Lead acid storage battery

Abstract

To provide a long-life lead acid storage battery.SOLUTION: A lead acid storage battery includes: an electrode plate group 30 housed in a plurality of cell chambers 24; and an electrolytic solution. Each electrode plate group includes: a positive electrode intermediate electrode column 34P extending from a positive electrode strap 32P along a partition wall 23; and a negative electrode intermediate electrode column 34N extending from a negative electrode strap 32N along the partition wall. The positive electrode intermediate electrode column and the negative electrode intermediate electrode column are connected by an intercell connection part 35 penetrating the partition wall, a liquid surface of the electrolytic solution is disposed below a lower end of the intercell connection part. The positive electrode strap includes a fragile part 36 in which a groove 37 recessed from an upper surface is formed. When a direction in which the positive electrode plate 30P and the negative electrode plate 30N are arranged in each cell chamber is a first direction, a length of the positive electrode strap in the first direction excluding the positive electrode intermediate electrode column is W, a distance L1 between the fragile part and the positive electrode intermediate electrode column in the first direction is 0.15 W or more. The fragile part is disposed at a position closer to the positive electrode intermediate electrode column than an ear part of the positive electrode plate disposed at a position farthest from the positive electrode intermediate electrode column in the first direction.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to lead-acid batteries. [Background technology]

[0002] A known lead-acid battery is described in Japanese Patent Laid-Open No. 2020-68068 (Patent Document 1 below). Patent Document 1 describes a lead-acid battery comprising: "a battery case having a plurality of cell chambers separated by partition walls; and a plurality of electrode plate groups housed in each of the plurality of cell chambers, the electrode plate group including a plurality of alternatingly arranged negative and positive electrode plates; a separator disposed between the negative and positive electrode plates; negative electrode straps and positive electrode straps disposed above the plurality of negative and positive electrode plates, connecting the plurality of negative and positive electrode plates together in the thickness direction at different positions in the width direction; and negative electrode intermediate poles and positive electrode intermediate poles rising from the negative electrode straps and positive electrode straps, respectively; the negative electrode intermediate poles disposed in one of two adjacent cell chambers and the positive electrode intermediate poles disposed in the other are connected by metal parts filling through holes formed in the partition walls; and the negative electrode plates and the positive electrode plate each have a substrate on which an active material is held, and a metal lug that protrudes upward from the substrate and is connected by the negative electrode strap and the positive electrode strap, wherein the antimony (Sb) content of the metal forming the lug is 20 ppm or less, the ratio (A / B) of the length A of the negative electrode strap and the positive electrode strap along the thickness direction to the length B of the lug along the height direction is 2.0 or more and 4.0 or less, the center positions of the lugs in the width direction are the same as the center positions of the widths of the negative electrode strap and the positive electrode strap, and the ratio (C / D) of the distance C along the width direction between the center of the lug in the width direction and one edge of the substrate in the width direction and the distance D (>C) along the width direction between the center of the lug in the width direction and the other edge of the substrate in the width direction is 0.40 or more and 0.75 or less. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-68068 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, efforts have been made to increase design flexibility by reducing the amount of electrolyte compared to conventional lead-acid batteries. Repeated charge / discharge cycles in lead-acid batteries can cause growth of the grid of the positive plate. This can lead to warping of the positive electrode strap and the positive electrode intermediate pole, leading to cracks in the metal parts (corresponding to the inter-cell connection parts of the present disclosure). When these cracks occur in lead-acid batteries with a low amount of electrolyte, oxygen and sulfuric acid can penetrate the cracks, causing corrosion of the metal parts. As the corrosion of the metal parts progresses, the sealing of the cell chambers is compromised, resulting in gas leaks. As a result, as charge / discharge cycles are repeated, the state of charge of the plate groups in each cell chamber varies greatly, leading to a decrease in the capacity of the lead-acid battery. This shortens the life of the lead-acid battery. [Means for solving the problem]

[0005] The lead-acid battery disclosed herein comprises a battery case having a plurality of cell chambers separated by partition walls, a plurality of electrode plate groups housed in each of the plurality of cell chambers, and an electrolyte injected into the plurality of cell chambers, each of the electrode plate groups comprising a plurality of positive and negative electrode plates alternately stacked with separators interposed therebetween, a positive electrode strap connected to a lug provided on each of the positive electrode plates, a negative electrode strap connected to a lug provided on each of the negative electrode plates, a positive electrode intermediate electrode post extending from the positive electrode strap along the partition wall, and a negative electrode intermediate electrode post extending from the negative electrode strap along the partition wall, and the positive electrode intermediate electrode post and the negative electrode intermediate electrode post are connected by an inter-cell connector penetrating the partition wall. a lead-acid battery in which the liquid level of the electrolyte is located below a lower end of the cell-to-cell connection portion, and the positive strap has a fragile portion formed with a groove recessed from an upper surface of the positive strap, and when a direction in which the positive plate and the negative plate are arranged in each of the cell chambers is defined as a first direction, the length of the positive strap in the first direction excluding the positive electrode intermediate post is W, and the distance between the fragile portion and the positive electrode intermediate post in the first direction is 0.15 W or more, and the fragile portion is located closer to the positive electrode intermediate post than the lug of the positive plate that is located at a position farthest from the positive electrode intermediate post in the first direction. [Effects of the Invention]

[0006] According to the present disclosure, a lead-acid battery with a long life can be provided. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a perspective view of a lead-acid battery according to an embodiment. [Figure 2] FIG. [Figure 3] 2 is a cross-sectional view taken along the line AA in FIG. 1. [Figure 4] FIG. 4 is a diagram schematically illustrating a part of the cross section BB in FIG. [Figure 5] FIG. 5 is a schematic diagram showing a conventional lead-acid battery, and is a cross-sectional view corresponding to FIG. 4. [Figure 6]10A and 10B are explanatory diagrams illustrating deformation of a positive electrode strap of a conventional lead-acid battery. [Figure 7] FIG. 2 is a side view of a positive electrode strap and a positive electrode intermediate post. [Figure 8] FIG. 2 is a plan view of a positive electrode strap and a positive electrode intermediate post. [Figure 9] FIG. 10 is a side view of a positive electrode strap and a positive electrode intermediate post having a U-shaped groove. [Figure 10] FIG. 10 is a side view of a positive electrode strap and a positive electrode intermediate post having a V-shaped groove. [Figure 11] 10A and 10B are explanatory diagrams illustrating deformation of a positive electrode strap having a fragile portion. [Figure 12] 1 is a graph showing the relationship between the cycle life of a lead-acid battery and the position of a weak portion. DETAILED DESCRIPTION OF THE INVENTION

[0008] (Outline of this embodiment) (1) A lead-acid battery according to the present disclosure includes a battery case having a plurality of cell chambers separated by partition walls, a plurality of electrode plate groups housed in each of the cell chambers, and an electrolyte injected into the cell chambers. Each electrode plate group includes a plurality of positive and negative electrode plates alternately stacked with separators interposed therebetween, a positive electrode strap connected to a lug provided on each of the positive electrode plates, a negative electrode strap connected to a lug provided on each of the negative electrode plates, a positive electrode intermediate pole extending from the positive electrode strap along the partition wall, and a negative electrode intermediate pole extending from the negative electrode strap along the partition wall. The positive electrode intermediate pole and the negative electrode intermediate pole are connected to each other by an inter-cell connector penetrating the partition wall. a lead-acid battery in which the positive electrode strap is connected to the positive electrode plate by a portion where the liquid level of the electrolyte is located below a lower end of the cell-to-cell connection portion, the positive electrode strap has a fragile portion where a groove is formed that is recessed from an upper surface of the positive electrode strap, and when a direction in which the positive electrode plates and the negative electrode plates are arranged in each of the cell chambers is defined as a first direction, the length of the positive electrode strap in the first direction excluding the positive electrode intermediate post is W, the distance between the fragile portion and the positive electrode intermediate post in the first direction is 0.15 W or more, and the fragile portion is located closer to the positive electrode intermediate post than the lug of the positive electrode plate that is located at a position farthest from the positive electrode intermediate post in the first direction.

[0009] With this configuration, when the grid of the positive plate expands and stress is applied to the positive strap, the weakened portion primarily deforms, thereby preventing stress from being applied from the positive strap to the inter-cell connection via the positive intermediate pole. This prevents cracks from forming in the inter-cell connection, which would allow electrolyte and oxygen to penetrate into the cracks and corrode the inter-cell connection. This prevents gas leaks caused by loss of airtightness in the cell chamber and shortens the lifespan of the lead-acid battery.

[0010] In lead-acid batteries, where the electrolyte level is lower than the bottom of the inter-cell connections, cracks in the inter-cell connections caused by the stress of grid expansion in the positive plates are exposed to the gas phase. When oxygen penetrates the cracks, the lead in the inter-cell connections converts to lead oxide, and the electrolyte then penetrates, producing lead sulfate. The lead oxide in the inter-cell connections then converts to lead sulfate and expands, pushing the gap between the inter-cell connections and the positive intermediate pole, further corroding the inter-cell connections. This results in a gas leak, which compromises the airtightness of adjacent cell chambers. In contrast, in conventional flooded lead-acid batteries, the electrolyte level is higher than the bottom of the inter-cell connections, making it difficult for oxygen to penetrate the cracks in the inter-cell connections, preventing the formation of lead oxide. In other words, even in conventional flooded lead-acid batteries, cracks in the inter-cell connections do not progress to the above-mentioned mechanism, and no gas leaks occur.

[0011] Examples of lead-acid batteries in which the electrolyte level is lower than the bottom of the inter-cell connections include flooded lead-acid batteries in which the electrolyte level is lower than the bottom of the positive strap (the inter-cell connections and positive strap are exposed to the gas phase) and lead-acid batteries in which the electrolyte is impregnated in a glass mat (the top of the impregnated glass mat is considered the electrolyte level). Even in these lead-acid batteries, the electrolyte can travel down the partition wall to the inter-cell connections and seep into cracks in the inter-cell connections, causing lead oxide to convert to lead sulfate and expand, resulting in corrosion of the inter-cell connections. This can lead to gas leaks, which compromise the airtightness between adjacent cell compartments. Here, the electrolyte level in a flooded lead-acid battery refers to the electrolyte level when the battery case is filled to the upper level indicated on the battery case. If the battery case does not indicate the upper level, the upper level refers to the electrolyte level in an unused lead-acid battery.

[0012] Considering the tendency of corrosion to progress at the inter-cell connections, the configuration of the present disclosure is more preferably applied to lead-acid batteries in which the inter-cell connections and the positive electrode strap are exposed to a gas phase. When a crack occurs at the inter-cell connection, a coating layer of lead sulfate is formed at the crack due to the gas absorption reaction shown in the following formula 1. At this time, the sulfuric acid concentration decreases partially near the inter-cell connection, and when the sulfuric acid concentration decreases, the solubility of lead sulfate increases, making it more likely for lead sulfate to dissolve.

[0013] (Formula 1) Pb+1 / 2O2+SO4 2- +2H + →PbSO4+H2O

[0014] In a lead-acid battery where the electrolyte level is at or above the bottom end of the positive strap, the positive strap and the electrolyte come into contact, and the electrolyte easily travels down the positive strap to the cell-to-cell connection, or the electrolyte level is close to the bottom end of the cell-to-cell connection, so the sulfuric acid concentration at the lowered cell-to-cell connection is likely to increase.

[0015] On the other hand, in a lead-acid battery in which the inter-cell connections and the positive electrode strap are exposed to the gas phase (the electrolyte level is lower than the bottom end of the positive electrode strap), the distance between the inter-cell connections and the electrolyte level is long, making it more difficult for the electrolyte to be supplied to the inter-cell connections than when the electrolyte level is higher than the bottom end of the positive electrode strap. As a result, it takes a relatively long time for the sulfuric acid concentration to increase. As the sulfuric acid concentration decreases, the solubility of lead sulfate increases, making it more likely for the lead sulfate to dissolve, partially dissolving the coating layer and exposing the lead underneath. In the exposed lead portion, the reaction represented by Equation 1 occurs again, forming a new layer of lead sulfate. This reaction is repeated in cracks that occur in the inter-cell connections, further promoting corrosion of the inter-cell connections. Therefore, in a configuration in which the inter-cell connections and the positive electrode strap are exposed to the gas phase, gas leaks that compromise the airtightness between adjacent cell chambers are likely to occur, and therefore, the configuration of the present disclosure is preferably applied.

[0016] Considering the ease of suppressing corrosion at the cell-cell connections, the separator preferably includes a glass mat impregnated with an electrolyte in the configuration of the present disclosure. With this configuration, oxygen generated from the positive electrode plate is consumed in a reaction at the negative electrode plate, making it difficult for oxygen to be supplied to the vicinity of the cell-cell connections. This further suppresses corrosion at the cell-cell connections.

[0017] (2) In the lead-acid battery of (1) above, the positive electrode strap may be made of a Pb—Sn alloy that does not contain Sb.

[0018] (3) In the lead-acid battery of (1) or (2) above, when the thickness of the positive electrode strap is T, it is preferable that the depth of the groove is 0.2T or more and 0.6T or less.

[0019] With this configuration, the strength of the fragile portion can be appropriately adjusted. Also, by setting the depth of the groove to 0.6 T or less, it is possible to prevent a deterioration in the high-rate discharge characteristics of the lead-acid battery.

[0020] (4) In any one of the lead-acid batteries (1) to (3) above, it is preferable that the length of the groove in the first direction is 2 mm or more and is equal to or less than the distance between the ears of the adjacent positive electrode plates, and that the groove is arranged at a position different from the ears of the positive electrode plates.

[0021] This configuration makes it easy to form the groove and to appropriately adjust the strength of the fragile portion. In addition, by arranging the groove at a position different from the lug of the positive electrode plate, the strength of the portion of the positive electrode strap that is connected to the lug can be maintained.

[0022] (5) In the lead-acid battery of any one of (1) to (4) above, it is preferable that the shape of the groove is V-shaped when the groove is viewed from a direction perpendicular to both the first direction and the depth direction of the groove.

[0023] With this configuration, it is possible to suppress a reduction in the cross-sectional area of ​​the positive electrode strap due to the formation of the groove, and to suppress a deterioration in the high-rate discharge characteristics of the lead-acid battery.

[0024] <Embodiment> An embodiment of the present disclosure will be described with reference to Figures 1 to 12. In the following description, the front-rear direction, left-right direction, and up-down direction are based on the front-rear direction, left-right direction, and up-down direction shown in Figure 1. In this embodiment, the front-rear direction is an example of a first direction.

[0025] 1. Battery configuration The lead-acid battery 10 is mounted on a mobile object such as a four-wheeled vehicle or a two-wheeled vehicle. As shown in FIG. 1, the lead-acid battery 10 includes a battery case 20 and a lid member 50 having a positive electrode terminal 60P and a negative electrode terminal 60N. The battery case 20 is made of synthetic resin. As shown in FIG. 2, the battery case 20 has four outer walls 21A to 21D and a bottom wall 22, and is box-shaped with an open top. The interior of the battery case 20 is divided into a plurality of cell chambers 24 by partition walls 23. Six cell chambers 24 are provided, lined up in the front-rear direction. Each cell chamber 24 contains a plate assembly 30 (see FIG. 3) together with a flowable electrolyte.

[0026] 1, the lid member 50 is made of synthetic resin and seals the top surface of the battery case 20. A negative electrode terminal 60N and a positive electrode terminal 60P are provided at the front and rear ends of the lid member 50, respectively.

[0027] As shown in Figures 3 and 4, the electrode plate group 30 includes a plurality of positive electrode plates 30P, a plurality of negative electrode plates 30N, and a separator SP that separates the adjacent electrode plates 30P, 30N. In each cell chamber 24, the positive electrode plates 30P and the negative electrode plates 30N are aligned in the front-to-rear direction. Each electrode plate 30P, 30N is formed by filling an active material into a grid. The active material of the positive electrode plates 30P is mainly composed of lead dioxide, and the active material of the negative electrode plates 30N is mainly composed of lead.

[0028] 3 and 4, ears 31P, 31N are provided on the top of each of the electrode plates 30P, 30N. The ears 31P of the multiple positive electrode plates 30P are connected by a positive electrode strap 32P. The ears 31N of the multiple negative electrode plates 30N are connected by a negative electrode strap 32N.

[0029] Each strap 32P, 32N is, for example, a plate-like shape elongated in the front-rear direction. Each strap 32P, 32N is made of, for example, a Pb-Sn alloy. One positive electrode strap 32P and one negative electrode strap 32N are provided in each cell chamber 24, and are aligned in the left-right direction. The cell chambers 24 located at the ends (in this embodiment, the front and rear ends) of the multiple cell chambers 24 house straps 32P, 32N connected to the respective terminals 60P, 60N. For example, as shown in FIG. 3 , the negative electrode strap 32N located in the front cell chamber 24 is connected to the negative electrode terminal 60N via a negative electrode end pole 33N. The negative electrode end pole 33N is integral with the negative electrode strap 32N and extends upward from the negative electrode strap 32N. Similarly, the positive electrode strap 32P located in the rear cell chamber 24 is connected to the positive electrode terminal 60P via a positive electrode end pole.

[0030] Furthermore, each strap 32P, 32N that is not provided with an end pole is provided with an intermediate pole 34P, 34N. Specifically, as shown in FIGS. 3 and 4, the positive strap 32P is provided with a positive intermediate pole 34P extending upward from the front or rear end of the positive strap 32P. As shown in FIG. 4, the negative strap 32N is provided with a negative intermediate pole 34N extending upward from the front or rear end of the negative strap 32N. Each intermediate pole 34P, 34N extends along the partition wall 23. The positive intermediate pole 34P and the negative intermediate pole 34N, which are arranged adjacent to each other in the front-rear direction across the partition wall 23, are connected by an inter-cell connection 35. The inter-cell connection 35 penetrates the partition wall 23. In the lead-acid battery 10 of this embodiment, the liquid level of the electrolyte is located below the lower end of the inter-cell connection 35. Furthermore, the liquid level of the electrolyte is located below the lower ends of the positive electrode straps 32P and negative electrode straps 32N. The positive electrode straps 32P, negative electrode straps 32N, and inter-cell connections 35 are exposed above the liquid level of the electrolyte and are located in the gas phase.

[0031] FIG. 5 is a cross-sectional view showing a conventional lead-acid battery 100 not included in this disclosure. In this lead-acid battery 100, the positive electrode strap 132P is plate-shaped with a certain thickness (vertical dimension), but the other configurations are similar to those of the lead-acid battery 10. It is known that repeated charge and discharge of the lead-acid battery 100 causes growth in the positive electrode plate 30P, causing the positive electrode plate 30P to elongate in the vertical direction. This causes the positive electrode strap 132P connecting multiple positive electrode plates 30P to be pushed upward. Meanwhile, the positive electrode intermediate post 34P extending from the positive electrode strap 132P is fixed by an inter-cell connector 35 penetrating the partition wall 23. As a result, as shown in FIG. 6 , the portion of the positive strap 132P away from the positive intermediate post 34P is pushed upward, causing the positive strap 132P to warp and deform. This generates stress at the connection between the positive intermediate post 34P and the inter-cell connection 35, causing the positive intermediate post 34P to peel off from the inter-cell connection 35. This causes cracks in the inter-cell connection 35, allowing oxygen and sulfuric acid to penetrate into the cracks, corroding the inter-cell connection 35. As corrosion of the inter-cell connection 35 progresses, the airtightness of the cell chamber 24 is compromised, causing gas leakage to the adjacent cell chamber 24. During the charge cycle, oxygen is generated in the positive plate 30P, which is already fully charged. If this oxygen migrates to the adjacent cell chamber 24 through the corroded portion of the inter-cell connection 35, a negative electrode absorption reaction occurs in the negative plate 30N, consuming oxygen. As a result, the negative electrode plate 30N that is not yet fully charged is not charged, and variations in the state of charge occur among the electrode plate groups 30 arranged in each cell chamber 24. As charge / discharge cycles are repeated, such variations in the state of charge increase, resulting in a decrease in the capacity of the lead-acid battery 100 and a shortened lifespan of the lead-acid battery 100. In particular, when deep charge / discharge cycles are repeated, the variations in the state of charge among the electrode plate groups 30 arranged in each cell chamber 24 are likely to increase.

[0032] In this embodiment, in order to suppress gas leakage between adjacent cell chambers 24 due to damage to the inter-cell connection 35 as described above, we considered forming a fragile portion 36 in the positive electrode strap 32P that is prone to deformation preferentially when positive electrode growth occurs. In addition, we conducted detailed experiments to investigate a suitable form of the fragile portion 36.

[0033] 2. Configuration of the vulnerable part 4, the positive electrode strap 32P of this embodiment has a groove 37 recessed from the top surface of the positive electrode strap 32P. The portion where the dimension (thickness) in the vertical direction is reduced due to the formation of the groove 37 is the fragile portion 36. Because the fragile portion 36 has a smaller thickness than other portions of the positive electrode strap 32P, it is thought that the fragile portion 36 will deform preferentially when stress is applied to the positive electrode strap 32P.

[0034] The positive electrode strap 32P of this embodiment may be made of a Pb—Sn alloy that does not contain Sb. Here, a Pb—Sn alloy is defined as an alloy containing 2.0% or more Sn and 0.002% or less Sb. A Pb—Sn alloy that does not contain Sb has lower strength than a Pb—Sn alloy that does contain Sb. Therefore, when the positive electrode strap 32P is made of a Pb—Sn alloy that does not contain Sb, it is considered that the positive electrode strap 32P is particularly susceptible to deformation due to positive electrode growth, and a load is likely to be applied to the inter-cell connection 35. However, by providing a fragile portion 36 at a suitable position on the positive electrode strap 32P as in this embodiment, gas leakage from the inter-cell connection 35 can be suppressed.

[0035] As shown in Fig. 8, the groove 37 extends in the left-right direction, and both left-right ends of the groove 37 coincide with both left-right ends of the positive strap 32P. As shown in Fig. 7, the dimension of the groove 37 (fragile portion 36) in the front-rear direction is designated X. The dimension (depth) of the groove 37 in the up-down direction is designated Z. The thickness of the positive strap 32P is designated T. The length of the positive strap 32P in the front-rear direction excluding the positive intermediate electrode post 34P is designated W. The distance between the fragile portion 36 and the positive intermediate electrode post 34P in the front-rear direction is designated L1.

[0036] Considering ease of molding, the dimension X of the groove 37 in the front-rear direction is preferably 2 mm or more. Furthermore, the dimension X of the groove 37 in the front-rear direction is preferably equal to or less than the distance between the lugs 31P of adjacent positive electrode plates 30P, and the groove 37 is preferably positioned differently from the lugs 31P of the positive electrode plates 30P. In other words, as shown in FIG. 4 , the groove 37 is preferably formed between adjacent lugs 31P. The upper portions of the lugs 31P of the positive electrode plates 30P are embedded in the positive electrode strap 32P from the lower surface of the positive electrode strap 32P to approximately half the thickness T of the positive electrode strap 32P. As described above, forming the groove 37 between adjacent lugs 31P prevents the upper portions of the lugs 31P from being scraped off during the formation of the groove 37. This maintains the strength of the portion of the positive electrode strap 32P connected to the lug 31P.

[0037] 7, the shape of the groove 37 of the positive electrode strap 32P when viewed from the left and right (side view shape) may be concave. That is, the groove 37 may be composed of a bottom surface and two side surfaces that connect both ends of the bottom surface to the top surface of the positive electrode strap. The bottom surface is approximately parallel to the horizontal direction (front-rear and left-right planar direction), and the side surfaces and the bottom surface are approximately perpendicular.

[0038] As shown in Fig. 9, the groove 37 of the positive electrode strap 32P may have a U-shape in side view. As shown in Fig. 10, the groove 37 of the positive electrode strap 32P may have a V-shape in side view. In particular, when the groove 37 has a V-shape in side view, it is possible to suppress a decrease in the cross-sectional area of ​​the positive electrode strap 32P that would otherwise be caused by the formation of the groove 37. This is expected to have the effect of suppressing a deterioration in the high-rate discharge characteristics of the lead-acid battery 10.

[0039] As shown in FIG. 8 , the positive electrode strap 32P may include a first portion 40 having a constant dimension in the left-right direction, and a second portion 41 disposed between the positive electrode intermediate pole 34P and the first portion 40 and having a dimension in the left-right direction that increases toward the positive electrode intermediate pole 34P in the front-rear direction. In a plan view, the first portion 40 is rectangular, and the second portion 41 is trapezoidal. The fragile portion 36 may be provided in either the first portion 40 or the second portion 41. The dimension of the first portion 40 in the front-rear direction is defined as D1. The dimension of the second portion 41 in the front-rear direction is defined as D2. The dimension of the first portion 40 in the left-right direction is defined as D3. The dimension (maximum dimension) of the second portion 41 in the left-right direction is defined as D4 (>D3).

[0040] As shown in FIG. 7 , a portion of the positive strap 32P closer to the positive intermediate pole 34P than the fragile portion 36 in the front-rear direction is designated as the third portion 42. A portion of the positive strap 32P farther from the positive intermediate pole 34P than the fragile portion 36 in the front-rear direction is designated as the fourth portion 43. When one or more lugs 31P of a positive plate 30P are connected to the fourth portion 43, stress due to positive growth is applied. As shown in FIG. 11 , this causes the fourth portion 43 to tilt upward relative to the third portion 42, bending the positive strap 32P at the fragile portion 36. This is thought to reduce the stress applied to the inter-cell connection portion 35. Therefore, it is preferable that one or more lugs 31P are connected to the fourth portion 43. In other words, it is preferable that the fragile portion 36 be positioned closer to the positive intermediate pole 34P than the lug 31P of the positive plate 30P that is positioned farthest from the positive intermediate pole 34P in the front-rear direction. Conversely, if the ear portion 31P is not connected to the fourth portion 43, it is conceivable that the stress applied to the inter-cell connection portion 35 due to deformation of the fragile portion 36 cannot be reduced.

[0041] 3. Experiment To investigate the preferred form of the fragile portion, various fragile portions were formed in the positive electrode strap, and experiments were conducted to evaluate the cycle life and high-rate discharge characteristics of lead-acid batteries (voltage 12 V, nominal capacity 52 Ah (3-hour rate)) equipped with the positive electrode strap. The experimental results are shown in Table 1 and Figure 12. In addition, in "3. Experiment" and "4. Discussion" of this specification, configurations that are not included in this disclosure will also be explained, and therefore no reference numerals will be assigned.

[0042] The charge-discharge cycle test was conducted in a 60°C environment. In the charge-discharge cycle test, discharging was performed at a discharge current of 20 A until the discharge capacity reached 36 Ah. Charging was performed using a five-stage constant current charging method. Specifically, charging was performed using the following method. First, constant current charging was performed at 12 A, and when the charging voltage reached the switching voltage, the charging current was reduced to 6 A. The charging voltage decreased as the charging current was reduced, and when the charging voltage reached the switching voltage again, the charging current was reduced to 3 A. When the charging voltage reached the switching voltage again, the charging current was reduced to 1.5 A. When the charging voltage reached the switching voltage again, the charging current was maintained at 1.5 A, and charging continued until the charge capacity reached 42.48 Ah. In this manner, five stages of charging were performed. The switching voltage was 13.35 V.

[0043] A capacity confirmation test (3-hour rate capacity test) was conducted in a 25°C environment every 50 cycles, and when the confirmed capacity was less than 43 Ah, the number of cycles was defined as the cycle life.

[0044] [Table 1]

[0045] In this experiment, the positive electrode strap is connected to the lugs of 11 positive plates. The upper ends of the positive electrode plate lugs are located 2.5 mm below the top surface of the positive electrode strap. The distance between the lugs of adjacent positive plates in the front-to-back direction is 4 mm. The thickness T of the positive electrode strap is 5 mm.

[0046] In this experiment, the front-to-back dimension D1 of the first part is 35.5 mm. The front-to-back dimension D2 of the second part is 18 mm. The front-to-back length W of the positive electrode strap excluding the positive electrode intermediate pole is 53.5 mm. The left-to-right dimension D3 of the first part is 13 mm. The left-to-right dimension (maximum dimension) D4 of the second part is 24 mm.

[0047] In this experiment, the groove was concave. The dimension X of the groove in the front-rear direction was 4 mm. In other words, the dimension X of the groove in the front-rear direction was equal to the distance between the ears of adjacent positive electrode plates in the front-rear direction.

[0048] In this experiment, samples S1 to S12 were produced, each with a different groove depth Z and a different distance L1 between the weak portion and the positive electrode intermediate post in the front-to-rear direction. FIG. 12 is a graph showing the relationship between cycle life and L1 / W for each of samples S1 to S12. Note that data points with different groove depths Z are shown using different markers. As will be described later, samples S1 and S2 are not included in this disclosure, but samples S3 to S12 are included in this disclosure. Particularly good results were obtained with samples S6 to S11.

[0049] The cycle life in this experiment is the number of cycles required for each of samples S1 to S12 to reach the capacity life when the charge-discharge cycle test is performed under the above conditions, and is expressed as a percentage of the cycle life of a conventional lead-acid battery that does not have a groove (weakened portion) in the positive electrode strap. In other words, a cycle life of more than 100% can be considered to be a good result.

[0050] The high-rate discharge characteristics in Table 1 are the terminal voltage 5 seconds after the start of discharge when a lead-acid battery is discharged at a discharge current of 150 A in a 0°C environment, and are expressed as a ratio to the high-rate discharge characteristics of a conventional lead-acid battery.

[0051] 4. Discussion Table 1 and Figure 12 show that when L1 / W is 0.15 or greater, the cycle life is longer than that of conventional lead-acid batteries. Furthermore, when L1 / W is 0.07 and 0.13 (samples S1 and S2), the wire life is shorter than that of conventional lead-acid batteries. These results indicate that when the weak spot is located near the positive intermediate pole, stress is more likely to be applied to the inter-cell connection. In the conventional configuration, even if the positive plate located near the base end of the positive intermediate pole (the portion near the positive strap) grows and generates upward stress, the stress is directed in a different direction because the positive intermediate pole and the inter-cell connection are fixed. On the other hand, when the weak spot is located near the positive intermediate pole, the upward stress generated by the growth of the positive plate is more likely to escape toward the weak spot, making the base end more likely to open. Therefore, when charge-discharge cycles are repeated, the base end of the positive intermediate post is more likely to deform and separate from the partition wall than in conventional configurations (see Figure 6), and load is more likely to be applied to the inter-cell connection. This type of deformation, in which the base end of the positive intermediate post separates from the partition wall, is more pronounced in Pb-Sn alloys that do not have high strength (for example, Pb-Sn alloys that do not contain Sb).

[0052] 12, it can be seen that the cycle life is particularly long when L1 / W is 18 to 80%. Therefore, it is preferable that the weak portion be located in a portion of the positive electrode strap other than both ends in the front-rear direction. It is preferable that the weak portion be located in a portion of the positive electrode strap closer to the center in the front-rear direction.

[0053] When L1 / W is close to 100%, i.e., when the weak portion is located near the end opposite the positive electrode intermediate pole, the number of lugs connected to the fourth portion of the positive electrode strap is reduced, and the effect of providing the weak portion on the cycle life is not significant. For example, when L1 / W is 93% (sample S12), the lug of one positive electrode plate is connected to the fourth portion, and the cycle life is 105%.

[0054] Samples S5 to S8 have a constant L1 / W of 0.24 and different groove depths Z. It can be seen that the cycle life of samples S5 to S8 increases as the groove depth increases. This is thought to be because the fragile parts become more easily deformed as the groove depth increases. Conversely, although not shown in Table 1, it is thought that if the groove is too shallow, the fragile parts become less likely to deform. In this experiment, particularly good cycle life was obtained when the groove depth Z was 1 mm or more (samples S6 to S8).

[0055] Furthermore, Table 1 shows that sample S8, which has the deepest grooves among samples S5 to S8, had a high-rate discharge characteristic of 99%, which is slightly lower than that of conventional lead-acid batteries. This is thought to be due to the reduction in the cross-sectional area of ​​the positive electrode strap caused by the formation of the grooves. Although not shown in Table 1, it is expected that the deterioration in high-rate discharge characteristics will become more serious if the grooves are deeper than sample S8, i.e., if the grooves exceed 3 mm.

[0056] Based on the above results, from the viewpoints of both cycle life and high-rate discharge characteristics, in this experiment, it is preferable that the groove depth Z is 1 mm or more and 3 mm or less. Here, when the thickness T of the positive electrode strap (= 5 mm) is used, it is preferable that the groove depth Z is 0.2 T or more and 0.6 T or less.

[0057] 5. Effects As described above, the lead-acid battery 10 according to this embodiment includes a battery case 20 having a plurality of cell chambers 24 separated by partition walls 23, a plurality of electrode plate groups 30 housed in each of the cell chambers 24, and an electrolyte injected into the plurality of cell chambers 24. Each electrode plate group 30 includes a plurality of positive electrode plates 30P and negative electrode plates 30N stacked alternately with separators SP interposed therebetween, a positive electrode strap 32P connected to an ear 31P provided on each positive electrode plate 30P, a negative electrode strap 32N connected to an ear 31N provided on each negative electrode plate 30N, a positive electrode intermediate electrode post 34P extending from the positive electrode strap 32P along the partition wall 23, and a negative electrode intermediate electrode post 34N extending from the negative electrode strap 32N along the partition wall 23. and the positive electrode strap 32P are connected by inter-cell connection parts 35 that penetrate the partition wall 23, and the liquid level of the electrolyte is located below the lower end of the inter-cell connection part 35, and the positive electrode strap 32P has a fragile part 36 in which a groove 37 that is recessed from the upper surface of the positive electrode strap 32P is formed, and when the direction in which the positive electrode plate 30P and the negative electrode plate 30N are lined up in each cell chamber 24 is defined as a first direction (front-rear direction), the length in the first direction of the positive electrode strap 32P excluding the positive electrode intermediate pole 34P is W, and the distance L1 between the fragile part 36 and the positive electrode intermediate pole 34P in the first direction is 0.15W or more, and the fragile part 36 is located closer to the positive electrode intermediate pole 34P than the lug part 31P of the positive electrode plate 30P that is located at a position farthest from the positive electrode intermediate pole 34P in the first direction.

[0058] With this configuration, when the grid of the positive plate 30P expands and stress is applied to the positive strap 32P, the weakened portion 36 primarily deforms, thereby preventing stress from being applied from the positive strap 32P to the inter-cell connection 35 via the positive intermediate pole 34P. This prevents cracks from forming in the inter-cell connection 35, which would allow electrolyte and oxygen to enter the cracks and corrode the inter-cell connection 35. This also prevents gas leaks caused by loss of airtightness of the cell chamber 24. This prevents a decrease in capacity of the lead-acid battery 10 due to gas leaks.

[0059] In this embodiment, the positive electrode strap 32P may be made of a Pb—Sn alloy that does not contain Sb.

[0060] In this embodiment, when the thickness of the positive electrode strap 32P is T, the depth Z of the groove 37 is preferably 0.2T or more and 0.6T or less.

[0061] This configuration makes it possible to appropriately adjust the strength of the fragile portion 36. Furthermore, by setting the depth Z of the groove 37 to 0.6 T or less, it is possible to suppress a deterioration in the high-rate discharge characteristics of the lead-acid battery 10.

[0062] In this embodiment, the length X of the groove 37 in the first direction is 2 mm or more and is equal to or less than the distance between the ear portions 31P of adjacent positive electrode plates 30P, and it is preferable that the groove 37 is arranged at a position different from the ear portions 31P of the positive electrode plates 30P.

[0063] This configuration makes it easy to form the groove 37 and to appropriately adjust the strength of the fragile portion 36. Furthermore, by arranging the groove 37 at a position different from the lug 31P of the positive electrode plate 30P, it is possible to maintain the strength of the portion of the positive electrode strap 32P that is connected to the lug 31P.

[0064] In this embodiment, when the groove 37 is viewed from a direction perpendicular to both the first direction and the depth direction (vertical direction) of the groove 37, the shape of the groove 37 is preferably V-shaped.

[0065] With this configuration, it is possible to prevent a reduction in the cross-sectional area of ​​the positive electrode strap 32P due to the formation of the groove 37, and it is possible to prevent a deterioration in the high-rate discharge characteristics of the lead-acid battery 10.

[0066] In this embodiment, the separator SP preferably comprises a glass mat impregnated with an electrolyte solution.

[0067] With this configuration, oxygen generated from the positive electrode plate 30P is consumed in a reaction in the negative electrode plate 30N, making it difficult for oxygen to be supplied to the vicinity of the inter-cell connection 35. Therefore, corrosion of the inter-cell connection 35 is further suppressed.

[0068] <Other embodiments> The present disclosure is not limited to the embodiments described above and illustrated in the drawings, but is intended to include all modifications within the scope and meaning equivalent to the claims. The technical scope of the present disclosure also includes, for example, the following embodiments.

[0069] While the positive electrode strap 32P in the above embodiment includes a first portion 40 and a second portion 41, the positive electrode strap of the present disclosure does not necessarily have to include a first portion and a second portion. For example, the positive electrode strap may have a shape that has a constant dimension in the direction perpendicular to the first direction and the depth direction of the groove (hereinafter referred to as the width direction). In other words, the positive electrode strap may have a rectangular shape when viewed from the depth direction of the groove.

[0070] The width of the groove may be slightly smaller than the width of the positive electrode strap. In other words, the groove may not be open in the width direction, but may be located inside the positive electrode strap in the width direction. [Explanation of symbols]

[0071] 10:Lead acid battery 20: Battery case 23: Bulkhead 24: Cell Room 30: Plate group 30N: Negative plate 30P: Positive electrode plate 31N: Ear of negative electrode plate 30N 31P: Ear of positive electrode plate 30P 32N: Negative electrode strap 32P: Positive strap 34N: Negative intermediate pole 34P:Positive intermediate pole 35: Inter-cell connection 36: Weak part 37: Groove L1: Distance between the fragile portion 36 and the positive electrode intermediate pole 34P in the front-rear direction (first direction) SP: Separator T: Thickness of positive electrode strap 32P W: Length in the front-to-rear direction (first direction) of the positive electrode strap 32P excluding the positive electrode intermediate electrode post 34P X: Dimension of groove 37 in the front-to-rear direction (first direction) Z: Depth of groove 37

Claims

1. a battery container having a plurality of cell chambers separated by partition walls; a plurality of electrode plate assemblies housed in the plurality of cell chambers, respectively; an electrolyte solution injected into the plurality of cell chambers; each of the electrode plate groups includes a plurality of positive electrode plates and negative electrode plates stacked alternately with separators interposed therebetween, a positive electrode strap connected to an ear portion provided on each of the positive electrode plates, a negative electrode strap connected to an ear portion provided on each of the negative electrode plates, a positive electrode intermediate electrode post extending from the positive electrode strap along the partition wall, and a negative electrode intermediate electrode post extending from the negative electrode strap along the partition wall; the positive electrode intermediate pole and the negative electrode intermediate pole are connected by an inter-cell connector that penetrates the partition wall, A lead-acid battery in which a liquid level of the electrolyte is located below a lower end of the inter-cell connection portion, the positive electrode strap has a weakened portion having a groove recessed from an upper surface of the positive electrode strap; When the direction in which the positive electrode plates and the negative electrode plates are arranged in each of the cell chambers is defined as a first direction, The length of the positive electrode strap excluding the positive electrode intermediate pole in the first direction is W, a distance between the fragile portion and the positive electrode intermediate pole in the first direction is 0.15 W or more; the fragile portion is disposed at a position closer to the positive electrode intermediate pole than the lug portion of the positive electrode plate disposed at a position farthest from the positive electrode intermediate pole in the first direction.

2. 2. The lead-acid battery of claim 1, wherein the positive electrode strap is made of a Pb-Sn alloy that does not contain Sb.

3. 3. The lead-acid battery according to claim 1, wherein the depth of the groove is 0.2 T or more and 0.6 T or less, where T is a thickness of the positive electrode strap.

4. The length of the groove in the first direction is 2 mm or more and is equal to or less than the distance between the ear portions of the adjacent positive electrode plates, 3. The lead-acid battery according to claim 1, wherein the groove is disposed at a position different from the lug of the positive electrode plate.

5. 3. The lead-acid battery according to claim 1, wherein the groove has a V-shape when viewed from a direction perpendicular to both the first direction and the depth direction of the groove.

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