Current collector for bipolar batteries

Abstract

When recycling bipolar lithium-ion secondary batteries, it is not easy to peel off the metal foils, such as aluminum or copper foils, that act as current collectors from the conductive adhesive layer. [Solution] The current collector for a bipolar battery comprises a first current collector foil, a second current collector foil, and a conductive adhesive layer, wherein the first current collector foil and the second current collector foil are bonded together via the conductive adhesive layer, satisfying the relationship: tensile strength of each of the first and second current collector foils × foil thickness > adhesive strength due to the conductive adhesive layer.

Description

[Technical Field]

[0001] The present disclosure relates to a current collector for a bipolar battery. [Background Art]

[0002] Patent Document 1 discloses that, as a method for producing a connecting member excellent in production efficiency, the thickness of a first metal base material and a second metal base material is preferably 1 µm (micrometer) or more and 200 µm or less, more preferably 3 µm or more and 100 µm or less, and still more preferably 6 µm or more and 50 µm or less, and as an example of the first metal base material, aluminum having a thickness of 50 µm and a conductive adhesive layer having an average thickness of 4.0 µm are disclosed.

[0003] On the other hand, for example, when recycling a bipolar lithium ion secondary battery, it is required to peel off a metal foil such as an aluminum foil or a copper foil that is a current collector foil from the conductive adhesive layer in the current collector. [Prior Art Literature] [Patent Literature]

[0004] [Patent Literature 1] Japanese Patent No. 7137251 [Summary of the Invention] [Problems to be Solved by the Invention]

[0005] However, since it is not easy to peel the metal foil from the conductive adhesive layer, for example, the metal foil may break and cannot be recovered as a recycled component in some cases.

[0006] The present disclosure has been made in view of the foregoing, and an object of the present disclosure is to more easily peel a metal foil from a conductive adhesive layer in a current collector for a bipolar battery. [Means for Solving the Problems]

[0007] The current collector for a bipolar battery according to this disclosure comprises a first current collector foil, a second current collector foil, and a conductive adhesive layer, wherein the first current collector foil and the second current collector foil are bonded together via the conductive adhesive layer, satisfying the relationship: tensile strength of the first current collector foil and the second current collector foil × foil thickness > adhesive strength of the conductive adhesive layer. [Effects of the Invention]

[0008] According to this disclosure, the metal foil can be more easily peeled off the conductive adhesive layer in the current collector for a bipolar battery. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of a current collector for a bipolar battery according to an embodiment. [Figure 2] Figure 2 shows the process of peeling the current collector foil from the conductive adhesive layer in a current collector for a bipolar battery according to the embodiment. [Figure 3] Figure 3 is a diagram illustrating the relationship between the conductive adhesive layer and the current collector foil in a current collector for a bipolar battery according to the embodiment. [Modes for carrying out the invention]

[0010] A current collector for a bipolar battery according to the embodiments of this disclosure will be described with reference to the drawings. Note that the components in the following embodiments include those that are easily substituted or substantially identical to those that are easily substituted by those skilled in the art.

[0011] A current collector for a bipolar battery according to an embodiment will now be described. The current collector for a bipolar battery according to the embodiment is, for example, a component of an energy storage module mounted on a vehicle. The vehicle on which the energy storage module is mounted is, for example, an electric vehicle (BEV: Battery Electric Vehicle), a hybrid vehicle (HEV: Hybrid Electric Vehicle), a plug-in hybrid vehicle (PHEV: Plug-in Hybrid Electric Vehicle), and the like.

[0012] Figure 1 is a schematic cross-sectional view showing an example of a current collector for a bipolar battery according to an embodiment. As shown in Figure 1, the current collector 1 for a bipolar battery comprises, for example, a current collector foil 11, a current collector foil 12, and a conductive adhesive layer 10. The current collector foil 11 and the current collector foil 12 are bonded together via the conductive adhesive layer 10.

[0013] The current collector foils 11 and 12 correspond to, for example, a first current collector foil and a second current collector foil, respectively. Furthermore, if the battery using the current collector 1 is a bipolar lithium-ion secondary battery, the current collector foils 11 and 12 are, for example, metal foils such as copper foil, copper alloy foil, nickel foil, aluminum foil, aluminum alloy foil, or stainless steel foil. Also, for example, if the current collector foil 11 is the positive electrode current collector foil, the current collector foil 11 may be aluminum foil, and the current collector foil 12, which is the negative electrode current collector foil, may be copper foil.

[0014] The conductive adhesive layer 10 is composed of a conductive adhesive, which is a mixture of an adhesive and a conductive component, but the material is not particularly limited. An example of such adhesive is a curable resin such as an olefin resin or an acrylic resin. The conductive component only needs to have higher conductivity than the adhesive and may include, for example, metal particles such as gold and silver, alloy particles such as aluminum-magnesium alloys, metal oxide particles such as tin oxide, metal particles such as nickel coated with precious metals such as platinum, non-conductive particles such as glass coated with precious metals, non-conductive particles such as plastic plated with metal, and carbon particles such as graphite.

[0015] Here, for example, when recycling a bipolar battery, the current collector 1 shown in Figure 1 requires the current collector foils 11 and 12 to be peeled off from the conductive adhesive layer 10.

[0016] FIG. 2 is a diagram showing how a current collector foil is peeled off from a conductive adhesive layer in a current collector for a bipolar battery according to an embodiment. As shown in FIG. 2, since the current collector foil 11 and the current collector foil 12 are adhered to the conductive adhesive layer 10, it is not easy to peel them off without breaking. Here, the breakage of the current collector foil 11 and the current collector foil 12 is caused, for example, by the relationship between the tensile strength and thickness of the current collector foil 11 or the current collector foil 12, and the adhesive strength of the conductive adhesive layer 10.

[0017] FIG. 3 is a diagram for explaining the relationship between a conductive adhesive layer and a current collector foil in a current collector for a bipolar battery according to an embodiment. As shown in FIG. 3, for example, the tensile strength TS [N / mm in each of the current collector foil 11 and the current collector foil 12 2 (Newton per square millimeter)] and the foil thickness t [mm], and the adhesive strength τ [N / mm] of the conductive adhesive layer 10 satisfy the relationship "TS×t>τ", breakage is less likely to occur when the current collector foil 11 or the current collector foil 12 is peeled off from the conductive adhesive layer 10.

[0018] Therefore, in the embodiment of the present disclosure, a current collector for a bipolar battery is configured such that the current collector foil 11, the current collector foil 12, and the conductive adhesive layer 10 satisfy the relationship of "TS×t>τ".

[0019] The strength of general aluminum foil (1000 series) is about 100N / mm 2 , and the strength of copper foil is about 250N / mm 2 . In addition, for the strength of general adhesives, for example, in the case of an epoxy / acrylic adhesive, the T-peel strength is about 2 to 4 N / mm (the peel strength is about 25N / mm 2 ).

[0020] Using these values (the maximum T-peel strength of 4N / mm is adopted), the thicknesses of the current collector foil 11 and the current collector foil 12 in which breakage is less likely to occur during peeling are specifically obtained. The thicknesses of the current collector foil 11 and the current collector foil 12 obtained here are the thickness of aluminum foil (1000 series), which is an example of a positive current collector foil, and copper foil, which is an example of a negative current collector foil, in a current collector for a bipolar-structured lithium ion secondary battery.

[0021] First, convert "TS×t>τ" to obtain "t>τ / TS". Substituting the respective values described above into this formula gives a thickness t>4 / 100 mm=40 μm for aluminum foil (1000 series) and a thickness t>4 / 250 mm=16 μm for copper foil. These thicknesses are the minimum required thicknesses at which breakage is unlikely to occur when peeled from the conductive adhesive layer 10. For reference, in the case of general lithium ion secondary batteries, for example, the thickness of aluminum foil, which is an example of a positive electrode current collector foil, is 10 to 15 μm, and the thickness of copper foil, which is an example of a negative electrode current collector foil, is 7 to 8 μm. These thicknesses are not more than half the minimum required thickness, and it can be seen that breakage easily occurs.

[0022] In consideration of workability during recycling operations and other factors, a safety factor such as 1.5 may be multiplied by the minimum required thickness. Further, for example, by using 3000-series aluminum foil, the minimum required thickness can be reduced. More specifically, the strength of 3000-series aluminum foil is about 150 N / mm 2 Therefore, the thickness t of 3000-series aluminum foil is t>4 / 150 mm=27 μm, so the thickness and the usage amount can be reduced compared to the minimum required thickness of 40 μm for 1000-series aluminum foil.

[0023] Further, when peeling the current collector foil 11 and the current collector foil 12 from the conductive adhesive layer 10, in consideration of workability for example, as shown in FIG. 2, there are cases where the current collector foil 11 and the current collector foil 12 in a state of being bonded to the conductive adhesive layer 10 are peeled off all at once. Therefore, by making the strength of the current collector foil 11 and the current collector foil 12 equal, the workability of such a peeling operation can be improved. That is, when the current collector foil 11 and the current collector foil 12 are aluminum foil (Al) and copper foil (Cu), respectively, by satisfying the relationship "tensile strength TS(Al) of aluminum foil × thickness t(Al) = tensile strength TS(Cu) of copper foil × thickness t(Cu)", the workability of the peeling operation can be improved.

[0024] More specifically, first, we transform "TS(Al)×t(Al)=TS(Cu)×t(Cu)" to "t(Al) / t(Cu)=TS(Cu) / TS(Al)". Then, for example, when using aluminum (1000 series), substituting the above values ​​into this formula, we get t(Al) / t(Cu)=250 / 100=2.5. In other words, for example, by configuring the current collector with a thickness ratio of 2.5 between the aluminum foil and copper foil of the 1000 series, the workability of the recycling process can be improved. Similarly, when using aluminum (3000 series), the thickness ratio is t(Al) / t(Cu)=150 / 100=1.5.

[0025] According to the current collector for a bipolar battery as described above, the current collector foils 11 and 12 and the conductive adhesive layer 10 of the current collector 1 are configured such that the relationship between the tensile strength of each of the current collector foils 11 and 12 × the thickness of the foil > the adhesive strength provided by the conductive adhesive layer 10 is satisfied. This makes it easier to peel the current collector foils 11 and 12 from the conductive adhesive layer 10.

[0026] Furthermore, according to the current collector for a bipolar battery according to the embodiment, the current collector foils 11 and 12 of the current collector 1 are configured such that the relationship tensile strength TS of current collector foil 11 × thickness = tensile strength TS of current collector foil 12 × thickness is satisfied. This improves the workability when peeling the current collector foils 11 and 12 from the conductive adhesive layer 10.

[0027] Further effects and modifications can be readily derived by those skilled in the art. Therefore, broader aspects of this disclosure are not limited to the specific details and representative embodiments expressed and described above. Accordingly, various modifications are possible without departing from the spirit or scope of the overall concept of the invention as defined by the appended claims and their equivalents. [Explanation of Symbols]

[0028] 1 Current collector 10 Conductive adhesive layer 11 Current collector foil 12 Current collector foil

Claims

[Claim 1] It comprises a first current collector foil, a second current collector foil, and a conductive adhesive layer. The first current collector foil and the second current collector foil are bonded together via the conductive adhesive layer. A current collector for a bipolar battery that satisfies the relationship: tensile strength in each of the first and second current collector foils × foil thickness > adhesive strength by the conductive adhesive layer.

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