Patent Description:
In recent years, the price of energy sources increases due to the depletion of fossil fuels, the interest in environmental pollution is amplified, and the demand for eco-friendly alternative energy sources is becoming an indispensable factor for future life. Accordingly, studies on various power generation technologies such as solar power, wind power, and tidal power are continuing, and power storage devices such as batteries for more efficiently using the generated electrical energy are also of great interest.

Furthermore, as technology development and demand for electronic mobile devices and electric vehicles using batteries increase, the demands for batteries as energy sources are rapidly increasing. Thus, many studies on batteries which are capable of meeting various demands have been conducted.

In particular, in terms of materials, there is a high demand for lithium secondary batteries such as lithium ion batteries and lithium ion polymer batteries having advantages such as high energy density, discharge voltage, and output stability.

The secondary batteries are classified into cylindrical batteries and prismatic batteries, in which an electrode assembly is embedded in a cylindrical or prismatic metal can, and pouch-type batteries, in which an electrode assembly is embedded in a pouch-type case made of an aluminum laminate sheet according to shapes of battery cases. In addition, recently, a thin film can-type battery using a metal thin film has been developed and used due to an increase in customer preference for a high output and long lifespan.

Such a thin film can-type battery is generally manufactured by accommodating an electrode assembly in a can, covering the electrode assembly, and performing laser welding (the thin film can means a thin metal). Also, in the laser welding, it is necessary to manufacture a product having excellent sealing properties by preventing a non-welded portion from occurring.

However, in the related art, in the laser welding, strong clamping is performed to prevent the non-welded portion from occurring through the strong adhesion, but in this case, deformation of the metal thin film occurs to cause a problem. However, if it is not clamped strongly, there is a problem because the adhesion is not made properly, resulting in non-welded portion and poor sealing properties.

<CIT> discloses a method of manufacturing an electrochemical device by laser welding of a lid onto the frame part using an appropriate jig.

The present invention has been devised to solve the above problems, and an object of the present invention is to provide a method for manufacturing a secondary battery, in which, when a thin film can is welded, a bonding portion is improved in adhesion to prevent an non-welded portion from occurring, thereby remarkably improving sealing properties, and a secondary battery manufactured by using the manufacturing method.

A method for manufacturing a secondary battery according to the present invention comprises: a welding preparation process of preparing a lower can comprising an accommodation part in which an electrode assembly is accommodated, and an upper cover covering an upper opening of the lower can; a gripping process of gripping an end of a lower can circumferential portion and an end of an upper cover circumferential portion at upper and lower portions by using an upper jig and a lower jig in order to weld the lower can circumferential portion that is a portion extending outward from an edge of the accommodation part to the upper cover circumferential portion that is a circumferential area of the upper cover; and a welding process of irradiating laser onto a bonding portion that is a point, at which the lower can circumferential portion and the upper cover circumferential portion are bonded to each other, to bond the lower can circumferential portion to the upper cover circumferential portion through laser welding.

In the welding process, the laser welding may be performed in a state in which a height (b) of the accommodation part is formed to be higher than a height (a) of the end of the lower can circumferential portion.

In the welding process, a height of a central point of the upper cover may be higher than the height b of the accommodation part.

The lower jig may comprise a bottom part on which the lower can is placed and a sidewall formed on a circumference of the bottom part, the height (b) may mean a distance from the bottom part to an upper end of the accommodation part, and the height (a) of the end of the lower can circumferential portion may mean a distance from the bottom part to the end of the lower can circumferential portion.

In the welding process, an upper pressing surface that is a surface pressing the end of the upper cover circumferential portion in the upper jig and a lower pressing surface that is a surface pressing the end of the lower can circumferential portion in the lower jig may be parallel to the bottom part.

A value (b-a) obtained by subtracting the height (a) of the end of the lower can circumferential portion from the height (b) of the accommodation part may be greater than or equal to a thickness of a thinner base material of the lower can and the upper cover, which are welding base materials, and be less than three times the thickness of the thinner base material.

In a welding process, an upper pressing surface that is a surface pressing the end of the upper cover circumferential portion in the upper jig may further extend in a direction of the laser than a lower pressing surface that is a surface pressing the end of the lower can circumferential portion in the lower jig.

A width (c) of the upper pressing surface may be greater than a width (d) of the lower pressing surface.

An outer end point of the upper pressing surface and an outer end point of the lower pressing surface may be disposed in the same vertical line.

The upper jig may be provided in a right-angled triangle shape in cross section, and in the welding process, the upper jig may be disposed so that an oblique side of the right-angled triangle faces the laser.

A secondary battery according to the present invention comprises: an electrode assembly; a lower can comprising an accommodation part in which the electrode assembly is accommodated; and an upper cover configured to cover an upper opening of the lower can, wherein the lower can comprises a lower can circumferential portion that is a portion extending outward from an edge of the accommodation part, the upper cover comprises an upper cover circumferential portion bonded to the lower can circumferential portion as a circumferential area of the upper cover, and a bonding portion that is a point at which the lower can circumferential portion and the upper cover circumferential portion are bonded to each other has a height lower than a height (b) of the accommodation part.

A height of a central point of the upper cover may be higher than the height (b) of the accommodation part.

The method for manufacturing the secondary battery according to the present invention may comprise: the welding preparation process of preparing the lower can comprising the accommodation part in which the electrode assembly is accommodated, and the upper cover covering the upper opening of the lower can; the gripping process of gripping the end of the lower can circumferential portion and the end of the upper cover circumferential portion at the upper and lower portions by using the upper jig and the lower jig in order to weld the lower can circumferential portion that is the portion extending outward from the edge of the accommodation part to the upper cover circumferential portion that is the circumferential area of the upper cover; and the welding process of irradiating laser onto the bonding portion that is the point, at which the lower can circumferential portion and the upper cover circumferential portion are bonded to each other, to bond the lower can circumferential portion to the upper cover circumferential portion through laser welding, and thus, when the thin film can is welded, the adhesion of the bonding portion, it is possible to prevent the non-welded portion from occurring, thereby realizing the significantly improved sealing properties in the thin film can-type battery.

The secondary battery according to the present invention may comprise: the electrode assembly; the lower can comprising the accommodation part in which the electrode assembly is accommodated; and the upper cover configured to cover the upper opening of the lower can, wherein the lower can may comprise the lower can circumferential portion that is the portion extending outward from the edge of the accommodation part, the upper cover may comprise the upper cover circumferential portion bonded to the lower can circumferential portion as the circumferential area of the upper cover, and a bonding portion that is the point at which the lower can circumferential portion and the upper cover circumferential portion may be bonded to each other has the height lower than the height (b) of the accommodation part. Therefore, it may be possible to realize the significantly improved sealing properties in the thin film can-type battery.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be implemented in several different forms and is not limited or restricted by the following examples.

In order to clearly explain the present invention, detailed descriptions of portions that are irrelevant to the description or related known technologies that may unnecessarily obscure the gist of the present invention have been omitted, and in the present specification, reference symbols are added to components in each drawing. In this case, the same or similar reference numerals are assigned to the same or similar elements throughout the specification.

<FIG> is a cross-sectional view illustrating a method for manufacturing a secondary battery through laser welding according to a related art that is Comparative Example.

Referring to <FIG>, in a method for manufacturing a secondary battery according to Comparative Example of the present invention, first, a lower can <NUM> comprising an accommodation part <NUM> in which an electrode assembly <NUM> is accommodated, and an upper cover <NUM> covering an upper opening of the lower can <NUM> may be prepared, and a lower can circumferential portion <NUM> and an upper cover circumferential portion <NUM> may be welded to manufacture a secondary battery. Here, each of the lower can <NUM> and the upper cover <NUM> may be a thin film can made of a thin metal.

The lower can circumferential portion <NUM> and the upper cover circumferential portion <NUM> may be disposed to overlap each other to weld the lower can circumferential portion <NUM> that is a portion extending outward from an edge of the accommodation part <NUM> to the upper cover circumferential portion <NUM> that is a circumferential area of the upper cover <NUM>. In addition, an end <NUM> of the lower can circumferential portion and an end <NUM> of the upper cover circumferential portion may be gripped at upper and lower portions thereof by using an upper jig <NUM> and a lower jig <NUM>. When there is no gap between the lower can circumferential portion <NUM> and the upper cover circumferential portion <NUM> during laser welding, a non-welded portion may not occur, and the welding may be performed well. For example, when welding a thin plate having a thickness of <NUM> (micrometer), the non-welded portion may occur even if a gap between base metals exceeds <NUM> (micrometer).

After being gripped at upper and lower portions by using an upper jig <NUM> and a lower jig <NUM>, laser L is irradiated onto a bonding portion that is a point, at which the lower can circumferential portion <NUM> and the upper cover circumferential portion <NUM> are bonded to each other, to bond the lower can circumferential portion <NUM> to the upper cover circumferential portion <NUM> through laser welding.

However, in Comparative Example, in the laser welding process, the laser welding is performed in a state in which a height b of the accommodation part <NUM> and a height a of the end <NUM> of the lower can circumferential portion are equal to each other.

Specifically, the lower jig <NUM> comprises a bottom part <NUM> on which the lower can <NUM> is placed and a sidewall <NUM> formed on a circumference of the bottom part <NUM>. A height b means a distance from the bottom part <NUM> to an upper end of the accommodation part <NUM>, and a height a of the end <NUM> of the lower can circumferential portion means a distance from the bottom part <NUM> to the end <NUM> of the lower can circumferential portion.

Also, when a surface pressing an end <NUM> of the upper cover circumferential portion is referred to as an upper pressing surface <NUM> in the upper jig <NUM>, and a surface pressing the end <NUM> of the lower can circumferential portion is referred to as a lower pressing surface <NUM>, a width c of the upper pressing surface <NUM> and a width d of the lower pressing surface <NUM> are formed to be the same in Comparative Example. That is, the upper pressing surface <NUM> and the lower pressing surface <NUM> have widths corresponding to each other and face each other vertically, and an orthographic projection of the upper pressing surface <NUM> becomes the lower pressing surface <NUM>. In this case, an inner end point of the upper pressing surface <NUM> and an inner end point of the lower pressing surface <NUM> may be disposed in the same vertical line.

According to the related art, the secondary battery is manufactured through the laser welding in the same manner as in Comparative Example. In this case, even though two base materials, that is, the lower can circumferential portion <NUM> and the upper cover circumferential portion <NUM> are in close contact with each other at both ends, possibility of occurrence of the gap is high at a portion at which actual welding is performed. Therefore, there is a problem because adhesion is not performed properly, resulting in non-welded portion and poor sealing properties.

<FIG> is a cross-sectional view illustrating a method for manufacturing a secondary battery through laser welding according to Embodiment <NUM> of the present invention.

Referring to <FIG>, a method for manufacturing a secondary battery according to Example <NUM> of the present invention comprises a welding preparation process, a gripping process, and a welding process.

The welding preparation process is a process of preparing a lower can <NUM> comprising an accommodation part <NUM> in which an electrode assembly <NUM> is accommodated, and an upper cover <NUM> covering an upper opening of the lower can <NUM>. The accommodation part <NUM> of the lower can <NUM> may have a space recessed downward, and the upper cover <NUM> may have a flat plate shape. Each of the lower can <NUM> and the upper cover <NUM> may be a thin film can made of a thin metal.

In order to weld a lower can circumferential portion <NUM> that is a portion extending outward from an edge of the accommodation part <NUM> to an upper cover circumferential portion <NUM> that is a circumferential area of the upper cover <NUM>, in the gripping process, the lower can circumferential portion <NUM> and the upper cover circumferential portion <NUM> are disposed to overlap each other, and an end <NUM> of the lower can circumferential portion and an end <NUM> of the upper cover circumferential portion are gripped at upper and lower portions thereof by using an upper jig <NUM> and a lower jig <NUM>.

After being gripped at upper and lower portions by using an upper jig <NUM> and a lower jig <NUM>, in the welding process, laser L is irradiated onto a bonding portion that is a point, at which the lower can circumferential portion <NUM> and the upper cover circumferential portion <NUM> are bonded to each other, to bond the lower can circumferential portion <NUM> to the upper cover circumferential portion <NUM> through laser welding.

In the method for manufacturing the secondary battery according to Embodiment <NUM> of the present invention, in the welding process, the laser welding is performed in a state in which a height b of the accommodation part <NUM> is formed to be higher than a height a of the end <NUM> of the lower can circumferential portion.

Specifically, the lower jig <NUM> comprises a bottom part <NUM> on which the lower can <NUM> is placed and a sidewall <NUM> formed on a circumference of the bottom part <NUM>. The height b means a distance from the bottom part <NUM> to an upper end of the accommodation part <NUM>, and the height a of the end <NUM> of the lower can circumferential portion means a distance from the bottom part <NUM> to the end <NUM> of the lower can circumferential portion.

The method for manufacturing the secondary battery according to Embodiment <NUM> of the present invention may realize significantly improved sealing properties by preventing an occurrence of a non-welded portion by improving adhesion of the bonding portion through the welding in this manner.

One method of interpreting this may be interpreted that, as the bottom part <NUM> of the lower jig <NUM> pushes up the accommodation part <NUM> of the lower can <NUM>, an edge of the accommodation part <NUM> applies the force of pushing up the lower can circumferential portion <NUM> so that the close contact is reliably realized at the bonding portion.

Another method of interpreting this may be interpreted that the upper jig <NUM> applies relatively downward pushing force to the end <NUM> of the upper cover circumferential portion so that the close contact is reliably realized at the bonding portion.

In addition, in the method for manufacturing the secondary battery according to Embodiment <NUM> of the present invention, in the welding process, the upper pressing surface <NUM> that is a surface pressing the end <NUM> of the upper cover circumferential portion in the upper jig <NUM> and the lower pressing surface <NUM> that is a surface pressing the end <NUM> of the lower can circumferential portion in the lower jig <NUM> may be parallel to the bottom part <NUM> of the lower jig <NUM>. When formed in this manner, force at which an edge of the accommodation part <NUM> pushes up the lower can circumferential portion <NUM> may act more strongly. Alternatively, force at which the upper jig <NUM> pushes relatively down the end <NUM> of the upper cover circumferential portion may act more strongly.

In addition, a height of a central point <NUM> of the upper cover may be higher than the height b of the accommodation part <NUM>. This may be a shape that appears because the upper cover <NUM> is provided as a thin film can.

In the method of manufacturing the secondary battery according to Embodiment <NUM> of the present invention, a value b-a obtained by subtracting the height a of the end <NUM> of the lower can circumferential portion from the height b of the accommodation part <NUM> may be greater than or equal to a thickness of a thinner base material of the lower can <NUM> and the upper cover <NUM>, which are welding base materials, and be less than three times the thickness of the thinner base material.

If the value b-a is less than the thickness of the thinner base material, an effect of the present invention described above may be weakened. In addition, when the value b-a is greater than three times the thickness of the thinner base material, deformation of the thin film can becomes severe, and an inclination of each of the lower can circumferential portion <NUM> and the upper cover circumferential portion <NUM> increases to cause a problem, in which welding performance and efficiency are relatively deteriorated.

In the method for manufacturing the secondary battery according to Embodiment <NUM> of the present invention, a width c of the upper pressing surface <NUM> and a width d of the lower pressing surface <NUM> are formed to be the same. That is, the upper pressing surface <NUM> and the lower pressing surface <NUM> have widths corresponding to each other and face each other vertically, and an orthographic projection of the upper pressing surface <NUM> becomes the lower pressing surface <NUM>.

In this case, the height b of the accommodation part <NUM> may be higher than a height f of the lower can circumferential portion <NUM>, and the height f of the lower can circumferential portion <NUM> may be higher than the height a of the end <NUM> of the lower can circumferential portion. This may be because a sequential inclination is formed from an upper end of the accommodation part <NUM> to the end <NUM> of the lower circumferential portion through the lower can circumferential portion.

In the method for manufacturing the secondary battery according to Embodiment <NUM> of the present invention, since the width c of the upper pressing surface <NUM> and the width d of the lower pressing surface <NUM> are the same as each other, an effect of the force at which the upper jig <NUM> pushes relatively downward the end <NUM> of the upper cover circumferential portion may be less than that in Embodiment <NUM> that will be described below.

Embodiment <NUM> according to the present invention may be different from Embodiment <NUM> in that an upper pressing surface and a lower pressing surface have shapes different from those in Embodiment <NUM>.

The contents that are duplicated with Embodiment <NUM> will be omitted as much as possible, and Embodiment <NUM> will be described with a focus on the differences. That is, it is obvious that the contents that are not described in Embodiment <NUM> may be regarded as the contents of Embodiment <NUM> if necessary.

Referring to <FIG>, in the method for manufacturing the secondary battery according to Embodiment <NUM> of the present invention, in a welding process, an upper pressing surface <NUM> that is a surface pressing an end <NUM> of an upper cover circumferential portion in an upper jig <NUM> may further extend in a direction to laser L than a lower pressing surface <NUM> that is a surface pressing an end <NUM> of a lower can circumferential portion in a lower jig <NUM>.

In this case, force at which the upper jig <NUM> pushes relatively down the end <NUM> of the upper cover circumferential portion <NUM> may act more strongly. Thus, close contact may be made more reliably at a bonding portion at which welding is performed.

In Embodiment <NUM> of the present invention, a height b of the accommodation part <NUM> may be higher than a height a of the end <NUM> of the lower can circumferential portion. This is the same as in Embodiment <NUM>.

Also, in Embodiment <NUM> of the present invention, a width c of the upper pressing surface <NUM> may be greater than a width d of the lower pressing surface <NUM>. In addition, an outer end point <NUM>-<NUM> of the upper pressing surface and an outer end point <NUM>-<NUM> of the lower pressing surface may be disposed in the same vertical line. When each of the upper jig <NUM> and the lower jig <NUM> has the above-described shape, the lower can circumferential portion <NUM> and the upper cover circumferential portion <NUM> may be gripped and supported remarkably stably at upper and lower portions thereof without shaking.

In the method for manufacturing the secondary battery according to Embodiment <NUM> of the present invention, the upper jig <NUM> is provided in a right-angled triangle shape in cross section, and in the welding process, the upper jig <NUM> may be disposed so that an oblique side <NUM> of the right-angled triangle faces the laser L. When formed as described above, when the laser irradiates the bonding portion onto the circumferential portion of the cover, possibility that a laser nozzle moves to collide with the upper cover <NUM> may be reduced. Thus, more stable welding may be possible.

A secondary battery according to the present invention comprises a lower can, an upper cover, and an electrode assembly and may have the following characteristics.

The electrode assembly may be formed by alternately stacking electrodes and separators. The lower can may comprise an accommodation part in which the electrode assembly is accommodated. The upper cover may have a shape to cover an upper opening of the lower can.

The lower can comprises a lower can circumferential portion that is a portion extending outward from an edge of the accommodation part, and the upper cover comprises an upper cover circumferential portion bonded to the lower can circumferential portion as a circumferential area of the upper cover. A bonding portion that is a point at which the lower can circumferential portion and the upper cover circumferential portion are bonded to each other may have a height less than a height b of the accommodation part. In addition, a height of a central point of the upper cover may be higher than the height b of the accommodation part.

The secondary battery according to the present invention may have significantly improved sealing properties at the bonding portion.

A lower can and an upper cover were welded to each other. Welding was performed using 500W class laser of IPG company. The welding was performed under conditions, in which a laser beam size is <NUM> to <NUM> (micrometer), power is <NUM> W to <NUM> W, a material of the lower can is SUS316L, a thickness of the lower can is <NUM>, a material of the upper cover is SUS316L, and a thickness of the upper cover is <NUM>.

In Comparative Example <NUM>, the welding was performed under a condition, in which a value b-a obtained by subtracting a height a of an end of the lower can circumferential portion from a height b of an accommodation part is <NUM>.

A lower can and an upper cover were welded to each other according to the present invention. Welding was performed using 500W class laser of IPG company. The welding was performed under conditions, in which a laser beam size is <NUM> to <NUM> (micrometer), power is <NUM> W to <NUM> W, a material of the lower can is SUS316L, a thickness of the lower can is <NUM>, a material of the upper cover is SUS316L, and a thickness of the upper cover is <NUM>.

In Manufacturing Example <NUM>, the welding was performed under a condition, in which a value b-a obtained by subtracting a height a of an end of the lower can circumferential portion from a height b of an accommodation part is <NUM>.

Welding was performed under the same condition as in Manufacturing Example <NUM> except that the welding was performed under the condition, in which a value b-a obtained by subtracting a height a of an end of a lower can circumferential portion from a height b of an accommodation part is <NUM>.

<FIG> is a view illustrating experimental results of testing weldability for each of Comparative Example and Manufacturing Examples <NUM> and <NUM>.

In the case of Comparative Example <NUM>, in which the welding is performed under the condition, in which the value b-a is <NUM>µ m (i.e., values of a and b are the same), a cross-sectional view of the welded portion is illustrated at a left ① in <FIG>. In Comparative Example <NUM>, it is seen that an non-welded portion occurs due to an occurrence of a gap between the lower can and the upper cover.

In the case of Manufacturing Example <NUM>, in which the welding is performed under the condition, in which the value b-a is <NUM> (i.e., the value b is greater <NUM> than the value a), a cross-sectional view of the welded portion is illustrated in the middle ② in <FIG>. In the case of Manufacturing Example <NUM>, it is seen that good welding is achieved because a gap does not occur between the lower can and the upper cover.

In the case of Manufacturing Example <NUM>, in which the welding is performed under the condition, in which the value b-a is <NUM>µ m (i.e., the value b is greater <NUM>µ m than the value a), a cross-sectional view of the welded portion is illustrated at a right ③ in <FIG>. In the case of Manufacturing Example <NUM>, it is seen that the welding is performed in a state in which strong adhesion is provided between the lower can and the upper cover, and stronger bonding is provided rather than that of Manufacturing Example <NUM>.

Claim 1:
A method for manufacturing a secondary battery, the method comprising:
a welding preparation process of preparing a lower can (<NUM>)
comprising an accommodation part (<NUM>) in which an electrode
assembly is accommodated, and an upper cover (<NUM>) covering an
upper opening of the lower can;
a gripping process of gripping an end of a lower can circumferential portion (<NUM>)
and an end of an upper cover circumferential portion (<NUM>)
at upper and lower portions by using an upper jig (<NUM>) and a lower jig (<NUM>)
in order to weld the lower can circumferential portion that is a portion extending outward from an edge of the accommodation part to the upper cover circumferential portion that is a circumferential area of the upper cover; and
a welding process of irradiating laser (L) onto a bonding
portion that is a point, at which the lower can circumferential portion (<NUM>)
and the upper cover circumferential portion (<NUM>)
are bonded to each other, to bond the lower can circumferential portion to the upper cover circumferential portion through laser welding,
wherein, in the welding process, the laser welding is performed in a state in which a height (b) of the accommodation part is formed to be higher than a height (a) of the end (<NUM>)
of the lower can circumferential portion.