Power storage module

Abstract

To provide a power storage module with excellent bonding strength between a current collector and a voltage detection terminal.SOLUTION: A power storage module includes: a current collector that includes a pair of metal foils, one of the metal foils being thicker than the other; and a metal terminal joined to the thicker one of the metal foils for detecting voltage.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an energy storage module. [Background technology]

[0002] Demand for secondary batteries as energy storage modules is expanding, and various types of secondary batteries are being considered. One example of a known secondary battery is a bipolar secondary battery, in which a current collector and multiple bipolar electrodes, each having a positive electrode disposed on one side of the current collector and a negative electrode disposed on the other side, are stacked so that the negative electrode and the positive electrode face each other with an electrolyte layer sandwiched therebetween. In secondary batteries, a conductive single-layer metal layer or a bonded current collector, in which a negative electrode current collector and a positive electrode current collector are bonded via a conductive adhesive layer, is used as the current collector.

[0003] In addition, a voltage detection terminal for detecting voltage may be connected to the current collector. For example, Patent Document 1 discloses a bipolar secondary battery having an adhesive layer that bonds either one of the positive electrode current collector and the negative electrode current collector to the voltage detection terminal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-061221 Summary of the Invention [Problem to be solved by the invention]

[0005] When detecting voltage through the current collector, it is desirable to ensure sufficient bonding strength between the current collector and the voltage detection terminal connected thereto.

[0006] An object of one embodiment of the present disclosure is to provide an electricity storage module having excellent bonding strength between a current collector and a voltage detection terminal. [Means for solving the problem]

[0007] Specific means for achieving the above object include the following aspects. <1> An energy storage module according to one embodiment of the present disclosure includes a pair of metal foils, one of which is a current collector thicker than the other of the pair of metal foils, and a metal terminal joined to one of the metal foils thicker than the other for detecting voltage.

[0008] An energy storage module according to one embodiment of the present disclosure includes a pair of metal foils (preferably a positive electrode foil and a negative electrode foil) serving as current collectors, each having a different thickness. A metal terminal for detecting voltage (hereinafter also referred to as a voltage detection terminal) is bonded to the thicker metal foil in the stacking direction of the pair of metal foils, thereby providing the voltage detection terminal on the thicker "one of the metal foils." With this configuration, when the current collector and the voltage detection terminal are joined by, for example, fusion welding or solid-state welding, the current collector and the voltage detection terminal can be joined by stacking the thin foil current collector, the thick foil current collector, and the voltage detection terminal in this order. A jig (rib) for fusion welding or solid-state welding can be inserted into the current collector from the thin foil side and brought close to the joining interface. This effectively improves the joining strength between the current collector and the voltage detection terminal, regardless of the material of the metal foil, compared to joining the voltage detection terminal to the thinner "other metal foil."

[0009] <2> The aforementioned <1> In the present invention, it is preferable that the current collector includes an adhesive layer disposed between the opposing surfaces of the pair of metal foils, and that one of the pair of metal foils, which is thicker than the other, has a lower hardness than the other metal foil.

[0010] An adhesive layer is provided between the pair of metal foils, and the hardness of one of the pair of metal foils, which is connected to the voltage detection terminal, is lower than the hardness of the other metal foil, so that the voltage detection terminal and the current collector are joined via the softer metal foil. When the pair of metal foils are firmly connected to each other and the current collector and the voltage detection terminal are connected by, for example, fusion welding or solid-state welding, the fluidity of the metal at the interface is improved, thereby further improving the bonding strength between the voltage detection terminal and the current collector.

[0011] <3> The aforementioned <1> or <2> In the above, the metal terminal and one of the metal foils having a thickness greater than that of the other metal foil are preferably fixed to each other by metallic bonding. <4> The aforementioned <3> In the above, it is more preferable that a fusion welded portion or a solid-state welded portion is provided between the metal terminal and one of the metal foils, which is thicker than the other, to form a metallic bond and fix the metal terminal to the other. <5> The aforementioned <4> In this case, the thickness of the fusion welded portion or solid-state welded portion is preferably 1 μm or less.

[0012] The metal bond between the current collector and the voltage detection terminal can be effectively improved by forming a metal bond by fusion welding or solid-state bonding, and the metal terminal and the "one metal foil" have a fusion welded portion or solid-state bonded portion, so that the current collector and the voltage detection terminal exhibit excellent bonding strength.

[0013] <6> The aforementioned <1> ~ <5> In any one of the above, the battery preferably has at least two bipolar electrodes including a current collector, a positive electrode active material layer disposed on one surface of the current collector, and a negative electrode active material layer disposed on the other surface of the current collector, and an electrolyte layer disposed between the negative electrode active material layer of one of the adjacent bipolar electrodes and the positive electrode active material layer of the other of the adjacent bipolar electrodes.

[0014] The present disclosure provides an electricity storage module having at least two bipolar electrodes stacked in the thickness direction, and a stacked structure of a negative electrode active material layer in one of two adjacent bipolar electrodes / an electrolyte layer / a positive electrode active material layer in the other of the two adjacent bipolar electrodes, in which the bonding strength between the current collector and the voltage detection terminal is more effectively improved. [Effects of the Invention]

[0015] According to one embodiment of the present disclosure, an energy storage module is provided that has excellent bonding strength between a current collector and a voltage detection terminal. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic cross-sectional view illustrating an example of an electricity storage module according to the present disclosure. [Figure 2] These are test pieces prepared for a test to confirm the effectiveness of the energy storage module according to the present disclosure. FIG. 2(A) shows a test piece according to Example 1, FIG. 2(B) shows a test piece according to Example 2, and FIG. 2(C) shows a test piece according to Comparative Example 1. [Figure 3] 10 is a graph showing the results of an effect confirmation test of the energy storage module according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0017] An energy storage module according to one embodiment of the present disclosure includes a pair of metal foils, one of which is a current collector thicker than the other of the pair of metal foils, and a metal terminal (voltage detection terminal) joined to one of the metal foils thicker than the other for detecting voltage. An electricity storage module according to an embodiment of the present disclosure is mounted on a vehicle such as an electric vehicle (BEV) or a hybrid electric vehicle (HEV), and is used as an in-vehicle power supply.

[0018] Hereinafter, a power storage module according to an embodiment will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view showing an example of an energy storage module according to the present disclosure. In Fig. 1, the arrow UP indicates the upper side in the vertical direction of the energy storage module, the arrow LH indicates the left side in the horizontal direction of the energy storage module, and the arrow D indicates the stacking direction of the bipolar batteries. The top of the energy storage module coincides with the top of a vehicle in which the energy storage module is mounted.

[0019] 1, the power storage module 10 is a secondary battery known as a bipolar battery, and has a rectangular shape with the stacking direction aligned with the vertical direction of the vehicle when mounted on the vehicle. The power storage module 10 may be, for example, a lithium-ion secondary battery, a nickel-metal hydride secondary battery, or the like.

[0020] The electricity storage module 10 includes current collectors 11, separators 40 that separate the current collectors 11, voltage detection terminals 50, and an electrolyte (not shown).

[0021] The current collector 11 is a laminated current collector (metal foil pair) formed by laminating a positive electrode current collector 21, which is an aluminum foil, and a negative electrode current collector 31, which is a copper foil. The current collector 11 is laminated with an adhesive layer (not shown) disposed between the opposing surfaces of the positive electrode current collector 21 and the negative electrode current collector 31.

[0022] The positive electrode current collector 21 and the negative electrode current collector 31 that make up the current collector 11 have a thickness relationship of positive electrode current collector 21 > negative electrode current collector 31, and the voltage detection terminal 50 is joined to the positive electrode current collector 21, which is thicker than the other. With this positional relationship, when joining the voltage detection terminal 50 to the current collector, a joining jig (a so-called rib shaped like a pyramid or the like) can be inserted into the current collector from the thin foil side and brought close to the joining interface, and therefore the joining strength between the current collector and the voltage detection terminal is improved regardless of the material of the metal foil compared to when the voltage detection terminal is joined to the negative electrode current collector 31 side, which is thinner. In the embodiment shown in FIG. 1, the thickness relationship is positive electrode current collector 21>negative electrode current collector 31, but the thickness relationship may be negative electrode current collector 31>positive electrode current collector 21.

[0023] Furthermore, the positive electrode current collector 21 and the negative electrode current collector 31 that make up the current collector 11 have a hardness relationship of positive electrode current collector 21 < negative electrode current collector 31, with the positive electrode current collector 21 that is joined to the voltage detection terminal being softer than the negative electrode current collector 31. This increases the fluidity of the metal at the interface between the voltage detection terminal and the current collector during joining, further improving the joining strength. In this disclosure, hardness is evaluated using a value expressed as Vickers hardness. Specifically, hardness is measured based on the area of ​​the indentation (indentation) created when a rigid diamond pyramid (indenter) is pressed into the test object.

[0024] The current collector 11 and the voltage detection terminal 50 are joined by fusion welding or solid-state welding, and a fusion weld or solid-state joint (not shown) is formed at the interface between the voltage detection terminal and the current collector. At the fusion weld or solid-state joint (not shown) between the voltage detection terminal and the current collector, the two are joined by a metallic bond, so the joint is strong.

[0025] Examples of the metal foil constituting the current collector 11 include aluminum foil, copper foil, nickel foil, titanium foil, and stainless steel foil. A coating layer may be formed on the surface of the current collector 11. The coating layer may be formed by a known method (for example, plating, spray coating, etc.). The thickness of the current collector 11 (the length in the direction of the arrow D) may be 1 μm to 100 μm. The positive electrode current collector 21 is preferably an aluminum foil, and the negative electrode current collector 31 is preferably a copper foil.

[0026] The positive electrode active material layer 22 is provided on the other surface of the positive electrode current collector 21 opposite to the one surface having the negative electrode current collector 31. The positive electrode active material layer 22 is formed on part of the other surface of the positive electrode current collector 21. The thickness of the positive electrode active material layer (length in the direction of arrow D) may be 2 μm to 500 μm.

[0027] The positive electrode active material layer 22 contains a positive electrode active material. The positive electrode active material is not particularly limited, and conventionally known materials can be appropriately used. Examples of the positive electrode active material include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. The positive electrode active material particles may be Hi-Nickel (a positive electrode active material with a high Ni ratio), a Li-Ni-Co-Mn-based composite oxide, or a ternary positive electrode active material.

[0028] The negative electrode active material layer 32 is provided on the other surface of the negative electrode current collector 31 opposite to the surface having the positive electrode current collector 21. The negative electrode active material layer 32 is formed on a part of the other surface of the negative electrode current collector 31. The thickness of the negative electrode active material layer (the length in the direction of arrow D) may be 2 μm to 500 μm, and may be the same as or different from the thickness of the positive electrode active material layer.

[0029] The negative electrode active material layer 32 contains a negative electrode active material. Examples of the negative electrode active material include natural graphite, artificial graphite, hard carbon (carbon with low graphitization property), or soft carbon (carbon with high graphitization property), Si, SiO x (0 < x < 2), Si-based alloy, Sn, SnO x (0 < x < 2), Li, Li-based alloy, and Li4Ti5O 12 At least one selected from the group consisting of can be mentioned. Examples of artificial graphite include highly oriented graphite, mesocarbon microbeads, etc. Artificial graphite is preferred as the negative electrode active material.

[0030] Each of the positive electrode active material layer and the negative electrode active material layer may further contain, as necessary, a conductive aid for improving electronic conductivity, a binder, an electrolyte supporting salt (lithium salt) for improving ionic conductivity, a polymer electrolyte, and additives (e.g., trifluoropropylene carbonate, a filler as a reinforcing material, etc.). Examples of conductive aids include carbon nanofibers, acetylene black, carbon black, and graphite. Examples of binders include fluorine-containing resins (e.g., polyvinylidene fluoride, polytetrafluoroethylene, fluororubber, etc.), thermoplastic resins (e.g., polypropylene, polyethylene, etc.), imide-based resins (e.g., polyimide, polyamide-imide, etc.), alkoxysilyl group-containing resins, acrylic resins (e.g., acrylic acid, methacrylic acid, etc.), styrene-butadiene rubber (SBR), carboxymethyl cellulose, alginates (e.g., sodium alginate, ammonium alginate, etc.), water-soluble cellulose ester crosslinked bodies, starch-acrylic acid glycol, etc. RAFT polymers, etc. These binders may be used alone or in combination.

[0031] The separator 40 is disposed between the positive electrode active material layer 22 and the negative electrode active material layer 32, and separates the current collectors 11 to prevent the occurrence of contact short circuits and to allow charge carriers such as lithium ions to pass through. The separator maintains a gap between the positive electrode active material layer and the negative electrode active material layer. Examples of the separator include a porous resin sheet or a nonwoven fabric. Examples of materials for the porous resin sheet include polyolefin (polypropylene, polyethylene, etc.) or polyester. Examples of materials for the nonwoven fabric include polypropylene, polyethylene terephthalate, or methylcellulose.

[0032] 1, the bipolar battery, which is the power storage module 10, is a laminate (laminate 12 in FIG. 1) in which a plurality of bipolar electrodes, each having a laminated structure of positive electrode active material layer 22 / current collector 11 (=positive electrode current collector 21 / negative electrode current collector 31) / negative electrode active material layer 32, are stacked in the direction of the arrow D with a separator 40 sandwiched between them. The bipolar electrode may have a known configuration.

[0033] The spacer 42 is formed in a frame shape so as to surround the periphery of the laminate 12. The spacer 42 can be formed in a frame shape, for example, by disposing a molten thermoplastic resin on the periphery of the laminate 12 and cooling it. The spacer 42 holds the peripheries of the positive electrode current collector 21, the negative electrode current collector 31, and the separator 40, and also seals the space S formed between the positive electrode current collector 21 and the negative electrode current collector 31. An electrolyte solution is injected into the space S, and the positive electrode active material layer 22, the negative electrode active material layer 32, and the separator 40 are impregnated with the electrolyte solution.

[0034] The voltage detection terminal 50 is a rectangular plate-shaped metal terminal disposed on the current collector 11, and is disposed at one end (the right end in FIG. 1) in the in-plane direction perpendicular to the arrow direction D of the bipolar electrode so as to protrude from the side of the laminate 12. The voltage detection terminal 50 is disposed on the positive electrode current collector 21 of the laminated current collectors forming the current collectors of the bipolar electrodes, and detects the voltage of each bipolar electrode. Specifically, the voltage of each cell is measured using voltage detection terminals attached to adjacent bipolar electrodes of the bipolar electrodes stacked in the arrow direction D. Examples of metals used for the voltage detection terminals include conductive materials such as stainless steel alloy (SUS), copper, aluminum, and gold.

[0035] The voltage sensing terminal may be suitably joined to the current collector by fusion welding or solid state welding. Examples of fusion welding methods include laser welding. Examples of solid-state joining methods include diffusion bonding, room-temperature bonding, ultrasonic bonding, and friction stir welding. Diffusion bonding is a method of integrating materials by heating them in a tightly contacted state. Room-temperature bonding is a method of integrating materials by activating the surfaces and then bringing them into close contact. Ultrasonic bonding is a method of integrating materials by applying ultrasonic vibrations and pressure. Friction stir welding is a method of integrating materials by pressing a rotating jig against the joint to induce plastic flow. Whether the material has been joined by fusion welding or solid-state welding can be determined by visually inspecting the fusion welded or solid-state welded joint or by checking the cross-sectional shape of the joint from a cross-sectional view. The fusion welded joint is a molten layer in which metals are mixed, and has a thickness of 20 nm to 300 nm. The thickness of the solid-state welded joint is 1 μm or less. The thickness of the fusion welded or solid-state welded joint is preferably 1 μm or less.

[0036] The voltage detection terminal 50 is connected to a voltage detection device by a lead wire (not shown). [Example]

[0037] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. Unless otherwise specified, "parts" are based on mass.

[0038] Example 1 A pair of metal foils was prepared: a positive electrode current collector 21, which was an Al foil with a thickness of 50 μm, and a negative electrode current collector 31, which was a Cu foil with a thickness of 8 μm. A current collector A having a laminated structure of Al foil / adhesive layer / Cu foil was fabricated. The thickness relationship was Al foil > Cu foil. An olefin-based resin containing epoxy was used for the adhesive layer. As shown in FIG. 2(A), a stainless steel terminal was placed on the main surface of the positive electrode current collector 21, which was thicker than the negative electrode current collector 31, of the current collector A. The current collector was then placed on the ultrasonic horn side connected to the ultrasonic vibrator, with the ribs (protrusions) on the horn side pressed inward from the negative electrode current collector 31. The stainless steel terminal was placed on the anvil side. The ultrasonic welding machine was operated under conditions of an amplitude (Ap-p) of 25-30 μm, a pressure of 200 N, and a frequency of 40 kHz, generating frictional heat at the interface and ultrasonically bonding the positive electrode current collector 21 / terminal interface. In this way, a test piece 10A was obtained in which the current collector and voltage detection terminal 50 were joined together with a solid-state weld.

[0039] Example 2 A pair of metal foils was prepared: a positive electrode current collector 21, which was an 8 μm-thick Al foil, and a negative electrode current collector 31, which was a 50 μm-thick Cu foil. A current collector B having a laminated structure of Al foil / adhesive layer / Cu foil was fabricated. The thickness relationship was Cu foil > Al foil. An olefin-based resin containing epoxy was used for the adhesive layer. As shown in FIG. 2(B), a stainless steel terminal was placed on the main surface of the negative electrode current collector 31, which was thicker than the positive electrode current collector 21, of the current collector B. The current collector was then placed on the ultrasonic horn side connected to the ultrasonic vibrator, with the ribs (protrusions) on the horn side pressed inward from the positive electrode current collector 21. A stainless steel terminal was placed on the anvil side. The ultrasonic welding machine was operated under conditions of an amplitude (Ap-p) of 25-30 μm, a pressure of 200 N, and a frequency of 40 kHz, generating frictional heat at the interface and ultrasonically bonding the positive electrode current collector 21 / terminal interface. In this way, a test piece 10B was obtained in which the current collector and voltage detection terminal 50 were joined together with a solid-state weld.

[0040] (Comparative Example 1) A comparative test piece 10C was obtained in the same manner as in Example 2, except that the positional relationship between the positive electrode current collector 21 and the negative electrode current collector 31 was changed.

[0041] (evaluation) (1)Hardness In Examples 1 and 2 and Comparative Example 1, the Al foil had a lower Vickers hardness and was softer than the Cu foil. (2)Join strength A voltage detection terminal 50 having a width of 5 mm and a length of 36 mm was joined to a collector 11 cut into a 40 mm square so as to overlap by 4.5 mm, and a tensile shear load was applied in a direction parallel to the joining interface at a tensile speed of 10 mm / min to measure the joining strength. The measurement results are shown in Figure 3. As is clear from Figure 3, test piece 10A and test piece 10B exhibited superior bonding strength compared to comparative test piece 10C. Among them, test piece 10A, in which Al foil, which is softer and has lower hardness than Cu foil, was arranged in a positional relationship of SUS terminal / Al foil / Cu foil, exhibited superior bonding strength. [Explanation of symbols]

[0042] 10 Energy storage module, 10A to 10C Test piece, 11 Current collector, 12 Laminate, 21 Positive electrode current collector, 22 Positive electrode active material layer, 31 Negative electrode current collector, 32 Negative electrode active material layer, 40 Separator, 42 Spacer, 50 Voltage detection terminal, D Stacking direction, S Space

Claims

1. a current collector including a pair of metal foils, one of which is thicker than the other; a metal terminal for detecting a voltage, the metal terminal being joined to one of the metal foils having a thickness greater than that of the other metal foil; A storage module equipped with

2. the current collector includes an adhesive layer disposed between opposing surfaces of the pair of metal foils, The energy storage module according to claim 1 , wherein the one metal foil that is thicker than the other metal foil has a lower hardness than the other metal foil.

3. 3 . The energy storage module according to claim 1 , wherein the metal terminal and one of the metal foils, which is thicker than the other, are fixed together by metallic bonding.

4. The energy storage module according to claim 3 , wherein the metal bond is formed by a fusion welded portion or a solid-state welded portion between the metal terminal and one of the metal foils that is thicker than the other metal foil.

5. The energy storage module according to claim 4 , wherein the fusion welded portion or the solid-state welded portion has a thickness of 1 μm or less.

6. at least two bipolar electrodes including the current collector, a positive electrode active material layer disposed on one surface of the current collector, and a negative electrode active material layer disposed on the other surface of the current collector; 3. The electricity storage module according to claim 1, further comprising an electrolyte layer disposed between the negative electrode active material layer of one of the adjacent bipolar electrodes and the positive electrode active material layer of the other of the adjacent bipolar electrodes.

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