Lead-acid

Abstract

To improve the cycle life of a lead-acid battery by suppressing breakage of a joint part without increasing the content of organic fibers in an AGM separator formed in a bag shape.SOLUTION: Each of the AGM separators 24 contains organic fibers and glass fibers and has a welded portion 24A where a side edge portion 24A of a portion on one side of the positive electrode plate 22 in a plate thickness direction of the positive electrode plate 22 and a side edge portion 24B of a portion on the other side of the positive electrode plate 22 in the plate thickness direction of the positive electrode plate 22 are welded to each other, and the side edge portion 24A is bent so as to face an end surface of the positive electrode plate 22. In the lead acid storage battery 1, a welded part 24A formed at a bent part of a side edge part 24B is positioned between an internal wall surface of a battery jar 11 and an end surface of a positive electrode plate 22.SELECTED DRAWING: Figure 9B

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a lead-acid battery. [Background technology]

[0002] Conventionally, there has been known a lead-acid battery that includes an electrode plate and a separator that is formed in a bag shape that opens upward and houses the electrode plate therein, the separator containing organic fiber and glass fiber (see, for example, Patent Document 1). In the following description, a separator containing organic fibers and glass fibers is referred to as an AGM (Absorbed Glass Mat) separator. An AGM separator is formed into a bag shape by joining the edge of a portion of the separator located on one side of the electrode plate in the thickness direction to the edge of a portion of the separator located on the other side. In the following description, the joined portion of the edges is referred to as the joint.

[0003] Some separators are made of nonwoven synthetic resin fabrics such as polypropylene (PP) and polyethylene (PE), but AGM separators are known to have better liquid retention and absorption properties than synthetic resin separators. However, it is known that AGM separators swell with the progress of charge / discharge cycles, causing delamination at the joint interface. This phenomenon, along with the expansion of the electrode plates with the progress of cycles, places stress on the joint, which may cause the joint to separate. In the following explanation, this separation of the joint is referred to as joint failure. Joint failure can lead to a short circuit between the positive and negative electrodes inside the battery. A short circuit prevents further use of the lead-acid battery, reducing its cycle life.

[0004] Increasing the organic fiber content of AGM can improve bonding strength. However, because organic fibers are uniformly dispersed throughout the AGM and have low electrolyte retention, the tradeoff is that the electrolyte retention capacity of the AGM separator decreases. This decrease in electrolyte retention capacity reduces the cycle life of lead-acid batteries.

[0005] For this reason, a technique for varying the content of organic fibers in the thickness direction of the separator has been disclosed (see, for example, Patent Document 1). Specifically, Patent Document 1 describes a separator for a sealed lead-acid battery containing glass fibers and organic fibers, in which the content of organic fibers is high only on the surface side of the separator to be heat-sealed, and low in other parts, thereby reducing the content of organic fibers in the entire separator. The same document also describes that the separator has excellent liquid retention and absorption properties, as well as excellent heat-sealing properties.

[0006] Furthermore, a technique for sealing the edge portions of a pouch-shaped separator with a thermoplastic resin has also been disclosed (see, for example, Patent Document 2). Specifically, Patent Document 2 describes a pouch-shaped separator for a lead-acid battery, in which a porous sheet mainly made of an inorganic material such as glass fiber is folded into a U-shape and both ends are sealed, in which both side edges of the porous sheet are coated with a molten thermoplastic resin so that both overlapping pieces on the side are integrally wrapped from the outside, and the thermoplastic resin is then cooled and hardened to seal both side edges. Furthermore, the same document describes that the adhesive seal portion of the pouch-shaped separator has high adhesive strength and does not impair the electrolyte retention of the adhesive seal portion.

[0007] Furthermore, pouch-shaped separators with folded edges have also been known (see, for example, Patent Document 3). Specifically, Patent Document 3 describes a method of constructing a pouch-shaped separator by folding a single separator material sheet in half and joining two separator members located on either side of the folded portion. The same document also describes a method of forming upstanding portions by folding a pair of sides of two separator members so that they each stand in the same direction relative to the main surface of the separator member, positioning one separator member's upstanding portion inside the other separator member's upstanding portion, and joining the edges of the two corresponding upstanding portions to form a joint. The same document also describes that by configuring the upstanding portions to be folded, the distance between the electrode plate and the wall of the battery case is shortened, thereby increasing the energy density of the battery relative to the battery case volume.

[0008] Furthermore, conventionally, a separator has been known in which both sides of a U-shaped mat separator are not joined together, but are simply folded in one direction of the thickness of the electrode plate (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 11-307074 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-042766 [Patent Document 3] Japanese Patent Application Publication No. 10-326608 [Patent Document 4] Japanese Patent Application Laid-Open No. 2007-103287 Summary of the Invention [Problem to be solved by the invention]

[0010] The separators described in Patent Documents 1 to 4 have room for improvement in terms of improving the cycle life of lead-acid batteries. One aspect of the present invention aims to suppress joint failure in a bag-shaped AGM separator without increasing the organic fiber content, thereby improving the cycle life of a lead-acid battery. [Means for solving the problem]

[0011] A lead-acid battery according to one embodiment of the present invention comprises an electrode plate, a separator formed in a bag shape that opens upward and houses the electrode plate inside, and a battery case in which the separator is housed, wherein the separator contains organic fibers and glass fibers and has a joint where an edge of a portion on one side of the electrode plate in the plate thickness direction is joined to an edge of a portion on the other side of the electrode plate, the edge being bent to face an end face of the electrode plate, and the joint formed in the bent portion of the edge being located between the inner wall surface of the battery case and the end face. [Effects of the Invention]

[0012] According to the above configuration, in the AGM separator formed in a bag shape, joint breakage can be suppressed without increasing the organic fiber content, thereby improving the cycle life of the lead-acid battery. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a perspective view of a lead-acid battery according to a first embodiment; [Figure 2] Perspective view of the battery case [Figure 3] Partial cross section of a lead-acid battery [Figure 4] Cross section of the positive electrode plate [Figure 5] Front view of the lattice [Figure 6] A perspective view of the AGM separator and positive electrode plate [Figure 7] Side view of AGM separator [Figure 8] Top view of the electrode plate assembly housed in the battery case [Figure 9A] Top view showing the separator and part of the positive electrode plate housed in the battery case (when new) [Figure 9B] Top view showing the separator and part of the positive electrode plate housed in the battery case (after some use) [Figure 10] Table showing the results of charge / discharge cycle tests (conventional products) [Figure 11] Table showing test results of charge / discharge cycle test (Example) [Figure 12A] FIG. 10 is a top view showing a part of a battery case, a separator, and a positive electrode plate according to a comparative example (when new); [Figure 12B] FIG. 1 is a top view showing a battery case, a separator, and a portion of a positive electrode plate according to a comparative example (after some use); DETAILED DESCRIPTION OF THE INVENTION

[0014] [Outline of the embodiment] First, an outline of the embodiments of the present disclosure will be listed and described.

[0015] (1) A lead-acid battery according to an embodiment includes a plate, a separator formed in a bag shape that opens upward and houses the plate, and a battery case in which the separator is housed. The separator contains organic fibers and glass fibers and has a joint where an edge of a portion of the plate on one side in the plate thickness direction is joined to an edge of a portion of the plate on the other side, the edge being bent to face an end face of the plate, and the joint formed in the bent portion of the edge being located between the inner wall surface of the battery case and the end face.

[0016] The above-mentioned "bent portion of the edge" can also be rephrased as "a portion of the edge extending in the plate thickness direction of the electrode plate."

[0017] First, we will explain joint tearing due to electrode plate expansion with reference to a comparative example shown in FIGS. 12A and 12B. FIG. 12A shows a top view of a portion of a pouch-shaped separator 100 housed in a battery case 102. As shown in FIG. 12A, the separator 100 according to the comparative example is pouch-shaped with a joint 104 formed at an edge 103 (the portion of the separator 100 forward of the electrode plate 101), but the edge 103 is not bent. As shown in FIG. 12B, when the electrode plate 101 expands in a direction parallel to the plate surface (the front-to-back direction in FIG. 12B), the end of the electrode plate 101 penetrates the joint 104, and a force acts in a direction that peels the joint 104. In addition, when the electrode plate 101 expands in the plate thickness direction (the left-to-right direction in FIG. 12B), a force acts in a direction that peels the joint 104. These forces may cause joint tearing.

[0018] In the separator for a sealed lead-acid battery described in Patent Document 1, the organic fiber content is increased only on the surface side of the separator that is heat-welded, thereby reducing the organic fiber content of the separator as a whole. However, the surface side still needs to have a content that is sufficient to ensure welding strength that can withstand the above-mentioned forces. The pouch-shaped separator for a lead-acid battery described in Patent Document 2 may be subject to breakage of the joints when the electrode plates expand in the plate thickness direction. The pouch-shaped separator described in Patent Document 3 is made of polyethylene, but even if the structure of the pouch-shaped separator described in the same document is applied to an AGM separator, there is a possibility that the joint will break if the electrode plate expands in the plate thickness direction. The mat separator described in Patent Document 4 is simply folded without joining both sides, so that as charge / discharge cycles and the like progress, the active material may protrude from the gaps between both sides, potentially causing a short circuit.

[0019] After studying this issue, the inventors of the present application discovered that joint tearing is less likely to occur if the end face of the expanded electrode plate presses the joint formed in the bent edge of the separator against the inner wall of the battery case. Specifically, when the electrode plate expands in a direction parallel to the plate surface, the end face of the electrode plate presses the joint against the inner wall of the battery case, making it less likely that a force will act in a direction that would pull the joint apart. This makes joint tearing less likely to occur when the electrode plate expands in a direction parallel to the plate surface. Furthermore, pressing the joint against the inner wall of the battery case also makes joint tearing less likely to occur when the electrode plate expands in the plate thickness direction.

[0020] In the lead-acid battery described in (1) above, the separator edge is bent to face the end face of the electrode plate, and the joint formed at the bent portion of the edge is located between the inner wall surface of the battery case and the end face of the electrode plate. Therefore, the end face of the expanded electrode plate presses the joint against the inner wall surface of the battery case. Therefore, even without increasing the organic fiber content, breakage of the joint due to the expansion of the electrode plate can be suppressed. Furthermore, by not increasing the organic fiber content, a decrease in the electrolyte retention capacity can be suppressed. Therefore, according to the lead-acid battery described in (1) above, in the AGM separator formed in a bag shape, joint breakage can be suppressed without increasing the organic fiber content, thereby improving the cycle life of the lead-acid battery.

[0021] (2) In the lead-acid battery described in (1) above, at least a part of the joint may be in contact with the inner wall surface.

[0022] According to the lead-acid battery described in (2) above, it is possible to eliminate a gap between at least a part of the joint and the inner wall surface, so that when the electrode plate expands in the plate surface direction, at least a part of the joint can be more reliably pressed against the inner wall surface of the battery case.

[0023] (3) In the lead-acid battery according to (1) or (2) above, at least a part of the joint may be in contact with another part of the separator that covers the end face.

[0024] According to the lead-acid battery described in (3) above, it is possible to eliminate a gap between at least a part of the joint and the other part of the separator covering the end face of the electrode plate, so that when the electrode plate expands in the plate surface direction, at least a part of the joint can be more reliably pressed against the inner wall surface of the battery case.

[0025] (4) In the lead-acid battery according to any one of (1) to (3) above, when a direction parallel to the bottom surface of the battery case and parallel to the plate surfaces of the electrode plates is defined as a width direction, the separator may have the joints formed on both side edge portions in the width direction, and the ratio of the width of the electrode plates in the width direction to the internal dimension of the battery case in the width direction may be 0.85 or more and 0.99 or less.

[0026] Experiments conducted by the inventors of the present application have shown that when the ratio of the width of the electrode plate in the width direction to the inner dimension of the battery case in the width direction is 0.85 or more and 0.99 or less, the cycle life of the lead-acid battery is improved compared to when the edges of the separator are not bent. According to the lead-acid battery described in (4) above, the ratio is 0.85 or more and 0.99 or less, so that the cycle life of the lead-acid battery is improved compared to a case where the edge portion is not bent.

[0027] (5) In the lead-acid battery according to any one of (1) to (4) above, when a direction parallel to a bottom surface of the battery case and parallel to plate surfaces of the electrode plates is defined as a width direction, the separator may have the joints formed on both side edge portions in the width direction, and the length of the side edge portions in the width direction may be 1 mm or more and 10 mm or less.

[0028] Experiments conducted by the inventors of the present application have shown that when the length of the side edge is 1 mm or more and 10 mm or less, the cycle life of the lead-acid battery is improved compared to when the separator edge is not bent. According to the lead-acid battery described in (5) above, the length of the side edge is 1 mm or more and 10 mm or less, so that the cycle life of the lead-acid battery is improved compared to when the edge is not bent.

[0029] (6) In the lead-acid battery according to any one of (1) to (5) above, the separator may have a thickness of 0.5 mm or more and 1.4 mm or less.

[0030] According to the lead-acid battery described in (6) above, the separator has a thickness of 0.5 mm or more, which increases the tensile strength and puncture strength of the separator, thereby preventing manufacturing defects due to separator damage during manufacturing and shortening the lifespan of the lead-acid battery due to separator deterioration and damage during use. Furthermore, the separator has a thickness of 1.4 mm or less, which prevents the electrode group pressure from becoming too high and makes manufacturing difficult. Furthermore, the positive and negative electrode plates can be made thicker, which improves energy density.

[0031] (7) In the lead-acid battery according to any one of (1) to (6) above, the separator may contain 10% by mass to 60% by mass of organic fibers.

[0032] According to the lead-acid battery described in (7) above, the separator contains 10% by mass to 60% by mass of organic fibers, so that it is easy to form a joint by thermal welding, ultrasonic welding, mechanical sealing, or the like, and the joint strength of the joint can also be increased.

[0033] (8) In the lead-acid battery according to any one of (1) to (7) above, the electrode plate may have a grid body and an electrode material filled in the grid body, and the grid body may be an expanded grid.

[0034] Known methods for manufacturing grids include casting and expanding. Expanding methods include the reciprocating method, in which a blade is pressed against a Pb alloy sheet along its length to make cuts while the sheet is pressed down to form a grid, and the rotary method, in which a Pb alloy sheet is cut in a zigzag pattern along its length and then expanded widthwise to form a grid. Grids manufactured by the expanding method (expanded grids) tend to expand more easily than grids manufactured by casting. In the lead-acid battery described in (8) above, the expanded expanded grid presses the joint against the inner wall surface of the battery case, making the joint less likely to break. Therefore, this is particularly effective when an expanded grid is used as the grid.

[0035] [Details of the embodiment] The present disclosure will be described in detail with reference to the exemplary embodiments, but the present disclosure is not limited to these examples and is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0036] <Embodiment 1> The first embodiment will be described with reference to Figures 1 to 11. 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 the following description, the reference numerals in the drawings may be omitted for the same components, with some exceptions.

[0037] (Overall structure of lead-acid battery) A lead-acid battery 1 according to a first embodiment will be described with reference to Fig. 1. The lead-acid battery 1 is a vehicle-driving lead-acid battery that is mounted on a vehicle (EV: Electric Vehicle) such as a forklift that runs on an electric motor and supplies power to the electric motor. The lead-acid battery 1 according to the first embodiment is a valve-regulated lead-acid battery in which an electrolyte is impregnated into the separator.

[0038] Lead-acid batteries include engine-starting lead-acid batteries used to start automobile engines. Engine-starting lead-acid batteries draw a large current when starting an engine, but only for a few seconds. In contrast, vehicle-driving lead-acid batteries 1 draw a large current for a relatively long period of time, making them prone to high temperatures. Furthermore, they discharge from a high state of charge (SOC) to a low state of charge, resulting in a deep discharge depth. In other words, lead-acid batteries 1 are used in cycle applications requiring higher temperatures and deeper discharge depths than engine-starting lead-acid batteries.

[0039] The lead-acid battery 1 includes a synthetic resin case 11 that is open upward, and a synthetic resin lid 12 that closes the opening of the case 11. The lid 12 is provided with a positive electrode external terminal 13 and a negative electrode external terminal 14. The positive electrode external terminal 13 and the negative electrode external terminal 14 penetrate the lid 12 in the vertical direction, and are connected to a positive electrode strap 20 and a negative electrode strap 21, which will be described later.

[0040] As shown in Fig. 2, five partition walls 15 are formed at equal intervals in the left-right direction inside the battery case 11 according to embodiment 1. The partition walls 15 divide the inside of the battery case 11 into six cell chambers 16. Each partition wall 15 has a through-hole 17 formed therein. In the following description, the direction perpendicular to the arrangement direction of the cell chambers 16 in a top view (i.e., the front-to-rear direction) is referred to as the width direction of the battery case 11. The width direction can also be referred to as the direction parallel to the bottom surface of the battery case 11 and the plate surface of the positive electrode plate 22 described later.

[0041] As shown in Fig. 3, a partition wall 18 on the lid portion 12 side is formed on the back surface of the lid portion 12 at a position corresponding to the partition wall 15 of the battery case 11, and the lower end surface of the partition wall 18 formed on the back surface of the lid portion 12 is connected by heat welding or the like to the upper end surface of the partition wall 15 formed on the battery case 11. This separates the cell chambers 16.

[0042] Each cell chamber 16 houses an electrode group 19, a positive electrode strap 20, and a negative electrode strap 21. The electrode group 19 has a plurality of positive electrode plates 22 (an example of electrode plates), a plurality of AGM separators 24 (an example of separators) formed in a bag shape that opens upward, and a plurality of negative electrode plates 25. Each positive electrode plate 22 is housed in an AGM separator 24. The positive electrode plates 22 and negative electrode plates 25 are stacked alternately in the arrangement direction of the cell chambers 16 with the plate surfaces oriented perpendicular to the arrangement direction (left-right direction) of the cell chambers 16.

[0043] The positive electrode strap 20 is made of a Sn—Pb alloy and is formed in an L-shape. A current collecting lug 33 (see FIG. 5 ), which will be described later, of the positive electrode plate 22 is connected to the lower surface of the positive electrode strap 20. The negative electrode strap 21 is also made of a Sn—Pb alloy and is formed in an L-shape. A current collecting lug 33 of the negative electrode plate 25 is connected to the lower surface of the negative electrode strap 21.

[0044] The positive electrode strap 20 is connected by ICW (intercell welding) connection to the negative electrode strap 21 housed in the cell chamber 16 adjacent to the cell chamber 16 housing the positive electrode strap 20 (if other cell chambers 16 are adjacent to both sides of the cell chamber 16 housing the positive electrode strap 20 in the left-right direction of FIG. 2 , the negative electrode strap 21 housed in one of the cell chambers 16). The ICW connection is a method of electrically connecting the positive electrode strap 20 and the negative electrode strap 21 by welding or the like through a through hole 17 formed in the partition wall 15.

[0045] (positive electrode plate) The positive electrode plate 22 will be described in more detail with reference to Fig. 4. The positive electrode plate 22 includes a grid 30 made of a Pb alloy containing at least one of Sn and Ca, and an electrode material 31 containing lead powder that appropriately contains tin or the like. As shown in Fig. 5, the grid element 30 has upper frame ribs 32 that form the upper side, current collecting lugs 33 provided on the upper part of the upper frame ribs 32, and a mesh portion 34 provided on the lower part of the upper frame ribs 32. The grid element 30 according to the first embodiment is an expanded grid manufactured by a rotary method. In the following description, the grid element 30 may also be referred to as the expanded grid 30. The width of the positive electrode plate 22 in the front-to-rear direction (width direction) is smaller than the inner dimension of the battery case 11 in the front-to-rear direction. Specifically, when the positive electrode plate 22 according to the first embodiment is new (i.e., not yet expanded), the ratio of the width of the positive electrode plate 22 in the front-to-rear direction to the inner dimension of the battery case 11 in the front-to-rear direction is 0.85 or more and 0.99 or less.

[0046] (AGM separator) The bag-shaped AGM separator 24 will be described with reference to Figure 6. The AGM separator 24 is formed by bending a single glass fiber mat (AGM: Absorbed Glass Mat) containing organic fibers and glass fibers into a U-shape and heat-welding both side edges in the front-to-rear direction (width direction). Examples of organic fibers include polyester fibers and polyolefin fibers, with polyester fibers being preferred, and polyethylene terephthalate fibers being more preferred.

[0047] In the following description, the portions of the AGM separator 24 in front of and behind the positive electrode plate 22 are referred to as side edge portions 24A. The side edge portions 24A on both the front and rear sides of the portion of the AGM separator 24 to the left of the positive electrode plate 22 (an example of an edge portion on one side of the electrode plate in the plate thickness direction) are referred to as side edge portion 24Aa, and the side edge portions 24A on both the front and rear sides of the portion of the AGM separator 24 to the right of the positive electrode plate 22 (an example of an edge portion on the other side) are referred to as side edge portion 24Ab. When there is no need to distinguish between the side edge portions 24Aa and 24Ab, they are simply referred to as side edge portions 24A.

[0048] Because the AGM separator 24 is bent into a U shape, the AGMs overlap in the left-right direction, and a front side edge 24Aa of the portion to the left of the positive electrode plate 22 and a front side edge 24Ab of the portion to the right of the positive electrode plate 22 are heat-welded to form a front welded portion 24B (an example of a joint). Similarly, a rear side edge 24Aa of the portion to the left of the positive electrode plate 22 and a rear side edge 24Ab of the portion to the right of the positive electrode plate 22 are heat-welded to form a rear welded portion 24B (an example of a joint).

[0049] An example of a method for manufacturing the AGM separator 24 will be described with reference to Fig. 7. The AGM used to manufacture the AGM separator 24 according to embodiment 1 has a thickness of 0.25 mm or more and 0.7 mm or less, and contains 10% to 60% by mass of organic fibers. To manufacture AGM separator 24, a single horizontally elongated AGM sheet is bent upward into a U-shape below the vertical midpoint. The AGM is then heat-sealed across the entire length at equally spaced horizontal positions, forming vertically extending welds 24B at equally spaced intervals. Multiple AGM separators 24 are then manufactured by cutting the AGM vertically at the horizontal midpoints of each weld 24B.

[0050] The AGM separator 24 according to the first embodiment has a width in the front-to-rear direction that is wider than the width of the cell chamber 16. The length W of the side edge 24A of the AGM separator 24 in the width direction (front-to-rear direction shown in FIG. 7) is 1 mm or more and 10 mm or less. The thickness of the AGM separator 24 is equivalent to that of two AGMs, so it is 0.5 mm or more and 1.4 mm or less.

[0051] As shown in Figure 8, the AGM separator 24 is wider in the front-to-rear direction than the cell chamber 16, so it is housed in the cell chamber 16 with its front and rear side edges 24A bent approximately 90 degrees. More specifically, the AGM separator 24 is housed in the cell chamber 16 in the following state. The side edge 24A is bent so as to face the end face of the positive electrode plate 22. The welding portion 24B formed in the bent portion of the side edge portion 24A (in other words, the portion of the side edge portion 24A extending in the thickness direction of the positive electrode plate 22) is located between the inner wall surface of the battery case 11 and the end face of the positive electrode plate 22. At least a part of the welded portion 24B is in contact with the inner wall surface of the battery case 11. At least a portion of the welded portion 24B is in contact with another portion of the AGM separator 24 that covers the end face of the positive electrode plate 22.

[0052] (Action of the positive electrode plate) As shown in FIG. 9A, when the lead-acid battery 1 is new, a certain amount of gap K is secured between the end face of the positive electrode plate 22 and the AGM separator 24 in anticipation of expansion of the positive electrode plate 22. 9B shows the positive electrode plate 22 after the lead-acid battery 1 has been used to a certain extent. As the positive electrode plate 22 expands with use in a direction parallel to the plate surface (hereinafter simply referred to as the plate surface direction) and in the plate thickness direction, the gap between the end face of the positive electrode plate 22 and the inner wall surface of the battery case 11 becomes narrower. The AGM separator 24 has a welded portion 24B formed in the bent portion of the side edge 24A, which is located between the inner wall surface of the battery case 11 and the end face of the positive electrode plate 22. Therefore, when the positive electrode plate 22 expands to a certain extent in the plate surface direction, at least a portion of the welded portion 24B is pressed against the inner wall surface of the battery case 11 by the end face of the positive electrode plate 22.

[0053] [Example] The conventional product and the embodiment will be described with reference to FIGS.

[0054] <Lead-acid battery used in the test> The lead acid battery used in the charge-discharge cycle test was produced according to the following procedure.

[0055] (1) Preparation of the positive electrode plate A positive electrode paste (electrode material 31) was prepared by mixing lead oxide, a reinforcing material (synthetic resin fiber), tin sulfate, water, and sulfuric acid. The positive electrode paste was filled into the mesh portion 34 of an expanded grid 30 made of an antimony-free Pb-Ca-Sn alloy with a Pb-Sn foil attached to one side of the expanded grid, and the grid was aged and dried to obtain an unformed positive electrode plate 22.

[0056] (2) Preparation of the negative electrode plate A negative electrode paste (an example of an electrode material) was prepared by mixing lead oxide, carbon black, barium sulfate, lignin, a reinforcing material (synthetic resin fiber), water, and sulfuric acid. The negative electrode paste was filled into the mesh portion 34 of an expanded grid 30 made of an antimony-free Pb-Ca-Sn alloy, which had Pb-Sn foil attached to both sides of the non-expanded area (the upper frame 32 and the current collecting tabs 33). The grid was then aged and dried to obtain an unformed negative electrode plate 25.

[0057] (3) Preparation of lead-acid battery Unformed positive electrode plates 22 housed inside AGM separators 24 containing 30% by mass of polyethylene terephthalate fiber as organic fiber were arranged and stacked alternately with unformed negative electrode plates 25. An electrode group 19 was formed by the 12 unformed negative electrode plates 25 and the 11 unformed positive electrode plates 22.

[0058] The current collecting lugs 33 of the positive electrode plates 22 and the current collecting lugs 33 of the negative electrode plates 25 were welded to the positive electrode strap 20 and the negative electrode strap 21, respectively, using the cast-on-strap method. The electrode group 19 was inserted into a polypropylene battery case 11, electrolyte was poured in, a control valve was placed in the lid 12, and chemical formation was performed inside the battery case 11 to assemble a valve-regulated lead-acid battery with a rated voltage of 12 V and a 3-hour rate capacity of 52 Ah. The 3-hour rate capacity refers to the capacity when discharged at a current (A) that is 1 / 3 the Ah value listed for the rated capacity. Six electrode groups 19 were connected in series inside the battery case 11. The electrolyte used was an aqueous sulfuric acid solution, and the specific gravity of the electrolyte after formation at 20°C was 1.28.

[0059] (4) Charge / discharge cycle test 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 amount reached 36 Ah. Charging was performed using a five-stage constant current charging method. Specifically, charging was performed using the following method.

[0060] First, constant current charging was performed at 12A, and when the charging voltage reached the switching voltage, the charging current was reduced to 6A. 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 3A. When the charging voltage reached the switching voltage again, the charging current was reduced to 1.5A. When the charging voltage reached the switching voltage again, the charging current was maintained at 1.5A, and charging continued until the charge reached 42.48Ah. In this way, five stages of charging were performed. The switching voltage was 13.35V. Every 25 cycles, the battery was discharged at 20 A in a 25°C environment until the voltage reached 9.9 V. When the confirmed discharge capacity was less than 43 Ah, the number of cycles was defined as the cycle life.

[0061] <Test Results> Among the conventional products 1 to 15 shown in Figure 10, conventional products 1 to 12 are AGM separators in which the side edge 24A is not folded. Conventional products 1 to 12 differ from each other in the combination of the length of the side edge 24A (the length parallel to the bottom surface of the battery case) and the ratio of the width of the positive electrode plate 22 in the width direction to the inner width dimension of the battery case 11 (plate width / case width).

[0062] Conventional product 13 is an asymmetric AGM separator, like the separator in Patent Document 3. Conventional product 14 is an AGM separator in which the side edge 24A is not joined but is simply folded, like Patent Document 4. Conventional product 15 is an AGM separator in which a resin cover is formed on the side edge 24A, like Patent Document 2.

[0063] In Figure 10, the degradation modes indicate the causes of the lead-acid battery reaching the end of its life. Among the degradation modes, a short circuit due to weld fracture (an example of joint fracture) means that expansion of the positive electrode plate 22 caused fracture of the weld in the AGM separator, resulting in an internal short circuit between the positive electrode plate 22 and the negative electrode plate 25, leading to the end of its life. Grid corrosion means that no weld fracture occurred, but corrosion of the positive electrode plate 22 due to use led to the end of its life.

[0064] As can be seen from Figure 10, if the cycle life of Conventional Product 2 (or Conventional Product 6) is taken as 100%, the cycle life ratios of the other Conventional Products 1, 3 to 5, and 7 to 15 were less than 100%. In other words, of Conventional Products 1 to 15, Conventional Products 3 and 6 had the longest life. Furthermore, the degradation mode of Conventional Products 1 to 6 and 13 to 15 was weld fracture, while that of Conventional Products 7 to 12 was grid corrosion.

[0065] The reason why conventional products 7 to 12 did not experience weld breakage is that the ratio of the width of the positive electrode plate 22 to the widthwise internal dimension of the battery case 11 (plate width / case width) is small, allowing for some expansion of the positive electrode plate 22 in the plate surface direction, making weld breakage less likely to occur. However, reducing this ratio requires reducing the width of the positive electrode plate 22, which reduces the amount of electrode material 31 that can be filled. As a result, the cycle life is shorter than that of conventional product 2 (or conventional product 6).

[0066] Examples 1 to 11 shown in Fig. 11 are AGM separators 24 according to embodiment 1. As shown in Fig. 11, in Examples 1 to 11, the ratio of the width of the positive electrode plate 22 in the width direction to the inner dimension of the battery case 11 in the width direction (plate width / battery case width) is 0.85 or more and 0.99 or less. Furthermore, in Examples 1 to 11, the length W of the side edge portion 24A in the direction parallel to the bottom surface of the battery case 11 is 1 mm or more and 10 mm or less.

[0067] In Examples 1 to 11, even the shortest cycle life (Examples 6 and 7) was 153% of the conventional cycle life, which is significantly longer than the conventional product. In Examples 1 to 11, the degradation mode was grid corrosion, and none of the batteries reached the end of their life due to short circuits caused by weld breakage.

[0068] In Examples 1 to 11, the length W of the side edge 24A is 1 mm or more and 10 mm or less. Therefore, in order to extend the cycle life compared to conventional products, the length W of the side edge 24A is preferably 1 mm to 10 mm. Furthermore, in Examples 1 to 11, the ratio of the width of the positive electrode plate 22 in the width direction to the inner width dimension of the battery case 11 (plate width / case width) is 0.85 or more and 0.99 or less, so in order to extend the cycle life, it is preferable that the ratio of the width of the positive electrode plate 22 in the width direction to the inner width dimension of the battery case 11 (plate width / case width) is 0.85 or more and 0.99 or less.

[0069] (Effects of the First Embodiment) In the lead-acid battery 1, the side edge 24A of the AGM separator 24 is bent to face the end face of the positive electrode plate 22, and the welded portion 24B formed at the bent portion of the side edge 24A is located between the inner wall surface of the battery case 11 and the end face of the positive electrode plate 22. Therefore, the end face of the expanded positive electrode plate 22 presses the welded portion 24B against the inner wall surface of the battery case 11. Therefore, even without increasing the organic fiber content, breakage of the welded portion due to the expansion of the battery case 11 can be suppressed. Furthermore, by not increasing the organic fiber content, a decrease in the retained electrolyte capacity can be suppressed. Therefore, in the lead-acid battery 1, breakage of the welded portion can be suppressed without increasing the content of organic fibers in the AGM separator 24 formed in a bag shape, thereby improving the cycle life of the lead-acid battery 1.

[0070] In the lead-acid battery 1, at least a portion of the welded portion 24B is in contact with the inner wall surface, so that a gap between at least a portion of the welded portion 24B and the inner wall surface can be eliminated. Therefore, when the positive electrode plate 22 expands in the plate surface direction, at least a portion of the welded portion 24B can be more reliably pressed against the inner wall surface of the battery case 11.

[0071] In the lead-acid battery 1, at least a portion of the welded portion 24B contacts another portion of the AGM separator 24 that covers the end face of the positive electrode plate 22, eliminating a gap between at least a portion of the welded portion 24B and the other portion of the AGM separator 24 that covers the end face of the positive electrode plate 22. Therefore, when the positive electrode plate 22 expands in the plate surface direction, at least a portion of the welded portion 24B can be more reliably pressed against the inner wall surface of the battery case 11.

[0072] In the lead-acid battery 1, the ratio of the front-to-rear width of the positive electrode plate 22 to the front-to-rear inner dimension of the battery case 11 is 0.85 or more and 0.99 or less, so the cycle life of the lead-acid battery 1 is improved compared to when the side edge portion 24A is not bent.

[0073] In the lead-acid battery 1, the length of the side edge 24A of the AGM separator 24 in the direction parallel to the bottom surface of the battery case 11 is 1 mm or more and 10 mm or less, so the cycle life of the lead-acid battery 1 is improved compared to when the edge is not bent.

[0074] In the lead-acid battery 1, the thickness of the AGM separator 24 is 0.5 mm or more and 1.4 mm or less, so the group pressure on the electrode group 19 does not become too high, and manufacturing is not difficult. Furthermore, the thickness of the positive electrode plate 22 and the negative electrode plate 25 can be increased, so the energy density is improved.

[0075] In the lead-acid battery 1, the AGM separator 24 contains 10% to 60% by mass of organic fiber, so that the welded portion 24B can be easily formed by thermal welding, and the bonding strength of the welded portion 24B can also be increased.

[0076] In the lead-acid battery 1, the grid 30 is an expanded grid. In the lead-acid battery 1, the expanded expanded grid presses the welded portion 24B against the inner wall surface of the battery case 11, making it difficult for the welded portion to break. For this reason, this is particularly effective when an expanded grid is used as the grid 30.

[0077] <Other embodiments> The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments, for example, are also included within the technical scope of the present invention.

[0078] (1) In the above embodiment 1, an example was given of forming the welded portion 24B (joint portion) by thermally welding the side edge portion 24A of the AGM, but the welded portion may be formed by ultrasonic welding the AGM, or the joint portion may be formed by mechanically sealing it.

[0079] (2) In the above-described first embodiment, a case was illustrated in which at least a portion of the welded portion 24B of the AGM separator 24 was in contact with the inner wall surface of the battery case 11 when the lead-acid battery 1 was new. In contrast, at least a portion of the welded portion 24B does not need to be in contact with the inner wall surface of the battery case 11 when the lead-acid battery 1 was new. Even in this case, when the positive electrode plate 22 expands to a certain extent, at least a portion of the welded portion 24B is pressed against the inner wall surface of the battery case 11 by the end face of the positive electrode plate 22.

[0080] (3) In the above-described first embodiment, a case was illustrated in which, when the lead-acid battery 1 was new, at least a portion of the welded portion 24B was in contact with another portion of the AGM separator 24 that covered the end face of the positive electrode plate 22. In contrast, when the lead-acid battery 1 was new, at least a portion of the welded portion 24B did not have to be in contact with another portion of the AGM separator 24 that covered the end face of the positive electrode plate 22. Even in this case, when the positive electrode plate 22 expands to a certain extent, at least a portion of the welded portion 24B is pressed against the inner wall surface of the battery case 11 by the end face of the positive electrode plate 22.

[0081] (4) In the above-described first embodiment, the ratio of the width of the positive electrode plate 22 in the front-rear direction to the inner dimension of the battery case 11 in the front-rear direction is 0.85 or more and 0.99 or less. However, this ratio is not limited to this and may be less than 0.85 or greater than 0.99.

[0082] (5) In the above-described first embodiment, the length of the side edge 24A of the AGM separator 24 in the direction parallel to the bottom surface of the battery case 11 is 1 mm or more and 10 mm or less. However, this length is not limited to this and may be less than 1 mm or greater than 10 mm.

[0083] (6) In the first embodiment, the thickness of the AGM separator 24 is 0.5 mm or more and 1.4 mm or less. However, the thickness is not limited to this and may be less than 0.5 mm or greater than 1.4 mm.

[0084] (7) In the first embodiment, the AGM separator 24 contains 10 to 60% by mass of organic fiber. However, the organic fiber content is not limited to 10 to 60% by mass, and may be less than 10% by mass or greater than 60% by mass.

[0085] (8) In the first embodiment, an expanded grid is used as the grid 30, but the grid 30 may be manufactured by casting or punching.

[0086] (9) In the first embodiment, the positive electrode plate 22 is exemplified as the electrode plate, but the negative electrode plate 25 may also be used.

[0087] (10) A coating layer having a higher Sn content than the grid frame may be provided on at least a portion of the surface of the grid 30 described in the above embodiment. The provision of the coating layer increases the mechanical strength and corrosion resistance of the grid 30, thereby extending the life of the lead-acid battery 1.

[0088] (11) In the above embodiment, the lead storage battery 1 is exemplified as a lead storage battery 1 for driving a vehicle, but the lead storage battery 1 is not limited to this. For example, the lead storage battery 1 may be a lead storage battery 1 for starting an engine.

[0089] (12) In the above embodiment, a valve-regulated lead-acid battery is exemplified as the lead-acid battery 1, but the lead-acid battery may also be a flooded type. [Explanation of symbols]

[0090] 1: Lead acid battery 11: Battery case 22: Positive electrode plate (example of electrode plate) 24: AGM separator (example of separator) 24A: Side edge (an example of an edge) 24B: Welded part (an example of a joint) 30: Expanded lattice (an example of a lattice) 31: Electrode material

Claims

1. The electrode plate and a separator formed in a bag shape that is open upward and that houses the electrode plates therein; a battery case in which the separator is housed; Equipped with The separator is Contains organic fibers and glass fibers, The electrode plate has a joint portion in which an edge portion of a portion on one side in the plate thickness direction of the electrode plate and an edge portion of a portion on the other side are joined, The edge portion is bent so as to face the end surface of the electrode plate, The joint formed in the bent portion of the edge is located between the inner wall surface of the battery case and the end surface.

2. The lead-acid battery according to claim 1 , wherein at least a portion of the joint is in contact with the inner wall surface.

3. 3. The lead-acid battery according to claim 1, wherein at least a portion of the joint portion is in contact with another portion of the separator that covers the end surface.

4. When the direction parallel to the bottom surface of the battery case and the plate surface of the electrode plate is defined as the width direction, The separator has the joining portions formed on both side edge portions in the width direction, 3. The lead-acid battery according to claim 1, wherein a ratio of the width of the electrode plates in the width direction to an inner dimension of the battery case in the width direction is 0.85 or more and 0.99 or less.

5. When the direction parallel to the bottom surface of the battery case and the plate surface of the electrode plate is defined as the width direction, The separator has the joining portions formed on both side edge portions in the width direction, 3. The lead-acid battery according to claim 1, wherein the length of the side edge portion in the width direction is 1 mm or more and 10 mm or less.

6. 3. The lead-acid battery according to claim 1, wherein the separator has a thickness of 0.5 mm or more and 1.4 mm or less.

7. 3. The lead-acid battery according to claim 1, wherein the separator contains 10% by mass to 60% by mass of organic fibers.

8. The electrode plate includes a grid and an electrode material filled in the grid, 3. The lead-acid battery according to claim 1, wherein the grid is an expanded grid.

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