KR20200076282A - A cell pouch with improved high-temperature stability and secondary battery including the same - Google Patents

Abstract

In one aspect, the present invention provides a cell pouch with high-temperature stability, comprising: a sealant layer; a metal layer formed on the sealant layer; and an outer layer formed on the metal layer, wherein the sealant layer has a multi-layered structure consisting of an indirect contact sealant layer, an intermediate sealant layer, and a direct contact sealant layer.

Description

A cell pouch with improved high temperature stability and a secondary battery comprising the same {A CELL POUCH WITH IMPROVED HIGH-TEMPERATURE STABILITY AND SECONDARY BATTERY INCLUDING THE SAME}

The present invention relates to a cell pouch for a secondary battery with improved high temperature stability to prevent an explosion risk of the secondary battery and a secondary battery comprising the same.

Lithium secondary batteries (LiB) are applied to many applications based on various advantages such as high energy density and excellent output. However, care must be taken in handling because there is a risk of explosion when exposed to high temperatures. In this regard, when manufacturing a battery, it must satisfy the IEEE-1625/1725 standardization. Therefore, in order to evaluate the high temperature stability of the lithium secondary battery, the high temperature stability is evaluated through a hot box test (how to store the lithium secondary battery at high temperature to evaluate the performance of the battery).

When the secondary battery is stored in a high temperature condition, pressure is generated due to the gas generated therein, and if the gas rapidly escapes to the outside of the secondary battery, an explosion risk of the secondary battery may occur. Therefore, it is important to induce a heat-adhesive layer made of a PP layer into a gas discharge passage in order to discharge gas generated under high temperature conditions within a short time.

The manufacturing method of the lithium secondary battery pouch can be largely classified into an extrusion coating (EC) method and a dry-dry lami (SDL) method. In the case of the pouch produced by the extrusion coating method, it is common that the pouch produced by the dry lamination method has excellent high temperature stability. This is because in the case of the dry lame type pouch, it is very difficult for gas generated under high temperature conditions to be discharged through the heat-adhesive layer made of the PP layer.

Polypropylene (PP) has been widely used as a cell-pouch inner layer material for secondary batteries due to its excellent mechanical properties such as tensile strength and impact strength, as well as excellent thermal adhesion and heat resistance. However, the stability of the lithium secondary battery may decrease depending on the heat resistance of the inner layer made of polypropylene. When a relatively low heat-resistant material is applied to increase the heat adhesion, the high temperature stability of the secondary battery becomes very weak. Conversely, when a high heat-resistant material is applied, the risk of explosion increases due to the expansion phenomenon from inside the battery due to the gas generated inside the secondary battery during high temperature storage.

Therefore, in this study, the pouch made by dry lame method is secondary to high-temperature storage based on the composite design of multi-layered structure with polyethylene (PE), polypropylene (PP), and elastomer (Elastomer) material of the inner layer film of the pouch. The expansion phenomenon due to the gas generated inside the battery was designed to be discharged before the secondary battery exploded to increase the stability.

Embodiments of the present invention are to provide a cell pouch for reducing the risk of explosion due to gas generated therein when the secondary battery is stored at high temperature.

Embodiments of the present invention is to provide a cell pouch having excellent high temperature stability and excellent heat adhesion.

One embodiment of the present invention is a sealant layer; A metal layer formed on the sealant layer; And an outer layer formed on the metal layer, wherein the sealant layer has a multilayer structure, and includes an indirect contact sealant layer, an intermediate sealant layer, and a direct contact sealant layer.

In an exemplary embodiment, the thickness of the direct contact sealant layer may be 10-20% of the total thickness of the sealant layer.

In an exemplary embodiment, the direct contact sealant layer includes a main raw material comprising polypropylene, and the melting point (Tm) of the main raw material may be 130-150°C.

In an exemplary embodiment, the direct contact sealant layer further includes an antiblocking agent or an amide-based slip agent, and the content of the antiblocking agent or amide-based slip agent is 1-10% by weight based on the total weight of the direct contact sealant layer. Can.

In an exemplary embodiment, the amide-based slip agent may include one or more of Erucamide, Behenamide, and Oleamide.

In an exemplary embodiment, the intermediate layer comprises a main raw material and an elastic polymer comprising polypropylene, the elastomer is a polypropylene-based elastomer, and the melting point (Tm) of the elastomer is 50-80° C. than the melting point of the main raw material. It can be lower.

In an exemplary embodiment, the content of the elastomer may be 10-60% by weight based on the total weight of the intermediate layer.

In an exemplary embodiment, the thickness of the intermediate layer may be 50-80% thick relative to the total thickness of the sealant layer.

In an exemplary embodiment, the sealant layer may be formed by a dry lamination method.

Another embodiment of the present invention provides a secondary battery comprising the high temperature stability cell pouch according to the present invention.

Another embodiment of the present invention comprises the steps of laminating the outer layer and the metal layer; And forming a sealant layer on the uncoated side of the metal layer, wherein the sealant layer has a multi-layered structure, and includes an indirect contact sealant layer, an intermediate sealant layer, and a direct contact sealant layer. Provides a method for manufacturing a pouch.

In an exemplary embodiment, in the forming of the sealant layer, a sealant layer is formed by a dry lamination method, and the indirect contact sealant layer, the intermediate sealant layer, and the direct contact sealant layer may have different melting points.

In an exemplary embodiment, the step of forming the sealant layer may further include an anti-blocking agent or an amide-based slip agent in the direct contact sealant layer.

The cell pouch according to the embodiment of the present invention includes a multi-layer sealant layer, and the strength, durability and water vapor of other gas barriers, heat sealability, heat sealability with electrode terminals, etc. are excellent. , It provides a cell pouch (external packaging material) for secondary batteries with improved stability even at high temperatures.

1 is a schematic view showing a sealant layer having a single-layer structure in a cell pouch according to Comparative Example 1 of the present invention.
2 is a schematic view showing a sealant layer having a multi-layer structure in a cell pouch according to Comparative Example 2 of the present invention.
3 is a schematic view showing a sealant layer having a multi-layer structure in a cell pouch according to Example 1 of the present invention.
4 is a schematic view showing a sealant layer having a multi-layer structure in a cell pouch according to Example 2 of the present invention.
5 is a schematic view showing a sealant layer having a multi-layer structure in a cell pouch according to Example 3 of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Although embodiments of the present invention have been described with reference to the accompanying drawings, this is for illustrative purposes, and the technical spirit of the present invention and its configuration and application are not limited thereby.

In the present specification, the term "cell" means a battery, and is the broadest meaning including all of various batteries such as a secondary battery such as a lithium ion battery or a lithium polymer battery or a portable storage battery.

As used herein, "cell pouch" is a cell component such as an anode, a cathode, and a separator, which is impregnated and stored in an electrolyte, and has a gas barrier property, an electrolyte resistance, and a gas barrier property to accommodate the cell component. It is the broadest meaning including all of the films having a laminated structure in consideration of thermal adhesion, etc., processed in a bag shape or a box shape.

As used herein, "barrier property" refers to the ability to block underwater groups from outside the cell.

High temperature stability cell pouch

One embodiment of the present invention is a sealant layer; A metal layer formed on the sealant layer; And an outer layer formed on the metal layer, wherein the sealant layer has a multilayer structure, and includes an indirect contact sealant layer, an intermediate sealant layer, and a direct contact sealant layer.

In one embodiment, the sealant layer may include a sealing resin for thermal adhesion as the cell is received (built-in) and then adhered (heat-sealed) by heat to impart sealing properties. . For example, the sealing resin may be a resin having insulation, electrolytic solution resistance and/or cold resistance, etc. together with thermal adhesion.

In one embodiment, the direct contact sealant layer may include a main raw material comprising polypropylene, and the melting point (Tm) of the main raw material may range from 130 to 150°C. Specifically, the direct contact sealant layer may include a main raw material containing polypropylene to allow thermal adhesion and melting at high temperature storage (130 to 150°C).

In one embodiment, the direct contact sealant layer may further include an antiblocking agent or an amide-based slip agent, thereby imparting slimness. Specifically, the content of the anti-blocking agent or amide-based slip agent may be 1-10% by weight based on the total weight of the direct contact sealant layer. When the content of the antiblocking agent or the amide-based slip agent is less than 1% by weight, the slipping property of the cell pouch may be insufficient, so that a molding process for battery manufacturing may not be possible. Although it may be advantageous for the process, the components that impart slip properties may be transferred to the back side of the film in contact with each other, so that the thermal adhesion strength of the cell pouch and the adhesion strength with the metal layer may be reduced.

In addition, for example, the amide-based slip agent may include one or more of Erucamide, Behenamide, Oleamide.

In one embodiment, the thickness of the direct contact sealant layer may be 10-20% of the total thickness of the sealant layer. In addition, the thickness of the direct contact sealant layer may be 3-10 μm. When the thickness of the direct contact sealant layer is less than 10% relative to the total thickness of the sealant layer, the adhesive strength with the metal layer may decrease, and if it exceeds 20%, the adhesive strength with the metal layer and the electrolyte resistance may decrease.

In one embodiment, the intermediate layer may include a main raw material including polypropylene and an elastomer, and the elastomer may be a polypropylene-based elastomer.

In an exemplary embodiment, the intermediate layer may include polypropylene (PP)-based resin. More specifically, the interlayer uses alone one or more polypropylene (PP) systems selected from homo polypropylene (homo-PP), polypropylene copolymer (PP co-polymer) and polypropylene terpolymer (PP ter-polymer). It may include a material formed by mixing, and may also include a material formed by mixing polyethylene (PE) or ethylene vinyl acetate (EVA) with the polypropylene (PP). In general, polypropylene (PP)-based resins are useful in the present invention because they have excellent thermal adhesion (sealability) and insulation properties, as well as mechanical properties such as tensile strength, rigidity and surface hardness, and chemical resistance such as electrolyte resistance. Can be used.

In one embodiment, the content of the main raw material may be 40-90% by weight relative to the total weight of the intermediate layer. The high temperature stability of the cell pouch at the main raw material content may be excellent.

In addition, the melting point (Tm) of the elastomer may be 50-80°C lower than the melting point of the main raw material. At this time, when the melting point (Tm) of the elastic polymer is lower than 50°C than the melting point of the main raw material, the possibility of explosion may increase because a gas leak path is not generated when evaluating high-temperature stability. Due to the large difference in melting point, the sealant layer may be excessively collapsed during thermal bonding, thereby blocking a gas leakage path. Therefore, the intermediate layer may include a main raw material that is a material having a relatively high melting point (Tm about 150°C or higher) and an elastomer having a relatively low melting point (below Tm about 150°C). As the content of high Tm material (Tm 150℃ or higher) increases, the heat resistance and heat adhesion of the film increase, but when the pressure inside the secondary battery increases, the risk of explosion of the secondary battery increases, deteriorating the high temperature stability of the cell pouch. On the other hand, as the content of the low Tm material (below Tm 150°C) increases, when the internal pressure increases at a temperature above Tm of the material, the gas inside the secondary battery becomes easier to discharge, but the heat resistance and heat adhesion are poor.

Therefore, the cell pouch according to the present invention is designed to have a sealant layer in a multi-layered structure, and by controlling the Tm and density of the direct contact sealant layer and the adjacent layer that are in direct contact during thermal bonding, both heat resistance, thermal adhesion and high temperature stability are stably Can be implemented.

In one embodiment, the content of the elastomer may be 10-60% by weight relative to the total weight of the intermediate layer. Specifically, when the content of the elastomer is included in a range of 10-60% by weight, the gas generated inside the secondary battery may be easily discharged when stored at a high temperature. At this time, for heat resistance, it is preferable that the main raw material has a Tm of 150°C or higher and the elastic polymer has a difference between the main raw material and the Tm of about 50 to 80°C.

In one embodiment, the thickness of the intermediate layer may be 50-80% of the total thickness of the sealant layer. In addition, the thickness of the intermediate layer may be 10-40㎛. If the thickness of the intermediate layer is less than 50% relative to the total thickness of the sealant layer, sufficient heat resistance cannot be secured, and if it is more than 80%, metal adhesion and heat adhesion may be deteriorated.

In one embodiment, the indirect contact sealant layer is adjacent to the metal layer, and may include a main raw material having a Tm of 150°C or higher.

In one embodiment, the thickness of the indirect contact sealant layer may be 10-20% of the total thickness of the sealant layer, and may have excellent metal adhesion, electrolyte resistance, and insulation in the thickness range.

In one embodiment, the sealant layer may be formed by a dry lamination method. In general, the method of manufacturing a pouch for a lithium secondary battery can be roughly divided into an extrusion coating (EC) method and a dry-dry lami (SDL) method. In the case of the pouch produced by the extrusion coating method, it is common that the pouch produced by the dry lamination method has excellent high temperature stability. This is because in the case of the dry lame type pouch, it is very difficult for gas generated under high temperature conditions to be discharged through the heat-adhesive layer made of the PP layer. However, the high temperature stability cell pouch according to the embodiment of the present invention may form a sealant layer having a multi-layered structure through a dry lamination method to reduce the risk of explosion at high temperatures and have excellent high temperature stability.

In one embodiment, the metal layer may be a barrier layer. Here, if the barrier layer is a metal having a gas barrier property, the material is not limited. In addition, the barrier layer may block the entry and exit of moisture or air from the outside and gas generated therein. The barrier layer may include one or more selected from a metal thin film and a metal deposition layer. At this time, the metal thin film may be used a metal foil (metal foil), the metal deposition layer is a separate plastic film, for example, polyethylene terephthalate (PET), polyethylene (PE) or polypropylene (PP) film, etc. It can be formed by vacuum deposition.

For example, the metal constituting the barrier layer, specifically, the metal constituting the metal thin film or metal deposition layer, for example, aluminum (Al), iron (Fe), copper (Cu), nickel (Ni), tin ( Examples include one or more selected from the crowd consisting of Sn), zinc (Zn), indium (In), and tungsten (W) (a single metal or a mixture of single metals), or two or more alloys selected from them. Can. The metal is preferably selected from aluminum (Al) or aluminum alloy (Al alloy). In addition, the barrier layer may be used for corrosion resistance, surface treatment with phosphoric acid, chromium, or the like.

In an exemplary embodiment, the barrier layer may have a thickness of 15 μm or less, and preferably the barrier layer may have a thickness of 9 to 15 μm. When the thickness of the barrier layer is 9 µm or less, it is not easy to implement the secondary battery as a cell pouch, and when the thickness of the barrier layer is 15 µm or more, the battery capacity may be drastically reduced in the bendability test of the flexible cell pouch.

In one embodiment, the outer layer may be to protect the barrier layer. The outer layer preferably has abrasion resistance, such as heat resistance, cold resistance, pinhole resistance, insulation, solvent resistance and/or formability (shape retention when processing a flexible cell pouch into a predetermined shape (box, etc.)), etc. It may include a resin having properties.

Specifically, the outer layer may include one or more resins selected from nylon resins, polyethylene terephthalate (PET) resins, and polyolefin-based resins. At this time, the polyolefin-based resin may be exemplified by polyethylene (PE) and polypropylene (PP). Also in one exemplary embodiment, the outer layer may include a nylon resin.

In one exemplary embodiment, the thickness of the outer layer is not particularly limited, but may have, for example, a thickness of 10 μm to 50 μm, preferably 5 μm to 30 μm, and more preferably 10 μm to 25 μm. Can have

In addition, another embodiment of the present invention provides a secondary battery comprising a high temperature stability cell pouch according to an embodiment of the present invention.

High temperature stability cell pouch manufacturing method

One embodiment of the present invention comprises the steps of laminating the outer layer and the metal layer; And forming a sealant layer on the uncoated side of the metal layer, wherein the sealant layer has a multi-layered structure, and includes an indirect contact sealant layer, an intermediate sealant layer, and a direct contact sealant layer. Provides a method for manufacturing a pouch.

Since the specific components of the outer layer, the metal layer, and the sealant layer are the same as the above-described high temperature stability cell pouch, detailed description thereof will be omitted.

In one embodiment, the sealant layer forming step is a sealant layer is formed by a dry lamination method, the indirect contact sealant layer, the intermediate sealant layer, and the direct contact sealant layer may be different melting points from each other.

In order to form a sealant layer of a multi-layer structure, after mixing the raw materials (resins) corresponding to each layer, it is manufactured by melt extrusion through a T-die device designed to form a multi-layer structure.

The method of manufacturing the cell pouch is largely divided into an extrusion coating (EC) method and a dry-dry lami (SDL) method.

The extrusion coating method is a method of making a cell pouch by injecting molten adhesive resin through high temperature extrusion between a multi-layered or single-layered sealant layer and a metal layer, and extruding a resin capable of forming an adhesive resin and a sealant layer on the metal layer. There is a cooling method. The former method of injecting the adhesive resin is prepared by applying a film that can be used as a sealant layer in advance, but the latter method of extruding the adhesive resin and the resin for forming the sealant layer is different in that the film is not prepared and applied in advance.

On the other hand, the dry lamination method produces and applies a film used as a sealant layer, but when bonding to a metal layer, a cell-pouch is produced by laminating by coating an adhesive.

In the case of the pouch produced by the extrusion coating method, it is common to have high temperature stability compared to the pouch produced by the dry lamination method. In the case of the pouch produced by the dry lamination method, the gas generated under the high temperature condition is a heat-adhesive layer made of a polypropylene layer. This is because it is very difficult to discharge through.

The high temperature stability cell pouch according to the embodiment of the present invention includes a sealant layer having a multi-layer structure to reduce the risk of explosion at high temperatures and have excellent high temperature stability.

In one embodiment, the step of forming the sealant layer may further include an antiblocking agent or an amide-based slip agent in the direct contact sealant layer.

The present invention is explained in more detail through the following examples. However, the examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

In the following Examples and Comparative Examples, the A layer corresponds to the indirect contact sealant layer, the B layer corresponds to the intermediate layer, and the C layer corresponds to the direct contact sealant layer, PP refers to a polypropylene raw material, and PP-EL refers to a polypropylene elastomer. do. As described above, in order to form a multilayer structure sealant layer, after mixing the raw materials (resins) corresponding to each layer, it is manufactured by a melt extrusion method through a T-die equipment designed to form a multilayer structure.

Comparative Example 1: Existing single layer structure sealant layer

PP and PP-EL having a Tm of 150°C or higher were mixed to prepare a single layer sealant layer. It was designed with a total thickness of 30㎛, and was prepared as shown in FIG. 1.

Comparative Example 2: Conventional multilayer structure sealant layer

The A and C layers used PP with a Tm of 150°C or higher, and the B layer used PP and PP-EL with a Tm of 150°C or higher [existing material mixing ratio (PP: PP-EL = 75: 25)]. The total thickness of 30㎛, A layer C layer was designed to 4 ~ 5㎛, B layer was designed to 20 ~ 22㎛, it was prepared as shown in FIG.

Example 1: Sealant layer with Tm of the direct contact sealant layer adjusted

The A layer used PP with a Tm of 150°C or higher, and the B layer used PP with a Tm of 150°C or higher and PP-EL [mixing ratio PP: PP-EL = 75: 25], and the C layer had a Tm of 150°C or lower. Prepared using PP.

Total thickness is 30㎛, A layer C layer is 4 ~ 5㎛ respectively, B layer is 20 ~ 22㎛ was designed in the same manner as the existing sealant layer, it was prepared as shown in FIG.

Example 2: Sealant layer with Tm of the intermediate layer adjusted

The A layer and the c layer used PP having a Tm of 150°C or higher, and the B layer was prepared by adding 25% of the main raw material having a Tm of 150°C or higher and PP-EL having a Tm of 70 to 100°C. The total thickness of 30㎛, A layer C layer was designed to 4 ~ 5㎛, B layer was designed to 20 ~ 22㎛, it was prepared as shown in FIG.

Example 3: Sealant layer with Tm of intermediate layer and direct contact sealant layer adjusted

For layer A, PP with a Tm of 150°C or higher was used. For layer B, 25% of the main raw material with a Tm of 150°C or higher and PP-EL with a Tm of 70 to 100°C were added 25%. It was prepared. The total thickness of 30㎛ was designed as A layer C layer 4 ~ 5㎛, B layer 20 ~ 22㎛, it was prepared as shown in FIG.

Experimental Example 1: Hot box test

Comparative Example 1-2 and Example 1-3 were molded into a cell pouch with a mold (3 cm X 6.5 cm), and a lithium secondary battery was manufactured using the molded cell pouch.

Gas leakage due to the breakage of the heat-adhesive surface was evaluated by time under high temperature conditions (130~150℃), and if gas leakage occurred within 2 hours at 130℃ and within 20 minutes at 150℃, the final evaluation was passed. Did.

The experimental results are shown in Table 1-2 below.

130℃ Storage Time (Min) Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 30 X X X X X 60 X X X X X 90 X X X X O 120 X X X X - 150 X X O O - 180 X X - - - Sum/pay fail fail fail fail pass

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

150℃ storage time (Min) Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 10 X X X X O 20 X X O O - 30 X X - - - 40 X O - - - 50 O - - - - Sum/pay fail fail pass pass pass

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

[Analysis of experimental results]

When stored at 130°C, in Comparative Examples 1 and 2, gas did not leak even after 3 hours had elapsed. Gas was not leaked when PP and PP-EL over 150℃ were applied.

In the case of Examples 1 and 2, the gas leaked after 150 minutes. When PP and PP-EL below 150°C are applied, it can be seen that a passage through which gas may leak may be generated, but not generated within a reference time (120 minutes).

In the case of Example 3, the gas leaked when 90 minutes elapsed, and a gas outflow passage can be generated within a reference time only when a raw material of less than 150°C is applied to the direct contact layer and the intermediate layer.

When stored at 150°C, in the case of 1,2, gas leaked after 40 minutes or more. The gas leakage path may be generated because it was stored at a temperature close to Tm of the applied raw material of the sealant layer, but it can be seen that it was not generated within the existing time (20 minutes).

In the case of Examples 1, 2, and 3, the gas leaked within 20 minutes, and a gas leakage path was created within the existing time. Deformation of raw materials below 150°C occurs at 150°C storage conditions, and a gas leakage path is generated within a relatively quick time.

Claims (13)

Sealant layer;
A metal layer formed on the sealant layer; And
And an outer layer formed on the metal layer.
The sealant layer has a multi-layer structure, and includes an indirect contact sealant layer, an intermediate sealant layer, and a direct contact sealant layer, a high temperature stability cell pouch. According to claim 1,
The thickness of the direct contact sealant layer is 10-20% of the total thickness of the sealant layer, a high temperature stability cell pouch. According to claim 1,
The direct contact sealant layer comprises a main raw material comprising polypropylene, and the melting point (Tm) of the main raw material is 130-150°C, a high temperature stability cell pouch. According to claim 1,
The direct contact sealant layer further comprises an antiblocking agent or an amide-based slip agent, and the content of the antiblocking agent or amide-based slip agent is 1-10% by weight relative to the total weight of the direct contact sealant layer, a high temperature stability cell pouch. According to claim 4,
The amide-based slip agent comprises one or more of Erucamide, Behenamide, Oleamide, high temperature stability cell pouch. According to claim 1,
The intermediate layer includes a main raw material containing polypropylene and an elastomer,
The elastomer is a polypropylene-based elastomer, and the melting point (Tm) of the elastomer is 50-80°C lower than the melting point of the main raw material, and a high temperature stability cell pouch. The method of claim 6,
The content of the elastomer is 10-60% by weight relative to the total weight of the intermediate layer, high temperature stability cell pouch. According to claim 1,
The intermediate layer has a thickness of 50-80% of the total thickness of the sealant layer, a high temperature stability cell pouch. According to claim 1,
The sealant layer is formed by a dry lamination method, a high temperature stability cell pouch. A secondary battery comprising the high temperature stability cell pouch according to claim 1. Laminating the outer layer and the metal layer; And
Including; forming a sealant layer on the non-coated side of the metal layer;
The sealant layer has a multi-layer structure, a method of manufacturing a high temperature stability cell pouch comprising an indirect contact sealant layer, an intermediate sealant layer, and a direct contact sealant layer. According to claim 1,
In the step of forming the sealant layer, a sealant layer is formed by a dry lamination method, and the indirect contact sealant layer, the intermediate sealant layer, and the direct contact sealant layer have different melting points from each other. According to claim 1,
The step of forming the sealant layer further comprises an anti-blocking agent or an amide-based slip agent in the direct contact sealant layer.

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