Battery

Abstract

A battery is provided with: an electrode winding group that is a charge / discharge body and includes a positive electrode having a configuration in which positive electrode active material layers are formed on both surfaces of a positive electrode current collector, the positive electrode active material layers containing a positive electrode active material and a binder, and a negative electrode having a configuration in which positive electrode active material layers are formed on both surfaces of the positive electrode current collector; the adhesive comprises a first adhesive with relatively high peel strength and a second adhesive with relatively low peel strength, and the content of the second adhesive is higher than that of the first adhesive. As a result, it is possible to prevent breakage of the bent portion in the electrode winding group, and to improve the safety of the battery.

Description

Technical Field

[0001] This disclosure relates to a battery. Background Technology

[0002] In the automotive industry, countries and regions are strengthening fuel consumption and environmental regulations. To comply with these regulations, the development of technologies such as battery-powered electric vehicles that emit no carbon dioxide and fuel cells that use hydrogen as fuel has attracted much attention.

[0003] However, electric vehicles face challenges such as insufficient charging infrastructure and longer charging times compared to refueling. Fuel cell vehicles, on the other hand, face issues such as the enormous costs associated with building hydrogen station infrastructure and the high price of fuel cells.

[0004] Therefore, PHEVs (plug-in hybrid electric vehicles) and HEVs (hybrid electric vehicles), which use both internal combustion engines and batteries as power sources and emit less carbon dioxide, have become strong candidates for meeting fuel consumption and environmental regulations.

[0005] In PHEV or HEV, lithium-ion rechargeable batteries are used.

[0006] Patent Document 1 describes the following: A positive electrode plate for a lithium-ion secondary battery that is well bonded to the positive electrode current collector and the positive electrode active material layer and has low resistance of the positive electrode active material layer has a positive electrode active material layer containing a first binder composed of polyacrylic acid with a molecular weight of less than 50,000 and a second binder composed of polyacrylic acid with a molecular weight of more than 300,000 in a specified ratio.

[0007] Patent Document 2 describes a positive electrode for a non-aqueous electrolyte secondary battery that improves the characteristics of the battery while maintaining the flexibility of the positive electrode active material layer. The electrode comprises a positive electrode active material and a mixed adhesive comprising a first adhesive, a second adhesive, and a third adhesive. The first adhesive comprises one or more selected from polyvinylidene fluoride (PVDF), acid-modified PVDF, and copolymers containing acid-modified PVDF, and the proportion and tensile modulus of the first adhesive are set within a specified range. Furthermore, Patent Document 2 specifies that hydrogenated acrylonitrile butadiene rubber is preferred as the second adhesive, and a copolymer containing PVDF is preferred as the third adhesive.

[0008] Patent document 3 describes the following: A positive electrode for electrical equipment, used to improve the discharge voltage and rate characteristics of electrical equipment, comprises: a first adhesive composed of a vinylidene fluoride copolymer and a second adhesive composed of a vinylidene fluoride polymer. The first adhesive is in direct contact with the positive electrode active material, has a weight-average molecular weight of 300,000 to 400,000, and an intrinsic viscosity of 1.2 dL / g to 1.5 dL / g. The second adhesive is bonded to the first adhesive, has a weight-average molecular weight of 800,000 to 1,000,000, and an intrinsic viscosity of 2.0 dL / g to 3.0 dL / g.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2017-022020

[0012] Patent Document 2: Japanese Patent Application Publication No. 2017-147206

[0013] Patent Document 3: Japanese Patent Application Publication No. 2018-101472 Summary of the Invention

[0014] The problem the invention aims to solve

[0015] The positive electrode described in Patent Documents 1 and 3 does not involve mixing multiple adhesives from the viewpoint of preventing breakage when bent.

[0016] On the other hand, the positive electrode described in Patent Document 2 uses a mixture of three binders and has been evaluated from the viewpoints of capacity retention and flexibility. However, Patent Document 2 describes a second binder among the three binders that has the function of improving flexibility, but this may lead to a decrease in battery characteristics.

[0017] The purpose of this disclosure is to prevent breakage of the bent portion of the electrode winding and improve battery safety.

[0018] Problem-solving methods

[0019] The present disclosure discloses a battery comprising: an electrode winding assembly serving as a charge / discharge body, including a positive electrode, a negative electrode, and a separator disposed therebetween; the positive electrode having a configuration in which a positive electrode active material layer is formed on both surfaces of a positive electrode current collector; the positive electrode active material layer comprising a positive electrode active material and an adhesive; the adhesive comprising a first adhesive with relatively high peel strength and a second adhesive with relatively low peel strength, the content of the second adhesive being higher than that of the first adhesive.

[0020] The effects of the invention

[0021] According to this disclosure, it is possible to prevent the bending portion of the electrode winding from breaking, thereby improving battery safety. Attached Figure Description

[0022] Figure 1 This is a perspective view of the appearance of a lithium-ion secondary battery according to an embodiment.

[0023] Figure 2 It means built into Figure 1 A three-dimensional view of the charge / discharge mechanism in a lithium-ion secondary battery 1.

[0024] Figure 3 It is a local expansion representation Figure 2 A three-dimensional view of the charging and discharging body 100.

[0025] Figure 4 This is a cross-sectional view of a charge-discharge body, showing a partial embodiment of the winding process.

[0026] Figure 5A This is a partial cross-sectional view of the charge-discharge body of the comparative example.

[0027] Figure 5B This is a partial cross-sectional view of the charging and discharging body in an embodiment. Detailed Implementation

[0028] This disclosure relates to batteries used in various industrial equipment, and particularly to lithium-ion secondary batteries.

[0029] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the various drawings, the size and proportions of the constituent components are sometimes exaggerated for ease of understanding. In the various drawings, the same symbols are used to represent the same components. In the various drawings, arrows indicate the width direction X, depth direction Y, and height direction Z of the lithium-ion secondary battery and its constituent components. However, in the various drawings, the width direction X, depth direction Y, and height direction Z represent relative directional relationships. That is, for example, when the lithium-ion secondary battery is rotated 180 degrees to reverse the upper and lower surfaces, or when the lithium-ion secondary battery is rotated 90 degrees to make the upper surface a side surface, the width direction X, depth direction Y, and height direction Z of the lithium-ion secondary battery will change.

[0030] (The configuration of a lithium-ion secondary battery with a positive electrode according to the embodiment)

[0031] Reference Figures 1-4 The structure of a lithium-ion secondary battery with a positive electrode is explained in the embodiments.

[0032] Figure 1 This is a perspective view of the appearance of a lithium-ion secondary battery according to an embodiment.

[0033] In this figure, the lithium-ion secondary battery 1 has a configuration in which a charge / discharge element (not shown) is housed in a container consisting of a housing 201 and a cover 202. A positive terminal 301 and a negative terminal 302 are mounted on the cover 202 in an insulated manner. The cover 202 engages with the opening of the housing 201, sealing the charge / discharge element together with the housing 201.

[0034] In addition, when multiple lithium-ion secondary batteries 1 are used to form a battery pack, the positive terminal 301 of adjacent lithium-ion secondary batteries 1 and the negative terminal 302 of other adjacent lithium-ion secondary batteries 1 are connected via a busbar.

[0035] Figure 2 It means built into Figure 1 A three-dimensional view of the charge / discharge mechanism in a lithium-ion secondary battery 1.

[0036] Figure 2 The charge / discharge body 100 shown has a configuration in which a separator is sandwiched between the positive and negative electrodes. That is, the charge / discharge body 100 is an electrode winding assembly. The charge / discharge body 100 has a positive electrode tab 111b and a negative electrode tab 121b. The positive electrode tab 111b and... Figure 1 The positive terminal 301 is connected. The negative terminal tab 121b is connected to... Figure 1 The negative extreme of 302 is connected.

[0037] The charging / discharging body 100 is encapsulated Figure 1 In the state of the lithium-ion secondary battery 1, electrolyte is injected through the injection port provided on the cover 202. Thus, the charge / discharge body 100 is immersed in the electrolyte. After the electrolyte is injected, the injection port is sealed with an injection plug. The electrolyte includes an organic solvent, a supporting salt, and additives. The organic solvent may be, for example, carbonate. The supporting salt may be, for example, lithium salt. The additives include materials for forming a negative electrode coating. The material for forming the negative electrode coating may be, for example, vinylene carbonate.

[0038] In another example of a lithium-ion secondary battery, the minimum radius of curvature of the innermost circumference of the positive electrode of the electrode winding is 0.46 mm.

[0039] Figure 3 It indicates partial expansion. Figure 2 A three-dimensional view of the charging and discharging body 100.

[0040] like Figure 3 As shown, the positive electrode 110, negative electrode 120, and separator 130 constituting the charging / discharging body are each formed as an elongated strip extending along the X-axis direction. A positive electrode tab 111b is provided on the positive electrode 110. A negative electrode tab 121b is provided on the negative electrode 120. The positive electrode tab 111b and the negative electrode tab 121b protrude in the same direction (positive Z-axis direction).

[0041] A separator 130 is sandwiched between the positive electrode 110 and the negative electrode 120. Furthermore, to prevent direct contact between the positive electrode 110 and the negative electrode 120 during winding, a separator 130 is also disposed on the opposite side of the negative electrode 120. In other words, in this figure, the negative electrode 120 is sandwiched between two separators 130. The separator 130 insulates the positive electrode 110 and the negative electrode 120. Lithium ions pass through the separator 130 via the electrolyte.

[0042] Compared to the positive electrode current collector of the positive electrode 110, the negative electrode current collector of the negative electrode 120 is wider in the short side direction (Z-axis direction). Compared to the positive electrode 110 and the negative electrode 120, the separator 130 is also wider in the short side direction (Z-axis direction).

[0043] Figure 4 This is a cross-sectional view of a charge-discharge body, showing a partial embodiment of the winding process.

[0044] The figure shows a charge / discharge body manufactured by winding a strip-shaped positive electrode 110, a negative electrode 120, and a separator 130 around a core 40. The negative electrode 120 is in direct contact with the core 40. The separator 130 and the positive electrode 110 are sequentially arranged on the outside of the negative electrode 120. The separator 130 and the negative electrode 120 are sequentially arranged on the outside of the positive electrode 110.

[0045] The positive electrode 110 has a positive active material layer formed on both surfaces of the positive current collector 115. The negative electrode 120 has a negative active material layer formed on both surfaces of the negative current collector.

[0046] The positive electrode active material layer comprises a positive electrode active material and a binder. Additionally, the positive electrode active material layer preferably also contains a conductive additive and a dispersant.

[0047] Here, the defects in the charge / discharge mechanism of the comparative example lithium-ion secondary battery will be described.

[0048] Figure 5A This is a partial cross-sectional view of the charge-discharge body of the comparative example.

[0049] In this diagram, other components are omitted to represent the state of the positive electrode 110 being broken.

[0050] Tensile stress is applied along the length of the positive electrode 110 wound around the shaft. As a result, the positive current collector and the positive active material layer constituting the positive electrode 110, which are sometimes located on the outer side of the end of the shaft, eventually break.

[0051] Example

[0052] Figure 5B This is a partial cross-sectional view of the charging and discharging body in an embodiment.

[0053] In this diagram, with Figure 5ASimilarly, the components other than the positive electrode 110 are omitted.

[0054] like Figure 5B As shown, in the charging / discharging body of the embodiment, compressive stress caused by bending is applied to the positive electrode active material layer on the axial side of the positive electrode 110, causing the axial side of the positive electrode active material layer to buckle and partially peel off. This reduces the tensile stress applied to the positive electrode current collector and the outer positive electrode active material layer, preventing the overall breakage of the positive electrode 110.

[0055] Next, the positive electrode, negative electrode, and separator used in the battery of the embodiment will be described.

[0056] Regarding the positive electrode, NCM622 (Li) is used. 1.05 Ni 0.6 Co 0.2 Mn 0.2 O2) is used as the positive electrode active material, acetylene black is used as the conductive material particle, and aluminum foil (13.3 μm thick) is used as the current collector. Furthermore, as the binder, Kureha KF polymer W#9700 (Modified polymer, Mw=8.8×10⁻⁶) manufactured by Kureha Co., Ltd. is used. 5 g / mol) and Wu Yu KF polymer W#1100 (Homo-polymer, Mw=2.8×10) 5 These two types (g / mol)

[0057] The particle size (median particle size D50) of the positive electrode active material NCM622 is 13.3 μm. Furthermore, the positive electrode active material NCM622 is a mixture of positive electrode active material with a large particle size (median particle size D50) of 17 μm and positive electrode active material with a small particle size (median particle size D50) of 4.6 μm at a mass ratio of 7:3. The particle size was determined by laser diffraction scattering.

[0058] Furthermore, mixing positive electrode active materials with different particle sizes is one method for achieving high-density positive electrodes. However, when mixing positive electrode active materials with different particle sizes, if high-density formation is achieved through stamping during positive electrode fabrication, deformation such as ripples may sometimes occur in the aluminum foil of the current collector. Such deformation is considered to lead to a decrease in foil strength. Therefore, to prevent this situation, the inventors conducted in-depth research and found that using the two adhesives disclosed herein is effective.

[0059] Regarding peel strength, Kureha KF polymer W#9700 exhibits 5.2–5.5 gf / mm at an electrode density of 3.0–3.4 g / ml, while Kureha KF polymer W#1100 exhibits 0.7–1.5 gf / mm at an electrode density of 3.0–3.8 g / ml. Here, Kureha KF polymer W#9700, with its relatively high peel strength, acts as the "first adhesive," while Kureha KF polymer W#1100, with its relatively low peel strength, acts as the "second adhesive." Here, electrode density refers to the density of the positive electrode active material layer.

[0060] The molecular weight (Mw) of the adhesive, in the case of the first adhesive, is preferably 7.8 × 10⁻⁶. 5 ~9.8×10 5 g / mol, more preferably 8.3 × 10 g / mol. 5 ~9.3×10 5 g / mol. Additionally, in the case of a second binder, 1.8 × 10⁻⁶ g / mol is preferred. 5 ~3.8×10 5 g / mol, more preferably 2.7 × 10 g / mol. 5 ~2.9×10 5 g / mol.

[0061] In addition, the method for determining peel strength is as follows: using a rubber roller, an adhesive tape (18 mm wide) conforming to JIS Z1522 is pasted onto the surface of the adhesive, which is adhered to the aluminum or copper foil that serves as a current collector. A test is then conducted using a force gauge to peel the adhesive tape (the force gauge moves at a speed of 5 mm / sec and the load angle is 180 degrees).

[0062] The two adhesives mentioned above are vinylidene fluoride resins, which are generally considered to cause less reduction in battery characteristics.

[0063] The negative electrode uses graphite as the negative electrode active material, acrylic-based materials as binders, and copper foil (8μm thick) as the current collector.

[0064] The diaphragm is made of polypropylene resin sheets. Alternatively, the diaphragm can also be made of other materials such as polyethylene resin.

[0065] Generally, adhesives with high flexibility have low adhesion, while adhesives with high adhesion have low flexibility. Therefore, it is preferable to use both in combination. By using both, it is possible to achieve high density of the positive electrode, suppression of deformation of the aluminum foil as a current collector, and improvement of peel strength.

[0066] The preferred density of the positive electrode active material layer is 3.30 g / cm³. 3 The above 3.72g / cm 3 the following.

[0067] The adhesive consists of a first adhesive with relatively high peel strength and a second adhesive with relatively low peel strength.

[0068] The content of the second adhesive is higher than the content of the first adhesive. When the proportion of the second adhesive is lower than the proportion of the first adhesive, it is possible to produce… Figure 5A The positive electrode 110 shown is broken.

[0069] Based on weight, the mixing ratio of the first adhesive to the second adhesive is preferably 1:9 to 3:7, more preferably 1.5:8.5 to 2.5:7.5. In other words, it is preferably in the range of 1 part by weight of the first adhesive and 9 parts by weight of the second adhesive to 3 parts by weight of the first adhesive and 7 parts by weight of the second adhesive, more preferably in the range of 1.5 parts by weight of the first adhesive and 8.5 parts by weight of the second adhesive to 2.5 parts by weight of the first adhesive and 7.5 parts by weight of the second adhesive.

[0070] The positive electrode active material layer preferably contains 98.2 to 98.7 parts by weight of positive electrode active material and 0.5 to 1.0 parts by weight of binder.

[0071] Finally, the effects of this disclosure will be explained in detail.

[0072] According to this disclosure, by using less adhesive to reduce battery characteristics, it is possible to prevent breakage of the bent portion of the positive electrode located on the innermost side of the electrode winding assembly, thereby improving battery safety.

[0073] Furthermore, according to this disclosure, a small buckling is generated with a weak force at the bending portion of the positive electrode located at the innermost side of the electrode winding assembly, that is, a portion of the positive electrode active material layer on the inner circumference side of the positive electrode is peeled off, thereby preventing large breakage.

[0074] Explanation of symbols

[0075] 1: Lithium-ion secondary battery; 40: Core; 100: Charge / discharge body; 110: Positive electrode; 111b: Positive electrode tab; 115: Positive current collector; 120: Negative electrode; 121b: Negative electrode tab; 130: Separator; 201: Outer casing; 202: Cover; 301: Positive terminal; 302: Negative terminal.

Claims

1. A battery, characterized in that, have: The electrode winding assembly, which is a charge / discharge body, includes a positive electrode, a negative electrode, and a separator disposed between them. The positive electrode has a structure in which positive electrode active material layers are formed on both surfaces of the positive electrode current collector. The positive electrode active material layer comprises a positive electrode active material and a binder. The adhesive comprises a first adhesive with relatively high peel strength and a second adhesive with relatively low peel strength. The content of the second adhesive is higher than that of the first adhesive.

2. The battery according to claim 1, characterized in that, The mixing ratio of the first adhesive to the second adhesive is 1:9 to 3:7 by weight.

3. The battery according to claim 1 or 2, characterized in that, The positive electrode active material layer contains 98.2 to 98.7 parts by weight of the positive electrode active material and 0.5 to 1.0 parts by weight of the binder.

4. The battery according to claim 1 or 2, characterized in that, The positive electrode active material layer also contains conductive additives and dispersants.

5. The battery according to claim 1 or 2, characterized in that, The first adhesive and the second adhesive are vinylidene fluoride resins.

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