Method for measuring the thickness of long sheets used for electrode formation.

Abstract

To solve the problem that an attempt to measure a thickness of an elongate sheet, consisting of a front-side electrode layer formed on a front surface of an elongate conductive foil and a back-side electrode layer formed on a back surface thereof, while the elongate sheet is aligned with an outer peripheral surface of a free roller may produce a gap between the outer peripheral surface of the free roller and an inner peripheral surface of the elongate sheet, causing an error in a thickness measurement result.SOLUTION: A thickness of an elongate sheet is measured by orienting the elongate film such that an electrode layer with a greater elongation rate during electrode layer formation is in contact with an outer peripheral surface of a free roller, and ensuring the electrode layer is in tight contact with the outer peripheral surface of the free roller.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] Disclosed herein is a method for measuring the thickness of a long sheet for forming an electrode. [Background Art]

[0002] Patent Document 1 discloses a method for manufacturing a long sheet for forming a battery electrode. This manufacturing method comprises a step of applying a back-side active material to the back surface of a metal foil and performing roll pressing, and a step of applying a front-side active material to the front surface of the metal foil and performing roll pressing. [Prior Art Document] [Patent Document]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2021-82504

[0004] In order to improve battery performance, it is necessary to apply a thick active material to form a thick electrode layer, and it is necessary to control the thickness of the long sheet. In order to control the thickness of the long sheet, it is necessary to measure the thickness of the long sheet. The back surface of the long sheet, in which a front-side electrode layer is formed on the front surface of a metal foil and a back-side electrode layer is formed on the back surface, is supported by a free roller, and the thickness of the long sheet can be measured by measuring the distance between the surface of the front-side electrode layer of the long sheet and the outer peripheral surface of the free roller. [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] When the thickness of a long sheet was measured by the above method, it was found that the measured thickness values varied even though the thickness was actually uniformly controlled. When the reason was not clear, it was found that the following phenomena are involved. 1) When forming an electrode layer, an active material is applied to a conductive foil (typically a metal foil), and the applied active material is compressed. 2) As a result of carrying out the process in 1) above, the electrode layer expands (the negative electrode layer may contract, but at least the positive electrode layer expands). 3) The elongation rate of the surface electrode layer and the elongation rate of the back electrode layer do not match. 4) As a result of the difference in elongation rates, the long sheet will curve in a direction where the electrode layer with the lower elongation rate (or the electrode layer that shrinks) faces inward. 5) Typically, the thickness is measured with the inner surface of the curved shape supported by a free roller. 6) In this case, as will be described later with reference to Figure 2, the curved long sheet adheres tightly to the free roller at position A where it begins to contact the free roller and at position B where it separates from the free roller, but a gap G is created between the outer surface of the free roller and the inner surface of the long sheet in the region C between the contact start position A and the contact end position B. 7) In the thickness measurement method using a free roller, the distance between the outer surface of the free roller and the outer surface of the long sheet is measured. However, if a gap G occurs between the outer surface of the free roller and the inner surface of the long sheet, the dimension of the gap G will be included in the thickness measurement, resulting in an error in the measurement.

[0006] The above describes the case where the elongation rate of the electrode layer on the front side does not match the elongation rate of the electrode layer on the back side. However, in some long sheets, an electrode layer is formed only on one side of the conductive foil, and no electrode layer is formed on the opposite side of the conductive foil. In this case, the elongation rate of the electrode layer is greater than the elongation rate of the conductive foil, and the long sheet curves in a direction where the conductive foil is on the inside. In this case as well, if the inner surface of the curved shape is supported by a free roller, a gap G is created between the outer surface of the free roller and the inner surface of the long sheet, and an error is introduced into the thickness measurement value.

[0007] This specification discloses techniques for preventing the occurrence of the aforementioned gaps and techniques for improving the accuracy of measuring the thickness of long sheets. [Means for solving the problem]

[0008] The technology disclosed herein is applicable to both long sheets in which an electrode layer is formed on only one side of a conductive foil (typically a metal foil) and long sheets in which electrode layers are formed on both the front and back sides of the conductive foil. In the former case, the following method is employed. That is, a method for measuring the thickness of a long sheet in which an electrode layer is formed on one side of a long conductive foil, comprising an electrode layer formation step of coating one side of the conductive foil with an active material and then roll pressing, and a measurement step of measuring the distance between the outer surface of the free roller and the outer surface of the long sheet while the long sheet after the electrode layer formation step is aligned with the outer surface of the free roller. The elongation rate of the electrode layer during electrode layer formation is greater than the elongation rate of the conductive foil. In the method disclosed herein, the electrode layer is oriented so that it is in contact with the outer surface of the free roller. This provides a region in which the electrode layer is in close contact with the outer surface of the free roller without any gaps, and the distance (the distance between the outer surface of the free roller and the outer surface of the long sheet) is measured within that region.

[0009] When an electrode layer with a high elongation rate and a conductive foil with a low elongation rate are laminated, the electrode layer curves outwards and the conductive foil inwards. When supporting a curved long sheet with a free roller, the free roller usually supports the conductive foil, which is located on the inside of the curve. However, in this case, as shown in Figure 2, a gap G is created between the outer surface of the free roller and the inner surface of the long sheet, introducing an error into the measurement of the sheet's thickness. It is possible to reduce the gap G by applying tension to the long sheet, but there are limits to the tension that can be applied, and it is difficult to eliminate the gap G by applying tension.

[0010] However, it was found that by applying tension to the long sheet and pressing it against the free roller, the electrode layer, which was facing outwards, reverses to face inwards when in contact with the free roller. This relationship allows the electrode layer to adhere closely to the free roller, creating a region where no gap is created between the outer surface of the free roller and the inner surface of the long sheet. By reversing the orientation of the long sheet placed on the free roller, it becomes possible to measure the thickness while preventing gaps from forming.

[0011] For long sheets of conductive foil with electrode layers formed on both the front and back surfaces, the following measurement method is applied. This measurement method comprises a front-side electrode layer formation step of applying a front-side active material to the front surface of the conductive foil and then roll-pressing it; a back-side electrode layer formation step of applying a back-side active material to the back surface of the conductive foil and then roll-pressing it; and a measurement step of measuring the distance between the outer surface of the free roller and the outer surface of the long sheet while the long sheet, after both steps have been performed, is aligned with the outer surface of the free roller. In the measurement method disclosed herein, the electrode layer with the greater elongation rate during electrode layer formation is oriented to contact the outer surface of the free roller, thereby obtaining a region in which the electrode layer with the greater elongation rate is in close contact with the outer surface of the free roller, and the distance is measured within that region.

[0012] When electrode layers with high and low elongation rates are stacked, the sheet curves so that the high-elongation layer faces outwards and the low-elongation layer faces inwards. If the low-elongation electrode layer on the inside is supported by a free roller, a gap will form between the outer surface of the free roller and the inner surface of the sheet, introducing errors into the measurement of the sheet's thickness. While it is possible to reduce the gap by applying tension to the sheet, there are limits to the applicable tension, and it is difficult to eliminate the gap by applying tension alone.

[0013] However, it was discovered that when tension is applied to the long sheet and it is pressed against the free roller, if the electrode layer that was facing outwards (the electrode layer with a high elongation rate) is reversed to face inwards and in contact with the free roller, the electrode layer with a high elongation rate adheres closely to the free roller, creating a region where no gap is created between the outer surface of the free roller and the inner surface of the long sheet. By reversing the orientation of the long sheet placed on the free roller, it becomes possible to measure the thickness while preventing the formation of gaps.

[0014] Details of the technology disclosed herein and further improvements are described in the following "Modes for Carrying Out the Invention". [Brief explanation of the drawing]

[0015] [Figure 1] Shows the orientation of a conventional thickness measurement method. [Figure 2] Shows problems of a conventional thickness measurement method. [Figure 3] Shows the orientation of the thickness measurement method disclosed in the present specification. [Figure 4] Shows how problems are solved by the thickness measurement method disclosed in the present specification. [Figure 5] Shows the relationship between compressive stress applied to an electrode layer and elongation rate. [Figure 6] Shows measurement results obtained by a conventional thickness measurement method. [Figure 7] Shows measurement results obtained by the thickness measurement method disclosed in the present specification. Mode for Carrying Out the Invention

[0016] FIG. 1 and FIG. 3 show a method for measuring the thickness of a long sheet 2 in a state where the long sheet 2 is supported by a free roller 14, wherein a non-contact type distance measuring device 16 measures the distance to the outer peripheral surface of the long sheet 2. In FIG. 1 and FIG. 3, the orientation of the long sheet 2 relative to the free roller 14 is reversed. In FIG. 1, the negative electrode layer 8 is in contact with the free roller 14, whereas in FIG. 3, the positive electrode layers 4a, 4b, 4c... are in contact with the free roller 14. The relative positional relationship between the distance measuring device 16 and the free roller 14 is fixed, and the distance from the distance measuring device 16 to the outer periphery of the free roller 14 is known. Therefore, it can be said that the distance measuring device 16 measures the distance from the outer peripheral surface of the free roller 14 to the outer peripheral surface of the long sheet 2. In the present specification, not only the case of directly measuring the distance from the outer peripheral surface of the free roller 14 to the outer peripheral surface of the long sheet 2, but also the case of obtaining the distance from the outer peripheral surface of the free roller to the outer peripheral surface of the long sheet by measuring the distance from the distance measuring device to the outer peripheral surface of the long sheet is referred to as measuring the distance from the outer peripheral surface of the free roller to the outer peripheral surface of the long sheet.

[0017] (Reference Example) In FIG. 1, positive electrode layers 4a, 4b, 4c... are formed on the upper surface of a conductive foil 6, and a negative electrode layer 8 is formed on the lower surface of the conductive foil 6. The positive electrode layers 4a, 4b, 4c... are intermittently formed in the length direction of the long conductive foil 6. FIG. 1 illustrates a step of compressing (roll-pressing) the positive electrode layer 4a by a pair of rollers 10 and 12. The negative electrode layer 8 has been roll-pressed prior to this step (the roll-pressing step for the negative electrode layer 8 is not illustrated).

[0018] In FIG. 5, the horizontal axis represents the compressive stress applied in the roll pressing step, and the vertical axis represents the elongation percentage of the electrode layer. In the present specification, when describing a phenomenon common to the positive electrode layers 4a, 4b, 4c..., it is referred to as the positive electrode layer 4. Circular marks indicate the elongation percentage of the positive electrode layer 4, and triangular marks indicate the elongation percentage of the negative electrode layer 8. The negative electrode layer 8 hardly elongates. More precisely, it has a small negative value and slightly contracts. In contrast, the positive electrode layer 4 elongates when it is roll-pressed. The positive electrode layer 4 elongates more than the negative electrode layer 8. Due to the positive electrode layer 4 elongating more than the negative electrode layer 8, the long sheet 2 curves such that the positive electrode layer 4 faces outward and the negative electrode layer 8 faces inward when no external force is applied thereto.

[0019] In the case of FIG. 1, the inward-facing negative electrode layer 8 is supported by a free roller 14. In this case, as shown in FIG. 2, a gap G is formed between the outer circumferential surface of the free roller 14 and the inner circumferential surface of the negative electrode layer 8. In the case of FIG. 2, the relationship "thickness of the long sheet 2 = distance from the distance measuring device 16 to the outer circumferential surface of the free roller 14 - measured value of the distance measuring device 16 - dimension of the gap G" holds. Since the unknown dimension of the gap G affects the measurement, the measurement accuracy of the thickness of the long sheet 2 decreases.

[0020] (Example) In Figure 3, the top and bottom of the long sheet 2 are reversed compared to Figure 1. That is, the positive electrode layer 4 is in contact with the free roller 14. The positive electrode layer 4 has a greater elongation rate than the negative electrode layer 8, and if no external force is applied, it will curve so that the positive electrode layer 4 faces outwards. In Figure 3, by placing the long sheet 2 on the free roller 14 and applying tension to the long sheet 2, the long sheet 2 reverses from its natural curved shape, and stretches along the outer circumference of the free roller 14 with the positive electrode layer 4 facing inwards. In this case, as shown in Figure 4, the long sheet 2 adheres tightly to the outer surface of the free roller 14 without any gaps in the region C between the contact start position A and the contact end position B. In Figure 4, the relationship is "thickness of long sheet 2 = distance from distance measuring device 16 to outer surface of free roller 14 - measurement value of distance measuring device 16". When measured in the relationship of Figure 4, the gap G that exists in Figure 2 does not occur, so the thickness of the long sheet 2 can be measured accurately.

[0021] Figure 6 shows the measured values ​​obtained using the relationship shown in Figure 2, and Figure 7 shows the measured values ​​obtained using the relationship shown in Figure 4. The horizontal axis indicates the position along the length of the long sheet, and the vertical axis indicates the measured value. The interval indicated by arrow D indicates the average interval of the measured values, and the average sheet thickness for interval D was calculated by averaging the values ​​measured multiple times within interval D. Comparing Figure 6 and Figure 7, it is clear that the variation in multiple measured values ​​within interval D is smaller in Figure 7 than in Figure 6. Furthermore, the variation in the average value for each interval is also smaller in Figure 7 than in Figure 6. Here, the measured long sheet was specially manufactured to minimize the change in thickness along its longitudinal direction, and the magnitude of the aforementioned variation corresponds to the error included in the measured value. Figure 7 shows that the variation is smaller than in Figure 6. In other words, it can be seen that measurement is more accurate when performed according to the relationship in Figure 4 rather than Figure 2. In particular, when the thickness of the long sheet is 300 μm or more, measuring according to the relationship in Figure 4 rather than Figure 2 significantly improves the accuracy of thickness measurement. The techniques disclosed herein are also useful when the negative electrode layer 8 is not formed.

[0022] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings can achieve multiple objectives simultaneously, and achieving even one of these objectives itself constitutes technical usefulness. [Explanation of Symbols]

[0023] 2: Long sheet 4(4a,4b,4c)... Positive electrode layer 6: Conductive foil 8: Negative electrode layer 10,12: Press roller 14: Free roller 16: Non-contact distance measuring device

Claims

1. This is a method for measuring the thickness of a long sheet in which an electrode layer is formed on one side of a long conductive foil. The electrode layer formation step involves coating one side with an active material and then performing a roll press, The system includes a measurement step of measuring the distance between the outer surface of the free roller and the outer surface of the long sheet while the long sheet is aligned with the outer surface of the free roller after the electrode layer formation step has been performed. The elongation rate of the electrode layer during the formation of the electrode layer is greater than the elongation rate of the conductive foil. The electrode layer is oriented to contact the outer circumferential surface of the free roller, A measurement method characterized by measuring the distance within a region in which the electrode layer is in close contact with the outer surface of the free roller.

2. This is a method for measuring the thickness of a long conductive foil sheet in which a surface electrode layer is formed on the surface and a back electrode layer is formed on the back surface. A surface electrode layer formation step is performed by coating the surface with a surface-side active material and then roll-pressing it, The process of forming a back-side electrode layer involves coating the back surface with a back-side active material and then performing a roll press, The system includes a measurement step in which, with the long sheet after both of the above steps aligned with the outer surface of the free roller, the distance between the outer surface of the free roller and the outer surface of the long sheet is measured. The electrode layer with the greater elongation rate during electrode layer formation is oriented to contact the outer circumferential surface of the free roller. A measurement method characterized by measuring the distance within a region in which the electrode layer with the larger elongation rate is in close contact with the outer circumferential surface of the free roller.

3. The thickness of the aforementioned long sheet is 300 μm or more. The measurement method according to claim 1 or 2, characterized in that the distance to the outer surface of the long sheet is measured non-contact in the measurement step.

Images