JP6965587B2 - Electrode assembly - Google Patents

Description

One aspect of the present invention relates to an electrode assembly.

A lithium ion battery cell including a large number of metal foils constituting a positive electrode or a negative electrode is known (see, for example, Patent Document 1). In this lithium-ion battery cell, a large number of metal foils are sandwiched between a pair of conductive members, and they are connected by welds. The weld is formed by laser welding.

Japanese Unexamined Patent Publication No. 2016-30280

When a large number of metal foils (tabs) are laminated on a conductive member, each metal foil may warp around the welded portion due to heat generated when forming the welded portion. As the amount of warping of each metal foil (the amount of deformation in the laminating direction) increases, the amount of warping of the entire laminated metal foil also increases. As a result, the metal foil closest to the conductive member may be separated from the conductive member, and the laminated metal foil and the conductive member may not be welded to each other.

One aspect of the present invention is to provide an electrode assembly in which the amount of warpage of the tab laminate is small.

The electrode assembly according to one aspect of the present invention is an electrode assembly having a plurality of sheet-like electrodes each including a tab, and the conductive member and the tabs of the plurality of electrodes are laminated on the conductive member. A tab laminate having an upper surface opposite to the conductive member in the stacking direction of the tabs, and the tabs of the plurality of electrodes and the conductive member are formed on the upper surface of the tab laminate. The maximum length of the welded portion is 4 mm or less in each cross section of the welded portion that is connected by a welded portion formed by welding in the laminating direction.

In this electrode assembly, the amount of warpage of each tab is smaller than that of the case where the maximum length of the welded portion in each cross section orthogonal to the stacking direction exceeds 4 mm, so that the amount of warpage of the tab laminate is also small. This is because the amount of heat given to the tab laminate when forming the welded portion is relatively small.

The tab of the plurality of electrodes and the conductive member are connected by the plurality of welded portions, and the maximum length of the welded portion is 4 mm or less in each cross section orthogonal to the stacking direction in each of the plurality of welded portions. It may be. In this case, by increasing the number of welded portions, the total cross-sectional area of each welded portion orthogonal to the stacking direction of the tabs can be increased.

The number of stacked tabs may be 50 or more. When the number of stacked tabs is as large as 50 or more, the amount of warpage of the tab laminated body becomes large. Even in such a case, if the maximum length of the welded portion in each cross section orthogonal to the stacking direction is 4 mm or less, the amount of warpage of the tab laminated body can be relatively small.

The tab may be made of aluminum and the thickness of the tab may be 20 μm or less. When the thickness of the tab made of aluminum is as thin as 20 μm or less, the amount of warpage of the tab is large, so that the amount of warpage of the tab laminate is also large. Even in such a case, if the maximum length of the welded portion in each cross section orthogonal to the stacking direction is 4 mm or less, the amount of warpage of the tab laminated body can be relatively small.

The tab may be made of copper and the thickness of the tab may be 15 μm or less. When the thickness of the tab made of copper is as thin as 15 μm or less, the amount of warpage of the tab is large, so that the amount of warpage of the tab laminate is also large. Even in such a case, if the maximum length of the welded portion in each cross section orthogonal to the stacking direction is 4 mm or less, the amount of warpage of the tab laminated body can be relatively small.

According to one aspect of the present invention, an electrode assembly having a small amount of warpage of the tab laminate can be provided.

It is an exploded perspective view which shows the power storage device which comprises the electrode assembly which concerns on one Embodiment. It is sectional drawing along the line II-II of FIG. It is a perspective view of the electrode assembly shown in FIG. It is a top view which shows a part of the electrode assembly shown in FIG. It is sectional drawing along the VV line of FIG. It is a figure which shows an example of the process of forming a welded part. It is a top view which shows a part of the electrode assembly which concerns on a modification. It is a figure which shows typically the example of the cross section of the welded part in the stacking direction of a tab. It is a graph which shows the example of the relationship between the maximum length of a welded part and the warpage ratio in each cross section orthogonal to a stacking direction.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and duplicate description is omitted.

FIG. 1 is an exploded perspective view showing a power storage device including the electrode assembly according to the embodiment. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. The power storage device 1 shown in FIGS. 1 and 2 is configured as a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.

The power storage device 1 includes, for example, a case 2 having a substantially rectangular parallelepiped shape and an electrode assembly 3 housed in the case 2. The case 2 is made of a metal such as aluminum. The case 2 has a main body portion 2a opened on one side and a lid portion 2b that closes the opening of the main body portion 2a. Although not shown, a non-aqueous (organic solvent-based) electrolytic solution is injected into the case 2, for example. The positive electrode terminal 4 and the negative electrode terminal 5 are arranged on the lid portion 2b of the case 2 so as to be separated from each other. The positive electrode terminal 4 is fixed to the case 2 via the insulating ring 6, and the negative electrode terminal 5 is fixed to the case 2 via the insulating ring 7. Further, an insulating film F is arranged between the electrode assembly 3 and the inner side surface and the bottom surface of the case 2, and the insulating film F insulates the case 2 from the electrode assembly 3. The lower end of the electrode assembly 3 is in contact with the inner bottom surface of the case 2 via the insulating film F. By arranging the spacer SP between the electrode assembly 3 and the case 2, the gap between the electrode assembly 3 and the case 2 is filled.

The electrode assembly 3 has a plurality of sheet-shaped positive electrodes 8 each having a tab 14b, and a plurality of sheet-shaped negative electrodes 9 each having a tab 16b. In the electrode assembly 3, a plurality of positive electrodes 8 and a plurality of negative electrodes 9 are alternately laminated via a bag-shaped separator 10. The positive electrode 8 is wrapped in a bag-shaped separator 10. The positive electrode 8 in a state of being wrapped in the bag-shaped separator 10 is configured as a positive electrode 11 with a separator. Therefore, the electrode assembly 3 has a structure in which a plurality of positive electrodes 11 with separators and a plurality of negative electrodes 9 are alternately laminated. The separator 10 may be in the form of a sheet instead of the shape of a bag. The electrodes located at both ends of the electrode assembly 3 are negative electrodes 9.

The positive electrode 8 has, for example, a metal foil 14 which is a positive electrode current collector made of aluminum, and a positive electrode active material layer 15 formed on both sides of the metal foil 14. The metal foil 14 has a main body portion 14a having a rectangular shape in a plan view and a tab 14b integrated with the main body portion 14a. The tab 14b projects from the upper edge of the main body 14a. The tab 14b penetrates the separator 10. The tab 14b is connected to the positive electrode terminal 4 via, for example, a plate-shaped conductive member 12. The plurality of tabs 14b are laminated on the conductive member 12. The plurality of stacked tabs 14b are arranged between the conductive member 12 and the protective plate 23 thinner than the conductive member 12 (see FIG. 3). The conductive member 12 and the protective plate 23 are formed in a rectangular flat plate shape from the same material as the metal foil 14 of the positive electrode 8, for example. The electrode assembly 3 does not have to include the protective plate 23.

The positive electrode active material layer 15 is formed on both the front and back surfaces of the main body portion 14a. The positive electrode active material layer 15 is a porous layer formed by containing the positive electrode active material and the binder. Examples of the positive electrode active material include composite oxides, metallic lithium, sulfur and the like. Composite oxides include, for example, at least one of manganese, nickel, cobalt and aluminum and lithium.

The negative electrode 9 has, for example, a metal foil 16 which is a negative electrode current collector made of copper, and a negative electrode active material layer 17 formed on both sides of the metal foil 16. The metal foil 16 has a main body portion 16a having a rectangular shape in a plan view and a tab 16b integrated with the main body portion 16a. The tab 16b projects from the upper edge of the main body 16a. The tab 16b is connected to the negative electrode terminal 5 via, for example, a plate-shaped conductive member 13. The plurality of tabs 16b are laminated on the conductive member 13. The plurality of stacked tabs 16b are arranged between the conductive member 13 and the protective plate 25 thinner than the conductive member 13 (see FIG. 3). The conductive member 13 and the protective plate 25 are made of the same material as the metal foil 16 of the negative electrode 9, and are formed in a rectangular flat plate shape, for example. The electrode assembly 3 does not have to include the protective plate 25.

The negative electrode active material layer 17 is formed on both the front and back surfaces of the main body portion 16a. The negative electrode active material layer 17 is a porous layer formed by containing the negative electrode active material and the binder. Examples of the negative electrode active material include graphite, highly oriented graphite, mesocarbon microbeads, carbon such as hard carbon and soft carbon, alkali metals such as lithium and sodium, metal compounds, and SiOx (0.5 ≦ x ≦ 1.5). ) And other metal oxides or boron-added carbon and the like.

The separator 10 has a rectangular shape in a plan view. Examples of the material for forming the separator 10 include a porous film made of a polyolefin resin such as polyethylene (PE) and polypropylene (PP), or a woven cloth or non-woven fabric made of polypropylene, polyethylene terephthalate (PET), methyl cellulose and the like. ..

FIG. 3 is a perspective view of the electrode assembly shown in FIG. As shown in FIG. 3, in the electrode assembly 3, the assembly main body 20 in which a plurality of positive electrodes 8 and a plurality of negative electrodes 9 are alternately laminated via a separator 10 and tabs 14b of the plurality of positive electrodes 8 are laminated. It has a tab laminate 21 and a tab laminate 22 in which tabs 16b of a plurality of negative electrodes 9 are laminated.

The tab laminates 21 and 22 project from one side surface of the assembly main body 20 in the X-axis direction. The X-axis direction is a direction that intersects (here, orthogonal) with the longitudinal direction (Y-axis direction) of the assembly main body 20 and the stacking direction (Z-axis direction) of the positive electrode 8 and the negative electrode 9. The tab laminates 21 and 22 are arranged apart from each other in the Y-axis direction.

The tab laminate 21 has two side surfaces 21a, a tip surface 21b and an upper surface 21c. The front end surface 21b and the upper surface 21c connect the side surfaces 21a. The upper surface 21c is located on the side opposite to the conductive member 12 in the stacking direction (Z-axis direction) of the tabs 14b. The tab 14b is not provided with the positive electrode active material layer 15. Further, the number of tabs 14b constituting the tab laminate 21 is about half the number of electrodes constituting the electrode assembly 3. Therefore, the tip surface 21b of the tab laminate 21 formed by laminating the tabs 14b according to the height of one side surface of the assembly main body 20 becomes thinner toward the tip of the tab laminate 21. It is an inclined surface like this. The tab laminate 21 is placed on the conductive member 12. A protective plate 23 is placed on the upper surface 21c of the tab laminate 21. Therefore, the tab laminate 21 is sandwiched by the conductive member 12 and the protective plate 23 in the Z-axis direction.

The thickness of the conductive member 12 is larger than the thickness of the tab 14b. The thickness of the protective plate 23 is larger than the thickness of the tab 14b, but smaller than the thickness of the conductive member 12. The length of the conductive member 12 in the Y-axis direction is larger than the length of the tab laminate 21 in the Y-axis direction. Although the tip position of the tab laminate 21 coincides with the edge portion of the conductive member 12, it may protrude from the edge portion of the conductive member 12 in the X-axis direction. The length of the protective plate 23 in the Y-axis direction is equal to the length of the tab laminate 21 in the Y-axis direction. The materials of the conductive member 12 and the protective plate 23 are the same as those of the metal foil 14.

On the upper surface of the protective plate 23, a welded portion 24 formed by welding the protective plate 23, the tab 14b, and the conductive member 12 is provided. A plurality of welded portions 24 may be provided. FIG. 3 shows an example in which two welds 24 are provided. The welded portion 24 extends from the upper surface of the protective plate 23 to the conductive member 12 in the stacking direction (Z-axis direction) of the tabs 14b.

The tab laminate 22 has two side surfaces 22a, a tip surface 22b and an upper surface 22c. The front end surface 22b and the upper surface 22c connect the side surfaces 22a. The upper surface 22c is located on the side opposite to the conductive member 13 in the stacking direction (Z-axis direction) of the tabs 16b. The tab 16b is not provided with the negative electrode active material layer 17. Further, the number of tabs 16b constituting the tab laminate 22 is about half the number of electrodes constituting the electrode assembly 3. Therefore, the tip surface 22b of the tab laminate 22 formed by laminating the tabs 16b according to the height of one side surface of the assembly main body 20 becomes thinner toward the tip of the tab laminate 22. It is an inclined surface like this. The tab laminate 22 is placed on the conductive member 13. A protective plate 25 is placed on the upper surface 22c of the tab laminate 22. Therefore, the tab laminate 22 is sandwiched in the Z-axis direction by the conductive member 13 and the protective plate 25.

The thickness of the conductive member 13 is larger than the thickness of the tab 16b. The thickness of the protective plate 25 is larger than the thickness of the tab 16b, but smaller than the thickness of the conductive member 13. The length of the conductive member 13 in the Y-axis direction is larger than the length of the tab laminate 22 in the Y-axis direction. Although the tip position of the tab laminate 22 coincides with the edge portion of the conductive member 13, it may protrude from the edge portion of the conductive member 13 in the X-axis direction. The length of the protective plate 25 in the Y-axis direction is equal to the length of the tab laminate 22 in the Y-axis direction. The materials of the conductive member 13 and the protective plate 25 are the same as those of the metal foil 16.

On the upper surface of the protective plate 25, a welded portion 26 formed by welding the protective plate 25, the tab 16b, and the conductive member 13 is provided. A plurality of welded portions 26 may be provided. FIG. 3 shows an example in which two welds 26 are provided. The welded portion 26 extends from the upper surface of the protective plate 25 to the conductive member 13 in the stacking direction (Z-axis direction) of the tabs 16b.

FIG. 4 is a plan view showing a part of the electrode assembly shown in FIG. FIG. 5 is a cross-sectional view taken along the line VV of FIG. As shown in FIGS. 4 and 5, each welded portion 26 connects the protective plate 25, the tab laminate 22, and the conductive member 13 to each other in the stacking direction of the tab 16b. As shown in FIGS. 4 and 5, the maximum length L of the welded portion 26 is 4 mm or less in each cross section (XY cross section) orthogonal to the stacking direction of the tabs 16b in each welded portion 26. The maximum length L may be 3 mm or less, 2 mm or less, or 1 mm or less. The maximum length L may be 1 mm or more, 2 mm or more, or 3 mm or more. For example, when the tab laminated body 22 (upper surface 22c of the tab laminated body) is viewed from the stacking direction of the tab 16b, the welded portion 26 has a maximum length L. In the example shown in FIG. 4, the welded portion 26 is exposed on the upper surface of the protective plate 25 when viewed from the Z-axis direction, and each cross section of the welded portion 26 orthogonal to the Z-axis direction extends in the Y-axis direction. It has an elliptical shape with a long axis and a short axis extending in the X-axis direction. The welded portion 26 is, for example, a cone having an ellipse as a bottom surface. When the electrode assembly 3 does not include the protective plate 25, the welded portion 26 is exposed on the upper surface 22c of the tab laminate 22. FIG. 5 is an XZ cross section including the X-axis direction and the Z-axis direction. Each cross section of the welded portion 26 orthogonal to the Z-axis direction may have an elliptical shape having a short axis extending in the Y-axis direction and a long axis extending in the X-axis direction. As shown in FIG. 5, the welded portion 26 penetrates the protective plate 25 and the tab laminate 22 in the Z-axis direction, but does not penetrate the conductive member 13. In FIG. 5, the length W of the welded portion 26 in the X-axis direction decreases from the upper surface 22c (or the upper surface of the protective plate 25) of the tab laminate 22 toward the conductive member 13. Similarly, the length of the welded portion 26 in the Y-axis direction decreases from the upper surface 22c (or the upper surface of the protective plate 25) of the tab laminate 22 toward the conductive member 13. The maximum length D of the welded portion 26 in the Z-axis direction (that is, the maximum depth of the welded portion 26) is, for example, 1.75 to 2.55 mm. A groove 26a recessed in the Z-axis direction is provided on the exposed surface of the welded portion 26. The depth TD of the groove portion 26a is larger than the thickness 25D of the protective plate 25. The groove portion 26a extends in the Y-axis direction. The welded portion 24 provided on the tab laminate 21 also has the same configuration as the welded portion 26.

FIG. 6 is a diagram showing an example of a process of forming a welded portion. As shown in FIG. 6, the welded portion 26 is formed by irradiating the upper surface of the protective plate 25 with an energy beam B for welding. The irradiation direction (welding direction) of the energy beam B is the Z-axis direction. For example, by scanning the irradiation spot of the energy beam B in the Y-axis direction, a welded portion 26 having an elliptical shape having a long axis in which each cross section orthogonal to the Z-axis direction extends in the Y-axis direction is formed. The energy beam B is emitted from the irradiation device 30. The irradiation device 30 is a scanner head including, for example, a lens and a galvanometer mirror. A beam generator is connected to the scanner head via a fiber. The irradiation device 30 may be composed of a refracting optical system such as a prism. The energy beam B is a high energy beam capable of performing welding. The energy beam B is, for example, a laser beam or an electron beam. The irradiation of the energy beam B is performed in an atmosphere of an inert gas. The welded portion 24 provided on the tab laminate 21 is also formed by the same method as the welded portion 26.

When the tab 14b, the conductive member 12 and the protective plate 23 are made of aluminum, the output of the energy beam B is, for example, 700 to 1200 W, and the scanning speed of the energy beam B is, for example, 3 to 20 mm / s. When the tab 16b, the conductive member 13 and the protective plate 25 are made of copper, the output of the energy beam B is, for example, 1300 to 1800 W, and the scanning speed of the energy beam B is, for example, 3 to 20 mm / s.

When the tab 14b is made of aluminum, the thickness of the tab 14b may be, for example, 8 μm or more, or 20 μm or less. The number of stacked tabs 14b may be, for example, 50 or more, or 150 or less. When the tab 16b is made of copper, the thickness of the tab 16b may be, for example, 5 μm or more, or 15 μm or less. The number of stacked tabs 16b may be, for example, 50 or more, or 150 or less.

When the protective plate 23 is made of aluminum, the thickness of the protective plate 23 may be, for example, 0.1 mm or more, or 0.3 mm or less. When the protective plate 25 is made of copper, the thickness of the protective plate 25 may be, for example, 0.1 mm or more, or 0.3 mm or less. When the conductive member 12 is made of aluminum, the thickness of the conductive member 12 may be, for example, 0.5 mm or more, or 2.0 mm or less. When the conductive member 13 is made of copper, the thickness of the conductive member 13 may be, for example, 0.5 mm or more, or 2.0 mm or less.

As described above, the maximum length L of the welded portion 26 is 4 mm or less in each cross section of the welded portion 26 orthogonal to the Z-axis direction. Therefore, since the amount of warpage of each tab 16b and the protective plate 25 is smaller than that in the case where the maximum length of the welded portion in each cross section orthogonal to the Z-axis direction exceeds 4 mm, the warpage of the tab laminate 22 and the protective plate 25 is small. The amount is also small. This is because the amount of heat given to the tab laminate 22 and the protective plate 25 when forming the welded portion 26 is relatively small. When the amount of warpage of the tab laminate 22 and the protective plate 25 is small, the electrical resistance between the tab laminate 22 and the conductive member 13 can be reduced, and the peel strength between the tab laminate 22 and the conductive member 13 is increased. be able to.

Further, the maximum length L of the welded portion 24 is 4 mm or less in each cross section orthogonal to the Z-axis direction in the welded portion 24 that passes from the protective plate 23 through the tab laminate 21 and reaches the conductive member 12. Therefore, the same effect as that of the tab laminate 22 can be obtained for the tab laminate 21.

Further, since the tab laminate 22 is provided with a plurality of welded portions 26, the total cross-sectional area of each welded portion 26 orthogonal to the Z-axis direction can be increased by increasing the number of welded portions 26. Can be done. As a result, the electrical resistance between the tab laminate 22 and the conductive member 13 can be further reduced, and the peel strength between the tab laminate 22 and the conductive member 13 can be further increased. When a scanner head including a lens and a galvanometer mirror is used as the irradiation device 30 of the energy beam B, a plurality of welded portions 26 can be formed at high speed. Since the tab laminate 21 is also provided with a plurality of welded portions 24, the same effect as that of the tab laminate 22 can be obtained for the tab laminate 21.

Further, when the tab 14b is made of aluminum and the thickness of the tab 14b is as thin as 20 μm or less, the amount of warpage of the tab is large, so that the amount of warpage of the tab laminate is also large. Even in such a case, if the maximum length of the welded portion 24 in each cross section orthogonal to the Z-axis direction is 4 mm or less, the amount of warpage of the tab laminate 21 can be relatively small.

Further, when the tab 16b is made of copper and the thickness of the tab 16b is as thin as 15 μm or less, the amount of warpage of the tab is large, so that the amount of warpage of the tab laminate is also large. Even in such a case, if the maximum length L of the welded portion 26 in each cross section orthogonal to the Z-axis direction is 4 mm or less, the amount of warpage of the tab laminate 22 can be made relatively small.

FIG. 7 is a plan view showing a part of the electrode assembly according to the modified example. In the electrode assembly 3a shown in FIG. 7A, a plurality of (for example, 6) welded portions 26 are arranged in a staggered pattern. The tab laminate 22 projects from the edge of the conductive member 13 in the X-axis direction. The protective plate 25 is not provided, and the welded portion 26 is exposed on the upper surface 22c of the tab laminate 22. Other than that, the electrode assembly 3a has the same configuration as the electrode assembly 3 shown in FIG.

The electrode assembly 3a shown in FIG. 7A also has the same effect as that of the electrode assembly 3. In the electrode assembly 3a, since the amount of warpage of each tab 16b is small, the amount of warpage of the tab laminate 22 is also small. This is because the amount of heat given to the tab laminate 22 when forming the welded portion 26 is relatively small. When the amount of warpage of the tab laminate 22 is small, the electrical resistance between the tab laminate 22 and the conductive member 13 can be reduced, and the peel strength between the tab laminate 22 and the conductive member 13 can be increased.

In the electrode assembly 3b shown in FIG. 7B, a plurality of (for example, five) welded portions 26 are arranged in a staggered pattern. Each welded portion 26 has a circular shape when the tab laminate 22 is viewed from the Z-axis direction. In this case, the maximum length L of the welded portion 26 is the diameter of the circle. Other than that, the electrode assembly 3b has the same configuration as the electrode assembly 3a shown in FIG. 7A. The circular weld 26 can be formed, for example, by scanning the energy beam B in both the X-axis and Y-axis directions. The electrode assembly 3b shown in FIG. 7B also has the same effect as that of the electrode assembly 3a.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment.

For example, in the above embodiment, the power storage device 1 is a lithium ion secondary battery, but the power storage device 1 is, for example, another secondary battery such as a nickel hydrogen battery, or a power storage device such as an electric double layer capacitor or a lithium ion capacitor. There may be.

Further, in the above embodiment, the electrode assembly 3 includes a plurality of welded portions 24, but a single welded portion 24 may be provided. Similarly, the electrode assembly 3 includes a plurality of welds 26, but may include a single weld 26.

(Experimental example)
Hereinafter, the present invention will be described in more detail based on Experimental Examples, but the present invention is not limited to the following Experimental Examples.

First, 90 tabs (one sheet having a thickness of 15 μm) made of aluminum were laminated on a conductive member made of aluminum. Next, a protective plate (thickness 0.2 mm) made of aluminum was laminated on the tab laminate. Then, by irradiating the upper surface of the protective plate with a laser, a welded portion extending from the protective plate toward the conductive member was formed. When the tab laminate was viewed from the tab stacking direction, the welded portion exposed on the upper surface of the protective plate had an elliptical shape with a major axis length of 1 mm. That is, the maximum length of the welded portion in each cross section orthogonal to the stacking direction of the tabs was 1 mm. In this way, an electrode assembly having the welded portion of Experimental Example 1 was produced. Similarly, the electrode assembly having the welded portions of Experimental Examples 2 to 7 is set so that the maximum lengths of the welded portions in each cross section orthogonal to the stacking direction of the tabs are 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, and 7 mm, respectively. A solid was made.

Subsequently, the cross section of the welded portion in the stacking direction of the tabs was observed. FIG. 8A schematically shows a cross section of the welded portion of Experimental Example 4 (a cross section including the tab stacking direction and the tab protruding direction). In FIG. 8A, although the tab laminate 22 and the protective plate 25 are slightly warped in the stacking direction of the tab 16b, the welded portion 26 passes from the protective plate 25 through the tab laminate 22 to the conductive member 13. It has reached. The conductive member 13 is not warped. In such a welded portion 26, the electric resistance between the tab laminate 22 and the conductive member 13 can be lowered, and the peel strength between the tab laminate 22 and the conductive member 13 can be increased.

FIG. 8B schematically shows a cross section of the welded portion of Experimental Example 5 (a cross section including the tab stacking direction and the tab protruding direction). In FIG. 8B, the tab laminate 122 and the protective plate 125 are warped in the stacking direction of the tab 16b. In particular, the amount of warpage of the tab laminate 122 is large. As a result, the welded portion 126 extends from the protective plate 125 to the tab laminate 122, but does not reach the conductive member 113. The conductive member 113 is not warped. A gap V is formed between the tab laminate 122 and the conductive member 113. In such a welded portion 126, the tab laminate 122 and the conductive member 113 are not electrically or mechanically connected to each other.

Further, for the electrode assembly having the welded portions of Experimental Examples 1 to 7, the warpage ratios of the tab laminate and the protective plate were calculated as follows. Before forming the welded portion, the value obtained by measuring the distance from the upper surface of the conductive member to the upper surface of the protective plate (total thickness of the tab laminate and the protective plate) was set to D1 (mm) (see FIG. 6). After forming the welded portion, the value obtained by measuring the distance from the upper surface of the conductive member to the upper surface of the protective plate was defined as D2 (mm). D1 and D2 were measured using a caliper at the edge of the welded portion when the tab laminate was viewed from the protective plate side in the tab stacking direction. D2 is illustrated in FIGS. 8 (a) and 8 (b).

The warpage rate R (%) is calculated from the following formula. The value of (D2-D1) in the formula is the total value of the warp amount of the tab laminate and the warp amount of the protective plate.
R = (D2-D1) / D1 × 100

FIG. 9 is a graph showing the relationship between the maximum length (mm) of the welded portion and the warpage rate (%) in each cross section orthogonal to the stacking direction of the tabs for the electrode assembly having the welded portions of Experimental Examples 1 to 7. Is. As shown in FIG. 9, the warpage rate is 50% or less in Experimental Examples 1 to 4 having a maximum length of 4 mm or less, and the warpage rate is 100% or more in Experimental Examples 5 to 7 having a maximum length of more than 4 mm. there were. As described above, in Experimental Examples 1 to 4, the warpage rate was remarkably smaller than that in Experimental Examples 5 to 7.

1 ... Power storage device, 3,3a, 3b ... Electrode assembly, 8 ... Positive electrode, 9 ... Negative electrode, 12, 13 ... Conductive member, 14b, 16b ... Tab, 21,22 ... Tab laminate, 21c, 22c ... Top surface, 24, 26 ... Welded part.

Claims (5)

An electrode assembly each having a plurality of sheet-like electrodes including tabs.
Conductive members and
A tab laminate formed by laminating the tabs of the plurality of electrodes on the conductive member and having an upper surface on the side opposite to the conductive member in the stacking direction of the tabs.
With
The tabs of the plurality of electrodes and the conductive member are connected by a plurality of welded portions formed by welding from the upper surface of the tab laminate in the stacking direction.
In each section perpendicular to the stacking direction of each of the plurality of weld state, and are the 4mm or less than the maximum length of the weld,
When the direction perpendicular to the stacking direction and the direction in which the welded portion has the maximum length is defined as the maximum length direction, in each of the cross sections, the welded portion has a long axis extending in the maximum length direction. Has an elliptical shape
The plurality of welds are electrode assemblies including two or more welds aligned along the maximum length direction of one weld. The electrode assembly according to claim 1 , wherein the plurality of welded portions are arranged in a staggered pattern on the upper surface of the tab laminate. The electrode assembly according to claim 1 or 2, wherein the number of stacked tabs is 50 or more. The tab is made of aluminum
The electrode assembly according to any one of claims 1 to 3, wherein the thickness of the tab is 20 μm or less. The tab is made of copper
The electrode assembly according to any one of claims 1 to 3, wherein the thickness of the tab is 15 μm or less.

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