JP2001185220A - Cylindrical lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylindrical lithium ion battery whose separator, positive electrode plate and negative electrode plate can be made easily to be positioned at winding them, and where weaving and short circuit are hard to be generated. SOLUTION: After four sheets of separator 24 made of polyethylene have been made to be piled up, the tip part is fusion-bonded and unified. Then, after the unified tip of the separator 24 has been made to be fusion-bonded to an axis core 21 to join them together, winding groups 6 are made by winding the, while making the condition that 2 sheets of the separator are made between a positive electrode plate 22 and a negative electrode plate 23, and the cylindrical lithium ion battery is prepared by using the winding groups 6.

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 a conventional cylindrical lithium ion battery, since high capacity is strongly required, the number of separators between the positive electrode plate and the negative electrode plate is one. However, with one separator, a case where a short circuit occurred between the positive electrode plate and the negative electrode plate was observed. That is, during the production of a cylindrical lithium-ion battery, when foreign matter is mixed between the positive electrode plate and the separator or between the negative electrode plate and the separator, it becomes a protrusion, which breaks through the separator during winding and breaks the positive electrode plate and the negative electrode plate. In some cases, a short circuit occurred between them. In addition, when using a cylindrical lithium ion battery, a case where a short circuit was caused by a pinhole formed during the production of the separator was also observed.

In order to solve these problems, a method of increasing the thickness of the separator has been studied. However, when the separator is made thicker, short-circuiting due to entry of foreign matter can be prevented, but short-circuiting due to pinholes formed during the manufacture of the separator cannot be suppressed.

[0005] In view of this, a method of suppressing a short circuit of a pinhole by stacking a plurality of separators has been studied. However, using this method, the separator,
There are problems in that the positioning of the positive electrode plate and the negative electrode plate becomes difficult, and that the winding is likely to be displaced at the time of winding, thereby lowering production efficiency.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a cylindrical lithium ion battery in which the alignment of the separator, the positive electrode plate and the negative electrode plate can be easily performed, and the winding and short circuit do not easily occur during winding. It is.

[0007]

In order to solve the above-mentioned problems, a first invention is to form a winding group by winding a positive electrode plate and a negative electrode plate around an axis through a separator. In a cylindrical lithium ion battery containing the wound group in a cylindrical battery container, the wound group has a separator in which two sheets are stacked between the positive electrode plate and the negative electrode plate,
The tip portions of the separators are integrated by welding, and the integrated tip portions are joined to the shaft core.

[0008] A second invention is characterized in that the integrated tip portion of the separator is joined to the shaft core by welding, and the third invention is characterized in that the integrated tip portion of the separator is provided. Is characterized by being joined to the shaft core by an adhesive tape.

[0009]

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, and the mass ratio is
90: 4.5: 5.5, and this mixture was mixed with N
After adding -methyl-2-pyrrolidone, knead to form a slurry. This slurry was applied to both sides of a 20 μm-thick aluminum foil (positive electrode current collector) to form a positive electrode mixture layer.
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 length of 5500 mm. The thickness of the positive electrode mixture layer (however, the thickness of the current collector was not included) was 260 μm, and the coating amount of the positive electrode active material per one side of the current collector was 344 g / m ² .

A portion of the uncoated portion having a width of 50 mm formed on the positive electrode plate was removed to form a rectangular portion, which was used as a lead piece 9 for current collection. Note that the width of the lead piece 9 is about 10 m
m, the interval between adjacent lead pieces 9 was set to about 20 mm.

2. Preparation of negative electrode plate Carbotron P which is amorphous carbon as the negative electrode active material
4.8 parts by mass of a vapor-grown carbon fiber (trade name: VGCF, manufactured by Showa Denko KK, hereinafter abbreviated as VGCF) as a conductive additive to 87.6 parts by mass (trade name: manufactured by Kureha Chemical Industry Co., Ltd.) A slurry is prepared by adding 7.6 parts by mass of polyvinylidene fluoride as a binder, adding N-methyl-2-pyrrolidone as a dispersion solvent to the mixture, and kneading the mixture. This slurry,
The negative electrode mixture layer was formed by applying the composition to both sides of a rolled copper foil (negative electrode current collector) having a thickness of 10 μm. At the time of applying the slurry, 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. A negative electrode plate was prepared in which the thickness of the negative electrode mixture layer (excluding the thickness of the current collector) was 167 μm, the length was 5680 mm, and the applied amount of the negative electrode active material per one side of the current collector was 81.8 g / m ² . . The bulk density of the negative electrode mixture layer was 0.98 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.

In the width direction of the positive electrode plate and the negative electrode plate, the application area of the negative electrode active material is applied so that the application area of the positive electrode active material and the application area of the negative electrode active material do not shift. The width was larger than the width of the coated portion of the positive electrode active material.

3. Production of Battery The above positive electrode plate and negative electrode plate were
A group of windings 6 is formed by winding with a polyethylene separator of 40 μm sandwiched therebetween. The lead pieces 9 of the positive electrode plate and the lead pieces 9 of the negative electrode plate were wound so as to be located on opposite sides of the winding group 6, respectively. By cutting the positive electrode plate, the negative electrode plate or the separator at an appropriate length during winding, the diameter of the winding group 6 was set to 65 ± 0.1 mm.

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 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 insulated 8
Cover with. As the insulating coating 8, an adhesive tape made of polyimide having an adhesive made of hexamethacrylate coated on one side 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. The battery container 5
Has a cylindrical shape with an outer shape of 67 mm and an inner diameter of 66 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 is provided on a portion of the battery lid 4 which comes into contact with the outer surface of the battery cover 4 by a positive external terminal 1a and a negative external terminal 1b.
Into each tip. Then, the first ceramic washer 3a is placed on the battery cover 4, and each of the positive external terminal 1a and the negative external terminal 1b is connected to the first ceramic washer 3a.
Through.

Thereafter, the peripheral end surface of the battery lid 4 having a disk 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 protrudes outside through a hole in the center of the battery lid 4. 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 an initial discharge capacity. Charging conditions: 4.2V (constant voltage charging), 90A (limit current), 3.5
h, 25 ° C Discharge conditions: 30A (constant current discharge), cut-off voltage 2.7V, 25 ° C A part of the cylindrical lithium ion battery whose initial discharge capacity was measured was charged and discharged at 25 ° C under the above conditions. A test was performed and the discharge capacity at the 200th cycle was measured. Also, 200
After cycling charge and discharge, the state of the occurrence of a minute short circuit was measured by being left in a fully charged state.

5. Leaving test Part of the cylindrical lithium-ion battery that was subjected to the initial discharge test was left at 50 ° C and fully charged for 4 weeks, and then left at 25 ° C.
Discharge to 30A (constant current discharge), 2.7V cutoff voltage. Then, a charge / discharge test was performed under the following conditions to measure a discharge capacity. Charging conditions: 4.2V (constant voltage charging), 90A (limit current), 3.5
h, 25 ° C Discharge conditions: 30A (constant current discharge), final voltage 2.7V, 25 ° C

[0023]

The results of the present invention will be described in detail below. Comparative Example 1 As shown in FIG. 3, the polyethylene separator 24 was used in a folded state. And the axis 21
Then, the leading end portion of the separator 24 was brought into contact with the separator 24, and the separator 24 between the positive electrode plate 22 and the negative electrode plate 23 was wound into a single sheet to form a winding group 6. Other fabrication conditions and test conditions for the cylindrical lithium ion battery are as described above. Comparative Example 2 As shown in FIG. 4, two polyethylene separators 24 were used. Then, the front end portion of the separator 24 is brought into contact with the shaft core 21 and the positive electrode plate
The winding group 6 was prepared by winding the separator 24 between the 22 and the negative electrode plate 23 into one sheet. Other fabrication conditions and test conditions for the cylindrical lithium ion battery are as described above. Heretofore, a winding group has been produced by this method. Comparative Example 3 As shown in FIG. 5, four polyethylene separators 24 were used. Then, the front end portion of the separator 24 is brought into contact with the shaft core 21 and the positive electrode plate
The winding group 6 was prepared by winding the separator 24 between the 22 and the negative electrode plate 23 in two sheets. Other fabrication conditions and test conditions for the cylindrical lithium ion battery are as described above. (Example 1) After stacking four polyethylene separators 24, their ends are integrated by welding. And
As shown in FIG.
After welding and joining the tips of the positive electrode plate 22 and the negative electrode plate
The winding group 6 was formed by winding the separator 23 in the state of having two sheets between 23. Other fabrication conditions and test conditions for the cylindrical lithium ion battery are as described above. (Embodiment 2) After stacking four polyethylene separators 24, their ends are welded and integrated. And
As shown in FIG.
Was joined with an adhesive tape 27, and then wound with two separators 24 between the positive electrode plate 22 and the negative electrode plate 23 to form a winding group 6. Other fabrication conditions and test conditions for the cylindrical lithium ion battery are as described above.

Table 1 shows the results of the test performed under the above conditions. As shown in Table 1, when two separators 24 of Comparative Examples 2 and 3 are stacked, the misalignment at the time of winding is smaller than that obtained by folding the separator 24 of Comparative Example 1. However, when compared in detail, Comparative Example 3 is not preferable because the rate of occurrence of winding deviation during winding is slightly higher than that of Comparative Example 2.

In addition, when two separators 24 of Comparative Example 3 are stacked, the occurrence of short-circuits after 200 cycles of charge / discharge and after standing for 4 weeks is smaller in the case where four separators 24 in Comparative Example 2 are stacked. . It is considered that the reason for this is that the positions of the pin holes of the separators 24 are different from each other, and it is difficult to cause a minute short circuit by overlapping two sheets.

Examples 1 and 2 using the present invention are comparative examples 1
Compared with Nos. 1 to 3, the positioning of the separator 24, the positive electrode plate 22, and the negative electrode plate 23 at the time of winding is easier, and the winding displacement and the short-circuit rate at the time of winding are small, which is extremely excellent. Further, when the present invention is used, occurrence of a short circuit after charge / discharge for 200 cycles and after standing for 4 weeks can be significantly suppressed, and the discharge capacity is high. The reason for this is that the four separators 24 are fixed to the shaft core 21 so that the winding deviation at the time of winding is reduced, and that the two separators 24 are stacked, so that the position of the pinhole of each separator 24 is reduced. This is considered to be due to the fact that a slight short circuit between the positive electrode plate 22 and the negative electrode plate 23 became difficult to occur.

[0027]

[Table 1]

In this embodiment, an example of a large-sized cylindrical lithium-ion battery has been described. However, the same applies to a relatively small-sized lithium-ion battery in which a bottomed cylindrical battery container is used and the upper lid is closed by caulking. Good results were obtained.

In this embodiment, a polyimide adhesive tape coated with an adhesive made of hexamethacrylate on one side is used for the insulating coating 8, 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 can also be used.

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.

As an electrolyte, 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.

[0033]

According to the cylindrical lithium ion battery using the present invention, the positioning of the separator, the positive electrode plate, and the negative electrode plate is easy, and the winding deviation during winding can be suppressed. Furthermore, it is possible to greatly suppress the occurrence of short circuit at the time of winding, after 200 cycles of charge / discharge, and after leaving for 4 weeks, and to increase the discharge capacity after 200 cycles or after leaving for 4 weeks. is there.

[0034]

[Brief description of the drawings]

FIG. 1 is a schematic diagram of Example 1 at the start of winding.

FIG. 2 is a schematic diagram of Example 2 at the start of winding.

FIG. 3 is a schematic diagram of Comparative Example 1 at the start of winding.

FIG. 4 is a schematic diagram of Comparative Example 2 at the start of winding.

FIG. 5 is a schematic diagram of Comparative Example 3 at the start of winding.

FIG. 6 is a cross-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, 9: lead piece, 10: cleavage valve, 11: metal washer, 12: O-ring, 13: injection port, 20: cylindrical lithium ion battery, 21: shaft core, 22: positive electrode plate, 23: negative electrode plate, 24: separator, 25: welded part, 26: adhesive part, 27: adhesive tape

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Katsunori Suzuki 2-8-7 Nihonbashi Honcho, Chuo-ku, Tokyo F-term in Shin-Kobe Electric Co., Ltd. 5H028 AA05 BB00 BB05 BB08 CC13 5H029 AJ12 AK03 AL06 AM03 AM05 AM06 BJ02 BJ14 CJ05 CJ07 DJ04

Claims (3)

[Claims] 1. A cylindrical lithium ion battery in which a positive electrode plate and a negative electrode plate are wound around an axis through a separator to form a winding group, and the winding group is housed in a cylindrical battery container. The winding group has a distance of 2 between the positive electrode plate and the negative electrode plate.
A cylindrical lithium ion, wherein there are stacked separators, and the respective tip portions of the separators are integrated by welding, and the integrated tip portions are joined to the shaft core. battery. 2. The cylindrical lithium ion battery according to claim 1, wherein an integrated front end portion of the separator is joined to the shaft core by welding. 3. The cylindrical lithium ion battery according to claim 1, wherein the integrated front end of the separator is joined to the shaft core with an adhesive tape.