Lithium ion battery and manufacturing method thereof

Abstract

To suppress the generation of LiAl alloy in aluminum foil in a lithium ion battery in which the aluminum foil is used as a packaging container for an electrolyte.SOLUTION: A packaging container 10 includes a laminate material 11 in which a resin film 13 is laminated on both sides of aluminum foil 12. A positive electrode 20 and a negative electrode 30 are sealed within the packaging container 10 and are insulated from the aluminum foil 12. An electrolyte 50 is sealed within the packaging container 10 and contains lithium ions that conduct current between the positive electrode 20 and the negative electrode 30 during charging and discharging. A portion of the resin film 13 is removed to bring the aluminum foil 12 into contact with the electrolyte 50. This lithium ion battery 1 is configured such that the potential of the negative electrode is charged to 0.5 V or less relative to Li / Li+.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a lithium-ion battery and a method for manufacturing the same.

Background Art

[0002] For example, Patent Document 1 (Japanese Patent No. 6564188) discloses a lithium-ion battery using a laminate material in which resin films are laminated on both sides of a metal foil as an exterior material. Aluminum foil may be used as the material of the laminate material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a lithium-ion battery including an aluminum foil, a laminate material formed by laminating resin films on both sides thereof, and an electrolytic solution, the potential of the negative electrode is Li / Li +There are those that are charged up to 0.5 V or less. In such a lithium battery, for example, after injecting the electrolyte solution, an insulation check is performed between the aluminum foil of the laminate material and the negative electrode, and those that pass the check are regarded as good products. Therefore, a lithium ion battery regarded as a good product has been confirmed by inspection to have the aluminum foil and the electrolyte solution separated and insulated by a resin film. However, in such a lithium battery, when used for a long time, cracks may occur in the portion of the resin film that is in contact with the electrolyte solution. When cracks occur, the insulation resistance between the aluminum foil and the negative electrode decreases, and when the condition that the crack in the resin film of the laminate material and the component of the negative electrode potential are close overlaps, the LiAl alloy of the aluminum foil may progress. When the LiAl alloy of the aluminum foil progresses, through holes may occur in the aluminum foil, and liquid leakage may occur.

[0005] An object of the present invention is to suppress the generation of the LiAl alloy in the aluminum foil in a lithium ion battery in which the aluminum foil is used as a packaging container for the electrolyte solution.

Means for Solving the Problem

[0006] The lithium ion battery according to the first aspect of the present invention includes a packaging container, a positive electrode, a negative electrode, and an electrolyte solution. The packaging container includes a laminate material in which resin films are laminated on both sides of an aluminum foil. The positive electrode is enclosed in the packaging container and is insulated from the aluminum foil. The negative electrode is enclosed in the packaging container and is insulated from the aluminum foil. The electrolyte solution is enclosed in the packaging container and contains lithium ions that conduct current between the positive electrode and the negative electrode during charge and discharge. A part of the resin film is removed, and the aluminum foil and the electrolyte solution are in contact. This lithium ion battery is configured such that the potential of the negative electrode can be charged to 0.5 V or less with respect to Li / Li + In the lithium ion battery according to the first aspect, in the removal region where a part of the resin film is removed, the aluminum foil and the electrolyte solution are in contact. In this lithium ion battery, the potential of the negative electrode is Li / Li + ​Although it can be charged to 0.5 V or less, in the removal region, since the aluminum foil and the electrolytic solution are in contact with each other, the potential of the aluminum foil becomes less likely to drop to the potential at which LiAl alloy is generated compared to the conventional case where no removal region is formed in the resin film.

[0007] The lithium-ion battery according to the second aspect of the present invention is the lithium-ion battery according to the first aspect, wherein the resistance value between the aluminum foil and the electrolytic solution is 1 MΩ or less. In the lithium-ion battery according to the second aspect, even if the value of the insulation resistance between the aluminum foil and the negative electrode decreases, the resistance value between the aluminum foil and the electrolytic solution is likely to be kept lower than the value of the insulation resistance between the aluminum foil and the negative electrode. Even if the value of the insulation resistance between the aluminum foil and the negative electrode decreases after manufacturing, by reducing the possibility that the potential of the aluminum foil drops to the potential at which LiAl alloy is generated, the possibility that the potential of the aluminum foil generates LiAl alloy can be suppressed to a low level. The lithium-ion battery according to the third aspect of the present invention is the lithium-ion battery according to the first or second aspect, wherein the insulation resistance between the aluminum foil and the negative electrode before injecting the electrolytic solution is 100 kΩ or more. In the lithium-ion battery according to the third aspect, since the insulation resistance between the aluminum foil and the negative electrode before injecting the electrolytic solution is 100 kΩ or more, the possibility that the potential of the aluminum foil drops to the potential at which LiAl alloy is generated can be further reduced. The lithium-ion battery according to the fourth aspect of the present invention is the lithium-ion battery according to the first or second aspect, wherein a constraint pressure of 0.01 MPa or more is applied to the laminate material. In the lithium-ion battery according to the fourth aspect, by applying and constraining a constraint pressure of 0.01 MPa or more to the laminate material, for example, a module in which a plurality of lithium-ion batteries are stacked can be firmly assembled.

[0008] The method for manufacturing a lithium-ion battery according to the fifth aspect of the present invention includes a step of removing a part of the resin film of a packaging container including a laminate material in which resin films are laminated on both sides of an aluminum foil by a laser, and a step of enclosing a positive electrode insulated from the aluminum foil, a negative electrode insulated from the aluminum foil, and an electrolytic solution containing lithium ions in the packaging container and bringing the electrolytic solution into contact with the aluminum foil, and a step of charging the negative electrode to a potential of 0.5 V or less with respect to Li / Li + and a step of charging to 0.5 V or less with respect to Li / Li In the method for manufacturing a lithium-ion battery according to the fifth aspect, in the removal region where a part of the resin film is removed by a laser, the aluminum foil and the electrolytic solution come into contact with each other. In such a lithium-ion battery, the negative electrode is charged to a potential of 0.5 V or less with respect to Li / Li + However, in the removal region, since the aluminum foil and the electrolytic solution are in contact with each other, it becomes difficult for the potential of the aluminum foil to drop to the potential at which LiAl alloy is generated as compared with the conventional case where no removal region is formed in the resin film. Further, since the mechanical damage given to the aluminum foil is small by removing it with a laser, cracks are less likely to occur in the aluminum foil and the resin film outside the aluminum foil. As a result, it is possible to suppress the occurrence of defective products caused by removing a part of the resin film.

Advantages of the Invention

[0009] According to the lithium-ion battery or the method for manufacturing a lithium-ion battery of the present invention, generation of LiAl alloy can be suppressed in the aluminum foil of the laminate material of the packaging container.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0011] (1) Configuration of a lithium-ion battery As shown in FIG. 1, the lithium-ion battery 1 includes a packaging container 10. The packaging container 10 is filled with an electrolytic solution 50 (see FIG. 2). The packaging container 10 includes a laminate material 11 in which resin films 13 are laminated on both sides of an aluminum foil 12, as shown in FIG. 2. The packaging container 10 is formed by bonding two laminate materials 11 together. The resin films 13 disposed inside each laminate material 11 are heat-sealed to each other. The heat-sealed portion is the portion disposed at the flange portion 10f of the packaging container 10 in the resin film 13. For the resin film 13, for example, a polyolefin-based film, a polyimide film, a polyamide film, or a polyester film can be used. The materials of the resin films 13 on both sides of the aluminum foil 12 may be the same or different. The resin film 13 may be a composite film in which a plurality of types of films having different materials are laminated together. By bonding two laminate materials 11 together, a space for enclosing the positive electrode 20, the negative electrode 30, and the electrolytic solution 50 is formed in the portion surrounded by the flange portion 10f. The electrolyte 50 is enclosed in the packaging container 10. The electrolyte 50 contains lithium ions that conduct current between the positive electrode 20 and the negative electrode 30 during charge and discharge. The electrolyte 50 contains, for example, a lithium salt and an organic solvent (please modify as appropriate). Examples of the lithium salt include lithium hexafluorophosphate (LiPF6), LiClO4, LiBF4, LiCF3SO3, LiCF3CO2, and LiAsF6, and one or more of these can be used. Examples of the organic solvent used in the electrolyte 50 include ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethylformamide, dioxolane, and acetonitrile. These may be used alone or in combination of two or more. As shown in FIG. 2, the lithium ion battery 1 includes a positive electrode 20 and a negative electrode 30. In FIG. 2, for ease of viewing and explanation of the figure, a set of positive electrode 20 and negative electrode 30 facing each other with a separator 40 interposed therebetween is shown. As the separator 40, for example, a microporous membrane made of polyolefin or a non-woven fabric made of cellulose can be used. Examples of the polyolefin constituting the microporous membrane include polyethylene (PE), polypropylene (PP), and polymethylpentene. Further, as the separator 40, a laminated separator composed of a porous layer mainly containing an inorganic filler can be used. However, in the actual lithium ion battery 1, unlike that shown in FIG. 2, a plurality of sets of positive electrodes 20 and negative electrodes 30 are stacked. For example, 20 sets of positive electrodes 20 and negative electrodes 30 are stacked. A separator 40 is interposed between the positive electrode 20 and the negative electrode 30, and the positive electrode 20 and the negative electrode 30 are separated by the separator 40. In the lithium ion battery 1, for example, they are stacked in the order of separator 40, positive electrode 20, separator 40, negative electrode 30, separator 40, positive electrode 20, separator 40, negative electrode 30, ···, separator 40. Separators 40 are disposed between the laminate material 11 and the positive electrode 20 and between the laminate material 11 and the negative electrode 30.

[0012] The positive electrode 20 and the negative electrode 30 are enclosed in the packaging container 10. The positive electrode 20 and the negative electrode 30 are immersed in the electrolytic solution 50 in the packaging container 10. The positive electrode 20 and the negative electrode 30 are insulated from two aluminum foils 12 in the packaging container 10 by a resin film 13. A positive electrode lead 21 is connected to the positive electrode 20, and a negative electrode lead 31 is connected to the negative electrode 30. The positive electrode lead 21 and the negative electrode lead 31 are drawn out from one side of the packaging container 10 having a rectangular parallelepiped shape in plan view to the outside of the packaging container 10. In FIG. 2, the positive electrode lead 21 and the negative electrode lead 31 are depicted as being drawn out in different directions, but this is a conceptual illustration for ease of viewing the figure. Therefore, the structure of the actual lithium ion battery 1 is, for example, the structure shown in FIGS. 1 and 3. FIG. 3 shows the state in which the lithium-ion battery 1 of FIG. 1 is disassembled into two laminate materials 11 and a battery core 60. The battery core 60 includes a plurality of layers of positive electrodes 20, a plurality of layers of negative electrodes 30, a separator 40, a current collector 70, a positive electrode lead 21, and a negative electrode lead 31. The current collector 70 serves to connect the positive electrode 20 and the negative electrode 30 inside the lithium-ion battery 1 to the positive electrode lead 21 and the negative electrode lead 31. The current collector 70 is composed of a metal foil such as a copper foil, for example.

[0013] As shown in FIGS. 3 and 4, a part of the resin film 13 of the laminate material 11 is removed, and for example, the oxide film of the aluminum foil 12 is in contact with the electrolytic solution 50. The locations where a part of the resin film 13 is removed are referred to as removal regions AR1 and AR2. The resin films 13 in which the removal regions AR1 and AR2 are formed are respectively disposed inside the aluminum foil 12. The removal regions AR1 and AR2 are provided in portions that do not contact the positive electrode 20, the negative electrode 30, the positive electrode lead 21, the negative electrode lead 31, and the current collector 70. By providing the removal regions AR1 and AR2, the potential of the aluminum foil 12 will approach the potential of the electrolytic solution 50 as compared with the case where the removal regions AR1 and AR2 are not provided. The resistance between the aluminum foil 12 and the electrolytic solution 50 is maintained at a resistance value greater than, for example, 10 GΩ when the removal regions AR1 and AR2 are not provided. When the removal regions AR1 and AR2 are provided, for example, if the potential of the electrolytic solution 50 is 1.3 V, the potential of the aluminum foil 12 also approaches 1.3 V. Therefore, even if the value of the insulation resistance between the negative electrode 30 and the resin film 13 (or the aluminum foil 12) becomes small due to some factor, the contact of the aluminum foil 12 with the electrolytic solution 50 in the removal regions AR1 and AR2 increases the possibility that the potential of the aluminum foil 12 is maintained at a potential close to that of the electrolytic solution 50. As a result, it becomes difficult for the potential of the aluminum foil 12 to drop to the potential at which the LiAl alloy progresses, and it becomes difficult for through holes or the like to occur in the aluminum foil 12. The size of the removal regions AR1 and AR2 only needs to be such that the electrolytic solution can penetrate. As the size for the electrolytic solution to penetrate, a size equal to or larger than that of the pores of the porous separator 40 used in the lithium-ion battery 1 is preferable. As the pore diameter, for example, 0.1 μm or more is sufficient. If it is smaller than 0.1 μm, it becomes difficult for the electrolytic solution to penetrate. On the other hand, if the removal regions AR1 and AR2 are too large, they are likely to come into contact with the components at the negative electrode potential. Therefore, the size of the removal regions AR1 and AR2 is limited to a range that can sufficiently prevent contact with the components at the negative electrode potential. The location for removal is preferably away from the components at the negative electrode potential and a location where the electrolytic solution can easily soak in. The removal regions AR1 and AR2 are preferably arranged, for example, at a position closer to the positive electrode lead 21 than the point equidistant from the positive electrode lead 21, the negative electrode lead 31, and the laminate in which the positive electrode 20 and the negative electrode 30 are laminated. As an example of the location for removal, directly above the positive electrode lead 21 can also be mentioned. However, depending on the external atmospheric pressure, mechanical stress may be applied to the removal regions AR1 and AR2, which can be a starting point for breakage. Therefore, it is preferably arranged at a position closer to the positive electrode lead 21 than the point equidistant from the positive electrode lead 21, the negative electrode lead 31, and the laminate.

[0014] (2) Method for manufacturing a lithium-ion battery The method for manufacturing the lithium-ion battery 1 will be described along the flow shown in FIG. 5. A positive electrode 20 is formed by forming a positive electrode active material on a metal foil (step S1). As the positive electrode active material, for example, a transition metal composite oxide containing lithium (lithium-containing transition metal composite oxide) is used. As the lithium-containing transition metal composite oxide used for the positive electrode active material, for example, a lithium-containing transition metal composite oxide having a layered structure can be used. Examples of such lithium-containing transition metal composite oxides having a layered structure include lithium cobalt oxide (LiCoO2), LiNiO2, LiNiCoMnO2, LiMn2O4, LiFePO4, etc. having a layered structure. Only one of these may be used, or two or more may be used in combination. Also, a negative electrode 30 is formed by forming a negative electrode active material on a metal foil (step S2). Examples of the negative electrode active material include graphite (LiC6), a silicon compound, and metallic lithium. In the battery assembly process (step S3), as shown in FIG. 3, the battery core 60 of the lithium-ion battery 1 is sandwiched between laminate materials 11 and enclosed in the packaging container 10. A film-like insulator 15 is disposed between the positive electrode lead 21 and the negative electrode lead 31 and the laminate material 11. The insulator 15 is, for example, a maleic anhydride-modified polypropylene film. In this assembly process (step S3), a part of the resin film 13 of the laminate material 11 is removed, for example, by a laser, or a cut is made in the resin film 13 with a blade. As the laser used for removing the resin film 13, for example, a wavelength that does not damage the aluminum foil 12 and is absorbed only by the resin (the fundamental wavelength is in the range of 1064 nm to 10600 nm) is preferable. For example, a CO2 laser marker and a YVO4 laser marker are preferable. The cut with a blade is a half-cut in which the blade is inserted to the thickness of the resin film 13. In particular, a half-cut with the depth adjusted so that the blade is inserted into the laminate material 11 to the extent of touching the aluminum foil 12 is preferable.

[0015] In the next liquid injection pre-inspection process (step S4), at least the insulation resistance between the negative electrode lead 31 and the aluminum foil 12 is inspected. The insulation resistance between the negative electrode lead 31 and the aluminum foil 12 is, for example, 10 GΩ or more. The liquid injection pre-inspection process (step S4) is performed before the electrolytic solution 50 is injected into the packaging container 10. It is confirmed that the insulation resistance between the aluminum foil 12 and the negative electrode 30 is 100 kΩ or more. In this process, by measuring the resistance value, it is confirmed that the insulation resistance between the aluminum foil 12 and the negative electrode 30 is 100 kΩ or more. The electrolytic solution 50 is injected into the packaging container 10, and the electrolytic solution 50 is sealed in the packaging container 10. The electrolytic solution 50 is injected until it reaches the removal regions AR1, AR2 of the resin film 13 (step S5). After the electrolytic solution 50 is injected, the packaging container 10 is sealed. In the post-liquid injection inspection process (step S6) after the injection of the electrolytic solution 50, at least the resistance value between the aluminum foil 12 and the electrolytic solution 50 is measured. In the post-liquid injection inspection process (step S6), it is confirmed that the resistance value between the aluminum foil 12 and the electrolytic solution 50 is 1 MΩ or less. The resistance value between the aluminum foil 12 and the electrolytic solution 50 is measured, for example, by connecting a 1 GΩ as a digital multimeter DM7275 manufactured by Hioki Electric Co., Ltd. and a comparison resistor in parallel with the voltage probe of the digital multimeter and measuring the voltage. Using the measurement result, the resistance value between the aluminum foil 12 and the electrolytic solution 50 can be obtained from the equivalent circuit. In the assembling process of the module 90 (step S7), as shown in FIG. 6, a plurality of lithium ion batteries 1 are stacked and constrained by the constraining member 80. The constraining member includes a first end plate 81, a second end plate 82, for example, four bolts 83 and four nuts 84. In order to make it difficult for cracks to occur in the laminate material 11, the plurality of lithium ion batteries 1 are stacked with their respective wide surfaces F1, F2 (see FIG. 4) facing each other. A constraining pressure of 0.01 MPa or more is applied to each lithium ion battery 1 of the assembled module 90. A buffer material may be provided between adjacent lithium ion batteries 1. To apply a compressive pressure, for example, a machine including a frame on which an object to be loaded is placed, a cylinder for applying a load, and a load cell for measuring a load can be used. Such a machine includes, for example, a universal testing machine. First, the first end plate 81 is installed on the fixed side (frame) of the machine, and the second end plate 82 is pressed with a predetermined compressive pressure. While applying the predetermined compressive pressure, a bolt 83 is inserted into the long hole of the first end plate 81 and fixed with a nut 84 to connect the first end plate 81 and the second end plate 82. Then, if the load of the machine is released, a constrained state in which a predetermined compressive pressure is applied to the plurality of lithium ion batteries 1 by the first end plate 81 and the second end plate 82 can be maintained. In the next charging step (step S8), the lithium ion battery 1 is charged. Each lithium ion battery 1 is charged until the potential of the negative electrode 30 is 0.5 V or less with respect to Li / Li +

[0016] (3) Features (3-1) In the lithium ion battery 1 of the above embodiment, a part of the resin film 13 is removed. The locations where the resin film 13 is removed are the removal regions AR1 and AR2 shown in FIG. 4. In these removal regions AR1 and AR2, the aluminum foil 12 and the electrolytic solution 50 are in contact. The lithium ion battery 1 is charged until the potential of the negative electrode 30 is 0.5 V or less with respect to Li / Li + (3-2) ​​Since the resistance value between the aluminum foil 12 and the electrolytic solution 50 is 1 MΩ or less, even if the insulation resistance value between the aluminum foil 12 and the negative electrode 30 decreases, the resistance value between the aluminum foil 12 and the electrolytic solution 50 is likely to be kept lower than the insulation resistance value between the aluminum foil 12 and the negative electrode 30. Even if the insulation resistance value between the aluminum foil 12 and the negative electrode 30 decreases after manufacturing, by reducing the possibility that the potential of the aluminum foil 12 drops to the potential at which the LiAl alloy is generated, the possibility that the potential of the aluminum foil 12 generates the LiAl alloy can be suppressed low.

[0017] (3-3) Since the insulation resistance between the aluminum foil 12 and the negative electrode 30 before injecting the electrolytic solution 50 is 100 kΩ or more, the possibility that the potential of the aluminum foil 12 drops to the potential at which the LiAl alloy is generated can be further reduced. (3-4) As shown in FIG. 6, since the generation of the LiAl alloy in the aluminum foil 12 due to the crack in the resin film 13 is unlikely to occur, the module 90 can be firmly assembled by applying a restraint pressure of 0.01 MPa or more to the laminate material 11 for restraint.

[0018] (3-5) As described in the flowchart of FIG. 5, in the battery assembly process (step S3), a part of the resin film 13 is removed by a laser. By removing it with a laser, since the mechanical damage given to the aluminum foil 12 is small, cracks are less likely to occur in the aluminum foil 12 and the resin film 13 outside the aluminum foil 12. As a result, the occurrence of defective products due to removing a part of the resin film 13 can be suppressed. As described above, one embodiment of the present invention has been described, but the present invention is not limited to the above embodiment, and various changes are possible without departing from the gist of the invention. In particular, a plurality of embodiments and modifications described in this specification can be arbitrarily combined as necessary.

Explanation of reference numerals

[0019] 1 Lithium-ion battery 10 Packaging container 11 Laminate material 12 Aluminum foil 13 Resin film 15 Insulator 20 Positive electrode 30 Negative electrode 40 Separator 50 Electrolyte 90 Module AR1, AR2 Removal area

Claims

1. A packaging container including a laminate material obtained by laminating resin films on both sides of an aluminum foil, A positive electrode enclosed in the packaging container and insulated from the aluminum foil, A negative electrode enclosed in the packaging container and insulated from the aluminum foil, An electrolytic solution enclosed in the packaging container and containing lithium ions that conduct current between the positive electrode and the negative electrode during charge and discharge, comprising A part of the resin film is removed so that the aluminum foil and the electrolytic solution are in contact with each other, The potential of the negative electrode is configured to be charged to 0.5 V or less with respect to Li / Li ＋ A lithium-ion battery.

2. The lithium-ion battery according to claim 1, wherein the resistance value between the aluminum foil and the electrolytic solution is 1 MΩ or less.

3. The insulating resistance between the resin film and the negative electrode before injecting the electrolytic solution is 100 kΩ or more, The lithium-ion battery according to claim 1 or claim 2.

4. A restraining pressure of 0.01 MPa or more is applied to the laminate material, The lithium-ion battery according to claim 1 or claim 2.

5. A step of removing the part of the resin film of a packaging container including a laminate material obtained by laminating resin films on both sides of an aluminum foil by laser; A step of enclosing in the packaging container a positive electrode insulated from the aluminum foil, a negative electrode insulated from the aluminum foil, and an electrolytic solution containing lithium ions, and bringing the electrolytic solution into contact with the aluminum foil; A step of charging the potential of the negative electrode to 0.5 V or less with respect to Li / Li ＋ ; and A method for manufacturing a lithium-ion battery.

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