JP2001155776A - Cylindrical lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylindrical lithium ion battery cell of a large size with good safety and long lifetime. SOLUTION: Positive and negative electrode plates are prepared such that the amount of active materials being applied to the plates is different in one side of the plate relative to the other side thereof at a degree of 79-91 wt.%. A group of the plates are wound in a state that the amount of the active materials in the opposing sides has a proportional relation, and the wound group of electrode plates is received in a cylindrical vessel to provide a cylindrical lithium ion battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical lithium ion battery.

[0002]

2. Description of the Related Art Lithium ion batteries are mainly used for portable devices such as VTR cameras, notebook computers, and mobile phones, taking advantage of the high energy density. In recent years, research and development of large-sized lithium-ion batteries for electric vehicles and power storage have been actively conducted. In particular, in the automobile industry, development of electric vehicles using a motor as a power source and hybrid electric vehicles using both an internal combustion engine and a motor as a power source has been promoted in order to respond to environmental issues.
Some of them are already in practical use.

[0003] However, large-sized lithium-ion batteries used for these devices have high capacity and high output,
Security is strongly required. In addition, these lithium-ion batteries have a current cut-off mechanism (a kind of disconnection switch) that operates in response to a rise in the internal pressure of the battery, which is generally adopted in small lithium-ion batteries, inside the battery container. It is technically difficult to provide.

Therefore, when these large lithium ion batteries are used in an electric vehicle, 1) at the time of overcharging when the charge control system breaks down, 2) at the time of a crash due to an accidental collision, and 3) at the time of foreign matter At the time of piercing, or 4)
Ensuring safety in the event of an external short circuit has become a very important issue.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a large cylindrical lithium-ion battery excellent in safety.

[0006]

Therefore, in order to solve the above-mentioned problems, a first invention is to coat a positive electrode mixture layer containing a positive electrode active material, a conductive agent and a binder on both surfaces of a current collector. A positive electrode plate and a negative electrode plate obtained by applying a negative electrode mixture layer containing a negative electrode active material and a binder to both surfaces of a current collector are wound through a separator to form a winding group, and the winding group is formed. In a cylindrical lithium-ion battery containing a cylindrical battery container, the wound group uses a positive electrode plate and a negative electrode plate having different active material amounts applied on one surface and the other surface, and The second invention is characterized in that the positive electrode plate and the negative electrode plate on opposite surfaces are wound so that the active material amounts thereof are proportional to each other. 79 to 91% by mass of the coating amount of the positive electrode active material on the surface I have.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Preparation of positive electrode plate Lithium manganate (LiMn ₂ O ₄ ) powder, which is an active material for the positive electrode, and flaky graphite as a conductive agent (average particle size: 20 μm)
And polyvinylidene fluoride as a binder in a mass ratio
87: 8.7: 4.3, N-methyl-2-pyrrolidone is added as a dispersion solvent to this mixture, and then kneaded to prepare a slurry. This slurry was applied on both sides of a 20 μm-thick aluminum foil (positive electrode current collector) to form a positive electrode mixture layer. In addition, at the time of slurry application, as described later, one side of the aluminum foil and the positive electrode plate having the same amount of the positive electrode active material applied to the other surface were intentionally different. A positive electrode plate was prepared. The bulk density of the positive electrode mixture layer is 2.65 to 2.8 g / cm ³
I made it.

When the slurry was applied, an uncoated portion having a width of 50 mm was left on one of the side edges in the longitudinal direction of the aluminum foil. Thereafter, drying, pressing, and cutting were performed to obtain a positive electrode plate having a width of 300 mm and a predetermined length. The width formed on the positive electrode plate as described above
A part of the 50 mm uncoated portion was removed to form a rectangular part, which was used as a lead piece 9 for current collection. The width of the lead pieces 9 was set to about 10 mm, and the interval between the adjacent lead pieces 9 was set to about 20 mm.

[0009] 2. Preparation of negative electrode plate Carbotron P which is amorphous carbon as the negative electrode active material
8 parts by weight of polyvinylidene fluoride as a binder were added to 92 parts by weight (trade name: manufactured by Kureha Chemical Industry Co., Ltd.), and N-methyl-2-pyrrolidone as a dispersion solvent was added thereto.
Make a slurry by kneading. This slurry has a thickness of 10μ
m of rolled copper foil (negative electrode current collector). In addition,
When applying the slurry, a negative electrode plate was prepared in which the amount of the negative electrode active material applied to one surface of the copper foil and the other surface corresponded to the amount of the positive electrode active material applied as described below. did.

When the slurry was applied, an uncoated portion having a width of 50 mm was left on one of the side edges in the longitudinal direction of the copper foil. Thereafter, drying, pressing and cutting were performed to obtain a negative electrode plate having a width of 305 mm and a predetermined length. The bulk density of the negative electrode mixture layer was 0.9 to 1.0 g / cm ³ . A cutout was made in the above-mentioned uncoated portion having a width of 50 mm formed on the negative electrode plate, a part thereof was removed, and a rectangular portion was formed to be used as a lead piece 9 for current collection. The width of the lead pieces 9 was set to about 10 mm, and the interval between the adjacent lead pieces 9 was set to about 20 mm.

The charged amounts of the active materials for the positive electrode plate and the negative electrode plate were determined as follows. That is, the charged amount per unit area facing each other via the separator is a capacity capable of charging the positive electrode plate to a final charge potential of 4.5 V (vs. Li / Li ⁺ ),
The capacity of the negative electrode plate capable of charging up to a final voltage of 0 V (vs. Li / Li ⁺ ) was made the same. Note that lithium manganate as the positive electrode active material had a chargeable capacity per unit weight of 105 mAh / g, and the chargeable capacity of the negative electrode active material Carbotron P was 450 mAh / g. .

[0012] It is known that when the coated portion of the positive electrode plate protrudes from the coated portion of the opposite negative electrode plate, the discharge characteristics and safety of the lithium ion battery deteriorate. Therefore,
In a state where the above-described positive electrode plate and negative electrode plate are wound through a separator to form a winding group 6, while starting to be wound first from the negative electrode plate, the outermost periphery of the negative electrode plate is longer than the positive electrode plate. I made it. Therefore, the length of the negative electrode plate was made longer by about 18 cm than the length of the positive electrode plate. Also in the width direction of the positive electrode plate and the negative electrode plate, the width of the coated portion of the negative electrode active material is set so that the coated portion of the positive electrode active material and the coated portion of the negative electrode active material do not shift in position. , About 5 mm wider than the width of the coated part of the positive electrode active material
I made it bigger.

3. Production of Battery The positive electrode plate and the negative electrode plate described above are wound with a polyethylene separator having a thickness of 40 μm sandwiched therebetween to form a winding group 6. The lead piece 9 of the wound positive electrode plate and the lead piece 9 of the negative electrode plate
Each was wound so as to be located on the opposite side of the winding group 6.
By cutting the positive electrode plate, the negative electrode plate or the separator at the end of the winding, the diameter of the winding group 6 was set to 65 ± 0.1 mm. That is, their lengths were adjusted according to the thicknesses of the positive electrode plate and the negative electrode plate.

As shown in FIG. 1, the lead pieces 9 led out from the positive electrode plate are bent and deformed in a state of being collected and bundled, and then brought into contact with a flange portion 7 formed on the positive electrode external terminal 1a. Then, the lead piece 9 and the flange 7 are welded using an ultrasonic welding device to be electrically connected. In the same manner, for the negative electrode plate, the lead piece 9 and the flange portion 7 formed on the negative electrode external terminal 1b were electrically connected by ultrasonic welding.

Thereafter, the entire outer peripheral surface of the flange portion 7 of the positive electrode external terminal 1a, the flange portion 7 of the negative electrode external terminal 1b, and the winding group 6 is covered with an insulating coating 8.
Cover with. As the insulating coating 8, an adhesive tape made of polyimide having an adhesive made of hexamethacrylate coated on one surface was used. After adjusting the number of turns of the adhesive tape so that the outer peripheral portion of the winding group 6 is covered with the insulating coating 8 and slightly smaller than the inner diameter of the stainless steel battery container 5, the winding group 6 is removed from the battery container. Insert into 5. That is, a slight variation in the diameter of the winding group 6 due to a change in the composition of the positive electrode mixture layer described later was adjusted by the number of turns of the pressure-sensitive adhesive tape. The battery case 5 has an outer shape of 67 mm and an inner diameter of 6 mm.
It has a cylindrical shape of 6 mm.

Next, a second ceramic washer 3b having a thickness of 2 mm, an inner diameter of 16 mm, and an outer diameter of 25 mm at a portion in contact with the outer surface of the battery cover 4 is connected to the positive external terminal 1a and the negative external terminal 1a.
Fit each end of b. Then, the first ceramic washer 3a is placed on the battery cover 4, and the positive electrode external terminal 1a,
Each of the negative external terminals 1b is connected to a first ceramic washer.
Pass through 3a.

Thereafter, the peripheral end surface of the battery lid 4 having a disc shape is fitted into the opening of the battery container 5 and the entire area of the contact portion between the battery lid 4 and the battery container 5 is laser-welded. At this time, the positive external terminal
1a, the negative electrode external terminal 1b penetrates a hole in the center of the battery cover 4 and protrudes to the outside. And the thickness is 2mm, inner diameter is 1
6mm, 28mm outside diameter plate-shaped first ceramic washer 3
a, a metal washer 11 smoother than the bottom surface of the nut 2 is fitted into the positive external terminal 1a and the negative external terminal 1b in this order. The battery lid 4 is provided with a cleavage valve 10 that is cleaved in response to an increase in the internal pressure of the battery.
kg / cm ² . As described above, the present battery is not provided with a current cutoff mechanism that operates in response to a rise in pressure inside the battery.

A metal nut 2 is screwed to the positive external terminal 1a and the negative external terminal 1b, respectively, and the battery cover 4 is connected via the second ceramic washer 3b and the first ceramic washer 3a.
Is fixed between the collar 7 and the nut 2. The tightening torque value at this time is 6.86 N · m. By compressing the O-ring 12 made of rubber (made of EPDM) interposed between the back surface of the battery lid 4 and the flange portion 7 at the time of tightening, the power generating elements and the like inside the battery container are shut off from the outside air.

After a predetermined amount of electrolyte is injected into the battery container 5 from the liquid inlet 13 provided in the battery cover 4, the liquid inlet 13 is sealed to complete a cylindrical lithium ion battery. The electrolyte was prepared by mixing ethylene carbonate, dimethyl carbonate and diethyl carbonate at a volume ratio of 1: 1: 1, and then adding 1 mol of lithium hexafluorophosphate (LiPF ₆ ).
/ l dissolved organic electrolyte was used.

4. Charge / discharge cycle test The prepared cylindrical lithium ion battery is subjected to an initial charge / discharge test at 25 ° C under the following conditions to measure a discharge capacity. Charging conditions: 4.2V (constant voltage charging), 80A (limit current), 3.5
h, 25 ° C Discharge conditions: 20A (constant current discharge), final voltage 2.5V, 25 ° C Some of the cylindrical lithium-ion batteries that were initially subjected to the discharge test were subjected to a charge / discharge cycle test at 25 ° C under the above conditions. And the discharge capacity at the 200th cycle was measured.

5. Overcharge test Some cylindrical lithium-ion batteries that were subjected to the initial discharge test were continuously overcharged at a constant current of 25
Gas emission from zero occurs. Evaluation was made based on the state of gas release, the state of deformation of the container, and the state of maintenance of the battery weight accompanying the gas release.

[0022]

Embodiments of the present invention will be described below.

(Examples 1 and 2) A slurry having the composition described above was used.
Used, the positive electrode active material coating amount on one side of the current collector is 241 g /
m ^Two, The positive electrode active material coating amount on the other surface is 220 g / m^Two(Sunawa
(Approximately 91% of the coating amount on one side)
Create a positive electrode plate. On the other hand, the coating amount of the positive electrode active material is 241 g / m^Two
Negative electrode active material coating amount facing the surface of 57.3g / m^Two, Positive electrode active material
220g / m^TwoThe amount of negative electrode active material applied to the surface of
2.6g / m^TwoA negative electrode plate was prepared. That is, the negative electrode active material
Coating amount is proportional to the positive electrode active material coating amount on the opposite surface
I did it. A cylindrical shape using these positive and negative plates
A lithium-ion battery was fabricated and tested using the techniques described above.
Was.

(Embodiments 3 and 4)
Used, the positive electrode active material coating amount on one side of the current collector is 241 g /
m ^Two, The positive electrode active material coating amount on the other surface is 209 g / m^Two(Sunawa
(Approximately 87% of the coating amount on one side)
Create a positive electrode plate. On the other hand, the coating amount of the positive electrode active material is 241 g / m^Two
Negative electrode active material coating amount facing the surface of 57.3g / m^Two, Positive electrode active material
209 g / m^TwoNegative electrode active material coating amount facing the surface of
9.8g / m^TwoA negative electrode plate was prepared. That is, the negative electrode active material
Coating amount is proportional to the positive electrode active material coating amount on the opposite surface
I did it. A cylindrical shape using these positive and negative plates
A lithium-ion battery was fabricated and tested using the techniques described above.
Was.

(Examples 5 and 6) A slurry having the above-described composition was used.
Used, the positive electrode active material coating amount on one side of the current collector is 241 g /
m ^Two, The positive electrode active material coating amount on the other surface is 190 g / m^Two(Sunawa
(Approximately 79% of the coating amount on one side)
Create a positive electrode plate. On the other hand, the coating amount of the positive electrode active material is 241 g / m^Two
Negative electrode active material coating amount facing the surface of 57.3g / m^Two, Positive electrode active material
190g / m^TwoNegative electrode active material coating amount facing the surface of
5.4g / m^TwoA negative electrode plate was prepared. That is, the negative electrode active material
Coating amount is proportional to the coating amount of the positive electrode active material on the opposite surface.
It was to so. Cylinder using these positive and negative plates
A lithium ion battery was fabricated and tested using the techniques described above.
Was.

(Comparative Example 1) Using a slurry having the above-mentioned composition, a positive electrode plate in which the coating amount of the positive electrode active material was adjusted to 241 g / m ² on both surfaces of the current collector, and a negative electrode active material on both surfaces of the current collector A negative electrode plate whose coating amount was adjusted to 57.3 g / m ² was prepared, and a cylindrical lithium ion battery using the negative electrode plate was prepared and tested.

(Comparative Example 2) Using a slurry having the above composition, a positive electrode plate having a positive electrode active material coating amount adjusted to 220 g / m ² on both surfaces of the current collector, and a negative electrode active material on both surfaces of the current collector A negative electrode plate whose coating amount was adjusted to 52.6 g / m ² was prepared, and a cylindrical lithium ion battery using the negative plate was prepared and tested.

Comparative Example 3 Using a slurry having the above composition
The positive electrode active material coating amount on one side of the current collector is 220 g / m ^Two,
The positive electrode active material coating amount on the other surface is 190 g / m^Two(That is, one
Positive electrode plate adjusted to be about 95% of the coating amount on one side)
Create On the other hand, the positive electrode active material coating amount is 220 g / m^TwoIn terms of
52.6 g / m of coating amount of facing negative electrode active material^Two, Positive electrode active material coating
190 g / m^Two49.8g of negative electrode active material coating amount facing the surface of
/ m^TwoA negative electrode plate was prepared. These positive electrode plate and negative electrode
A cylindrical lithium-ion battery using a
Was tested in the following manner. That is, the coating amount of the negative electrode active material is
It was made to be proportional to the coating amount of the facing positive electrode active material.

Table 1 shows the test results of these cylindrical lithium ion batteries. From Table 1, (Examples 1 to 6) show better cycle characteristics than (Comparative Examples 1 to 3). In the case of continuous overcharging at a constant current of 80 A, the gas release from the cleavage valve 10 was slow in (Examples 1 to 6), but (Comparative Examples 2 and 3) released gas violently. Also, the change in battery weight was large. That is, the present invention (Examples 1 to 6) has a long life and is excellent in safety.

[0030]

[Table 1]

In this embodiment, an example of a large-sized cylindrical lithium-ion battery is shown. Good results were obtained.

In this embodiment, a polyimide pressure-sensitive adhesive tape coated with a pressure-sensitive adhesive made of hexamethacrylate on one side is used for the insulating coating, but the present invention is not limited to this. That is, an adhesive tape in which an acrylic adhesive such as hexamethacrylate or butyl acrylate is applied to one or both surfaces of a polyolefin such as polypropylene or polyethylene, or a tape made of polyolefin or polyimide to which no adhesive is applied is similarly used. it can.

In this embodiment, an example in which lithium manganate is used as the positive electrode active material has been described, but a lithium-cobalt composite oxide, a lithium-nickel composite oxide, or the like can also be used. Further, as the negative electrode active material, carbonaceous materials such as natural graphite, artificial graphite, and coke can be used, and their particle shapes are not particularly limited.

In this embodiment, poly (vinylidene fluoride) was used as the binder, but Teflon, polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber,
Styrene / butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethylcellulose, various latexes, polymers such as acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene and mixtures thereof can also be used.

The electrolyte may be LiCl
O ₄ , LiAsF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li
And mixtures thereof. In addition, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3
Dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitonyl, or a mixed solvent of two or more of these is also used.

[0036]

As described above, the cylindrical lithium ion battery using the present invention has a long service life, has a slow release of gas upon overcharging, and is excellent in safety. Suitable for lithium ion batteries.

[0037]

[Brief description of the drawings]

FIG. 1 is a sectional view of a cylindrical lithium ion battery for an electric vehicle.

[Explanation of symbols]

1a: positive external terminal, 1b: negative external terminal, 2: nut, 3a: first ceramic washer, 3b: second ceramic washer, 4: battery cover, 5: battery container,
6: wound group, 7: flange, 8: insulating coating, 9: lead piece, 10: cleavage valve, 11: metal washer, 12: O-ring, 13: liquid inlet, 20: cylindrical lithium ion battery

Claims (2)

[Claims] A positive electrode plate having a positive electrode mixture layer containing a positive electrode active material, a conductive agent and a binder applied on both surfaces of a current collector, and a negative electrode mixture containing a negative electrode active material and a binder on both surfaces of the current collector. A negative electrode plate coated with an agent layer is wound through a separator to form a winding group, and in the cylindrical lithium ion battery in which the winding group is housed in a cylindrical battery container, the winding group is A positive electrode plate and a negative electrode plate having different amounts of active material coated on one surface and the other surface are used, and the active material amounts of the positive electrode plate and the negative electrode plate on opposite surfaces are wound so as to be proportional. A cylindrical lithium-ion battery, characterized in that: 2. The cylindrical lithium-ion battery according to claim 1, wherein the mass of the positive electrode active material on one surface is 79 to 91% by mass of the amount of the positive electrode active material applied on the other surface.