Secondary battery and manufacturing method of the secondary battery

Abstract

To provide a secondary battery capable of suppressing an uneven distribution of a conductivity material of a positive electrode plate, and provide a manufacturing method of the secondary battery.SOLUTION: A secondary battery 1 contains: a first positive electrode mixture that is positioned to a collector 20 side; and a second positive electrode mixture that is positioned to a front layer side of a first positive plate 10. The first positive electrode mixture contains: a first active material having a hollow structure; and a fibrous conductive material. The first active material includes at least a first penetration hole penetrated to a front surface of the first active material. A size of at least the first penetration hole is larger than the size of a radial direction of the fibrous conductive material. The second positive electrode mixture contains: a second active material; and the fibrous conductive material. The second active material does not include a penetration hole that penetrates the front layer of the second active material, or includes a second penetration hole of the second active material. The size of the second penetration hole of the second active material is less than the size of the radial direction of the fibrous conductive material.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present disclosure relates to a secondary battery and a method for manufacturing the secondary battery.

Background Art

[0002] Currently, in electric vehicles, hybrid vehicles, plug-in hybrid vehicles, etc., secondary batteries such as lithium-ion batteries are adopted. Among such secondary batteries, there are those provided with a positive electrode plate containing a fibrous conductive material. In the manufacturing process of the positive electrode plate, usually, a mixture containing a fibrous conductive material is applied to a current collector and then dried. At this time, depending on the drying temperature, the fibrous conductive material may move to the surface layer side of the positive electrode plate and be unevenly distributed, which may deteriorate the conductive performance of the positive electrode.

[0003] Regarding this point, Patent Document 1 discloses a secondary battery including an electrode having a current collector, a particulate conductive material, and active material particles having a hollow portion. In this secondary battery, the particulate conductive material can move into the hollow portion of the active material particles through the through-holes of the active material particles.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the secondary battery disclosed in Patent Document 1, since the conductive material also enters the active material particles on the surface layer side of the electrode, when the conductive material existing on the current collector side moves to the surface layer side of the electrode, the conductive material may be unevenly distributed on the surface layer side of the electrode.

[0006] The present disclosure is for solving such problems, and an object thereof is to provide a secondary battery and a method for manufacturing the secondary battery capable of suppressing uneven distribution of the conductive material in the positive electrode plate.

Means for Solving the Problem

[0007] In a secondary battery including a positive electrode plate having a positive electrode composite material on a current collector according to the present disclosure, the positive electrode composite material includes a first positive electrode composite material located on the current collector side and a second positive electrode composite material located on the surface layer side of the positive electrode plate. The first positive electrode composite material includes a first active material having a hollow structure and a fibrous conductive material. The first active material has at least one first through hole penetrating the surface layer of the first active material. The size of at least one first through hole is larger than the radial size of the fibrous conductive material. The second positive electrode composite material includes a second active material and a fibrous conductive material. The second active material does not have a through hole penetrating the surface layer of the second active material, or has a second through hole penetrating the surface layer of the second active material. The size of the second through hole of the second active material is less than the radial size of the fibrous conductive material.

[0008] The ratio of the thickness of the first positive electrode composite material to the thickness of the second positive electrode composite material can be in the range of 10:1 to 1:10.

[0009] The size of at least one first through hole is in the range of 2 to 2000 nm. The radial size of the fibrous conductive material can be in the range of 1.5 to 100 nm.

[0010] The fibrous conductive material can be a carbon-based fibrous conductive material.

[0011] A method for manufacturing a secondary battery according to the present disclosure includes a first coating step of coating a first positive electrode composite material on a current collector, and a second coating step of coating a second positive electrode composite material on the first positive electrode composite material coated on the current collector. The first positive electrode composite material includes a first active material having a hollow structure and a fibrous conductive material. The first active material has at least one first through-hole penetrating the surface layer of the first active material, the size of the at least one first through-hole is larger than the radial size of the fibrous conductive material, The second positive electrode composite material includes a second active material and a fibrous conductive material. The second active material either has no through-hole penetrating the surface layer of the second active material or has a second through-hole penetrating the surface layer of the second active material. The size of the second through-hole of the second active material is less than the radial size of the fibrous conductive material.

[0012] The method for manufacturing a secondary battery according to the present disclosure further includes a drying step of drying the first positive electrode composite material applied to the current collector and the second positive electrode composite material applied to the first positive electrode composite material. When the temperature for drying the first positive electrode composite material and the second positive electrode composite material in the drying step is within the range of 120 to 150 °C, the ratio of the thickness of the first positive electrode composite material to the thickness of the second positive electrode composite material is within the range of 10:1 to 1:1. In the first coating step and the second coating step, the first positive electrode composite material and the second positive electrode composite material can be respectively coated.

[0013] The method for manufacturing a secondary battery according to the present disclosure further includes a drying step of drying the first positive electrode composite material applied to the current collector and the second positive electrode composite material applied to the first positive electrode composite material. When the temperature for drying the first positive electrode composite material and the second positive electrode composite material in the drying step is within the range of 150 to 180 °C, the ratio of the thickness of the first positive electrode composite material to the thickness of the second positive electrode composite material is within the range of 1:1 to 1:10. In the first coating step and the second coating step, the first positive electrode composite material and the second positive electrode composite material can be respectively coated.

Advantages of the Invention

[0014] According to the present disclosure, it is possible to provide a secondary battery and a method for manufacturing a secondary battery that can suppress the uneven distribution of the conductive material in the positive electrode plate.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0016] Hereinafter, an embodiment according to the present disclosure will be described with reference to the drawings. FIG. 1 is a diagram showing an example of a secondary battery 1 according to an embodiment. The secondary battery 1 includes a battery case 2 and an electrode body (not shown) housed in the battery case 2. The width direction shown in the figure indicates the width direction of the secondary battery 1 and the electrode body. The thickness direction indicates the thickness direction of the secondary battery 1 and the electrode body.

[0017] FIG. 2 is a diagram showing an example of an electrode body 3 according to an embodiment. The electrode body 3 is formed by laminating and winding a positive electrode plate, a negative electrode plate, and a separator that insulates the positive electrode plate and the negative electrode plate.

[0018] FIG. 3 is a diagram showing a manufacturing method of a secondary battery according to an embodiment. The manufacturing method of the secondary battery includes a positive electrode plate manufacturing step of manufacturing a positive electrode plate. The positive electrode plate manufacturing step includes a first coating step S1, a second coating step S2, a drying step S3, and a pressing step S4.

[0019] The first coating step S1 is a step of coating both sides of a current collector such as an aluminum foil with a first positive electrode composite material. The first positive electrode composite material includes a first active material having a hollow structure, a fibrous conductive material, and a binder. The first active material included in the first positive electrode composite material has at least one first through hole penetrating the surface layer of the first active material. The size of at least one first through hole is larger than the radial size of the fibrous conductive material. For example, when the size PD of the through hole of the first active material is in the range of 10 to 100 nm, the radial size FD of the fibrous conductive material can be in the range of 1.5 to 10 nm. The fibrous conductive material can be the volume accommodated in the first active material. In this case, the axial length of the fibrous conductive material is the length accommodated in the first active material. Note that the fibrous conductive material may have a volume in which, for example, more than 50% of its main part is accommodated in the first active material.

[0020] FIG. 4 is a schematic perspective view showing the first active material employed in this embodiment. In this figure, a through hole of the first active material having a size PD is shown.

[0021] FIG. 5 is a schematic cross-sectional view showing a cross section of the first active material. The shape of the through hole of the first active material is not a fixed geometric shape and can take various shapes. Therefore, in this embodiment, the size PD of the through hole of the first active material is the minimum width of the through hole.

[0022] The fibrous conductive material is a fibrous material having conductivity. Specific examples of the fibrous conductive material include carbon-based fibrous conductive materials such as carbon nanotubes (CNT) and carbon nanofibers. FIG. 6 is an electron micrograph of an example of CNT employed in this embodiment. The upper electron micrograph in FIG. 6 shows a plurality of CNTs. The lower electron micrograph in FIG. 6 is an enlarged photograph within the white line frame in the upper electron micrograph. The enlarged photograph shows the radial size FD of the fibrous conductive material. FD corresponds to the diameter of the fibrous conductive material.

[0023] The second coating step S2 is a step of coating a second positive electrode composite material on the first positive electrode composite material coated on the current collector. The second positive electrode composite material includes a second active material, a fibrous conductive material, and a binder. As the second active material, an active material having no second through-hole penetrating the surface layer of the second active material can be employed. Alternatively, as the second active material, an active material having a second through-hole penetrating the surface layer of the second active material can be employed. In this case, the size of the second through-hole of the second active material is less than the radial size of the fibrous conductive material. In other words, the size of the second through-hole of the second active material is less than the diameter of the fibrous conductive material.

[0024] FIG. 7 is a schematic cross-sectional view showing a cross-section of the positive electrode plate 10 according to an embodiment. As shown in FIG. 7, the positive electrode composite material of the positive electrode plate 10 is composed of a first positive electrode composite material layer located on the current collector 20 side and a second positive electrode composite material layer located on the surface layer side of the positive electrode plate 10.

[0025] The drying step S3 is a step of drying the positive electrode plate having the first positive electrode composite material and the second positive electrode composite material. It is preferable to adopt a temperature for drying the positive electrode plate according to the ratio of the thickness of the first positive electrode composite material to the thickness of the second positive electrode composite material. Conversely, it is preferable to select a ratio of the thickness of the first positive electrode composite material to the thickness of the second positive electrode composite material according to the temperature for drying the positive electrode plate.

[0026] Specifically, when the temperature for drying the first positive electrode composite material and the second positive electrode composite material in the drying step S3 is in the range of 120 to 150 ° C, it is preferable to coat the first positive electrode composite material and the second positive electrode composite material, respectively, in the first coating step and the second coating step so that the ratio of the thickness of the first positive electrode composite material to the thickness of the second positive electrode composite material is in the range of 10:1 to 1:1.

[0027] In addition, when the temperature for drying the first positive electrode composite material and the second positive electrode composite material in the drying step S3 is within the range of 150 to 180°C, in the first coating step and the second coating step, the first positive electrode composite material and the second positive electrode composite material are respectively coated such that the ratio of the thickness of the first positive electrode composite material to the thickness of the second positive electrode composite material is within the range of 1:1 to 1:10.

[0028] The pressing step S4 is a step of pressing the positive electrode plate dried in the drying step S3 with a pressing member such as a pressing roller.

[0029] FIG. 8 is a diagram showing the measurement results of the through-resistance of the positive electrode plate of the present embodiment and the positive electrode plates of two comparative examples. In this measurement test, as the fibrous conductive material, CNTs with a radial size FD of 20 nm were adopted. In addition, polyvinylidene fluoride (PVDF) was adopted as the binder.

[0030] In this measurement test, as the first active material of the first positive electrode composite material of the present embodiment, a first active material with a through-hole size PD of 100 nm was adopted. In addition, as the second active material of the second positive electrode composite material of the present embodiment, a second active material with a through-hole size PD of 10 nm was adopted.

[0031] For the first positive electrode composite material of the present embodiment, the mixing ratio of the first active material, CNT, and binder was 98.5:0.5:1. Similarly, for the second positive electrode composite material of the present embodiment, the mixing ratio of the second active material, CNT, and binder was 98.5:0.5:1. Note that the mixing ratio of the positive electrode composite material of the present embodiment is not limited to these values.

[0032] The positive electrode plate of Comparative Example 1 was produced by coating a single layer of positive electrode composite material on both sides of the current collector. As the active material of the positive electrode composite material of Comparative Example 1, an active material with a through-hole size PD of 10 nm was adopted. The positive electrode composite material of Comparative Example 1 had a mixing ratio of active material, CNT, and binder of 98.5:0.5:1.

[0033] Similarly, the positive electrode plate of Comparative Example 2 was fabricated by applying a single layer of positive electrode mixture on both sides of the current collector. As the active material of the positive electrode mixture of Comparative Example 2, an active material with a pore size PD of 100 nm was adopted. The mixing ratio of the active material, CNT, and binder in the positive electrode mixture of Comparative Example 1 was 98.5:0.5:1.

[0034] After fabricating three positive electrode plates of the present embodiment, three positive electrode plates of Comparative Example 1, and three positive electrode plates of Comparative Example 2 respectively, in the drying process, they were dried at 120 °C, 150 °C, and 180 °C. Subsequently, these dried positive electrode plates were pressed in the pressing process so that the mixture density became 2.5 g / ml (cc). Note that the mixture density of the positive electrode mixture of the present embodiment is not limited to this value.

[0035] As a result of measuring the through-resistance of the positive electrode plates of the present embodiment, the positive electrode plates of Comparative Example 1, and the positive electrode plates of Comparative Example 2, it was found that for the positive electrode plates with drying temperatures of 150 °C and 180 °C, the positive electrode plate of the present embodiment had the smallest through-resistance. From this, it can be seen that in the positive electrode plate of the present embodiment, the uneven distribution of CNT due to migration was suppressed, and the increase in through-resistance was suppressed.

[0036] On the other hand, for the positive electrode plates with a drying temperature of 120 °C, it was found that the positive electrode plate of Comparative Example 1 had the smallest through-resistance, followed by the positive electrode plate of the present embodiment, and the difference in these through-resistances was slight.

[0037] Also, it was found that the positive electrode plate of the present embodiment had a smaller through-resistance at all drying temperatures compared to the positive electrode plate of Comparative Example 2 composed of a single layer of positive electrode mixture (PD = 100 nm). From this, it was found that the configuration with the first positive electrode mixture (PD = 100 nm) on the current collector side and the second positive electrode mixture (PD = 10 nm) on the surface layer side of the positive electrode plate was more advantageous.

[0038] As described above, the secondary battery 1 includes a positive electrode plate 10 having a positive electrode mixture on a current collector 20. The positive electrode mixture includes a first positive electrode mixture located on the current collector 20 side and a second positive electrode mixture located on the surface layer side of the positive electrode plate 10. The first positive electrode mixture includes a first active material having a hollow structure and a fibrous conductive material. The first active material has at least one first through hole penetrating the surface layer of the first active material. The size of at least one first through hole is larger than the radial size of the fibrous conductive material. The second positive electrode mixture includes a second active material and a fibrous conductive material. The second active material does not have a through hole penetrating the surface layer of the second active material, or has a second through hole penetrating the surface layer of the second active material. The size of the second through hole of the second active material is less than the radial size of the fibrous conductive material.

[0039] By adopting this configuration, the fibrous conductive material located on the current collector 20 side is accommodated in the first active material of the first positive electrode mixture. Also, the fibrous conductive material located on the surface layer side of the positive electrode plate 10 is not accommodated in the second active material of the second positive electrode mixture. Therefore, it is possible to suppress the fibrous conductive material from being unevenly distributed on the surface layer side of the positive electrode plate 10 due to migration.

[0040] The present invention is not limited to the above-described embodiments, and can be appropriately modified without departing from the gist thereof.

Explanation of Reference Numerals

[0041] 1 Secondary battery 2 Battery case 3 Electrode body 10 Positive electrode plate 20 Current collector S1 First coating step S2 Second coating step S3 Drying step S4 Pressing step PD Size of through hole of active material FD Radial size of fibrous conductive material

Claims

1. A secondary battery comprising a positive electrode plate having a positive electrode composite material on a current collector, wherein the positive electrode composite material includes a first positive electrode composite material located on the current collector side and a second positive electrode composite material located on the surface layer side of the positive electrode plate, the first positive electrode composite material includes a first active material having a hollow structure and a fibrous conductive material, the first active material has at least one first through hole penetrating the surface layer of the first active material, the size of the at least one first through hole is larger than the radial size of the fibrous conductive material, the second positive electrode composite material includes a second active material and the fibrous conductive material, the second active material does not have a through hole penetrating the surface layer of the second active material, or has a second through hole penetrating the surface layer of the second active material, the size of the second through hole of the second active material is less than the radial size of the fibrous conductive material, A secondary battery.

2. The secondary battery according to claim 1, wherein the ratio of the thickness of the first positive electrode composite material to the thickness of the second positive electrode composite material is in the range of 10:1 to 1:

10.

3. The size of the at least one first through hole is in the range of 2 to 2000 nm, The radial size of the fibrous conductive material is in the range of 1.5 to 100 nm. The secondary battery according to claim 1 or 2.

4. The secondary battery according to claim 1 or 2, wherein the fibrous conductive material is a carbon-based fibrous conductive material.

5. A method for manufacturing a secondary battery, including a first coating step of coating a first positive electrode composite material on a current collector, and a second coating step of coating a second positive electrode composite material on the first positive electrode composite material coated on the current collector, the first positive electrode composite material includes a first active material having a hollow structure and a fibrous conductive material, the first active material has at least one first through hole penetrating the surface layer of the first active material, the size of the at least one first through hole is larger than the radial size of the fibrous conductive material, the second positive electrode composite material includes a second active material and the fibrous conductive material, the second active material does not have a through hole penetrating the surface layer of the second active material, or has a second through hole penetrating the surface layer of the second active material, the size of the second through hole of the second active material is less than the radial size of the fibrous conductive material, A method for manufacturing a secondary battery.

6. Further comprising a drying step of drying the first positive electrode composite material applied to the current collector and the second positive electrode composite material applied to the first positive electrode composite material, When the temperature for drying the first positive electrode composite material and the second positive electrode composite material in the drying step is in the range of 120 to 150 ° C, the ratio of the thickness of the first positive electrode composite material to the thickness of the second positive electrode composite material is In the range of 10:1 to 1:1, in the first coating step and the second coating step, the first positive electrode composite material and the second positive electrode composite material are respectively applied. The method for manufacturing a secondary battery according to claim 5.

7. Further comprising a drying step of drying the first positive electrode composite material applied to the current collector and the second positive electrode composite material applied to the first positive electrode composite material, When the temperature for drying the first positive electrode composite material and the second positive electrode composite material in the drying step is in the range of 150 to 180 ° C, the ratio of the thickness of the first positive electrode composite material to the thickness of the second positive electrode composite material is In the range of 1:1 to 1:10, in the first coating step and the second coating step, the first positive electrode composite material and the second positive electrode composite material are respectively applied. The method for manufacturing a secondary battery according to claim 5.

8. The size of the at least one first through hole is in the range of 2 to 2000 nm, The radial size of the fibrous conductive material is in the range of 1.5 to 100 nm. The method for manufacturing a secondary battery according to any one of claims 5 to 7.

9. The fibrous conductive material is a carbon-based fibrous conductive material. The method for manufacturing a secondary battery according to any one of claims 5 to 7.

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