Battery

Abstract

To provide a battery that can suppress poor engagement of an upper insulating member and the occurrence of an internal short circuit, and that can reduce the amount of electrolyte remaining on the upper insulating member when an electrolyte is injected, thereby preventing leakage of the electrolyte.SOLUTION: A battery 2 is a battery including an outer can 10 with an open top, an electrode group 22 housed in the outer can 10, an upper insulating member 32 having electrical insulation properties arranged on top of the electrode group 22, an electrolyte injected into the outer can 10 and impregnating the electrode group 22, and a sealing body 11 that is fixed to an opening 35 of the outer can 10 to seal the opening 35, and the upper insulating member 32 is made of an insulating thin plate and includes a liquid inlet 38 for passing the electrolyte, and an umbrella-shaped portion 50 that extends at a downward slope from the periphery of the liquid inlet 38.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a battery, and more particularly to a battery having an insulating member on top of an electrode group inside an outer can. [Background technology]

[0002] A typical battery includes a cylindrical outer can with a bottom that also serves as a negative electrode terminal, an electrode group housed in the outer can together with an electrolyte, the electrode group consisting of a positive electrode, a negative electrode, and a separator, and a sealing body that seals the top opening of the outer can, the sealing body including a positive electrode terminal.

[0003] In such a battery, the outermost negative electrode of the electrode group is in contact with the inner wall of the outer can, thereby electrically connecting the negative electrode and the outer can (negative electrode terminal), while the positive electrode of the electrode group is electrically connected to the positive electrode terminal of the sealing body via a positive electrode tab made of a thin metal plate.

[0004] However, when a battery is subjected to vibration or impact, a portion of the positive or negative electrode of the electrode group may come into contact with the sealing body, positive electrode tab, outer can, or the like connected to the other electrode, potentially causing an internal short circuit. Therefore, insulating members are provided on the upper and lower parts of the electrode group to prevent the above-mentioned internal short circuit. For example, as shown in Patent Document 1, such insulating members are circular, flat, and include an electrolyte injection hole, an insertion hole for the positive electrode tab, and the like.

[0005] The above-described battery is manufactured, for example, as follows. First, a cylindrical electrode assembly is prepared by spirally winding strip-shaped positive and negative electrodes with a strip-shaped separator sandwiched therebetween. A cylindrical outer can with a bottom and an open top is then prepared. A lower insulating member is placed in the bottom of the outer can, and the electrode assembly obtained as described above is then housed inside the outer can. A circular, flat upper insulating member is then placed on the top of the electrode assembly inside the outer can.

[0006] Next, in order to prevent the electrode group inside the outer can from moving toward the upper opening, a predetermined position on the outer can between the upper insulating member on the electrode group and the upper opening of the outer can is deformed to form a ring-shaped protrusion that protrudes into the interior of the outer can. Specifically, while the outer can housing the electrode group and the upper insulating member is rotated at high speed, the outer peripheral surface of the outer can at the predetermined position is pressed against a groove-making rotary blade to form a groove around the entire circumference of the outer peripheral surface of the outer can (grooving process). As a result, a ring-shaped protrusion corresponding to the groove is formed around the entire circumference on the inner peripheral surface of the outer can. The ring-shaped protrusion obtained by forming this groove prevents the electrode group, on which the upper insulating member is placed, from moving upward inside the outer can.

[0007] Next, an electrolyte is poured into the exterior can that has undergone the above-described groove forming process, and then a sealing body is placed in the top opening of the exterior can via an insulating gasket. A positive electrode terminal, a safety valve, etc. are attached to this sealing body. The sealing body and gasket are then fixed to the opening edge of the exterior can by crimping the opening edge of the exterior can, and the opening of the exterior can is sealed. This results in a sealed battery.

[0008] After the electrolyte is injected into the outer can, some of the electrolyte may remain on the upper surface of the upper insulating member. Because the upper insulating member is a flat plate, the electrolyte is likely to remain on its upper surface. This remaining electrolyte may travel along the inner wall of the outer can due to vibration or other factors and reach the crimped portion of the sealing body. Generally, the crimped portion of a battery may have minute gaps inside due to distortion of the top opening of the outer can. Therefore, there is a risk that the electrolyte may leak out of the battery through the gaps in the crimped portion due to capillary action. The leaked electrolyte may cause problems such as corrosion of other components around the battery.

[0009] To address such a problem, for example, Patent Document 2 proposes an embodiment in which the upper insulating member is made cone-shaped. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 06-243857 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-134107 Summary of the Invention [Problem to be solved by the invention]

[0011] During the above-described groove-forming process, the outer can is rotated at high speed, which can cause the upper insulating member to lift up and become tilted. If groove-forming is performed while the upper insulating member is tilted, the upper insulating member 132 may ride up on the annular protrusion 15 on the back side of the groove 13, as shown in FIG. 10 . If a crimping process is performed to secure the sealing member in this state, the upper insulating member may become trapped in the crimped portion of the opening edge of the outer can. Such a poor engagement prevents the upper insulating member from fulfilling its intended function of electrical insulation, increasing the likelihood of an internal short circuit. Furthermore, if the upper insulating member becomes trapped, the sealing performance of the crimped portion is impaired, increasing the likelihood of electrolyte leakage.

[0012] The cone-shaped upper insulating member as described in Patent Document 2 above has the problem that it is unstable when placed on the electrode group and is more likely to ride up onto the annular protrusion, causing poor engagement.

[0013] Another possible solution is to improve the shape of the upper insulating member by providing a protrusion in the center of the upper insulating member to prevent misalignment of the upper insulating member to prevent poor engagement. However, improving the shape increases the labor required for molding and the number of parts used, which increases the manufacturing cost of the battery.

[0014] Therefore, there is a need to develop a battery that can prevent the occurrence of poor biting while suppressing increases in manufacturing costs, and that can reduce the amount of electrolyte remaining on the upper insulating member to prevent leakage.

[0015] The present invention has been made in light of the above circumstances, and its object is to provide a battery that can suppress poor engagement of the upper insulating member and the occurrence of internal short circuits, and that can reduce the amount of electrolyte remaining on the upper insulating member when the electrolyte is injected, thereby preventing leakage of the electrolyte. [Means for solving the problem]

[0016] In order to achieve the above object, according to the present invention, there is provided a battery comprising: a cylindrical outer can having an open top and a closed bottom; an electrode group formed by stacking positive and negative electrodes with a separator interposed between them and wound in a spiral shape and housed in the outer can; an upper insulating member having electrical insulation properties and disposed above the electrode group; an electrolyte injected into the outer can and impregnating the electrode group; and a sealing body that is fixed to the opening in the outer can and thereby seals the opening, wherein the upper insulating member is made of an insulating thin plate and includes a liquid fill port for passing the electrolyte, and an umbrella-shaped portion extending at a downward angle from the periphery of the liquid fill port. [Effects of the Invention]

[0017] In the battery according to the present invention, the upper insulating member disposed above the electrode assembly is made of an insulating thin plate and includes a filler hole for passing the electrolyte and an umbrella-shaped portion extending downward from the periphery of the filler hole. Therefore, since the outer periphery of the umbrella-shaped portion contacts the vicinity of the upper periphery of the electrode assembly, the upper insulating member is less likely to tilt and maintains a stable posture, thereby suppressing the occurrence of poor engagement of the upper insulating member. Furthermore, since the umbrella-shaped portion extends downward, the electrolyte flows down near the upper periphery of the electrode assembly and is smoothly introduced into the electrode assembly, reducing the amount of electrolyte remaining on the insulating member. This suppresses electrolyte seepage from the crimped portion of the battery. As described above, the present invention provides a battery that suppresses poor engagement of the upper insulating member and suppresses the occurrence of internal short circuits, while also reducing the amount of electrolyte remaining on the upper insulating member when electrolyte is injected, thereby preventing electrolyte leakage. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a partially cutaway perspective view of a cylindrical nickel-metal hydride secondary battery according to the present invention; [Figure 2] 1A and 1B are a plan view and a side view showing an upper insulating member. [Figure 3] FIG. 2 is a perspective view showing an upper insulating member. [Figure 4] FIG. 10 is a cross-sectional view schematically showing a state in which an upper insulating member is placed on an electrode group. [Figure 5] 5A to 5C are cross-sectional views schematically showing a manufacturing process of the upper insulating member. [Figure 6] FIG. 10 is a cross-sectional view schematically showing a mode in which an upper insulating member is placed on an electrode group. [Figure 7] FIG. 10 is a perspective view schematically illustrating a grooving step. [Figure 8] FIG. 10 is a cross-sectional view schematically showing a liquid injection step. [Figure 9] 10 is a schematic cross-sectional view for explaining the inclination angles of an upper mold, a lower molding mold, and an upper insulating member. FIG. [Figure 10] 10 is a cross-sectional view schematically showing a state in which a conventional upper insulating member rides on a circular protrusion portion. DETAILED DESCRIPTION OF THE INVENTION

[0019] An AA size cylindrical nickel-metal hydride secondary battery (hereinafter also simply referred to as battery) 2 according to one embodiment will be described below with reference to the drawings.

[0020] The battery 2 includes a cylindrical outer can 10 with a bottom and an open top. The outer can 10 is electrically conductive, and its bottom wall 8 functions as a negative electrode terminal. An electrode group 22 is housed within the outer can 10. A sealing body 11 is fixed to an opening 35 of the outer can 10. The sealing body 11 includes a lid plate 14 and a positive electrode terminal 20, and seals the outer can 10 while providing the positive electrode terminal 20. The lid plate 14 is a disc-shaped member that is electrically conductive. The lid plate 14 and a ring-shaped insulating gasket 12 that surrounds the lid plate 14 are disposed within the opening 35 of the outer can 10. The insulating gasket 12 and the lid plate 14 are fixed to the opening edge 37 of the outer can 10 by crimping the opening edge 37 of the outer can 10. In other words, the lid plate 14 and the insulating gasket 12 cooperate to seal the opening 35 of the outer can 10.

[0021] The cover plate 14 has a central through-hole 16 in the center, and a rubber valve body 18 that closes the central through-hole 16 is disposed on the outer surface of the cover plate 14. Furthermore, a metallic positive electrode terminal 20 that is cylindrical with a flange and covers the valve body 18 is electrically connected to the outer surface of the cover plate 14. This positive electrode terminal 20 presses the valve body 18 toward the cover plate 14. The positive electrode terminal 20 is provided with a gas vent hole (not shown).

[0022] Normally, the central through-hole 16 is airtightly closed by the valve body 18. On the other hand, if gas is generated inside the outer can 10 and the internal pressure increases, the valve body 18 is compressed by the internal pressure and opens the central through-hole 16, resulting in the gas being released from inside the outer can 10 to the outside through the central through-hole 16 and a gas vent hole (not shown) in the positive terminal 20. In other words, the central through-hole 16, the valve body 18, and the positive terminal 20 form a safety valve for the battery 2.

[0023] Here, in outer can 10, groove 13 is formed around the entire circumference on the outer peripheral surface between electrode group 22 and sealing body 11. By forming this groove 13, a circular protrusion 15 is formed around the entire circumference on the inner peripheral surface of outer can 10 corresponding to the back side of groove 13. This circular protrusion 15 functions to restrict movement of electrode group 22 inside outer can 10 towards opening 35.

[0024] The electrode group 22 includes a strip-shaped positive electrode 24, a strip-shaped negative electrode 26, and a strip-shaped separator 28. More specifically, the positive electrode 24 and the strip-shaped negative electrode 26 are spirally wound with the separator 28 sandwiched therebetween. That is, the positive electrode 24 and the strip-shaped negative electrode 26 are stacked on top of each other with the separator 28 interposed therebetween. The outermost periphery of the electrode group 22 is formed by a part (outermost periphery) of the negative electrode 26, and is in contact with the inner circumferential wall of the outer can 10. That is, the negative electrode 26 and the outer can 10 are electrically connected to each other.

[0025] One end of a positive electrode tab 30 made of a strip-shaped metal material is connected to the positive electrode 24, and the other end of this positive electrode tab 30 is connected to the cover plate 14. Therefore, the positive electrode terminal 20 and the positive electrode 24 are electrically connected to each other via the positive electrode tab 30 and the cover plate 14. An upper insulating member 32 is disposed between the lower part of the cover plate 14, which is also the lower part of the annular protruding portion 15 of the outer can 10, and the upper part of the electrode group 22, and the positive electrode tab 30 extends through a tab insertion hole 40 provided in the upper insulating member 32. In addition, a lower insulating member 34 is also disposed between the lower part of the electrode group 22 and the inner surface of the bottom wall 8 of the outer can 10.

[0026] As is clear from Fig. 2(a), the upper insulating member 32 has a circular shape in a plan view, and a circular liquid inlet 38 through which the electrolyte can be inserted is provided in the center thereof. A tab insertion hole 40 through which the positive electrode tab 30 passes is provided in a predetermined position of the upper insulating member 32. The upper insulating member 32 can be made of an electrically insulating synthetic resin, such as polypropylene, polyethylene, or polyvinyl chloride. In order to ensure a certain level of strength, the upper insulating member 32 preferably has a thickness of 0.15 mm to 0.3 mm.

[0027] The diameter of the upper insulating member 32 is set to a dimension within a range that is smaller than the maximum inner diameter of the outer can 10 and larger than the inner diameter of the annular protruding portion 15 of the outer can 10. As is clear from the perspective view of FIG. 3, the upper insulating member 32 has a truncated conical shape that widens from the pouring hole 38 toward the outer peripheral edge 42. In other words, the upper insulating member 32 includes an umbrella-shaped portion 50 that extends in an umbrella-like manner, sloping downward from the peripheral edge 39 of the pouring hole 38 toward the outer peripheral edge 42. Therefore, as shown in the side view of FIG. 2(b), the shape of the upper insulating member 32 in side view is an isosceles trapezoid, with the pouring hole 38 portion as an upper base 38a, the outer peripheral edge 42 portion as a lower base 42a, and the umbrella-shaped portion 50 as legs 50a, 50a.

[0028] The umbrella-shaped portion 50 is provided to smoothly guide the electrolyte to the electrode group 22 when the electrolyte is poured into the exterior can 10 and to reduce the amount of the electrolyte remaining on the upper insulating member 32 .

[0029] Here, as shown in FIG. 4 , when the upper insulating member 32 is viewed from the side, a virtual line extending along the portion of the outer periphery 42 that forms the lower base 42a is defined as a reference line SL, and a virtual line extending along the portion of the umbrella-shaped portion 50 that forms the legs 50a is defined as an inclination line IL. The inclination angle α of the inclination line IL with respect to the reference line SL is preferably 3 degrees or greater, and the inclination angle α is preferably 3 degrees or greater and is inclined downward relative to the reference line SL. This allows the electrolyte to flow down the umbrella-shaped portion 50 and enter the electrode group 22 through the gap between the outer periphery 42 of the upper insulating member 32 and the inner circumferential surface of the outer can 10, making it difficult for the electrolyte to remain on the umbrella-shaped portion 50. If the inclination angle α is less than 3 degrees, the electrolyte is more likely to remain on the upper insulating member 32. Since the amount of remaining electrolyte decreases as the inclination angle α increases, it is more preferable that the inclination angle α be 5 degrees or greater. On the other hand, if the inclination angle α exceeds 10 degrees, when the opening of the outer can 10 is sealed with a sealing member, the sealing member and the positive electrode tab 30 welded thereto will interfere with the upper insulating member 32. In this case, there is a risk that the upper insulating member 32 will deform and no longer maintain proper insulation. In such a case, the upper part of the electrode group 22 will also be compressed and deformed, which may cause a short circuit. To avoid these problems, it is necessary to reduce the volume of the electrode group 22 to secure space, but doing so makes it difficult to secure the desired battery capacity. Therefore, it is preferable that the upper limit of the inclination angle α be 10 degrees. From the above, it can be said that the inclination angle α of the umbrella-shaped portion 50 is preferably 3 degrees or more and 10 degrees or less.

[0030] Here, the upper insulating member 32 has a truncated conical shape including a circular inlet 38 for passing the electrolyte and an umbrella-shaped portion 50 that extends concentrically from the periphery 39 of the inlet 38 and at a downward slope toward the outer periphery 42, as described above, but is not limited to this truncated conical shape and various modifications are possible. For example, the upper insulating member may have a polygonal truncated cone shape that includes a polygonal inlet and an umbrella-shaped portion that extends at a downward slope from the periphery of the polygonal inlet.

[0031] 1, in the battery 2, a lower insulating member 34 is disposed between the electrode group 22 and the bottom wall 8 of the outer can 10. This lower insulating member 34 has a flat, circular shape. As with the upper insulating member 32, the lower insulating member 34 may be made of polypropylene, polyethylene, polyvinyl chloride, or the like. It is also preferable that the thickness of the lower insulating member 34 be 0.15 mm to 0.3 mm.

[0032] Furthermore, a predetermined amount of alkaline electrolyte (not shown in FIG. 1 ) is present within the exterior can 10. This alkaline electrolyte is impregnated into the positive electrode 24, the negative electrode 26, and the separator 28, and promotes charge / discharge reactions between the positive electrode 24 and the negative electrode 26. The type of alkaline electrolyte is not particularly limited as long as it is one used in ordinary alkaline secondary batteries. Suitable examples of the alkaline electrolyte include an aqueous solution of sodium hydroxide, an aqueous solution of lithium hydroxide, an aqueous solution of potassium hydroxide, and a mixture of two or more of these.

[0033] The battery 2 according to this embodiment can be manufactured, for example, as follows. First, a cylindrical outer can 10 with a bottom is prepared (outer can preparation step). A circular lower insulating member 34 made of an insulating material, which has been prepared in advance, is inserted into the bottom of the prepared outer can 10 (lower insulating member inserting step).

[0034] An electrode group 22 is manufactured by spirally winding a strip-shaped positive electrode 24 and a strip-shaped negative electrode 26 with a strip-shaped separator 28 interposed therebetween, and the obtained electrode group 22 is housed in an outer can 10 (electrode group housing step). Here, a positive electrode tab 30 is connected to the positive electrode 24, and this positive electrode tab 30 protrudes from the upper end of the electrode group 22.

[0035] Additionally, an upper insulating member 32 is prepared on a separate line (upper insulating member preparation process). Specifically, as shown in FIGS. 5(a) and 5(b), a resin sheet 60 such as polypropylene is placed on a lower mold 62, and an upper mold 64 is lowered toward the lower mold 62 to perform a punching process, thereby producing a precursor 31 of the upper insulating member 32. As shown in FIG. 5(b), this precursor 31 has a circular shape in plan view, a circular liquid inlet 38 in the center, and a roughly crescent-shaped tab insertion hole 40 located closer to the outer periphery than the liquid inlet 38. Thus, the precursor 31 has a shape similar to that of a conventional flat upper insulating member. As shown in FIG. 5(c), the obtained precursor 31 is adsorbed by an upper mold 64 equipped with a vacuum mechanism and moved above a molding lower mold 66 heated to a predetermined temperature. The molding lower mold 66 has a conical portion 68, and the upper mold 64 includes a recess 70 that matches the conical portion 68 of the molding lower mold 66. Next, as shown in Fig. 5(d), the precursor 31 adsorbed on the upper mold 64 is pressed against the heated lower molding mold 66 and molded as the upper mold 64 moves downward, thereby obtaining the upper insulating member 32 including the umbrella-shaped portion 50 inclined at a predetermined angle.

[0036] In this embodiment, a flat upper insulating member (precursor 31) obtained by conventional punching is simply heat-molded into a shape including a sloped umbrella-shaped portion 50, without any additional steps or parts, thereby preventing increases in manufacturing costs. Furthermore, if the mold can be improved so that the umbrella-shaped portion 50 can be formed simultaneously with punching, the manufacturing costs can be further reduced.

[0037] The upper insulating member 32 obtained as described above is transported above the outer can 10 accommodating the electrode group 22 while being attracted to the upper mold 64, as shown in Fig. 6(a). Then, the upper insulating member 32 is inserted into the outer can 10 accommodating the electrode group 22 while being attracted to the upper mold 64, as shown in Fig. 6(b), and then, as shown in Fig. 6(c), it is removed from the upper mold 64 and placed on the electrode group 22 (upper insulating member inserting step). In this upper insulating member inserting step, although not shown, the positive electrode tab 30 protruding from the upper end of the electrode group 22 is inserted into the tab insertion hole 40 of the upper insulating member 32.

[0038] Next, a groove is formed around the entire circumference of the outer circumferential surface of the outer can 10 accommodating the lower insulating member 34, the electrode group 22, and the upper insulating member 32 (grooving process). More specifically, as shown in Fig. 7 , the outer can 10 accommodating the electrode group 22 and the like is rotated at high speed around an axis passing through the center of the circular bottom wall 8 and the center of the circular opening 35 at the top. Then, a predetermined location on the outer circumferential surface 101 of the outer can 10 above the portion where the upper insulating member 32 is located is pressed against a grooving rotary blade 72. As a result, a groove 13 is formed around the entire circumference of the outer circumferential surface 101 of the outer can 10, and accordingly, an annular protrusion 15 is formed around the entire circumference of the inner circumferential surface 102 of the outer can 10.

[0039] As shown in FIG. 8( a), after the groove forming process, the outer can 10 has the annular protrusion 15 protruding above the peripheral edge 32a of the upper insulating member 32 disposed on the electrode group 22. An electrolyte is then injected into the outer can 10 (electrolyte injection process). Specifically, as shown in FIG. 8( b), a sealing pipe 74 and an injection nozzle 76 are inserted into the outer can 10 through the opening 35 of the outer can 10. The sealing pipe 74 is a cylindrical resin pipe, and its tip is in close contact with the annular protrusion 15. A vacuum pump (not shown) is connected to the sealing pipe 74, which maintains the interior of the outer can 10 at a pressure below atmospheric pressure. The injection nozzle 76 is located in the center of the sealing pipe 74. An electrolyte E is supplied to the injection nozzle 76 from an electrolyte supply device (not shown), and the electrolyte E can be ejected from the tip of the injection nozzle 76. In the outer can 10 into which the sealing pipe 74 and the injection nozzle 76 are inserted, the pressure inside the outer can 10 is reduced to below atmospheric pressure by operating a vacuum pump. With the pressure inside the outer can 10 reduced in this manner, electrolyte E is discharged from the tip of the injection nozzle 76, and injection begins ( FIG. 8( c) ). Thereafter, injection of the electrolyte E is stopped when a predetermined amount of electrolyte E has been injected ( FIG. 8( d) ). At this time, the electrolyte E has accumulated from the top of the electrode group 22 up to a predetermined height within the sealing pipe 74. Next, the pressure reduction is stopped, and the pressure inside the outer can 10 is returned to atmospheric pressure. As a result, as shown by arrows AP in FIG. 8( e) , atmospheric pressure forces the electrolyte E to permeate the electrode group 22. At this time, the electrolyte E pressurized by the atmosphere is forced toward the electrode group 22 through the injection port 38 and the gap between the peripheral edge 32 a of the upper insulating member 32 and the inner circumferential surface 102 of the outer can 10. This completes the injection of the electrolyte E.

[0040] Thereafter, the positive electrode tab 30 is welded to the underside of the lid plate 14 of the sealing body 11 (sealing body welding step). After welding of the positive electrode tab 30 to the lid plate 14 is completed, the sealing body 11 is placed in the opening 35 of the outer can 10 together with the ring-shaped insulating gasket 12 that surrounds the lid plate 14 of the sealing body 11. Then, in this state, the opening edge 37 of the outer can 10 is crimped, and the sealing body 11 is fixed to the opening edge 37 of the outer can 10 (sealing step). In this way, the battery 2 is assembled.

[0041] The assembled battery 2 is washed to remove any dirt adhering to the periphery (cleaning process). In this way, the finished battery 2 is obtained. The obtained battery 2 is subjected to an initial activation process to make the battery 2 usable (initial activation process).

[0042] [Example] 1. Assembling an AA-size cylindrical nickel-metal hydride secondary battery Example 1 A positive electrode 24 and a negative electrode 26 used in a typical nickel-metal hydride secondary battery were spirally wound with a separator 28 made of a nonwoven polypropylene fiber fabric sandwiched between them to produce an electrode group 22. At this time, a positive electrode tab 30 was welded to the positive electrode 24. This positive electrode tab 30 protruded and extended from the upper end surface of the electrode group 22.

[0043] Next, a cylindrical outer can 10 with a bottom for AA size was prepared (outer can preparation process), a disk-shaped lower insulating member 34 made of polypropylene was inserted into this outer can 10 (lower insulating member insertion process), and the above-mentioned electrode group 22 was accommodated on top of it (electrode group accommodation process).

[0044] Next, the upper insulating member 32 was prepared in the following manner (upper insulating member preparation step). First, as shown in Fig. 5(a), a polypropylene sheet 60 having a thickness of 0.2 mm was punched to form a precursor 31 of the upper insulating member 32 as shown in Fig. 5(b). This precursor 31 was circular and had a diameter of 13.0 mm, and was provided with a liquid injection port 38 in the form of a through-hole having a diameter of 2.0 mm in the center, and a roughly crescent-shaped tab insertion hole 40 at a position closer to the outer periphery than the liquid injection port 38. The width of the tab insertion hole 40 was 8.0 mm.

[0045] The obtained precursor 31 is adsorbed by an upper mold 64 equipped with a vacuum mechanism, and is transported above a lower molding mold 66 heated to 60°C, as shown in FIG. 5(c).

[0046] Here, the lower molding die 66 has a conical portion 68 having a conical shape, and the upper molding die 64 includes a recessed portion 70 that matches the lower molding die 66. In this Example 1, as shown in Fig. 9, the lower molding die 66 used has an inclination angle α1 of the conical portion 68 of the lower molding die 66, which is formed by a base line BL extending along the bottom surface of the conical portion 68 of the lower molding die 66 and a generatrix ML connecting an apex 68T of the conical portion 68 and a point on the periphery of the bottom surface, of 3 degrees. Note that the inclination angle α2 of the recessed portion 70 in the upper molding die 64 that matches the conical portion 68 of the lower molding die 66 is also 3 degrees.

[0047] Next, as shown in Fig. 5(d), the precursor 31 adsorbed on the upper mold 64 was pressed against a heated lower molding mold 66 by moving the upper mold 64 downward, thereby molding the precursor 31 and forming an upper insulating member 32. As shown in Fig. 3, the obtained upper insulating member 32 has a circular liquid inlet 38 at its upper end and includes an umbrella-shaped portion 50 extending concentrically and downwardly from the periphery of the liquid inlet 38.

[0048] When the obtained upper insulating member 32 is viewed from the side, as shown in FIG. 9, it has the shape of an isosceles trapezoid, with the pouring port 38 portion being the upper base 38a, the outer peripheral edge 42 of the umbrella-shaped portion 50 being the lower base 42a, and the inclined surface of the umbrella-shaped portion 50 being the legs 50a, 50a.

[0049] Let us define a reference line SL as an imaginary straight line extending along the lower base 42a of the isosceles trapezoid described above, and a slant line IL as an imaginary straight line extending along the legs 50a corresponding to the inclined surfaces of the umbrella-shaped portion 50. The angle between the reference line SL and the slant line IL is defined as the inclination angle α of the umbrella-shaped portion 50. Here, the inclination angle α is expressed as - when the slant line IL extends downward relative to the reference line SL, and as + when the slant line IL extends upward relative to the reference line SL. Furthermore, when the slant line IL and the reference line SL overlap, the inclination angle α is 0 degrees, indicating a flat plate shape.

[0050] In the upper insulating member 32 of Example 1 obtained as described above, the above-mentioned leg 50a, which corresponds to the inclined surface of the umbrella-shaped portion 50, is inclined at an angle of 3 degrees downward from the reference line SL, so the inclination angle α is -3 degrees.

[0051] Next, the upper insulating member 32, while being attracted to the upper mold 64, was transported above the exterior can 10 accommodating the electrode group 22 (FIG. 6(a)), and then inserted into the exterior can 10 accommodating the electrode group 22 (FIG. 6(b)), and placed on top of the electrode group 22 (FIG. 6(c)). At this time, although not shown in the drawings, the upper insulating member 32 was placed so that the positive electrode tab 30 protruding from the upper end of the electrode group 22 was inserted into the tab insertion hole 40 of the upper insulating member 32 (upper insulating member insertion step).

[0052] Next, while the outer can 10 housing the lower insulating member 34, the electrode group 22, and the upper insulating member 32 was being rotated at high speed, a predetermined location on the outer peripheral surface 101 of the outer can 10 above the portion where the upper insulating member 32 was located was pressed against a grooving rotary blade 72 (see FIG. 7 ). As a result, a groove 13 was formed around the entire circumference on the outer peripheral surface 101 of the outer can 10, and an annular protrusion 15 was formed around the entire circumference on the inner peripheral surface 102 of the outer can 10 (grooving process).

[0053] After the above-described grooving step, a visual inspection was performed to determine whether the upper insulating member 32 arranged on the upper part of the electrode group 22 had climbed up onto the annular protrusion 15 formed on the inner circumferential surface 102 of the outer can 10, and the number of battery precursors in which the upper insulating member 32 had climbed up onto the annular protrusion 15 was counted and recorded. Then, for the battery precursors in which the upper insulating member 32 had climbed up onto the annular protrusion 15, the upper insulating member 32 was repositioned and the battery precursors were sent to the next step, the electrolyte injection step.

[0054] Here, the mass of the battery precursor was measured before the alkaline electrolyte was poured in. The obtained result was recorded as the mass before the pouring.

[0055] Thereafter, as shown in FIG. 8(b), a sealing pipe 74 and an injection nozzle 76 were inserted into the outer can 10 through the opening 35 of the outer can 10, where the annular protrusion 15 had been formed by grooving the outer can 10. With the tip of the sealing pipe 74 in close contact with the annular protrusion 15, a vacuum pump (not shown) was driven to reduce the pressure inside the outer can 10 to below atmospheric pressure, and the low pressure state was maintained. Thereafter, as shown in FIG. 8(c), alkaline electrolyte E was discharged from the tip of the injection nozzle 76, and 3000 mg of alkaline electrolyte E was injected into the outer can 10 (electrolyte injection step). As the alkaline electrolyte E, an aqueous solution containing KOH and LiOH was prepared.

[0056] As shown in FIG. 8(d), the alkaline electrolyte E injected as described above accumulates from the top of the electrode group 22 up to a predetermined height within the sealing pipe 74. Next, the vacuum pump was stopped to terminate the decompression and return the pressure inside the outer can 10 to atmospheric pressure. As a result, as shown in FIG. 8(e), the alkaline electrolyte E accumulated above the electrode group 22 is forced toward the electrode group 22 by atmospheric pressure through the liquid filling hole 38 and the gap between the peripheral edge 32a of the upper insulating member 32 and the inner circumferential surface 102 of the outer can 10. Because the positive electrode 24 and the negative electrode 26 included in the electrode group 22 have a porous structure with numerous pores, the alkaline electrolyte E permeates into these pores. Furthermore, because the separator 28 is made of a polypropylene fiber nonwoven fabric with numerous pores inside, the alkaline electrolyte E permeates into these pores. Thus, most of the alkaline electrolyte E is impregnated into the electrode group 22.

[0057] Next, the mass of the battery precursor after the alkaline electrolyte was injected was measured. The result was recorded as the mass after injection. The amount of alkaline electrolyte was then adjusted so that the injection amount calculated by the following formula (I) was within ±3 mg of 3000 mg. Injection amount [mg] = Mass after injection [mg] - Mass before injection [mg]...(I)

[0058] After adjusting the amount of alkaline electrolyte E as described above, the lower surface of the cover plate 14 of the sealing body 11 was welded to the tip of the positive electrode tab 30 (sealing body welding step). As a result, the positive electrode terminal 20 and the positive electrode 24 included in the sealing body 11 were electrically connected.

[0059] Next, a ring-shaped insulating gasket 12 was fitted around the periphery of the lid plate 14 of the sealing body 11. This combination of the insulating gasket 12 and the sealing body 11 was then placed in the opening 35 of the outer can 10. Thereafter, the opening edge 37 of the outer can 10 was crimped to fix the sealing body 11 to the opening edge 37 of the outer can 10, thereby sealing the outer can 10 (sealing process). In this way, the battery 2 was assembled.

[0060] The assembled battery 2 was washed to remove any dirt adhering to the periphery (washing step). This resulted in a finished battery 2. The obtained battery 2 was subjected to an initial activation treatment to prepare it for use (initial activation step).

[0061] The nickel-metal hydride secondary battery 2 obtained in this manner is referred to as battery A. 1000 batteries A were assembled.

[0062] Example 2 A nickel-metal hydride secondary battery (battery B) similar to battery A of Example 1 was assembled, except that an upper insulating member 32 in which the inclination angle α of the umbrella-shaped portion 50 was −5 degrees was obtained using a lower molding mold 66 in which the inclination angle α1 was 5 degrees and an upper mold 64 in which the inclination angle α2 of the recessed portion 70 was 5 degrees.

[0063] Example 3 A nickel-metal hydride secondary battery (battery C) similar to battery A of Example 1 was assembled, except that an upper insulating member 32 in which the inclination angle α of the umbrella-shaped portion 50 was −10 degrees was obtained using a lower molding mold 66 in which the inclination angle α1 was 10 degrees and an upper mold 64 in which the inclination angle α2 of the recessed portion 70 was 10 degrees.

[0064] (Comparative Example 1) A nickel-metal hydride secondary battery (battery D) was assembled similar to battery A in Example 1, except that the precursor 31 was used as the upper insulating member 32. That is, the upper insulating member 32 of battery D was flat with an inclination angle α of 0 degrees.

[0065] (Comparative Example 2) A nickel-metal hydride secondary battery (battery E) similar to battery A of example 1 was assembled, except that the upper insulating member 32 of example 1 was placed upside down on the electrode group 22. That is, the upper insulating member 32 of battery E had a tilt angle α of +3 degrees and a cone shape.

[0066] (Comparative Example 3) A nickel-metal hydride secondary battery (battery F) similar to battery B of example 2 was assembled, except that the upper insulating member 32 of example 2 was placed upside down on the electrode group 22. That is, the upper insulating member 32 of battery F had a tilt angle α of +5 degrees and a cone-like shape.

[0067] Comparative Example 4 A nickel-metal hydride secondary battery (battery G) similar to battery C of Example 3 was assembled, except that the upper insulating member 32 of Example 3 was placed upside down on the electrode group 22. That is, the upper insulating member 32 of this battery G had a tilt angle α of +10 degrees and a cone-like shape.

[0068] 2. Battery evaluation (1) Occurrence rate of the upper insulating member climbing onto the annular protrusion For batteries A to G, the percentage of the number of batteries in which the upper insulating member was riding on the annular protrusion was calculated from the recorded number of batteries in which the upper insulating member was riding on the annular protrusion after the grooving process and the total number of batteries manufactured. The results are shown in Table 1 as the incidence rate of upper insulating member riding on the annular protrusion. A higher incidence rate of upper insulating member riding on the annular protrusion indicates a higher likelihood of a jamming defect, in which the upper insulating member is jammed in the crimped portion of the opening edge of the outer can.

[0069] (2) Inspection of the amount of electrolyte remaining on the upper insulating member After the electrolyte injection step during the manufacture of batteries A to G and before measuring the post-injection mass, the amount of alkaline electrolyte remaining on the upper insulating member of 10 randomly selected battery precursors was measured. Specifically, the alkaline electrolyte remaining on the upper insulating member was wiped off with a waste cloth whose mass (initial mass) had been measured in advance. The mass of the waste cloth after wiping was then measured. This mass was taken as the post-wiping mass. The initial mass was then subtracted from the post-wiping mass to determine the amount of alkaline electrolyte remaining on the upper insulating member. The average amount of alkaline electrolyte remaining in the selected 10 battery precursors was then calculated. The results are shown in Table 1 as the amount of residual electrolyte.

[0070] (3) Leakage occurrence rate After applying vibration to batteries A to G for 6 hours, the crimped portions were visually observed and wiped with litmus paper. If leakage was confirmed visually or if the litmus paper changed color from red to blue, it was determined that leakage had occurred, and the number of leaking batteries was counted. The number of leaking batteries was recorded as the number of leaking batteries. The leakage occurrence rate was then calculated using equation (II). Leakage occurrence rate (%) = (number of leaked batteries / total number of assembled batteries) × 100 (II) The results obtained are shown in Table 1.

[0071] [Table 1]

[0072] 3. Discussion (1) Comparing Examples 1 to 3 (Batteries A to C) and Comparative Examples 2 to 4 (Batteries E to G), which have upper insulating members with inclined surfaces on both the positive and negative sides, with Comparative Example 1 (Battery D), which has a flat, non-inclined upper insulating member, it is clear that Examples 1 to 3 and Comparative Examples 2 to 4 have a lower leakage incidence rate than Comparative Example 1. This is thought to be because, in the batteries of Examples 1 to 3 and Comparative Examples 2 to 4, the inclined surfaces allow the electrolyte to be quickly guided to the inlet and peripheral edge of the upper insulating member during electrolyte injection, minimizing the amount of electrolyte remaining on the upper insulating member. This is also evident from the fact that the remaining amount of electrolyte in the batteries of Examples 1 to 3 and Comparative Examples 2 to 4 is 18 mg or less, compared to 43 mg in the battery of Comparative Example 1.

[0073] (2) Furthermore, as is clear from the results of Examples 1 to 3 and Comparative Examples 2 to 4, when the angle of the inclined surface is 5 degrees or more, regardless of whether it is on the positive or negative side, the occurrence rate of liquid leakage is 0%, which shows that it is effective to provide the upper insulating member with an inclination of 5 degrees or more.

[0074] (3) However, the incidence of the upper insulating member climbing onto the annular protrusion was 0.4 to 1.1% in Comparative Examples 2 to 4, which was higher than the 0 to 0.2% in Examples 1 to 3. Therefore, when a cone-shaped upper insulating member with a slope toward the positive side is used, as in the batteries of Comparative Examples 2 to 4, there is a high possibility of the crimped portion becoming inadequately engaged, which may result in an internal short circuit or electrolyte leakage due to impaired sealing of the crimped portion. In contrast, the umbrella-shaped upper insulating member with a slope toward the negative side used in the batteries of Examples 1 to 3 has a flared shape and its position above the electrode assembly is stable, resulting in an extremely low incidence of the upper insulating member climbing onto the annular protrusion. Therefore, in the batteries of Examples 1 to 3, there is a low possibility of the crimped portion becoming inadequately engaged, and there is also a low risk of the internal short circuit or electrolyte leakage due to impaired sealing of the crimped portion.

[0075] (4) From the above, it can be said that the batteries of Examples 1 to 3, which employ umbrella-shaped upper insulating members with a slope toward the negative side, can suppress the failure of the upper insulating member to fit properly and prevent the occurrence of internal short circuits, and can also reduce the amount of electrolyte remaining on the upper insulating member when the electrolyte is injected, thereby preventing leakage of the electrolyte. [Explanation of symbols]

[0076] 2 Nickel-metal hydride secondary battery (battery) 10 Outer can 11 Sealing body 12 Insulation gasket 14 Lid plate 20 Positive terminal 22 electrode groups 24 Positive electrode 26 negative electrode 28 Separator 32 Upper insulating member 38 Filling port 40 Tab insertion hole 50 Umbrella

Claims

1. a cylindrical outer can having an open top and a closed bottom; an electrode group in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween and wound in a spiral shape, the electrode group being accommodated in the outer can; an upper insulating member having electrical insulation properties and disposed on an upper portion of the electrode group; an electrolyte injected into the outer can and impregnating the electrode group; a sealing body that is fixed to the opening of the outer can to seal the opening, The upper insulating member is It consists of an insulating thin plate, a liquid injection port for passing the electrolyte; an umbrella-shaped portion extending downwardly from the periphery of the liquid filling port.

2. the upper insulating member has a shape, when viewed from the side, of an isosceles trapezoid with the liquid pouring port as its upper base, an outer peripheral edge of the umbrella-shaped portion as its lower base, and inclined surfaces of the umbrella-shaped portion as its legs, 2. The battery of claim 1, wherein, when a virtual straight line extending in a direction along the lower base of the isosceles trapezoid is taken as a reference line, the leg corresponding to the inclined surface of the umbrella-shaped portion is inclined downward at an angle of 3 degrees or more from the reference line.

3. 3. The battery of claim 2, wherein the legs are inclined downward from the reference line at an angle of 5 degrees or more.

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