Method for manufacturing a secondary battery and secondary battery

Abstract

To provide a method of manufacturing a secondary battery, which can reduce a thickness of an electrode body.SOLUTION: A method of manufacturing a secondary battery includes: a first pressurization step S3 of pressurizing a positive electrode sheet using a composite material, while moving it at a predetermined speed; a winding step S6 of winding the positive electrode sheet pressurized in the first pressurization step, a negative electrode sheet, and a separator in an overlapping state; and a second pressurization step S7 of pressurizing an electrode body, which is formed by the wound positive electrode sheet, the negative electrode sheet, and the separator, by a predetermined load. A thermal resistance layer is not formed on at least a surface which is brought into contact with the positive electrode sheet, of surfaces possessed by the separator.SELECTED DRAWING: Figure 1

Description

Technical Field

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

[0002] Conventionally, secondary batteries have been used in vehicles such as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles. Some secondary batteries include a wound electrode body formed by winding a positive electrode sheet, a negative electrode sheet, and a separator. When inserting the wound electrode body into a case during the manufacture of a secondary battery, usually, the wound electrode body is compressed to reduce its thickness. However, due to the repulsive force in the curved portion of the wound electrode body, it may not be possible to sufficiently reduce the thickness of the wound electrode body. As a result, there is a problem that the wound electrode body cannot be inserted into the case, and the secondary battery cannot be stably produced.

[0003] Regarding this point, Patent Document 1 discloses a secondary battery in which the O / C ratio of the surface of the separator facing the electrode is within a predetermined range, the roughness of the surface of the facing surface of the separator is within a predetermined range, and the ratio of the roughness of the surface of the facing surface of the separator to the roughness of the surface of the electrode is within a predetermined range.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the secondary battery disclosed in Patent Document 1 has a problem that the repulsive force in the curved portion of the wound electrode body cannot be sufficiently suppressed, so the thickness of the electrode body cannot be reduced.

[0006] The present disclosure has been made to solve such problems, and an object thereof is to provide a method for manufacturing a secondary battery and a secondary battery capable of reducing the thickness of an electrode body. [Means for solving the problem]

[0007] A method for manufacturing a secondary battery according to one embodiment is a method for manufacturing a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator that insulates the positive electrode sheet and the negative electrode sheet, A first pressurizing step involves applying pressure to a positive electrode sheet coated with a composite material while moving it at a predetermined speed, The process involves a winding step in which a pressurized positive electrode sheet, a negative electrode sheet, and a separator are stacked and wound together in a first pressurizing step, The process includes a second pressurizing step of applying pressure to an electrode body formed by a wound positive electrode sheet, a negative electrode sheet, and a separator with a predetermined load, A key feature is that no thermal resistance layer is formed on at least one of the surfaces of the separator that is in contact with the positive electrode sheet.

[0008] Furthermore, it is preferable that the composite material of the positive electrode sheet contains carbon nanotubes.

[0009] Furthermore, a method for manufacturing a secondary battery according to one embodiment may include a step of bending the positive electrode sheet that has been pressurized in the first pressurizing step, and removing any positive electrode sheets that do not fold when the bent positive electrode sheet is compressed.

[0010] Furthermore, a method for manufacturing a secondary battery according to one embodiment may include a step of removing positive electrode sheets whose surface glossiness is below a predetermined glossiness.

[0011] Furthermore, the default speed may be the speed at which the glossiness of the surface of the positive electrode sheet becomes equal to or greater than a predetermined glossiness.

[0012] Furthermore, the predetermined load may be such that, in the second pressurizing step, a bend occurs in the curved portion of the positive electrode sheet, extending more than 20% from the innermost positive electrode sheet included in the electrode body.

[0013] A secondary battery according to one embodiment comprises an electrode body in which a positive electrode sheet, a negative electrode sheet, and a separator that insulates the positive electrode sheet and the negative electrode sheet are wound. At least one of the surfaces of the separator that is in contact with the positive electrode sheet does not have a thermal resistance layer formed on it. The positive electrode sheet has a predetermined gloss level.

[0014] Furthermore, in the secondary battery according to one embodiment, it is preferable that a fold occurs in the curved portion of the positive electrode sheet, extending at least 20% from the innermost positive electrode sheet. [Effects of the Invention]

[0015] The present invention provides a method for manufacturing a secondary battery and a secondary battery that can reduce the thickness of the electrode body. [Brief explanation of the drawing]

[0016] [Figure 1] This is a flowchart showing a method for manufacturing a secondary battery according to one embodiment. [Figure 2] This diagram shows the method for compression testing. [Figure 3] This diagram illustrates the folding of the positive electrode sheet. [Figure 4] This figure shows the stress applied to the positive electrode sheet during compression testing. [Figure 5] This figure shows the experimental results for the positive electrode sheet and electrode body. [Modes for carrying out the invention]

[0017] Hereinafter, exemplary embodiments will be described with reference to the drawings. Figure 1 is a diagram showing an example of a method for manufacturing a secondary battery according to one embodiment. The method for manufacturing a secondary battery according to one embodiment is a method for manufacturing a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator that insulates the positive electrode sheet and the negative electrode sheet.

[0018] In step S1, a positive electrode composite material is produced. Specifically, the positive electrode composite material can be produced by kneading a positive electrode active material (such as nickel cobalt manganese), a binder, and carbon nanotubes. The amount of carbon nanotubes contained in the positive electrode composite material is preferably about 1% (weight percent) of the entire positive electrode composite material.

[0019] In step S2, the positive electrode composite material produced in step S1 is applied to a positive electrode foil (such as an aluminum foil) to produce a positive electrode sheet.

[0020] In step S3, while moving the positive electrode sheet produced in step S2 at a predetermined speed, it is pressed with a predetermined load. Step S3 corresponds to the first pressing step. The predetermined speed used in step S3 is preferably 30 m / min or more. Also, the predetermined load is preferably 20 t or more. By step S3, the surface layer of the positive electrode sheet is cured.

[0021] In step S4, the positive electrode sheet is inspected. Specifically, for example, as shown in FIG. 2, when the positive electrode sheet 1 pressed in step S3 is curved into a cylindrical shape and the cylindrical positive electrode sheet 1 is compressed at a constant speed by the pressing portion 20 of the pressing device, a compression inspection can be performed to check whether the positive electrode sheet 1 breaks. Here, "break" means that, as shown in FIG. 3, in a state where the distance between two opposing inner surfaces of the cylindrical positive electrode sheet 1 is 5 mm or less, when the pressing portion 20 of the pressing device moves about 1 mm so as to compress the cylindrical positive electrode sheet 1, the stress applied by the pressing portion 20 to the cylindrical positive electrode sheet 1 does not increase.

[0022] FIG. 4 is a diagram showing the stress applied to the positive electrode sheet in the compression inspection. As shown in FIG. 4, in this embodiment, in section A of about 1 mm, the stress applied by the pressing portion 20 of the pressing device to the cylindrical positive electrode sheet 1 did not increase. This means that the positive electrode sheet 1 of this embodiment broke in section A.

[0023] In step S5, a predetermined positive electrode sheet is excluded. For example, a positive electrode sheet that did not break during the compression test in step S4 can be excluded. In step S5, a positive electrode sheet manufactured at the same time as the positive electrode sheet that did not break can also be excluded. For example, if a compression test is used in step S4, a portion of the positive electrode sheet manufactured under pressure in step S3 can be cut out and subjected to the compression test. In this case, a positive electrode sheet that was integrated with the positive electrode sheet that did not break during the compression test can be excluded in step S5.

[0024] In step S6, the positive electrode sheet, the negative electrode sheet, and the separator that were not removed in step S5 are stacked and wound together. The positive electrode sheet, the negative electrode sheet, and the separator are stacked so that the separator insulates the positive electrode sheet and the negative electrode sheet. The separator can be manufactured from a material such as polyolefin. A thermal resistance layer is not formed on at least the surface of the separator that is in contact with the positive electrode sheet. Note that it is not necessary to form a thermal resistance layer on both sides of the separator.

[0025] In step S7, the electrode body formed by the positive electrode sheet, negative electrode sheet, and separator wound in step S6 is pressed with a predetermined load. Step S7 corresponds to the second pressing step. The predetermined load used in step S7 is preferably 40 kN or more. In the compression of the electrode body in step S7, it is preferable that a fold occurs in the curved portion of the positive electrode sheet from the innermost positive electrode sheet for at least 20% of the way. In other words, the predetermined load used in step S7 can be a load that causes a fold to occur in the curved portion of the positive electrode sheet from the innermost positive electrode sheet included in the electrode body for at least 20% of the way.

[0026] As described above, the method for manufacturing a secondary battery according to this disclosure includes a first pressurizing step, a winding step, and a second pressurizing step. In the first pressurizing step, a positive electrode sheet to which the composite material has been applied is pressed while being moved at a predetermined speed. In the winding step, the positive electrode sheet pressed in the first pressurizing step, the negative electrode sheet, and the separator are overlapped and wound together. In the second pressurizing step, the electrode body formed by the wound positive electrode sheet, negative electrode sheet, and separator is pressed with a predetermined load. A thermal resistance layer is not formed on at least the surface of the separator that is in contact with the positive electrode sheet. The positive electrode sheet also has a predetermined glossiness. Furthermore, the composite material of the positive electrode sheet may contain carbon nanotubes.

[0027] Figure 5 shows the experimental results of the embodiment and comparative example according to this disclosure. In the secondary battery manufacturing method according to this embodiment, the movement speed of the positive electrode sheet under pressure was 60 m / min, and the load on the electrode body under pressure was 40 kN. In this embodiment, a positive electrode composite material containing carbon nanotubes (CNTs) and a separator without a thermal resistance layer were used in the manufacturing of the secondary battery.

[0028] Compression testing of the positive electrode sheet according to this embodiment revealed that the sheet was bent. Furthermore, the defect rate regarding the insertability of the electrode body into the case according to this embodiment was less than 1%. In other words, more than 99% of the electrode bodies manufactured by the secondary battery manufacturing method according to this embodiment could be easily inserted into the case.

[0029] The method for manufacturing the secondary battery according to Comparative Example 1 is the same as the method for manufacturing the secondary battery according to this embodiment, except that a positive electrode composite material without carbon nanotubes was used. Compression testing was performed on the positive electrode sheet according to Comparative Example 1, and no folds were observed in the positive electrode sheet (Figure 4). Furthermore, the defect rate regarding the insertability of the electrode body into the case according to Comparative Example 1 was 1 or more and less than 10%. From these experimental results, it can be seen that it is preferable for the positive electrode composite material to contain carbon nanotubes.

[0030] The method for manufacturing a secondary battery according to Comparative Example 2 is the same as the method for manufacturing a secondary battery according to this embodiment, except that the movement speed of the positive electrode sheet under pressure (10 m / min) is lower than that of this embodiment. Compression testing was performed on the positive electrode sheet according to Comparative Example 2, and no folds were found in the positive electrode sheet (Figure 4). In addition, the defect rate regarding the insertability of the electrode body into the case according to Comparative Example 2 was 10% or more. From these experimental results, it is preferable that the movement speed of the positive electrode sheet under pressure is greater than 10 m / min, and preferably 30 m / min.

[0031] The method for manufacturing a secondary battery according to Comparative Example 3 is the same as the method for manufacturing a secondary battery according to this embodiment, except that the separator has a thermal resistance layer. The defect rate regarding the insertability of the electrode body into the case in Comparative Example 3 was 10% or more. From these experimental results, it can be seen that it is preferable for the separator not to have a thermal resistance layer.

[0032] The method for manufacturing a secondary battery according to Comparative Example 4 is the same as the method for manufacturing a secondary battery according to this embodiment, except that the load (20 kN) applied to the electrode body during pressurization is smaller than that applied to the electrode body during pressurization in this embodiment. The defect rate regarding the insertability of the electrode body into the case in Comparative Example 4 was 10% or more. From these experimental results, it is preferable that the load applied to the electrode body during pressurization is greater than 20 kN, and preferably 40 kN.

[0033] Furthermore, focusing on the glossiness of the positive electrode sheets of Comparative Examples 1 and 2, in which no folds occurred, their glossiness was 28% and 21%, respectively, which was lower than the glossiness of this embodiment (52%). From this, it is highly likely that positive electrode sheets with a surface glossiness of less than 30% when incident light is at an incident angle of 60 degrees will not fold. Therefore, in the inspection of step S4 described above, by inspecting the surface glossiness of the positive electrode sheet without performing a compression inspection of the positive electrode sheet, it is possible to distinguish between positive electrode sheets that fold and those that do not. In this case, in step S5 described above, positive electrode sheets with a surface glossiness below a predetermined glossiness, specifically less than 30%, can be excluded. In this embodiment, the predetermined speed and load used in step S3 can be set to a speed and load such that the surface glossiness of the positive electrode sheet becomes a predetermined glossiness (for example, 30%).

[0034] The present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. [Explanation of symbols]

[0035] 1 Positive electrode sheet 10 Curved section 20 Pressing part

Claims

1. A method for manufacturing a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator that insulates the positive electrode sheet and the negative electrode sheet, A first pressurizing step involves applying pressure to the positive electrode sheet to which the composite material has been applied while moving it at a predetermined speed, A winding step in which the positive electrode sheet, the negative electrode sheet, and the separator that have been pressurized in the first pressurizing step are stacked and wound together, The process includes a second pressurizing step of applying pressure to the electrode body formed by the wound positive electrode sheet, the negative electrode sheet, and the separator with a predetermined load, The separator is characterized in that no thermal resistance layer is formed on at least the surface that contacts the positive electrode sheet. The composite material of the positive electrode sheet contains carbon nanotubes, The aforementioned predetermined speed is 30 m / min or more. The aforementioned predetermined load is 40 kN or more. A method for manufacturing secondary batteries.

2. The method for manufacturing a secondary battery according to Claim 1, wherein the predetermined speed is 60 m / min or more.

3. The method for manufacturing a secondary battery according to claim 1, wherein the load applied to pressurize the positive electrode sheet in the first pressurizing step is 20 tons or more.

4. A method for manufacturing a secondary battery according to claim 1 or 2, further comprising the step of bending the positive electrode sheet that has been pressurized in the first pressurizing step, and removing any positive electrode sheets that do not fold when the bent positive electrode sheet is compressed.

5. The process further includes a step of removing positive electrode sheets whose surface glossiness is less than a predetermined glossiness, The method for manufacturing a secondary battery according to claim 1 or 2, wherein the predetermined gloss level is 30%.

6. The method for manufacturing a secondary battery according to claim 1 or 2, wherein the predetermined load is a load that causes bending to occur in the curved portion of the positive electrode sheet from the innermost positive electrode sheet included in the electrode body by 20% or more during the second pressurizing step.

7. A secondary battery comprising an electrode body in which a positive electrode sheet, a negative electrode sheet, and a separator insulating the positive electrode sheet and the negative electrode sheet are wound, A thermal resistance layer is not formed on at least one of the surfaces of the separator that is in contact with the positive electrode sheet. The positive electrode sheet has a glossiness of 30% or more. The composite material of the positive electrode sheet contains carbon nanotubes, Secondary battery.

8. The secondary battery according to claim 7, characterized in that a fold occurs in the curved portion of the positive electrode sheet extending 20% ​​or more from the innermost positive electrode sheet.

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