KR20220007511A - Secondary battery having a Gas discharge unit for exhausting gas and manufacturing method having the same - Google Patents

Abstract

The present invention relates to a secondary battery which improve safety while improving the performance and lifespan of the secondary battery by providing a gas discharge unit that discharges only gas, and a method for manufacturing a secondary battery, and specifically, to a secondary battery including: an electrode assembly; and a case including an accommodating unit for accommodating the electrode assembly, a sealing unit formed by sealing the periphery of the accommodating unit, and the gas discharge unit in which one end thereof comes in contact with the accommodating unit and the other end thereof comes in contact with the outside to selectively discharge only gas in the sealing unit.

Description

A secondary battery and a secondary battery manufacturing method including a gas discharge unit for discharging gas

This application claims the benefit of priority based on Korean Patent Application No. 2020-0085641 dated July 10, 2020, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification.

The present invention relates to a secondary battery including a gas exhaust filter and a method for manufacturing a secondary battery, and more particularly, includes a case having a gas exhaust part capable of selectively exhausting internal gas while blocking moisture inflow into the secondary battery It relates to a secondary battery and a secondary battery manufacturing method.

Recently, as devices using batteries are diversified, the demand for high-capacity and high-density batteries is increasing. In particular, interest in pouch-type secondary batteries that can obtain high-capacity and high-density batteries by reducing the thickness of the aluminum laminate sheet is increasing.

A pouch-type secondary battery is generally formed by forming an aluminum laminate sheet to form an accommodating part, and then accommodating an electrode assembly including a positive electrode, a separator, and a negative electrode in the accommodating part. The aluminum laminate sheet is easily deformable and can be manufactured in various shapes to form a pouch-type secondary battery suitable for various electronic devices. In addition, since the aluminum laminate sheet is lightweight unlike the conventional cylindrical secondary battery or prismatic secondary battery, there is an advantage in that the energy density per weight of the pouch-type secondary battery can be improved.

1 is a perspective view of a pouch-type secondary battery according to the prior art.

A pouch-type secondary battery according to the prior art includes an electrode assembly 10 from which an electrode lead 11 protrudes, and a case 20 having an accommodating part 21 for accommodating the electrode assembly 10 . In the pouch-type secondary battery, after accommodating the electrode assembly 10 in the accommodating part 21 , the periphery of the accommodating part 21 is sealed to form a sealing part 22 . Although the sealing part 22 is formed so that materials existing inside the pouch-type secondary battery do not react with external air, a separate member for removing gas generated inside the storage part does not exist. In the pouch-type secondary battery having the above structure, it is difficult to efficiently remove the gas generated during charging and discharging of the secondary battery. It can also cause problems that can leak gas or chemicals.

In order to improve the safety of the pouch-type case, in the pouch-type secondary battery according to the prior art, a gas removing material is placed therein to remove gas, or a gas storage part is provided separately in addition to the storage part. However, when a substance that removes gas is placed, the efficiency of the battery is reduced by interfering with the operation of the pouch-type secondary battery. There is a problem with this decreasing.

In order to solve this problem, in Patent Document 1, a hydrogen permeable material is formed on at least a part of the metal tab leads exposed to the outside of the exterior material, and the hydrogen permeable material is continuously present from the inside to the outside of the exterior material. However, in Patent Document 1, the hydrogen permeable material is used to prevent moisture from penetrating into the battery, which may interfere with the operation of the battery, and has a disadvantage in that gas other than hydrogen cannot be efficiently discharged.

In Patent Document 2, the electrode lead is formed in a porous structure, and a gas absorbing material is coated on the inner surface of the pores of the electrode lead, but there is a fear that the gas absorbing material acts as a resistance to reduce the efficiency of the entire battery.

Accordingly, there is a need for a configuration capable of improving the safety of the battery without reducing the performance and efficiency of the battery.

Japanese Patent Laid-Open No. 2014-212034 Republic of Korea Patent Publication No. 2017-0082239

In order to solve the above problems, in the present invention, a gas discharge unit for selectively discharging only gas is placed in the sealing part of the pouch-type secondary battery to efficiently discharge gas without infiltration of moisture from the outside to maintain battery performance while improving safety.

In addition, an object of the present invention is to provide a method for manufacturing a secondary battery having a low battery defect rate while facilitating gas discharge because the case is well sealed by providing a method of sealing the gas discharge unit, the case, and the electrode lead together.

A secondary battery according to the present invention for solving the above problems includes a housing unit for accommodating an electrode assembly, a sealing unit formed by sealing the periphery of the receiving unit, and one end of the sealing unit is in contact with the receiving unit and the other end is outside. It may include a pouch-type case having a gas discharge unit that selectively discharges only gas by contact.

The gas discharging unit may be made of a gas discharging material having a gas permeability greater than a water permeability.

The outgassing material may have a moisture penetration rate of 50 ppm or less for one year.

The outgassing material may be polypropylene (PP), polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene tetraphthalate (PET), or a mixture thereof.

The thickness of the gas discharge part may be 100 μm or more and 600 μm or less.

The gas discharge part may surround the electrode lead protruding to the outside from the electrode assembly.

The pouch-type case may include a laminate sheet, and the gas discharge part and the laminate sheet contact part may be coated with polypropylene.

The secondary battery according to the present invention comprises the pouch-type case and the electrode assembly. The present invention provides a step of (S1) applying a gas-discharging material having a gas permeability greater than that of water permeability to at least a portion of the electrode lead surface of the electrode assembly. ; and (S2) accommodating the electrode assembly in a receiving unit inside a pouch-type case provided with a gas discharge unit and sealing the electrode assembly.

In the secondary battery manufacturing method according to the present invention, the gas-discharge material may include polypropylene (PP), polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene tetraphthalate (PET), or a mixture thereof. can

In the secondary battery manufacturing method according to the present invention, in the step (S2), the gas-discharge material and the pouch-type case may be combined by thermal fusion at least once to 10 times.

In the secondary battery manufacturing method according to the present invention, the gas discharge unit may undergo a surface modification process.

In the secondary battery manufacturing method according to the present invention, the thickness of the gas discharge part may be 100 μm or more and 600 μm or less.

In the present invention, one or two or more non-conflicting configurations among the above configurations may be selected and combined.

The secondary battery according to the present invention includes a gas discharge unit that selectively discharges only gas, thereby efficiently discharging internal gas, thereby improving safety while maintaining performance of the secondary battery.

In addition, since the secondary battery has a small amount of permeation of moisture inside the battery, and safety is maintained even when a large amount of electrode assembly is accommodated therein compared to a conventional battery, the performance and lifespan characteristics of the battery are improved.

In addition, while manufacturing the secondary battery in a simple manner, sealing force is also improved, thereby reducing the battery defect rate and reducing the cost of manufacturing the secondary battery.

1 is a perspective view of a pouch-type secondary battery according to the prior art.
2 is a perspective view of a pouch-type secondary battery according to the present invention.
3 is a cross-sectional view according to the first embodiment of the pouch-type secondary battery according to the present invention.
4 is a cross-sectional view according to the second embodiment of the pouch-type secondary battery according to the present invention.
Figure 5 is a graph comparing the moisture permeability when the polypropylene is used in the gas discharge part according to the present invention and when the gas discharge part is not provided.
6 is a graph comparing gas permeability when polypropylene is used in the gas outlet according to the present invention and when the gas outlet is not provided.

In the present application, terms such as "comprises", "have", or "include" are intended to designate that the features, numbers, steps, components, parts, or combinations thereof described in the specification exist, and one or more other It should be understood that this does not preclude the possibility of addition or presence of features or numbers, steps, operations, components, parts, or combinations thereof.

In addition, the same reference numerals are used throughout the drawings for parts having similar functions and functions. Throughout the specification, when a part is said to be connected to another part, it includes not only a case in which it is directly connected, but also a case in which it is indirectly connected with another element interposed therebetween. In addition, the inclusion of any component does not exclude other components unless otherwise stated, but means that other components may be further included.

Hereinafter, a secondary battery and a secondary battery manufacturing method according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a perspective view of a pouch-type secondary battery according to the present invention.

The pouch-type secondary battery according to the present invention includes an electrode assembly 100 from which an electrode lead 110 protrudes, a housing 210 accommodating the electrode assembly 100, and a periphery of the accommodating part 210 . A case ( 200) is included.

The electrode assembly 100 is a jelly-roll-type assembly having a structure in which a separator is interposed between a long sheet-shaped positive electrode and a negative electrode and then wound up, or a unit of a structure in which a rectangular positive electrode and a negative electrode are stacked with a separator interposed therebetween. A stacked assembly consisting of cells, a stack-folding assembly in which unit cells are wound by a long separation film, or a lamination-stacking assembly in which unit cells are stacked with a separator interposed therebetween and attached to each other, etc. can be done, but is not limited thereto. The electrode assembly according to the present invention preferably has a stack-folding type, lamination-stack type structure in which physical stress is minimal when forming a curved module.

The electrode lead 110 may have a structure in which the positive electrode tab and the negative electrode tab of the electrode assembly 100 are electrically connected to each other and then exposed to the outside of the case, and the electrode lead 110 is directly connected without the positive electrode tab and the negative electrode tab. It may have a structure connecting the outside of the electrode assembly 100 and the case 200, but is not limited thereto. Since the secondary battery as described above corresponds to generally known configurations, a more detailed description thereof will be omitted.

The case 200 typically has a laminate sheet structure of an inner layer/metal layer/outer layer. Since the inner layer is in direct contact with the electrode assembly, it must have insulation and electrolyte resistance, and for sealing with the outside, the sealing property, that is, the sealing portion where the inner layers are thermally bonded to each other must have excellent thermal bonding strength. The material of the inner layer may be selected from polyolefin resins such as polypropylene, polyethylene, polyethylene acrylic acid, polybutylene, etc., polyurethane resins and polyimide resins having excellent chemical resistance and good sealing properties, but is not limited thereto, Polypropylene excellent in mechanical properties such as tensile strength, rigidity, surface hardness, and impact resistance and chemical resistance is the most preferable.

The metal layer in contact with the inner layer corresponds to a barrier layer that prevents moisture or various gases from penetrating into the battery from the outside.

And an outer layer is provided on the other side of the metal layer, and this outer layer can be made of a heat-resistant polymer with excellent tensile strength, moisture permeability and air permeability prevention so as to secure heat resistance and chemical resistance while protecting the electrode assembly. As an example, nylon or polyethylene terephthalate may be used, but is not limited thereto.

The accommodating part 210 may be formed in both the upper and lower portions of the case 200 , or may exist only in either one of the upper and lower portions. At this time, it may be more preferable to exist only in either the upper or lower part because it can reduce the surplus space of the terrace part.

In addition, the case 200 seals the outer surface of the accommodating part 210 to prevent substances in the accommodating part 210 from being discharged to the outside. At this time, the sealing portion 220 formed by sealing is bent in the direction of the receiving portion 210 to improve the energy density of the battery module. At this time, the terrace portion from which the electrode lead 110 protrudes in one direction or in both directions among the sealing portion 220 protrudes from the receiving portion 210 .

The gas discharge part 230 may be located in the sealing part 220 . The gas discharge part 230 may be present in any part of the sealing part 220 . For example, the gas discharge unit 230 may be disposed at a portion where the electrode lead 100 is present as shown in FIG. 2 .

3 is a cross-sectional view according to the first embodiment of the pouch-type secondary battery according to the present invention.

In the first embodiment of the pouch-type secondary battery according to the present invention, a material constituting the gas discharge unit 230 is applied to the sealing unit 220 of the case 200 , that is, a laminate sheet to the electrode lead 110 . may be combined with Through such a structure, a gas discharge passage may be secured while increasing the coupling force between the gas discharge unit 230 and the sealing unit 220 .

4 is a cross-sectional view showing a second embodiment of the pouch-type secondary battery according to the present invention.

In the gas discharge unit 230 according to the first embodiment as shown in FIG. 3 , a material constituting the gas discharge unit 230 is coated on the surface of the electrode lead 110 and bonded thereto, and then this is applied to the case 200 . A form combined with is also possible. This may reduce a space that may be formed of the electrode lead 110 , that is, an unsealed portion, while enabling smooth movement of the gas discharged through the gas discharge unit 230 . In this case, the gas discharge part 230 may serve to couple the electrode lead 100 and the sealing part 220 between the electrode lead 100 and the sealing part 220 . The gas discharge unit 230 includes the case 200 made of a laminate sheet, that is, the inner layer 221 of the sealing unit 220 including the outer layer 221 , the metal layer 222 , and the inner layer 221 , and In order to increase the bonding force of the gas discharge unit 230, the gas penetrating unit 231 located on the electrode lead 110 facing surface and the coating unit 232 for improving bonding strength on the inner layer 22 facing surface may be provided. can

The gas penetrating part 231 may include at least one of fluorine-based, olefin-based, acrylic-based polymer and ceramic, and is attached to the lead metal bonding surface for MAH (Maleic) adhesion performance with the lower lead metal. anhydride) treatment or other chemical treatment capable of forming -OH (hydroxyl) groups. This is advantageous in improving the bonding strength of the two materials to be bonded. The gas penetrating portion 231 may include a layer including pores for gas permeation in a horizontal direction.

The coating part 232 may be directly coated on the gas exhaust part 230 or may be coated on the inner layer 221 to be coupled to the gas exhaust part 230 . For the coating part 232 , a material having high bonding strength between the material constituting the gas discharge unit 230 and the material constituting the inner layer 221 may be used. For example, the coating part 232 may be made of a polypropylene material. In the present invention, the thickness of the coating portion 232 may be 50 μm to 500 μm. When the coating part 232 is fused with the pouch, the thickness may be reduced by heat and pressure, and if it is too thin, there is a risk that the sealing strength may be reduced. The presence of the coating part 232 makes it possible to better seal between the sealing part 220 and the electrode lead 110 .

The gas discharge unit 230 may be made of a gas discharge material that is stable under the secondary battery operating condition and has a gas permeability greater than a water permeability. As the gas-discharge material, a material having a moisture penetration rate of 50 ppm or less for one year may be used.

The outgassing material may be, for example, polypropylene, polytetrafluoroethylene, polyethylene, polyethylene tetraphthalate, or a mixture thereof. The polypropylene, polyvinylidene difluoride, polytetrafluoroethylene, polyethylene, polyethylene tetraphthalate, or a mixture thereof has a characteristic that can suppress moisture penetration while discharging gases such as carbon dioxide, methane, ethane, It is possible to ensure that the operation of the battery can be stably maintained while discharging the gas mainly generated by the lithium-ion battery. At this time, in consideration of the bonding strength with the laminate sheet, it may be more preferable to use polypropylene, polyvinylidene difluoride, etc., which has a high bonding strength with the laminate sheet and is easy to seal than other materials.

The thickness of the gas permeable part 230 may be 100 μm or more and 600 μm or less. When the gas permeation part 230 is 100 μm or less, the amount of gas passing through the gas transmission part 230 is limited, so that a desired gas discharge effect may not be obtained, and when the gas transmission part 230 exceeds 600 μm Since the gas permeation part 230 is too thick, the thickness of the secondary battery may be increased, and a desired sealing force may not be obtained.

The secondary battery according to the present invention comprises the steps of (S1) applying a gas-discharge material having a gas permeability greater than water permeability to at least a portion of the electrode lead surface of the electrode assembly, and (S2) the number of inside the case made of a laminate sheet for the electrode assembly It may include a step of sealing after receiving the payment.

In this case, in step (S1), a gas-discharge material may be applied to the case instead of the electrode lead surface. Its position may be changed according to the bonding force and sealing force of the gas emitting material.

Examples of the outgassing material include polypropylene (PP), polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene tetraphthalate (PET), or a mixture thereof, of which polypropylene is the electrode lead. The bonding force between the case and the laminate sheet is high, so it can be placed in any part of the sealing part of the case, but in the case of polytetrafluoroethylene, a lot of time and high temperature are required for sealing, so that the above It is preferable that the electrode lead is disposed in a portion through which the overall sealing force of the secondary battery is not reduced.

In the step (S2), the gas exhaust material and the case may be combined by thermal fusion at least once to 10 times. The number and time of thermal fusion may vary depending on the characteristics of the gas-discharging material and the bonding force between the electrode lead and the case. The thermal fusion method may be a method of pressing with a force of 1kg/mm to 100kg/mm while applying heat of 150°C to 250°C. When pressurized at a temperature higher than the above temperature, the electrode assembly and the case may be damaged, and when fused at a temperature lower than the above, the adhesive material may not melt properly. In addition, if the pressing force is too strong, the electrode lead may be damaged, and if the pressing force is weak, the sealing force may be reduced and the pouch-type secondary battery may be damaged even during normal operation of the battery. In this case, the thermal fusion method may be performed using a laser in addition to a method using heat.

In addition to the thermal fusion as described above, a laminate sheet or electrode lead used as a case may be immersed in a solution made of a gas-discharge material to be coated. The dipping method may be exemplified by spin coating, slot-die coating, doctor blading, bar coating, dipping process, and the like.

The gas discharge unit may be subjected to a surface modification process in order to increase bonding force with the electrode lead or the case. The surface modification process may be performed using UV curing or plasma.

In addition, the thickness of the gas outlet may be 100 μm or more and 600 μm or less. When the thickness of the gas discharge part is too thin, it is difficult to smoothly discharge gas and moisture penetrates, whereas when the thickness of the gas discharge part is too thick, moisture penetration is easy due to the thickness of the gas discharge part, thereby reducing the performance of the battery Because.

<Experimental Example 1>

A dummy cell without an electrode and a separator was formed in the shape according to the first embodiment of the present invention. At this time, the gas outlet was coated with polypropylene having a thickness of 100 μm.

<Experimental Example 2>

Since it is the same as Experimental Example 1 except for coating the gas outlet with polypropylene having a thickness of 200 μm, other descriptions will be omitted.

<Comparative Example 1>

Except that nothing was coated on the gas discharge part, it is the same as in Experimental Example 1, so other descriptions will be omitted.

How to measure water penetration

Moisture permeation of the dummy cell is measured by accelerating the rate of water permeation in a high-temperature and high-humidity environment, and after accelerated storage, a portion of the solution in the sealed container is extracted and titrated using a titrator. In order to test the water penetration of the dummy cell, samples were placed in a chamber set at high temperature and high humidity (60° C., RH 90%) and the change in water penetration was measured for one week. At this time, the moisture content penetrating into the secondary battery was measured by increasing the concentration of HF formed according to the reaction of the electrolyte. In the present invention, when water permeates for 16 weeks in an accelerated water permeation environment, 0.1 g of HF in the secondary battery corresponds to 500 ppm permeation of water (H 2 O) for 10 years.

5 is a graph comparing moisture permeability when polypropylene is used in the gas outlet according to the present invention and when the gas outlet is not provided. As can be seen in FIG. 5, it can be seen that the moisture permeation rate of Experimental Example 1 (Ex. 1) and Experimental Example 2 (Ex. 2) according to the present invention is not as good as that of Comparative Example 1 (Comp.Ex. 1). This is due to the nature of the pouch-type case that is not sealed, and some moisture may penetrate. However, when comparing Experimental Example 1 and Experimental Example 2, it can be seen that when the thickness of the gas discharge part is increased, the moisture permeability is decreased. That is, by providing a gas discharge unit, it is possible to control the amount of gas within the permitted moisture range. This is because polypropylene (PP), polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene tetraphthalate (PET) or a mixture thereof used in the present invention has a low water permeability and a large amount of gas emission compared to other materials. , as the thickness increases, the water discharge decreases and the gas discharge increases.

<Second Experimental Example 1>

The pressure change inside the pouch-type secondary battery in which polypropylene (Second Experimental Example 1, Ex.1) of 100 μm thick was placed in the gas outlet according to the present invention was measured for 24 hours.

<Second Comparative Example 1>

Since the pouch-type secondary battery not provided with a gas discharge unit is the same as that of the second experimental example 1, other descriptions will be omitted.

At this time, the inside of the pouch-type secondary battery was artificially injected with carbon dioxide gas generated a lot in the secondary battery from the outside. At this time, about 0.0161 atm of carbon dioxide gas was injected for 20 hours.

6 is a graph comparing the gas permeability when 100 μm thick polypropylene is used in the gas outlet according to the present invention and when the gas outlet is not provided. As can be seen in FIG. 7 , in the case of the second experimental example 1 (Ex.1), it can be seen that the pressure inside the pouch-type secondary battery was reduced because the gas was discharged more than that of the second comparative example 1 (Comp.Ex.1).

As described above, it can be seen that when a material selectively discharging only gas to the gas discharge unit according to the present invention, that is, a material having high gas permeability and high water permeability is used, gas discharge can be performed more smoothly.

As the specific parts of the present invention have been described in detail above, for those of ordinary skill in the art, these specific descriptions are only preferred embodiments, and the scope of the present invention is not limited thereby, It is obvious to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention, and it is natural that such variations and modifications fall within the scope of the appended claims.

10, 100: electrode assembly
11, 110: electrode lead
20, 200: case
21, 210: storage unit
22, 220: sealing part
221: outer layer
222: metal layer
221: inner layer
230: gas outlet
231: gas penetration
232: coating part

Claims (13)

A pouch type having an accommodating part for accommodating the electrode assembly, a sealing part formed by sealing the periphery of the accommodating part, and a gas discharge part in the sealing part having one end in contact with the receiving part and the other end in contact with the outside to selectively discharge only gas case. According to claim 1,
The gas discharge unit is a pouch-type case, characterized in that the gas permeability is made of a gas discharging material greater than the water permeability. 3. The method of claim 2,
The pouch-type case, characterized in that the gas-discharge material has a moisture penetration rate of 50 ppm or less for one year. 4. The method of claim 3,
The pouch-type case comprising the gas emitting material is polypropylene (PP), polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene tetraphthalate (PET) or a mixture thereof. According to claim 1,
A pouch-type case, characterized in that the thickness of the gas discharge portion is 100㎛ or more and 600㎛ or less. According to claim 1,
The pouch-type case, characterized in that the gas discharge part surrounds the electrode lead protruding to the outside from the electrode assembly. According to claim 1,
The pouch-type case consists of a laminate sheet,
The pouch-type case, characterized in that the gas discharge portion and the laminate sheet contact portion is coated with polypropylene. A pouch-type case according to any one of claims 1 to 7; and
Secondary battery comprising; electrode assembly. (S1) applying a gas-discharge material having a gas permeability greater than a water permeability to at least a portion of the electrode lead surface of the electrode assembly; and
(S2) storing the electrode assembly in a storage unit inside a pouch-type case provided with a gas discharge unit and sealing the electrode assembly; 10. The method of claim 9,
The gas-discharge material is a secondary battery manufacturing method comprising polypropylene (PP), polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene tetraphthalate (PET), or a mixture thereof. 10. The method of claim 9,
The method for manufacturing a secondary battery, characterized in that in the step (S2), the gas-discharge material and the pouch-type case are combined by thermal fusion at least once to 10 times. 10. The method of claim 9,
The method for manufacturing a secondary battery, characterized in that the gas discharge unit undergoes a surface modification process. 10. The method of claim 9,
The thickness of the gas discharge part is a secondary battery manufacturing method, characterized in that not less than 100㎛ 600㎛.

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