Manufacturing method of secondary battery, and secondary battery

Abstract

To provide a manufacturing method of a secondary battery capable of reducing the resistance to ion movement while suppressing the occurrence of micro-short circuits, and a secondary battery.SOLUTION: The manufacturing method of a secondary battery 1 includes: a first applying step S1 of applying a positive electrode mixture that contains a diamagnetic fibrous conductive material to a current collector; a first magnetic field application step S2 of applying a magnetic field to the current collector and positive electrode mixture in the thickness direction of a positive electrode plate; a drying step S3 of, after the first magnetic field application step S2, drying the current collector and positive electrode mixture; a second applying step S4 of, after the drying step S3, of applying a positive electrode mixture that includes diamagnetic fibrous conductive material to the positive electrode mixture in which the magnetic field has been applied in the first magnetic field application step S2; and a second magnetic field application step S5 of, after the second applying step S4, applying a magnetic field in the direction of the positive plate surface to the current collector and the positive electrode mixture.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a secondary battery and a 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. In such secondary batteries, a minute short circuit may occur due to metal foreign matter mixed in the secondary battery. For this reason, various techniques for suppressing such a minute short circuit have been proposed.

[0003] As an example of such a technique, Patent Document 1 discloses a secondary battery including an electrode composed of a layer of randomly oriented fibrous carbon and a layer of fibrous carbon oriented in the plane direction.

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, the ion migration resistance increases in the layer of randomly oriented fibrous carbon, and there is a possibility that the DC resistance deteriorates.

[0006] The present disclosure is for solving such problems, and an object thereof is to provide a method for manufacturing a secondary battery and a secondary battery capable of suppressing the occurrence of a minute short circuit and reducing the ion migration resistance.

Means for Solving the Problems

[0007] The method for manufacturing a secondary battery according to the present disclosure is A first coating step of applying a positive electrode composite material containing a diamagnetic fibrous conductive material to a current collector; A first magnetic field application step of applying a magnetic field to the current collector and the positive electrode composite material in the thickness direction of the positive electrode plate; After the first magnetic field application step, a drying step of drying the current collector and the positive electrode composite material; After the drying step, a second coating step of applying a positive electrode composite material containing a diamagnetic fibrous conductive material to the positive electrode composite material to which a magnetic field was applied in the first magnetic field application step; After the second coating step, a second magnetic field application step of applying a magnetic field to the current collector and the positive electrode composite material in the plane direction of the positive electrode plate.

[0008] Moreover, the ratio of the thickness of the positive electrode composite material applied in the first coating step to the thickness of the positive electrode composite material applied in the second coating step can be in the range of 7:3 to 3:7.

[0009] Furthermore, the diamagnetic fibrous conductive material can be a carbon-based fibrous conductive material.

[0010] 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 contains a diamagnetic fibrous conductive material, The positive electrode composite material is formed of a first positive electrode composite material layer located on the current collector side and a second positive electrode composite material layer located on the surface layer side of the positive electrode plate, When the angle formed by the longitudinal axis of the plurality of first diamagnetic fibrous conductive materials in the first positive electrode composite material layer and the plane direction of the positive electrode plate is θ1, the representative value of sinθ1 of the plurality of first diamagnetic fibrous conductive materials is the longitudinal axis of the second diamagnetic fibrous conductive materials in the second positive electrode composite material layer and the plane direction of the positive electrode plate It is characterized by being larger than the representative value of sinθ2 of the plurality of second diamagnetic fibrous conductive materials when the angle formed is θ2.

[0011] Moreover, the representative value of sinθ1 is the average value or median value of sinθ1 of the plurality of first diamagnetic fibrous conductive materials, The representative value of sinθ2 can be the average value or median value of sinθ2 of the plurality of second diamagnetic fibrous conductive materials.

Advantages of the Invention

[0012] According to the present disclosure, it is possible to provide a method for manufacturing a secondary battery and a secondary battery that can suppress the occurrence of minute short circuits and reduce the ion migration resistance.

Brief Description of the Drawings

[0013]

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Embodiments for Carrying Out the Invention

[0014] Hereinafter, with reference to the drawings, an embodiment according to the present disclosure will be described. 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.

[0015] 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. Note that the electrode body manufactured by the method for manufacturing a secondary battery according to the present disclosure is not limited to such a wound electrode body, and also includes a non-wound electrode body.

[0016] FIG. 3 is a diagram showing a method for manufacturing a secondary battery according to an embodiment. The method for manufacturing a 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 first magnetic field application step S2, a first drying step S3, a second coating step S4, a second magnetic field application step S5, a second drying step S6, and a pressing step S7.

[0017] The first coating step S1 is a step of coating both surfaces of a current collector such as an aluminum foil with a positive electrode composite material containing a diamagnetic fibrous conductive material. The positive electrode composite material includes an active material, a diamagnetic fibrous conductive material, and a binder. The diamagnetic fibrous conductive material is a fibrous material having diamagnetism and conductivity. Specific examples of the diamagnetic fibrous conductive material include carbon-based fibrous conductive materials such as carbon nanotubes (CNT) and carbon nanofibers.

[0018] The first magnetic field application step S2 is a step of applying a magnetic field in the thickness direction of the positive electrode plate to the current collector and the positive electrode composite material to which the positive electrode composite material has been applied in the first coating step S1. The thickness direction of the positive electrode plate is the thickness direction of the positive electrode plate 10 shown in FIG. 4. For example, the magnetic flux density is preferably 0.3 T or more, and the viscosity of the slurry is preferably 2000 mPa·s@1sec-1 or less. The time for applying the magnetic field is preferably, for example, 10 seconds or more.

[0019] The first drying step S3 is a step of drying the current collector and the positive electrode composite material after the first magnetic field application step S2. The temperature in the first drying step S3 can be, for example, 100 to 200 (°C). Also, the humidity in the first drying step S3 can be, for example, 0.2 to 25 (%). Furthermore, the drying time can be 2 minutes or more.

[0020] The second coating step S4 is a step of coating the positive electrode composite material containing a diamagnetic fibrous conductive material on the positive electrode composite material dried with a magnetic field applied thereto. The ratio of the thickness of the positive electrode composite material coated in the first coating step to the thickness of the positive electrode composite material coated in the second coating step is preferably within the range of 7:3 to 3:7. In the first coating step S1 and the second coating step S4, the amount of the positive electrode composite material is adjusted so that the ratio of the thickness of the positive electrode composite material is within such a range.

[0021] The second magnetic field application step S5 is a step of applying a magnetic field to the current collector and the positive electrode composite material in the plane direction of the positive electrode plate after the second coating step S4. The plane direction of the positive electrode plate is a direction perpendicular to the thickness direction of the positive electrode plate 10 shown in FIG. 4 and is an arbitrary direction along the plane of the positive electrode plate.

[0022] The second drying step S6 is a step of drying the current collector and the positive electrode composite material after the second magnetic field application step S5. The temperature, humidity, and drying time in the second drying step S6 can be the same as those in the first drying step S3.

[0023] The pressing step S7 is a step of pressing the positive electrode plate with a pressing member such as a pressing roller after the second drying step S6.

[0024] FIG. 5 is a schematic diagram showing an example of a cross section of a positive electrode plate manufactured by the above-described positive electrode plate manufacturing process. As shown in FIG. 5, the positive electrode plate 10 has a positive electrode mixture 12 coated on a current collector 20. The positive electrode mixture 12 is formed of a first positive electrode mixture layer located on the current collector 20 side and a second positive electrode mixture layer located on the surface layer side of the positive electrode plate 10. As shown in FIG. 5, in the positive electrode plate 10 manufactured by the above-described positive electrode plate manufacturing process, the diamagnetic fibrous conductive material in the first positive electrode mixture layer is substantially oriented in the thickness direction of the positive electrode plate 10, and the diamagnetic fibrous conductive material in the second positive electrode mixture layer is substantially oriented in the plane direction of the positive electrode plate.

[0025] FIG. 6 is a diagram showing angles θ1 and θ2 formed by the longitudinal axis of the diamagnetic fibrous conductive material and the plane direction of the positive electrode plate. As shown in FIG. 6, let the angle formed by the longitudinal axis of the first diamagnetic fibrous conductive material in the first positive electrode mixture layer and the plane direction of the positive electrode plate be θ1. Let the angle formed by the longitudinal axis of the second diamagnetic fibrous conductive material in the second positive electrode mixture layer and the plane direction of the positive electrode plate be θ2.

[0026] FIG. 7 is a diagram showing an example of the measurement results of the representative values of sin θ1 and sin θ2 of the positive electrode plate manufactured by the above-described positive electrode plate manufacturing process. The representative value of sin θ1 can be the average value or the median value of sin θ1 of a plurality of first diamagnetic fibrous conductive materials. Also, the representative value of sin θ2 can be the average value or the median value of sin θ2 of a plurality of second diamagnetic fibrous conductive materials. In this measurement, the average values of sin θ1 and sin θ2 were used as the representative values. From the measurement results shown in FIG. 7, it can be seen that the representative value of sin θ1 is larger than the representative value of sin θ2. Therefore, in the positive electrode plate manufactured by the above-described positive electrode plate manufacturing process, the representative value of sin θ1 of the plurality of first diamagnetic fibrous conductive materials included in the first positive electrode mixture layer is larger than the representative value of sin θ2 of the plurality of second diamagnetic fibrous conductive materials included in the second positive electrode mixture layer. Note that the measurement results shown in FIG. 7 are exemplary, and the representative values of sin θ1 and sin θ2 of the positive electrode plate manufactured by the above-described positive electrode plate manufacturing process can be various values on the condition that the representative value of sin θ1 is larger than the representative value of sin θ2.

[0027] Figure 8 shows the ion transfer resistance (Ω) of the positive electrode plate of the present embodiment and the measurement results of the ion transfer resistance of the positive electrode plates of four comparative examples 1 to 4. In this measurement test, CNT was adopted as the fibrous conductive material. In addition, polyvinylidene fluoride (PVDF) was adopted as the binder. The mixing ratio of the active material, CNT, and the binder in the positive electrode composite used in this measurement test was 98.5:0.5:1. Note that the mixing ratio of the positive electrode composite of the present embodiment is not limited to these values.

[0028] The positive electrode plate according to the present embodiment was manufactured by the above-described positive electrode plate manufacturing process. In the pressing process, the positive electrode plate was pressed so that the composite density became 2.5 g / ml (cc).

[0029] The positive electrode plate of Comparative Example 1 had a single layer of positive electrode composite on both sides. The positive electrode plate of Comparative Example 1 was manufactured by applying a single layer of positive electrode composite on both sides of the current collector, drying it, and then pressing it so that the composite density became 2.5 g / ml. In other words, the positive electrode plate of Comparative Example 1 was manufactured without applying a magnetic field. Therefore, the orientation of the CNTs contained in the positive electrode plate of Comparative Example 1 was random.

[0030] The positive electrode plate of Comparative Example 2 had a single layer of positive electrode composite on both sides. The positive electrode plate of Comparative Example 2 was manufactured by applying a single layer of positive electrode composite on both sides of the current collector, applying a magnetic field in the thickness direction of the positive electrode plate and drying it, and then pressing it so that the composite density became 2.5 g / ml. Therefore, the orientation of the CNTs contained in the positive electrode plate of Comparative Example 2 was substantially in the thickness direction of the positive electrode plate.

[0031] The positive electrode plate of Comparative Example 3 had a single layer of positive electrode composite on both sides. The positive electrode plate of Comparative Example 3 was manufactured by applying a single layer of positive electrode composite on both sides of the current collector, applying a magnetic field in the plane direction of the positive electrode plate and drying it, and then pressing it so that the composite density became 2.5 g / ml. Therefore, the orientation of the CNTs contained in the positive electrode plate of Comparative Example 3 was substantially in the plane direction of the positive electrode plate.

[0032] The positive electrode plate of Comparative Example 4 had two layers of positive electrode composite material on both sides. In the manufacturing process of the positive electrode plate of Comparative Example 4, a single layer of positive electrode composite material was applied to both sides of the current collector and then dried. Next, another single layer of positive electrode composite material was applied on the dried single layer of positive electrode composite material, a magnetic field was applied in the plane direction of the positive electrode plate and dried, and it was manufactured by pressing so that the composite material density became 2.5 g / ml. Therefore, in the positive electrode plate of Comparative Example 4, the orientation of CNTs in the positive electrode composite material layer on the current collector side was random, and the orientation of CNTs in the positive electrode composite material layer on the surface layer side was substantially in the plane direction of the positive electrode plate.

[0033] As a result of measuring the ion migration resistance of the positive electrode plate of this embodiment and the positive electrode plates of Comparative Examples 1 to 4 at 25°C, it was found that the positive electrode plate of this embodiment had a smaller ion migration resistance than the positive electrode plate of Comparative Example 4. Therefore, it was found that the positive electrode plate of this embodiment can reduce the ion migration resistance more than the positive electrode plate disclosed in Patent Document 1.

[0034] FIG. 9 is a diagram for explaining another performance index value r1 / r2 of the positive electrode plate. FIG. 9 shows how ions diffuse from metal foreign substances mixed in the positive electrode plate 10. r1 is the diffusion distance of ions in the plane direction of the positive electrode plate inside the positive electrode composite material. r2 is the diffusion distance of ions in the plane direction of the positive electrode plate on the surface of the positive electrode composite material adjacent to the separator 30.

[0035] FIG. 10 is a diagram showing the relationship between the performance index value r1 / r2 of the positive electrode plate and the short-circuit resistance (Ω), which is the resistance value when a micro short circuit occurs. As shown in FIG. 10, the smaller r1 / r2 is, the larger the short-circuit resistance becomes. Therefore, the smaller r1 / r2 is, the larger the resistance value when a micro short circuit occurs, so it becomes difficult for a micro short circuit to occur.

[0036] FIG. 11 is a diagram showing the performance index value r1 / r2 of the positive electrode plate according to the present embodiment and the positive electrode plates according to Comparative Examples 1 to 4. From this measurement result, it was found that the positive electrode plate of the present embodiment has the smallest performance index value r1 / r2. On the contrary, it was found that the positive electrode plate of the present embodiment has the largest r2 / r1, which is the reciprocal of the performance index value r1 / r2. In other words, it was found that in the positive electrode plate of the present embodiment, the diffusion distance of ions in the surface direction of the positive electrode composite material with respect to the diffusion distance of ions in the surface direction inside the positive electrode composite material is the largest. Therefore, in the positive electrode plate of the present embodiment, since ions easily diffuse in the surface direction of the positive electrode plate on the surface of the positive electrode composite material, the minimum short circuit can be most effectively suppressed.

[0037] The present invention is not limited to the above-described embodiments, and can be appropriately modified without departing from the spirit thereof.

Explanation of Signs

[0038] 1 Secondary battery 2 Battery case 3 Electrode body 10 Positive electrode plate 12 Positive electrode composite material 20 Current collector 30 Separator

Claims

1. A method for manufacturing a secondary battery, comprising: a first coating step of coating a current collector with a positive electrode composite material containing a diamagnetic fibrous conductive material; a first magnetic field application step of applying a magnetic field to the current collector and the positive electrode composite material in the thickness direction of the positive electrode plate; a drying step of drying the current collector and the positive electrode composite material after the first magnetic field application step; a second coating step of coating the positive electrode composite material, to which a magnetic field was applied in the first magnetic field application step, with a positive electrode composite material containing a diamagnetic fibrous conductive material after the drying step; a second magnetic field application step of applying a magnetic field to the current collector and the positive electrode composite material in the plane direction of the positive electrode plate after the second coating step A method for manufacturing a secondary battery, comprising:

2. The ratio of the thickness of the positive electrode composite material coated in the first coating step to the thickness of the positive electrode composite material coated in the second coating step is in the range of 7:3 to 3:

7. The method for manufacturing a secondary battery according to Claim 1.

3. The diamagnetic fibrous conductive material is a carbon-based fibrous conductive material. The method for manufacturing a secondary battery according to Claim 1 or 2.

4. A secondary battery comprising a positive electrode plate having a positive electrode composite material on a current collector, wherein the positive electrode composite material contains a diamagnetic fibrous conductive material, the positive electrode composite material is formed of a first positive electrode composite material layer located on the current collector side and a second positive electrode composite material layer located on the surface layer side of the positive electrode plate, The angle formed by the longitudinal axis of the first diamagnetic fibrous conductive material in the first positive electrode composite layer and the plane direction of the positive electrode plate is θ １ When this is the case, the representative value of sinθ of the plurality of first diamagnetic fibrous conductive materials １ is greater than the representative value of sinθ of the plurality of second diamagnetic fibrous conductive materials when the angle formed by the longitudinal axis of the second diamagnetic fibrous conductive material in the second positive electrode composite layer and the plane direction of the positive electrode plate is θ ２ This is characterized by being ２ greater than the representative value of A secondary battery.

5. The aforementioned sinθ １ The representative value of is the average value or the median value of sinθ of the plurality of first diamagnetic fibrous conductive materials, １ and is The above-mentioned sinθ ２ The representative value of is the sinθ of the plurality of second diamagnetic fibrous conductive materials ２ The secondary battery according to claim 4, which is an average value or a median value of

6. The first diamagnetic fibrous conductive material and the second diamagnetic fibrous conductive material are carbon-based fibrous conductive materials. The secondary battery according to Claim 4 or 5.

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