the conductive agent, and 2 to 7 wt. % of the binder.
[0071] As the current collector, a porous conductive board or
intact conductive board may be used. The conductive board is
manufactured from, for example, aluminum or stainless steel.
[0072] The positive electrode is fabricated, for example, by
suspending the positive electrode active material, conductive
agent, and binder in a proper solvent, applying the suspension on
the current collector, drying, and pressing one to five times at a
desired pressure.
[0073] The filling density of positive electrode after pressing is
desired to be between 2.8 and 4.0 g/cm.sup.3.
[0074] The current collector is preferably made of aluminum. The
aluminum made positive electrode current collector is stable at a
positive electrode potential, and excellent in electrical
conductivity, and hence can contribute to enhancement of rate
characteristic and cycle performance of the battery.
[0075] Further, a positive electrode tab is desirably welded to an
exposed region of the current collector of the positive
electrode.
3) Negative Electrode
[0076] The negative electrode comprises a negative electrode
current collector, and a negative electrode layer containing a
negative electrode material and a binder, the negative electrode
layer being carried on one side or both sides of the negative
electrode current collector.
[0077] The negative electrode material is preferably a carbonaceous
matter for intercalating and deintercalating lithium ions. Examples
of the carbonaceous matter include a graphitic material or
carbonaceous material such as graphite, coke, carbon fiber and
spherical carbon, thermosetting resin, isotropic pitch, mesophase
pitch, and a graphitic material or carbonaceous material obtained
by heating mesophase pitch carbon fiber or mesophase spherule at
500 to 3000.degree. C.
[0078] A preferable example of the carbonaceous matters is the
graphitic material containing graphite crystals, which is obtained
by heat treatment at 2000.degree. C. or higher temperature, and
whose plane interval d002 is between 0.336 and 0.34 nm.
[0079] Examples of the binder include polytetrafluoroethylene,
polyvinylidene fluoride, ethylene-propylene-diene copolymer,
styrene-butadiene rubber, and carboxy methyl cellulose.
[0080] The blending rate of the negative electrode active material,
conductive agent, and binder is preferably in a range of 80 to 98
wt. % of the negative electrode active material, 3 to 30 wt. % of
the conductive agent, and 1 to 7 wt. % of the binder.
[0081] As the current collector, a porous conductive board or
intact conductive board may be used. The conductive board is
manufactured from, for example, copper, stainless steel, or nickel.
The thickness of the current collector is desirably 5 to 20 .mu.m.
This is because balance of electrode strength and weight reduction
is assured in this range.
[0082] The negative electrode is fabricated, for example, by
suspending the negative electrode active material, conductive
agent, and binder in a proper solvent, applying the suspension on
the current collector, drying, and pressing once to five times at a
desired pressure. The application quantity of the negative
electrode is preferably between 50 and 140 g/m.sup.2 on one side of
the current collector.
[0083] The filling density of the negative electrode after pressing
is desired to be between 1.3 and 1.8 g/cm.sup.3 in the central area
of the electrode in the lateral direction.
[0084] As the negative electrode material, aside from the above
carbonaceous matter for intercalating and deintercalating lithium
ions, other materials may be also used such as metal for
intercalating and deintercalating lithium ions, metal oxide, metal
sulfide, metal nitride, lithium metal, and lithium alloy.
[0085] Examples of the metal oxide include tin oxide, silicon
oxide, lithium titanium oxide, niobium oxide, and tungsten
oxide.
[0086] Examples of the metal sulfide include tin sulfide, and
titanium sulfide.
[0087] Examples of the metal nitride include lithium cobalt
nitride, lithium iron nitride, and lithium manganese nitride.
[0088] Examples of the lithium alloy include lithium aluminum
alloy, lithium tin alloy, lithium lead alloy, and lithium silicon
alloy.
[0089] When other material capable of intercalating and
deintercalating lithium than the graphitic material or carbonaceous
material is used as the negative electrode active material, it is
desired to use, for example, acetylene black, carbon black,
graphite or the like as the conductive agent.
4) Separator
[0090] The separator is desirably formed of a porous sheet.
[0091] As the porous sheet, for example, a porous film or nonwoven
cloth may be used. The porous sheet is preferred to be made of at
least one material selected from, for example, polyolefin and
cellulose. The polyolefin includes, for example, polyethylene and
polypropylene. The porous film made of polyethylene, or
polypropylene, or both is preferred because the safety of the
secondary battery is enhanced.
[0092] The thickness of the separator is desired to be 30 .mu.m or
less. A more preferred range is 5 to 30 .mu.m, and a further
preferred range is 8 to 25 .mu.m.
[0093] The separator is preferred to be 20% or less in heat
shrinkage after heating for 1 hour at 120.degree. C. More
preferably, heat shrinkage is 15% or less.
[0094] Porosity of the separator is preferred to be in a range of
30 to 70%. A more preferred range of the porosity is 35 to 70%.
[0095] Air permeability of the separator is preferred to be 700
sec/100 cm.sup.3 or less. The air permeability refers to time
(seconds) required for 100 cm.sup.3 of air to pass through a porous
sheet. A more preferred range is 30 to 500 sec/100 cm.sup.3, and a
further preferred range is 50 to 150 sec/100 cm.sup.3.
[0096] An end of the separator along the lateral direction is
desired to project 0.25 to 2 mm from an end of the negative
electrode along the lateral direction.
5) Nonaqueous Electrolyte
[0097] The nonaqueous electrolyte may be used in a form of liquid,
gel or solid (high molecular solid electrolyte).
[0098] The liquid nonaqueous electrolyte (nonaqueous electrolytic
solution) is obtained, for example, by dissolving an electrolyte
(for example, lithium salt) in a nonaqueous solvent. The gel
nonaqueous electrolyte contains a nonaqueous electrolytic solution
and a high molecular material to which the nonaqueous electrolytic
solution is held. Examples of the high molecular material include
polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide,
polyvinyl chloride, polyacrylate, and polyvinylidene fluoride
hexafluoropropylene.
[0099] The nonaqueous solvent is not particularly limited, and any
known nonaqueous solvent as a solvent for a nonaqueous electrolyte
secondary battery can be used. It is preferred to use a nonaqueous
solvent consisting mainly of a mixed solvent of ethylene carbonate,
and one or more nonaqueous solvents (hereinafter called second
solvents) lower in melting point than the ethylene carbonate and
having 18 or less donors. Such a nonaqueous solvent is stable in
the presence of substances for composing the negative electrode,
low in risk of reduction decomposition or oxidation decomposition
of the electrolyte, and high in conductivity. Examples of the
second solvent include dimethyl carbonate, methyl ethyl carbonate,
diethyl carbonate, ethyl propionate, methyl propionate, propylene
carbonate, .gamma.-butyrolactone, acetonitrile, ethyl acetate,
toluene, xylene, and methyl acetate. Above all, chain carbonate is
preferred. The second solvent may be used either alone or in a
mixture of two or more types.
[0100] Viscosity of the mixed solvent is preferred to be 28 mp or
less at 25.degree. C. The content of ethylene carbonate in the
mixed solvent is preferred to be 10 to 80% by volume. If out of
this range, the conductivity may be lowered or the solvent may be
decomposed, so that the charge and discharge efficiency may be
lowered. A more preferred content of the ethylene carbonate is 20
to 75% by volume. By increasing the content of ethylene carbonate
in the nonaqueous solvent to 20% by volume, the ethylene carbonate
can be easily dissolved in lithium ions, and therefore,
decomposition suppressing effect of the solvent can be
enhanced.
[0101] A more preferred composition of the mixed solvent is a mixed
solvent of EC and MEC; EC, PC and MEC; EC, MEC and DMC; and EC,
MEC, PC and DEC, and the ratio of MEC is preferred to be 30 to 80%
by volume. Thus, by adjusting the ratio of MEC to 30 to 80% by
volume, or more preferably 40 to 70% by volume, the conductivity
can be enhanced. On the other hand, from the view point of
suppressing reduction decomposition reaction of the solvent, when
an electrolytic solution having carbon dioxide dissolved therein is
used, it is effective for enhancing the capacity and cycle
life.
[0102] Major impurities existing in the mixed solvent are, for
example, water and organic peroxides (for example, glycols,
alcohols, carboxylic acids). These impurities may cause to lower
the cycle life or capacity. They may also increase the
self-discharge when stored at high temperature (60.degree. C. or
more) Accordingly, in the nonaqueous electrolyte containing the
nonaqueous solvent, such purities are preferably reduced as much as
possible. Specifically, the water content is preferred to be 50 ppm
or less, and the organic peroxides is preferred to be 1000 ppm or
less.
[0103] Examples of the electrolyte include lithium salts such as
lithium perchlorate, lithium phosphate hexafluoride (LiPF.sub.6),
lithium borate tetrafluoride (LiBF.sub.4), lithium arsenate
hexafluoride (LiAsF.sub.6), lithium trifluoromethasulfonate
(LiCF.sub.3SO.sub.3), and lithium bistrifluoromethyl sulfonylimide
[LiN(CF.sub.3SO.sub.2).sub.2]. Among them, LiPF.sub.6, LiBF.sub.4,
and LiN(CF.sub.3SO.sub.2).sub.2 are particularly preferred.
[0104] The dissolving amount of the electrolyte in the nonaqueous
solvent is preferred to be in a range of 0.5 to 2 mol/L.
[0105] In the nonaqueous electrolyte secondary battery according to
the first embodiment shown in FIGS. 1 to 4, the operation will be
explained in various modes, that is, (1) normal mode, (2) abnormal
mode (external short-circuiting), and (3) abnormal mode
(overcharging).
(1) Normal Mode
[0106] In the normal charge and discharge mode, the PTC element 13
placed, for example, in the current path of the positive electrode
is an intact plate (for example, disk shape). As compared with the
conventional ring-shaped PTC element, the area of the PTC element
13 is wider and the resistance is lower, that is, the internal
resistance of the battery can be lowered. Consequently, higher
output, that is, an excellent large current discharge
characteristic and pulse discharge characteristic can be
obtained.
(2) External Short-Circuiting Mode
[0107] When a large current flows due to external short-circuiting,
the PTC element 13 positioned between the current breaking member
12 and the terminal plate 15 is actuated by heat generation due to
own resistance, and the resistance increases suddenly. Accordingly,
by suppressing the current flow, heat generation and elevation of
the internal pressure due to a continuous large current can be
avoided.
(3) Overcharging Mode
[0108] When, due to overcharging, the temperature in the external
can 1 elevates, gas is generated due to reaction between the
electrode assembly 2 and the nonaqueous electrolyte and due to
decomposition of the nonaqueous electrolyte, and the internal
pressure climbs up, the gas passes through the holes 6, 7 in the
insulating presser plate 8, the three sector holes 19 opened in the
stripper 16 of the current breaking member 12, and the opening in
the insulating sheet 17 to reach the rupture plate 18, and pushes
up the rupture plate 18 to the terminal plate 15 side. When the
rupture plate 18 is pushed up, the stripper 16 and the conductive
thin film 21 are not deformed. Therefore, the protrusion 22 of the
rupture plate 18 is departed from the conductive thin film 21, and
the conduction path of the positive electrode is electrically cut
off. As a result, further heat generation and elevation of the
internal pressure due to continuous current can be avoided.
[0109] If the internal pressure further climbs up after cutting off
the current transmission path of the positive electrode, a higher
gas pressure is applied to the rupture plate 18 of the current
breaking member 12 through the gas passage. At this time, since the
notches 23, 24 are formed in the rupture plate 18 as shown in FIG.
2, the rupture plate 18 is broken from the notches 23, 24 due to
the applied pressure of gas. As the rupture plate 18 is broken, the
gas further flows into the circular PTC element 13. Then, since the
PTC element 13 has the notches 27, 28 as shown in FIGS. 2 to 4, the
PTC element 13 is broken with these notches 27, 28 as a starting
point, and thus, the gas is smoothly released outside through the
gas vent 14 of the terminal plate 15 from the broken position of
the PTC element 13. As a result, destruction of the battery due to
excessive elevation of the internal pressure can be prevented.
[0110] In the event of impact such as heavy drop, in addition to
the rupture plate 18, the PTC element 13 is provided which has a
rupture function and has the notches 27, 28 formed therein. Thus,
even if one rupture function member (for example, rupture plate 18)
is broken, the PTC element 13 having the rupture function maintains
a normal state without being broken. Consequently, even if water
invades from outside through the gas vent 14 of the terminal plate
15, it can be cut off by the normal PTC element 13, and invasion of
water into the nonaqueous electrolyte (for example, nonaqueous
electrolytic solution) in the external can 1 can be blocked. In
addition, discharge of the nonaqueous electrolytic solution in the
external can 1 can be blocked by the normal PTC element 13, and
leak of the nonaqueous electrolytic solution can be prevented.
[0111] As a result, deterioration of the electrolytic solution due
to invasion of water can be prevented, and excellent battery
performance can be maintained. In addition, when the secondary
battery is assembled as, for example, a battery pack, prevention of
leakage of the nonaqueous electrolytic solution makes it possible
to avoid various problems such as short-circuiting of a protective
circuit by the nonaqueous electrolytic solution, smoking, and
firing.
[0112] Therefore, according to the first embodiment, the resistance
of the PTC element which is a constituent member of the battery is
lowered in the normal state, so that discharge of high output is
realized. On the other hand, in the event of abnormality such as
external short-circuiting or overcharging, heat generation
(temperature rise) and elevation of the internal pressure can be
prevented. Further, even if gas generation or elevation of the
internal pressure is caused by temperature rise, the PTC element
itself is broken, the gas passage is formed to release gas
promptly, and breakage or the like can be prevented from occurring.
Moreover, double rupture function members of the rupture plate and
intact PTC element are provided, whereby in the event of impact
such as a fall, invasion of water from outside or leakage of the
nonaqueous electrolytic solution can be prevented. As a result, it
is possible to provide a nonaqueous electrolyte secondary battery
having a high output characteristic, high safety, and high
reliability.
[0113] According to the nonaqueous electrolyte secondary battery of
the invention, since a high output can be obtained without reducing
the thickness of the electrode assembly, the electrode reaction
volume can be increased, and the battery capacity can be
increased.
[0114] Further, since a bundling structure of lead wires can be
avoided, not only the productivity is increased, but also the
effective area in the battery can be increased and the battery
capacity is further increased.
[0115] In the cylindrical nonaqueous electrolyte secondary battery
of the first embodiment shown in FIGS. 1 and 2, the sealing plate
group may also have a conductive support plate shown in FIGS. 7 to
10.
[0116] As shown in FIG. 7, the conductive support plate 41 is
disposed so as to cover the entire surface (upper surface) of the
PTC element 13 at the terminal plate side. The conductive support
plate 41 is composed of: a conductive disk 42 which is crimped and
fixed in the insulating gasket 10; a notch, for example, a circular
notch 43 which is formed in the conductive disk 42 and easily
broken by elevation of the internal pressure due to gas generation;
and eight linear notches 44 which extend radially to outside from
the notch 43.
[0117] When, in the conductive support plate 41 having the
configuration as shown in FIG. 7, the internal pressure of the
external can is raised due to gas generation, the rupture plate 18
is broken, and further the PTC element 13 is broken and gas
pressure is applied, it is broken from the notches 43, 44, and gas
is released.
[0118] As shown in FIG. 8, a conductive ring plate 45 serving as a
conductive support plate is fixed and crimped in the insulating
gasket 10 so as to cover the entire surface (upper surface) of the
PTC element 13 at the terminal plate side.
[0119] As shown in FIG. 9, a conductive support plate 46 is
disposed so as to cover the entire surface (upper surface) of the
PTC element 13 at the terminal plate side. The conductive support
plate 46 is composed of: a conductive ring plate 47 which is
crimped and fixed in the insulating gasket 10; a circular thin
plate 48 fixed to cover the hollow space at least at one side (for
example, upper surface) of the ring plate 47 excluding the fixed
portion by the insulating gasket 10; a notch, for example, a
circular notch 49 formed in the thin plate 48, the notch being a
fragile portion to be easily broken by elevation of the internal
pressure due to gas generation; and eight linear notches 50 which
extend radially to outside from the notch 49. The circular thin
plate is made of, for example, aluminum or nickel, and formed in a
thickness of 0.05 to 0.3 mm so as to be broken easily by elevation
of the internal pressure due to gas generation.
[0120] When, in the conductive support plate 46 having the
configuration shown in FIG. 9, the internal pressure in the
external can is raised by gas generation, the rupture plate 18 is
broken, and further the PTC element 13 is broken and gas pressure
is applied, it is broken from the notches 49, 50 formed in the thin
plate 48, and gas is released.
[0121] As shown in FIG. 10, a conductive support plate 51 is
disposed so as to cover the entire surface (upper surface) of the
PTC element 13 at the terminal plate side. The conductive support
plate 51 is composed of: a conductive ring plate 52 which is
crimped and fixed in the insulating gasket 10; and a circular high
molecular resin layer 53 disposed in tight contact with the inside
of a hollow space of the ring plate 52. The circular high molecular
resin layer 53 is preferred to be fused at about 150 to 200.degree.
C., and is preferably made of, for example, polyvinylidene fluoride
or polypropylene.
[0122] When, in the conductive support plate 50 shown in FIG. 10,
the internal pressure in the external can is raised by gas
generation, the rupture plate 18 is broken, and further the PTC
element 13 is broken and gas pressure is applied at a relatively
high temperature, the circular high molecular resin layer 53 is
fused to form a gas passage, and gas is released through the gas
passage.
[0123] The conductive disk 42 and conductive ring plates 45, 47, 52
composing the conductive support plates 41, 46, 51 shown in FIGS. 7
to 10 are used for crimping and fixing the PTC element 13 and
rupture plate 18 stably with respect to the insulating gasket 10.
Accordingly, if the conductive disk and conductive ring plate are
too thin, the expected function may not be exhibited sufficiently.
Conversely, if the conductive disk and conductive ring plate are
too thick, the thickness of the sealing lid group is increased, so
that the accommodation capacity of the electrode group is
substantially lowered. Therefore, the conductive disk and
conductive ring plate are desired to have a thickness of 0.1 to 0.5
mm, or more preferably 0.2 to 0.35 mm.
[0124] The conductive disk and conductive ring plate composing the
conductive support plate are preferred to be manufactured from a
conductive material of relatively large Young's modulus (Young's
modulus at 25.degree. C. of 1.times.10.sup.11 to
3.27.times.10.sup.11 Pa) in order to exhibit the function
effectively. For example, they can be manufactured from iron,
nickel, copper, cobalt, chromium, or their alloys, or molybdenum
and tantalum.
[0125] According to the configuration shown in FIGS. 7 to 10, the
crimping fixing strength of the rupture plate 18 and PTC element 13
in the peripheral edge thereof with respect to the insulating
gasket 10 is improved by the conductive support plate, and
therefore, it is possible to prevent deformation of the peripheral
edge of these members due to elevation of the internal pressure of
the external can caused by gas generation. As a result,
fluctuations of working pressure at the time of breakage of the
rupture plate 18 and the PTC element 13 can be suppressed, so that
a stable rupture function is assured.
[0126] In particular, the conductive support plate 41 having the
notches 43, 44 shown in FIG. 7, the conductive support plate 46
having the circular thin plate 48 having formed therein the notches
49, 50 shown in FIG. 9, and the conductive support plate 51 having
the circular high molecular resin layer 53 shown in FIG. 10 have
the rupture function as mentioned individually. Accordingly,
together with the rupture plate 18 and intact PTC element 13,
triple rupture function members may be provided, and even in the
event of impact such as drop, invasion of water from outside or
leakage of the nonaqueous electrolytic solution can be prevented
more securely.
[0127] The conductive support plates shown in FIGS. 7 to 10 are
disposed on the surface of the PTC element 13 at the terminal plate
side, but not limited thereto and may be also disposed between the
PTC element 13 and the rupture plate 18.
Second Embodiment
[0128] FIG. 11 is a partial sectional view showing a cylindrical
nonaqueous electrolyte secondary battery according to a second
embodiment of the invention, and FIG. 12 is an exploded perspective
view showing essential parts of a sealing lid group assembled in
the cylindrical nonaqueous electrolyte secondary battery in FIG.
11. In FIGS. 11 and 12, the same members as in FIGS. 1 and 2 are
identified with same reference numerals, and explanation thereof is
omitted.
[0129] In FIGS. 11 and 12, the sealing lid group 9 is composed of a
conductive current breaking member 61, an insulating ring 62, a
rupture plate 63, and a hat-shaped terminal plate 15 having a PTC
element 13 and gas vents 14 and serving as the other polarity
terminal (for example, positive electrode terminal), which are
crimped and fixed in this order by the insulating gasket 10 at
their peripheral edges.
[0130] The current breaking member 61 is formed like a dish as
shown in FIG. 12, and a peripheral edge of the current breaking
member has a stripper 64 crimped and fixed by the insulating gasket
10. The stripper 64 has, for example, three holes 65 as gas
passages at a position corresponding to the hollow space in the
insulating ring 62. The stripper 64 has a protrusion 66 projecting
toward the rupture plate 63 near the center, and the leading end of
the protrusion 66 is connected to the rupture plate 63 through the
hollow space in the insulating ring 62. The stripper 64 is made of
stainless steel or aluminum, and has a thickness of 0.1 to 0.3 mm.
For example, a folding type lead wire 11 made of a metal such as
aluminum is connected to one electrode (for example, positive
electrode 3) of the electrode assembly 2 at one end thereof, and
connected to the bottom of the stripper 64 at the other end
thereof.
[0131] The insulating ring 62 has a thickness of, for example, 0.05
to 0.5 mm.
[0132] The rupture plate 63 is in a plate as shown in FIG. 12, and
a peripheral edge of the rupture plate 63 is crimped and fixed by
the insulating gasket 10. In the rupture plate 63, a notch, for
example, a circular notch 67 is formed at the surface of the PTC
element 13 side, and, for example, eight linear notches 68
extending radially to the peripheral edge from the circular notch
67 are formed. The rupture plate 63 is made of stainless steel or
aluminum, and has a thickness of 0.1 to 0.2 mm.
[0133] The PTC element 13 has the same structure as that explained
in the first embodiment.
[0134] In the nonaqueous electrolyte secondary battery in the
second embodiment shown in FIGS. 11 and 12, since the operation in
the normal mode and abnormal mode (external short-circuiting) is
same as that in the first embodiment, only the operation in the
abnormal mode (overcharging) will be described below.
3) Overcharging Mode
[0135] When, due to overcharging, temperature in the external can 1
elevates, gas is generated due to reaction between the electrode
assembly 2 and the nonaqueous electrolytic solution and due to
decomposition of the nonaqueous electrolytic solution, and the
internal pressure climbs up, the gas passes through the holes 6, 7
in the insulating presser plate 8, the three holes 65 opened in the
stripper 61, and the hollow space in the insulating ring 62 to
reach the rupture plate 63, and pushes up the rupture plate 63 to
the terminal plate 15 side. When the rupture plate 63 is pushed up,
the stripper 61 having the protrusion 66 contacting with the bottom
of the rupture plate 63 is not deformed, and therefore, the
protrusion 66 is departed from the rupture plate 63, and the
conduction path of the positive electrode is electrically cut off.
As a result, further heat generation and elevation of the internal
pressure due to continuous current can be avoided.
[0136] If the internal pressure further climbs up after cutting off
the current transmission path of the positive electrode, a higher
gas pressure is applied to the rupture plate 63 through the gas
passage. At this time, since the notches 67, 68 are formed in the
rupture plate 63 as shown in FIG. 12, the rupture plate 63 is
broken from the notches 67, 68 due to the applied pressure of gas.
As the rupture plate 63 is broken, the gas further flows into the
circular PTC element 13. Then, since the PTC element 13 has notches
27, 28 as shown in FIG. 12, the PTC element 13 is broken from these
notches 27, 28, and thus, the gas is smoothly released outside
through the gas vent 14 of the terminal plate 15 from the broken
position of the PTC element 13. As a result, destruction of the
battery due to excessive elevation of the internal pressure can be
prevented.
[0137] In the event of impact such as a heavy drop, in addition to
the rupture plate 63, the PTC element 13 is provided which has a
rupture function and has the notches 27, 28 formed therein. Thus,
even if one rupture function member (for example, rupture plate 63)
is broken, the PTC element 13 having the rupture function maintains
a normal state without being broken. Even if water invades from
outside through the gas vent 14 of the terminal plate 15, it can be
cut off by the normal PTC element 13, and invasion of water into
the nonaqueous electrolyte (for example, nonaqueous electrolytic
solution) in the external can 1 can be blocked. In addition,
discharge of the nonaqueous electrolytic solution in the external
can 1 can be blocked by the normal PTC element 13, and leakage of
the nonaqueous electrolytic solution can be prevented.
[0138] Therefore, according to the second embodiment, the
resistance of the PTC element which is a constituent member of the
battery is lowered in the normal state, and discharge of high
output is realized. On the other hand, in the event of an
abnormality such as external short-circuiting or overcharging, heat
generation (temperature rise) and elevation of the internal
pressure can be prevented. Further, even if gas generation or
elevation of the internal pressure is caused by temperature rise,
the PTC element itself is broken, a gas passage is formed to
release gas promptly, and breakage can be prevented. Moreover,
double rupture function members of the rupture plate and intact PTC
element are provided, whereby in the event of impact such as a
fall, invasion of water from outside or leak of the nonaqueous
electrolytic solution can be prevented. As a result, it is possible
to provide a nonaqueous electrolyte secondary battery having a high
output characteristic, high safety, and high reliability.
Third Embodiment
[0139] FIG. 13 is a partial sectional view showing a cylindrical
nonaqueous electrolyte secondary battery according to a third
embodiment of the invention, and FIG. 14 is an exploded perspective
view showing essential parts of a sealing lid group assembled in
the cylindrical nonaqueous electrolyte secondary battery in FIG.
13. In FIGS. 13 and 14, the same members as in FIGS. 1 and 2 are
identified with same reference numerals, and explanation thereof is
omitted.
[0140] In FIGS. 13 and 14, the sealing lid group 9 is composed of a
rupture plate 71, a PTC element 13, a first half insulating ring
72, a current breaking member 73, a second half insulating ring 74,
and a hat-shaped terminal plate 15 having gas vents 14 opened and
serving as the other polarity terminal (for example, positive
electrode terminal), which are crimped and fixed in this order from
the electrode assembly 2 side by the insulating gasket 10 at their
peripheral edges.
[0141] The rupture plate 71 is formed like a dish as shown in FIG.
14, and a peripheral edge of the rupture plate 71 is crimped and
fixed by the insulating gasket 10. In the rupture plate 71, a
notch, for example, a circular notch 75 is formed in the recess at
the surface of the PTC element 13 side, and, for example, eight
linear notches 76 extending radially to the peripheral edge from
the circular notch 75 are formed. A folding type lead wire 11 made
of, for example, a metal such as aluminum is connected to one
electrode (for example positive electrode 3) of the electrode
assembly 3 at one end thereof, and connected to the bottom of the
rupture plate 71 at the other end thereof. The rupture plate 71 is
made of, for example, stainless steel or aluminum, and has a
thickness of 0.1 to 0.3 mm.
[0142] The PTC element 13 has the same structure as that explained
in the first embodiment.
[0143] The current breaking member 73 comprises two half conductive
rings 77a, 77b as shown in FIG. 14, and peripheral edges of these
half conductive rings 77a, 77b are crimped and fixed by the
insulating gasket 10 so as to be apart from each other across a
desired gap between both ends thereof. The half conductive rings
77a, 77b are made of, for example, stainless steel or aluminum, and
have a thickness of 0.1 to 0.3 mm. A temperature fuse 78 is
disposed near the center of the half conductive rings 77a, 77b, and
connected to the half conductive rings 77a, 77b by way of lead
terminals 79a, 79b. The temperature fuse 78 has a structure in
which, for example, a low melting point metal strip which is a
fusible member is sealed in a flat tube closed at both ends made of
a plastic material, and both ends of the low melting point metal
strip are connected to the lead terminals 79a, 79b through a
terminal wire made of high melting point metal.
[0144] Peripheral edges of the first and second half insulating
rings 72, 74 are crimped and fixed by the insulating gasket 10 so
as to be symmetrical across the half conductive rings 77a, 77b.
That is, the first half insulating ring 72 is disposed so as to
contact with the lower surface of the half conductive ring 77a, and
the second half insulating ring 74 is disposed so as to contact
with the upper surface of the half conductive ring 77b.
[0145] In the operation of the PTC element 13 and temperature fuse
78, the PCT element 13 is designed and selected to be actuated at a
lower current than the melting current of the temperature fuse 78
in order than the PTC element 13 operates by priority.
[0146] In the nonaqueous electrolyte secondary battery according to
the third embodiment shown in FIGS. 13 and 14, since the operation
in the normal mode and abnormal mode (external short-circuiting) is
same as that in the first embodiment, only the operation in the
abnormal mode (overcharging) is described below.
Overcharging Mode
[0147] When, due to overcharging, temperature elevates by abnormal
voltage and heat generation, the temperature fuse 78 connected in
series to the PTC element 13 by way of the half conductive ring 77b
and lead terminal 79b is melted down, and the conduction path of
the positive electrode is electrically cut off. As a result,
further heat generation and elevation of the internal pressure due
to continuous current can be avoided.
[0148] If the internal pressure further climbs up after cutting off
the current transmission path of the positive electrode due to heat
generation and gas generation, a higher gas pressure is applied to
the rupture plate 71. At this time, since the notches 75, 76 are
formed in the rupture plate 71 as shown in FIG. 14, the rupture
plate 71 is broken from the notches 75, 76 due to the applied
pressure of gas. As the rupture plate 71 is broken, the gas further
flows into the circular PTC element 13. Then, since the notches 27,
28 as shown in FIG. 14, for example, are formed in the PTC element
13, the PTC element 13 is broken from these notches 27, 28, and
thus, the gas is smoothly released outside through the hollow space
of the half conductive rings 77a, 77b and the gas vent 14 of the
terminal plate 15 from the broken position of the PTC element 13.
As a result, destruction of the battery due to excessive elevation
of the internal pressure can be prevented.
[0149] In the event of impact such as a heavy drop, in addition to
the rupture plate 71, the PTC element 13 is provided which has a
rupture function and has the notches 27, 28 formed therein. Thus,
even if one rupture function member (for example, rupture plate 71)
is broken, the PTC element 13 having the rupture function maintains
a normal state without being broken. Accordingly, even if water
invades from outside through the gas vent 14 of the terminal plate
15 and the hollow space in the half conductive rings 77a, 77b, it
can be cut off by the normal PTC element 13, and invasion of water
into the nonaqueous electrolyte (for example, nonaqueous
electrolytic solution) in the external can 1 can be blocked. In
addition, discharge of the nonaqueous electrolytic solution in the
external can 1 can be blocked by the normal PTC element 13, and
leakage of the nonaqueous electrolytic solution can be
prevented.
[0150] Therefore, according to the third embodiment, the resistance
of the PTC element which is a constituent member of the battery is
lowered in the normal state, and discharge of high output is
realized. On the other hand, in the event of an abnormality such as
external short-circuiting or overcharging, heat generation
(temperature rise) and elevation of the internal pressure can be
prevented. Further, even if gas generation or elevation of the
internal pressure is caused by temperature rise, the PTC element
itself is broken, a gas passage is formed to release gas promptly,
and breakage can be prevented. Moreover, double rupture function
members of the rupture plate and intact PTC element are provided,
whereby in the event of impact such as fall, invasion of water from
outside or leakage of the nonaqueous electrolytic solution can be
prevented. As a result, it is possible to provide a nonaqueous
electrolyte secondary battery having a high output characteristic,
high safety, and high reliability.
[0151] The sealing lid group in the cylindrical nonaqueous
electrolyte secondary battery according to the second and third
embodiments may further include a conductive support plate
explained in FIGS. 7 to 10.
[0152] The current breaking member is not limited to the
configuration explained in the first to third embodiments and may
be any means or structure as far as the current can be cut off as
required due to increase of pressure in the battery. For example, a
folding type lead wire may be realized by a member for conducting
and cutting off the current to be deformed to approach or depart by
compression due to increase of pressure in the battery, and a
member to be broken at the time of elevation of the internal
pressure may be used as a valve membrane.
[0153] Examples of the invention will be specifically described
below by referring to FIGS. 1 and 2.
EXAMPLE 1
<Fabrication of Positive Electrode>
[0154] A slurry was prepared by dissolving 91 wt. % of powder of
lithium cobalt oxide (Li.sub.XCoO.sub.2; X being in a range of
0<x.ltoreq.1), 3 wt. % of acetylene black, 3 wt. % of graphite,
and 3 wt. % of polyvinylidene fluoride (PVdF) as a binder in
N-methyl-2-pyrrolidone (NMP) as a solvent. The slurry was applied
on both sides of a current collector composed of an aluminum foil
of 15 .mu.m in thickness excluding one end at the lateral direction
side, dried and pressed to thereby fabricate a positive electrode
of 3.2 g/cm.sup.3 in density.
<Fabrication of Negative Electrode>
[0155] A carbonaceous matter was prepared as powder of mesophase
pitch carbon fiber heated at 3000.degree. C. {the fiber diameter
was 8 .mu.m, the average fiber length was 20 .mu.m, the aspect
ratio was 0.4, the plane interval (d.sub.002) of (002) plane
determined by powder X-ray diffraction was 0.3360 nm, and the
specific surface area by a BET method was 1 m.sub.2/g}. A slurry
was prepared by dissolving 93 wt. % of the carbonaceous matter and
7 wt. % of polyvinylidene fluoride (PVdF) as a binder in
N-methyl-2-pyrrolidone (NMP) as a solvent. The slurry was applied
on both sides of a current collector composed of a copper foil of
12 .mu.m in thickness, dried and pressed to thereby fabricate a
negative electrode of 1.35 g/cm.sup.3 in filling density.
<Separator>
[0156] A separator was prepared by using a polyethylene porous film
having thickness of 25 .mu.m, heat shrinkage of 20% in 1 hour at
120.degree. C., and porosity of 50%.
<Preparation of Nonaqueous Electrolytic Solution>
[0157] In a mixed solvent of ethylene carbonate (EC) and methyl
ethyl carbonate (MEC) (mixed volume ratio 1:2), lithium phosphate
hexafluoride (LiPF.sub.6) was dissolved to concentration of 1
mole/L, and a nonaqueous electrolytic solution was prepared.
<Fabrication of Electrode Assembly>
[0158] A strip-shaped positive electrode tab was welded to an
exposed region of the current collector at one end (winding start
end) of the positive electrode in the lateral direction. A
strip-shaped negative electrode lead was welded to the current
collector of the negative electrode. Subsequently, the positive
electrode and negative electrode were wound spirally together with
the separator interposed therebetween, and the electrode assembly
was fabricated.
<Assembling of Battery>
[0159] The electrode assembly was put in a cylindrical external can
with a bottom made of iron, the external can serving also as a
negative electrode terminal, and an insulating presser plate having
two semicircular holes and a tiny hole in the center was disposed
on the electrode assembly. The nonaqueous electrolytic solution was
poured into the external can containing the electrode assembly
through the holes of the insulating presser plate. Subsequently, a
current breaking member having an open valve which conducts and
cuts off current and which is broken by elevation of the internal
pressure by gas generation, a PTC element, and a hat-shaped
terminal plate serving as a positive electrode terminal, the
terminal plate having a gas vent, were laminated in this sequence,
and a sealing lid group was prepared. The current breaking member
comprises a stripper to which a conductive thin film is bonded as
shown in FIGS. 1 to 3, and a rupture plate overlaid on the stripper
by way of an insulating sheet. The PTC element is 16 mm in
diameter, and has a notch of 3 mm in diameter, 100 .mu.m in width
and 5 .mu.m in depth formed in the electrode of 25 .mu.m in
thickness at the terminal plate side.
[0160] A folding type lead welded to the positive electrode of the
electrode assembly was connected to the conductive thin film of the
sealing lid group, the sealing lid group was disposed on the upper
end opening of the external can, the members of the current
breaking member, the PTC element, and the peripheral edge of the
terminal plate were crimped and fixed by way of the insulating
gasket, and the electrode assembly and nonaqueous electrolytic
solution were sealed tightly, so that a cylindrical lithium ion
secondary battery of 18 mm in outside diameter, 65 mm in height,
and 2100 mAh in battery capacity as shown in FIGS. 1 and 2 was
assembled. Then, by constant voltage charging at 4.2V for 12 hours
at 0.2 C as an initial charging process, a cylindrical lithium ion
secondary battery was manufactured.
EXAMPLES 2 to 9
[0161] Eight types of cylindrical lithium ion secondary batteries
were manufactured in the same manner as in Example 1, except the
PCT element having the shape, depth, width, and opening area of the
notch shown in Table 1 was used.
COMPARATIVE EXAMPLES 1, 2
[0162] Two types of cylindrical lithium ion secondary batteries
were manufactured in the same manner as in example 1, except that
the PCT element having the shape, depth, width, and opening area of
the notch shown in Table 1 was used.
[0163] The obtained secondary batteries in Examples 1 to 9 and
Comparative examples 1 and 2 were charged at a charging current of
2100 mAh up to 4.2V in 3 hours, and discharged to 3V at 2100 mA,
and the battery capacity (1 C capacity) was measured. Then, after
charging at a charging current of 2100 mAh up to 4.2V in 3 hours,
and discharging to 3V at 8400 mA, the battery capacity was
measured, and the capacity ratio to 1 C capacity (capacity
retaining rate) was calculated.
[0164] Further, five cells of each secondary battery were prepared,
the secondary batteries were evaluated by oven test in a
thermostatic oven, by charging at charging current of 2100 mAh up
to 4.2V in 3 hours, and heating to 200.degree. C. at a heating
speed of 10.degree. C. To evaluate in the oven test, the duration
from the time of the thermostatic oven reaching 200.degree. C.
until ignition of the secondary battery (average time of five cells
of each secondary battery) was measured, and presence or absence of
popping-out of the electrode assembly per five cells of each
secondary battery was observed in order to check the actuation of
the rupture.
[0165] Results are shown in Table 1. TABLE-US-00001 TABLE 1 Notch
of PTC element Oven test Shape Opening Capacity Top: time to
ignition of PTC Posi- Depth Width area retaining Bottom: electrode
element Shape tion (.mu.m) (.mu.m) (mm2) rate (%) assembly popping
out Example 1 Disk Diameter One 5 100 7.1 60 20 min 3 mm, side 5/5p
none circular Example 2 Disk Diameter One 5 100 7.1 63 22 min 3 mm,
side 5/5p none blade Example 3 Disk Regular One 5 100 3.9 61 18 min
triangle, side 5/5p none side 3 mm Example 4 Disk Square, One 5 100
9 59 15 min side 3 mm side 5/5p none Example 5 Disk Right angle One
5 100 7.5 61 17 min line side 5/5p none crossing (3 mm) Example 6
Disk Diameter Two 5 100 7.1 60 20 min 3 mm, sides 5/5p none
circular Example 7 Disk Diameter One 2 100 7.1 58 15 min 3 mm, side
5/5p none circular Example 8 Disk Diameter One 5 30 7.1 65 16 min 3
mm, side 5/5p none circular Example 9 Disk Square, One 5 100 1.44
61 15 min side side 5/5p none 1.2 mm Comparative Ring -- -- -- --
63.6 20 25 min example 1 5/5p none Comparative Disk -- -- -- -- 0
63 5 min example 2 5/5p present
[0166] As clear from Table 1, the secondary batteries of Examples 1
to 9 are excellent in discharge capacity at a current more than
four times that usual in the secondary battery of Comparative
example 1 having the PTC element of ring shape assembled therein.
Further, as compared with the secondary battery of Comparative
example 2 having the disk-shaped PTC element without notch
assembled therein, the secondary batteries of Examples 1 to 9 are
found to be extremely high in safety, and capable of discharging
the gas generated inside quickly to the outside, releasing the
heat, and thereby extending the time until ignition, and also
preventing the electrode assembly from popping out.
EXAMPLE 10
[0167] A cylindrical lithium ion secondary battery having the same
structure as that in Example 1 was manufactured except that the PTC
element was 16 mm in diameter, having formed therein a circular
recess of 8 mm in diameter and 0.1 mm in depth from the terminal
plate side.
[0168] The obtained secondary battery of Example 10 was evaluated
in capacity retaining rate, time to ignition in the oven test
(average of five cells of the secondary battery), and presence or
absence of popping-out of the electrode assembly per five cells of
the secondary battery, in the same manner as in Examples 1 to 9. As
a result, the capacity retaining rate was 62%, the time to ignition
in the oven test was 20 minutes, and presence or absence of
popping-out of the electrode assembly was none in 5/5 p.
* * * * *