KR20200107280A - Method for Optimizing Ultrasonic Welding Process of Lithium Secondary Battery and Apparatus Thereof - Google Patents

Abstract

The present invention relates to an ultrasonic weldig process optimizing method of a lithium secondary battery. Specifically, the present invention relates to a method for optimizing process conditions for ultrasonic welding an electrode tab of the lithium secondary battery to an electrode lead. According to the ultrasonic welding process optimizing method of the present invention, compared to a conventional method, welding defects of an object to be welded are reduced, welding strength is excellent, and optimal ultrasonic welding conditions can be easily derived. An ultrasonic welding method includes the following steps of: (s1) setting an inspection area on the object to be welded; (s2) performing ultrasonic welding; (s3) measuring a temperature and surface pressure of the inspection area; (s4) calculating a yield stress of the object to be welded; and (s5) adjusting the welding conditions.

Description

Ultrasonic welding method and apparatus for lithium secondary battery {Method for Optimizing Ultrasonic Welding Process of Lithium Secondary Battery and Apparatus Thereof}

The present invention relates to a method of ultrasonic welding of a lithium secondary battery, and more particularly, to a method of optimizing process conditions for ultrasonic welding an electrode tab of a lithium secondary battery to an electrode lead.

As the price of energy sources rises due to the depletion of fossil fuels and interest in environmental pollution increases, the demand for eco-friendly alternative energy sources is becoming an indispensable factor for future life. In particular, technology development for mobile devices As the demand and demand increase, the demand for secondary batteries as an energy source is rapidly increasing.

Typically, in terms of the shape of the battery, there is a high demand for prismatic secondary batteries and pouch-type secondary batteries that can be applied to products such as mobile phones with a thin thickness. In terms of materials, lithium-ion batteries with high energy density, discharge voltage, and output stability, There is high demand for lithium secondary batteries such as lithium ion polymer batteries.

In general, a secondary battery refers to a battery capable of charging and discharging unlike a primary battery that cannot be charged, and is widely used in electronic devices such as mobile phones, notebook computers, camcorders, or electric vehicles. In particular, lithium secondary batteries have an operating voltage of about 3.6V, about three times the capacity of nickel-cadmium batteries or nickel-hydrogen batteries, which are widely used as power sources for electronic equipment, and have a high energy density per unit weight. There is a trend of increasing rapidly.

These lithium secondary batteries mainly use lithium-based oxides and carbon materials as a positive electrode active material and a negative electrode active material, respectively. A lithium secondary battery includes a cell assembly in which unit cells having a structure in which a positive electrode plate and a negative electrode plate are respectively coated with such a positive electrode active material and a negative electrode plate are disposed with a separator therebetween, and an exterior material case for sealing and storing the cell assembly together with an electrolyte. Equipped.

Lithium secondary batteries are classified into a can-type secondary battery in which a cell assembly is embedded in a metal can and a pouch-type secondary battery in which a cell assembly is embedded in a pouch case of an aluminum laminate sheet according to the shape of the case of the case.

Pouch-type secondary batteries are in the spotlight as a power source for electric vehicles or hybrid vehicles recently because they have advantages in that manufacturing costs are low, energy density is high, and a large-capacity battery pack can be easily configured through series or parallel connection.

Such a pouch-type secondary battery has a structure in which a cell assembly to which an electrode lead formed in a plate shape is connected is sealed together with an electrolyte in a pouch case. Part of the electrode lead is exposed to the outside of the pouch case, and the exposed electrode lead is electrically connected to a device in which the secondary battery is mounted, or is used to electrically connect the secondary batteries to each other. Specifically, as shown in FIG. 1, an electrode assembly 10, a plurality of electrode tabs 20 extending from the electrode assembly, an electrode lead 30 welded to and coupled to the electrode tabs 20, and an electrode assembly ( It is configured to include a pouch exterior material 40 to accommodate 10).

On the other hand, among the techniques used when welding the electrode tab 20 and the electrode lead 30, ultrasonic welding has an advantage in that it has a good heat-affected zone (HAZ) and is easy to weld thin metal foils. Ultrasonic welding generally refers to a solid state welding in which an ultrasonic vibration of 10000Hz to 75000Hz is generated, and ultrasonic vibration is applied locally between metals to weld without melting the object to be welded. That is, when ultrasonic vibration is applied by an ultrasonic welding machine in a state in which the electrode tab 20 and the electrode lead 30, which are the object to be welded, are in contact with each other, the vibration and vibration on the contact surface of the electrode tab 20 and the electrode lead 30 While frictional heat is generated together, the electrode tab 20 and the electrode lead 30 are welded to each other without melting.

The anode structure composed of the anode tab and the anode lead is mainly aluminum, and the cathode structure composed of the cathode tab and the cathode lead is mainly copper or nickel-plated copper. Due to this dualized material, conditions of the ultrasonic welding process Will also be different.

Particularly, in the case of the anode structure made of aluminum, due to weak temperature and pressure, some over-welded portions are partially broken, causing welding failure. The defect caused by the overall fracture of the welding area can be visually confirmed, but the partial welding defect at a specific point is very difficult to confirm with the naked eye.

In this regard, as a method of checking the state of ultrasonic welding, in the prior art, a point where the color of the pressure-sensitive paper appears through a pressure-sensitive paper on the object to be welded is visually inspected to confirm the welding state and defects of the object to be welded. .

However, the above method is to find the optimal value by using the Trial & Error method while visually checking the result that only appears as color difference on the pressure-sensitive paper and adjusting the process conditions arbitrarily, so finely adjusting the ultrasonic process conditions in which various variables exist impossible. In addition, since the problem of unwelding or over-welding that is not checked with the naked eye may occur, the reliability is not high.

In this regard, Korean Patent Publication No. 10-2012-0096621 (Patent Document 1) and Korean Patent Publication No. 10-2015-0033268 (Patent Document 2) propose a method for increasing the reliability by the vision check. In addition, in the ultrasonic welding process of high difficulty, a method for precisely optimizing the welding conditions has not been proposed.

Korean Patent Publication No. 10-2012-0096621 Korean Patent Publication No. 10-2015-0033268

An object of the present invention is to make it possible to precisely adjust the ultrasonic process condition setting by converting the ultrasonic welding state checked with the naked eye through a vision inspection using a pressure-sensitive paper. Further, it is an object of the present invention to provide a method capable of more easily deriving optimized ultrasonic welding conditions even in the case of high-difficulty ultrasonic welding, which has been difficult to find an optimum condition due to easy fracture by the conventional method.

In order to achieve the above object, the ultrasonic welding method according to the present invention may include the following steps.

Setting an inspection area on the object to be welded (s1);

Performing ultrasonic welding on the welded portion including the inspection area of the object to be welded (s2);

Measuring the temperature and surface pressure of the inspection area (s3);

Calculating the yield stress of the object to be welded at the temperature measured in step s3 (s4);

Comparing the measured surface pressure in the step s3 and the yield stress in the step s4 to adjust the welding condition (s5).

By optimizing the ultrasonic welding conditions through the above process, it is possible to reduce the deviation of the welding state, and it is also possible to further increase the welding strength.

The surface pressure is a pressure applied to the inspection area from the horn of the welding machine, and when a pressure greater than the yield stress of the object to be welded is applied during ultrasonic welding, the object to be welded may be deformed or broken, resulting in defects.

On the other hand, in step s5, the welding conditions can be more precisely adjusted by comparing the elastic modulus of the object to be welded together with the yield stress and the surface pressure.

In this case, the welding condition is one or two or more of the ultrasonic frequency, the welding pressure, and the welding time, so that the welding state of the welding part is changed accordingly.

Among the welding conditions, the ultrasonic frequency is usually 10000 to 75000 Hz, but as a frequency suitable for ultrasonic welding of electrode tabs and electrode leads of a secondary battery, it may be 15000 to 40000 Hz, and more preferably 20000 to 25000 Hz. If the frequency is less than 15000Hz, welding may not be performed, or even if welding is performed, only partial welding may cause defects. In addition, when the frequency exceeds 40000Hz, fracture may easily occur when welding a material of weak rigidity such as an electrode tab.

In addition, the welding pressure may be preferably 100 to 900 kPa, more preferably 300 to 700 kPa. The welding pressure is the pressure applied by the horn to the object to be welded, and if it is less than 100 kPa, the vibration is not sufficiently transmitted to the object to be welded, so that the welding area may be reduced or welding may not be possible. On the other hand, when it exceeds 900 kPa, over-welding or fracture may occur when welding electrode tabs for a thin film type secondary battery.

The welding time may be 0.1 seconds to 2 seconds, more preferably 0.2 to 1 second. If the welding time is too short (less than 0.1 seconds), welding may not be possible, and if the welding time exceeds 2 seconds, excessive frictional heat is generated, and welding deviation may increase or overwelding may occur.

The object to be welded may be specifically made of copper or aluminum, and more specifically, may be an electrode lead and/or an electrode tab of a secondary battery.

The temperature and pressure are measured by arranging a sheet-type pressure sensor and a sheet-type temperature sensor on an object to be welded. By using a sheet-type, it is possible to easily stack and place on the object to be welded in the form of a thin film. The stacking order of the temperature sensor and the pressure sensor may be any first, but in order to more accurately measure the temperature of the object to be welded, it is preferable to place it on the object, and the pressure sensor is the pressure transmitted from the horn. It is preferable to place it on the temperature sensor in order to accurately measure the temperature.

The inspection area may consist of two or more measurement points spaced apart at the same interval. Since each of the sensors can measure temperature and pressure at a plurality of points, respectively, when a plurality of measurement points are set for each location within an area of a welding area, a welding state can be further determined in detail.

Specifically, it is preferable that the welding condition adjustment is made within a range in which the surface pressure of the inspection area is less than the yield stress. The surface pressure of the inspection area is due to the force applied from the horn, and if it is greater than the yield stress, deformation and/or fracture of the welded object may occur, so it is important to adjust the conditions to a range smaller than the yield stress. .

The ultrasonic welding process optimization apparatus for performing the optimization method may include the following configuration.

A secondary battery including an electrode tab and an electrode lead;

An ultrasonic welding machine including a horn and an anvil, and welding the electrode tabs and electrode leads using ultrasonic waves;

A sensor that measures the temperature and pressure of the welding area during ultrasonic welding.

The ultrasonic welding machine controls the electrode tab and the electrode lead of the secondary battery to ultrasonically weld, and at the same time, measures the temperature and pressure of the welded part, and the ultrasonic frequency described above based on the measurement result using this optimization device. It is possible to adjust the welding conditions, such as welding pressure and welding time.

In addition, the sensor for measuring the temperature and pressure is preferably in the form of a sheet and interposed on the electrode tab and the electrode lead, and the stacking order of the sensors may be any first, but the temperature sensor and the pressure sensor are sequentially stacked. It is more preferable to do it.

The present invention is an improvement of the existing method of repetitive trial and error through a vision inspection to visually check the ultrasonic welding condition in setting the ultrasonic welding process conditions, and optimizing the ultrasonic welding process conditions arbitrarily. The method for optimizing ultrasonic processing conditions according to the present invention is a method of optimizing ultrasonic processing conditions based on measured data such as temperature and pressure applied to the surface of a welded object during ultrasonic welding, yield stress, and elastic modulus. According to the method, it is possible to easily derive ultrasonic welding conditions, which were difficult to set by the conventional method, through monitoring each data of the physical properties and process conditions of the object to be welded.

In addition, when ultrasonic welding is performed by optimizing the process conditions according to the method of the present invention, welding defects are significantly reduced, and the welding strength of the object to be welded may be higher than that of the conventional method.

1 is an exploded perspective view showing the structure of a generally used pouch-type lithium secondary battery.
2 shows each configuration according to an embodiment of the ultrasonic welding process optimization apparatus according to the present invention.
3 is a perspective view illustrating an embodiment in which a horn of an ultrasonic welding process optimizing apparatus welds an electrode structure comprising an electrode tab and an electrode lead according to the ultrasonic welding process of the present invention.
4 illustrates a detailed structure of a horn according to an embodiment of the ultrasonic welding process optimization apparatus according to the present invention.
5 shows an example in which a plurality of measurement points are set in an inspection area of an object to be welded according to the present invention.
6 is a photograph of a pressure-sensitive paper used for vision inspection according to an existing ultrasonic welding state checking method.

Terms used in the present specification and claims are not limited to their usual or dictionary meanings and should not be interpreted, and that the inventor can appropriately define the concept of terms in order to describe his own invention in the best way. Based on the principle, it should be interpreted as a meaning and concept consistent with the technical idea of the invention. Therefore, the configuration shown in the embodiments described in the present specification is only one of the most preferred embodiments of the present invention, and does not represent all the technical spirit of the present invention, and various equivalents that can replace them at the time of the present application And it should be understood that there may be variations.

In the entire specification of the present application, when a certain part is said to be ``connected'' with another part, this includes not only ``directly connected'' but also ``electrically connected'' with another element interposed therebetween. .

Throughout this specification, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, actions, elements, parts, or combinations thereof described in the specification, but one or more other It is to be understood that the presence or addition of features, numbers, steps, actions, components, parts, or combinations thereof, does not preclude in advance the possibility of being excluded. Further, when a part such as a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the case where the other part is "directly above", but also the case where there is another part in the middle. Conversely, when a part such as a layer, film, region, plate, etc. is said to be "under" another part, this includes not only the case where the other part is "directly below", but also the case where there is another part in the middle. In addition, in the present application, the term "over" may include not only the upper part but also the lower part.

The terms "about" and "substantially" used throughout this specification are used as meanings at or close to the numerical values when manufacturing and material tolerances specific to the stated meanings are presented, and are accurate to aid understanding of the present application. Or absolute figures are used to prevent unfair use of the stated disclosure by unconscionable infringers.

In the entire specification of the present application, the term "combination(s) thereof" included in the expression of the Makushi form means one or more mixtures or combinations selected from the group consisting of the constituent elements described in the expression of the Makushi form, It means to include at least one selected from the group consisting of the above components.

Hereinafter, the present invention will be described in detail with reference to the drawings.

1 is an example of an object to be welded according to the present invention, showing a structure of an electrode tab, an electrode lead, and a pouch-type secondary battery including the same. The pouch-type secondary battery includes an electrode assembly 10, a plurality of electrode tabs 20 extending from the electrode assembly, an electrode lead 30 welded to and coupled to the electrode tabs 20, and an electrode assembly 10 It is configured to include a pouch packaging material 40 for accommodating, and the electrode tab 20 and the electrode lead 30 are electrically connected by welding. At this time, thermal welding or ultrasonic welding techniques may be used, but thermal welding has a disadvantage that may affect the internal electrode assembly, and since uniformity is lower than that of ultrasonic welding, ultrasonic welding is more preferred. Accordingly, the present invention provides an ultrasonic welding method based on measurement data in thin metal foil welding such as welding of electrode tabs and electrode leads.

2 is a view showing the configuration of an ultrasonic welding apparatus according to an embodiment of the present invention.

3 is a diagram illustrating an electrode structure of a secondary battery that is ultrasonically welded by an ultrasonic welding apparatus according to an exemplary embodiment of the present invention.

2 and 3, the ultrasonic welding apparatus 100 according to an embodiment of the present invention includes an ultrasonic oscillator 110, an ultrasonic vibrator 120, a booster 130, and a horn 140. Includes.

The ultrasonic oscillator 110 converts an AC current of 60 Hz into a high-frequency current of 20 kHz or more and supplies it to the ultrasonic vibrator 120.

The ultrasonic vibrator 120 serves to convert electrical energy into mechanical energy, and is also called ultrasonic piezoelectric. That is, the high-frequency current generated by the ultrasonic oscillator 110 is converted into ultrasonic waves by the ultrasonic vibrator 120, and the converted ultrasonic waves move to the booster 130. The booster 130 amplifies the received ultrasonic wave and delivers it to the horn 140.

The horn 140 pressurizes the surfaces of a plurality of electrode tabs placed on the anvil 170 with a predetermined load and simultaneously applies the amplified ultrasonic waves transmitted from the booster 130 to the electrode tabs, thereby Each of the electrode tabs 20 made of tabs is first welded. In addition, the horn 140 presses the surface of the electrode lead 30 with a constant load in a state in which the electrode tab 20 and the electrode lead, which have been first welded, are in contact with each other, and the amplified ultrasonic wave transmitted from the booster 130 is By applying to the electrode lead 30, the electrode lead 30 and the electrode tab 20 are respectively welded.

That is, the horn 140 presses the electrode lead 30 in contact with the electrode tab 20 with a predetermined pressure and applies the amplified ultrasonic wave received from the booster 130 to the electrode lead 30. Accordingly, friction heat is generated on the contact surface between the electrode tab 20 and the electrode lead 30, and the electrode tab 20 and the electrode lead 30 are electrically connected while being welded to each other through the generated friction heat.

4 is an embodiment of the horn 140, which is configured to transmit ultrasonic vibration more evenly.

Referring to FIG. 4, it may include a plurality of contact members 141 that transmit ultrasonic vibrations to the horn 140 and the electrode lead 30 and/or the electrode tab 20.

The end of the contact member 141 is formed in a predetermined area, and the end area of the contact member 141 determines the density of the pressing surface of the horn 140. Here, the pressure surface density of the horn 140 is a density with respect to the end area of the horn 140 that transmits ultrasonic waves while pressing the electrode lead 30, and is included in the unit area of the lower surface of the horn 140 ( It means the end area of 141).

The end areas of the contact members 141 formed on the horn 140 are the same, but if necessary, a plurality of contact members 141 may be densely formed, and accordingly, it is larger than the sum of the end areas. It is possible to form a high pressure surface density. Incidentally, in order to improve the welding strength to a high level, it is possible to set the pressing surface density high.

Meanwhile, a sheet-shaped sensor may be stacked on the electrode tab and the electrode lead, respectively. Specifically, the pressure sensor 150 and the temperature sensor 160 may be stacked. The order of stacking the pressure sensor 150 and the temperature sensor 160 may be any first, but the electrode tab 20 and/or First stacking the temperature sensor 160 on the electrode lead 30 to accurately measure the temperature change of the object to be welded, and then stacking the pressure sensor 150 on it, more accurately measures the pressure received from the horn 140 It is more preferable because it is advantageous for the following.

In addition, the shape of the contact member 141 of the present invention is shown to be a pin shape in FIG. 4, but the present invention is not limited thereto, and the shape of a square pillar, a triangular pillar, a tapered shape, a hemispherical shape, a horn It should be clarified that contact members of various shapes such as shape, wedge shape, etc. are adopted and can be applied to ultrasonic welding.

Meanwhile, in the present invention, an inspection area is set during ultrasonic welding, and a temperature and pressure are measured in the inspection area by a sensor. In this case, the inspection area may include a plurality of measurement points as shown in FIG. 5. The more the measurement points are formed at uniform intervals as possible, the more precisely the welding state can be determined.

Hereinafter, the ultrasonic welding method and apparatus therefor according to the present invention will be described in more detail.

The ultrasonic welding method according to the present invention may include the following steps.

Setting an inspection area on the object to be welded (s1);

Performing ultrasonic welding on the welded portion including the inspection area of the object to be welded (s2);

Measuring the temperature and surface pressure of the inspection area (s3);

Calculating the yield stress of the object to be welded at the temperature measured in step s3 (s4);

Comparing the measured surface pressure in the step s3 and the yield stress in the step s4 to adjust the welding condition (s5).

By optimizing the ultrasonic welding conditions through the above process, it is possible to reduce the deviation of the welding state, and it is also possible to further increase the welding strength.

The surface pressure is a pressure applied to the inspection area from the horn of the welding machine, and when a pressure greater than the yield stress of the object to be welded is applied during ultrasonic welding, the object to be welded may be deformed or broken, resulting in defects.

On the other hand, in step s5, the welding conditions can be more precisely adjusted by comparing the elastic modulus of the object to be welded together with the yield stress and the surface pressure. Specifically, in adjusting the surface pressure according to the yield stress, it is possible to more precisely adjust the numerical range adjusted accordingly in consideration of the magnitude of the elastic modulus.

In this case, the welding condition is one or two or more of the ultrasonic frequency, the welding pressure, and the welding time, so that the welding state of the welding part is changed accordingly.

Among the welding conditions, the ultrasonic frequency is preferably usually 10000 to 75000 Hz, but as a frequency suitable for ultrasonic welding of electrode tabs and electrode leads of a secondary battery, it may be 15000 to 40000 Hz, more preferably 20000 to 25000 Hz. I can. If the frequency is less than 15000Hz, welding may not be performed, or even if welding is performed, only partial welding may cause defects. In addition, when the frequency exceeds 40000Hz, fracture may easily occur when welding a material of weak rigidity such as an electrode tab.

In addition, the welding pressure may be preferably 100 to 900 kPa, more preferably 300 to 700 kPa. The welding pressure is the pressure applied by the horn to the object to be welded, and if it is less than 100 kPa, the vibration is not sufficiently transmitted to the object to be welded, so that the welding area may be reduced or welding may not be possible. On the other hand, when it exceeds 900 kPa, over-welding or fracture may occur when welding electrode tabs for a thin film type secondary battery.

The welding time may be 0.1 seconds to 2 seconds, more preferably 0.2 to 1 second. If the welding time is too short (less than 0.1 seconds), welding may not be possible, and if the welding time exceeds 2 seconds, excessive frictional heat is generated, and welding deviation may increase or overwelding may occur.

The object to be welded may be specifically made of copper or aluminum, and copper may be plated. More preferably, the structure of the secondary battery may be an electrode tab and/or an electrode lead, which is composed of a thin film.

The temperature and pressure are measured by arranging a sheet-type pressure sensor and a sheet-type temperature sensor on an object to be welded. By using a sheet-type, it is possible to easily stack and place on the object to be welded in the form of a thin film. The stacking order of the temperature sensor and the pressure sensor may be any first, but in order to more accurately measure the temperature of the object to be welded, it is preferable to place it on the object, and the pressure sensor is the pressure transmitted from the horn. It is preferable to place it on the temperature sensor in order to accurately measure the temperature.

The inspection area may consist of two or more measurement points spaced apart at the same interval. Since each of the sensors can measure temperature and pressure at multiple points, a plurality of measurement points can be set for each location within the area of the welding area, and the greater the number of set measurement points, the more detailed analysis of the welding state can be performed. I can.

Specifically, it is preferable that the welding condition adjustment is made within a range in which the surface pressure of the inspection area is less than the yield stress. The surface pressure of the inspection area is due to the force applied from the horn, and if it is greater than the yield stress, deformation and/or fracture of the welded object may occur, so it is important to adjust the conditions to a range smaller than the yield stress. .

The ultrasonic welding process optimization apparatus for performing the optimization method may include the following configuration.

A secondary battery including an electrode tab and an electrode lead;

An ultrasonic welding machine including a horn and an anvil, and welding the electrode tabs and electrode leads using ultrasonic waves;

A sensor that measures the temperature and pressure of the welding area during ultrasonic welding.

The ultrasonic welding machine controls the electrode tab and the electrode lead of the secondary battery to ultrasonically weld, and at the same time, measures the temperature and pressure of the welded part, and the ultrasonic frequency described above based on the measurement result using this optimization device. It is possible to adjust the welding conditions, such as welding pressure and welding time.

For example, when the ultrasonic frequency is increased, the temperature rise due to frictional heat caused by vibration becomes steep, and the welding time can be shortened. However, in this case, since the yield stress is lowered, there is a problem in that deformation or fracture can easily occur.

In the case of welding time, if the time is too short, welding may not be sufficiently performed. However, if welding is performed for an excessively long time, the temperature of the object to be welded may rise excessively, resulting in welding failure due to deformation.

In the case of the welding pressure, the higher the pressure, the higher the efficiency of transmitting the vibration generated from the ultrasonic vibrator through the horn, but when a pressure exceeding the yield stress of the object to be welded is applied, deformation and welding failure may occur.

Therefore, the above three conditions need to be adjusted in consideration of each interaction. Accordingly, the present invention provides a welding method capable of optimizing the above conditions based on specific data.

In addition, the sensor for measuring the temperature and pressure is preferably interposed on the electrode tab and the electrode lead, and the order of interposition of the sensor may be any first, but the temperature sensor is interposed first based on the anvil This is a method of interposing a pressure sensor on the top, and is more preferable when sequentially stacked. In this case, it is preferable to use the temperature and pressure sensor in the form of a sheet.

Hereinafter, examples will be described in detail to aid understanding of the present invention. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited by the following examples. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example 1

In the ultrasonic welding process optimizing apparatus 100 as shown in FIG. 2, two aluminum thin films, which are materials for the positive electrode tab and the positive electrode lead, were prepared and ultrasonic welding was performed. The thickness of the aluminum thin film used was 50 μm and 200 μm, respectively.

First, the thin films were placed on the anvil 170 so as to overlap. Then, the sheet-shaped temperature sensor 160 and the pressure sensor 150 were sequentially placed on the overlapping thin films.

The inspection area to measure temperature and pressure was set in the center based on the welding area where the overlapping thin films are welded.

After operating the ultrasonic oscillator 110, ultrasonic welding was performed by applying a vibration of 20000 Hz to the thin film with the horn 140 for 0.3 seconds. At this time, a final temperature raised by frictional force due to vibration and surface pressure applied by the horn 140 in the inspection area was measured using a temperature sensor and a pressure sensor.

Example 2

After ultrasonic welding was performed in the same manner as in Example 1, except that a copper thin film of 50 μm and 200 μm, which is a material of the negative electrode tab and the negative electrode lead, was prepared, respectively, surface pressure and temperature were measured.

Meanwhile, the yield stress of the same to-be-welded (50 μm in thickness) as in Examples 1 and 2 was calculated according to the tensile test method of ATM E8 standard under the measured maximum temperature conditions of Examples 1 and 2. Yield stress refers to the maximum amount of stress that can be applied to a material without causing plastic deformation. It is the stress at which the material exhibits a certain permanent deformation and is a practical approximation of the elastic limit. This is measured from the stress-strain plot of the offset yield strength. It is the stress corresponding to the intersection (crossing line) in the stress-strain curve, and it is a straight line that is translated in parallel due to the offest of its straight section at a specific strain. In this example, it was carried out at an offset of 0.2%, which is usually carried out in metal. Meanwhile, the elastic modulus of the temperature condition was additionally calculated and shown in Table 1 below together with the measurement results.

division Material Thin film thickness
(㎛) Welding time
(second) Maximum temperature
(℃) Surface pressure
(kPa) Yield stress
(kPa) Modulus of elasticity evaluation Example 1 aluminum 50 0.3 46 700 600 69 Overwelding 200 Example 2 Copper 50 0.3 48 700 800 110 fitness 200

As shown in Table 1, in the case of Example 2 in which the copper thin film was welded, the welding condition was found to be suitable, but in the case of Example 1 using aluminum, it can be seen that the surface pressure was higher than the yield stress and over-welding occurred. Therefore, in order to obtain a suitable welding state, it is possible to adjust the welding conditions within an optimum range, such as lowering the frequency, shortening the welding time, or directly lowering the applied pressure. In this case, in consideration of the size of the elastic modulus, a numerical range to be adjusted when the process conditions are changed accordingly may be determined.

Comparative Example 1

Instead of measuring two aluminum thin films as in Example 1 using a temperature sensor and a pressure sensor, an experiment was conducted using a conventional pressure-sensitive paper. The results are shown in FIG. 6. In the case of the experiment of Comparative Example 1, it was predicted that the experiment was conducted under the same conditions as in Example 1 except for the measurement method, and thus it was expected to be over-welded as in Example 1. However, as shown in FIG. 6, it was not possible to determine whether or not overwelded was performed only by observing the pressure-sensitive paper with the naked eye.

10: electrode assembly
20: electrode tab
30: electrode lead
40: pouch exterior material
100: ultrasonic welding process optimization device
110: ultrasonic oscillator
120: ultrasonic oscillator
130: booster
140: horn
141: contact member
150: pressure sensor
160: temperature sensor
170: anvil

Claims (15)

Setting an inspection area on the object to be welded (s1);
Performing ultrasonic welding on the welded portion including the inspection area of the object to be welded (s2);
Measuring the temperature and surface pressure of the inspection area (s3);
Calculating the yield stress of the object to be welded at the temperature measured in step s3 (s4);
Comprising the measured surface pressure in the step s3 and the yield stress in the step s4 to adjust the welding condition (s5).
The method of claim 1,
The surface pressure is a pressure applied to the inspection area from the horn of the welding machine.
The method of claim 1,
The ultrasonic welding method to adjust the welding conditions by comparing the elastic modulus of the object to be welded together in step s5.
The method of claim 1,
The welding conditions in step s5 are ultrasonic frequency, welding pressure, and welding time.
The method of claim 4,
The ultrasonic welding method is that the ultrasonic frequency is 15000 to 40000Hz.
The method of claim 4,
The ultrasonic welding method that the welding pressure is 100 to 900 kPa
The method of claim 4,
The ultrasonic welding method that the welding time is 0.1 seconds to 2 seconds
The method of claim 1,
The ultrasonic welding method that the object to be welded is a copper or aluminum material.
The method of claim 1,
The ultrasonic welding method that the object to be welded is an electrode lead or an electrode tab.
The method of claim 1,
The temperature and pressure are measured by placing a sheet-type sensor on the inspection area.
The method of claim 1,
The ultrasonic welding method, wherein the inspection area is made of two or more measuring points spaced at equal intervals.
The method of claim 1,
The welding condition adjustment is made within a range in which the surface pressure of the inspection area is smaller than the yield stress.
A secondary battery including an electrode tab and an electrode lead;
An ultrasonic welding machine including a horn and an anvil, and welding the electrode tabs and electrode leads using ultrasonic waves;
Includes; a sensor for measuring the temperature and pressure of the object to be welded during ultrasonic welding,
The ultrasonic welding machine controls the electrode tab and the electrode lead of the secondary battery to be ultrasonically welded, and at the same time,
An ultrasonic welding device that adjusts welding conditions by measuring the temperature of the object to be welded and the pressure applied to the object to be welded.
The method of claim 13,
The welding conditions are ultrasonic frequency, welding pressure, and welding time of the ultrasonic welding device.
The method of claim 13,
The ultrasonic welding device that the sensor for measuring the temperature and pressure is interposed on the object to be welded.

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