KR102673916B1 - Pouch film for secondary battery with low before-molding curl characteristics for high-efficiency processes, secondary battery using the same and method for preparing the secondary battery - Google Patents

Abstract

A secondary battery pouch film, wherein at least an outer layer, a barrier layer, and a sealant layer are sequentially laminated, and the secondary battery pouch film has a curl value of 0.8 or less before molding, and a method of manufacturing the same. A secondary battery used and a method for manufacturing the same are disclosed. By controlling the curl of the secondary battery pouch film before molding and further controlling the elongation and/or elasticity, the efficiency of the secondary battery manufacturing process can be improved by reducing the curling phenomenon that occurs during the high molding process. there is. These secondary battery pouch films are particularly useful in the manufacturing process of medium-to-large secondary battery pouches for electric vehicles or energy storage devices.

Description

Pouch film for secondary batteries with low before-molding curl characteristics for high-efficiency processes, secondary battery using the same and method for manufacturing the same for preparing the secondary battery}

This specification relates to a pouch film for secondary batteries having low curl characteristics before molding for a high-efficiency process, a secondary battery using the same, and a method for manufacturing the same. In detail, the elongation rate, elastic modulus, and curl before molding are adjusted to By reducing the curling phenomenon that occurs during the high molding process, the efficiency of the secondary battery manufacturing process using secondary battery pouch films can be improved. Accordingly, pouch films for secondary batteries that are particularly suitable for manufacturing medium to large-sized batteries, secondary batteries using the same, and their It is about manufacturing method.

Lithium secondary batteries (LiB) are being applied to many applications based on various advantages such as high energy density and excellent output.

Secondary battery pouch film is a packaging laminated film with a multi-layer structure that surrounds the electrode group and electrolyte of these secondary batteries. It is a key component material that determines the stability, life characteristics, and operating sustainability of the battery, and has mechanical flexibility and strength, and a high oxygen/water vapor barrier. Resistance, high thermal sealing strength, chemical resistance to electrolyte solutions, electrical insulation, and high temperature stability are required.

Secondary battery pouch films usually consist of an outer layer/barrier layer/inner sealant layer.

The outer layer or outermost layer is made of nylon, a blend of nylon and PET (polyethylene terephthalate), OPP (oriented polypropylene), polyethylene, etc. Required properties of this outer layer or outermost layer include heat resistance, pinhole resistance, chemical resistance, moldability, and insulation.

The barrier layer requires formability as well as barrier properties against water vapor and other gases. In this respect, moldable metals such as aluminum (Al), iron (Fe), copper (Cu), and nickel (Ni) are used in the barrier layer, and aluminum is currently used the most.

The sealant layer of the inner layer requires electrolyte resistance, insulation resistance, etc. in that it is a layer in contact with the electrolyte, as well as thermal adhesiveness and formability.

Meanwhile, as the application field of lithium secondary batteries is expanding from small to medium to large sized for automobiles or ESS, secondary battery pouch films are also required to have properties suitable for medium to large sized. In particular, they must be highly safe and have solid properties.

In relation to this, the cell size and secondary battery pouch molding depth of an automotive-type lithium secondary battery (LiB) are factors that greatly affect secondary battery capacity. In the case of the cell size, it is larger than the general compact type and requires high formability. Since the forming depth of the cell determines the capacity of the cell, the deeper the forming depth, the higher the capacity required for next-generation secondary batteries, which is 700 Wh/L. It can be said to be a prerequisite for going to .

However, the curling phenomenon frequently occurs in secondary battery pouch films manufactured through this high molding process. This curling phenomenon reduces the efficiency of the secondary battery manufacturing process.

In exemplary embodiments of the present invention, in one aspect, a pouch film for a secondary battery capable of reducing the curling phenomenon that occurs during a high molding process, a secondary battery externally coated with the pouch film, and a manufacturing method thereof are provided. I want to do it.

In exemplary embodiments of the present invention, in another aspect, the curling phenomenon that occurs during the high molding process is reduced as described above, thereby improving the efficiency of the secondary battery manufacturing process using the secondary battery pouch film, especially the automated continuous process. The object of the present invention is to provide a pouch film for secondary batteries, a secondary battery exteriorized with the pouch film, and a method for manufacturing the same, which can improve the efficiency of the secondary battery manufacturing process when an air intake is used.

In exemplary embodiments of the present invention, the secondary battery pouch film is one in which at least an outer layer, a barrier layer, and a sealant layer are sequentially laminated, and the curl value of the secondary battery pouch film before molding according to the following measurement method is 0.8. The following secondary battery pouch film is provided.

[How to measure curl before plastic surgery]

Make a secondary battery pouch film specimen in a square shape of 15cm

Make a 15cm long do.

The sum of the measured MD two-point values divided by the sum of the TD two-point values is defined as the MD sum/TD sum of the curl before molding.

Exemplary embodiments of the present invention also provide a secondary battery externally packaged with the above-described secondary battery pouch film.

Additionally, exemplary embodiments of the present invention provide a method for manufacturing a secondary battery, including the step of packaging the secondary battery with the above-described secondary battery pouch film.

In exemplary embodiments of the present invention, the curl of the secondary battery pouch film is adjusted before molding, and further the elongation and/or elastic modulus are adjusted to reduce the curling phenomenon accompanying the high molding process. The efficiency of the secondary battery manufacturing process can be improved. These secondary battery pouch films are particularly useful in the manufacturing process of medium-to-large secondary battery pouches for electric vehicles or energy storage devices.

1 is a photograph showing a method for evaluating curl before molding in exemplary embodiments of the present invention.
Figure 2 is a photograph showing the evaluation of curling after molding of Example 1 (Figure 2a) and Comparative Example 1 (Figure 2b) of the present invention.

Term Definition

In this specification, when each layer of the secondary battery pouch is included, it does not necessarily consist of only that layer, and additional layers may be included.

In this specification, being formed ‘on’ a specific layer includes not only being formed directly on that layer, but also being formed after interposing another additional layer.

Description of Exemplary Implementations

Exemplary implementations of the present invention are described in detail below.

High formability of the secondary battery pouch film is an essential characteristic for medium to large-sized batteries, but the so-called curling phenomenon, in which the ends of the secondary battery pouch film are curled up after forming, occurs very seriously as a result of high formability. This curling phenomenon reduces the efficiency of the secondary battery manufacturing process. In particular, the secondary battery manufacturing process is an automated continuous process, and an air intake is frequently used in this process. In this case, the curled part is further rolled up toward the air intake, which further reduces process efficiency. .

Therefore, it is necessary to reduce the curling phenomenon that occurs during the high molding process, but the factors that affect curling after molding are very diverse, such as process conditions and the materials and physical properties of each layer, so the curling phenomenon that occurs during the high molding process can be reduced. Curling is difficult to suppress. Accordingly, when manufacturing secondary battery pouch films, curling phenomenon inevitably occurs after molding.

The present inventors confirmed that the curling phenomenon after molding can be easily suppressed by controlling the curl of the secondary battery pouch film before molding, and arrived at the present invention through repeated research.

Furthermore, it was confirmed that curling after molding could be suppressed by further controlling the elongation and elastic modulus.

1 is a photograph showing a method for evaluating curl before molding in exemplary embodiments of the present invention.

In exemplary embodiments of the present invention, it is a secondary battery pouch film in which at least an outer layer, a barrier layer, and a sealant layer are sequentially laminated, and the curl value of the secondary battery pouch film before molding according to the following measurement method is 0.8 or less. Secondary battery pouch film is provided.

[How to measure curl before plastic surgery]

A secondary battery pouch film specimen is manufactured in a square shape of 15cm

As shown in Figure 1, a 15cm long Measure the height lifted upward, that is, the curled height, at each of two points on the TD (lateral direction) side (positions marked ③ and ④ in Figure 1).

The sum of the measured MD two-point values divided by the sum of the TD two-point values is defined as the MD sum/TD sum of the curl before molding.

In one exemplary embodiment, the curl value before molding is 0.8 or less, 0.78 or less, 0.76 or less, 0.74 or less, 0.72 or less, 0.7 or less, 0.68 or less, 0.66 or less, 0.64 or less, 0.62 or less, 0.6 or less, 0.58 or less. , may be 0.56 or less, 0.54 or less, 0.52 or less, or 0.5.

In an exemplary embodiment, the MD elongation of the secondary battery pouch film may be 99% or more, 103% or more, or 106% or more.

In one exemplary embodiment, the TD elongation of the secondary battery pouch film may be 96% or more.

In an exemplary embodiment, the MD elastic modulus / TD elastic modulus obtained by dividing the MD elastic modulus of the secondary battery pouch film by the TD elastic modulus may be 1.2 to 1.23.

In an exemplary embodiment, the outer layer may be composed of nylon, PET (polyethylene terephthalate), PBT (polybutylene terephthalate), a mixed layer of nylon and PET (laminated film of nylon and PET), etc.

In an exemplary embodiment, the nylon film of the outer layer preferably has a thickness of 20 ㎛ or more, and more preferably 25 ㎛ or more, in terms of formability. However, if the nylon film thickness exceeds 30 ㎛, the breakdown voltage may decrease. Accordingly, a preferred nylon film thickness may be 20 μm to 30 μm, preferably 25 μm to 30 μm.

In an exemplary embodiment, the thinner the PET film and the thicker the nylon film among the outer layers are, the more advantageous it is for moldability. However, the thinner the PET film thickness, the more disadvantageous it may be in terms of breakdown voltage, so from this point of view, it is preferable that the PET film is 7㎛ to 12㎛.

In one exemplary embodiment, the sealant layer is composed of a polypropylene layer (PP), such as a non-stretched polypropyl (CPP) film, and the polypropylene (PP) layer and the barrier layer are formed by extrusion coating of a polypropylene-based resin. It can be joined by an EC) layer.

In an exemplary embodiment, the polypropylene (PP) layer of the sealant layer may contain various additives (rubber, elastomer, slip agent, etc.) depending on the required physical properties.

In an exemplary embodiment, the metal layer may be made of a metal such as aluminum, SUS alloy, or copper, and has moisture permeability and impact resistance.

In an exemplary embodiment, the total thickness of the secondary battery pouch film may be, for example, 60 to 185 μm.

In an exemplary embodiment, the metal layer thickness may be, for example, 20 to 80 μm, preferably 40 to 60 μm .

In an exemplary embodiment, the sealant layer thickness may be, for example, 20 to 80 μm.

In an exemplary embodiment, the thickness of the non-stretched polypropylene (CPP) film layer of the sealant layer may be, for example, 20 to 80 μm.

In an exemplary embodiment, the thickness of the extruded polypropylene (PP) layer of the sealant layer may be, for example, 0 to 60 μm.

In an exemplary embodiment, curl properties, elongation, and elastic modulus properties before molding can be appropriately adjusted by varying the materials of each layer. For example, the sealant layer includes a polypropylene resin and a rubber additive, and by changing the content of the rubber additive, the curl characteristics, elongation rate, and elastic modulus characteristics before molding can be adjusted.

Additionally, exemplary embodiments of the present invention provide a secondary battery externally packaged with the above-described secondary battery pouch film. These secondary batteries may typically be lithium secondary batteries, and in particular, they may be medium to large-sized secondary batteries such as electric vehicles (EV) or energy storage systems (ESS).

Additionally, exemplary embodiments of the present invention provide a secondary battery manufacturing method including the step of packaging the secondary battery with the above-described secondary battery pouch film.

Exemplary embodiments of the present invention are explained in more detail through the following examples. The embodiments disclosed herein are illustrated for illustrative purposes only, and the embodiments of the present invention may be implemented in various forms and should not be construed as limited to the embodiments described herein.

[Experimental Method]

As in the normal manufacturing method, the outer layer uses a laminated film of the outermost polyethylene terephthalate (PET) film (12㎛ thick) and the inner nylon (Ny) film (25㎛ thick), and the barrier layer uses aluminum. (thickness 60㎛), and the sealant layer was laminated using a polypropylene layer (thickness 80㎛) to produce a secondary battery pouch film. The total thickness of the pouch film is 183㎛ including the adhesive layer thickness.

In the examples and comparative examples, in addition to the polypropylene (PP) resin, a rubber component that affects the curl, elongation, and elastic modulus characteristics before molding was added to the polypropylene (PP) layer as an additive, as shown in Table 1 below. Similarly, the content of rubber additives in Examples and Comparative Examples was varied. The manufacturing methods of Examples and Comparative Examples were the same, except that the rubber additive content was different.

[Table 1]

In the examples and comparative examples, curl evaluation, elongation rate, and elastic modulus evaluation before molding were evaluated as follows.

<Curl evaluation before plastic surgery>

Secondary battery pouch film specimens of Examples and Comparative Examples were manufactured in a square shape of 15cm

As shown in Figure 1, a 15cm long The height lifted upward, that is, the curled height, was measured at each of two points on the TD (lateral direction) side (positions marked ③ and ④ in Figure 1). The unit of measurement is cm.

The sum of the measured MD two-point values divided by the sum of the TD two-point values was defined as the MD sum/TD sum of the curl before molding, and this value was calculated.

<Elongation rate evaluation>

Secondary battery pouch film specimens of Examples and Comparative Examples were produced with a size of 150 mm x 15 mm (two MD and TD specimens were produced). Elongation was evaluated using a Universal Testing Machine (UTM). The evaluation speed was 50 mm/min and the grip gap was 30 mm. The room temperature was 25°C and humidity 30%. The measured value was used by converting the increased stroke length from the UTM equipment.

<Evaluation of elastic modulus>

In the same manner as the elongation measurement method, secondary battery pouch film specimens of Examples and Comparative Examples were produced to 150 mm x 15 mm (two MD and TD specimens were produced). The MD and TD elastic moduli of each specimen were evaluated using a Universal Testing Machine (UTM). The evaluation speed was 50 mm/min and the grip gap was 30 mm. The room temperature was 25°C and humidity 30%. The elastic modulus was obtained using the slope of the elastic modulus section in the SS (Stress Strain) curve. The MD elastic modulus was calculated by dividing it by the TD elastic modulus.

<Evaluation of curling after molding>

For the secondary battery pouch films of Examples and Comparative Examples, molded specimens of 26.6 (TD)

A 12 mm molding evaluation was performed at 0.3 MPa on a chrome-coated 1 cup molding machine. The R value (corner radius of curvature) of the molding machine is 4R (4mm). The forming size during molding was 90 mm x 120 mm, and single forming was performed.

Figure 2 is a photograph showing curling after molding in an experimental example of the present invention.

As shown in Figure 2, in order to evaluate curling that occurred after molding, double-sided tape was installed on a flat surface and the molded pouch was fixed on it to measure the height of curling that occurred. When measuring, the heights of the two corners with the most curls among the four corners were measured and marked as 1 and 2 in Table 6 below.

The curl values before each molding of the pouch films of the examples and comparative examples are shown in [Table 2], and the MD sum/TD sum of the curls before molding are shown in [Table 3].

[Table 2]

[Table 3]

In addition, the MD elongation rate and TD elongation rate of the pouch films of Examples and Comparative Examples are shown in [Table 4].

[Table 4]

In addition, the MD elastic modulus, TD elastic modulus, and MD elastic modulus/TD elastic modulus of the pouch films of Examples and Comparative Examples are shown in [Table 5].

[Table 5]

Meanwhile, the curling evaluation results after molding are shown in [Table 6]. As described above, the heights of the two corners with the most curling among the four corners were measured and marked as 1 and 2 in [Table 6] below.

[Table 6]

As seen above, it can be seen that the examples in which the MD sum/TD sum of curl before molding were 0.8 or less showed significantly lower curling after molding, unlike the comparative examples.

Although non-limiting and exemplary embodiments of the present invention have been described above, the technical idea of the present invention is not limited to the accompanying drawings or the above description. It is obvious to those skilled in the art that various forms of modification are possible without departing from the technical spirit of the present invention, and such types of modifications will fall within the scope of the patent claims of the present invention.

Claims (7)

As a secondary battery pouch film,
At least the outer layer, barrier layer, and sealant layer are sequentially laminated,
The MD sum/TD sum value of curl before molding of the secondary battery pouch film according to the following measurement method is 0.8 or less,
A secondary battery pouch film, wherein the sealant layer contains a rubber component.
[How to measure curl before plastic surgery]
Create a secondary battery pouch film specimen in a square shape of 15cm
Make a 15cm long box
The sum of the measured MD two-point values divided by the sum of the TD two-point values is defined as the MD sum/TD sum of the curl before molding. According to claim 1,
A secondary battery pouch film, characterized in that the MD elongation of the secondary battery pouch film is 99% or more. According to claim 1,
A secondary battery pouch film, characterized in that the TD elongation of the secondary battery pouch film is 96% or more. According to claim 1,
A secondary battery pouch film, characterized in that the MD elastic modulus / TD elastic modulus of the secondary battery pouch film divided by the TD elastic modulus is 1.2 to 1.23. A secondary battery, characterized in that it is exteriorized with the secondary battery pouch film of any one of claims 1 to 4. According to claim 5,
The secondary battery is characterized in that the secondary battery is for an electric vehicle or an energy storage device. As a secondary battery manufacturing method,
A secondary battery manufacturing method comprising: packaging the secondary battery with the secondary battery pouch film of any one of claims 1 to 4.