JP4865254B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery , and more particularly to a non-aqueous electrolyte secondary battery having a battery housing using a metal material.

  FIG. 6 is a perspective view in which a part of a normal lithium secondary battery, which is a nonaqueous electrolyte secondary battery, is broken. In the figure, reference numeral 1 denotes a battery can, 2 denotes a battery lid, and the battery lid 2 is welded and joined to the battery can 1 along its periphery to form a battery casing. The battery lid is provided with a liquid injection port 10 and a safety valve 15. Reference numeral 16 denotes a positive electrode plate, 17 denotes a negative electrode plate, and 18 denotes a separator. A plurality of positive electrode plates 16, separators 18, and negative electrode plates 17 are laminated in a substantially upright state to form an electrode group 19. Each positive electrode plate 16 is connected to the positive terminal 13, and each negative electrode plate 17 is connected to the negative terminal 14. A non-aqueous electrolyte is enclosed in the battery can.

  In the secondary battery, after the electrode group 19 is housed in the battery can 1, the battery lid is welded and joined to the upper part of the battery can to form a sealed structure, and then the electrolyte is injected from the liquid injection port 10 and injected after the initial charge. The liquid mouth is closed.

  Non-aqueous electrolyte secondary batteries decompose the electrolyte due to electrode reactions inside the battery and gradually generate gases such as carbon dioxide and methane, increasing the internal pressure, so a safety valve 15 is provided that opens when the internal pressure reaches about 0.5 MPag. It has been.

Usually, the battery lid 2 is often laser-welded to the battery can 1 along its circumference.
FIG. 7 shows a cross section of the laser welded portion between the battery lid 2 and the battery can 1. The laser beam is applied from above to the abutting surface (fitting surface) between the battery lid 2 and the battery can 1, but when the battery lid 2 is thick to some extent, the bead 3 is positioned at the lower end of the mating surface as seen in the figure. Often does not reach. In such a case, the lower end portion of the mating surface becomes a notch, the crack may start from the lower end portion of the bead 3, and the weld may break. In the case of a partial crack, even if the fracture does not occur, moisture permeates into the battery from the outside, leading to a decrease in the capacity retention rate of the battery.

The subject of this invention is providing the nonaqueous electrolyte secondary battery in which the above cracks do not generate | occur | produce.

In order to solve the above-mentioned problems, the present invention is to butt-weld the entire circumference of the fitting part by housing the electrode group in a bottomed battery can, fitting the outer peripheral surface of the battery lid to the upper part of the battery can, In a non-aqueous electrolyte secondary battery having a sealed structure, the bottom surface of the battery lid is chamfered to reduce the width of the butted surface to be smaller than the thickness of the battery lid, and the tip of the weld bead is lower than the bottom end of the butted surface. We propose a non-aqueous electrolyte secondary battery characterized by extending downward. When the thickness of the battery lid is T and the distance from the lid surface to the weld bead tip is B, the distance B from the battery lid upper surface to the weld bead bottom is 0.8 · T ≦ B ≦ 1.5 · T. It is good to make it.

  The pressure resistance of the battery casing is desirably 1 MPa or more, and the thickness of the battery can and the battery lid is set to withstand an internal pressure of 1 MPa or more. If the weld bead is too thin than the thickness of the casing, the strength of the welded portion decreases and the pressure resistance of the casing decreases, and if it is too thick, the upper surface of the bead sinks and the strength of the welded portion decreases. Therefore, it is appropriate to keep the length from the upper surface of the battery lid to the lower end of the bead within the range defined above.

Further, when the thickness of the battery lid is T, the width along the lower surface of the chamfer on the lower side of the butt surface of the battery lid is X, and the width in the direction along the butt surface is Y, the chamfer is expressed by the following formula: It is better to be satisfied with the chamfer
X ・ (Y / 2) ≧ 0.15 ・ π ・ T ² (1)

  If welding is performed so that the tip of the weld bead extends below the lower end of the butting surface of the battery lid to the battery can, the molten bead may fall into the battery. By chamfering the abutting surface of the battery lid to the battery can, a liquid reservoir is formed to prevent the molten bead from falling. However, if the cross-sectional area of the chamfered portion that becomes the liquid reservoir is small, it functions as a liquid reservoir. May be insufficient and the molten bead may fall. In order to prevent this, it is necessary to make the chamfer dimension satisfy the expression (1). Equation (1) does not mean that the cross-sectional area of the chamfered portion should be increased unnecessarily, but it means that the dimensions of X and Y should be determined in the vicinity where the equal sign of equation (1) holds.

  When the thickness of the battery cover is small, the bead cross-sectional area is small even if the chamfering is not performed. Therefore, even if the tip of the bead extends below the lower end of the abutting surface, the bead can be prevented from falling. In that case, 0.05 ≦ t / T ≦ 0.27 may be satisfied, where T is the thickness of the battery lid and t is the length from the lower end of the butt surface of the bead.

  In the present invention, welding is performed such that the angle between the surface of the weld bead extending from the lower end of the butting surface and the lower surface of the battery lid and the angle of the inner side surface of the battery can are both obtuse. When the angle formed by the lower end surface of the battery lid at the butt weld portion and the portion where the weld bead extends from the end surface is an acute angle, the acute angle portion becomes a notch, and a crack is likely to be generated from the notch. Also, on the inner surface of the battery can, if the weld bead forms an acute angle with the inner surface at the portion where the weld bead is connected to the inner surface of the battery can, the acute angle portion becomes a notch, and cracks are likely to occur from the notch. By welding so that the angle of the joint between the weld bead and the surface becomes an obtuse angle, a notch that becomes a starting point of crack generation is not formed in the joint, and a sealed structure in which cracks are hardly generated can be obtained.

  In a nonaqueous electrolyte secondary battery in which a battery case is formed by laser welding of a battery lid to a battery can, cracks are prevented from occurring near the tip of the bead melt.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  FIG. 1 is a diagram showing a cross section of laser welding in a battery sealing structure according to an embodiment of the present invention, in which 1 is a battery can with a bottom, 2 is a battery lid, and 3 is a weld bead. A chamfer 2a is applied to the lower side of the battery lid 2 to the battery can 1, and the width W of the abutting surface is made smaller than the thickness T of the battery lid 2 by the chamfering. And the bead 3 is welded so that it may extend below the lower end P of a butt | matching surface. In this case, when the thickness of the battery lid 2 is T and the distance from the lid surface to the weld bead tip is B, the distance B from the battery lid upper surface to the weld bead lower end is 0.8 · T ≦ B ≦ 1.5 · T. Laser welding to fit within range.

The chamfer 2a satisfies X · (Y / 2) ≧ 0.15 · π · T ² where X is the width along the bottom surface of the battery lid 2 and Y is the width along the butt surface. It is chamfered. In this equation, it does not mean that X · (Y / 2) is unnecessarily large, but it means that chamfering is performed so that X · (Y / 2) does not become smaller than 0.15 · π · T ² .

(Test Example 1)
FIG. 2 shows that the battery lid 2 has a thickness of 2 mm, and the bead thickness when the chamfer is applied to the lower side of the butt surface to the battery can 1, that is, the distance B from the battery lid surface to the bead tip is variously changed. Results of performance tests are shown. 2A shows a cross section of the welded portion, and FIG. 2B shows the test result. In FIG. 2 (B), B = 1.6, that is, B / T = 0.8, the withstand pressure is 1.0 MPa, and as B increases, the withstand pressure increases, but at B = 2.4, the maximum withstand pressure becomes 2.0 MPa. As B increases, the pressure resistance decreases. B = 3.0, that is, B / T = 1.5, and the pressure resistance is 1 MPa. This is because when B becomes large, the bead upper end surface sinks and the pressure resistance decreases. Since the nonaqueous electrolyte secondary battery desirably has a pressure resistance of 1 MPa, it is desirable that 0.8 ≦ B / T ≦ 1.5.

(Test Example 2)
FIG. 3 shows the result of examining the falling state of the bead by changing the chamfer dimensions X and Y when the plate thickness T of the battery lid is 1.5 mm, (A) shows the dimensions of each part, and (B) shows The test results are shown. In FIG. 3B, a cross indicates that the bead has dropped, and a circle indicates that the bead did not fall and was good. From this result, it was found that the chamfered cross-sectional area, that is, the cross-sectional area of the liquid reservoir, needs to be 15% or more of the cross-sectional area of the bead in order to maintain a good shape without dropping the bead. The bead cross-section is substantially semicircular and the lower end of the bead extends to the position of the lower end surface of the battery cover 2 so that the chamfer dimensions X and Y satisfy X · (Y / 2) ≧ 0.15 · π · T ^2. It can be said that it should be decided. Further, the value of θ when tan θ = Y / X is preferably in the range of 20 ° to 60 °.

(Test Example 3)
FIG. 4 is a view showing a cross-section of a joint portion between a base metal surface and a weld bead surface in a laser welded portion in a battery sealing structure, in which (A) shows a good bead shape, and (B) and (C) show defects. The bead shape is shown. In these figures, 1 is a battery can, 2 is a battery lid, and 3 is a weld bead. In FIG. 4A, the angle A ₁ between the lower surface 2a of the battery lid 2 and the bead surface at the joint between the lower surface and the weld bead 3 is an obtuse angle, and the inner side surface 1a of the battery can 1 and the inner side surface The angle B ₁ between the welded bead 3 and the bead surface is also an obtuse angle, indicating a good welded state. In FIG. 4B, A ₂ is an obtuse angle, but B ₂ is an acute angle, and cracks are likely to occur from this acute angle joint. In FIG. 4C, both A ₃ and B ₃ are acute angles, and cracks are likely to occur from these acute angle joints. Although FIG. 4 shows the case where chamfering is not performed on the lower side of the butted surface of the battery lid 2, the same applies to the case where chamfering is performed. In that case, the battery lid lower surface 2a in FIG. 4 is a chamfered surface, that is, an inclined surface. Such a case can be seen in FIG. When the chamfering is performed, the weld bead extending from the abutting portion tends to spread along the chamfered surface and does not fall vertically, so that an acute angle portion is hardly generated due to the surface tension of the dissolved bead.

  FIG. 4D shows a pressure resistance test result when the angle B in FIGS. 4A, 4B, and 4C is about 120 ° and the angle A is 80 ° to 120 °, and the angle A is about 120. The pressure test results are shown when the angle B is between 80 ° and 120 °. Since the pressure resistance is desirably 1 MPa or more, it is desirable that both the angles A and B are 90 ° or more, that is, an obtuse angle.

  FIG. 5 shows a case where laser welding is performed without chamfering the butting surface F of the battery lid 2 to the battery can 1, and the length t at which the tip of the bead 3 extends from the lower surface of the battery lid 2 is 0.05 ≦ t / T ≦. It is better to weld so that it is within the range of 0.27. Then, the angle between the surface of the bead 3 extending from the lower surface of the battery lid 2 and the lower surface becomes an obtuse angle, and the angle between the surface of the bead 3 and the inner surface of the battery can 1 becomes obtuse, and the bead 3 and these surfaces A notch, that is, an acute angle portion is not generated at the connection portion.

  FIG. 8 shows a situation where the tip of the bead does not reach the lower surface of the battery lid 2 and the lower end of the bead is notched and a crack C is generated from the lower side. FIG. 9 shows a case in which the length of the bead tip extending from the lower surface of the battery lid 2 is excessive, the depression of the upper surface of the bead 3 is large, and the crack C is generated from the upper surface of the bead.

  In a nonaqueous electrolyte secondary battery in which a battery lid is butt welded to a battery can by laser welding to form a sealed structure, a sealed structure is obtained in which cracks are prevented from being generated in the weld due to an increase in internal pressure when the battery is used.

It is a figure which shows the cross section of the laser welding part in the sealing structure of the battery which concerns on the Example of this invention. It is a figure which shows the test result which investigated the pressure resistance by changing the distance from a battery cover surface to a bead tip. It is a figure which shows the test result which investigated the fall condition into the battery of the welding bead by changing the chamfer dimension of a battery cover. It is a figure which shows the cross section and the pressure | voltage resistant test result of the junction part of the base material surface of a laser welding part in the sealing structure of a battery, especially a weld bead surface, and (B), (C) is a favorable bead shape. (D) is a figure which shows a pressure | voltage resistant test result with a bad bead shape. It is a figure which shows the cross section of the laser welding part in the sealing structure of the battery which concerns on the other Example of this invention. It is the perspective view which fractured | ruptured a part of lithium secondary battery. FIG. 3 is a cross-sectional view of a welded portion showing a state in which the tip of the weld bead does not reach the lower surface of the battery lid in the butt welding of the battery lid and the battery can. It is a welding part sectional view showing an example of the crack generation situation of the butt welding part of a battery lid and a battery can. It is a welding part sectional view showing other examples of the crack generation situation of the butt welding part of a battery lid and a battery can.

DESCRIPTION OF SYMBOLS 1 Battery can 2 Battery cover 2a Chamfer 3 Weld bead 10 Injection hole 13 Positive electrode terminal 14 Negative electrode terminal 15 Safety valve 16 Positive electrode plate 17 Negative electrode plate 18 Separator 19 Electrode group

Claims (4)

An electrode group is housed in a bottomed battery can, a battery lid outer peripheral surface is fitted to the upper part of the battery can, and the entire circumference of the fitting portion is butt welded by laser light irradiation to form a sealed structure. In the secondary battery, the bottom surface of the battery cover is chamfered to reduce the width of the surface of the battery than the thickness of the battery cover, and the tip of the weld bead extends below the lower end of the surface of the battery .
When the thickness of the battery lid is T and the distance from the lid surface to the weld bead tip is B, the distance B from the battery lid upper surface to the weld bead lower end is in the range of 0.8 · T ≦ B ≦ 1.5 · T. A non-aqueous electrolyte secondary battery . When the thickness of the battery lid is T, the width of the chamfer on the lower side of the butt surface of the battery lid is X along the width along the lower surface, and the width along the butt surface is Y, the chamfer satisfies the following formula: The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte secondary battery is chamfered.
X ・ (Y / 2) ≧ 0.15 ・ π ・ T ²           (1) An electrode group is housed in a bottomed battery can, a battery lid outer peripheral surface is fitted to the upper part of the battery can, and the entire circumference of the fitting portion is butt welded by laser light irradiation to form a sealed structure. In the secondary battery, the tip of the weld bead extends below the lower end of the butt surface,
A nonaqueous electrolyte secondary battery, wherein the thickness T of the battery lid and the length t from the lower end of the butting surface to the tip of the bead satisfy the relationship of 0.05 ≦ t / T ≦ 0.27. The angle between the surface of the weld bead extending beyond the lower end of the butting surface and the lower end surface of the battery lid and the angle with the inner side surface of the battery can are both obtuse angles. The nonaqueous electrolyte secondary battery according to any one of the above.

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