JP2001345085A - Nonaqueous electrolytic solution secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic solution secondary battery having a high reliability. SOLUTION: Via a separator S having a thickness of 50 μm wherein polypropylene(PP) of a thickness of 10 μm and polyethylene(PE) of a thickness of 30 mm are laminated in the order of PP/PE/PP to form a 3-layered structure, a positive electrode plate P and a negative electrode plate N are wound to form a wound group 6 in a cross-sectionally spiral state, and a cylindrical lithium-ion battery 20 is prepared. The separator S is made to have the 3-layered structure consisting of PE which has a superior shutdown property at the time of abnormality of the battery and PP which is superior in the mechanical strength, and the shutdown property and the mechanical strength are made to be equipped.

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, and more particularly, to a positive electrode using a lithium transition metal complex oxide capable of occluding and releasing lithium ions by charge and discharge as an active material, A negative electrode capable of releasing and occluding lithium ions, and an electrode group obtained by winding a negative electrode through a separator, dissolve a lithium salt in at least two or more kinds of organic solvents of ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate The present invention relates to a non-aqueous electrolyte secondary battery infiltrated with a non-aqueous electrolyte.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery, especially a lithium ion battery, is mainly used for portable equipment such as a VTR camera, a notebook computer, and a mobile phone, taking advantage of its high energy density. In recent years, research and development of large non-aqueous electrolyte secondary batteries for electric vehicles and for power storage have been actively conducted. In particular,
In order to respond to environmental issues, the automobile industry is developing electric vehicles that use a motor as a power source and hybrid electric vehicles that use both an internal combustion engine and a motor as a power source. Some are already in practical use.

[0003] Large non-aqueous electrolyte secondary batteries used in electric vehicles and the like are required to have high capacity and high output as well as high safety. For this reason, conventionally, large-sized non-aqueous electrolyte secondary batteries have been provided with lithium hexafluorophosphate (L
iPF ₆ ) is used, and a microporous polyethylene (PE) separator is used to ensure safety.
The polyethylene separator prevents an internal short circuit between the positive electrode and the negative electrode, and can shut down (close microporous holes to block the passage of lithium ions) in the event of an abnormality such as overcharging. Can be prevented.

[0004]

However, when polyethylene is used as a separator of a wound electrode group in a single layer (one sheet), the mechanical strength of polyethylene is low. Cracks were easily generated in some of them, and an internal short circuit between the positive electrode and the negative electrode sometimes occurred. In particular, this internal short circuit occurs remarkably in the case of a non-aqueous electrolyte secondary battery for a vehicle to which vibration is applied.

[0005] Further, the polyethylene separator is easily damaged by foreign substances mixed between the positive and negative electrodes, and is liable to cause a short circuit. That is, in the manufacturing process of the non-aqueous electrolyte secondary battery, when foreign matter is mixed between the positive electrode and the separator or between the negative electrode and the separator, the foreign matter becomes a protrusion, breaking through the separator when winding the positive and negative electrodes, In some cases, a short circuit occurred between the positive and negative electrodes.

Further, different metal ions (Fe, C
u) was eluted in the non-aqueous electrolyte, and dendrites grew on the negative electrode side during charging and discharging to cause a short circuit.
Further, when the growing foreign matter of Fe or Cu grown by dendrites on the negative electrode side reaches the positive electrode side and short-circuits, the separator takes in them and shuts down.
The conduction between the positive and negative electrodes cannot be cut off.

The present invention has been made in view of the above circumstances, and has as its object to provide a highly reliable non-aqueous electrolyte secondary battery.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a positive electrode using a lithium transition metal complex oxide capable of inserting and extracting lithium ions by charge and discharge as an active material; A negative electrode capable of releasing and occluding lithium ions, and an electrode group obtained by winding a separator through a separator, the lithium salt was dissolved in at least two or more kinds of organic solvents among ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate In a non-aqueous electrolyte secondary battery impregnated with a non-aqueous electrolyte, the separator has a multi-layer structure of polypropylene and polyethylene.

In the present invention, the separator has a multi-layer structure of polyethylene having excellent shutdown characteristics when the battery is abnormal and polypropylene having excellent mechanical strength, so that the separator has both shutdown characteristics and mechanical strength. For this reason, lithium ions are stored and stored by charging and discharging.
A positive electrode using a releasable lithium transition metal complex oxide as an active material, and a negative electrode capable of releasing and occluding lithium ions by charge and discharge, and an electrode group obtained by winding a separator through a separator, using lithium salt as ethylene carbonate, The reliability of a high-output non-aqueous electrolyte secondary battery infiltrated with a non-aqueous electrolyte dissolved in at least two or more organic solvents of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate can be improved.

In this case, if the lithium transition metal double oxide is lithium manganate and lithium hexafluorophosphate is used as the lithium salt, high output characteristics required for a large non-aqueous electrolyte secondary battery can be obtained. If the separator has a three-layer structure of polypropylene / polyethylene / polypropylene, polypropylene having high mechanical strength can be made thinner, and polyethylene covered with polypropylene can be made a single layer. As described above, the thickness of the separator may be sufficient to exhibit the shutdown characteristics without considering the mechanical strength, so that the entire separator can have an appropriate thickness.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a cylindrical lithium-ion battery mounted on a hybrid electric vehicle will be described below with reference to the drawings.

<Preparation of Positive Electrode> Lithium manganate (LiMn ₂ O ₄ ) powder as a positive electrode active material, flaky graphite (average particle size: 20 μm) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder ) And 90:
The mixture was mixed at a ratio of 4.5: 5.5, N-methyl-2-pyrrolidone (NMP) was added as a dispersion solvent to the mixture, and the mixture was kneaded to prepare a slurry. This slurry was applied to both surfaces of a 20 μm-thick aluminum foil (positive electrode current collector) to form a positive electrode mixture layer. During the application of 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 aluminum foil.

After that, it is dried, pressed, cut, and has a width of 300.
A positive electrode plate P having a predetermined length of 1 mm (see FIG. 1) was obtained. The thickness of the positive electrode mixture layer (excluding the thickness of the aluminum foil) was 260 μm, and the coating amount of the positive electrode active material per one side of the aluminum foil was 344 g / m ² . A part of the 50 mm-wide slurry-uncoated portion formed on the positive electrode plate was notched, and a part thereof was removed. The remaining part of the notch was used as a lead piece for current collection. Adjacent lead pieces were set at intervals of 20 mm, and the width of the lead pieces was set at 10 mm.

<Preparation of Negative Electrode Plate> As a negative electrode active material, 90 parts by mass of Carbotron P (trade name: manufactured by Kureha Chemical Industry Co., Ltd.), which is amorphous carbon, and 10 parts by mass of polyvinylidene fluoride as a binder were added. After adding N-methyl-2-pyrrolidone as a dispersion solvent, the mixture was kneaded to prepare a slurry. This slurry was applied to both sides of a rolled copper foil (negative electrode current collector) having a thickness of 10 μm. During the application of 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.

After drying, pressing and cutting, the width is 305 m.
m, a negative electrode plate N (see FIG. 1) having a predetermined length was obtained. The bulk density of the negative electrode mixture layer was about 1.0 g / cm ³ . A notch was formed in a 50 mm-wide slurry-uncoated portion formed on the negative electrode plate, a part of the cut was removed, and the remaining notch was used as a current collecting lead piece. The adjacent lead pieces were set at intervals of 20 mm, and the width of the lead pieces was set at 10 mm. Also, in the width direction of the positive electrode plate and the negative electrode plate, the width of the negative electrode active material applied portion is set to be equal to the width of the positive electrode active material so as to prevent a positional shift from occurring between the positive electrode active material applied portion and the negative electrode active material applied portion. About 5mm more than the width of the coating part
I made it bigger.

<Preparation of Wound Group> The above-prepared strip-shaped positive electrode plate and negative electrode plate were laminated with polypropylene (PP) having excellent mechanical strength and polyethylene (PE) having a heat-shutdown effect, As described below, a separator S having a three-layer structure of PP / PE / PP having a predetermined thickness (FIG. 1)
) To form a spirally wound group. At this time, the lead pieces (see reference numeral 9 in FIG. 1) of the positive electrode plate and the negative electrode plate were wound so as to be located on the opposite sides of the wound group. By cutting the positive electrode plate, the negative electrode plate and the separator at an appropriate length during winding, the diameter of the wound group can be reduced to 65 mm.
± 0.1 mm.

In order to form a structure in which the positive electrode plate is always covered by the negative electrode plate at the outermost periphery of the winding group, the length of the negative electrode plate was set to be 18 cm longer than the length of the positive electrode plate.
Then, on the outermost periphery of the wound group, a positive electrode plate and a negative electrode plate are provided on one side.
Those with a deviation of 5 mm or more were excluded as defective.

<Preparation of Battery> As shown in FIG. 1, lead pieces 9 led out from the positive electrode plate are collected and bundled to be bent and deformed. After gathering and contacting around the periphery of the flange 7 integrally projecting from the periphery of a certain pole (positive electrode external terminal 1), the lead piece 9 and the periphery of the flange 7 are ultrasonically welded to each other to attach the lead 9 It was connected and fixed to the peripheral surface of the flange 7. The connection operation between the negative external terminal 1 'and the lead piece 9 derived from the negative electrode plate was performed in the same manner as the connection operation between the positive external terminal 1 and the lead piece 9 derived from the positive electrode plate.

Thereafter, the entire outer periphery of the flange portion 7 of the positive electrode external terminal 1 and the negative electrode external terminal 1 ′ and the winding group 6 was covered with an insulating coating 8. As this insulating coating 8, a polyimide adhesive tape having an adhesive made of hexamethacrylate applied on one side was used. After adjusting the number of windings 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 battery container 5 made of stainless steel, the winding group 6
Was inserted into the battery container 5. The battery container 5 has an outer diameter 67.
mm and a cylindrical shape having an inner diameter of 66 mm were used.

A portion made of alumina, which is in contact with the back surface of the disc-shaped battery lid 4, has a thickness of 2 mm, an inner diameter of 16 mm, and an outer diameter of 25 mm.
The second ceramic washer 3 'having a diameter of 2 mm was fitted into a pole having a positive electrode external terminal 1 at the tip and a pole having a negative external terminal 1' at the tip. A first ceramic washer 3 made of alumina and having a thickness of 2 mm, an inner diameter of 16 mm, and an outer diameter of 28 mm is placed on the battery cover 4, and the positive external terminal 1 and the negative external terminal 1 ′ are respectively connected to the first ceramic. Passed through washer 3. Thereafter, the peripheral end face of the battery lid 4 was fitted into the opening of the battery container 5, and the entire area of both contact portions was laser-welded. At this time, the positive external terminal 1 and the negative external terminal 1 ′
Penetrates a hole formed in the center of the battery cover 4 and
It protrudes outside. Then, as shown in FIG.
The ceramic washer 3 and the metal washer 14 smoother than the bottom surface of the metal nut 2 were fitted into the positive external terminal 1 and the negative external terminal 1 'in this order. The battery cover 4
Is provided with a cleavage valve 10 that is cleaved in response to an increase in the internal pressure of the battery. The cleavage pressure of the cleavage valve 10 is 1.3 to 1.8 ×
It was 10 ⁶ Pa.

Next, the nut 2 is screwed to the positive external terminal 1 and the negative external terminal 1 ', respectively, and the battery cover 4 is closed via the second ceramic washer 3', the first ceramic washer 3, and the metal washer 14. It was fixed between the part 7 and the nut 2 by tightening. The tightening torque value at this time is 6.
86 N · m. The metal washer 14 did not rotate until the fastening operation was completed. In this state, the compression of the rubber (EPDM) O-ring 16 interposed between the back surface of the battery lid 4 and the flange portion 7 blocks the power generation element inside the battery container 5 from the outside air.

Thereafter, a predetermined amount of a non-aqueous electrolyte is injected into the battery container 5 from a liquid inlet 13 provided in the battery cover 4, and then the liquid inlet 13 is sealed with a lid 15. 20 was completed.

The non-aqueous electrolyte contains lithium hexafluorophosphate (L) in a mixed solution of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1: 1: 1.
iPF ₆ ) dissolved at 1 mol / liter was used.
The cylindrical lithium ion battery 20 has a battery container 5
There is no current interrupting mechanism for interrupting the current in response to an increase in the internal pressure of the battery.

[0024]

Next, an example of the cylindrical lithium ion battery 20 manufactured according to this embodiment will be described. A cylindrical lithium ion battery of a comparative example produced for comparison is also described.

(Example) In this example, as shown in Table 1 below, polypropylene (PP) having a thickness of 10 μm and a thickness of 3
0 mm polyethylene (PE) and 10 μm thick polypropylene (PP) are combined with P to protect the PE with PP.
P / PE / PP laminated in order to form a three-layer structure, thickness 5
A positive electrode plate P and a negative electrode plate N were wound via a 0 μm separator S (hereinafter, referred to as a three-layer separator) to form a winding group 6, and a large number of cylindrical lithium ion batteries 20 were produced.

[0026]

[Table 1]

Comparative Example In a comparative example, as shown in Table 1, a positive electrode plate P and a negative electrode plate N were wound via a single-layer, 50 μm-thick polyethylene separator (hereinafter, referred to as a single-layer separator). This was turned into a winding group 6, and a large number of cylindrical lithium ion batteries were produced.

<Test> Each battery of Examples and Comparative Examples produced as described above was charged to 4.2 V, and then
After discharging to 5 V, the battery was charged again to 4.2 V, and the battery whose voltage after one day fell below 4.15 V was excluded as a defective product having a partial short circuit. Then, each of the 20 non-defective batteries of the example and the comparative example was changed from a fully charged state of 4.2 V to 30.
The battery was left for 5 days, and the battery voltage was measured every 5 days. In addition, the difference between the battery voltage immediately after charging and the battery voltage after leaving for 30 days is 1
The voltage drop per day was calculated as a voltage drop rate (mV / day).

FIG. 2 and Table 2 below show the average voltage transition of each of the 20 good batteries.

[0030]

[Table 2]

As shown in Table 2, the battery of the embodiment using the three-layer separator has a voltage drop rate of 1.867 (mV / da).
y) and 8.2 of the battery of the comparative example using the single-layer separator.
It shows a very good voltage holding characteristic as compared with 00 (mV / day). This seems to indicate that the number of micro short circuits inside the winding group 6 is extremely small.

As described above, the cylindrical lithium ion battery 20 of the present embodiment has a three-layer structure of polypropylene / polyethylene / polypropylene in which the separator S is formed by laminating polyethylene having excellent shutdown characteristics and polypropylene having excellent mechanical strength. As a result, it has mechanical strength while ensuring shutdown characteristics. For this reason, the yield at the time of manufacturing the winding group 6 can be improved, and as shown in the examples, a highly reliable battery in which an internal (small) short circuit hardly occurs even with time can be obtained. . In addition, since the separator S is covered with polypropylene having excellent mechanical strength, foreign matter mixed during winding and dendritic growth of a dissimilar metal on the negative electrode side are also reduced.
Damage can be prevented more easily than in a single-layer separator. Furthermore, as shown in the above example, the polypropylene having a large mechanical strength can be thinned, and the thickness is such that the shutdown characteristics can be exhibited without considering the mechanical strength as in the case of using a single layer of polyethylene. Therefore, the cylindrical lithium ion battery 20 can be in a state of high output density even as a three-layer separator. The highly reliable cylindrical lithium-ion battery 20 using such a three-layer separator is, in particular,
It is suitable for power supplies for electric vehicles and hybrid electric vehicles that are subject to vibration.

In this embodiment, an example of a large cylindrical lithium ion battery is shown. However, a comparatively small lithium ion battery in which a bottomed cylindrical battery container is used and the upper lid is closed by caulking is also used. Good results were obtained. In addition, the present invention is not limited to the cylindrical battery shown in the embodiment, for example, the winding group is a cross-sectional triangle other than spiral shape,
The present invention is also applicable to lithium-ion batteries wound in a rectangular or polygonal shape.

In this embodiment, the thickness of the polypropylene is 10 μm and the thickness of the polyethylene is 30 μm.
Although the layer separator is exemplified, it is not limited to the thickness of the polypropylene or the polyethylene or the thickness of the entire separator,
The thickness may be such that reliability can be ensured according to the application.

In this embodiment, a polyimide adhesive tape in which an adhesive made of hexamethacrylate is applied to one surface of the insulating coating 8 is used for the insulating coating 8, but the present invention is not limited to this. For example, 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 may be similarly used. Can be.

Further, in this embodiment, an example is shown in which lithium manganate is used as the positive electrode active material.
A cobalt composite oxide, a lithium nickel composite oxide, or the like can also be used. However, since resources such as cobalt are scarce, it is preferable to use lithium manganate as the positive electrode active material in terms of cost. In addition, in addition to amorphous carbon, natural graphite,
Carbon materials such as artificial graphite and coke can also be used, and their particle shapes are not particularly limited.

In this embodiment, an example in which polyvinylidene fluoride is used as the binder is shown. However, Teflon (registered trademark), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide Polymers such as rubber, nitrocellulose, cyanoethylcellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, and chloroprene fluoride, and mixtures thereof can also be used.

As the electrolyte, other than lithium hexafluorophosphate, LiClO ₄ , LiAsF ₆ , Li
BF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, C
F ₃ SO ₃ Li or the like or a mixture thereof can be used. Also, as the organic solvent, ethylene carbonate,
At least two of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate may be used.

[0039]

As described above, according to the present invention,
Non-aqueous electrolyte secondary battery because the separator has a multi-layer structure of polyethylene with excellent shutdown characteristics at the time of battery abnormality and polypropylene with excellent mechanical strength, so that the separator has both shutdown characteristics and mechanical strength Can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a cylindrical lithium ion battery according to an embodiment to which the present invention is applied.

FIG. 2 is a graph showing an average voltage change of cylindrical lithium ion batteries of Examples and Comparative Examples.

[Explanation of symbols]

6 Winding group (electrode group) 20 Cylindrical lithium ion battery (non-aqueous electrolyte secondary battery) P Positive electrode plate (positive electrode) N Negative electrode plate (negative electrode) S Separator

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yuichi Takatsuka 2-87-7 Nihonbashi Honcho, Chuo-ku, Tokyo Inside Shin-Kobe Electric Machinery Co., Ltd. (72) Kensuke Hironaka 2-87 Nihonbashi Honcho, Chuo-ku, Tokyo F-term (reference) in Shin-Kobe Electric Co., Ltd.

Claims (2)

[Claims] A positive electrode using a lithium transition metal complex oxide capable of occluding and releasing lithium ions by charge and discharge as an active material, and a negative electrode capable of releasing and occluding lithium ions by charge and discharge via a separator In a non-aqueous electrolyte secondary battery in which the wound electrode group is infiltrated with a non-aqueous electrolyte in which a lithium salt is dissolved in at least two or more organic solvents of ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. A non-aqueous electrolyte secondary battery, wherein the separator has a multi-layer structure of polypropylene and polyethylene. 2. The lithium transition metal double oxide is lithium manganate, the lithium salt is lithium hexafluorophosphate, and the separator has a three-layer structure of polypropylene / polyethylene / polypropylene. The non-aqueous electrolyte secondary battery according to claim 1.