Secondary batteries

Abstract

To promptly re-permeate an electrolytic solution leached from an electrode laminate without reducing the battery capacity.SOLUTION: In a stacked battery cell 1, an electrode stack 4, which is constructed by stacking a positive electrode body 40 and a negative electrode body 41 with a separator 42 in between, is housed in a battery case 2 with a lower part immersed in an electrolytic solution 43. An insulating cover 5 interposed between the electrode stack 4 and the battery case 2 has a pair of side surfaces 51 and 51 extending along both side surfaces of the electrode stack 4. A plurality of vertical grooves 60 is formed on the electrode stack side surface of the side surfaces 51 and 51, extending upward from the portion immersed in the electrolytic solution 43.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The disclosed technology relates to a laminated secondary battery suitable for a power source for driving a vehicle or the like.

Background Art

[0002] Regarding the disclosed technology, although it is a separator, providing unevenness on its surface is disclosed in Patent Document 1. However, the unevenness aims to increase the contact area between oxygen gas and the negative electrode. Therefore, as the unevenness, a lattice shape, an intersecting linear shape, and a discontinuous multi-point shape are exemplified. Further, the secondary battery targets a cylindrical type (wound type) formed by winding electrode films of a positive electrode and a negative electrode sandwiching a separator in a roll shape.

[0003] On the other hand, a rectangular type (laminated type) secondary battery formed by laminating sheet-like electrodes and a separator, which is the target of the disclosed technology, is disclosed in Patent Document 2. Conventionally, in order to insulate an electrode laminate (electrode assembly in Patent Document 2) constituted by laminating these electrodes and the like from a metal case, it has been covered with an insulating sheet. In Patent Document 2, it aims to improve the productivity of the process of covering the electrode laminate with the insulating sheet.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Hybrid vehicles and electric vehicles, which use the output of an electric motor to propel themselves, are equipped with high-voltage batteries as their power source. High-voltage batteries are generally composed of a large number of battery cells (secondary batteries) made of lithium-ion batteries connected together.

[0006] In vehicles, depending on the driving conditions, high output may be required from the motor, or the motor may be used as a generator to produce high output power. In such cases, high-voltage batteries are charged and discharged with very large currents. It is known that when such high-current charging and discharging are repeated in a short period of time, the internal resistance of the battery cells increases irreversibly, accelerating the degradation of the high-voltage battery's performance (so-called high-rate degradation).

[0007] One of the contributing factors is thought to be that the internal state of the battery becomes uneven during charging and discharging, and it takes time for this to resolve. In other words, when a secondary battery is charged and discharged, the electrode stack expands or contracts. Consequently, the electrolyte penetrates or leaches out of the electrode stack. When the electrolyte leaches out of the electrode stack, the internal resistance increases, but when the electrolyte re-penetrates the electrode stack, the internal resistance decreases and returns to its original value.

[0008] However, inside the battery cell, the electrolyte that leaches from the electrode stack accumulates at the bottom of the cell. As a result, the top of the electrode stack is exposed above the electrolyte level, and it takes time for the electrolyte to re-permeate and distribute to the appropriate amount. On the other hand, if an increase in internal resistance occurs superimposed before the internal resistance recovers, the internal resistance will increase irreversibly. Therefore, if high-current charging and discharging are repeated in a short period of time, high-rate degradation is accelerated.

[0009] Alternatively, one could consider forming numerous vertical grooves in the separator to facilitate upward flow of the electrolyte, but this would inevitably increase the thickness of the separator. A thicker separator reduces the battery capacity accordingly. Since the electrode stack contains multiple separators, the reduction in battery capacity will be proportionally greater.

[0010] Therefore, the disclosed technology aims to quickly re-permeate the electrolyte that has leached out from the electrode stack without reducing the battery capacity. [Means for solving the problem]

[0011] The technology being disclosed relates to a stacked secondary battery.

[0012] The secondary battery comprises an electrode stack formed by stacking a sheet-shaped positive electrode and a sheet-shaped negative electrode via a sheet-shaped separator, a battery case that houses the electrode stack and the electrolyte with the lower part of the electrode stack immersed in the electrolyte, and a cover member interposed between the electrode stack and the battery case.

[0013] The cover member has a pair of side portions that extend along both sides of the electrode stack, and a plurality of vertical grooves are formed on the side portion facing the electrode stack, extending upward from the portion immersed in the electrolyte.

[0014] In other words, in this secondary battery, of the pair of side surfaces of the cover member interposed between the electrode stack and the battery case, multiple vertical grooves are formed on the side facing the electrode stack, extending upward from the portion immersed in the electrolyte. Since there is only one cover member in the battery case, unlike separators which are included in multiples, forming vertical grooves does not increase the thickness significantly. Therefore, it hardly reduces the battery capacity.

[0015] These longitudinal grooves extend upward from the parts immersed in the electrolyte. Therefore, the electrolyte can circulate to the parts not immersed in the electrolyte, and the electrolyte that has leached out from the electrode stack can be quickly re-penetrated.

[0016] The width of the longitudinal groove is preferably 0.1 mm or less.

[0017] This numerical range is set based on physical conditions such as the density of the electrolyte. By setting the width of each longitudinal groove to these dimensions, surface tension and capillary action make it possible to draw the electrolyte from the bottom to the top of the battery case against gravity. Therefore, the electrolyte can be continuously supplied to the top of the electrode stack, and any electrolyte that has leached out of the electrode stack can be re-penetrated more quickly.

[0018] The cover member may further have a lower surface portion that is connected to each of the pair of side portions and extends along the lower surface of the electrode stack, and a plurality of lower horizontal grooves that communicate with each other and also with the vertical grooves may be formed on the upper surface of the lower surface portion.

[0019] This ensures that the underside of the electrode stack is in contact with the electrolyte, allowing the electrolyte to permeate from the underside of the electrode stack. Furthermore, these lower horizontal grooves are connected to each of the vertical grooves. Therefore, the electrolyte can be supplied to each of the vertical grooves aligned in the longitudinal direction without bias.

[0020] The cover member may further have an upper surface portion that is connected to each of the pair of side portions and extends along the upper surface of the electrode stack, and a plurality of upper transverse grooves extending in the stacking direction of the electrode stack and communicating with the longitudinal grooves may be formed on the lower surface of the upper surface portion.

[0021] This allows the electrolyte, which has been drawn up to the top of the electrode stack through each longitudinal groove, to be further supplied to the entire stacking direction by flowing through the upper transverse groove. Therefore, variations in electrolyte penetration along the stacking direction of the electrode stack can be suppressed.

[0022] The electrode laminate may have a terminal component at its upper part, the cover member may have a terminal opening that exposes the terminal component, and the vertical groove or the upper horizontal groove located around the terminal opening may communicate with each other via an edge groove formed to extend along the edge of the terminal opening.

[0023] In this case, the electrolyte pulled up around the terminal opening can be dispersed without stagnation through the edge groove into the vertical grooves and upper horizontal grooves around it.

[0024] It is also possible that the upper surface of the electrode laminate is inclined and the central portion in the stacking direction is relatively lower.

[0025] In this case, the electrolyte supplied to the upper part of the electrode laminate can be guided to the central portion of the upper surface of the electrode laminate by utilizing the inclination. Thereby, the variation in the penetration of the electrolyte in the stacking direction of the electrode laminate can be suppressed. The electrolyte can be supplied to the entire electrode laminate in a balanced manner.

Advantages of the Invention

[0026] According to the secondary battery to which the disclosed technology is applied, without reducing the battery capacity, the electrolyte leached from the electrode laminate can be quickly re-permeated. As a result, high-rate deterioration is suppressed, and the performance degradation of the secondary battery can be reduced.

Brief Description of the Drawings

[0027] [Figure 1] It is a schematic diagram showing the structure of a battery cell (secondary battery) to which the disclosed technology is applied. [Figure 2] It is a schematic diagram showing the structure of an electrode laminate. [Figure 3] It is a developed view of an insulating cover. [Figure 4] It is a diagram for explaining the configuration and assembly of an insulating cover. [Figure 5] It is a schematic perspective view showing the assembled insulating cover. [Figure 6] It is a diagram for explaining the action of an insulating cover. [Figure 7] It is a diagram for explaining a secondary battery of a modified example.

Embodiments for Carrying Out the Invention

[0028] The embodiments of the disclosed technology will be described in detail below with reference to the drawings. However, the following description is essentially illustrative and does not limit the invention, its applications, or its uses.

[0029] <Overall configuration of a secondary battery> Figure 1 shows a battery cell 1 (secondary battery) to which the disclosed technology is applied. The upper part of Figure 1 is a perspective view showing the external appearance of the battery cell 1. The lower left part of Figure 1 (a) is a schematic cross-sectional view taken from the direction indicated by arrow (a) in the upper part of Figure 1, and the lower right part of Figure 1 (b) is a schematic cross-sectional view taken from the direction indicated by arrow (b) in the upper part of Figure 1.

[0030] Battery cell 1 has a roughly rectangular parallelepiped shape (prismatic type) in Figure 1, being shorter in the left-right direction and longer in the front-back and up-down directions. This battery cell 1 is mainly intended for automotive use. In other words, the high-voltage drive battery installed in a vehicle is composed of an integrated number of these battery cells 1.

[0031] The battery cell 1 consists of a battery case 2, a pair of terminals 3, an electrode stack 4, and an insulating cover 5 (cover component). The insulating cover 5 in this battery cell 1 is specially designed. Details of the insulating cover 5 will be described separately.

[0032] The battery case 2 has a storage section 20 which is a container with an open top, and a lid section 21 which closes the top of the storage section 20. The storage section 20 and the lid section 21 are made of a metal such as aluminum. The storage section 20 is a single molded product and is composed of thin walls that are connected to each other. The lid section 21 is formed in the shape of a thin plate. By attaching the lid section 21 to the storage section 20, the inside of the battery case 2 is sealed.

[0033] Terminal holes 22 are formed in two locations on the lid portion 21, which are located separately from each other, and penetrate the plate surface. A terminal member 23 made of a metal conductor is attached to each of these terminal holes 22 in an electrically insulated state by interposing a resin plug member 24. The upper end portion of the terminal member 23 is located outside the battery case 2, and the lower end portion of the terminal member 23 is located inside the battery case 2. One of these terminal members 23 is the positive terminal 3, and the other is the negative terminal 3.

[0034] The electrode stack 4 is slightly smaller than the internal shape of the battery case 2 and has a rectangular parallelepiped shape similar to that of the battery case 2. The electrode stack 4 is housed in the battery case 2 with an insulating cover 5 interposed between it and the battery case 2. As a result, the insulating cover 5 is in close contact with both the inner surface of the battery case 2 and the outer surface of the electrode stack 4.

[0035] As shown in Figure 2, the electrode stack 4 has a positive electrode 40, a negative electrode 41, and a separator 42, all of which are thin, sheet-like materials. The positive electrode 40, the negative electrode 41, and the separator 42 are formed in a rectangular shape corresponding to the battery case 2.

[0036] The electrode stack 4 is constructed by repeatedly stacking positive electrodes 40 and negative electrodes 41 with separators 42 in between. In other words, this battery cell 1 is of the stacked type. One battery element is composed of one positive electrode 40 and one negative electrode 41 separated by one separator 42. Therefore, the electrode stack 4 contains multiple battery elements.

[0037] The positive electrode 40 is composed of, for example, a metal foil and an active material containing a lithium transition metal composite oxide attached to both sides thereof. The negative electrode 41 is composed of, for example, a metal foil and an active material containing graphite attached to both sides thereof. The separator 42 is a porous plastic sheet that insulates the positive electrode 40 and the negative electrode 41.

[0038] The battery case 2 contains an electrolyte 43 along with an electrode stack 4. The electrolyte 43 consists of an organic solvent containing lithium ions. In other words, this battery cell 1 is a lithium-ion battery. The electrolyte 43 is contained so as not to fill the inside of the battery case 2.

[0039] In detail, as shown in the lower diagram of Figure 1, the electrolyte 43 is contained such that, when the battery case is stationary, the liquid level is located midway between the bottom and top surfaces of the housing 20, and the lower part of the electrode stack 4 is immersed in the electrolyte 43. Inside the battery case 2, there is a space around the upper part of the electrode stack 4 that occupies a larger space than the electrolyte 43 that accumulates at the bottom of the battery case 2.

[0040] A positive electrode flange 40a is provided on one end of the upper edge of the positive electrode body 40, projecting upward for connection to the positive electrode terminal 3. Similarly, a negative electrode flange 41a is provided on the other end of the upper edge of the negative electrode body 41, projecting upward for connection to the negative electrode terminal 3. Therefore, when the electrode stack 4 is formed, the group of positive electrode flanges 40a and the group of negative electrode flanges 41a are arranged in a line and project from the top of the electrode stack 4, as shown in the upper diagram of Figure 2.

[0041] A group of positive electrode flanges 40a is connected to the lower end portion of the positive electrode terminal 3 via a positive electrode connecting fitting 44. A group of negative electrode flanges 41a is connected to the lower end portion of the negative electrode terminal 3 via a negative electrode connecting fitting 45. Each of the groups of positive electrode flanges 40a and negative electrode flanges 41a constitutes a terminal component.

[0042] (High rate degradation) As described above, when charging and discharging occur in the battery cell 1, the active material present on the electrode stack 4, specifically on the surface of the negative electrode, expands and contracts. Consequently, the electrolyte 43 penetrates or leaches out from the electrode stack 4.

[0043] When the electrolyte 43 leaches out of the electrode stack 4 and the amount of electrolyte held by the electrode stack 4 decreases, the internal resistance increases. When the electrolyte 43 re-permeates the electrode stack 4 and the amount of electrolyte held by the electrode stack 4 increases, the internal resistance decreases. As re-permeation progresses and the amount of electrolyte held by the electrode stack 4 returns to its original level, the internal resistance also recovers to its original value.

[0044] However, as mentioned above, the upper part of the electrode stack 4 is exposed above the surface of the electrolyte 43. Therefore, for the electrolyte 43 to return to the upper part of the electrode stack 4, it is necessary for the electrolyte 43 to re-permeate from the lower part of the electrode stack 4 and spread to the upper part of the electrode stack 4. Consequently, it takes time for the upper part of the electrode stack 4, where the amount of electrolyte has decreased, to return to its original state.

[0045] On the other hand, if an increase in internal resistance occurs superimposed before the internal resistance can recover, there is a problem in that the internal resistance increases irreversibly (so-called high-rate degradation). In contrast, charging and discharging with high current greatly increases internal resistance, so if charging and discharging with high current is repeated in a short period of time, high-rate degradation is accelerated.

[0046] One possible solution is to form multiple grooves extending vertically in the separator 42. This would allow the electrolyte 43 to flow upward through the grooves, making it easier for the electrolyte 43 to return to the top of the electrode stack 4. For example, if the battery cell 1 moves up and down as the vehicle moves, the electrolyte 43 will also move up and down through the grooves, thus shortening the time it takes for the top of the electrode stack 4 to return to its original state.

[0047] However, forming grooves in the separator 42 requires increasing the thickness of the separator 42. This is especially true if the cross-section of the grooves is made larger to allow the electrolyte 43 to flow more easily. If the thickness of the separator 42 increases, the thickness of the electrode stack 4 also increases. Since the electrode stack 4 contains multiple separators 42, the thickness of the electrode stack 4 increases even further. Moreover, the separator 42 is a component that does not directly contribute to the battery capacity. Therefore, this measure creates a new problem: a decrease in battery capacity.

[0048] Therefore, the inventors focused on the insulating cover 5 and devised a structure for the insulating cover 5 so that even if the electrolyte 43 seeps out from the top of the electrode stack 4, the electrolyte 43 can spread to the top of the electrode stack 4 in a short time.

[0049] (Structure of insulating cover 5) Figure 3 shows an unfolded view of the insulating cover 5. The insulating cover 5 is a component for insulating the electrode laminate 4 from the battery case 2. The insulating cover 5 is formed, for example, by press-forming a plastic film or sheet. It may also be formed by laminating multiple films together.

[0050] The inner surface of the insulating cover 5, which is in contact with the electrode stack 4, has a minute uneven surface structure. Figure 3 exaggerates the thickness and uneven surface structure of the insulating cover 5 for clarity.

[0051] As shown in Figure 4, the insulating cover 5 has a bottom surface 50, a pair of side surfaces 51, a top surface 52, and a pair of end surfaces 53. The insulating cover 5 is configured to be a rectangular parallelepiped shape that closely covers the electrode laminate 4, as shown in Figure 5, by folding each of these surfaces and joining predetermined edges, as indicated by the arrows in the lower part of Figure 4.

[0052] The lower portion 50 is the part that extends along the lower surface of the electrode stack 4 when the electrode stack 4 is covered. The lower portion 50 has substantially the same shape and area as the lower surface of the electrode stack 4. Both sides of the lower portion 50 are connected to the lower edges of each of the pair of side portions 51. The pair of side portions 51 are the parts that extend along both sides of the electrode stack 4 when the electrode stack 4 is covered. Each side portion 51 has substantially the same shape and area as the side of the electrode stack 4.

[0053] The upper portion 52 is the part that extends along the upper surface of the electrode stack 4 when the electrode stack 4 is covered. The upper portion 52 is divided into a pair of upper surface pieces 52a, with one side of each upper surface piece 52a connected to the upper side of each side portion 51. The upper portion 52 is formed by joining the other sides of both upper surface pieces 52a, 52a.

[0054] The upper surface portion 52 has substantially the same shape and area as the upper surface of the electrode stack 4. However, two terminal openings 54, one for the positive electrode and one for the negative electrode, are formed in the upper surface portion 52 in order to expose a group of positive electrode flanges 40a and a group of negative electrode flanges 41a (terminal components) that protrude upward from the electrode stack 4.

[0055] Each of the pair of end face portions 53 is a portion that extends along the end face of the electrode stack 4 when the electrode stack 4 is covered. Each end face portion 53 is divided into a pair of end face pieces 53a, and one side of each end face piece 53a is connected to the end side of each side portion 51. The end face portion 53 is formed by joining the other sides of the end face pieces 53a, 53a.

[0056] Each end face portion 53 has substantially the same shape and area as the end face of the electrode stack 4. However, a flow opening 55 is formed at the lower part of each end face portion 53 to allow the electrolyte 43 to enter and exit the insulating cover 5.

[0057] (Fine grooves) As described above, a minute uneven structure is formed on the inner surface of the insulating cover 5 facing the electrode stack 4. As a result, specific fine grooves are formed on each of the lower surface 50, the pair of side surfaces 51, and the upper surface 52, as shown in Figures 3 and 5.

[0058] Multiple vertical grooves 60 are formed on the inner surface of each side portion 51, extending vertically from its lower end to its upper end. The dimensions of these vertical grooves 60 are designed based on the physical properties of the insulating cover 5 and the electrolyte 43, such as density, contact angle, and surface tension, and are formed so that the electrolyte 43 can be drawn up to the top of the electrode stack 4 by surface tension and capillary action.

[0059] Specifically, the width W of each vertical groove 60 is set to 0.1 mm or less. The depth H of each vertical groove 60 is less than or equal to the width W. By setting each vertical groove 60 to these dimensions, the electrolyte 43 can be drawn up against gravity from the bottom to the top of the battery case 2 (assuming a width of 0.1 mm equals 70 mm) due to surface tension and capillary action.

[0060] Multiple lower horizontal grooves 61 are formed on the upper surface of the lower surface portion 50, communicating with each other and also with the vertical grooves 60. In detail, the lower horizontal grooves 61 consist of multiple grooves extending in both the front-to-back and left-to-right directions, forming a grid pattern. The width and depth of the lower horizontal grooves 61 are approximately the same as those of the vertical grooves 60, and each lower horizontal groove 61 extending in the left-to-right direction is arranged to be continuous with each vertical groove 60. However, the width and depth of the lower horizontal grooves 61 may differ from those of the vertical grooves 60.

[0061] Multiple upper lateral grooves 62 are formed on the lower surface of the upper portion 52, extending in the left-right direction, which is the stacking direction of the electrode stack 4, and communicating with the vertical grooves 60. In this battery cell 1, each upper lateral groove 62 is formed by extending each vertical groove 60 onto the upper portion 52. Therefore, each upper lateral groove 62 has the same width and depth as the vertical grooves 60. Note that the width and depth of the upper lateral grooves 62 may also differ from those of the vertical grooves 60.

[0062] An edge groove 63 is formed around the terminal opening 54, extending along its edge. The longitudinal grooves 60 or upper transverse grooves 62 located around the terminal opening 54 are in communication with each other via this edge groove 63. The width and depth of the edge groove 63 may be approximately the same as or different from those of the longitudinal grooves 60.

[0063] Since the depths of these vertical grooves 60, lower horizontal groove 61, upper horizontal groove 62, and edge groove 63 are minute, even if they are provided on the insulating cover 5, the increase in its thickness is minimal. Moreover, unlike the separator 42, the insulating cover 5 is a single piece, so the internal capacity of the battery case 2 hardly changes. Therefore, even if such a fine uneven structure is provided on the insulating cover 5, there is no concern that the battery capacity will decrease.

[0064] (Function of the insulating cover) The upper part of Figure 6 shows a battery cell 1 fitted with the aforementioned insulating cover 5 without the fine grooves, as a comparative example. The lower part of Figure 6 shows the battery cell 1 of this embodiment. For convenience, the same reference numerals are used for the same components in the comparative example as well.

[0065] If electrolyte 43 leaches out from the electrode stack 4 during charging and discharging, in the comparative example battery cell 1, the only way to recover the amount of electrolyte in the upper part of the electrode stack 4 is to wait for the electrolyte 43 that has re-penetrated from the lower part of the electrode stack 4, which is immersed in the electrolyte 43, to gradually seep into the upper part that is not immersed in the electrolyte 43. It takes time for the upper part of the electrode stack 4 to return to its original state.

[0066] Even in the lower part of the electrode stack 4 immersed in the electrolyte 43, the lower surface of the electrode stack 4 is in close contact with the insulating cover 5. Therefore, the electrolyte 43 can only penetrate the lower part of the electrode stack 4, specifically the front and rear end faces. Consequently, it takes even longer for the upper part of the electrode stack 4 to return to its original state.

[0067] In contrast, in the battery cell 1 of the embodiment, a lower horizontal groove 61 is formed on the upper surface of the lower surface portion 50. Therefore, the lower surface of the electrode stack 4 is in contact with the electrolyte 43, and the electrolyte 43 can penetrate from the lower surface of the electrode stack 4 as well. Furthermore, these lower horizontal grooves 61 are in communication with each vertical groove 60. Therefore, the electrolyte 43 can smoothly enter each vertical groove 60 as well.

[0068] Each vertical groove 60 extends upward from the portion immersed in the electrolyte 43, reaching the top of the electrode stack 4. As described above, the vertical grooves 60 are formed in such a way that the electrolyte 43 can be drawn up from the bottom to the top of the battery case 2 against gravity by surface tension and capillary action.

[0069] Therefore, as shown by the solid arrows in the lower part of Figure 6, the electrolyte 43 can always be supplied to the upper part of the electrode stack 4. Since vertical grooves 60 are formed over the entire surface of the side portion 51, the electrolyte 43 can be drawn up evenly over the entire surface of the side of the electrode stack 4.

[0070] As these vertical grooves 60 extend from the upper surface portion 52, multiple upper horizontal grooves 62 extend in the left-right direction (the stacking direction of the electrode stack 4). Therefore, the electrolyte 43 drawn up along the vertical grooves 60 is further supplied to the central part in the width direction of the electrode stack 4 via the upper horizontal grooves 62. This allows the electrolyte 43 to be supplied to each battery element without significant bias.

[0071] Furthermore, a perimeter groove 63 is formed around the terminal opening 54, and the surrounding vertical grooves 60 and upper horizontal groove 62 communicate with the perimeter groove 63. Therefore, the electrolyte 43 that is drawn up to the perimeter of the terminal opening 54 can be dispersed around it through the perimeter groove 63 without stagnation.

[0072] In this way, the fine grooves provided in the insulating cover 5 allow the electrolyte 43 to be supplied to the upper part of the electrode stack 4 in a balanced manner at all times. Similar to the battery cell 1 of the comparative example, the electrolyte 43 also re-penetrates from the lower part of the electrode stack 4. Moreover, the lower horizontal groove 61 promotes this re-penetration.

[0073] Therefore, with the battery cell 1 employing this insulating cover 5, even if a large amount of electrolyte 43 leaches out from the electrode stack 4 due to high-current charging and discharging, the electrolyte 43 that leached out from the electrode stack 4 can be quickly re-penetrated from above and below, and the electrode stack 4 can be restored to its original state in a short time. As a result, high-rate degradation is suppressed, and the performance degradation of the secondary battery can be reduced.

[0074] <Variation> Figure 7 shows a modified version of the battery cell 1 described above (modified battery cell 1A). In this modified battery cell 1A, the shape of the electrode stack 4 differs from that of the secondary battery described above. The other components are the same as those of the secondary battery described above. Therefore, the same reference numerals are used for components that are the same, and their explanations are omitted.

[0075] As shown in Figure 7, the electrode stack 4 of the deformed battery cell 1A has an inclined surface 70 on its upper surface. That is, the upper surface of the deformed battery cell 1A is inclined, and the central part in the stacking direction is relatively lower. More specifically, the upper surface of the electrode stack 4 gradually slopes downward from both ends toward the center.

[0076] The shape of the inclination (cross-sectional shape) can be straight or curved. It is sufficient that the central part of the upper surface of the electrode stack 4 is lower than the end parts throughout the entire area from both ends to the center. It is sufficient that a height difference Δh exists between the ends and the center of the upper surface of the electrode stack 4. Note that in Figure 7, the inclination is exaggerated for clarity.

[0077] The inclined surface 70 may be formed by making the vertical dimensions of the positive electrode 40, negative electrode 41, and separator 42 constituting the electrode stack 4 different on the end side and the central side of the electrode stack 4. Alternatively, the inclined surface 70 may be formed by pushing the central side of the electrode stack 4 downward relative to the end side, thereby creating a recess in the central side of the electrode stack 4. In this case, it is preferable to interpose a posture holder between the lower surface of the battery case 2 and the lower surface of the electrode stack 4 in order to maintain its shape.

[0078] By providing such an inclined surface 70 on the upper surface of the electrode stack 4, the electrolyte 43 that has been drawn up to the top of the electrode stack 4 can be guided to the center of the upper surface of the electrode stack 4 using the inclination. This suppresses differences in the degree of electrolyte 43 penetration between the battery elements located at the ends of the electrode stack 4 and the battery elements located in the center of the electrode stack 4. The electrolyte 43 can be supplied evenly throughout the entire electrode stack 4.

[0079] The disclosed technology is not limited to the embodiments described above, but also encompasses various other configurations. For example, in the embodiments, an insulating cover 5 is exemplified as a cover member, but the cover member may be provided separately from the insulating cover 5. In the embodiments, the cover member covers substantially the entire electrode stack 4, but it may cover only a part of the electrode stack 4. [Explanation of symbols]

[0080] 1. Battery cell (rechargeable battery) 2 Battery Case 3 terminals 4-electrode stack 5. Insulating cover (cover component) 40 Positive pole body 41 Negative electrode 42 Separators 43 Electrolyte 50 Bottom part 51 Side part 52 Top part 53 End face part 54 Terminal opening 55 Flow opening 60 vertical grooves 61 Lower Yokomizo 62 Upper horizontal groove 63 Edge groove

Claims

1. It is a stacked type secondary battery, An electrode laminate is constructed by stacking a sheet-shaped positive electrode and a sheet-shaped negative electrode via a sheet-shaped separator, A battery case containing the electrode stack and the electrolyte, with the lower part of the electrode stack immersed in the electrolyte, A cover member interposed between the electrode stack and the battery case, Equipped with, The cover member is A pair of side portions extending along both sides of the electrode stack, An upper surface portion that is connected to each of the pair of side portions and extends along the upper surface of the electrode stack, Yes, Multiple vertical grooves are formed on the side surface of the electrode stack that is immersed in the electrolyte, extending upward from the portion that is immersed in the electrolyte. A secondary battery in which a plurality of upper horizontal grooves are formed on the lower surface of the upper portion, extending in the stacking direction of the electrode stack and communicating with the vertical grooves.

2. In the secondary battery according to claim 1, A secondary battery in which the width of the aforementioned vertical groove is 0.1 mm or less.

3. In the secondary battery according to claim 1, The cover member further has a lower surface portion that is connected to each of the pair of side portions and extends along the lower surface of the electrode stack, A secondary battery having a plurality of lower horizontal grooves formed on the upper surface of the lower portion, which communicate with each other and also with the vertical grooves.

4. In the secondary battery according to claim 1, The electrode laminate has terminal components at its upper part, The cover member has a terminal opening that exposes the terminal component, A secondary battery in which the vertical groove or the upper horizontal groove located around the terminal opening communicate with each other via an edge groove formed to extend along the edge of the terminal opening.

5. In the secondary battery according to claim 1, A secondary battery in which the upper surface of the electrode stack is inclined, and the central part in the stacking direction is relatively lower.

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