JP3204040B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery having high energy density and improved safety.

[0002]

2. Description of the Related Art Conventionally, in a non-aqueous electrolyte secondary battery, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese composite oxide (LiMn ₂ O ₄ ), and molybdenum disulfide have been used as positive electrode active materials. (Mo
S ₂ ), titanium disulfide (TiS ₂ ), manganese dioxide (M
Transition metal sulfides or oxides such as nO ₂ ) and vanadium pentoxide (V ₂ O ₅ ) are used. On the other hand, in recent years, a non-metallic material capable of inserting and extracting lithium ions, together with metallic materials such as metallic lithium, lithium-aluminum alloy and lithium-wood alloy, has been used for the negative electrode active material.
For example, carbon materials such as natural graphite, artificial graphite, and amorphous carbon having a lower crystallinity than these are used. Further, as a novel nonmetallic material capable of inserting and extracting lithium ions, metal compounds such as iron oxide (FeO ₂ ) and tungsten oxide (WO ₂ ), or various inorganic layered compounds (LiN ₃ , BC ₂ N) and high molecular compounds (polythiophene, polyacetylene, etc.) have been proposed.

In addition, propylene carbonate (PC) in which lithium salt is dissolved, ethylene carbonate (EC), gamma-butyrolactone (GBL), diethyl carbonate (DEC), 2-methyltetrahydrofuran (MTHF) and the like are often used as the electrolyte. ing.

In recent years, among non-aqueous electrolyte secondary batteries using these positive / negative electrodes and electrolytes, the average discharge voltage is about 3.6V.
A battery system having a high voltage and a high energy density has attracted attention as a power supply for various electronic devices. LiCoO ₂ , LiNiO ₂ and LiM
A lithium composite oxide such as n ₂ O ₄ is used, and a graphite or amorphous carbon material is used as a negative electrode active material.

[0005] These battery-type cylindrical batteries, prismatic batteries, and the like employ an electrode group configuration in which a separator is interposed between positive and negative electrode plates and wound. Generally, a metal foil is used as a substrate for the electrode plates of these batteries. For example, a copper foil is used for a negative electrode substrate and an aluminum foil is used for a positive electrode substrate. A mixture layer composed of an active material, a conductive material, and a binder is applied and fixed on these substrates to form a main body of the electrode plate.
In addition, a porous substrate such as a metal expanded metal or a mesh may be used. A metal current collector is connected to the main body of these electrode plates to form an electrode plate, and the other end of the current collector is connected to a battery container to achieve conduction to a battery terminal.

[0006]

When the above-mentioned metal substrate is used, the specific gravity of the substrate is large, which causes a reduction in the energy density per unit weight of the battery. Further, since the volume occupied by the substrate is large, the amount of active material per unit volume of the electrode plate is significantly reduced. Generally, for the negative electrode, the substrate occupies about 5% of the volume, and for the positive electrode, about 16%.
Occupying a large volume, which is a major obstacle to improving the volumetric energy density.

[0007] In general, a non-aqueous electrolyte secondary battery is designed to ensure sufficient safety during handling under normal use conditions. However, as a method of evaluating a very high level of safety, a severe test in which a short circuit inside a battery is intentionally caused by a crash test or nail penetration may be performed. In the crash test, a metal round bar of a predetermined diameter is crushed to a predetermined size perpendicular to the winding direction of the electrode plate group, or a metal flat plate is crushed to a predetermined size at a predetermined pressure, deforming the electrode plate in the battery Alternatively, the positive and negative electrodes are brought into contact with each other by breaking to cause an internal short circuit. In the nail piercing test, there is a method of piercing a battery with a nail having a predetermined diameter, penetrating the battery, and causing an internal short circuit. When such a test is performed, a conventional non-aqueous electrolyte secondary battery mainly using a metal foil as a substrate may generate significant heat due to an internal short circuit and may ignite. As a result of analyzing these heat generation and ignition phenomena, almost no heat is generated by a short circuit between the positive / negative electrode mixture or by contact between the mixture and the substrate, and significant heat is generated by a short circuit between the positive and negative electrode metal substrates. I understood that. Therefore, in order to further enhance the safety of the battery,
In any case, it is necessary to adopt a configuration in which there is no concern that the positive and negative metal materials contact each other.

In order to solve the above-mentioned problems in the prior art, the present invention increases the amount of active material per unit weight and volume of the electrode plate to increase the energy of the battery.
It is an object of the present invention to provide a non-aqueous electrolyte secondary battery having a high degree of safety with little heat generation even if an intentional internal short circuit is generated by an extremely severe safety test.

[0009]

According to the present invention, in order to solve the above-mentioned problems in a non-aqueous electrolyte secondary battery having a wound type electrode plate group structure, at least one of positive and negative electrode plates of the battery is provided. By not using a metal substrate for the main body of the electrode plate but only using a nonmetallic material such as a nonmetallic active material, a binder, and a conductive material, the amount of the active material in the electrode plate can be reduced. Increases the energy density of the battery by increasing it, and even if an internal short circuit occurs, there is no concern that the metallic materials with high conductivity between the positive and negative electrodes will come into contact with each other, and improves the safety of the battery by reducing heat generation It was made.

In order to form an electrode plate whose main body is made of only a non-metallic material, it is necessary to easily handle the electrode plate in the forming process and to obtain the mechanical strength required for winding the electrode plate group. It is necessary to use a binder which can secure flexibility and is chemically stable in the battery. For that purpose, a fluororesin, especially a tetrafluoroethylene resin (PTF) is used as the binder.
E) It is preferable to use at least one fluororesin such as a tetrafluoroethylene-6-fluoropropylene copolymer resin and polyvinylidene fluoride (PVDF).

As means for electrically connecting the battery terminal with the electrode plate whose main body is made of only a non-metallic material, a metal current collecting piece is connected to the electrode plate main body, A method of connecting the other end of the electric piece to a battery member such as a battery container which is electrically connected to the battery terminal can be adopted. In that case,
An effective means is to use a rivet-shaped current collecting piece and connect it to the electrode plate body by caulking. The rivet-shaped current collecting piece has a hollow needle-like projection on the current collecting piece. After the electrode plate body is penetrated by the projection, the needle tip is torn apart and crimped together with the electrode plate body. It is also possible to achieve conduction between the electrode plate body and the metal current collecting piece by bringing them into contact with each other. can do. Further, as another means for electrically connecting between battery terminals using an electrode plate whose main body portion is formed only of a non-metallic material, the bottom end surface of the negative electrode plate of the wound electrode plate group is a battery container on the negative electrode side. And a configuration in which the outer surface of the negative electrode plate at the outermost periphery of the wound electrode plate group is brought into contact with the inner surface of the battery container on the negative electrode side.

[0012]

In the present invention, since a metal substrate is not used, a large amount of active material can be filled by effectively utilizing the weight and volume of the electrode plate, so that the weight energy density and volume energy density are reduced by about 10%. improves. Also in terms of safety,
Since a short circuit between the metal substrates of the negative electrode does not occur, heat generation is suppressed even if an internal short circuit of the battery is intentionally generated by an extremely severe method, so that a non-aqueous electrolyte secondary battery with high safety and high energy density is provided. Is obtained.

[0013]

【Example】

Embodiment 1 FIG. 1 is a view showing one embodiment of a positive electrode plate used for a non-aqueous electrolyte secondary battery of the present invention, wherein FIG.
(B) is a sectional view of the AA 'part. The composition of the positive electrode mixture is a mixture of 100 parts by weight of LiCoO ₂ and 3 parts by weight of acetylene black and 7 parts by weight of PTFE. Is added and stirred, and 4
After standing at 5 ° C. for 12 hours, a sheet was formed using a rolling roller, and the thickness was adjusted to 150 to 180 μm. Reference numeral 1 denotes a positive electrode plate body portion obtained by cutting the sheet into a predetermined size, and 2 denotes a rivet-shaped positive electrode current collector, which is attached to the positive electrode plate body portion 1 by a caulking method. The rivet-shaped positive electrode current collector piece 2 is formed by pressing a flat stainless steel plate with a metal nail having a diameter smaller than 1/3 of the width thereof to penetrate the same, and forming a perforation and a burr around the periphery thereof. .
After the hollow protrusion formed by the burr is penetrated through the positive electrode plate main body portion 1, the burr portion is further torn open, pressed until it can be fixed to the positive electrode plate main body portion 1, and caulked to form the positive electrode plate. Configured.

Embodiment 2 FIG. 2 is a view showing one embodiment of a negative electrode plate used in the non-aqueous electrolyte secondary battery of the present invention.
(A) is a front view, and (b) is a cross-sectional view of a BB 'portion. The composition of the negative electrode mixture is based on 100 parts by weight of the spherical graphite.
PTFE was mixed with 7 parts by weight. To the mixture obtained by mixing the above materials, 20 parts by weight of methyl alcohol was added, and the mixture was stirred and allowed to stand at 45 ° C. for 12 hours. The thickness was adjusted to be. Reference numeral 3 denotes a negative electrode plate body portion obtained by cutting the sheet into a predetermined size, and reference numeral 4 denotes a rivet-shaped negative electrode current collector made of nickel produced in the same manner as in the first embodiment. A negative electrode plate was formed by attaching to the negative electrode plate main body 3 by a method.

Embodiment 3 FIG. 3 is a view showing one embodiment of a positive electrode plate used for a non-aqueous electrolyte secondary battery of the present invention.
(A) is a front view, (b) is a cross-sectional view of a CC ′ portion. Reference numeral 1 denotes a positive electrode plate main body portion prepared in the same manner as in Example 1, and 2 denotes a flat plate-shaped positive electrode current collector made of stainless steel.
The positive electrode current collector 2 was fixed to the surface of the positive electrode plate main body 1 with an adhesive tape 5 made of a fluororesin to form a positive electrode plate. The contact state between the positive electrode plate main body portion 1 and the positive electrode current collecting piece 2 is further strengthened by being pressed by the group pressure of the electrode plate group at the time of constituting the battery, and the electrical conduction between them is maintained.

Example 4 FIG. 4 is a view showing one example of a negative electrode plate used in the nonaqueous electrolyte secondary battery of the present invention.
(A) is a front view, (b) is sectional drawing of DD 'part. Reference numeral 3 denotes a negative electrode plate main body portion prepared in the same manner as in Example 2, and reference numeral 4 denotes a nickel plate-shaped negative electrode current collector piece.
The negative electrode current collecting piece 4 was fixed to the surface of the negative electrode plate main body portion 3 with an adhesive tape 5 made of a fluororesin to form a negative electrode plate. The contact state between the negative electrode plate main body portion 3 and the negative electrode current collecting piece 4 is further strengthened by being pressed by the group pressure of the electrode plate group at the time of constituting the battery, and the electrical conduction between them is maintained.

Embodiment 5 FIG. 5 is a longitudinal sectional view showing an embodiment of the nonaqueous electrolyte secondary battery of the present invention. 1 is Example 1
The positive electrode plate main body portion 2 prepared in the same manner as described above is a rivet-shaped positive electrode current collector piece similar to that of the first embodiment attached to the positive electrode plate main body portion 1, and one end thereof is spot-welded to the inner surface of the sealing plate 6. It is electrically connected to the positive terminal 7. 8 is a gasket. Reference numeral 9 denotes a polyethylene separator, which is impregnated with an electrolytic solution obtained by dissolving an electrolyte in an organic solvent. Reference numeral 3 denotes a negative electrode plate main body portion prepared in the same manner as in Example 2, and a lower end surface thereof has a battery container 1
0 is installed so as to be in contact with the inner bottom surface and to be electrically conductive.

Embodiment 6 FIG. 6 is a cross-sectional view showing an embodiment of the nonaqueous electrolyte secondary battery of the present invention. 1 is Example 1
Example 5 is a positive electrode plate main body portion prepared in the same manner as in Example 5.
And is electrically connected to the positive electrode terminal. 2
Is a negative electrode plate main body portion produced in the same manner as in Example 2. The outer surface of the outermost peripheral portion of the negative electrode plate main body portion of the electrode plate group formed by winding is a battery container 10 without using a current collecting piece.
It is installed so as to be in contact with the inner surface of the device and have electrical continuity. Reference numeral 9 denotes a polyethylene separator, which is impregnated with an electrolytic solution obtained by dissolving an electrolyte in an organic solvent.

Comparative Example FIG. 7 is a diagram showing a positive electrode plate used for a non-aqueous electrolyte secondary battery of a comparative example, where (a) is a front view,
(B) is a sectional view of the EE 'portion. Reference numeral 11 denotes a positive electrode plate main body produced by applying a positive electrode mixture 13 to a positive electrode substrate 12 made of aluminum foil. The positive electrode plate body portion 11 is made of LiC
To 100 parts by weight of oO ₂ , 3 parts by weight of acetylene black and 100 parts by weight of a 1% solution of carboxymethylcellulose (CMC) were added to 7 parts by weight of PTFE, and mixed and stirred to prepare a paste that was easy to apply, and was then subjected to a doctor blade method. It was coated on an aluminum foil (thickness: 30 μm) of the positive electrode substrate 12, dried, and then rolled using a rolling roller so that the sheet thickness became 180 μm including the thickness of the positive electrode substrate. A positive electrode current collector 14 made of aluminum is welded to the exposed portion of the positive electrode substrate 12.

FIGS. 8A and 8B are diagrams showing a negative electrode plate used for a non-aqueous electrolyte secondary battery of a comparative example, wherein FIG. 8A is a front view, and FIG.
It is sectional drawing of the -F 'part. 15 is a negative electrode substrate 1 made of copper foil
6 is a negative electrode plate main body portion prepared by applying a negative electrode mixture 17 to 6. For the positive electrode plate body portion 13, 100 parts by weight of spheroidal graphite, 7 parts by weight of PTFE, and 100 parts by weight of a 1% solution of carboxymethylcellulose (CMC) were further added and mixed and stirred to prepare a paste that was easy to apply, and the doctor blade method was used. Then, after coating and drying on a copper foil (thickness: 14 μm) of the substrate, the sheet thickness was adjusted to 200 μm including the thickness of the substrate using a rolling roller. A negative electrode current collector piece 18 made of nickel is welded to an exposed portion of the substrate of the negative electrode plate main body portion 15.

FIG. 9 shows a comparative example having a diameter of 17 mm and a height of 50 m.
m is a vertical sectional view of the nonaqueous electrolyte secondary battery of FIG. Reference numeral 11 denotes a positive electrode plate main body portion, and 14 denotes a positive electrode current collector piece attached to the positive electrode plate main body portion 11, one end of which is connected to the inner surface of the sealing plate 19 by spot welding and is electrically connected to the positive electrode terminal 20. . 21 is a gasket. Reference numeral 22 denotes a polyethylene separator, which is impregnated with an electrolytic solution obtained by dissolving an electrolyte in an organic solvent. Reference numeral 15 denotes a negative electrode plate main body portion, and reference numeral 18 denotes a negative electrode current collector piece attached to the negative electrode plate main body portion 15, one end of which is spot-welded to the inner bottom surface of the battery container 23 and is installed so as to be electrically conductive. ing.

In order to compare the nonaqueous electrolyte secondary battery of the present invention with the nonaqueous electrolyte secondary battery of the comparative example, as shown in Table 1, the positive and negative electrode plates of Examples 1 to 4 were used. Each of the batteries 1 to 6, the batteries 7 and 8 having the configurations of Examples 5 and 6, and the battery 9 of the comparative example using the combination of the positive and negative electrodes of the comparative example and the batteries of the comparative example using the same method as the battery of the comparative example. The properties were evaluated.

[0023]

[Table 1]

A solute (LiPF) is contained in the electrolyte of these batteries.
₆ ) was dissolved at a concentration of 1 mol / liter in a mixed solvent of EC and DEC in a volume ratio of 1: 3, and a polyethylene porous film having a porosity of 50% and a film thickness of 25 microns was used. The thicknesses and lengths of the positive and negative electrode plates were adjusted so that the configurations of the batteries using the electrode plates of Examples 1 to 4 had the same positive electrode discharge utilization ratio and negative electrode discharge utilization ratio as those of the battery of the comparative example. The dimensions are shown below.

The dimensions of the main body of the positive electrode plate in Examples 1 and 3: width 3
7 mm, length 380 mm, thickness 0.015 mm Dimensions of the negative electrode plate body of Examples 2 and 4: width 39 mm, length 415.0 mm, thickness 0.0176 mm Dimensions of the positive electrode plate body of the comparative example: width 37 mm, length 350
mm, thickness 0.018 mm Dimensions of negative electrode plate main body of comparative example: width 39 mm, length 400
mm and a thickness of 0.020 mm (Table 2). The energy density calculated from the discharge capacity at the second cycle obtained in the charge / discharge test of the batteries 1 to 8 of the example is expressed as a ratio to the energy density of the battery 9 of the comparative example. Indicated. Batteries 1 to 9 perform a constant voltage charge of 4.2 V for 2 hours,
The discharge was performed at 3.0 CmA to 3.0 V.

[0026]

[Table 2]

As can be seen from Table 2, the battery 1 of the present invention
8 show that the volume energy density was improved by about 10% as compared with the battery using the conventional positive / negative electrode plate shown in the comparative example.

The number of ignitions of the batteries when each of the batteries 1 to 8 of the example and the battery 9 of the comparative example were crushed with a round bar having an outer diameter of 10 mm until the diameter of the battery was reduced to half (Table 2). It was shown to.
Each battery was subjected to a 4.2 V constant voltage charge for 2 hours, and then subjected to the crash test.

The number of ignitions of the batteries when 10 batteries each of the batteries 1 to 8 of the example and the battery 9 of the comparative example 9 were pierced through a central portion of the battery with a nail having an outer diameter of 2.5 mm and penetrated ( The results are shown in Table 2). Each of the batteries was subjected to this nail penetration test after 4.2 hours of constant voltage charging.

As can be seen from Table 2, the battery 1 of the present invention
No. 8 shows no fire even when the internal short circuit was forcibly performed by a crash test or nail penetration test, and the safety was improved over the battery 9 using the conventional positive / negative plate with the metal substrate shown in the comparative example. You can see that it is doing.

As a method of connecting the electrode plate main body and the current collecting pieces in the present invention, instead of caulking the rivet-shaped current collecting pieces shown in the embodiment, a flat-shaped current collecting piece having a small hole is used in advance. Insert the needle part of a thumbtack-shaped metal piece with a hollow needle into the electric piece, and after penetrating this needle part into the electrode plate main body, tear open the hollow part of the needle part and fix it to the positive electrode plate main body The same effect can be obtained even if the current collecting pieces are connected by pressing and caulking.

In the examples, the binder is PTF.
Although E was used, the effects of the present invention can be similarly obtained by using a fluororesin-based material such as a tetrafluoroethylene-6-fluoropropylene copolymer resin or polyvinylidene fluoride (PVDF).

[0033]

As is clear from the above test results, the present invention provides a non-aqueous electrolytic solution having high energy density and high reliability even when a forced internal short-circuit test is performed. A liquid secondary battery was obtained.

[Brief description of the drawings]

FIG. 1A is a front view of a positive electrode plate of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. FIG. 1B is a cross-sectional view taken along the line AA ′.

FIG. 2 (a) is a front view of a negative electrode plate of a non-aqueous electrolyte secondary battery in one embodiment of the present invention.

3A is a front view of a positive electrode plate of a non-aqueous electrolyte secondary battery according to one embodiment of the present invention. FIG. 3B is a cross-sectional view taken along the line CC ′.

FIG. 4 (a) is a front view of a negative electrode plate of a non-aqueous electrolyte secondary battery according to one embodiment of the present invention.

FIG. 5 is a longitudinal sectional view of a non-aqueous electrolyte secondary battery according to one embodiment of the present invention;

FIG. 6 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to one embodiment of the present invention;

FIG. 7A is a front view of a positive electrode plate of a conventional non-aqueous electrolyte secondary battery. FIG. 7B is a cross-sectional view taken along the line EE ′.

FIG. 8A is a front view of a negative electrode plate of a conventional non-aqueous electrolyte secondary battery. FIG.

FIG. 9 is a longitudinal sectional view of a conventional non-aqueous electrolyte secondary battery.

[Description of Signs] 1 Positive electrode plate main body 2 Positive electrode current collector 3 Negative electrode plate main body 4 Negative current collector 5 Adhesive tape 6 Sealing plate 7 Positive electrode terminal 8 Gasket 9 Separator 10 Battery container 11 Positive electrode plate main body 12 Positive electrode substrate 13 Positive electrode mixture 14 Positive electrode current collector 15 Negative electrode plate body 16 Negative substrate 17 Negative electrode mixture 18 Negative current collector 19 Sealing plate 20 Positive electrode terminal 21 Gasket 22 Separator 23 Battery container

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoko Nakagawa 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-7-65862 (JP, A) JP-A-7-65861 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/02-4 / 04 H01M 10/40 H01M 2/26

Claims (9)

(57) [Claims] 1. A non-aqueous electrolysis system comprising: an electrode group in which a rechargeable positive electrode and a negative electrode mainly composed of a nonmetallic negative electrode active material capable of inserting and extracting lithium are wound via a separator. in the nonaqueous electrolyte secondary battery using the liquid nonaqueous electrolyte secondary battery body portion of the positive electrode plate is characterized in that it is composed only of non-metallic material. 2. The method according to claim 1, wherein the main body is made of only a non-metallic material.
Some electrode plates use fluororesin as a binder.
Non-aqueous electrolyte secondary battery according to claim 1, wherein Rukoto. 3. A rechargeable positive electrode and lithium storage / release.
Negative electrode mainly composed of negative electrode active material made of carbon
And an electrode group wound through a separator.
In the non-aqueous electrolyte secondary battery using the solution, the body of the negative electrode
The part does not include a sheet-like current collector and is made of only non-metallic material.
That is made and uses a fluororesin as a binder
Non-aqueous electrolyte secondary battery characterized by the above-mentioned . 4. The fluororesin used as the binder is at least one of ethylene tetrafluoride resin (PTFE), tetrafluoroethylene hexafluoropropylene copolymer resin, and polyvinylidene fluoride (PVDF). The non-aqueous electrolyte secondary battery according to claim 2 or 3, wherein: 5. The non-aqueous electrolyte according to claim 1-4 in which the body portion, characterized in that the metal-made current collecting plates to the plate that consists of only a non-metallic material is connected Rechargeable battery. 6. The non-aqueous electrolyte secondary battery according to claim 5, wherein the metal current collector is attached to the main body of the electrode plate in a rivet manner. 7. The non-aqueous electrolyte secondary battery according to claim 5, wherein a metal current collector is brought into contact with the main body of the electrode plate. 8. A negative electrode plate whose main body is made of only a non-metallic material, wherein the bottom end surface of the negative electrode plate of the rolled electrode plate group comes in contact with the inner bottom surface of the battery container to be electrically conductive. The non-aqueous electrolyte secondary battery according to claim 3, wherein 9. A negative electrode plate whose main body is made of only a non-metallic material, wherein the outer surface of the negative electrode plate at the outermost peripheral portion of the wound electrode plate group comes into contact with the inner surface of the battery container and is electrically connected. 4. The non-aqueous electrolyte secondary battery according to claim 3, wherein the battery is conductive.