KR102626933B1 - Sealant film for cell pouch in which easy gas discharge is performed through interface separation control, cell pouch including the same and method for preparing the same - Google Patents

Abstract

In the sealant film for a cell pouch including a first skin layer on the barrier layer side, a core layer, and a second skin layer that is a heat sealing layer, the melting temperature (Tm) and crystallinity of the second skin layer are determined by the melting temperature (Tm) of the core layer ( A sealant film for a cell pouch that has a lower Tm) and crystallinity and facilitates gas discharge through control of interfacial peeling, a cell pouch containing the same, and a method of manufacturing the same are disclosed. In this way, by designing the melting temperature (Tm) and crystallinity of the polymers (polypropylene, polyethylene, elastomer, etc.) used in the sealant layers of the multilayer sealant film for cell pouches to be different, delamination of the interface between layers is achieved when gas is generated in a high temperature and high humidity environment. By inducing, accidents such as cell explosion can be prevented in advance.

Description

Sealant film for cell pouch that facilitates gas discharge through interface separation control, cell pouch including the same, and method of manufacturing the same {Sealant film for cell pouch in which easy gas discharge is performed through interface separation control, cell pouch including the same and method for preparing the same}

This specification relates to a sealant film for a cell pouch that facilitates gas discharge through control of interfacial peeling, a cell pouch containing the same, and a method of manufacturing the same.

Lithium-ion batteries have been manufactured in various shapes such as square, cylindrical, and pouch-shaped depending on the times, and require physical properties such as high energy density, productivity, and stability. In particular, pouch-type lithium-ion batteries have recently been applied to many applications based on various advantages such as energy density and excellent output, but they must be handled with caution because there is a risk of explosion when exposed to high temperatures.

In this regard, when manufacturing batteries, the IEEE-1625/1725 standardization must be satisfied, and accordingly, in order to evaluate the high temperature stability of lithium secondary batteries, a hot box test (a method of evaluating battery performance by storing lithium secondary batteries at high temperatures) is used. Evaluate high temperature stability through .

On the other hand, secondary batteries generate gas due to internal electrolyte decomposition reaction under high temperature and high humidity conditions. If this gas is not discharged, it can induce expansion of the pouch and cause destruction of the battery cell. Additionally, if gas that cannot be discharged suddenly escapes from the secondary battery, there may be a risk of explosion of the secondary battery.

Japanese Patent No. 6640523

In exemplary embodiments of the present invention, in one aspect, the sealant film of the cell pouch is designed with an easy peel concept to maintain existing durability, gas barrier properties, and thermal adhesiveness while maintaining the same properties when gas is generated in a high temperature and high humidity environment. The present invention seeks to provide a sealant film for a cell pouch, a cell pouch containing the same, and a method of manufacturing the same, which can facilitate gas discharge by inducing peeling of a specific interface and thereby prevent accidents such as cell explosion.

In exemplary embodiments of the present invention, in the sealant film for a cell pouch including a first skin layer on the barrier layer side, a core layer, and a second skin layer that is a heat sealing layer, the melting temperature (Tm) of the second skin layer is and a sealant film for a cell pouch whose crystallinity is lower than the melting temperature (Tm) and crystallinity of the core layer.

Exemplary embodiments of the present invention also provide a cell pouch including the above-described sealant film and a secondary battery including the same.

In exemplary embodiments of the present invention, the cell pouch manufacturing method also includes manufacturing a sealant film having a multi-layer structure including a first skin layer, a core layer, and a second skin layer, wherein a sealant film is manufactured between the core layer and the second skin layer. The melting temperature (Tm) difference is 15 degrees or more, the crystallinity difference is 30% or more, the melting temperature (Tm) difference between the first skin layer and the core layer is 10 ℃ or less, and the crystallinity difference is 20%. It provides a method of manufacturing a cell pouch including a step of ensuring that the percentage is less than or equal to %.

Exemplary embodiments of the present invention also provide a method for improving gas emissions from a cell pouch, wherein a sealant film having a multilayer structure including a first skin layer, a core layer, and a second skin layer is manufactured, wherein the core layer and the second skin layer are manufactured. The melting temperature (Tm) difference between the layers is 15 degrees or more, the crystallinity difference is 30% or more, and the melting temperature (Tm) difference between the first skin layer and the core layer is 10 degrees Celsius or less, and the crystallinity difference is 30% or more. Provides a method including a step of ensuring that is 20% or less.

According to exemplary embodiments of the present invention, high temperature When gas is generated in a high humidity environment, accidents such as cell explosion can be prevented by inducing separation of the interface between layers.

1 is a schematic diagram showing the layer configuration of a cell pouch and the multilayer structure of a sealant film according to an exemplary embodiment of the present invention.
Figure 2 is a schematic diagram showing the arrangement of sealant layers during heat bonding in one exemplary embodiment of the present invention.
3A to 3D are schematic diagrams showing the layer configuration of comparative examples and examples of the present invention.

In this specification, the concept of easy peel refers to peeling being induced along the interface of two layers having differences in crystallinity.

In this specification, high temperature may mean overheating temperature (generally 100°C or higher) when a problem occurs in the battery usage environment. For reference, Easy Peel can usually occur at 130 to 150 degrees Celsius.

In this specification, melting temperature (Tm) can be measured by DSC. In other words, most of the raw materials used in the inner layer film are polymers, and the melting temperature of polymers can generally be measured through DSC. DSC is an equipment that analyzes the physical and chemical properties of a sample from temperature and heat change data obtained from energy supplied to the sample and reference furnace. It changes the temperature of the sample and reference. While doing so, the energy input difference is measured as a function of temperature.

Quantitative information can be obtained from the location, shape, and number of peaks analyzed in this way. When the temperature is raised at a certain rate, after the glass transition temperature (Tg) appears, another peak occurs due to heat absorption at a certain temperature, and that temperature is called the melting temperature. For reference, amorphous polymers melt at a certain temperature and become molten. While the entire crystal melts and becomes molten, the given heat is absorbed into the material as latent heat of melting, and crystalline polymers melt when the last crystal completely disperses. The temperature becomes the melting temperature.

Measurement of crystallinity or crystallinity herein can likewise be performed through DSC. For reference, while the glass transition temperature (Tg) and melting temperature (Tm) are graphs that appear when heating, the crystallization temperature (Tc) is a graph in which the polymer exists in an amorphous state at a high temperature and crystallizes around the crystallization temperature when the temperature is cooled at a constant rate. This refers to the temperature at which this occurs. At this time, a peak occurs due to an exothermic reaction, and the crystallization temperature of general crystalline polymers appears in a wide range, and the temperature at which the peak is maximum is defined as the crystallization temperature.

The degree of crystallinity can be obtained using the area of the peak where the crystallization temperature appears. Crystallinity (Crtstallinity) can be expressed by the following equation, where △H is the area of the part indicated by the peak, and △H (at 100%) is the enthalpy change value (REF theoretical value) when 100% crystallized.

[Equation]

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Polyolefins such as polypropylene (PP) are widely used as inner layer materials for cell pouches for secondary batteries due to their excellent mechanical properties such as tensile strength and impact resistance, as well as thermal adhesiveness and heat resistance. However, the stability of the cell may be reduced depending on the heat resistance characteristics. do. If a relatively low heat resistance material is applied to increase thermal adhesion, the high temperature stability of the cell becomes very weak. Conversely, when using a high heat-resistant material, gases generated inside the cell when stored at high temperatures cause expansion from inside the cell, increasing the risk of explosion.

In order to ensure that gas generated under high-temperature and high-humidity conditions in a cell pouch is discharged within a short period of time without being left inside, it is necessary to guide a heat-sealing layer made of a polyolefin layer such as polypropylene into the gas discharge passage.

The present inventors made the sealant film of the cell pouch into a multi-layer structure, and controlled the melting temperature (Tm) and crystallinity difference in the multi-layer sealant layers to induce peeling along a specific interface between the sealant layers. Improve the high temperature stability of the cell pouch.

1 is a schematic diagram showing the layer configuration of a cell pouch and the multilayer structure of a sealant film according to an exemplary embodiment of the present invention. Figure 2 is a schematic diagram showing the arrangement of sealant layers during heat bonding in one exemplary embodiment of the present invention.

As shown in Figures 1 and 2, the sealant film of the cell pouch consists of a multi-layer sealant layer, especially a first skin layer on the barrier layer (usually a metal layer such as Al), a core layer, and a second skin layer (thermal bonding layer). do.

For reference, the first skin layer requires electrolyte resistance, hydrofluoric acid resistance, and insulation as well as adhesion to the metal that is the barrier layer. The core layer requires electrolyte resistance, hydrofluoric acid resistance, and insulation along with heat resistance and thermal adhesiveness. The second skin layer requires slip properties, adhesion to contaminants, heat adhesiveness, electrolyte resistance, and insulation properties.

In exemplary embodiments of the present invention, the first skin layer and the core layer, and the core layer and the second skin layer (thermal bonding layer) are designed to have a predetermined difference in melting temperature (Tm) and crystallinity. This design induces peeling at specific interfaces between sealant layers, and as a result, the expansion phenomenon caused by gas generated inside the cell when stored at high temperature and high humidity is designed to be discharged before the cell explodes, thereby increasing cell stability. .

As described above, as the content of material with a high melting temperature (Tm) (Tm 150°C or higher) increases, the heat resistance and thermal adhesiveness of the film increase, but when the internal pressure of the secondary battery increases, the risk of explosion of the secondary battery increases, which increases the risk of cell pouches. Reduces high temperature stability. On the other hand, as the content of a material with a low melting temperature (Tm) (Tm less than 150°C) increases, it becomes easier to discharge internal gas from the secondary battery when the internal pressure increases under temperature conditions exceeding the melting temperature (Tm) of the material, but the heat resistance decreases. and poor heat adhesion.

Meanwhile, the inner layer film of the multi-layer structure is extruded, for example, in three layers through a T-die, and the first skin layer and core layer are designed to have high crystallinity, and the second skin layer is designed to have low crystallinity.

Accordingly, during the extrusion process, a phase separation phenomenon occurs between the core layer and the second skin layer due to the difference in crystallinity.

Separation of phases not only increases the number of interfaces between crystals, but also weakens cohesion. In other words, when the same pressure is applied by gas, an easy-peel phenomenon occurs between the phase bound by high Tm and crystallinity (first skin layer, core layer) and the phase bound by low Tm and crystallinity (second skin layer). (Interfacial peeling between layers) may occur, and gas outflow can be easily induced through this phenomenon.

Therefore, the melting temperature (Tm) and crystallinity of the sealant layer of the cell pouch are adjusted to stably achieve heat resistance, heat adhesion, and high temperature stability.

In an exemplary embodiment, the first skin layer (metal layer adhesive surface such as Al) and the core layer have a melting temperature (Tm) and crystallinity relatively high compared to the second skin layer (thermal adhesive layer), and the second skin layer (thermal adhesive layer) The skin layer (thermal bonding layer) may have a melting temperature (Tm) and crystallinity that are relatively lower than those of the first skin layer (metal layer adhesive surface such as Al) and the core layer.

In an exemplary embodiment, the melting temperature (Tm) difference between the first skin layer and the core layer is preferably 10° C. or less, and the crystallinity difference is preferably 30% or less.

In detail, the first skin layer and the core layer must have similar Tm and crystallinity so that phase separation does not occur and they can act as one layer. Therefore, if the Tm difference is greater than 10℃ or the crystallinity difference is greater than 30%, phase separation between layers may occur and the overall physical properties of the resin that makes up the sealant layer, usually PP layer (e.g., durability, gas barrier properties, insulation properties, It may have a negative effect on thermal adhesion and interfacial properties. Therefore, it is desirable that the melting temperature (Tm) difference between the first skin layer and the core layer be 10°C or less, and the crystallinity difference be 30% or less, preferably 20% or less.

also. The melting temperature (Tm) difference between the core layer and the second skin layer (thermal bonding layer) is preferably 10°C or more, preferably 15°C or more, and the crystallinity difference is 15% or more, preferably 30% or more. The difference in crystallinity may be less than 50%. Considering the influence of the second skin layer compared to the entire sealant layer (20-25% when calculating thickness), if the difference in crystallinity is more than 50%, it will have a negative effect on the physical properties of the cell pouch.

That is, in the case between the core layer and the second skin layer (thermal bonding layer), contrary to what was explained above, the Tm must be 10°C or more and the crystallinity difference must be 15% or more, preferably 30% or more, to induce phase separation. It can induce an easy feel.

In an exemplary embodiment, since most of the properties required for a sealant film can be realized from this core layer, the core layer preferably has a thickness corresponding to 50 to 80% of the entire sealant film, and the first skin layer and The second skin layer preferably has a thickness equivalent to 10 to 20% of the total sealant layer for metal adhesion and electrolyte resistance. For example, the thickness of the core layer may be 20 to 40 μm, and the thickness of the first skin layer and the second skin layer (thermal bonding surface) may be approximately 5 to 10 μm, respectively.

In an exemplary embodiment, the sealant film for a cell pouch must have excellent thermal adhesiveness (sealing strength), insulation resistance, mechanical strength, and chemical resistance, so it is advantageous to use a polyolefin-based film.

In an exemplary embodiment, the core layer may use one or more of homo polypropylene (Homo-PP), polypropylene copolymer (Co-PP), and polypropylene terpolymer (Ter-PP), and various other additional layers. Elastomer, CaCO ₃ , TiO ₂ , amine, or GMS-based additives may be used.

In an exemplary embodiment, the elastomer is capable of improving thermal bonding strength and barrier layer adhesion properties, such as ethylene propylene rubber (EPR), ethylene butane rubber (EBR), and LLDPE-based Elastomers such as thermoplastic polyolefin elastomer (TPO), RTPO (reactor made thermoplastic olefin), and thermoplastic polyurethane (TPU) can be used.

In an exemplary embodiment, the skin layer includes polyolefins such as polypropylene (PP), polyethylene (PE), and their composite resins or derivatives (LLDPE, HDPE, LDPE, Homo-PP, Co-PP, Ter-PP). ), inorganic hygroscopic additives (CaCO ₃ , BaSO ₄ , TiO ₂ , zeolite, silica), special resin (MAH-g-PP, maleic acid grafted polypropylene), nucleating agent (α or β nucleating agent), etc. there is.

In a non-limiting example, the first skin layer may have a thickness of 10 to 20% of the sealant film and may be made of PP (Tm 150°C or higher, crystallinity 40 to 70%).

The core layer has a thickness of 60 to 80% of the sealant film and can be constructed using PP (Tm 160°C or higher, crystallinity 70% or higher).

The second skin layer can be constructed using a sealant film with a thickness of 10 to 20% and PP (Tm 130 to 155°C, crystallinity 40% or less). In addition, AB agents and slip agents (amide-based Erucamide, Behenamide, Oleamide, etc.) can be used in the second skin layer in an amount of about 1 to 10% by weight of the second skin layer.

In an exemplary embodiment, the skin layer can be divided into a first skin layer on the barrier layer side that is adhered to the barrier layer layer (usually a metal layer such as Al) and a second skin layer in which thermal bonding (sealing) occurs, and the film extrusion And/or to improve workability during winding, at least one of a slip agent or an anti-blocking agent is included, especially in the second skin layer.

The slip agent can be made of various organic substances such as wax-based, oleic acid amide series (Erucamide, Oleamide, Behenamide), siloxane, or silicone to reduce the friction coefficient and provide lubricity to the film surface, and the anti-blocking agent can be used to prevent adhesion between films. Inorganic particles such as silica, diatomaceous earth, talc, and kaolin can be used to prevent this.

In a non-limiting example, the first skin layer may further include elastomer and special resin (MAH-g-PP) in addition to Random PP, Ter PP, and Block PP, and the second skin layer may further include Random PP, Ter PP, In addition to Block PP, elastomers, slip agents, and anti-blocking agents may be included.

When the cell pouches of the exemplary embodiments of the present invention designed above are sealed at a temperature of 180 to 200 ° C, considering the amount of heat transferred through the outer layer and the barrier layer (metal layer such as Al) and the remaining thickness of the pouch film, The proportion of the second skin layer (thermal bonding surface) involved in thermal bonding is 20 to 25% based on the thickness, which is an advantageous condition for interfacial peeling with the core layer.

For reference, the ratio of involvement in thermal bonding based on thickness can be calculated as a percentage of the thickness of the second skin layer to the thickness of the sealant layer involved in thermal bonding, considering the thickness of the entire sealant layer and the residual rate after thermal bonding. For example, assuming that the PP residual rate during actual heat bonding is about 70% (56um) based on an 80um thick PP layer, the total PP thickness involved in heat bonding is less than 30μm (24μm), and the second skin layer 2 Since the thickness is approximately 5㎛, the proportion involved in thermal bonding can be said to be approximately 25%.

Meanwhile, exemplary embodiments of the present invention provide a cell pouch containing the above-described sealant film and a secondary battery externally packaged with the cell pouch. 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).

In an exemplary embodiment, the cell pouch may include, for example, an outer layer containing nylon, a barrier layer containing aluminum, and the sealant film.

In one exemplary embodiment, the cell pouch may further include an outermost layer containing polyethylene terephthalate (PET) as the outermost layer of the outer layer. In this way, the configuration further including PET as the outermost layer can be particularly applied to medium to large-sized secondary batteries.

In exemplary embodiments of the present invention, in the above-described cell pouch manufacturing method, the cell has a multi-layered sealant layer including a first skin layer on the barrier layer side, a core layer, and a second skin layer that is a heat sealing layer. A pouch sealant film is manufactured, wherein the melting temperature (Tm) and crystallinity of the first skin layer and the core layer are higher than those of the second skin layer, and the melting temperature (Tm) and crystallinity of the second skin layer are higher than those of the first skin layer. And providing a method of manufacturing a cell pouch including a step of lowering the core layer.

In addition, in exemplary embodiments of the present invention, as a method of improving gas discharge of a cell pouch, the method includes a multi-layered sealant layer including a first skin layer on the barrier layer side, a core layer, and a second skin layer that is a heat sealing layer. A cell pouch sealant film is manufactured, wherein the melting temperature (Tm) and crystallinity of the first skin layer and the core layer are higher than those of the second skin layer, and the melting temperature (Tm) and crystallinity of the second skin layer are higher than those of the first skin layer. Provided is a method for improving gas emissions from a cell pouch including a step of lowering the layer and the core layer.

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.

Manufacturing of pouches

The pouches of the examples and comparative examples below were designed with a common outermost layer of PET of 12㎛, an outer layer of NY (nylon) of 15㎛, a barrier layer of Al of 40㎛, and an inner layer of sealant film of 50㎛. In addition, the first skin layer and the second skin layer of the inner sealant film are composed of 5㎛, and the core layer is 40㎛, and the cell pouch is made by applying a CPP film manufactured by adjusting the Tm of the inner sealant layer as follows. After manufacturing, a hot box test was performed.

[Experiment 1]

[Comparative Example 1]

In Comparative Example 1, a single-layer sealant layer was designed (see Figure 3a). As the single-layer sealant layer, a polypropylene (Homo-PP) series with a Tm of 160°C and a crystallinity of 70% was used, and the total thickness was designed to be 50㎛.

[Comparative Example 2]

In Comparative Example 2, the A layer (first skin layer), B layer (core layer), and C layer (second skin layer) were all made of polypropylene (Homo-PP) with a Tm of 160°C and a crystallinity of 70%. was used, and the total thickness was set at 50㎛, the A and C layers were designed at 5㎛, and the B layer was designed at 40㎛ (see Figure 3b).

[Example 1]

In this Example 1, the interlayer Tm was adjusted by changing the main raw material.

That is, the raw materials and mixing ratio of the A layer (first skin layer) and B layer (core layer) were the same as in Comparative Example 2, but the main raw material of the C layer (second skin layer) was changed. That is, the C layer (second skin layer) was constructed using polypropylene (Block-PP) with a Tm of 145°C and a crystallinity of 55% (crystallinity difference from the core layer of 15%). The total thickness was designed to be 50㎛, with the A and C layers being 5㎛ and the B layer being 40㎛ (see Figure 3c).

[Example 2]

In this Example 2, the A layer (first skin layer) and B layer (core layer) had the same raw materials and mixing ratio as Example 1, but the C layer (second skin layer) had a Tm of 145°C and was crystalline. It was constructed using 40% polypropylene (Block-PP) (30% difference in crystallinity from the core layer). The total thickness was designed to be 50㎛, the A and C layers were designed to be 5㎛, and the B layer was designed to be 40㎛ (see Figure 3d).

[Example 3]

In this Example 2, the A layer (first skin layer) and B layer (core layer) had the same raw materials and mixing ratio as Example 1, but the C layer (second skin layer) had a Tm of 145°C and was crystalline. It was constructed using 30% polypropylene (Random-PP) (40% difference in crystallinity from the core layer). The total thickness was designed to be 50㎛, the A and C layers were designed to be 5㎛, and the B layer was designed to be 40㎛ (see Figure 3d).

[Example 4]

In this Example 2, the A layer (first skin layer) and B layer (core layer) had the same raw materials and mixing ratio as Example 1, but the C layer (second skin layer) had a Tm of 145°C and was crystalline. It was constructed using 20% polypropylene (Ter-PP) (50% difference in crystallinity from the core layer). The total thickness was designed to be 50㎛, the A and C layers were designed to be 5㎛, and the B layer was designed to be 40㎛ (see Figure 3d).

[Experiment 1 - Hotbox Test]

Hot box testing was performed as follows.

- The cell pouch was molded using a mold (3 cm

- A lithium secondary battery was manufactured using a molded cell pouch.

- Gas leakage due to damage to the thermally bonded surface was evaluated over time under high temperature conditions (120~150℃).

- If gas leakage occurs within 2 hours at 120℃ or within 20 minutes at 150℃, it is evaluated as passing.

The evaluation results are shown in Tables 1 and 2 below.

Temperature: 120℃
Comparative Example 1
Comparative example 2
Example 1
Example 2
Example 3
Example 4 Storage time (Min) 30 X X X X X X 60 X X X X O O 90 X X X O - - 120 X X X - - - 150 X X O - - - 180 X X - - - - Yes/No fail fail fail pass pass pass

O: Gas leak occurs X: Gas leak does not occur

Temperature: 150℃
Comparative Example 1
Comparative example 2
Example 1
Example 2
Example 3
Example 4 Storage time (Min) 10 X X X O O O 20 X X O - - - 30 X X - - - - 40 X O - - - - 50 O - - - - - Yes/No fail fail pass pass pass pass

O: Gas leak occurs X: Gas leak does not occur

[Experiment 2 - Characteristics Evaluation]

<Evaluation of heat bonding strength>

For thermal bonding strength, a sample was prepared by folding the pouch in half and compressing it to a CPP residual rate of 70% by adjusting the pressure at a temperature of 180°C. The prepared sample was cut to 15 mm in width, the interface between CPP and CPP was separated at an angle of 180 degrees, and the thermal bonding strength between the two layers was measured. The thermal bond strength was evaluated using the AGS-1kNX model (UTM) of SHIMADZU, Japan.

<Moldability evaluation>

To evaluate moldability, the pouch sample was cut to 266mm x 240mm, placed with the inner surface (CPP) side on top, and evaluated using a molding machine specified for the product. The molding machine used was a test mold from Yulchon Chemical.

<Insulation resistance evaluation>

For the evaluation of insulation resistance, the mold was molded to a depth of 5 mm using the same test mold from Yulchon Chemical as in the formability evaluation above, and then a dummy cell was manufactured through side sealing and tab sealing based on 2 ml of electrolyte. The number of samples is 10 per sample. After manufacturing the dummy cell, the resistance when 1KV voltage is applied 24 hours later is measured.

Experiment items
Comparative Example 1
Comparative example 2
Example 1
Example 2
Example 3
Example 4 Heat bonding strength ◎ ◎ ◎ ○ △ X Insulation Resistance ◎ ◎ ◎ ○ △ △ Formability ◎ ◎ ◎ ◎ ◎ ◎ Yes/No pass pass pass pass pass fail

Test related to physical properties (excellent (◎), good (○), average (△), unsatisfactory (X)

For reference, the criteria for excellent, good, average, and unsatisfactory are listed in the table below.

item Great Good commonly dissatisfaction Heat bonding strength (N/15mm) over 120 120~100 100~80 less than 80 Formability (mm) over 13 13~11 11~9 less than 9 Insulation resistance (GΩ) over 80 80~60 60~40 less than 40

[Analysis of experiment results]

Referring to Table 1, when stored at 120°C, in Comparative Examples 1 and 2, no gas leaked even after 3 hours. Even if it was a single-layer or multi-layer structure, gas did not leak if the interlayer sealant composition was the same.

In Example 1, gas leaked after 150 minutes. If the Tm difference between the A layer, B layer, and C layer is more than 10℃ and the crystallinity difference is about 15%, a passage through which gas can leak may be created, but within the standard time (120 minutes) You can see that it was not created.

In Example 2, gas leaked after 90 minutes, and only when the Tm difference between the A layer, B layer, and C layer was 10°C or more, and the crystallinity difference was 30% or more, the gas leakage passage was established within the standard time. can be created.

In Examples 3 and 4, gas leaked after 60 minutes, the Tm difference between the A layer, B layer, and C layer was more than 10°C, and the crystallinity difference exceeded 30%, reaching 40% and 50% levels. If this happens, it is expected to be positive in terms of gas emissions, but have a negative impact on the physical properties of the pouch.

Referring to Table 2, when stored at 150°C, gas leaked after more than 40 minutes in cases 1 and 2 in comparison. Since it was stored at a temperature close to the Tm of the raw material applied to the sealant layer, a gas leak path may have been created, but it can be seen that it was not created within the existing time (20 minutes).

In Examples 1, 2, 3, and 4, gas leaked within 20 minutes, and a gas leak path was created within the existing time. Under 150℃ storage conditions, deformation of raw materials occurred below 150℃, and a gas leak path was created in a relatively short period of time.

Meanwhile, referring to Tables 3 and 4, when evaluating the physical properties of the pouch, a corresponding test was conducted to verify the effect of Tm and crystallinity on the physical properties of the pouch.

Comparative Examples 1 and 2 As in Examples 1, 2, and 3, when the Tm difference between the A layer, B layer, and C layer is 10°C or more and the crystallinity difference is 30% to 50%, the pouch physical properties are within the standard value. Confirmed entering.

On the other hand, if the Tm difference between the A layer, B layer, and C layer is more than 10°C and the crystallinity difference is more than 50% as in Example 4, the insulation resistance and heat bonding strength among the physical properties of the pouch are adversely affected. It was confirmed that it did not fall within the standard values.

Ultimately, if the Tm difference between the A layer, B layer, and C layer is 10°C or more, and the crystallinity difference is preferably 30% or more and less than 50%, it is possible to produce a pouch that satisfies good pouch physical properties and allows easy gas discharge. It is judged that it is possible.

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 (16)

In the cell pouch,
The cell pouch includes a sealant film including a first skin layer on the barrier layer side, a core layer, and a second skin layer that is a heat sealing layer,
A cell pouch, characterized in that the melting temperature (Tm) and crystallinity of the second skin layer, which is the heat-sealing layer, are lower than the melting temperature (Tm) and crystallinity of the core layer. According to claim 1,
The melting temperature (Tm) and crystallinity of the first skin layer and the core layer are higher than the melting temperature (Tm) and crystallinity of the second skin layer,
A cell pouch characterized in that the melting temperature (Tm) and crystallinity of the second skin layer are lower than the melting temperature (Tm) and crystallinity of the first skin layer and the core layer. According to claim 2,
A cell pouch characterized in that the melting temperature (Tm) difference between the core layer and the second skin layer is 10°C or more, and the crystallinity difference is 15% or more. According to claim 3,
A cell pouch characterized in that the difference in crystallinity between the core layer and the second skin layer is 30% or more. According to claim 4,
A cell pouch characterized in that the melting temperature (Tm) difference between the first skin layer and the core layer is 10°C or less, and the crystallinity difference is 30% or less. According to claim 5,
The thickness of the core layer is 20-40㎛,
A cell pouch, wherein the first skin layer and the second skin layer each have a thickness of 5 to 10 μm. According to claim 6,
The core layer contains one or more components selected from the group consisting of homo-polypropylene (Homo-PP), polypropylene copolymer (Co-PP), and polypropylene terpolymer (Ter-PP), or the one or more components include an elastomer. A cell pouch further comprising: According to claim 7,
The first skin layer further contains elastomer and Malay graft polypropylene in addition to Random PP, Ter PP, and Block PP.
A cell pouch characterized in that the second skin layer further contains an elastomer, a slip agent, and an anti-blocking agent in addition to Random PP, Ter PP, and Block PP. According to claim 1,
When the cell pouch is sealed at a temperature of 180 to 200°C, the cell pouch is characterized in that the second skin layer, which is a heat sealing layer, participates in heat bonding in a ratio of 40 to 60%. delete According to claim 1,
The cell pouch includes an outer layer containing one or more of nylon and polyethylene terephthalate (PET), a barrier layer containing aluminum, and the sealant film. A secondary battery, characterized in that it is externally equipped with the cell pouch of any one of claims 1 to 9 and 11. According to claim 12,
A secondary battery, characterized in that the secondary battery is a lithium secondary battery. According to claim 12,
A secondary battery, characterized in that the secondary battery is for an electric vehicle or an energy storage device. In the cell pouch manufacturing method of any one of claims 1 to 9 and 11,
A sealant film having a multilayer structure including a first skin layer, a core layer, and a second skin layer is manufactured, wherein the melting temperature (Tm) difference between the core layer and the second skin layer is 10°C or more, and the crystallinity difference is 30°C. % or more, the melting temperature (Tm) difference between the first skin layer and the core layer is 10°C or less, and the crystallinity difference is 30% or less. A cell pouch manufacturing method comprising a. . A method for improving gas emissions from the cell pouch of any one of claims 1 to 9 and 11, comprising:
Manufacturing a sealant film with a multi-layer structure including a first skin layer, a core layer, and a second skin layer,
The melting temperature (Tm) difference between the core layer and the second skin layer is 10℃ or more, the crystallinity difference is 30% or more, and the melting temperature (Tm) difference between the first skin layer and the core layer is 10℃. A method for improving gas emissions from a cell pouch, comprising the step of ensuring that the difference in crystallinity is 30% or less.