KR101770730B1 - Method for nonchromic surface treatment of the tab lead for secondary batteries - Google Patents

Abstract

The present invention relates to a chrome-free surface treatment method of a tab lead for a secondary battery, and more particularly, to a method for treating a chromium free surface of a tap lead comprising a tap lead comprising a step of forming a metal oxide layer on the surface of the metal tap through an anodic oxidation process using the metal tab as an anode A surface treatment method of the present invention. The surface treatment method according to the present invention has an effect of improving the bonding strength with the polymer film as compared with the metal tap before the surface treatment, and the lifetime of the tab lead is markedly improved as the bonding strength is improved. Especially, since the use of chromium is not used, the surface of the tab lead can be processed in a human-friendly and environmentally friendly manner, so that it is possible to cope with the regulatory policy on the use of chromium.

Description

TECHNICAL FIELD [0001] The present invention relates to a non-chrome surface treatment method of a tab lead for a secondary battery,

The present invention relates to a chromium-free surface treatment method of a tab lead for a secondary battery, and more particularly, to a method for treating a chromium free surface of a tab lead for a secondary battery, Tab lead of a metal tab is eco-friendly.

BACKGROUND ART Lithium-ion batteries and lithium polymer secondary batteries are widely used in electronic devices such as cellular phones and notebook computers. In recent years, electric bicycles, hybrid vehicles (HEV), electric vehicles (EV), plug- ), And energy storage devices (ESS).

BACKGROUND ART Generally, a pouch type secondary battery includes an electrode group in which an anode, a separator, and a cathode are stacked, a tab lead that is drawn out from the electrode group and connected to an external terminal, And a casing for packaging the electrode assembly.

 Among these, a tab lead is a part that performs an insulating function between a positive electrode, a negative electrode, and a terminal electrode in a battery and a packaging material. The tab lead is composed of a negative electrode lead interposing a negative electrode material inside the lithium polymer secondary battery and a positive electrode lead connected to the positive electrode, and is an important component affecting the output and stability of the battery. The tap lead mainly has a plate or rod shape and is formed of a composite of a metal tab and a polymer film. Further, the metal is made of a conductive metal selected from aluminum (Al), nickel (Ni), copper (Cu), and alloys thereof, which are advantageous in terms of conductivity.

The tab lead facilitates the adhesion of the metal tab and the polymer film, and it is necessary to perform the surface treatment of the metal tab in order to prevent the occurrence of defects such as corrosion or peeling due to stimulation of the inner and outer portions of the battery in the actual use environment after bonding. The surface treatment technique is a very important technique because it affects the performance such as adhesion strength with the film and electrolyte resistance depending on the physical and chemical resistance of the surface treatment layer of the metal tab.

On the other hand, hexavalent chromium has been used as a material for the conventional surface treatment technique for increasing the bonding strength between the metal tab and the film. However, surfaces coated with hexavalent chromium exhibit excellent bonding strength and electrolyte resistance, while methods of surface treatment using chromium are restricted in their use worldwide due to human health hazards and environmental problems And is used in a limited manner.

In addition, there is an example in which trivalent chromium is used instead of hexavalent chromium. However, there is a risk that trivalent chromium can be oxidized to become hexavalent chromium, and therefore, in the manufacturers of lithium polymer secondary batteries including Europe, . Therefore, development of eco-friendly surface treatment technology without using chromium is an indispensable task according to the demand of the market.

 In this regard, Japanese Patent Application No. 2002-216741 discloses a method of coating a surface portion of a lead wire metal (tab) sealed with an insulator with a chemical conversion treatment layer and a method of coating a chromium acid aqueous solution containing a phosphate A common phosphate chromate treatment that chemically produces a film is disclosed. It is also described that a chemical conversion coating is formed by dipping a chemical treatment liquid containing a phenol resin-containing resin and containing a metal salt such as titanium or zirconium. As described above, as a chemical treatment for hydrofluoric acid, a chromium-based chemical conversion treatment is useful and has been used in many fields. However, in the field of environmental pollution, a chrome-free chemical treatment technique is developed in each field, and it is expected that a chromium-free process in the whole chromium will be required in the future.

However, in case of using chrome-free system, the performance is insufficient compared with the case of using chromium. However, there is a continuing need for surface treatment methods that exclude chromium-based materials. In the future, it is necessary to develop excellent surface treatment methods while completely excluding chromium in preparation for the global regulation of chromium materials.

Accordingly, in the present invention, a method of surface treatment of tab leads by an environmentally friendly method using no chromium has been proposed. In the case of forming a metal oxide on the tab lead surface, the adhesion strength between the metal tab and the polymer film A surface treatment method was developed, and the chromium-free surface treatment method of the present invention was completed.

An object of the present invention is to provide a chrome-free surface treatment method of a tab lead for a secondary battery.

In order to achieve the above object,

And forming a metal oxide layer on the surface of the metal tab through an anodizing process using the metal tab as an anode.

Further, according to the present invention,

Polishing the metal tab surface (step 1); And

And a step (step 2) of forming a metal oxide layer on the surface of the metal tapped surface in the step 1 through an anodizing process using the metal taps as an anode (step 2).

Further,

Providing a tap lead having a surface treated by the surface treatment method and coated with a metal oxide,

And a lithium polymer secondary battery including the tab lead.

The surface treatment method according to the present invention has an effect of improving the bonding strength with the polymer film as compared with the metal tap before the surface treatment, and the lifetime of the tab lead is markedly improved as the bonding strength is improved. Especially, since the use of chromium is not used, the surface of the tab lead can be processed in a human-friendly and environmentally friendly manner, so that it is possible to cope with the regulatory policy on the use of chromium.

1 is a graph showing the results of analysis of adhesive strength of tab leads in Experimental Example 1,
2 is a graph showing the results of surface contact angle analysis of tap leads in Experimental Example 2,
3 is an image of an aluminum metal tap of a control group observed under an optical microscope and a scanning electron microscope,
4 is an image obtained by observing an aluminum metal tap subjected to only electrolytic polishing with an optical microscope and a scanning electron microscope,
5 is an image obtained by observing an aluminum metal tap having undergone both electrolytic polishing and anodic oxidation by an optical microscope and a scanning electron microscope,
6 is an image obtained by observing an aluminum metal tap subjected to anodization only under an optical microscope and a scanning electron microscope.

Hereinafter, the present invention will be described in detail.

According to the present invention,

And forming a metal oxide layer on the surface of the metal tab through an anodizing process using the metal tab as an anode.

The tap lead is composed of a negative lead (MINUS LEAD) that connects the anode material inside the lithium polymer secondary battery and the outside, and a positive lead (PLUS LEAD) that is connected to the cathode. It is an important part to influence.

At this time, such a tab lead can be formed of a composite of a metal tab and a film (high molecular weight type such as polyolefin). Since the adhesive strength between the film and the metal tab affects the safety of the secondary battery, Is a very important part when considering the stability of the secondary battery.

However, in the prior art, in the surface treatment of metal taps, negative materials such as hexavalent chromium have been used, and means for improving the bonding strength between the metal taps and the film without using chromium are required.

Therefore, in the surface treatment method of the present invention, the metal oxide layer is formed on the surface of the metal tab so that the adhesion strength between the metal tab and the film can be improved without using chromium. Particularly, Thereby forming a metal oxide layer.

In the anodizing process, an object to be oxidized is applied as an anode, an electric current is applied, and an oxide film is formed on the anode surface by oxygen generated from the anode. In the surface treatment method of the present invention, a metal oxide is formed on the surface of the metal tab in view of the fact that the metal tab constituting the tab lead can be applied as the anode of the anodization process.

At this time, the metal tab may include at least one metal such as aluminum (Al), nickel (Ni), copper (Cu)

The metal oxide formed in the step 1 may be an oxide oxidized with a metal such as aluminum (Al), nickel (Ni), copper (Cu) or the like constituting the metal tap.

For example, aluminum may be used when the metal tab is used as a positive electrode of a secondary battery, and metal plated with copper, nickel, or nickel may be used when used as a negative electrode. However, But is not limited to.

The anodizing process may be performed under a voltage condition of 30 to 50 V for 30 to 90 seconds.

If the anodic oxidation process is performed outside the voltage and time conditions, the adhesive strength between the metal tab and the film may be lowered.

The metal oxide film may be formed to a thickness of 10 to 500 nm. If the thickness is less than 10 nm, there may be a problem that the electrolyte resistance of the metal oxide becomes weak. If the thickness exceeds 500 nm, the metal oxide film may be vulnerable to physical shock due to cracking of the metal oxide film, The electrolyte may penetrate through the electrolyte membrane.

Further, according to the present invention,

Polishing the metal tab surface (step 1); And

And a step (step 2) of forming a metal oxide layer on the surface of the metal tapped surface in the step 1 through an anodizing process using the metal taps as an anode (step 2).

Hereinafter, the method of surface treatment of the tab lead according to the present invention will be described in detail for each step.

In the surface treatment method of the tab lead according to the present invention, the step 1 is a step of polishing the surface of the metal tab.

The tap lead to be surface-treated in the present invention may be composed of a composite of a metal tap and a film, and the adhesion strength between the film and the metal tab is a very important part in terms of safety of the secondary battery. The surface treatment method of the present invention is intended to improve the bonding strength between the metal tab and the film, and particularly to a surface treatment capable of improving the bonding strength between the metal tab and the film without using chromium, which is highly regulated.

Thus, in the step 1 according to the present invention, the surface of the tab lead is polished to roughen the surface, and as the surface of the tab lead is roughened, the degree of adhesion between the metal oxide and the tab lead to be formed later can be further improved, A degreasing effect for removing organic and inorganic contaminants which may be present in the tab lead can be expected.

At this time, the polishing of step 1 may be performed by appropriately selecting a means or a method of roughening the surface of the tab lead, but the surface of the tab lead can be polished through an electrolytic polishing process as an example.

The electrolytic polishing is a metal polishing using a method in which a portion of a metal having a micro-convexity is selectively dissolved in a surface of a metal on the anode during electrolysis, and the surface treatment method of the present invention polishes a metal-made tab It can be easily applied by the electrolytic polishing.

At this time, the electrolytic polishing may be performed under a voltage condition of 5 to 10 V for 20 to 30 seconds. If the electrolytic polishing is carried out outside the voltage and time conditions, the adhesion strength between the metal tab and the film may be deteriorated.

The metal tab may include one or more metals such as aluminum (Al), nickel (Ni), and copper (Cu). For example, when the metal tab is used as a cathode of a secondary battery, When used for a negative electrode, metals coated with copper, nickel or nickel may be used, but the material of the metal tab is not limited thereto.

In the surface treatment method of the tab lead according to the present invention, the step 2 is a step of forming a metal oxide layer on the surface of the metal tab through an anodic oxidation process using the metal tab as an anode.

In step 2, a metal oxide layer is formed on the surface of the polished metal tab in step 1 so as to improve the adhesion strength between the metal tab and the film without using chromium. In particular, A metal oxide layer is formed on the surface of the tab.

In the anodizing process, an object to be oxidized is applied as an anode, an electric current is applied, and an oxide film is formed on the anode surface by oxygen generated from the anode. In the step 2 of the present invention, metal oxides are formed on the surfaces of the metal tabs in view of the fact that the metal tabs constituting the tab leads can be applied as the anode of the anodizing process.

In the step 2, the anodizing step may be performed under a voltage condition of 30 to 50 V for 30 to 90 seconds.

If the anodic oxidation process is performed outside the voltage and time conditions, the adhesive strength between the metal tab and the film may be lowered.

The metal oxide film formed in the step 2 may be formed to a thickness of 10 to 500 nm. If the thickness is less than 10 nm, there may be a problem that the electrolyte resistance of the metal oxide becomes weak. If the thickness exceeds 500 nm, the metal oxide film may be vulnerable to physical shock due to cracking of the metal oxide film, The electrolyte may penetrate through the electrolyte membrane.

The metal oxide formed in step 2 may be an oxide oxidized with a metal such as aluminum (Al), nickel (Ni), copper (Cu) or the like constituting the metal tap. Normally, a metal tab made of aluminum is used as a positive electrode of a secondary battery, and a metal plated with copper, nickel, and nickel is used as a negative electrode of a secondary battery. Since the material of the metal tab can be selected in consideration of the application to the cathode or the anode to which the metal tab is applied, the metal oxide formed in the step 2 may be appropriately changed according to the material of the metal tab have.

As described above, in the present invention, when the surface of a tab lead used in a lithium polymer secondary battery is processed, a metal oxide is formed on the surface of a metal tab such as aluminum or nickel without using chrome at all, It is possible not only to prevent corrosion by the electrolytic solution but also to improve the adhesion with the polymer film to be bonded to the metal in a subsequent process. That is, the tab lead can be surface-treated by an environmentally friendly process that replaces the existing chromium-based surface treatment method.

Further, according to the present invention,

A tab lead is provided which has been surface treated in this way.

The tab lead according to the present invention has a metal oxide layer formed on the surface of the metal tab through an anodic oxidation process to prevent the surface of metal such as aluminum and nickel constituting the tab lead from being corroded by the electrolyte, And also has an advantage that the adhesion strength to the adhesive layer can be improved.

Further,

And a lithium polymer secondary battery including the tab lead.

The secondary battery is a pouch type lithium polymer secondary battery for sealing an anode, a cathode, and an electrolyte. The tab lead includes a cathode lead for connecting a cathode material inside the lithium polymer secondary battery and a cathode for a cathode, Consists of.

Further, the tab lead affects the output and stability of the battery, and is more environmentally friendly than conventional chromium, and can exhibit high adhesive strength to an adhesive film and electrolyte resistance.

Hereinafter, the present invention will be described in more detail with reference to examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

≪ Example 1 > Surface treatment of tab lead 1

Step 1: An aluminum metal tap having a width of 40 mm was prepared, and the prepared aluminum metal tap was washed with acetone for 60 seconds.

Step 2: The cleaned aluminum metal tab was secured to a Teflon cell and prepared as a working electrode.

In addition, a graphite rod was prepared as a reference & counter electrode.

The prepared working electrode and the reference electrode were immersed in a 0.3M oxalic acid solution, and an anodization process was performed in which a voltage of 40 V was applied and the reaction was performed for 90 seconds.

≪ Example 2 > Surface treatment of tab lead 2

Step 1: An aluminum metal tap having a width of 40 mm was prepared, and the prepared aluminum metal tap was washed with acetone for 60 seconds.

Step 2: The cleaned aluminum metal tab was secured to a Teflon cell and prepared as a working electrode.

In addition, a graphite rod was prepared as a reference & counter electrode.

The electrolytic solution was prepared by immersing the prepared working electrode and the reference electrode in a mixed solution of perchloric acid and ethanol in a volume ratio of 1: 4, and then electrolyzing at a voltage of 5 V and performing a reaction at 0 (sweep), 10 seconds, 20 seconds, A polishing process was performed.

Step 3: After the electrolytic polishing step of step 2 is performed, an aluminum metal tap (working electrode) and a graphite rod (reference electrode) are immersed in a 0.3M oxalic acid solution, and a voltage of 40 V is applied. Anodic oxidation process was performed.

Control group

No surface treatment was performed on the aluminum metal taps used in Examples 1 and 2 above.

≪ Experimental Example 1 >

In order to analyze the degree of adhesive strength according to the surface treatment, a polypropylene film was adhered to the aluminum metal tapes surface-treated in the above Examples 1 and 2 and the aluminum metal tap of the control group, and then peel test was performed.

At this time, the width of the polypropylene film was 9 mm, and a pressure of 0.3 MPa was applied for 30 seconds at 140 ° C, and the results of the peeling test are shown in Table 1 and FIG.

Electrolytic polishing Anodic oxidation Adhesive strength
(N) Adhesive strength
Increase rate
(%) Voltage
(V) time
(second) Voltage
(V) time
(second) - - - - 5.2
5

0 (sweep) - - 4.2 -19.2 10 - - 5.3 1.9 20 - - 6.5 25.0 30 - - 6.6 26.9
5

0 (sweep)
40
90
5.9 13.5 10 7.5 44.2 20 9.3 78.8 30 8.1 55.8 - - 40 90 6.8 30.8

As shown in the above Table 1 and Fig. 1, the tab lead of Example 1 (performed anodizing) had an adhesive strength of 30.8% higher than that of the aluminum tab lead of the control group in which electrolytic polishing and anodization were not performed at all .

In addition, it can be seen that the tab lead of Example 2, in which both electrolytic polishing and anodic oxidation were carried out, improved the bonding strength to about 13 to 78% though it was slightly different depending on the time of electrolytic polishing.

On the other hand, in the case where only electrolytic polishing was performed, the bonding strength values were compared. As a result, when the electrolytic polishing was performed for 10 seconds,

When the electrolytic polishing was carried out for 20 to 30 seconds, it was found that the adhesive strength was improved by about 25 to 26% as compared with the control group.

This shows that the bonding strength between the tab lead and the polymer film can be improved without using chromium by the surface treatment method of the present invention, and even when the electrolytic polishing process is performed for 20 to 30 seconds It was confirmed that the adhesive strength was improved.

EXPERIMENTAL EXAMPLE 2 Analysis of contact angle of tab lead surface

In order to analyze the contact angle change according to the surface treatment, 5 占 증 of distilled water was dropped on the surface of the aluminum metal tabs surface-treated in the examples 1 and 2 and the aluminum metal tabs of the control group, and then the contact angle was measured Respectively. The measurement results are shown in Table 2 and FIG.

Electrolytic polishing Anodic oxidation Contact angle
(°) Contact angle reduction rate
(%) Voltage
(V) time
(second) Voltage
(V) time
(second) - - - - 65.8 0
5

0 (sweep) - - 40.6 38.3 10 - - 35.8 45.6 20 - - 34.8 47.1 30 - - 43.0 34.7
5 0 (sweep)
40
90 31.1 52.7 10 16.2 75.4 20 17.3 73.7 30 19.6 70.2 - - 40 90 23.2 64.7

As shown in the above Table 2 and FIG. 2, the tab lead of Example 1 (performed anodizing) had a contact angle of 23.2 deg. As compared with the aluminum tab lead of the control group in which electrolytic polishing and anodization were not performed at all 60% or more.

In addition, it can be seen that the tab lead of Example 2 in which electrolytic polishing and anodic oxidation were both performed was slightly different depending on the time during which electrolytic polishing was performed, but the contact angle was about 16 to 31 deg.

The reduction in the contact angle means that organic and inorganic contaminants on the tab lead surface have been removed through the electrolytic polishing and the anodic oxidation due to the degreasing effect due to electrolytic polishing and anodic oxidation, And the adhesion strength of the polymer film can be improved.

<Experimental Example 3> Microstructure analysis of tab lead

In order to analyze the microstructural change of the tab lead surface according to the surface treatment, the aluminum metal tabs surface-treated in Examples 1 and 2 and the surface roughness of the aluminum metal tabs of the control group were observed through a 20 magnification optical microscope and a scanning electron microscope And the results are shown in Figs. 3 to 6. Fig.

3 is an optical microscope image of the surface, FIG. 3 (B) and (C) are SEM images of the surface, and FIG. 3 Is a scanning electron microscope image of a cross section.

At this time, it can be seen that a horizontal line pattern exists on the surface of the aluminum metal tab of the control group through the image of FIG.

4 is an optical microscope image of the surface, FIG. 4 (B) is a scanning electron microscope image of the surface, and FIG. 4 (C) Section is a scanning electron microscope image.

As can be seen from the image of FIG. 4, the surface of the aluminum metal tends to be tapered as the electropolishing time increases. Particularly, when the electrolytic polishing was performed for 10 seconds, the surface was irregularly shrunk and small pores were observed. When the polishing was performed for 20 seconds, the surface was rough and uniformly shaved off. In addition, when it is performed for 30 seconds, the surface is further shaved and the pointed portion becomes rather gentle.

5 is an optical microscope image of the surface, FIG. 5 (B) is a scanning electron microscope image of the surface, and FIG. 5 (C) is a scanning electron microscope image of a cross section.

5, when the anodizing process was performed after electrolytic polishing, pores were regularly formed along the horizontal line pattern of the surface until the electrolytic polishing reaction time was 20 seconds. Also, regardless of electrolytic polishing conditions, it was observed that the thickness of the metal oxide (AlO _x ) formed by anodic oxidation was about 200 to 300 nm and the pore size was about 20 to 80 nm.

6 is an optical microscope image of the surface, FIG. 6 (B) is a scanning electron microscope image of the surface, and FIG. 6 (C) and (D) is a scanning electron microscope image of a cross section.

6, it can be seen that pores having a size of about 20 to 80 nm are regularly formed in a straight line along the horizontal line pattern of the aluminum metal tab surface.

Claims (9)

A step (step 1) of performing an electrolytic polishing process in which a surface of a metal tab is mixed with a mixed solution of perchloric acid and ethanol in a volume ratio of 1: 4 in a voltage of 5 V and reacted for 20 seconds; And
After the electrolytic polishing step of step 1 is performed, the metal taps are immersed in a 0.3 M oxalic acid solution, and an anodic oxidation process is performed by applying a voltage of 40 V for 90 seconds. In step 1, And forming a metal oxide layer on the surface of the metal tab (step 2).
delete The method of claim 1, wherein the metal tab comprises at least one metal selected from the group consisting of aluminum (Al), nickel (Ni), and copper (Cu).
The method of claim 1, wherein the metal oxide is an oxide of a metal selected from the group consisting of aluminum (Al), nickel (Ni), and copper (Cu).
delete delete delete delete delete

Images