Secondary battery

Abstract

To suppress outflow of an electrolyte solution from an electrode body.SOLUTION: A secondary battery 1 includes an electrode body 3 including a positive electrode 32 including a positive electrode plate 32a and a positive electrode active material layer 32b, a negative electrode 33 including a negative electrode plate 33a and a negative electrode active material layer 33b, and a separator 31 held between the positive electrode 32 and the negative electrode 33, and current collector plates 4a and 5a connected to the respective end parts 3a and 3b of the positive electrode plate 32a and the negative electrode plate 33a in a central axis direction. The positive electrode plate 32a and the negative electrode plate 33a include an active material layer formation part P1 and an active material layer non-formation part P2. The separator 31 includes a plurality of projections 7 provided at predetermined intervals along a direction and extending in a first direction. At least some of the projections 7 each include a first protrusion 71 facing the active material layer formation part P1, and a second protrusion 72 facing the active material layer non-formation part P2 and protruding higher than the first protrusion 71 in a second direction.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The technology disclosed herein relates to a secondary battery. [Background technology]

[0002] For example, Patent Document 1 discloses a wound electrode body for a non-aqueous electrolyte secondary battery. Specifically, the electrode body (wound electrode body) disclosed in Patent Document 1 is configured by winding a laminate of a positive electrode sheet, a negative electrode sheet, and a separator (separator sheet) interposed between the positive electrode sheet and the negative electrode sheet in the longitudinal direction of the sheets. This electrode body is accommodated in a case (battery case) to configure the secondary battery according to Patent Document 1.

[0003] Here, the separator has thicker and thinner regions alternately arranged along the longitudinal direction, and by providing two types of regions alternately, the permeability of the electrolyte (non-aqueous electrolyte) in the longitudinal direction can be made lower than that in the width direction. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-57522 A Summary of the Invention [Problem to be solved by the invention]

[0005] Generally, when charging at a high rate, the electrolyte leaks out from the negative electrode side of the electrode assembly and spreads throughout the case. Although the leaked electrolyte is designed to return during discharge, it only returns from the part of the electrode assembly that is immersed in the electrolyte, so it takes a long time for the electrolyte to return sufficiently.

[0006] In view of this, as described in Patent Document 1, it is conceivable to provide a separator with regions of large thickness and regions of small thickness, thereby allowing the electrolyte to be held in grooves defined by these regions.

[0007] However, the amount of electrolyte that can be held in such grooves is insufficient to prevent the electrolyte from leaking out of the electrode body, and in this respect, the configuration disclosed in Patent Document 1 leaves room for improvement.

[0008] The technology disclosed herein has been made in consideration of the above points, and has an object to suppress the outflow of electrolyte from the electrode body. [Means for solving the problem]

[0009] A first aspect of the present disclosure relates to a secondary battery comprising: an electrode assembly including a positive electrode having a positive electrode plate and a positive electrode active material layer, a negative electrode having a negative electrode plate and a negative electrode active material layer, and a separator interposed between the positive electrode and the negative electrode; current collector plates connected to each end of the positive electrode plate and the negative electrode plate in a first direction; and an electrolyte solution contained in the electrode assembly.

[0010] According to the first aspect, the positive electrode plate and the negative electrode plate each have, when viewed along a second direction perpendicular to the first direction, active material layer-forming portions where each of the positive electrode plate and the negative electrode plate and a corresponding one of the positive electrode active material layer and the negative electrode active material layer overlap, and active material layer-non-forming portions provided at each end and where each of the electrode plates is exposed when viewed along the second direction, and the separator has a plurality of protrusions provided at predetermined intervals along a third direction perpendicular to the first direction and the second direction and each extending in the first direction, and at least a portion of the plurality of protrusions each have a first protrusion portion facing the active material layer-forming portion and a second protrusion portion facing the active material layer-non-forming portion and protruding higher than the first protrusion portion in the second direction.

[0011] According to the first aspect, one protrusion, together with other adjacent protrusions, forms a groove capable of holding an electrolyte. Here, the height of the portion (second protrusion portion) located at the end of each protrusion in the first direction is set to be higher than the height of the portion (first protrusion portion) located near the center in the first direction. By setting in this manner, the depth of the groove formed between the second protrusion portions is deeper than the depth of the groove formed between the first protrusion portions.

[0012] In this way, by making the grooves in the second protruding portions deeper, it becomes possible to hold a larger amount of electrolyte at each end of each electrode plate than before, thereby making it possible to prevent the electrolyte from leaking out of the electrode assembly.

[0013] Moreover, by making the ridges taller only in the portions facing the portions without the active material layer, rather than making the grooves deeper over the entire area in the first direction, the thickness of the portions with the active material layer formed can be maintained at the same thickness as before without increasing the thickness, thereby preventing the electrode body, and in turn the secondary battery, from becoming larger.

[0014] According to the second aspect, a width of the second protruding portion in the third direction may be narrower than or equal to a width of the first protruding portion in the third direction.

[0015] According to the second aspect, the width of the groove formed between the second protruding portions is wider than the width of the groove formed between the first protruding portions. By widening the groove width at each end of each electrode plate, more electrolyte can be held. This is advantageous in preventing the electrolyte from leaking out of the electrode assembly.

[0016] According to the third aspect, the plurality of protrusions may be composed of a plurality of first protrusions each lacking the second protrusion portion, and a plurality of second protrusions each having the second protrusion portion and arranged to sandwich the first protrusions from both sides in the third direction.

[0017] According to the third aspect, in the grooves formed at each end of each electrode plate, the second ridges define the side walls of the grooves, and the first ridges define the bottom walls of the grooves. This configuration allows the groove width to be further increased. By increasing the groove width, more electrolyte can be held. This is advantageous in suppressing the outflow of electrolyte from the electrode body.

[0018] According to the fourth aspect, the second ridges may be configured such that the second protrusion portions aligned in the third direction define second grooves having the second protrusion portions as inner walls, the number of rows of the first ridges sandwiched between the second ridges is defined as a number of adjacent rows, an area of ​​each of the second grooves when viewed from the front in the second direction is defined as a second area, and an area increase ratio is a ratio of the second area when the number of adjacent rows is a predetermined number of rows to the second area when the number of adjacent rows is one row, the area increase ratio may be set to be 1.5 or greater.

[0019] According to the fourth aspect, a second groove is defined between two second protrusions, with the area between them serving as the groove bottom. The second area, which indicates the area of ​​the second groove, increases or decreases according to the number of first ridges sandwiched between the second ridges (the number of adjacent rows). According to findings obtained through studies by the present inventors, a sufficient amount of electrolyte can be held in each second groove by setting the area increase ratio, which is an index of the second area, to 1.5 or more.

[0020] According to the fifth aspect, the groove width of each of the second groove portions in the third direction may be set to 1 cm or less.

[0021] Generally, the second groove portion prevents the electrolyte from flowing out by capillary action, so if the groove width of the second groove portion is made too wide, there is a concern that the electrolyte may flow out of the second groove portion.

[0022] According to the findings of the present inventors, by setting the groove width of the second groove portion to 1 cm or less as in the fifth embodiment, it is possible to suppress the outflow of electrolyte from the second groove portion.

[0023] Furthermore, according to the sixth aspect, at least a portion of the plurality of protrusions may each further have a third protrusion portion interposed between the first protrusion portion and the second protrusion portion and facing the portion without the active material layer, and the third protrusion portion may protrude lower in the second direction than the second protrusion portion.

[0024] According to the sixth aspect, by interposing the third protruding portion between the first protruding portion and the second protruding portion, it is possible to suppress interference between the positive electrode active material layer or the negative electrode active material layer and the second protruding portion. This configuration is particularly effective in manufacturing a secondary battery in that the electrode body can be assembled in the same manner as in the past. Effect of the Invention

[0025] As described above, according to the present disclosure, it is possible to suppress the outflow of electrolyte from the electrode assembly. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of a secondary battery. [Diagram 2] FIG. 2 is a perspective view illustrating an example of a layered structure of the electrode body. [Diagram 3] FIG. 3 is a vertical cross-sectional view of the electrode body. [Figure 4] FIG. 4 is a perspective view showing the electrode body with some parts omitted. [Diagram 5] FIG. 5 is a cross-sectional view of the electrode body. [Figure 6] FIG. 6 is a plan view of the separator. [Figure 7] FIG. 7 is a plot showing the relationship between the number of adjacent rows of the primary ridges and the area increase ratio. [Figure 8] FIG. 8 is a plot showing an example of FIG. [Figure 9] FIG. 9 is a table showing the results of comparing the examples and the comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. The following description is by way of example. Fig. 1 is a schematic diagram illustrating the configuration of a secondary battery. Fig. 2 is a perspective view illustrating the layered structure of an electrode body. Fig. 3 is a vertical cross-sectional view of the electrode body, Fig. 4 is a perspective view showing the electrode body with some parts omitted, and Fig. 5 is a horizontal cross-sectional view of the electrode body. Also, Fig. 6 is a plan view of a separator.

[0028] The secondary battery 1 according to this embodiment is suitable for use in electronic devices, electric vehicles, hybrid vehicles, etc. This secondary battery 1 is a so-called lithium ion secondary battery.

[0029] Overall Structure 1, the secondary battery 1 includes a box-shaped case 2, a flat electrode assembly 3, a positive electrode current collector plate (current collector) 4a and a negative electrode current collector plate (current collector) 5a connected to the electrode assembly 3, and a nonaqueous electrolyte (electrolyte) 6 contained in the electrode assembly 3. The electrode assembly 3, the positive electrode current collector plate 4a, the negative electrode current collector plate 5a, and the nonaqueous electrolyte 6 are all housed in the case 2.

[0030] The case 2 constitutes an outer casing for the secondary battery 1. The case 2 is provided with a positive terminal 4 formed by a positive current collector plate 4a and a negative terminal 5 formed by a negative current collector plate 5a, each of which protrudes from the upper surface of the case 2.

[0031] As shown in Figures 1 and 2, the electrode body 3 is composed of a sheet-shaped positive electrode 32, a sheet-shaped negative electrode 33, and a separator 31 that is also formed in a sheet shape and is interposed between the positive electrode 32 and the negative electrode 33.

[0032] Specifically, the electrode body 3 is a wound electrode body having an elliptical cross section and a flat shape, which is formed by stacking a plurality of sheet-like members (positive electrodes 32, negative electrodes 33, and separators 31) and winding these members around a central axis Oc.

[0033] Hereinafter, the direction along the central axis Oc is referred to as the “first direction” or the “central axis direction.” This first direction (central axis direction) coincides with the horizontal direction of the secondary battery 1 when the electrode body 3 is housed in the case 2.

[0034] More specifically, the electrode assembly 3 is formed by rolling a laminate obtained by stacking one separator 31, one negative electrode 33, one separator 31, and one positive electrode 32 in this order around the central axis Oc.

[0035] 2, the positive electrode 32 has a sheet-like positive electrode plate 32a and a positive electrode active material layer 32b laminated on a partial region (active material layer forming portion P1) of the positive electrode plate 32a. Similarly, the negative electrode 33 has a sheet-like negative electrode plate 33a and a negative electrode active material layer 33b laminated on a partial region (active material layer forming portion P1) of the negative electrode plate 33a.

[0036] Here, the left end (one end) 3a of the positive electrode plate 32a in the first direction protrudes toward one end side in the first direction (the left end side of the paper in Figs. 1 and 2) compared to the negative electrode plate 33a. The left end 3a here corresponds to the left end of the paper in Figs. 1 and 2. This left end 3a constitutes an active material layer-free portion P2 where the positive electrode active material layer 32b is not formed and the positive electrode plate 32a is exposed.

[0037] A current collector (positive current collector 4a) of the positive terminal 4 is joined to the left end 3a of the positive plate 32a. The positive current collector 4a is a plate-shaped member extending along the height direction of the secondary battery 1, and constitutes the lower portion of the positive terminal 4.

[0038] In addition, the left end of separator 31 in the first direction (the left end on the paper in FIGS. 1 and 2, like positive electrode plate 32a) protrudes slightly toward the left end in the first direction compared to negative electrode plate 33a. The amount of protrusion of separator 31 at the left end in the first direction is smaller than the amount of protrusion of positive electrode plate 32a in the same direction.

[0039] Moreover, the positive electrode active material layer 32b is formed on one of the front and back surfaces of the positive electrode plate 32a facing the separator 31. The positive electrode active material layer 32b faces the separator 31 and at the same time faces the negative electrode active material layer 33b with the separator 31 in between. The region of the positive electrode plate 32a where the positive electrode active material layer 32b is formed constitutes an active material layer forming portion P1 where the positive electrode active material layer 32b and the positive electrode plate 32a overlap each other.

[0040] The stacking direction of the positive electrode active material layer 32b and the positive electrode plate 32a is a direction perpendicular to the paper surface of Fig. 2 and corresponds to the up-down direction of the paper surface of Fig. 5. Hereinafter, this stacking direction is referred to as the "second direction". This second direction coincides with the thickness direction of each of the positive electrode 32, the negative electrode 33, and the separator 31.

[0041] The positive electrode plate 32a is a long, so-called positive electrode current collector, and is made of a conductive metal thin film (e.g., aluminum foil). The positive electrode active material layer 32b is formed by mixing a positive electrode active material and an auxiliary (binder and conductive auxiliary) and applying the mixture to the positive electrode plate 32a. As the positive electrode active material, it is preferable to use a composite metal oxide containing one or more elements selected from the group consisting of cobalt, manganese, and nickel and lithium, a phosphate-based lithium compound, a silicate-based lithium compound, or the like.

[0042] On the other hand, a right end (other end) 3b of the negative electrode plate 33a in the first direction protrudes toward the other end side in the first direction (the right end side of the paper in Figs. 1 and 2) compared to the positive electrode plate 32a. The right end 3b here corresponds to the right end of the paper in Figs. 1 and 2. This right end 3b, like the right end 3b of the positive electrode plate 32a, constitutes an active material layer-free portion P2 where the negative electrode active material layer 33b is not formed and the negative electrode plate 33a is exposed.

[0043] A current collector (negative current collector 5a) of the negative terminal 5 is joined to the right end 3b of the negative plate 33a. The negative current collector 5a is a plate-like member extending along the height direction of the secondary battery 1, and constitutes the lower portion of the negative terminal 5.

[0044] In addition, the right end of the separator 31 in the first direction (the right end in the paper of FIGS. 1 and 2, like the positive electrode plate 32a) protrudes slightly toward the right end in the first direction compared to the positive electrode plate 32a. The protrusion amount of the separator 31 at the right end in the first direction is smaller than the protrusion amount of the negative electrode plate 33a in the same direction.

[0045] The negative electrode active material layer 33b is formed on one of the front and back surfaces of the negative electrode plate 33a facing the separator 31. The negative electrode active material layer 33b faces the separator 31 and also faces the positive electrode active material layer 32b with the separator 31 in between. The region of the negative electrode plate 33a where the negative electrode active material layer 33b is formed constitutes an active material layer forming portion P1 where the negative electrode active material layer 33b and the negative electrode plate 33a overlap each other.

[0046] The negative electrode plate 33a is a long negative electrode current collector made of a conductive metal thin film (e.g., copper foil). The negative electrode active material layer 33b is formed by mixing a negative electrode active material and an auxiliary (binder and conductive auxiliary) and applying the mixture to the negative electrode plate 33a. It is preferable to use a graphite-based carbon material, i.e., artificial graphite and / or natural graphite, as the negative electrode active material.

[0047] As described above, the current collectors 4a, 5a are connected to the ends 3a, 3b of the positive and negative electrode plates 32a, 33a in the first direction (in other words, both ends of the electrode body 3 in the first direction). The positive and negative current collectors 4a, 5a are each connected to the active material layer-free portion P2 of a corresponding one of the positive and negative electrode plates 32a, 33a.

[0048] As shown in Fig. 3, each separator 31 has a base layer 31a and a ceramic layer 31b provided on the base layer 31a. Both the base layer 31a and the ceramic layer 31b are porous thin films. The base layer 31a is made of a synthetic resin such as polyethylene or polypropylene. The ceramic layer 31b is made of a ceramic material.

[0049] Separator 31 also has a number of ridges 7 provided at predetermined intervals along a third direction perpendicular to the first and second directions (see FIG. 3). Each of the ridges 7 extends along the first direction. Here, the "third direction" is the direction extending along the surface of separator 31, and corresponds to the left-right direction on the paper surface of FIG. 3. When a wound electrode body is used as electrode body 3, the third direction corresponds to the winding direction of the wound electrode body.

[0050] The multiple ridges 7 are formed on the ceramic layer 31b of the separator 31 and are arranged in multiple rows along the third direction. The multiple ridges 7 are each disposed so as to face at least the negative electrode active material layer 33b out of the positive electrode active material layer 32b and the negative electrode active material layer 33b.

[0051] A groove 8 capable of holding the non-aqueous electrolyte 6 is formed by one ridge 7 and another ridge 7 adjacent thereto. Each groove 8 extends in the first direction, similar to the ridges 7.

[0052] The nonaqueous electrolyte 6 held by each groove 8 is the electrolyte contained inside the electrode body 3. Specifically, the nonaqueous electrolyte according to this embodiment is prepared by dissolving a supporting electrolyte in a nonaqueous solvent. This nonaqueous electrolyte 6 is liquid at, for example, −40° C. to 70° C., and additives are added as necessary.

[0053] As already described, the positive electrode plate 32a and the negative electrode plate 33a each have an active material layer forming portion P1 and an active material layer non-forming portion P2. Here, the active material layer forming portion P1 corresponds to a portion where the positive electrode plate 32a and the negative electrode plate 33a overlap with the corresponding one of the positive electrode active material layer 32b and the negative electrode active material layer 33b when viewed in the second direction. On the other hand, the active material layer non-forming portion P2 is provided at each end 3a and 3b of the positive electrode plate 32a and the negative electrode plate 33a, and corresponds to a portion where the respective electrode plates 32a and 33a are exposed when viewed in the second direction.

[0054] The plurality of protrusions 7 described above are configured to correspond to the layout of the active material layer forming portion P1 and the active material layer non-forming portion P2. That is, at least some of the plurality of protrusions 7 each have a first protrusion portion 71 facing the active material layer forming portion P1, and a second protrusion portion 72 facing the active material layer non-forming portion P2 and protruding higher in the second direction than the first protrusion portion 71. The height H2 of the second protrusion portion 72 in the second direction is longer than the height H1 of the first protrusion portion 71 in the second direction (see FIG. 5).

[0055] The first protrusion portion 71 and the second protrusion portion 72 are aligned linearly in the first direction to form one protrusion 7. When one protrusion 7 is divided into a region facing the portion P1 where the active material layer is formed and a region facing the portion P where the active material layer is not formed, the former region corresponds to the first protrusion portion 71 and the latter region corresponds to the second protrusion portion 72. In this case, the groove 8 formed by each protrusion 7 can be divided into a first groove portion 81 formed by the first protrusion portion 71 and a second groove portion 82 formed by the second protrusion portion 72.

[0056] The first protruding portion 71 and the second protruding portion 72 are integrally configured via the third protruding portion 73, which is also arranged in a straight line. The first protruding portion 71, the third protruding portion 73, and the second protruding portion 72 are connected in a straight line in this order.

[0057] Specifically, the third protruding portion 73 is disposed between the first protruding portion 71 and the second protruding portion 72, and faces the portion P2 where the active material layer is not formed. The third protruding portion 73 protrudes lower in the second direction than the second protruding portion 72. For example, the third protruding portion 73 according to this embodiment is configured to be flush with the first protruding portion 71, and has the same height H1 as the first protruding portion 71 in the second direction (see FIG. 5).

[0058] Furthermore, the width of the second protruding portion 72 in the third direction (particularly the width at the end in the first direction) is set to be narrower than the width of the first protruding portion 71 in the third direction. In this case, the width of the first groove portion 81 corresponding to the first protruding portion 71 is wider than the width of the second groove portion 82 corresponding to the second protruding portion 72 that is taller than the first protruding portion 71.

[0059] The second protrusions 72 may be configured to be gradually narrowed toward the ends in the first direction, as shown in Fig. 6. In the example shown in Fig. 6, each of the second protrusions 72 has a triangular shape tapered toward both ends in the first direction in a plan view along the second direction. In this case, the second grooves 82 have a shape in which the groove width is tapered toward the ends in the third direction.

[0060] In the secondary battery 1 according to the present disclosure, all of the ridges 7 may have the second protrusion portions 72, or some of the ridges 7 may have the second protrusion portions 72. The latter configuration will be described below.

[0061] In this case, the multiple protrusions 7 can be divided into a multiple of first protrusions 7A each lacking a second protrusion portion 72, and second protrusions 7B each having a second protrusion portion 72 and arranged to sandwich the first protrusions 7A from both sides in the third direction, as shown in Figures 4 and 6.

[0062] The first protrusions 7A and the second protrusions 7B define the above-mentioned first grooves 81 with the first protrusions 71 as inner walls by the respective first protrusions 71 aligned in the third direction.

[0063] Further, the second protrusions 7B define the above-mentioned second grooves 82 with the second protrusions 72 serving as inner walls (side walls of the second grooves 82) by the second protrusions 72 aligned in the third direction.

[0064] Because the first protrusion 7A lacks the second protrusion portion 72, the number of second groove portions 82 is smaller than the number of first groove portions 81. Accordingly, the groove width W1 of the second groove portions 82 in the third direction is larger than the groove width W3 of the first groove portions 81 in the third direction (see also FIG. 6 for groove widths W1, W3).

[0065] 4, for example, the first ridges 7A and the second ridges 7B are arranged in alternate rows in the third direction. In this case, the first grooves 81 formed by the first protrusions 71 are formed in the same number as the total number of the first and second ridges 7A, 7B, and the second grooves 82 formed by the second protrusions 72 are formed in approximately half of the total number. In this case, the groove width of the second grooves 82 is more than twice the groove width of the first grooves 81.

[0066] 6, the first ridges 7A are provided continuously in two rows along the third direction. The second ridges 7B are provided to sandwich the two rows of the first ridges 7A from both sides in the third direction. In this case, the groove width W1 of the second grooves 82 is greater than three times the groove width W3 of the first grooves 81.

[0067] Incidentally, by increasing the proportion of the first protrusions 7A to all the protrusions 7 (in other words, the proportion of all the protrusions 7 that are lacking the second protrusion portions 72), it is believed that the volume of the second groove portions 82 at both ends can be expanded, and the amount of non-aqueous electrolyte 6 that can be held by these second groove portions 82 can be increased.

[0068] However, considering that the nonaqueous electrolyte is held by the surface tension of the grooves 8, it is believed that converting all of the ridges 7 into the first ridges 7A (in other words, removing the second protrusion portions 72 from all of the ridges 7) would impair the ability to hold the nonaqueous electrolyte 6. A certain upper limit can be set for the volume of the second groove portions 82 that can be expanded by increasing the proportion of the first ridges 7A. This upper limit can be set, for example, via the groove width W1 of each second groove portion 82 in the third direction (see FIG. 6).

[0069] As a result of intensive research by the present inventors, the findings obtained show that it is preferable to set the groove width W1 to 1 cm or less. When the groove width of the second groove portion 82 increases along the third direction, the groove width W1 may be the width seen at the boundary between the first protrusion portion 71 and the second protrusion portion 72 as shown in FIG. 6.

[0070] 5 and 6 show an example of the configurations of the first protruding portion 71, the second protruding portion 72, and the third protruding portion 73, and the configurations of the first protruding ridges 7A and the second protruding ridges 7B on the negative electrode 33 side, but the positive electrode 32 side may have a similar configuration. In that case, the explanation of each element described above, such as the magnitude relationship between the height H2 of the second protruding portion 72 and the height H1 of the first protruding portion 71, is also common to the positive electrode 32 side.

[0071] The present inventors have newly devised an index called "area increase ratio" as an index showing the volume ratio of the second groove portions 82 to the first groove portions 81. If the number of rows of the first ridges 7A sandwiched between the second ridges 7B is the number of adjacent rows, and the area of ​​each second groove portion 82 when viewed from the front in the second direction as in Fig. 6 is the second area, the area increase ratio can be the ratio of the second area when the number of adjacent rows is a predetermined number of rows to the second area when the number of adjacent rows is one row (i.e., the increase ratio of the second area when the number of adjacent rows is increased from one row).

[0072] Fig. 7 is a plot showing the relationship between the number of adjacent rows of the first protrusions 7A and the area increase ratio. As shown in Fig. 7, the area increase ratio tends to increase as the number of adjacent rows increases. This tendency indicates that the groove width W1 of the second groove portion 82 gradually increases as the number of missing portions of the second protrusion portion 72 increases.

[0073] 7, when the interval (groove width of first groove portion 81) W3 of first protrusion portion 71 is large relative to the width (protrusion width) W2 of first protrusion portion 71 in the third direction, the area increase ratio tends to be larger than when the interval (groove width of first groove portion 81) W3 is small or when the two are equal (see also FIG. 6 for W2 and W3). According to findings obtained as a result of intensive studies by the inventors of the present application, it is preferable to set the area increase ratio to 1.5 or more (see dashed line L1 in FIG. 7).

[0074] FIG. 8 is a plot showing an example of FIG.

[0075] The horizontal axis of the plot in Fig. 8 indicates the number of adjacent rows of first ridges 7A, as in Fig. 7. For example, "4" on the horizontal axis means that four rows of first ridges 7A lacking second protrusion portions 72 are arranged in succession. In this case, second ridges 7B having second protrusion portions 72 are provided every five rows.

[0076] As in Fig. 7, the vertical axis of the plot in Fig. 8 indicates the rate of increase (area increase ratio) of the area of ​​the groove bottom of the second groove portion 82 relative to the case where the first ridges 7A and the second ridges 7B are provided in every row (where the number of consecutive rows of the first ridges 7A is one row). For example, the area of ​​the second groove portion 82 when the first ridges 7A are provided in four consecutive rows is about 1.8 times the area of ​​the second groove portion 82 when the first ridges 7A are provided in one consecutive row. In this case, each second groove portion 82 can hold about 1.8 times the amount of nonaqueous electrolyte 6.

[0077] The calculation of the vertical axis in Figure 8 corresponds to a specific calculation result when the width of the first protrusion portion 71 in the third direction is the same as the width of the first groove portion 81 in the third direction, and the height H1 of the first protrusion portion 71 in the second direction is the same as the height H2 of the second protrusion portion 72 in the second direction (H1 = H2).

[0078] As a result of extensive research, the inventors of the present application have found that when H1=H2 is set, it is preferable to arrange the first protrusions 7A so that they are adjacent to each other in six or more rows along the third direction (see section R1 in FIG. 8). This finding is demonstrated by the examples described below. As shown by the dashed line L1 in FIG. 8, plots that fall within section R1 satisfy the above-mentioned condition that the area increase ratio is set to 1.5 or more.

[0079] (Creating a secondary battery) In the secondary battery 1 according to this embodiment, the shape of both ends of the ceramic layer 31b in the first direction is devised. That is, the ceramic layer 31b has, in addition to the conventionally known first protrusion portion 71, a second protrusion portion 72 having a different height from the first protrusion portion 71.

[0080] Such a shape having the first protruding portion 71 and the second protruding portion 72 can be realized, for example, by devising a structure for the roll press in the die coater. For example, by giving the roll press a structure with different depths at its center (the center in the direction of the rotation axis) and its ends, and transferring this structure to the ceramic layer 31b, it becomes possible to form the protrusions 7 as described above, and further the grooves 8 between the protrusions 7.

[0081] <Secondary battery verification> Secondary batteries 1 were prepared according to Comparative Examples 1 and 2 and Examples 1 to 3 described below. The configurations of the respective batteries are also shown in FIG. 9. The inventors of the present application examined the length of the excess portion of the separator 31 in the first direction required to hold a predetermined amount of the non-aqueous electrolyte solution 6. The excess portion length refers to the length (particularly the length along the first direction) of the second protruding portion 72 corresponding to the portion P2 where the active material layer is not formed. The shorter the excess portion length, the more compact the secondary battery 1 becomes.

[0082] In the following Comparative Examples 1 and 2 and Examples 1 to 3, the width of first protrusion portion 71 in the third direction and the width of first groove portion 81 in the third direction are the same. Separator 31 has a thickness of about several tens of μm, and each ridge 7 and groove 8 has a width of about several μm to several tens of μm.

[0083] The following Examples 1 to 3 correspond to a configuration in which the height of the second protruding portion 72 is formed to be higher than the height of the first protruding portion 71. Comparative Examples 1 and 2 correspond to a configuration in which the height of the second protruding portion 72 and the height of the first protruding portion 71 are set to be the same.

[0084] 9, in the separator 31 according to Comparative Example 1, all of the protrusions 7 have the second protrusion portion 72, and at the same time, the height H2 of the second protrusion portion 72 is equal to the height H1 of the first protrusion portion 71 (H1=H2). Comparative Example 1 corresponds to a configuration example in which no effort is made in adjusting the height of the second protrusion portion 72, and further, no protrusions 7 lacking the second protrusion portion 72 are provided.

[0085] Moreover, the separator 31 according to Comparative Example 2 has 10 rows of first protrusions 7A lacking the second protrusions 72, and is configured such that the height H2 of the second protrusions 72 is equal to the height H1 of the first protrusions 71 (H1=H2). Comparative Example 2 satisfies the condition that the area increase ratio is 1.5 or more. Comparative Example 2 corresponds to a configuration example in which protrusions 7 lacking the second protrusions 72 are prepared without any special effort being put into the height of the second protrusions 72.

[0086] 9, the separator 31 according to Example 1 is configured such that all the ridges 7 have the second protruding portions 72, and the height H2 of the second protruding portions 72 is greater than the height H1 of the first protruding portions 71 (H2>H1). In this case, the height H2 of the second protruding portions 72 corresponds to approximately half of the negative electrode 33. Example 1 corresponds to a configuration example in which, although the ridges 7 lacking the second protruding portions 72 are not provided, the height of the second protruding portions 72 is carefully designed.

[0087] Moreover, in the separator 31 according to Example 2, all the ridges 7 are provided with the second protrusion portions 72, and at the same time, the height H2 of the second protrusion portions 72 is configured to be even higher than that of Example 1 (i.e., H2 (Example 2)>H2 (Example 1)>H1). In this case, the height H2 of the second protrusion portions 72 is approximately the same as the thickness of the negative electrode 33. Example 2 does not have ridges 7 lacking the second protrusion portions 72, but corresponds to a configuration example in which the height of the second protrusion portions 72 is carefully designed.

[0088] Moreover, the separator 31 according to Example 3 has 10 continuous rows of first protrusions 7A lacking the second protrusion portions 72, and the height H2 of the second protrusion portions 72 is set to the same height as in Example 2 (i.e., H3 (Example 3) = H2 (Example 2) > H2 (Example 1) > H1). Example 2 satisfies the condition that the area increase ratio is 1.5 or more. Example 2 corresponds to a configuration example in which both the innovations of Comparative Example 2 and Example 2 are implemented.

[0089] As shown in the fourth column of the table in Fig. 9, the excess length was significantly shorter in Examples 1 to 3 compared to Comparative Examples 1 and 2. This result shows that by making the height H2 of the second protruding portion 72 greater than the height H1 of the first protruding portion 71, the retention function of the non-aqueous electrolyte 6 was improved compared to Comparative Examples 1 and 2. This tendency is considered to be brought about by making the grooves 8 formed by the second protruding portions 72 deeper, thereby increasing the volume capable of storing the non-aqueous electrolyte 6.

[0090] Here, as shown in the comparison between Example 1 and Example 2, the excess length was further shortened by increasing the height H2 of the second protruding portion 72. This result suggests that the deeper the groove 8 formed by the second protruding portion 72, the more improved the retention function of the nonaqueous electrolyte 6.

[0091] Furthermore, as shown in a comparison between Example 2 and Example 3, the excess length was further shortened by setting the height H2 of the second protrusion portions 72 relatively high and further by continuing the first protrusions 7A lacking the second protrusion portions 72 over 10 rows. This result is believed to be due to the fact that the volume capable of storing the nonaqueous electrolyte solution 6 was increased by continuing the second protrusion portions 72 corresponding to the active material layer forming portions P1.

[0092] (Prevention of non-aqueous electrolyte leakage) Generally, when charging at a high rate, there is a concern that the graphite component and the like expands on the negative electrode 33 side, causing the nonaqueous electrolyte 6 to leak out of the electrode assembly 3 and spread throughout the case 2. Although the leaked nonaqueous electrolyte 6 is designed to return during discharge, it only returns from the portion of the electrode assembly 3 that is immersed in the nonaqueous electrolyte 6, and so it takes a long time for it to return sufficiently.

[0093] In view of this, it is conceivable to provide grooves extending along the first direction at equal intervals on the surface of the separator 31, and to hold the nonaqueous electrolyte 6 in the grooves. However, the amount of nonaqueous electrolyte 6 that can be held in such grooves is insufficient to prevent the outflow of the nonaqueous electrolyte 6 from the electrode body 3, and there is room for improvement.

[0094] In contrast, according to the present embodiment, one protrusion 7, together with other adjacent protrusions 7, forms a groove 8 capable of holding a non-aqueous electrolyte 6, as shown in Fig. 4. Here, in each protrusion 7, the height H2 of a portion (second protrusion 72) located at the end in one direction is set to be higher than the height H1 of a portion (first protrusion 71) located near the center in the first direction, as shown in Fig. 5. By setting in this manner, the depth of the groove (second groove portion 82) formed between the second protrusions 72 becomes deeper than the depth of the groove (first groove portion 81) formed between the first protrusions 71.

[0095] In this way, by making the second groove portion 82 related to the second protruding portion 72 deeper, it becomes possible to hold a larger amount of nonaqueous electrolyte 6 than before at each end 3a, 3b of each electrode plate 32a, 33a. This makes it possible to suppress the outflow of nonaqueous electrolyte 6 from the electrode body 3.

[0096] Moreover, by making the ridges 7 taller only in the portions facing the portions P2 where the active material layer is not formed, rather than making the grooves 8 deeper over the entire area in the first direction, the active material layer-forming portions P1 can be made the same thickness as before without being made thicker. This makes it possible to prevent the electrode body 3, and in turn the secondary battery 1, from becoming larger.

[0097] 4 and 6, the width of the second grooves 82 formed between the second protruding portions 72 is wider than the width of the first grooves 81 formed between the first protruding portions 71. By widening the groove width at the ends 3a, 3b of the electrode plates 32a, 33a, a larger amount of nonaqueous electrolyte 6 can be held. This is advantageous in preventing the outflow of the nonaqueous electrolyte 6 from the electrode assembly 3.

[0098] 4 and other figures, in the second groove 82 formed between the second protrusions 72, the second ridges 7B define the side walls of the second groove 82, and the first ridges 7A define the bottom walls of the second groove 82. This configuration allows the groove width to be further increased. The increased groove width allows a larger amount of non-aqueous electrolyte 6 to be held. This is advantageous in preventing the outflow of the non-aqueous electrolyte 6 from the electrode body 3.

[0099] 8 and 9, six or more and ten or less rows of the first ridges are sandwiched between two second ridges 7B. As a result of extensive research, the inventors of the present application have found that a sufficient amount of nonaqueous electrolyte 6 can be held by arranging six or more rows of adjacent first ridges 7A.

[0100] 6 and other figures, a second groove 82 is defined between the two second protrusions 72, with the area between them serving as the groove bottom. A second area indicating the area of ​​the second groove 82 increases or decreases according to the number of first ridges 7A sandwiched between the second ridges 7B (the number of adjacent rows). As shown in Figs. 7 and 8, by setting the area increase ratio, which is an index of the second area, to 1.5 or more, a sufficient amount of nonaqueous electrolyte 6 can be held in each second groove 82.

[0101] Generally, the second groove portion 82 prevents the nonaqueous electrolyte 6 from flowing out by capillary action. Therefore, if the groove width W1 of the second groove portion 82 is excessively wide, there is a concern that the nonaqueous electrolyte 6 may flow out from the second groove portion 82.

[0102] According to the findings of the present inventors through their research, by setting the groove width W1 of the second groove portion 82 to 1 cm or less, as described above, it is possible to suppress the outflow of the non-aqueous electrolyte solution 6 from the second groove portion 82.

[0103] 5, by interposing the third protruding portion 73 between the first protruding portion 71 and the second protruding portion 72, it is possible to suppress interference between the positive electrode active material layer 32b or the negative electrode active material layer 33b and the second protruding portion 72. This configuration is particularly effective during the manufacture of the secondary battery 1 in that the electrode body 3 can be assembled in the same manner as in the past.

[0104] Other Embodiments In the above embodiment, a configuration using the electrode assembly 3 configured as a wound electrode assembly is illustrated, but the present disclosure is not limited to such a configuration. As the electrode assembly 3, a so-called laminated electrode assembly in which the positive electrode 32, the negative electrode 33, the separator 31, etc. are laminated without being wound may also be used.

[0105] In the above embodiment, each of the second protrusions 72 has a triangular shape tapered toward both ends in the first direction in a plan view along the second direction, but the present disclosure is not limited to such a configuration. For example, the width of each of the second protrusions 72 may be narrowed in a stepped manner.

[0106] 4, 6 and Example 3, it is not essential to provide the first ridges 7A lacking the second protrusions 72. All of the ridges 7 may be formed of second ridges 7B having the second protrusions 72. [Explanation of symbols]

[0107] 1 Secondary battery 3 Electrode body 31 Separator 32 Positive electrode 32a Positive electrode plate (electrode plate) 32b Positive electrode active material layer 33 Negative electrode 33a Negative electrode plate (electrode plate) 33b Negative electrode active material layer 3a Left end (end) 3b Right end (end) 4a Positive current collector (current collector) 5a Negative electrode current collector (current collector) 6 Nonaqueous electrolyte (electrolyte) 7 Multiple ridges 71 1st protrusion part 72 2nd protrusion part 73 Third protrusion part 7A First ridge 7B Second ridge 8 grooves 81 First Groove 82 Second groove P1 Active material layer forming part P2 Active material layer non-forming area W1 Groove width

Claims

1. an electrode assembly including a positive electrode having a positive electrode plate and a positive electrode active material layer, a negative electrode having a negative electrode plate and a negative electrode active material layer, and a separator interposed between the positive electrode and the negative electrode; a current collector connected to each end of the positive electrode plate and the negative electrode plate in a first direction; An electrolyte solution contained in the electrode assembly, The positive electrode plate and the negative electrode plate are each an active material layer forming portion where each of the positive electrode plate and the negative electrode plate overlaps with a corresponding one of the positive electrode active material layer and the negative electrode active material layer when viewed along a second direction perpendicular to the first direction; an active material layer non-forming portion provided at each end portion and in which each electrode plate is exposed when viewed in the second direction; the separator has a plurality of ridges that are provided at predetermined intervals along a third direction perpendicular to the first direction and the second direction and each ridge extends in the first direction; At least some of the plurality of protrusions are a first protrusion portion facing the active material layer forming portion; a second protruding portion that faces the portion where the active material layer is not formed and protrudes higher in the second direction than the first protruding portion; A secondary battery comprising:

2. 2. The secondary battery according to claim 1, The width of the second protruding portion in the third direction is narrower than or equal to the width of the first protruding portion in the third direction. A secondary battery comprising:

3. 3. The secondary battery according to claim 1, The plurality of protrusions are a plurality of first protrusions each lacking the second protrusion portion; a plurality of second protrusions provided to sandwich the first protrusion from both sides in the third direction, each of the second protrusions having the second protrusion portion; A secondary battery comprising:

4. 4. The secondary battery according to claim 3, the second protrusions define a second groove having an inner wall formed by the second protrusions arranged in the third direction, If the number of rows of the first ridges sandwiched between the second ridges is defined as the number of adjacent rows, the area of ​​each of the second groove portions when viewed from the front in the second direction is defined as a second area, and the ratio of the second area when the number of adjacent rows is a predetermined number of rows to the second area when the number of adjacent rows is one row is defined as an area increase ratio, The area increase ratio is set to be 1.5 or more. A secondary battery comprising:

5. 5. The secondary battery according to claim 4, The groove width of each of the second groove portions in the third direction is set to 1 cm or less. A secondary battery comprising:

6. The secondary battery according to any one of claims 1 to 5, At least some of the plurality of protrusions are a third protruding portion interposed between the first protruding portion and the second protruding portion and facing the portion without the active material layer, The third protruding portion protrudes lower than the second protruding portion in the second direction. A secondary battery comprising:

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