Lithium ion battery and production method for lithium ion battery

Abstract

[Problem] To suppress the generation of a LiAl alloy in an aluminum foil in a lithium ion battery in which the aluminum foil is used for a packaging container of an electrolytic solution. [Solution] A packaging container 10 includes a laminate material 11 in which a resin film 13 is laminated on both sides of an aluminum foil 12. A positive electrode 20 and a negative electrode 30 are sealed in the packaging container 10 and insulated from the aluminum foil 12. An electrolytic solution 50 is sealed in the packaging container 10, and contains lithium ions for conducting current between the positive electrode 20 and the negative electrode 30 during charging and discharging. A part of the resin film 13 is removed, and the aluminum foil 12 and the electrolytic solution 50 are in contact with each other. This lithium ion battery 1 is configured to be charged such that the negative electrode potential versus Li / Li+ is 0.5 V or less.

Description

Lithium-ion battery and method of manufacturing the same

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

[0002] For example, Patent Document 1 (Japanese Patent No. 6564188) discloses a lithium-ion battery whose exterior is a laminate material in which resin films are bonded to both sides of a metal foil. The laminate material may be made of aluminum foil.

[0003] Patent No. 6564188

[0004] In a lithium ion battery comprising an aluminum foil, a laminate material formed by laminating a resin film on both sides of the aluminum foil, and an electrolyte, the potential of the negative electrode is set to Li / Li ＋ Some lithium batteries are charged to 0.5 V or less relative to the negative electrode. For example, after injecting the electrolyte, an insulation test is conducted between the aluminum foil of the laminate material and the negative electrode, and batteries that pass the test are deemed to be good products. Therefore, a lithium-ion battery deemed to be good is one that has been tested to ensure that the aluminum foil and the electrolyte are separated and insulated by a resin film. However, with such lithium batteries, cracks may develop in the resin film that is in contact with the electrolyte over long periods of use. The cracks reduce the insulation resistance between the aluminum foil and the negative electrode, and if the cracks in the resin film of the laminate material are close to a component with a negative electrode potential, LiAl alloying of the aluminum foil may occur. If LiAl alloying of the aluminum foil progresses, holes may form in the aluminum foil, resulting in leakage.

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

[0006] A lithium ion battery according to a first aspect of the present invention comprises a packaging container, a positive electrode, a negative electrode, and an electrolyte. The packaging container includes a laminate material in which resin films are laminated on both sides of an aluminum foil. The positive electrode is sealed within the packaging container and is insulated from the aluminum foil. The negative electrode is sealed within the packaging container and is insulated from the aluminum foil. The electrolyte is sealed within the packaging container and contains lithium ions that conduct current between the positive electrode and the negative electrode during charging and discharging. A portion of the resin film is removed, bringing the aluminum foil into contact with the electrolyte. In this lithium ion battery, the potential of the negative electrode is Li / Li ＋ In the lithium ion battery according to the first aspect, the aluminum foil and the electrolyte are in contact with each other in the removed area where a part of the resin film is removed. In this lithium ion battery, the potential of the negative electrode is set to Li / Li ＋ However, since the aluminum foil and the electrolyte are in contact with each other in the removal area, the potential of the aluminum foil is less likely to drop to the potential at which the LiAl alloy is generated than in the conventional case where the removal area is not formed in the resin film.

[0007] A lithium ion battery according to a second aspect of the present invention is the lithium ion battery according to the first aspect, except that the resistance between the aluminum foil and the electrolyte is 1 MΩ or less. In the lithium ion battery according to the second aspect, even if the insulation resistance between the aluminum foil and the negative electrode decreases, the resistance between the aluminum foil and the electrolyte is likely to be maintained lower than the insulation resistance between the aluminum foil and the negative electrode. Even if the insulation resistance between the aluminum foil and the negative electrode decreases after manufacture, the possibility of the aluminum foil potential decreasing to a potential at which LiAl alloying occurs is reduced, thereby reducing the possibility of the aluminum foil potential decreasing to a potential at which LiAl alloying occurs. A lithium ion battery according to a third aspect of the present invention is the lithium ion battery according to the first or second aspect, except that the insulation resistance between the aluminum foil and the negative electrode before injection of the electrolyte is 100 kΩ or more. In the lithium ion battery according to the third aspect, the insulation resistance between the aluminum foil and the negative electrode before injection of the electrolyte is 100 kΩ or more, thereby further reducing the possibility of the aluminum foil potential decreasing to a potential at which LiAl alloying occurs. A lithium ion battery according to a fourth aspect of the present invention is the lithium ion battery according to the first or second aspect, wherein a confining 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 a confining pressure of 0.01 MPa or more to the laminate material to constrain it, for example, a module in which a plurality of lithium ion batteries are stacked can be firmly assembled.

[0008] A method for producing a lithium ion battery according to a fifth aspect of the present invention includes the steps of: removing a part of a resin film of a packaging container including a laminate material in which resin films are laminated on both sides of an aluminum foil, by using a laser; sealing a positive electrode insulated from the aluminum foil, a negative electrode insulated from the aluminum foil, and an electrolyte solution containing lithium ions in the packaging container, and bringing the electrolyte solution into contact with the aluminum foil; and heating the negative electrode so that the potential of the negative electrode becomes Li / Li ＋In the method for producing a lithium ion battery according to the fifth aspect, the aluminum foil and the electrolyte are in contact with each other in the removal area where a part of the resin film is removed by the laser. In such a lithium ion battery, the potential of the negative electrode is ＋ The aluminum foil is charged to 0.5 V or less relative to the surface of the battery, but since the aluminum foil and the electrolyte are in contact in the removal area, the potential of the aluminum foil is less likely to drop to the potential at which the LiAl alloy is generated, compared to conventional cases where no removal area is formed in the resin film. Furthermore, by removing the aluminum foil with a laser, mechanical damage to the aluminum foil is reduced, making it less likely for cracks to occur in the aluminum foil and the resin film outside the aluminum foil. As a result, the generation of defective products due to the removal of part of the resin film can be suppressed.

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

[0010] Fig. 1 is a perspective view showing an example of the configuration of a lithium ion battery according to an embodiment; Fig. 2 is a schematic cross-sectional view for explaining the configuration of a lithium ion battery according to an embodiment; Fig. 3 is an exploded perspective view for explaining the structure of the lithium ion battery of Fig. 1; Fig. 4 is a partially enlarged cross-sectional view for explaining a region where a resin film of a laminate material has been removed; Fig. 5 is a flowchart showing an outline of a method for manufacturing a lithium ion battery; Fig. 6 is a perspective view of a module in which a plurality of lithium ion batteries are stacked and restrained;

[0011] (1) Structure of 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 electrolyte 50 (see FIG. 2). As shown in 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. The packaging container 10 is constructed by bonding two laminate materials 11 together. The resin films 13 disposed on the inside of each laminate material 11 are heat-sealed to each other. The heat-sealed portions are portions of the resin film 13 disposed on the flange portion 10f of the packaging container 10. The resin film 13 can be, for example, a polyolefin film, a polyimide film, a polyamide film, or a polyester film. 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 also be a composite film formed by bonding together multiple types of films made of different materials. By bonding the two sheets of laminate material 11 together, a space for enclosing the positive electrode 20, the negative electrode 30, and the electrolyte solution 50 is formed in the area surrounded by the flange portion 10f. The electrolyte solution 50 is sealed in the packaging container 10. The electrolyte solution 50 contains lithium ions that conduct current between the positive electrode 20 and the negative electrode 30 during charging and discharging. The electrolyte solution 50 contains, for example, a lithium salt and an organic solvent (please modify as appropriate), and the lithium salt is, for example, lithium hexafluorophosphate (LiPF ６ ), LiClO ４ , LiBF ４ , LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６Examples of organic solvents that can be used in the electrolyte solution 50 include ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), 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. Note that, for ease of viewing and explanation, FIG. 2 shows a pair of the positive electrode 20 and the negative electrode 30 facing each other with a separator 40 sandwiched therebetween. The separator 40 can be, for example, a microporous membrane made of polyolefin or a nonwoven fabric made of cellulose. Examples of polyolefins that make up the microporous membrane include polyethylene (PE), polypropylene (PP), and polymethylpentene. Alternatively, a laminated separator composed of a porous layer primarily containing an inorganic filler can be used. However, unlike the structure shown in FIG. 2 , an actual lithium-ion battery 1 has multiple pairs of positive electrodes 20 and negative electrodes 30 stacked on top of each other. For example, 20 pairs of positive electrodes 20 and negative electrodes 30 are stacked on top of each other. A separator 40 is sandwiched between the positive electrodes 20 and negative electrodes 30, separating the positive electrodes 20 and negative electrodes 30. The lithium-ion battery 1 is stacked in the following order: 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 sealed in a packaging container 10. The positive electrode 20 and the negative electrode 30 are immersed in an electrolyte 50 in the packaging container 10. The positive electrode 20 and the negative electrode 30 are insulated from two sheets of aluminum foil 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 to the outside of the packaging container 10 from one side of the packaging container 10, which has a rectangular parallelepiped shape in a plan view. In FIG. 2, the positive electrode lead 21 and the negative electrode lead 31 are drawn in different directions, but this is a conceptual illustration for ease of understanding. Therefore, the actual structure of the lithium ion battery 1 is, for example, the structure shown in FIGS. 1 and 3. FIG. 3 shows the lithium ion battery 1 of FIG. 1 disassembled into two laminate materials 11 and a battery core 60. The battery core 60 includes multiple layers of positive electrodes 20, multiple 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 electrodes 20 and negative electrodes 30 to the positive electrode lead 21 and negative electrode lead 31 inside the lithium-ion battery 1. The current collector 70 is made of a metal foil such as copper foil.

[0013] As shown in FIGS. 3 and 4 , a portion of the resin film 13 of the laminate material 11 is removed, bringing the oxide film of the aluminum foil 12, for example, into contact with the electrolyte 50. The portions of the resin film 13 where the portions are removed are referred to as removal regions AR1 and AR2. The resin film 13 where the removal regions AR1 and AR2 are formed is located 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 becomes closer to the potential of the electrolyte 50 than when the removal regions AR1 and AR2 are not provided. When the removal regions AR1 and AR2 are not provided, the resistance between the aluminum foil 12 and the electrolyte 50 is maintained at a resistance value greater than, for example, 10 GΩ. With the removal regions AR1 and AR2, for example, if the potential of the electrolyte 50 is 1.3 V, the potential of the aluminum foil 12 also approaches 1.3 V. Therefore, even if the insulation resistance between the negative electrode 30 and the resin film 13 (or the aluminum foil 12) is reduced due to some factor, the aluminum foil 12 is likely to be maintained at a potential close to that of the electrolyte 50 by contacting the aluminum foil 12 with the electrolyte 50 in the removal regions AR1 and AR2. As a result, the potential of the aluminum foil 12 is less likely to drop to a potential at which the LiAl alloy advances, and through holes are less likely to form in the aluminum foil 12. The size of the removal regions AR1 and AR2 need only be large enough to allow the electrolyte to penetrate. The size of the removal regions AR1 and AR2 is preferably equal to or larger than the pores of the porous separator 40 used in the lithium-ion battery 1. The pore diameter may be, for example, 0.1 μm or larger. A pore diameter smaller than 0.1 μm makes it difficult for the electrolyte to penetrate. On the other hand, if the removal areas AR1 and AR2 are too large, they will likely come into contact with components with a negative electrode potential, so the size of the removal areas AR1 and AR2 is limited to a range that can sufficiently prevent contact with components with a negative electrode potential. The removal locations are preferably away from components with a negative electrode potential and in locations that are easily permeable by the electrolyte.The removal regions AR1 and AR2 are preferably disposed, for example, at positions closer to the positive electrode lead 21 than a point equidistant from the positive electrode lead 21, the negative electrode lead 31, and the laminate obtained by laminating the positive electrode 20 and the negative electrode 30. An example of the removal location is directly above the positive electrode lead 21, but depending on the external air pressure, mechanical stress may be applied to the removal regions AR1 and AR2, which may become a starting point for fracture. Therefore, the removal regions AR1 and AR2 are preferably disposed at positions closer to the positive electrode lead 21 than a point equidistant from the positive electrode lead 21, the negative electrode lead 31, and the laminate.

[0014] (2) Manufacturing Method of Lithium-Ion Battery A manufacturing method of the lithium-ion battery 1 will be described with reference to the flow shown in FIG. 5 . A positive electrode active material is formed on a metal foil to form a positive electrode 20 (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. As such a lithium-containing transition metal composite oxide having a layered structure, for example, lithium cobalt oxide (LiCoO ２ ), LiNiO ２ , LiNiCoMnO ２ , LiMn ２ O ４ , LiFePO ４ Examples of the negative electrode active material include lithium-containing transition metal composite oxides having a layered structure such as ... ６), silicon compounds, 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 sealed in a packaging container 10. A film-like insulator 15 is disposed between the laminate material 11 and the positive electrode lead 21 and negative electrode lead 31. The insulator 15 is, for example, a maleic anhydride-modified polypropylene film. In this assembly process (step S3), a portion of the resin film 13 of the laminate material 11 is removed, for example, by a laser, or the resin film 13 is cut with a blade. The laser used to remove the resin film 13 is preferably one with a wavelength (fundamental wavelength in the range of 1064 nm to 10600 nm) that is absorbed only by the resin without damaging the aluminum foil 12, such as CO ２ Laser marker, YVO ４ A laser marker is preferred. The incision with a blade is a half cut in which the blade is inserted to about the thickness of the resin film 13, and in particular, a half cut with a depth adjusted so that the blade is inserted into the laminate material 11 to the extent that it touches the aluminum foil 12 is preferred.

[0015] In the next pre-pouring inspection step (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 pre-pouring inspection step (step S4) is performed before the electrolyte 50 is poured 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 step, the resistance value is measured to confirm that the insulation resistance between the aluminum foil 12 and the negative electrode 30 is 100 kΩ or more. The electrolyte 50 is poured into the packaging container 10 and sealed in the packaging container 10. The electrolyte 50 is poured until it reaches the removal areas AR1 and AR2 of the resin film 13 (step S5). After the electrolyte 50 is poured, the packaging container 10 is sealed. In the post-pouring inspection process (step S6) after the injection of the electrolyte 50, at least the resistance between the aluminum foil 12 and the electrolyte 50 is measured. In the post-pouring inspection process (step S6), it is confirmed that the resistance between the aluminum foil 12 and the electrolyte 50 is 1 MΩ or less. The resistance between the aluminum foil 12 and the electrolyte 50 is measured by, for example, connecting a Hioki E.E. Corporation digital multimeter DM7275 and a 1 GΩ reference resistor in parallel with the digital multimeter's voltage probe. Using the measurement results, the resistance between the aluminum foil 12 and the electrolyte 50 can be calculated from an equivalent circuit. In the module 90 assembly process (step S7), as shown in FIG. 6 , multiple lithium-ion batteries 1 are stacked and restrained by restraining members 80. The restraining members include a first end plate 81, a second end plate 82, and, for example, four bolts 83 and four nuts 84. To prevent cracks from occurring in the laminate material 11, the multiple lithium-ion batteries 1 are stacked with their wide surfaces F1, F2 (see FIG. 4) facing each other. A confining pressure of 0.01 MPa or more is applied to each lithium-ion battery 1 in the assembled module 90. A buffer material may be provided between adjacent lithium-ion batteries 1. To apply the confining pressure, for example, a machine consisting of a frame on which an object to be loaded is placed, a cylinder for applying the load, and a load cell for measuring the load can be used.An example of such a machine is a universal testing machine. First, a first end plate 81 is placed on the fixed side (frame) of the machine, and a second end plate 82 is pressed against it with a predetermined confining pressure. While maintaining the predetermined confining pressure, bolts 83 are inserted into the elongated holes in the first end plate 81 and secured with nuts 84, connecting the first end plate 81 and the second end plate 82. After that, the load of the machine is released, and the first end plate 81 and the second end plate 82 maintain a confined state in which the predetermined confining pressure is applied to the multiple lithium-ion batteries 1. In the next charging step (step S8), the lithium-ion batteries 1 are charged. The potential of the negative electrode 30 of each lithium-ion battery 1 is Li / Li. + is charged to 0.5V or less.

[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 parts where the resin film 13 is removed are the removed areas AR1 and AR2 shown in FIG. 4. In the removed areas AR1 and AR2, the aluminum foil 12 and the electrolyte 50 are in contact with each other. In the lithium ion battery 1, the potential of the negative electrode 30 is Li / Li ＋ The aluminum foil 12 is charged to 0.5 V or less relative to the negative electrode 30. However, because the aluminum foil 12 and the electrolyte 50 are in contact with each other in the removed areas AR1 and AR2, the potential of the aluminum foil 12 is less likely to drop to the potential at which LiAl alloy formation occurs than in conventional cases where the removed areas AR1 and AR2 are not formed on the resin film 13. As a result, the occurrence of through holes in the aluminum foil 12 can be suppressed. (3-2) By keeping the resistance between the aluminum foil 12 and the electrolyte 50 at 1 MΩ or less, even if the insulation resistance between the aluminum foil 12 and the negative electrode 30 decreases, the resistance between the aluminum foil 12 and the electrolyte 50 is more likely to be kept lower than the insulation resistance between the aluminum foil 12 and the negative electrode 30. Even if the insulation resistance between the aluminum foil 12 and the negative electrode 30 decreases after manufacturing, the potential of the aluminum foil 12 is less likely to drop to the potential at which LiAl alloy formation occurs, thereby reducing the possibility of the potential of the aluminum foil 12 generating LiAl alloy.

[0017] (3-3) Because the insulation resistance between the aluminum foil 12 and the negative electrode 30 before the electrolyte 50 is injected is 100 kΩ or more, it is possible to further reduce the possibility that the potential of the aluminum foil 12 will drop to a potential at which LiAl alloys are generated. (3-4) As shown in Figure 6, because LiAl alloys are unlikely to be generated in the aluminum foil 12 due to cracks in the resin film 13, the module 90 can be firmly assembled by applying a constraining pressure of 0.01 MPa or more to the laminate material 11 to constrain it.

[0018] (3-5) As explained in the flowchart of FIG. 5, in the battery assembly process (step S3), a portion of the resin film 13 is removed by a laser. By removing it with a laser, mechanical damage to the aluminum foil 12 is reduced, so 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 the removal of a portion of the resin film 13 can be suppressed. Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the invention. In particular, the multiple embodiments and modifications described in this specification can be arbitrarily combined as needed.

[0019] REFERENCE SIGNS LIST 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 battery comprising: a packaging container including a laminate material in which a resin film is laminated on both sides of an aluminum foil; a positive electrode sealed in the packaging container and insulated from the aluminum foil; a negative electrode sealed in the packaging container and insulated from the aluminum foil; and an electrolyte solution containing lithium ions that is sealed in the packaging container and conducts current between the positive electrode and the negative electrode during charging and discharging; a part of the resin film is removed so that the aluminum foil and the electrolyte solution are in contact with each other; and the potential of the negative electrode is Li / Li ＋ The lithium ion battery is configured to be charged to 0.5V or less relative to the positive terminal of the battery.

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

3. The lithium ion battery according to claim 1 or 2, wherein an insulation resistance between the resin film and the negative electrode before the electrolyte is injected is 100 kΩ or more.

4. The lithium ion battery according to claim 1 or 2, wherein a confining pressure of 0.01 MPa or more is applied to the laminate material.

5. A process of removing the part of the resin film of a packaging container including a laminate material in which a resin film is laminated on both sides of an aluminum foil by using a laser; A process of sealing a positive electrode insulated from the aluminum foil, a negative electrode insulated from the aluminum foil, and an electrolyte containing lithium ions in the packaging container and bringing the electrolyte into contact with the aluminum foil; ＋ and charging the battery to 0.5 V or less.

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