JP2006156007A - Cylindrical lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylindrical lithium-ion secondary battery having high safety performance and high cycle characteristics under abnormally high temperatures. <P>SOLUTION: The cylindrical lithium-ion secondary battery is formed by spirally winding a positive plate in which an active material is applied to a belt-shaped current collector and a negative plate in which an active material is applied to a belt-shaped current collector through a separator to constitute a wound group, and sealing the wound group in a metallic outer packaging case together with a nonaqueous electrolyte, the ratio ψ1/ψ2 of the diameter (ψ1) of a space installed in the central part to the outer diameter (ψ2) of the wound group is made 0.20-0.30, and the ratio ψ2/ψ3 of the outer diameter (ψ2) of the wound group to the inner diameter (ψ3) of the battery case is made 0.94-0.97. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a cylindrical lithium ion secondary battery, and in particular, a positive electrode plate in which a positive electrode mixture containing a positive electrode active material is coated on both surfaces of a belt-shaped current collector, and lithium ion by charging and discharging the belt-shaped current collector. The present invention relates to a cylindrical lithium ion secondary battery including a wound group in which a negative electrode plate coated with an active material that can be inserted and removed is wound through a separator.

  Cylindrical lithium ion secondary batteries are mainly used as power sources for portable devices such as VTR cameras, notebook computers, and mobile phones, taking advantage of the high energy density.

  A cylindrical lithium ion secondary battery generally has the following structure. A strip-shaped separator is disposed between a positive electrode plate in which an active material is applied to a band-shaped current collector and a negative electrode plate in which an active material is applied to a band-shaped current collector. Has a group of times. This wound group is housed in a battery case together with a non-aqueous electrolyte. The opening of the battery case is sealed by caulking with a sealing plate via an insulating gasket.

Conventionally, by setting the ratio of the length of the positive electrode plate and the negative electrode plate to the outer diameter of the wound group to be 90 to 110, a battery having a high output density excellent in input / output characteristics has been proposed (for example, Patent Documents). 1).
Japanese Patent Laid-Open No. 2001-210382

  Such a conventional cylindrical lithium ion secondary battery enables a battery with a high output density by using high-density and thin-film electrodes, but there is a problem in safety performance. There are concerns about safety performance degradation due to increased output density, such as safety performance when an internal short circuit occurs, safety performance when exposed to a high temperature atmosphere, safety performance under abnormal charging conditions, etc. . One of the methods for evaluating the safety performance when exposed to this high-temperature atmosphere is generally a test in which the battery is left on a heated hot plate as an accelerated test that raises the battery to an abnormally high temperature. Has been done. The criterion of this accelerated test is that the heated battery does not burst and the electrode group in the battery case does not jump out.

  From this accelerated test, it is considered that the following is occurring inside the battery. As the temperature of the battery increases, the amount of gas generated increases, increasing the pressure in the battery case and opening the safety valve of the sealing plate. However, if the space provided in the center of the winding group is blocked by swelling / melting of the separator until the safety valve of the sealing plate is opened, the path of the generated gas to the safety valve of the sealing plate is blocked. Therefore, the time until the safety valve of the sealing plate detects the pressure increase in the battery case and opens is delayed. And the winding group is discharged out of the battery case due to the pressure in the battery case that increases rapidly with the generation of a large amount of gas, leading to rupture. Thus, this is a method for evaluating the ease of escape when the gas inside the battery at an abnormally high temperature escapes to the safety valve of the sealing plate.

  The present invention solves such a conventional problem, and an object of the present invention is to provide a cylindrical lithium ion secondary battery excellent in safety performance while maintaining cycle characteristics.

In order to solve the above-described problems, the present invention provides a positive electrode plate in which an active material is applied to a strip-shaped current collector, and a negative electrode plate in which the active material is applied to a strip-shaped current collector through a separator. In a secondary battery comprising a wound group wound in a shape and inserted into a battery case together with a non-aqueous electrolyte, the center of the wound group with respect to the outer diameter (φ ₂ ) of the wound group The ratio of the diameter (φ ₁ ) of the space provided in the section, φ ₁ / φ ₂ is 0.30 to 0.40, and the outer diameter (φ ₂ ) of the wound group with respect to the inner diameter (φ ₃ ) of the battery case The ratio φ ₂ / φ ₃ is set to 0.94 to 0.97.

  Abnormalities represented by the hot plate test by optimizing the ratio of the diameter of the space provided in the center of the wound group to the outer diameter of the wound group and the ratio of the outer diameter of the wound group to the inner diameter of the battery case It is possible to provide a cylindrical lithium ion secondary battery that does not rupture even when exposed to high temperatures, is highly safe, and has excellent cycle characteristics.

  In order to prevent explosion when the battery is exposed to an abnormally high temperature, it is necessary to efficiently release the generated gas to the outside. For this purpose, it is necessary to prevent the space provided at the center of the winding group or the space existing between the battery case and the winding group from being blocked by swelling and melting of the separator.

  A cylindrical lithium ion secondary battery according to the present invention includes a positive electrode plate in which an active material is applied to a strip-shaped current collector, and a negative electrode plate in which an active material is applied to a strip-shaped current collector through a separator. The winding group is inserted into a battery case together with a non-aqueous electrolyte.

When the ratio of the diameter (φ ₁ ) of the space provided in the center with respect to the outer diameter (φ ₂ ) of the wound group, that is, φ ₁ / φ ₂ is smaller than 0.30, the gas generated at an abnormally high temperature is efficiently obtained Since it is not released to the outside, the battery bursts and the electrode group in the battery case jumps to the outside. Conversely, if φ ₁ / φ ₂ is larger than 0.40, the capacity of the battery is significantly reduced. In addition, the ratio of the outer diameter (φ ₂ ) of the wound group to the inner diameter (φ ₃ ) of the battery case, that is, φ ₂ / φ ₃ , is within the range of φ ₁ / φ ₂ of 0.30 to 0.40. If it is smaller than 94, the battery capacity is remarkably reduced, and at the same time, the outer diameter of the electrode group is reduced, so that the amount of movement of the electrode group within the battery case is increased. As a result, positioning when the negative electrode lead is welded to the battery case becomes difficult, resulting in problems in the manufacturing process. On the other hand, if φ ₂ / φ ₃ is larger than 0.97, the outer diameter of the electrode group becomes large, so that it becomes very difficult to insert the battery group into the battery case. Phenomena such as a galling phenomenon that occurs depending on the case occurs, leading to an internal short circuit.

For the above reasons, the best mode for carrying out the present invention is that φ ₁ / φ ₂ is 0.30 to 0.40 and φ ₂ / φ ₃ is 0.94 to 0.97.

  The positive electrode in the cylindrical lithium ion secondary battery of the present invention includes at least a positive electrode active material, a binder, and a conductive agent. An example of the positive electrode active material is a lithium-containing composite oxide. As this complex oxide, lithium cobaltate, a modified product of lithium cobaltate, lithium nickelate, a modified product of lithium nickelate, lithium manganate, a modified product of lithium manganate, and the like are preferable. Some modified bodies contain elements such as aluminum and magnesium. There are also those containing at least two of cobalt, nickel and manganese.

  The binder used for the positive electrode is not particularly limited, and polytetrafluoroethylene, modified acrylonitrile rubber particles, polyvinylidene fluoride, and the like can be used. The polytetrafluoroethylene and modified acrylonitrile rubber particles are preferably used in combination with carboxymethyl cellulose, polyethylene oxide, modified acrylonitrile rubber and the like that serve as a thickener for the raw material paste of the positive electrode mixture layer. Polyvinylidene fluoride has a single function as both a binder and a thickener.

  As the conductive agent, acetylene black, ketjen black, various graphites and the like can be used. These may be used alone or in combination of two or more.

  The negative electrode includes at least a negative electrode active material and a binder. As the negative electrode active material, various natural graphites, various artificial graphites, silicon-containing composite materials such as silicide, and various alloy materials can be used. As the binder, various binders such as polyvinylidene fluoride and modified products thereof can be used.

In the non-aqueous electrolyte, various lithium salts such as lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ) can be used as solutes. As the non-aqueous solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and the like are preferably used, but are not limited thereto. Although a nonaqueous solvent can also be used individually by 1 type, it is preferable to use 2 or more types in combination. Moreover, as an additive, vinylene carbonate, cyclohexylbenzene, diphenyl ether, etc. can also be used.

  The separator is not particularly limited as long as it is made of a material that can withstand the use environment of the cylindrical lithium ion secondary battery, but it is common to use a microporous film made of a polyolefin-based resin such as polyethylene or polypropylene. . The microporous film may be a single layer film made of one kind of polyolefin resin or a multilayer film made of two or more kinds of polyolefin resin.

FIG. 1 is a schematic longitudinal sectional view of a cylindrical lithium ion secondary battery which is an embodiment of the present invention.

  In FIG. 1, a positive electrode plate 1 in which a positive electrode mixture (not shown) is coated on a strip-shaped aluminum foil current collector (not shown), and a negative electrode composite on a strip-shaped copper foil current collector (not shown). A negative electrode plate 2 coated with an agent (not shown) and a wound group 4 wound in a spiral shape with a separator 3 having a thickness of 20 μm interposed between the positive electrode plates are housed in a battery case 6 together with the electrolyte. Has been. The battery 5 is hermetically sealed by caulking the upper end opening of the battery case 6 to the outer periphery of the battery lid 7 via an insulating gasket 8. The positive electrode lead 9 is connected to the battery lid 7 by welding, and the negative electrode lead 10 is connected to the battery case 6 by welding. An upper insulating ring 11 is disposed above the winding group 4 to insulate it from the battery lid 7, and a lower insulating ring 12 is disposed below the winding group 4 to insulate from the battery case 6. Yes. The produced battery 5 is a 18650 size cylindrical lithium ion secondary battery having a diameter of 18 mm and a height of 65 mm, and has a battery capacity of 2000 mAh.

Below, the preparation methods of a positive electrode and a negative electrode, and the adjustment method of electrolyte solution are demonstrated in detail.
(A) Production of Positive Electrode 3 kg of lithium cobaltate and polyvinylidene fluoride as a binder (# 1320 manufactured by Kureha Chemical Co., Ltd. (N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) solution having a solid content of 12% by weight) ) (Hereinafter abbreviated as PVDF)), 90 g of acetylene black, and an appropriate amount of NMP are stirred in a double-arm kneader to prepare a positive electrode mixture paste. This paste is applied to an aluminum foil having a thickness of 15 μm, dried and rolled to form a positive electrode mixture layer.
(b) Preparation of negative electrode 3 kg of artificial graphite, 75 g of styrene-butadiene copolymer (BM-400B manufactured by Nippon Zeon Co., Ltd., aqueous dispersion having a solid content of 40% by weight) as a binder, 30 g of carboxymethyl cellulose and an appropriate amount of water are stirred with a double-arm kneader to prepare a negative electrode mixture paste. This paste is applied to a 10 μm thick copper foil, dried and then rolled to form a negative electrode mixture layer.
(C) Preparation of electrolyte solution In a mixed solvent obtained by mixing ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate in a volume ratio of 2: 3: 3, a concentration of 1 mol / L of lithium hexafluorophosphate (LiPF ₆ ) Then, 3% by weight of vinylene carbonate is added as an additive to prepare an electrolytic solution.

Hereinafter, the diameter φ _{1 of the} space 13 provided at the center of the wound group 4, the outer diameter φ ₂ of the wound group 4, and the inner diameter φ ₃ of the battery case 6 will be described in detail with reference to FIG.

<< Examples 1-5 >>
The ratio of φ _{1 to} φ ₂ when the diameter 13 of the space provided at the center of the wound group 4 is φ ₁ , the outer diameter of the wound group 4 is φ ₂ , and the inner diameter of the battery case 6 is φ ₃ , φ _{1 /} phi ₂ and phi ₃ for phi ₂ ratio, the φ _{2 /} φ ₃ to prepare a cylindrical lithium ion secondary battery so as to the values shown in Table 1.

<< Comparative Examples 1-4 >>
The ratio of φ _{1 to} φ ₂ when the diameter of the space 13 provided in the center of the wound group 4 is φ ₁ , the outer diameter of the wound group 4 is φ ₂ , and the inner diameter of the battery case 6 is φ ₃ , φ _{1 /} phi ₂ and phi ₃ for phi ₂ ratio, the φ _{2 /} φ ₃ to prepare a cylindrical lithium ion secondary battery so as to the values shown in Table 1.

  Table 2 shows the results of the hot plate test, the battery capacity test, and the charge / discharge cycle test performed on the battery thus manufactured.

  The hot plate test, battery capacity test, and charge / discharge cycle test were conducted as follows.

(Hot plate test)
The hot plate test is a test that is generally performed as an accelerated test in which a battery is left on a heated hot plate and the battery is heated to an abnormally high temperature.

  Using each of the 10 cylindrical lithium ion secondary batteries produced as described above, the battery voltage reaches 4.2 V after remaining discharge at a constant current of 2000 mA (1.0 ItA) to a final voltage of 3.0 V. Until 1400 mA (0.7 ItA) is charged at constant current, and then the fully charged battery charged until the current value decays to 100 mA (0.05 ItA) is left on a 250 ° C. hot plate, By measuring the time until the safety valve of the sealing plate was opened, the gas detachability was evaluated and the number of ruptures was confirmed.

(Battery capacity test)
Using each of the 10 cylindrical lithium ion secondary batteries produced as described above, the battery voltage reaches 4.2 V after remaining discharge at a constant current of 2000 mA (1.0 ItA) to a final voltage of 3.0 V. Up to 1400 mA (0.7 ItA) is charged at a constant current, and then a fully charged battery charged until the current value decays to 100 mA (0.05 ItA) at a constant current of 400 mA (0.2 ItA). The battery capacity at the second cycle of charge / discharge for discharging to a discharge end voltage of 3.0 V was measured, and the average value was calculated.

(Charge / discharge cycle test)
Using each of the 10 cylindrical lithium ion secondary batteries produced as described above, the charge / discharge cycle characteristics were such that the battery voltage remained after discharging at a constant current of 2000 mA (1.0 ItA) up to a final voltage of 3.0 V. When a constant current charge of 1400 mA (0.7 ItA) is performed until the voltage reaches 4.2 V, and then a cycle of discharging at a constant current of 2000 mA (1.0 ItA) to a final voltage of 3.0 V is repeated 500 times The capacity was measured, the capacity retention rate at the 500th cycle when the third cycle was taken as 100% was calculated, and the average value was calculated.

  In an abnormally high temperature state typified by the hot plate test, the preferred mode of breakage of the cylindrical lithium ion secondary battery is that the pressure in the battery case increases due to an increase in the generated gas and the safety valve on the sealing plate opens. In the meantime, the space provided in the central part of the winding group is not blocked by the swelling / melting of the separator. Since the passage of the generated gas to the safety valve of the sealing plate is blocked when the space is closed, the time until the safety valve of the sealing plate detects the pressure increase in the battery case and opens is delayed. And the winding group is discharged out of the battery case due to the pressure in the battery case that increases rapidly with the generation of a large amount of gas, leading to rupture.

  Regarding the cycle characteristics, one of the factors leading to cycle deterioration is an increase in impedance in the positive and negative electrodes as the cycle progresses. Further, as one of the factors that increase the impedance, there is “drying out” of the electrolyte present in both electrodes. Liquid depletion means that when both electrodes repeatedly swell and contract during charging / discharging, the electrolyte held in the electrode is pushed out of the electrode, and a portion where the electrolyte is depleted in the electrode is generated. The cycle characteristics are greatly deteriorated by this liquid withering.

  Therefore, it is possible to increase the amount of electrolyte by enlarging the space provided between the battery case and the winding group, or the space provided in the center of the winding group. The deterioration of characteristics can be improved.

  In Comparative Example 1, since the time until the safety valve is opened is long, the space provided at the center of the wound group is blocked by the swelling / melting of the separator, leading to rupture.

  In Examples 1 to 3, since the center diameter of the wound group is large, the space is maintained even if the separator is clogged. Therefore, the safety valve of the sealing plate operates normally, the generated gas is efficiently released to the outside, and the pressure in the battery case does not increase rapidly, so that the explosion does not occur.

  In Comparative Example 2, the wound group does not rupture because the center diameter of the wound group is large, but the capacity of the battery decreases as the center diameter of the wound group is increased.

  In Comparative Example 3, the release diameter of the generated gas was further improved by increasing the center diameter of the wound group and further reducing the outer diameter of the wound group, and safety performance was improved. The capacity of will decrease.

  In Examples 4 and 5, it was found that there was no problem in both safety performance and cycle characteristics. However, in Comparative Example 4, the outer diameter of the wound group and the inner diameter of the battery case were almost the same, so that they were inserted into the battery case. Was impossible.

From the above results, in order to obtain a cylindrical lithium ion secondary battery that does not rupture in the hot plate test, has high safety performance, high battery capacity, and good charge / discharge cycle characteristics, φ ₂ / φ ₁ = 0.30 to 0.40, and φ ₁ / φ ₃ = 0.94 to 0.97 is preferable.

  INDUSTRIAL APPLICABILITY The present invention can provide a cylindrical lithium ion secondary battery with high battery capacity, excellent charge / discharge cycle characteristics, and high safety, and is useful as a drive power source for electronic devices such as notebook computers and digital still cameras. .

1 is a schematic longitudinal sectional view of a cylindrical lithium ion secondary battery according to an embodiment of the present invention. Detailed view of XY cross section of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative electrode plate 3 Separator 4 Winding group 5 Battery 6 Battery case 7 Battery cover 8 Insulating gasket 9 Positive electrode lead 10 Negative electrode lead 11 Upper insulating ring 12 Lower insulating ring 13 Space provided in the center of winding group 4 φ ₁ The diameter of the space provided in the center of the winding group 4 φ ₂ The outer diameter of the winding group 4 φ ₃ The inner diameter of the battery case 1

Claims (1)

A positive electrode plate in which an active material is coated on a strip-shaped current collector and a negative electrode plate in which an active material is coated on a strip-shaped current collector are wound in a spiral shape with a separator interposed therebetween. A cylindrical lithium ion secondary battery in which a wound group is inserted into a battery case together with a non-aqueous electrolyte,
The ratio of the diameter (φ ₁ ) of the space provided at the center to the outer diameter (φ ₂ ) of the wound group, φ ₁ / φ ₂ is 0.30 to 0.40, and the inner diameter ( A cylindrical lithium ion secondary battery in which the ratio of the outer diameter (φ ₂ ) of the wound group to φ ₃ ), φ ₂ / φ ₃ is 0.94 to 0.97.