Electrode and secondary battery

Abstract

Provided is an electrode and a secondary battery that ensure sufficient capacity.　An electrode according to an embodiment includes a current collector, an electrode mixture layer provided on the current collector, and an insulating layer that is provided on the current collector and is adjacent to the electrode mixture layer. The insulating layer has a first portion at the boundary with the electrode mixture layer and a second portion having a smaller thickness than the first portion, wherein an external angle at the intersection of a virtual extension line from the surface of the first portion toward the second portion and the surface of the current collector is 80° or more and 120° or less.

Description

electrodes and secondary batteries

[0001] Embodiments of the present invention relate to electrodes and secondary batteries.

[0002] In recent years, secondary batteries such as lead-acid batteries and nickel-metal hydride batteries have been used as power sources for electric vehicles, hybrid vehicles, electric motorcycles, and forklifts. Recently, there has been a surge in development toward the adoption of lithium-ion secondary batteries, which have high energy density, and development is being carried out with consideration for long lifespan and safety.

[0003] For example, in lithium-ion secondary batteries (hereinafter referred to as secondary batteries), there are electrodes in which an electrode mixture layer is provided on a current collector, and an insulating layer is provided on either the current collector or the electrode mixture layer. In this case, depending on the cross-sectional shape of the electrode mixture layer and the insulating layer (for example, a sloping shape in which the electrode mixture layer is formed to be thinner towards the edges, or a shape in which the insulating layer overlaps the edges of the electrode mixture layer), there is a risk that the peel strength of the electrode mixture layer will decrease or the utilization rate of the electrode mixture layer will decrease at the edges of the electrode mixture layer.

[0004] Japanese International Publication No. 2014 / 162437, Japanese Patent Publication No. 2023-85907

[0005] The problem that this invention aims to solve is to provide electrodes and secondary batteries that ensure sufficient capacity.

[0006] To solve the above problems, the electrode of the embodiment comprises a current collector, an electrode mixture layer provided on the current collector, and an insulating layer provided on the current collector and adjacent to the electrode mixture layer. The insulating layer has a first portion at the boundary with the electrode mixture layer and a second portion that is thinner than the first portion, and the outer angle at the intersection of a virtual extension line from the surface of the first portion toward the second portion and the surface of the current collector is 80° or more and 120° or less.

[0007] A schematic plan view showing the electrode of the first embodiment. A schematic plan view showing a modified example of the electrode of the first embodiment. A cross-sectional view of the electrode as seen from the direction of the arrow along the line III-III in Figure 1 or Figure 2. An enlarged view of the area around the insulating layer in the cross-sectional view of Figure 3. An enlarged view of the area around the modified example of the insulating layer in the cross-sectional view of Figure 3. A schematic perspective view showing the secondary battery of the second embodiment. A partially unfolded perspective view of the electrode group used in the secondary battery of the second embodiment. A schematic perspective view showing a modified example of the secondary battery of the second embodiment. A partially unfolded perspective view of the electrode group used in the modified example of the secondary battery of the second embodiment.

[0008] The electrodes and secondary battery of the embodiment will be described below with reference to the drawings.

[0009] (First Embodiment) The electrode 2 of the first embodiment will be described with reference to Figure 1. Figure 1 is a schematic plan view showing the electrode 2 of the first embodiment. As shown in Figure 1, the electrode 2 comprises a current collector 70 and an electrode mixture layer 20 provided on the current collector 70. Furthermore, the electrode 2 comprises an insulating layer 10 provided on the current collector 70 and adjacent to the electrode mixture layer 20. The current collector 70 has an uncoated portion 70a where neither the electrode mixture layer 20 nor the insulating layer 10 is provided.

[0010] Here, the current collector 70 of electrode 2 is, for example, rectangular in shape with a long side 12 and a short side 14, the electrode mixture layer 20 is provided parallel to the long side 12, and the insulating layer 10 is provided adjacent to the electrode mixture layer 20. Figure 2 is a schematic plan view showing a modified example (electrode 2') of electrode 2 in the first embodiment. As shown in Figure 2, the electrode mixture layer 20 may be provided parallel to the short side 14 of the current collector 70. The electrode mixture layer 20 and the insulating layer 10 are provided on one or both sides of the current collector 70. In Figures 1 and 2, the X direction is parallel to the direction of the short side 14 (width direction) of electrode 2, and the Y direction is parallel to the direction of the long side 12 of electrode 2. The direction intersecting the boundary Q of electrode 2 is parallel to the X direction in Figure 1 and parallel to the Y direction in Figure 2.

[0011] The following description will focus on electrode 2 in Figure 1, but electrode 2' is similar. The electrode 2 of the first embodiment will be further described with reference to Figure 3. Figure 3 is a cross-sectional view of electrode 2 (electrode 2') taken from the direction of the arrow along the line III-III in Figure 1 or Figure 2. As shown in Figure 3, the insulating layer 10 of this embodiment has a first portion 10a at the boundary Q with the electrode mixture layer 20 and a second portion 10b that is thinner than the first portion 10a. Here, the boundary Q is the portion where the electrode mixture layer 20 and the insulating layer 10 are adjacent. Specifically, the boundary Q is the portion where the electrode mixture layer 20 and the insulating layer 10 are adjacent when observing the cross-section of electrode 2.

[0012] The first portion 10a and the second portion 10b of the insulating layer 10 will be further described with reference to Figure 4. Figure 4 is an enlarged view of the area around the insulating layer 10 in the cross-sectional view of Figure 3. As shown in Figure 4, a virtual extension line P is drawn from the surface of the first portion 10a toward the second portion 10b, and the intersection point of the virtual extension line P and the surface of the current collector 70 is defined as A. The virtual extension line P is, for example, a line segment passing through the highest point P1 on the surface of the first portion 10a and the intersection point A. The surface of the first portion 10a is defined as the surface of the first portion 10a that is exposed toward the second portion 10b (towards the width direction, X direction of the electrode 2), and the virtual extension line P is drawn along this exposed surface and so as to be continuous from the exposed surface toward the second portion 10b. In the electrode 2 of this embodiment, the outer angle B at the intersection point A is 80° or more and 120° or less. The outer angle B in Figure 3 is approximately 90°. Furthermore, in electrode 2', the direction of the longer side (Y direction), rather than the width direction (X direction), is parallel to the direction in which the first part 10a faces the second part 10b.

[0013] Figure 5 is an enlarged view of the area around a modified example (insulating layer 10') of the insulating layer 10 in the cross-sectional view of Figure 3. The difference between insulating layer 10' and insulating layer 10 lies in the cross-sectional shape of the first portion 10a, and the first portion 10a of insulating layer 10' is referred to as the first portion 10a'. Here, as in Figure 3, a virtual extension line P is drawn from the surface of the first portion 10a' toward the second portion 10b, and the intersection point of the virtual extension line P with the surface of the current collector 70 is denoted as A. The outer angle B at intersection point A is between 80° and 120°. In Figure 5, the outer angle B is approximately 120°. Note that in the examples of Figures 4 and 5, the exposed surface of the first portion 10a is parallel to the XY plane, but the exposed surface may be curved outward or inward. In this case, in the cross-section of electrode 2, the point with the highest height on the curved surface is defined as the starting point (P1), and the extension of the line from the starting point P1 to the ending point (the intersection of the surface of the first part 10a and the second part 10b) is defined as P.

[0014] In the electrode 2 of this embodiment, the insulating layer 10 has a first portion 10a, which is provided adjacent to the electrode mixture layer 20. Furthermore, the outer angle B at intersection A is 80° or more and 120° or less. In other words, due to this outer angle B, the first portion 10a is formed in a columnar shape in the thickness direction (Z direction), and because the columnar first portion 10a is provided adjacent to the end of the electrode mixture layer 20, the flow of the coating liquid for the electrode mixture layer can be suppressed when the electrode mixture layer 20 is formed. As a result, it is possible to suppress the end of the electrode mixture layer 20 from becoming a sloping shape that is formed thinly toward the insulating layer 10. Also, if the outer angle B at intersection A is less than 80°, the coating liquid for the insulating layer will spread in the width direction (X direction) of the electrode 2 when the insulating layer 10 is formed, and it will not be possible to easily form the columnar first portion 10a. Furthermore, if the outer angle B is greater than 120°, the volume of the columnar first portion 10a cannot be appropriately maintained to the extent that the inclined shape of the electrode mixture layer 20 can be suppressed. A preferred outer angle B is 90° or more and 120° or less.

[0015] In this embodiment, since the end of the electrode mixture layer 20 has a shape corresponding to the columnar first portion 10a of the insulating layer 10, the thickness of the electrode mixture layer 20 near the boundary Q is approximately equal to the thickness of the electrode mixture layer 20 outside the boundary Q (for example, the thickness of the central portion of the electrode 2). In the manufacturing process of the electrode 2, after the electrode mixture layer 20 is provided on the current collector 70, the entire electrode 2 may be pressed with a press machine. In this pressing of the electrode 2, in this embodiment, since the thickness of the electrode mixture layer 20 is approximately equal both near the boundary Q and outside the boundary Q, the entire electrode 2 can be pressed uniformly. As a result, even at the end of the electrode mixture layer 20, the electrode mixture layer 20 and the current collector 70 are sufficiently adhered by the press, and the peel strength of the electrode mixture layer 20 at the end of the electrode mixture layer 20 can be increased. Therefore, in the electrode 2 of this embodiment, the entire electrode mixture layer 20, including the end of the electrode mixture layer 20, is sufficiently adhered to the current collector 70, and an electrode 2 with sufficient peel strength can be provided. Furthermore, because the electrode 2 has sufficient peel strength, the peeling of the electrode mixture layer 20 from the current collector 70 is suppressed, and an electrode 2 with sufficient capacity can be provided. The thickness of the electrode mixture layer 20 can be determined by observing a cross-section obtained by cutting the electrode 2 along the lamination direction of the electrode mixture layer 20 with a scanning electron microscope (SEM).

[0016] Furthermore, in this embodiment, the first portion 10a of the insulating layer 10 is positioned such that when the electrodes 2 form an electrode group, and the ends of the electrode mixture layers 20 of other electrodes are positioned opposite the insulating layer 10 of electrode 2 via a separator, even if the ends of the electrode mixture layers 20 pierce the separator, the ends of the electrode mixture layers 20 will still come into contact with the insulating layer 10 of electrode 2, thereby suppressing a short circuit of the electrode group. In other words, the first portion 10a of the insulating layer 10 plays a role in preventing contact between the ends of the electrode mixture layers 20 of other electrodes and the current collector 70 beneath the insulating layer 10.

[0017] Furthermore, the second portion 10b of the insulating layer 10, like the first portion 10a, plays a role in preventing contact between the ends of the electrode mixture layers 20 of other electrodes and the current collector 70 below the insulating layer 10 when the electrodes 2 are arranged as an electrode group and the ends of the electrode mixture layers 20 of other electrodes are positioned opposite the insulating layer 10 of electrode 2 via a separator. The second portion 10b of the insulating layer 10 is thinner than the first portion 10a because the role of suppressing the inclined shape at the ends of the electrode mixture layers 20 is sufficient with only the first portion 10a, while both the first portion 10a and the second portion 10b suppress short circuits of the electrode group. As a result, when the electrodes 2 are arranged as an electrode group, the volume of the insulating layer 10 within the electrode group can be minimized, short circuits of the electrode group can be suppressed with the first portion 10a and the second portion 10b of the insulating layer 10, and sufficient capacity of the electrode group can be ensured.

[0018] Furthermore, as shown in Figures 4 and 5, at the boundary Q, the thickness (D) of the first portion 10a in the thickness direction (Z direction) of the current collector 70 is 0.8 or more and 1.0 or less than the thickness (D') of the electrode mixture layer 20. By having a thickness D of the first portion 10a of 0.8 or more than the thickness D' of the electrode mixture layer 20, the flow of the coating liquid for the electrode mixture layer can be sufficiently suppressed when the electrode mixture layer 20 is formed, and the end of the electrode mixture layer 20 can be shaped to correspond to the first portion 10a. As a result, the first portion 10a with a thickness D can sufficiently suppress the end of the electrode mixture layer 20 from becoming inclined toward the insulating layer 10. In addition, by having a thickness D of the first portion 10a of 1.0 or less than the thickness D' of the electrode mixture layer 20, it is possible to suppress the formation of the first portion 10a of the insulating layer 10 on top of the electrode mixture layer 20. Furthermore, by making the thickness D of the first portion 10a and the thickness D' of the electrode mixture layer 20 approximately equal, the entire electrode 2, including the insulating layer 10, can be uniformly pressed, and the electrode mixture layer 20 and the first portion 10a of the insulating layer 10 can be in close contact with the current collector 70. For example, Figure 4 shows the case where the thickness (D) of the first portion 10a is 1.0 relative to the thickness (D') of the electrode mixture layer 20, and Figure 5 shows the case where the thickness (D) of the first portion 10a is 0.9 relative to the thickness (D') of the electrode mixture layer 20.

[0019] Next, we will explain the lengths of the first portion 10a and the second portion 10b by comparing them. First, as shown in Figure 1, when the electrode mixture layer 20 is provided parallel to the long side 12 of the current collector 70, as shown in Figures 4 and 5, the length (T) of the first portion 10a in the direction parallel to the short side 14 of the current collector 70 (X direction) is 0.2% to 1.0% of the length (T') of the second portion 10b in the direction parallel to the short side 14 of the current collector 70 (X direction). On the other hand, as shown in Figure 2, when the electrode mixture layer 20 is provided parallel to the short side 14 of the current collector 70, as shown in Figures 4 and 5, the length (T) of the first portion 10a in the direction parallel to the long side 12 of the current collector 70 (X direction) is 0.2% to 1.0% of the length (T') of the second portion 10b in the direction parallel to the long side 12 of the current collector 70 (X direction). The lengths of the first portion 10a and the second portion 10b are determined by observing a cross-section obtained by cutting the electrode 2 along the stacking direction of the electrode mixture layer 20 using a scanning electron microscope (SEM).

[0020] When electrode 2 is used as an electrode group, the insulating layer 10 does not affect the capacitance of the electrode group, so it is preferable to minimize the volume occupied by the insulating layer 10 within the electrode group. This allows for a larger amount of electrode mixture layer 20 to be included in the electrode group, enabling a higher capacitance for the electrode group. In electrode 2 of this embodiment, the length T of the first portion 10a of the insulating layer 10 is 0.2% or more of the length T' of the second portion 10b, so that the first portion 10a has a length that can sufficiently suppress the slope at the end of the electrode mixture layer 20. Furthermore, the length T of the first portion 10a of the insulating layer 10 is 1.0% or less of the length T' of the second portion 10b, which is thinner than the first portion 10a, so that even when electrode 2 is used as an electrode group, the volume occupied by the insulating layer 10 within the electrode group can be minimized.

[0021] Furthermore, the lengths of the electrode mixture layer 20 and the insulating layer 10 will be explained while comparing them. First, as shown in Figure 1, when the electrode mixture layer 20 is provided parallel to the long side 12 of the current collector 70, as shown in Figures 4 and 5, the length of the insulating layer 10 in the direction parallel to the short side 14 of the current collector 70 (X direction) (T + T') is 1.5% to 3.0% of the length of the electrode mixture layer 20 in the direction parallel to the short side 14 of the current collector 70 (X direction). On the other hand, as shown in Figure 2, when the electrode mixture layer 20 is provided parallel to the short side 14 of the current collector 70, as shown in Figures 4 and 5, the length of the insulating layer 10 in the direction parallel to the long side 12 of the current collector 70 (X direction) (T + T') is 1.5% to 3.0% of the length of the electrode mixture layer 20 in the direction parallel to the long side 12 of the current collector 70 (X direction).

[0022] By ensuring that the length (T + T') of the insulating layer 10 is 1.5% or more of the length S of the electrode mixture layer 20, when electrode 2 is part of an electrode group, even if the end of the electrode mixture layer 20 faces an uncoated portion of the current collector of another electrode, the insulating layer 10 has sufficient length (T + T') relative to the uncoated portion of the current collector, thereby suppressing contact between the electrode mixture layer 20 and the uncoated portion of the current collector. Furthermore, as mentioned above, when electrode 2 is part of an electrode group, the insulating layer 10 does not affect the capacitance of the electrode group, so it is preferable to minimize the volume occupied by the insulating layer 10 within the electrode group. Therefore, by ensuring that the length (T + T') of the insulating layer 10 is 3.0% or less of the length S of the electrode mixture layer 20, the volume occupied by the insulating layer 10 within the electrode group can be minimized, even when electrode 2 is part of an electrode group. The length of the insulating layer 10 is determined by observing a cross-section obtained by cutting the electrode 2 along the lamination direction of the electrode mixture layer 20 using a scanning electron microscope (SEM).

[0023] The insulating layer 10 contains at least one type of insulating particle. Examples of insulating particles include solid particles of metal oxides, such as aluminum oxide (alumina), zirconium oxide (zirconia), magnesium oxide, and barium sulfate. The most preferred insulating particles are alumina or zirconia, which allow for the inexpensive and simple formation of the insulating layer 10.

[0024] The method for manufacturing the electrode 2 of this embodiment will now be described. As mentioned above, the electrode 2 is provided with an electrode mixture layer 20 on a current collector 70, and an insulating layer 10 adjacent to the electrode mixture layer 20. When providing the electrode mixture layer 20 and the insulating layer 10 on the current collector 70, an electrode mixture coating liquid containing the electrode mixture and an insulating layer coating liquid containing an insulating material are used. These electrode mixture coating liquids and insulating layer coating liquids are then applied to the current collector 70 simultaneously. After applying the electrode mixture coating liquids and insulating layer coating liquids, the electrode mixture layer 20 and the insulating layer 10 can be formed by drying both coating liquids. The process of forming the electrode mixture layer 20 and the insulating layer 10 by simultaneously applying the electrode mixture coating liquid and insulating layer coating liquids to the current collector 70 is called the coating process.

[0025] In this coating process, the electrode mixture layer coating liquid and the insulating layer coating liquid are simultaneously applied to the current collector 70 at 25°C and a shear rate of 1000 s. －１ The viscosity of the insulating layer coating liquid is 0.7 to 1.1 relative to the viscosity of the electrode mixture layer coating liquid. Having a viscosity of 0.7 or higher relative to the viscosity of the electrode mixture layer coating liquid allows the insulating layer coating liquid to suppress the spreading of the electrode mixture layer coating liquid when it is applied to the current collector 70, making the outer angle B at intersection A 80° to 120°. This allows the inclination of the edge of the electrode mixture layer 20 to be suppressed by the first portion 10a of the insulating layer 10. Furthermore, having a viscosity of 1.1 or lower relative to the viscosity of the electrode mixture layer coating liquid allows the drying speed of both coating liquids to be kept approximately constant.

[0026] Furthermore, in order to control the outer angle B at intersection A to be between 80° and 120°, in addition to adjusting the viscosity of the coating liquid for the electrode mixture layer and the coating liquid for the insulating layer, the flow rates of both coating liquids are also adjusted. Specifically, when the outer angle B at intersection A is to be between 80° and 100°, the amount of coating liquid for the electrode mixture layer is set to be greater than the amount of coating liquid for the insulating layer. On the other hand, when the outer angle B at intersection A is to be between 100° and 120°, the amount of coating liquid for the electrode mixture layer is set to be equal to the amount of coating liquid for the insulating layer. As a result, when the amount of coating liquid for the electrode mixture layer is set to be greater than the amount of coating liquid for the insulating layer, the spreading of the coating liquid for the electrode mixture layer in the width direction (X direction) can be sufficiently suppressed by the coating liquid for the insulating layer, so that the outer angle B at intersection A can be set to be between 80° and 100°. Furthermore, if the amount of coating liquid for the electrode mixture layer is equal to the amount of coating liquid for the insulating layer, the spreading of the coating liquid for the electrode mixture layer in the width direction (X direction) can be gently suppressed by the coating liquid for the insulating layer, so that the outer angle B at intersection A can be set to 100° or more and 120° or less. Here, the flow rate is expressed as L / (min·m). The flow rate of the coating liquid for the electrode mixture layer is the flow rate per unit length of the discharge port of the electrode mixture layer L / (min·m). The flow rate of the coating liquid for the insulating layer is the flow rate per unit length of the discharge port of the insulating layer L / (min·m).

[0027] Furthermore, in the electrode 2 of this embodiment, the second portion 10b of the insulating layer 10 is formed thinner than the first portion 10a. The difference in thickness between the first portion 10a and the second portion 10b is due to, as mentioned above, simultaneously applying the electrode mixture coating liquid and the insulating layer coating liquid onto the current collector 70, adjusting the viscosity of the insulating layer coating liquid to 0.7 or more and 1.1 or less relative to the viscosity of the electrode mixture coating liquid, and ensuring that no gap is provided at the discharge port of the coating liquid when applying both coating liquids. As a result, at the boundary Q between the electrode mixture coating liquid and the insulating layer coating liquid, the spreading of the insulating layer coating liquid is suppressed by the electrode mixture coating liquid. Consequently, the first portion 10a of the insulating layer 10 formed at the boundary Q with the electrode mixture coating liquid is formed thicker than the second portion 10b of the insulating layer 10 at a position away from the boundary Q.

[0028] Furthermore, in the electrode 2 of this embodiment, the edges of the electrode mixture layer 20 have a shape corresponding to the columnar first portion 10a of the insulating layer 10, so that the coating liquid for the electrode mixture layer can be uniformly dried in the thickness direction (Z direction) of the electrode mixture layer 20. As a result, for example, the binder contained in the coating liquid for the electrode mixture layer is uniformly dispersed even at the edges of the electrode mixture layer 20, and the peel strength of the electrode mixture layer 20 at the edges of the electrode mixture layer 20 can be increased.

[0029] In the electrode 2 of the first embodiment described above, the insulating layer 10 has a first portion 10a and a second portion 10b that is thinner than the first portion 10a, and the first portion 10a is provided adjacent to the electrode mixture layer 20. Furthermore, if a virtual extension line P is drawn from the surface of the first portion 10a toward the second portion 10b, and the intersection point of the virtual extension line P and the surface of the current collector 70 is taken as A, then the outer angle B at intersection point A is 80° or more and 120° or less. In other words, because the first portion 10a is formed in a columnar shape in the thickness direction (Z direction), and the columnar first portion 10a is provided adjacent to the end of the electrode mixture layer 20, the flow of the coating liquid for the electrode mixture layer can be suppressed when the electrode mixture layer 20 is formed. As a result, it is possible to suppress the end of the electrode mixture layer 20 from becoming a sloping shape that is formed thinner toward the insulating layer 10. Furthermore, if the outer angle B at intersection A is less than 80°, the insulating layer coating liquid will spread in the width direction (X direction) of the electrode 2 when the insulating layer 10 is formed, making it difficult to easily form the columnar first portion 10a. If the outer angle B is greater than 120°, the volume of the columnar first portion 10a cannot be appropriately maintained to the extent that the inclined shape of the electrode mixture layer 20 is suppressed.

[0030] In this embodiment, since the end of the electrode mixture layer 20 has a shape corresponding to the columnar first portion 10a of the insulating layer 10, the thickness of the electrode mixture layer 20 at the boundary Q is approximately equal to the thickness of the electrode mixture layer 20 outside the boundary Q (for example, the thickness of the central portion of the electrode 2). In the manufacturing process of the electrode 2, after the electrode mixture layer 20 is provided on the current collector 70, the entire electrode 2 may be pressed with a press machine. In this pressing of the electrode 2, in this embodiment, since the thickness of the electrode mixture layer 20 is approximately equal both at the boundary Q and outside the boundary Q, the entire electrode 2 can be pressed uniformly. As a result, even at the end of the electrode mixture layer 20, the electrode mixture layer 20 and the current collector 70 are sufficiently adhered by the press, and the peel strength of the electrode mixture layer 20 at the end of the electrode mixture layer 20 can be increased. Therefore, in the electrode 2 of this embodiment, the entire electrode mixture layer 20, including the end of the electrode mixture layer 20, is sufficiently adhered to the current collector 70, and an electrode 2 with sufficient peel strength can be provided. Furthermore, because the electrode 2 has sufficient peel strength, the peeling of the electrode mixture layer 20 from the current collector 70 is suppressed, and an electrode 2 with sufficient capacity can be provided.

[0031] Furthermore, in this embodiment, the electrode 2 has a second portion 10b of the insulating layer 10 that is thinner than the first portion 10a. This is because the role of suppressing the inclined shape at the edge of the electrode mixture layer 20 is sufficient with only the first portion 10a, while suppressing short circuits of the electrode group with both the first portion 10a and the second portion 10b. As a result, when the electrode 2 is used as an electrode group, the volume of the insulating layer 10 within the electrode group can be minimized, short circuits of the electrode group can be suppressed by the first portion 10a and the second portion 10b of the insulating layer 10, and sufficient capacity of the electrode group can be ensured.

[0032] (Second Embodiment) The secondary battery 1 of the second embodiment will be described with reference to Figure 6. Figure 6 is a schematic perspective view showing the secondary battery 1 according to the second embodiment. As shown in Figure 6, the secondary battery 1 comprises an outer case 3, and inside the outer case 3, a wound electrode group 5 using the electrodes 2 of the first embodiment and an electrolyte (not shown). The outer case 3 has an internal cavity (not shown) inside, and an opening 9 is provided on the top surface, and a lid member 7 is placed in the opening 9.

[0033] The electrode group 5 used in the secondary battery 1 will be described with reference to Figure 7. Figure 7 is a partially exploded perspective view of the electrode group 5 used in the secondary battery 1 according to the second embodiment. The electrode group 5 has the electrode 2 of the first embodiment, and the electrode 2 is wound around a separator 4. Specifically, the electrode 2 shown in Figure 1 and the other electrode 6 are wound facing each other with the separator 4 in between, and it is preferable that the insulating layer 10 of the electrode 2 is positioned to face the end of the electrode mixture layer of the other electrode 6.

[0034] Here, it is preferable that the other electrodes 6 have a different structure from electrode 2, and do not have an insulating layer 10. Preferably, electrode 2, which has an insulating layer 10, is the positive electrode, and the other electrodes 6 are the negative electrodes. The current collector 70 of electrode 2 is the positive electrode current collector, and the electrode mixture layer 20 of electrode 2 is the positive electrode mixture layer. This is because, when the electrode group 5 is used as a secondary battery, the width of the negative electrode mixture layer of the other electrodes 6 (in the X direction in Figure 1) may be formed wider than the width of the positive electrode mixture layer (in the X direction in Figure 1) in order to accept all the lithium ions supplied from the positive electrode mixture layer. In other words, in the electrode group 5, it is preferable that the insulating layer 10 of electrode 2, which is the positive electrode, is positioned to face the end of the negative electrode mixture layer of the other electrodes 6, which are the negative electrodes. Next, the positive electrode current collector, positive electrode active material, negative electrode current collector, and negative electrode active material will be described. The positive electrode current collector is preferably aluminum foil, or aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si. For example, oxides or sulfides can be used as the positive electrode active material. The positive electrode may contain one compound alone, or a combination of two or more compounds. Examples of oxides and sulfides include compounds that can insert and remove Li or Li ions. The negative electrode current collector material is preferably a substance that is electrochemically stable in the negative electrode potential range when alkali metal ions are inserted or removed. For example, the negative electrode current collector is preferably zinc (Zn) foil, aluminum foil, or aluminum alloy foil containing at least one element selected from magnesium (Mg), titanium (Ti), zinc, manganese (Mn), iron (Fe), copper (Cu), and silicon (Si). The negative electrode active material includes at least one selected from the group consisting of carbon materials, silicon, silicon oxides, and titanium-containing oxides. The negative electrode active material may include one or more of these materials. Examples of carbon materials include artificial graphite, natural graphite, and fusiform graphite obtained by compacting natural graphite and coating it with carbon.

[0035] As shown in FIG. 7, uncoated portions 70a of a current collector 70 in an electrode 2 and uncoated portions 70b of a current collector in another electrode 6 protrude from both ends of an electrode group 5. When the electrode group 5 is formed into a secondary battery, both uncoated portions (70a, 70b) may be connected to a conductive member.

[0036] A gas discharge valve 21 may be provided together with a sealing plate 19 on a surface of a lid member 7 of the secondary battery 1. Furthermore, for example, a pair of terminals 23 are attached to the surface of the lid member 7, and the terminals 23 are each electrically connected to the electrode group 5. A terminal insulator 35 may be provided between each terminal 23 and the lid member 7 to maintain insulation therebetween.

[0037] The secondary battery 1 includes the electrode group 5 having a wound structure that uses the electrode 2 according to the first embodiment. In the electrode 2 used for the secondary battery 1, the entire electrode mixture layer 20 is sufficiently in close contact with the current collector 70, and peeling of the electrode mixture layer 20 from the current collector 70 is suppressed. Therefore, when this electrode 2 is used in the secondary battery 1, it is possible to provide the secondary battery 1 including the electrode 2 in which peeling of the electrode mixture layer 20 from the current collector 70 is suppressed for the entire electrode group 5. Furthermore, since the electrode 2 has sufficient peel strength, peeling of the electrode mixture layer 20 from the current collector 70 is suppressed, and the secondary battery 1 that ensures sufficient capacity can be provided.

[0038] Furthermore, as shown in FIG. 7, in the electrode group 5, the insulating layer 10 of the electrode 2 is preferably arranged so as to face an end portion of an electrode mixture layer of another electrode 6. Accordingly, even when the end portion of the electrode mixture layer of the other electrode 6 breaks through the separator 4, the end portion of the electrode mixture layer of the other electrode 6 contacts the insulating layer 10 instead of the current collector 70 of the electrode 2. Therefore, it is possible to provide the secondary battery 1 in which short-circuiting between the electrode 2 and the other electrode 6 is suppressed.

[0039] FIG. 8 is a perspective view schematically showing a modified example (secondary battery 1') of the secondary battery 1 according to the second embodiment. The difference between the secondary battery 1' and the secondary battery 1 lies in the structure of the secondary battery 1'. As shown in FIG. 8, the secondary battery 1' includes an outer case 3', and an electrode group 5' having a laminated structure using the electrode 2' of the first embodiment and an electrolytic solution (not shown) inside the outer case 3'.

[0040] The electrode group 5' used in the secondary battery 1' will be described with reference to Figure 9. Figure 9 is a partially exploded perspective view of a modified example (electrode group 5') of the electrode group 5 used in the secondary battery 1' of the second embodiment. The difference between electrode group 5' and electrode group 5' lies in the structure of electrode group 5'. Electrode group 5' has the electrode 2' of the first embodiment, and has a laminated structure in which the electrode 2' is stacked with a separator 4' in between. Specifically, the electrode 2' shown in Figure 2 and the other electrode 6' are stacked facing each other with a separator 4' in between, and it is preferable that the insulating layer 10' of electrode 2' is positioned to face the end of the electrode mixture layer of the other electrode 6'.

[0041] As shown in Figure 9, the unpainted portion 70a' of the current collector 70' on electrode 2' and the unpainted portion 70b' of the current collector 70' on the other electrode 6' protrude from both ends of electrode group 5'. Here, in electrode group 5', a part of the unpainted portion 70a' of the current collector 70' on electrode 2' is cut off, but the shape is not limited to these. The unpainted portions (70a', 70b') of both may be connected to a conductive member when electrode group 5' is used as a secondary battery.

[0042] The secondary battery 1 of the second embodiment described above has an electrode group 5 using the electrode 2 of the first embodiment. The electrode 2 used in the secondary battery 1 has the entire electrode mixture layer 20 in sufficient contact with the current collector 70, and peeling of the electrode mixture layer 20 from the current collector 70 is suppressed. Therefore, when this electrode 2 is used in the secondary battery 1, it is possible to provide a secondary battery 1 equipped with an electrode 2 in which peeling of the electrode mixture layer 20 from the current collector 70 is suppressed for the entire electrode group 5. Furthermore, since the electrode 2 has sufficient peel strength, peeling of the electrode mixture layer 20 from the current collector 70 is suppressed, and a secondary battery 1 with sufficient capacity can be provided.

[0043] Furthermore, in the electrode group 5 used for the secondary battery 1, the insulating layer 10 of the electrode 2 is preferably arranged so as to face the end portion of the electrode mixture layer of another electrode 6. Accordingly, even when the end portion of the electrode mixture layer of another electrode 6 breaks through the separator 4, the end portion of the electrode mixture layer of another electrode 6 comes into contact with the insulating layer 10 instead of the current collector 70 of the electrode 2, whereby the secondary battery 1 in which short circuit between the electrode 2 and the another electrode 6 is suppressed can be provided. A method for taking out the electrode 2 from the secondary battery 1 when measuring the external angle B of the electrode 2 incorporated in the secondary battery 1 will be described. First, the secondary battery 1 is discharged until the open circuit voltage becomes from 2.0 V to 2.2 V. Next, the discharged battery is transferred into a glove box filled with argon where the dew point of the internal atmosphere is -70°C. The secondary battery 1 is opened in such a glove box. The electrode group 5 is taken out from the cut-open secondary battery 1. When the taken-out electrode group 5 includes a positive electrode conductive member and a negative electrode conductive member, the positive electrode conductive member and the negative electrode conductive member are cut while being careful not to short-circuit the positive electrode and the negative electrode. Next, the electrode group 5 is disassembled and decomposed into a positive electrode, a negative electrode, and a separator. The electrode 2 obtained in this way is washed using diethyl carbonate as a solvent. In this washing, the decomposed member is completely immersed in the diethyl carbonate solvent and left to stand in that state for 60 minutes. After washing, the electrode 2 is subjected to vacuum drying. For the vacuum drying, pressure is reduced in an environment of 25°C from the atmospheric pressure until the pressure becomes -97 kPa or more, and this state is maintained for 10 minutes. The external angle B is measured by observing the cross section of the electrode taken out through such a procedure with a scanning electron microscope (SEM: Scanning Electron Microscopy). In addition, the thickness of the electrode mixture layer 20, the lengths of the first portion 10a and the second portion 10b, and the length of the insulating layer 10 are measured by the aforementioned method for the electrode 2 taken out by the above method.

[0044] According to the electrode 2 of at least one embodiment described above, the insulating layer 10 has a first portion 10a and a second portion 10b that is thinner than the first portion 10a, and the first portion 10a is provided adjacent to the electrode mixture layer 20. Furthermore, if a virtual extension line P is drawn from the surface of the first portion 10a toward the second portion 10b, and the intersection point of the virtual extension line P and the surface of the current collector 70 is A, then the outer angle B at intersection point A is 80° or more and 120° or less. In other words, because the first portion 10a is formed in a columnar shape in the thickness direction (Z direction), and the columnar first portion 10a is provided adjacent to the end of the electrode mixture layer 20, the flow of the coating liquid for the electrode mixture layer can be suppressed when the electrode mixture layer 20 is formed. As a result, it is possible to suppress the end of the electrode mixture layer 20 from becoming a sloping shape that is formed thinner toward the insulating layer 10. Furthermore, if the outer angle B at intersection A is less than 80°, the insulating layer coating liquid will spread in the width direction (X direction) of the electrode 2 when the insulating layer 10 is formed, making it difficult to easily form the columnar first portion 10a. If the outer angle B is greater than 120°, the volume of the columnar first portion 10a cannot be appropriately maintained to the extent that the inclined shape of the electrode mixture layer 20 is suppressed.

[0045] Furthermore, in at least one embodiment of the electrode 2, the end of the electrode mixture layer 20 has a shape corresponding to the columnar first portion 10a of the insulating layer 10, so the thickness of the electrode mixture layer 20 at the boundary Q is approximately equal to the thickness of the electrode mixture layer 20 outside the boundary Q (for example, the thickness of the central portion of the electrode 2). In the manufacturing process of the electrode 2, after the electrode mixture layer 20 is provided on the current collector 70, the entire electrode 2 may be pressed with a press machine. In this pressing of the electrode 2, in this embodiment, since the thickness of the electrode mixture layer 20 is approximately equal both at the boundary Q and outside the boundary Q, the entire electrode 2 can be pressed uniformly. As a result, even at the ends of the electrode mixture layer 20, the electrode mixture layer 20 and the current collector 70 are sufficiently adhered by the press, and the peel strength of the electrode mixture layer 20 at the ends of the electrode mixture layer 20 can be increased. Therefore, in the electrode 2 of this embodiment, the entire electrode mixture layer 20 is sufficiently adhered to the current collector 70, and an electrode 2 with sufficient peel strength can be provided. Furthermore, because the electrode 2 has sufficient peel strength, the peeling of the electrode mixture layer 20 from the current collector 70 is suppressed, and an electrode 2 with sufficient capacity can be provided.

[0046] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0047] Examples are described below, but the present invention is not limited to the examples listed below, unless it exceeds the spirit of the present invention.

[0048] (Example 1) The secondary battery 1' of Example 1 was prepared by following the procedure below.

[0049] <Method for fabricating electrode 2'> As the active material in the electrode mixture layer 20' of electrode 2', LiNi ０．８ Co ０．１ Mn ０．１ O ２ A lithium nickel cobalt manganese composite oxide represented by [formula] was prepared. The active material, polyvinylidene fluoride as a binder, and acetylene black and graphite as conductive agents were mixed in a ratio of 82% by mass: 4.5% by mass: 9% by mass: 4.5% by mass. The active material, binder, conductive agents, and N-methylpyrrolidone (NMP) were placed in a planetary mixer. All the materials were stirred in the planetary mixer to obtain a coating solution for the electrode mixture.

[0050] Furthermore, alumina was prepared as insulating particles. Alumina and polyvinylidene fluoride as a binder were mixed in a ratio of 86% by mass:14% by mass. The alumina, binder, and NMP were placed in a planetary mixer. All the materials were stirred in the planetary mixer to obtain an alumina coating solution. Here, at 25°C and a shear rate of 1000 s, －１ In this study, the viscosity of the alumina coating solution was set to 1.0 relative to the viscosity of the electrode mixture coating solution.

[0051] The coating liquid for electrode mixture and the alumina coating liquid were simultaneously applied onto both surfaces of a current collector 70' made of aluminum foil, and the coating films were dried. Here, in order to adjust the external angle B at the intersection point A after drying, the flow rates of the coating liquid for electrode mixture and the alumina coating liquid were adjusted. Specifically, the flow rate of the coating liquid for electrode mixture layer was set to 1.05 relative to the flow rate "1" of the alumina coating liquid. The dried coating film was subjected to roll press treatment. In this manner, an electrode 2' having the structure shown in Fig. 2 was produced, wherein the external angle at the intersection point A is 90°, the ratio of the thickness D of the first portion 10a' of the insulating layer 10' to the thickness D' of the electrode mixture layer 20 is 1.0, the ratio of the length T of the first portion 10a' of the insulating layer 10' to the length T' of the second portion 10b' of the insulating layer 10' is 0.5%, and the ratio of the length (T+T') of the insulating layer 10' to the length S of the electrode mixture layer 20' is 2.5%.

[0052] <Method for producing other electrode 6'> As an active material in the electrode mixture layer of the other electrode 6', Li ４ Ti ５ O １２ lithium titanate having a spinel-type crystal structure represented by was prepared. A negative electrode active material, polyvinylidene fluoride as a binder, and graphite as a conductive agent were prepared such that the mixing ratio was 94 mass% : 2 mass% : 4 mass%. The active material, the binder, the conductive agent, and N-methyl-pyrrolidone (NMP) were charged into a planetary mixer. All the charged materials were stirred by the planetary mixer to obtain a coating liquid for electrode mixture.

[0053] The coating liquid for electrode mixture was applied onto both surfaces of a current collector made of aluminum foil, and the coating film was dried. Further, the dried coating film was subjected to roll press treatment.

[0054] <Production of electrode group 5'> The electrode 2' produced as described above and the other electrode 6' were laminated with a separator 4' interposed therebetween to produce an electrode group 5' having a laminated structure. At this time, the insulating layer 10' of the electrode 2' was opposed to the end portion of the electrode mixture layer 20' of the other electrode 6'.

[0055] <Preparation of non-aqueous electrolyte> As a mixed solvent, a mixed solvent of propylene carbonate and ethyl methyl carbonate (volume ratio 1:2) was prepared. Lithium hexafluorophosphate (LiPF ６The solution was dissolved at a concentration of 1.0 M. In this way, a non-aqueous electrolyte was prepared.

[0056] <Assembly> The electrode group 5' and non-aqueous electrolyte prepared as described above were placed inside the outer case 3', and the container was sealed to assemble the secondary battery 1'.

[0057] <Measurement of 0.2C Discharge Capacity> The 0.2C discharge capacity of secondary battery 1' was confirmed using the following procedure. First, the secondary battery was charged with a constant current (CC charging) at 1C until the battery voltage reached 2.7V, and then charged with a constant voltage (CV charging) at 2.7V for 2 hours. The secondary battery in this state was then discharged with a constant current of 0.2C until the battery voltage reached 1.5V, and the discharge capacity during this discharge was defined as the 0.2C discharge capacity.

[0058] (Example 2) The flow rate of the electrode mixture layer coating solution is set to 1 for every 1 flow rate of the alumina coating solution, making the exterior angle at intersection A 100°, and the rest is the same as in Example 1.

[0059] (Example 3) The flow rate of the electrode mixture layer coating solution is set to 0.9 relative to the flow rate of the alumina coating solution to 1, thereby making the exterior angle at intersection A 120°, and the rest is the same as in Example 1.

[0060] (Example 4) The flow rate of the electrode mixture layer coating solution is set to 1.1 relative to the flow rate of the alumina coating solution to 1, thereby making the exterior angle at intersection A 80°, and the rest is the same as in Example 1.

[0061] (Example 5) The thickness D of the first portion 10a' of the insulating layer 10' and the thickness D' of the electrode mixture layer 20 are set to 0.8, and the rest is the same as in Example 1.

[0062] (Example 6) The thickness D of the first portion 10a' of the insulating layer 10' and the thickness D' of the electrode mixture layer 20 are set to 0.5, and the rest is the same as in Example 1.

[0063] (Example 7) The length T of the first portion 10a' of the insulating layer 10' and the length T' of the second portion 10b' of the insulating layer 10' are set to 0.2%, and the rest is the same as in Example 1.

[0064] (Example 8) The length T of the first portion 10a' of the insulating layer 10' and the length T' of the second portion 10b' of the insulating layer 10' are set to 1.0%, and the rest is the same as in Example 1.

[0065] (Example 9) The length T of the first portion 10a' of the insulating layer 10' and the length T' of the second portion 10b' of the insulating layer 10' are set to 1.5%, and the rest is the same as in Example 1.

[0066] (Example 10) The length of the insulating layer 10' (T + T') / the length S of the electrode mixture layer 20' is set to 1.5%, and the rest is the same as in Example 1.

[0067] (Example 11) The length of the insulating layer 10' (T + T') / the length S of the electrode mixture layer 20' is set to 3.0%, and all other conditions are the same as in Example 1.

[0068] (Example 12) The length of the insulating layer 10' (T + T') / the length S of the electrode mixture layer 20' is set to 3.5%, and the rest is the same as in Example 1.

[0069] (Comparative Example 1) The flow rate of the electrode mixture layer coating solution is set to 0.75 relative to the flow rate of the alumina coating solution to 1, thereby making the exterior angle at intersection A 160°, and the rest is the same as in Example 1.

[0070] (Comparative Example 2) The flow rate of the electrode mixture layer coating solution is set to 0.8 for a flow rate of alumina coating solution of "1", thereby making the exterior angle at intersection A 140°, and the rest is the same as in Example 1.

[0071] Table 1 shows the evaluation of the 0.2C discharge capacity for each example and comparative example. Here, the 0.2C discharge capacity of Comparative Example 1 was used as the baseline. A double circle was used if the capacity was significantly higher than that of Comparative Example 1, a circle was used if the capacity was higher than that of Comparative Example 1, and a triangle was used if the capacity was the same as or lower than that of Comparative Example 1.

[0072]

[0073] As shown in Table 1, Examples 1 to 12 had a higher 0.2C discharge capacity compared to the comparative example. This confirmed that having an outer angle of 80° to 120° at intersection A (the presence of a columnar first portion 10a') suppresses the formation of a sloping shape where the end of the electrode mixture layer 20' is thinned toward the insulating layer 10', and also suppresses the peeling of the entire electrode mixture layer 20' from the current collector 70', thereby ensuring sufficient capacity. Furthermore, since sufficient capacity was ensured in the examples, it was confirmed that short circuits between electrode 2' and the other electrodes 6' can be suppressed by facing the end of the electrode mixture layer 20' of the other electrode 6' with the insulating layer 10' of electrode 2'.

[0074] Among Examples 1 to 12, the capacity was significantly higher than in the comparative examples when the thickness D of the first portion 10a' of the insulating layer 10' and the thickness D' of the electrode mixture layer 20 were 0.8% or more and 1.0% or less, when the length T of the first portion 10a' of the insulating layer 10' and the length T' of the second portion 10b' of the insulating layer 10' were 0.2% or more and 1.0% or less, and when the length (T + T') of the insulating layer 10' and the length S of the electrode mixture layer 20' were 1.5% or more and 3.0% or less.

[0075] From this, it was verified that the thickness D of the first portion 10a' of the insulating layer 10' and the thickness D' of the electrode mixture layer 20 are 0.8 or more and 1.0 or less, which sufficiently prevents the edge of the electrode mixture layer 20' from becoming inclined toward the insulating layer 10', and that the pressing of the entire electrode 2 ensures that the electrode mixture layer 20 and the first portion 10a of the insulating layer 10 are in close contact with the current collector 70.

[0076] Furthermore, it was verified that by having a ratio of the length T of the first portion 10a' of the insulating layer 10' to the length T' of the second portion 10b' of the insulating layer 10

[0077] Furthermore, it was verified that by having a ratio of the length of the insulating layer 10' (T + T') / the length S of the electrode mixture layer 20' of 1.5% to 3.0%, the insulating layer 10' has sufficient length to cover the uncoated portion of the current collector of the other electrode 6' facing electrode 2'. This suppresses contact between the electrode mixture layer 20' and the uncoated portion of the current collector of the other electrode 6' with the insulating layer 10', while minimizing the volume occupied by the insulating layer 10' within the electrode group 5', thereby ensuring sufficient capacity.

[0078] The above results are applied to the electrode 2 of this embodiment. Specifically, the insulating layer 10 of the electrode 2 has a first portion 10a and a second portion 10b that is thinner than the first portion 10a, and the first portion 10a is provided adjacent to the electrode mixture layer 20. Furthermore, if a virtual extension line P is drawn from the surface of the first portion 10a toward the second portion 10b, and the intersection point of the virtual extension line P and the surface of the current collector 70 is A, then the outer angle B at intersection point A is 80° or more and 120° or less. In other words, because the first portion 10a is formed in a columnar shape in the thickness direction (Z direction), and the columnar first portion 10a is provided adjacent to the end of the electrode mixture layer 20, it is possible to suppress the end of the electrode mixture layer 20 from becoming a sloping shape that is formed thinner toward the insulating layer 10. Furthermore, if the outer angle B at intersection A is less than 80°, the insulating layer coating liquid will spread in the width direction (X direction) of the electrode 2 when the insulating layer 10 is formed, making it difficult to easily form the columnar first portion 10a. If the outer angle B is greater than 120°, the volume of the columnar first portion 10a cannot be appropriately maintained to the extent that the inclined shape of the electrode mixture layer 20 is suppressed.

[0079] 1...Secondary battery, 2...Electrode, 3...Outer case, 4...Separator, 5...Electrode group, 6...Other electrodes, 7...Lid member, 9...Opening, 10...Insulating layer, 10a...First part, 10b...Second part, 12...Long side, 14...Short side, 19...Sealing plate, 20...Electrode mixture layer, 21...Gas discharge valve, 23...Terminal, 35...Terminal insulator, 70...Current collector, 70a,b...Unpainted parts.

Claims

1. An electrode comprising a current collector, an electrode mixture layer provided on the current collector, and an insulating layer provided on the current collector and adjacent to the electrode mixture layer, wherein the insulating layer has a first portion at the boundary with the electrode mixture layer and a second portion that is thinner than the first portion, and the outer angle at the intersection of a virtual extension line from the surface of the first portion toward the second portion and the surface of the current collector is 80° or more and 120° or less.

2. The electrode according to claim 1, wherein, at the boundary portion, the thickness of the first portion in the thickness direction of the current collector is 0.8 or more and 1.0 or less with respect to the thickness of the electrode mixture layer.

3. The electrode according to claim 1, wherein the current collector is rectangular in shape having a long side and a short side, the electrode mixture layer is provided parallel to the long side, and the length of the first portion of the electrode mixture layer in the direction parallel to the short side is 0.2% or more and 1.0% or less of the length of the second portion in the direction parallel to the short side.

4. The electrode according to claim 1, wherein the current collector is rectangular in shape having a long side and a short side, the electrode mixture layer is provided parallel to the short side, and the length of the first portion of the electrode mixture layer in the direction parallel to the long side is 0.2% or more and 1.0% or less of the length of the second portion in the direction parallel to the long side.

5. The electrode according to claim 3, wherein the length of the insulating layer in the direction parallel to the short side of the electrode mixture layer is 1.5% or more and 3.0% or less of the length of the electrode mixture layer in the direction parallel to the short side.

6. The electrode according to claim 4, wherein the length of the insulating layer in the direction parallel to the long side of the electrode mixture layer is 1.5% or more and 3.0% or less of the length of the electrode mixture layer in the direction parallel to the long side.

7. The electrode according to claim 1, wherein the current collector is a positive electrode current collector, and the electrode mixture layer is a positive electrode mixture layer.

8. A secondary battery comprising an electrode group in which electrodes according to any one of claims 1 to 7 are wound or stacked via a separator, and an electrolyte.

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