JP2004103369A - Flat square battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin flat square battery equipped with a safety valve structure. <P>SOLUTION: When an electrode plate group 4 is accommodated in a body case 2 having a recess 5 and a welding margin 8 formed around it, and a lid plate 3 is placed to cover the welding margin 8 and welded at the margin 8, an easy-to-rupture part 30 is formed on the welding seam W by dropping the welding strength partially, and the weld of the part 30 is made to be ruptured when the internal pressure rises abnormally, and the internal pressure is released to the outside. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a battery having a structure that enables a thinner prismatic battery, and more particularly to a flat prismatic battery provided with a safety valve structure that externally releases an abnormally increased internal pressure.
[0002]
[Prior art]
Mobile electronic devices, such as mobile phones and PDAs, have been significantly reduced in size and thickness as well as becoming more sophisticated. Batteries applied to them have been required to be smaller, thinner and have higher energy densities. As a result, the demand for flat-shaped lithium ion secondary batteries is increasing. The recent trend of portable electronic devices is to reduce the thickness rather than reduce the size, and it is easy to put them in pockets and bags, and it does not impair ease of use.
[0003]
In order to achieve a reduction in the thickness of the device, it is necessary to reduce the thickness of the battery that is the power source of the device. That is, the battery case has a structure in which the battery case is formed in a square cylinder with a bottom by drawing or handling, and the opening of the battery case accommodating the electrode plate group is sealed with a sealing plate. In such a case, the battery case is formed such that the opening area is smaller than the depth in the processing direction. However, as the shorter side dimension of the battery case having a rectangular or elliptical cross section becomes smaller, processing becomes more difficult, and it becomes more difficult to insert the electrode plate group into the battery case. In order to further reduce the thickness of the current flat prismatic battery, it is necessary to fundamentally change the structure of the battery case, and a body case in which the battery case is formed in a half-shell body, and a lid plate that closes the open part A battery structure has been developed in which an electrode group is accommodated in a main body case and an opening of the main body case is closed by a lid.
[0004]
For example, a battery in which a group of electrodes is accommodated in a container formed in a half-shell body, a cover plate is arranged at an opening of the container, and the inside of the container is sealed by laser welding the periphery of the cover plate to the container. It is known (see Patent Document 1). The structure in which the large opening of such a half-shell container is sealed with a lid plate is such that a step portion is formed at the opening end of the main case formed in the half-shell body so that the battery lid fits therein, and the electrode plate group is formed. There is also known a battery in which a battery cover is fitted into the stepped portion after the battery cover is housed in the main body case, and the inside of the main body case is sealed by laser welding the battery cover and the main body case around the battery cover (Japanese Patent Application Laid-Open No. H10-163873). 2). In addition, the electrode group is accommodated in the concave portion of the pair of half-shell members provided with the flange portion, and the two members containing the electrode group are sealed by laser welding the members with the flange portion. A battery that has been used is also known (Patent Document 3).
[0005]
[Patent Document 1]
JP 2001-250517 A (pages 3 and 4, FIG. 1)
[0006]
[Patent Document 2]
JP-A-2001-52658 (pages 4 to 6, FIG. 1)
[0007]
[Patent Document 3]
JP 2001-167744 A (pages 5 to 8, FIG. 1)
[0008]
[Problems to be solved by the invention]
Batteries with a high energy density, especially lithium ion secondary batteries, are required to have a structure that does not fall into a situation such as bursting or firing even when exposed to an external short circuit, overcharging, or high-temperature storage. Safety structure such as a battery and a battery protection circuit, and a mechanical safety structure such as a safety valve. Although the electrical safety structure can be configured externally, the mechanical safety structure must be provided on the battery itself. The safety valve structure has a structure in which the thickness of the outer case is partially thinned by forming a clad material or a groove in which a foil-like plate is attached to the opening and a part that is easily broken by abnormal internal pressure is provided, or provided in the opening In general, a structure in which an elastic valve element is opened due to abnormal internal pressure is used.
[0009]
However, it is difficult to apply the safety valve structure according to the related art to a flat prismatic battery configured for the purpose of thinning, and it is necessary to develop a safety valve structure suitable for the flat prismatic battery.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to provide a flat battery having a safety valve structure for releasing an abnormal internal pressure to the outside by controlling the welding strength when the battery case is welded and joined, and a method for manufacturing the same.
[0011]
[Means for Solving the Problems]
The first invention of the present application to achieve the above object is to form a main body case in a half-shell body in which a metal plate is processed and a flange is provided around an opening of a concave portion, and an electrode plate group is accommodated in the concave portion. In a flat rectangular battery in which a flange is joined by welding between a metal lid plate and a flange provided with a peripheral portion overlapped on the flange, a part of the flat battery is welded on a welding line for welding between the lid plate and the flange. Characterized in that an easily breakable portion having reduced welding strength is formed.
[0012]
According to the above configuration, since the easily broken portion is formed by partially reducing the welding strength during welding, when the internal pressure of the flat battery is abnormally increased due to an external short circuit, overcharge, high temperature, etc., the easily broken portion is easily broken. Since the welded part of the part is broken and the abnormal internal pressure is released to the outside, the rupture of the battery can be prevented without providing a separate safety valve. The formation position of the easily breakable portion is preferably the long side center portion where swelling is most likely to occur when the internal pressure of the battery abnormally rises.
[0013]
Further, the second invention of the present application is directed to forming a main body case in a half-shell body provided with a flange around an opening of a concave portion by processing a metal plate, accommodating an electrode group in the concave portion, and forming a metal cover plate. In a manufacturing method of a flat rectangular battery in which a peripheral portion is overlapped with the flange and the lid plate and the flange are joined by welding, at a predetermined portion on a welding line for welding the lid plate and the flange over the entire circumference, Welding is performed by controlling the welding so that the welding strength between the cover plate and the flange is reduced.
[0014]
According to the above manufacturing method, when welding is performed between the flange portion of the main body case and the peripheral portion of the lid, welding control is performed so that the welding strength of the predetermined portion is reduced. Ruptures when the battery internal pressure rises abnormally, and functions as a safety valve that releases the abnormal internal pressure to the outside.
[0015]
The above welding control can be performed by a method of controlling so as to reduce the welding current at a predetermined portion on the welding line, or a method of controlling so as to increase the moving speed of the welding electrode at a predetermined portion on the welding line.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings to facilitate understanding of the present invention. The embodiment described below is an example embodying the present invention, and does not limit the technical scope of the present invention.
[0017]
FIG. 1 shows the external shape of a flat prismatic battery 1 according to the present embodiment, which is configured as a lithium ion secondary battery. As shown in FIG. 2, a battery case 50 is formed by a main body case 2 formed in a half-shell body and a lid plate 3 that closes an open portion thereof. The electrode group 4 is accommodated in the concave portion 5 of the main body case 2, and the opening of the main body case 2 is sealed with the lid 3.
[0018]
As shown in FIG. 2, the main body case 2 is formed by pressing a metal plate to form a concave portion 5 having a stepped portion 6, and providing a welding margin 8 in a flange shape around the concave portion 5. The stepped portion 6 is a portion for forming external connection terminals of the positive electrode and the negative electrode. In this case, the terminal hole 7 formed in the stepped portion 6 is insulated from the main body case 2 by an outer gasket 11 and an inner gasket 12 while ensuring airtightness. Then, the rivet 10 serving as the positive electrode external connection terminal is fastened and fixed. Further, an injection port 14 for the electrolyte is formed in the step portion 6.
[0019]
An electrode group 4 in which a positive electrode plate and a negative electrode plate are wound via a separator is accommodated in the concave portion 5 of the main body case 2. The positive electrode lead 15 drawn from the positive electrode plate of the electrode plate group 4 is joined to the rivet 10, and the negative electrode lead 16 drawn from the negative electrode plate is joined on the step 6.
[0020]
As shown in FIG. 3, the electrode group 4 has a different winding direction in which the positive electrode plate and the negative electrode plate are wound via a separator, and the positive electrode lead 15 is pulled out from the winding end of the positive electrode plate. The electrode plate group 4a in which the lead 16 is pulled out from the winding end of the negative electrode plate can be used, and the bonding of the positive electrode lead 15 to the rivet 10 and the bonding of the negative electrode lead 16 to the step 6 are facilitated.
[0021]
The cover plate 3 is put on the open portion of the main body case 2 that accommodates the electrode plate group 4, and the periphery of the cover plate 3 and the welding margin 8 are welded, so that the concave portion 5 of the battery case is It is sealed by the cover plate 3. As the welding method, laser welding, electron beam welding, seam welding and the like are suitable.
[0022]
When welding between the welding margin 8 and the cover plate 3, an easily breakable portion 30 in which the welding strength is partially reduced is formed on one long side. In the normal state, the easily breakable portion 30 maintains the airtightness in the battery case to prevent leakage of the electrolyte, and when the internal pressure is abnormally increased due to an external short circuit, overcharge, or the like, the easily breakable portion 30 breaks. To release the abnormal internal pressure to the outside to prevent the battery case from rupture.
[0023]
A method for forming the easily breakable portion 30 when seam welding is applied as a welding method for welding between the welding margin 8 and the cover plate 3 will be described below.
[0024]
In seam welding, as shown in FIG. 4, an upper rotating electrode 31 and a lower rotating electrode 32 are arranged vertically above and below a welding margin 8 and a peripheral portion of the lid plate 3 overlapped therewith. Rotational movement is performed in a state where a pressing force is applied in the direction of the rotating electrode 32, and a welding current flows between the upper rotating electrode 31 and the lower rotating electrode 32 from the welding power source 35, and the traveling direction of the upper rotating electrode 31 and the lower rotating electrode 32. Is formed, and the gap between the welding margin 8 and the peripheral portion of the cover plate 3 is welded to seal the inside of the concave portion 5 of the main body case 2 in a sealed state. The seam welding is performed on a welding line W indicated by a broken line in FIG. 1, and an easily breakable portion 30 having partially reduced welding strength is formed at a central portion of one side in the longitudinal direction on the welding line W. A safety valve structure is configured.
[0025]
In the normal state of the flat battery 1, the easily breakable portion 30 maintains the hermeticity of the main body case 2 to prevent the electrolyte from leaking, and the flat battery 1 may have an internal pressure due to an external short circuit, overcharge, high temperature, or the like. When the pressure rises abnormally, it is required to operate as a safety valve for breaking the flat internal battery 1 by rupture from the welded portion to release the abnormal internal pressure to the outside and prevent the flat battery 1 from bursting.
[0026]
The welding condition factors in seam welding are a welding current, a pressing force, and a moving speed between the upper rotating electrode 31 and the lower rotating electrode 32. In the intermittent energizing method in which the welding current is intermittently applied, the energizing time and the pause are set. The ratio with time is added. In order to reduce the welding strength, at a portion where the easily breakable portion 30 is formed on the welding line W, the welding strength of the portion is reduced by implementing any one or a plurality of combinations of easily controllable welding condition factors. Can be reduced. For the most preferable control of the welding strength, a method of reducing the welding current at the easily breakable portion 30 is preferable because the control is easy. In the easily breakable portion 30 in which the welding current is reduced, the amount of heat generated by resistance heating of the contact portion between the welding margin 8 and the cover plate 3 is reduced, so that the molten volume accompanying heat generation, that is, the amount of nugget formation is also reduced. The welding strength at the easily breakable portion 30 decreases.
[0027]
When laser welding is used, the outer peripheral portion of the lid plate 3 and the welding margin 8 are welded to each other by irradiating a laser beam from above the outer peripheral portion of the lid plate 3 overlapping the welding margin 8 of the main body case 2. The inside of the second concave portion 5 is hermetically sealed. As shown in FIG. 5, if the easily breakable concave portion 41 is formed at one corner of the long side of the main body case 2 where the concave portion 5 is formed so as to be partially located on the welding line of laser welding, The weld width becomes narrower at the portion where the easily breakable recess 41 is formed, and a portion having reduced welding strength is formed similarly to the easily breakable portion 30 of the seam welding described above. The safety valve structure is formed in which the welding of the easily breakable portion 30 having a low breakage is broken and the abnormal internal pressure is externally released.
[0028]
In addition, the easily breakable portion 30 can be formed by reducing the welding strength of the laser welding on the portion where the easily breakable portion 30 is formed in the welding line. For controlling the welding strength in laser welding, it is an easy means to control the pulse width and time of the laser pulse.
[0029]
【The invention's effect】
As described above, according to the present invention, a safety valve structure is formed at the time of welding in a structure in which a metal lid is sealed by welding a metal lid to an open portion of a battery case obtained by processing a metal plate into a half shell. Therefore, there is no need to provide a separate step of providing a safety valve, and a member for the safety valve is not required, so that cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a perspective view showing the external shape of a flat prismatic battery according to an embodiment.
FIG. 2 is an exploded perspective view showing components of the flat rectangular battery.
FIG. 3 is an exploded perspective view showing components of a flat rectangular battery having a different configuration of an electrode plate group.
FIG. 4 is a schematic view showing a configuration of seam welding.
FIG. 5 is a perspective view showing a structure for forming an easily breakable portion by laser welding.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Flat battery 2 Body case 3 Cover plate 4 Electrode plate group 5 Concave part 6 Step part 8 Welding allowance (flange)
30 easy break

Claims (4)

A metal case is formed by processing a metal plate and forming a body case in a half-shell body provided with a flange around the opening of the concave portion, accommodating an electrode plate group in the concave portion, and superposing a peripheral portion on the flange. Flat battery formed by welding the lid plate and the flange made of
A flat rectangular battery, wherein an easily breakable portion having reduced welding strength is partially formed on a welding line for welding between the lid plate and the flange. A metal plate is processed to form a main body case in a half-shell body provided with a flange around the opening of the concave portion, an electrode group is accommodated in the concave portion, and a peripheral portion of a metal lid plate is overlapped with the flange. In a method of manufacturing a flat rectangular battery in which a lid plate and a flange are joined by welding,
A flat prismatic battery characterized in that at a predetermined portion on a welding line for welding the entire circumference between the cover plate and the flange, welding is performed by performing welding control so as to reduce the welding strength between the cover plate and the flange. Manufacturing method. The method for manufacturing a flat rectangular battery according to claim 2, wherein the welding control is performed so as to reduce a welding current at a predetermined portion on a welding line. The method according to claim 2, wherein the welding control is performed so as to increase a moving speed of the welding electrode at a predetermined position on the welding line.

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