KR20080064916A - Lithium secondary battery with improved safety against ignition and explosion - Google Patents

Abstract

The present invention is a battery cell in which the electrode assembly of the anode / separator / cathode structure is built in the cell case, the inside of the cell case includes an inert gas carrier having a structure for discharging the inert gas under abnormal operating conditions of the battery, The carrier provides a battery cell having a structure that ensures the safety of the battery against ignition and explosion by discharging an inert gas while mechanically broken by the increase in pressure inside the battery.

Description

Lithium Secondary Battery Having Improved Stability against Fire and Explosion

1 is an exploded perspective view of a general structure of a conventional pouch type secondary battery;

2 is a schematic side view of a pouch type secondary battery in which an inert gas carrier is placed inside a battery cell according to one embodiment of the present invention;

3 is a schematic diagram of a structure in which a container containing the inert gas carrier of FIG. 2 is broken;

4 is a schematic diagram of a structure in which an inert gas carrier is placed inside a battery pack according to another embodiment of the present invention;

FIG. 5 is a schematic diagram of a structure in which a container containing the inert gas carrier of FIG. 4 is ruptured; FIG.

6 is a schematic diagram of a structure in which the needle member and the inert gas carrier of FIG. 4 are installed on the outer surface of the battery cell and the inner surface of the pack case, respectively.

The present invention relates to a lithium secondary battery with improved safety against ignition and explosion, and more particularly, a battery cell in which an electrode assembly having a positive electrode / membrane / cathode structure is built in a cell case. An inert gas carrier having a structure for discharging an inert gas under abnormal operating conditions of the battery is included, and the support body discharges the inert gas while being mechanically damaged by an increase in pressure inside the battery, thereby ensuring the safety of the battery against explosions. It relates to a battery cell characterized in that.

As the development and demand for mobile devices increases, the demand for secondary batteries as a source of energy is increasing rapidly. Among them, many researches have been conducted and commercialized and widely used for lithium secondary batteries with high energy density and high discharge voltage. It is used.

However, conventional lithium secondary batteries have a risk of ignition / explosion when exposed to high temperatures. In addition, even when a large current flows within a short time due to overcharging, external short circuit, nail penetration, local crush, or the like, there is a risk of fire / explosion while the battery is heated by IR heating. As the temperature of the battery rises, the reaction between the electrolyte and the electrode is accelerated. As a result, heat of reaction is generated to further increase the temperature of the battery, which in turn accelerates the reaction between the electrolyte and the electrode. Thus, the temperature of the battery rises rapidly, which in turn accelerates the reaction between the electrolyte and the electrode. Due to such a vicious cycle, a thermal runaway phenomenon in which the temperature of the battery rises rapidly occurs, and when the temperature rises to a certain level or more, the battery may ignite. In addition, as a result of the reaction between the electrolyte and the electrode, gas is generated to increase the battery internal pressure, and the lithium secondary battery explodes above a certain pressure. The risk of ignition / explosion can be said to be the most fatal drawback of lithium secondary batteries.

Therefore, essential considerations for the development of a lithium secondary battery are to ensure safety. As an effort to secure such safety, there are a method of mounting a safety element on the outside of the cell and using a material inside the cell. PTC devices, CID devices, temperature protection circuits, and safety vents using changes in the breakdown voltage of the battery are examples of the former. The latter is the addition of substances that can be changed chemically and electrochemically.

However, the safety devices mounted on the outside of the cell do not provide safety when the flammable gas is already filled inside the cell due to an abnormal battery, and the CID device may be applied only to a cylindrical battery. In addition, it is known that a fast response time such as internal short circuit, bed penetration, local damage, etc. is not properly protected.

One method of using a substance inside a cell is to add an additive that improves safety to an electrolyte or an electrode. Chemical safety devices have the advantage that they can be applied to all kinds of batteries do not require additional processes and space, but has the problem that the performance of the battery is degraded due to the addition of materials. As such a material, a material which forms a passivation layer on the electrode, and a material that increases the resistance of the electrode as the volume expands when the temperature rises is reported. However, each of them has a problem in that by-products are generated during the formation of the passivation layer, thereby degrading the performance of the battery or increasing the volume of the battery.

In this regard, Japanese Patent Application Laid-Open Publication No. 2002-319436 discloses that when a pressure inside a battery cell rises, it is communicated with the outside by a pressure releasing means to lower the pressure inside the battery cell and melt at the boiling point of the electrolyte. A technology for preventing an ignition of a battery cell by storing an inert gas generator therein and discharging an inert gas when the temperature rises is disclosed. However, the above technique has a disadvantage in that the manufacturing process of the configuration in which the receiving member is melted to generate an inert gas while communicating with the outside by the pressure release means is not easy, and it does not effectively cope with a reaction such as rapid heating. have. Moreover, in order to generate an inert gas, the receiving member must be melted at the boiling point of the electrolyte, and in spite of the abnormality of the battery, when the temperature of the battery does not reach the boiling point of the electrolyte, the operation reliability is low. I also have

In addition, Japanese Patent No. 3297772 discloses a technique of releasing an inert gas into an inside of a battery cell from an inert gas encapsulation body located between the battery cell and the battery pack case when a sensor is attached to the inside of the battery cell. have. However, the above-mentioned technology has various problems such as a sensor, an operation circuit, and an opening / closing valve of an inert gas encapsulation, which increases manufacturing costs and complicates the manufacturing process. Moreover, there is a disadvantage that it is applicable only to a battery having a considerable degree of size since sufficient space for these members to be mounted is required.

Therefore, there is a high demand for the development of new safety means for preventing fire / explosion without degrading overall performance of the battery.

Accordingly, an object of the present invention is to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

The inventors of the present application after various experiments and in-depth studies to improve the safety of the battery cell, if the inert gas carrier ruptured under abnormal operating conditions inside the battery cell, ignition / explosion due to temperature rise It was confirmed that the safety of the battery can be greatly improved by preventing the occurrence of the present invention.

Accordingly, the battery cell according to the present invention is a battery cell in which an electrode assembly having a cathode / separation membrane / cathode structure is built in a cell case, and the inside of the cell case has an inert structure in which an inert gas is discharged under abnormal operating conditions of the battery. A gas carrier is included, and the carrier has a structure that ensures the safety of the battery by discharging an inert gas while mechanically broken by an increase in pressure inside the battery.

That is, in the battery cell according to the present invention, when the internal pressure of the battery increases due to the generation of flammable / volatile gas while the electrolyte is decomposed due to abnormal operation inside the battery or a short circuit caused by application of an external force, the inert gas carrier may be It is made of a structure that discharges the inert gas while mechanically broken, it is possible to improve the safety of the battery by reducing the concentration of the flammable / volatile gas to reach a concentration that can cause ignition / explosion. Such inert gas discharge may induce early operation of a safety vent and a CID element, in some cases, and may improve battery safety.

In one preferred embodiment, the inert gas carrier may have a structure in which an inert gas is sealed in a high pressure state in a container capable of being ruptured under abnormal operating conditions of the battery, and at the same time the inert gas inside the container is ruptured. The gas may be discharged to reduce the concentration of the flammable / volatile gas in the battery.

The container in which the high pressure inert gas is sealed is not particularly limited as long as it is a material that can be destroyed or ruptured under desired conditions with chemical resistance to the electrolyte solution inside the battery, and preferably a small bag made of a polymer resin ( bag).

The inert gas is not particularly limited as long as it is a non-combustible gas. For example, one gas selected from the group consisting of nitrogen, carbon dioxide, helium, argon, neon, krypton, xenon, and radon or two or more gases are mixed. It can be made in a configuration.

As another preferred example, the inert gas carrier may be formed of a structure in which a material ('gas generator') generating an inert gas by a chemical reaction is sealed in a container that may be damaged under abnormal operating conditions of the battery. Examples of the gas generating agent include, but are not limited to, potassium hydrogen carbonate (K ₂ CO ₃ ), sodium hydrogen carbonate (NaHCO ₃ ), manganese carbonate (MnCO ₃ ), etc., which generate pyrolysis and generate inert gas. It doesn't happen.

Therefore, the gas generating agent which generates an inert gas under predetermined conditions is sealed in the container, and when a container is broken under predetermined conditions, a chemical reaction can occur and an inert gas can be discharged.

As described above, the battery cell of the present invention is mechanically damaged due to the increase in pressure inside the battery, so that the operation reliability is high and does not affect the electrochemical action inside the battery. The mechanical breakage due to the pressure increase inside the battery means that the inert gas carrier is physically broken while the volume of the cell is increased or a change is caused in a specific part of the cell.

In one preferred example, the inert gas carrier may be a structure that is damaged by the physical change when the cell case is deformed by the pressure rise inside the battery. That is, the inert gas carrier is mounted in a fixed state in the cell case, and thus the carrier may be damaged while the fixed state is changed due to the deformation of the cell case.

As such, a battery cell that is likely to cause a change in the cell case due to an increase in the pressure inside the battery is, for example, in a state in which an electrode assembly is embedded in a pouch-type cell case of a laminate sheet including a resin layer and a metal layer. The pouch type battery cell which consists of a structure which heat-sealed the outer peripheral surface of a sheet | seat is mentioned.

In one preferred example, the inert gas carrier is located in the portion in contact with the heat sealing sealing portion of the pouch-type battery cell, it may be made of a structure that discharges the inert gas while the carrier is broken at the same time as the heat sealing seal portion rupture. have.

As a specific example, a pouch-type battery cell in which an electrode assembly is embedded in a battery case of a laminate sheet may be formed in a cell case including a case body including a concave shape accommodating portion into which the electrode assembly may be seated and a cover corresponding to the body. It is manufactured by accommodating the electrode assembly and sealing the edges of the case body and the cover, and having a structure in which a part of the inert gas carrier is engaged with the sealing portion to seal when the pressure inside the battery is abnormally increased. At the same time as the site is opened, the inert gas carrier is also damaged, and the inert gas is discharged.

In another preferred embodiment, the battery cell has a built-in electrode assembly in a rectangular metal can (cell case) and a safety vent is formed on the outer surface of the metal can to discharge gas when the internal pressure is abnormally increased. In addition, the inert gas carrier may be positioned in contact with the safety vent, and the inert gas carrier may be broken at the same time as the safety vent is ruptured, thereby discharging the inert gas.

The present invention also relates to a battery pack in which a battery cell in which an electrode assembly having a positive electrode / membrane structure / cathode structure is built in a cell case is mounted inside a predetermined pack case. While providing a battery pack having a structure containing an inert gas carrier having a structure for discharging an inert gas.

As described above, the battery pack according to the present invention also discharges the inert gas while the carrier is mechanically damaged when the pressure inside the battery increases. In one preferred example, a battery in the vicinity of the inert gas carrier It may be made of a structure that is provided with a needle member for rupturing the carrier so that the inert gas can be discharged under abnormal operating conditions of.

For example, the inert gas carrier is mounted on the outer surface of the battery cell, the needle member may be of a structure that is installed on the inner surface of the pack case at a position corresponding thereto, the inert gas carrier is the opposite of the battery cell It is mounted on an outer surface, the needle member may be of a structure that is installed on the inner surface of the pack case at a position corresponding thereto.

This structure is such that the internal pressure of the battery increases due to the gas generated by abnormal operation inside the battery cell, the cell case swells, and the needle member breaks the container containing the inert gas carrier so that the inert gas is discharged inside the battery pack. As a structure, there is an effect of preventing heat generation and explosion inside the battery pack.

The battery cell mounted in the pack case is not particularly limited, but a pouch-type battery cell that undergoes a large volume change due to a pressure increase in the battery is preferable. Such a pouch-type battery cell may be a lithium secondary battery in which safety is an issue in particular. The lithium secondary battery has a structure in which a lithium-containing electrolyte is impregnated into an electrode assembly having a cathode / separator / cathode structure, and a detailed structure of the lithium secondary battery and a method of manufacturing the same are known in the art. Omitted herein.

Hereinafter, although described with reference to the drawings according to an embodiment of the present invention, this is for easier understanding of the present invention, the scope of the present invention is not limited thereto.

FIG. 1 is a schematic exploded perspective view of a general structure of a conventional representative pouch type secondary battery.

Referring to FIG. 1, the pouch type secondary battery 10 includes two electrode leads connected to the electrode assembly 20 and the electrode tabs 21 and 22, respectively, on which the plurality of electrode tabs 21 and 22 protrude. 30 and 31, and a battery case 40 having a structure for accommodating and sealing the electrode assembly 20 so that a part of the electrode leads 30 and 31 are exposed to the outside.

The battery case 40 includes a lower case 42 including a concave accommodating portion 41 in which the electrode assembly 20 can be seated, and a seal of the lower case 42 to seal the electrode assembly 20. It consists of an upper case 43. In FIG. 1, the upper case 43 and the lower case 42 are shown as separate members, respectively, but they may also have a hinged structure in which one end portion is integrated and continuous.

The upper case 43 and the lower case 42 have heat-sealed edges with the electrode assembly 20 embedded therein, so that the upper sealing portion 44, the side sealing portions 45 and 46, and the lower sealing portion 47 are formed. ).

In the pouch type secondary battery 10, when internal pressure increases due to temperature rise and gas generation due to decomposition of an electrolyte due to abnormal operating conditions inside the battery, a portion of the heat-sealed sealing part is detached from the battery while its adhesion is separated. It consists of a structure that prevents explosion by discharging the gas inside the cell to the outside.

2 is a side view schematically illustrating a pouch-type secondary battery in which an inert gas carrier is placed in a battery cell according to an embodiment of the present invention.

Referring to FIG. 2, the pouch-type battery 100 has the electrode assembly 120 mounted on the lower case 142 having the concave accommodating portion as described in FIG. 1, covering the upper case 143, and heat-sealing the edges. The pouch type battery 100 is completed.

In the pouch-type battery 100, a dead space having a substantially triangular shape is formed between the electrode assembly 120 and the sealing portions of the cell cases 142 and 143. Therefore, the inert gas carrier 130 of the structure in which the inert gas is sealed under high pressure in the container 132 which may be ruptured under abnormal operating conditions of the battery or the gas generating agent is sealed, Since it is mounted on the space, no separate space for mounting is required.

The inert gas carrier 130 is mounted inside the pouch-type battery 100 in a state where a part of the container 132 is engaged while being engaged with the heat sealing seal 150. Therefore, due to an increase in the internal pressure of the battery, the heat-sealed portion of the sealing unit 150 is separated and at the same time, the container 132 is also damaged, thereby discharging the inert gas.

FIG. 3 schematically illustrates a structure in which a container containing the inert gas carrier of FIG. 2 is ruptured.

Referring to FIG. 3, when the temperature rises due to abnormal operation inside the battery and gas is generated, a high pressure is formed inside the battery, and a relatively weak portion of the heat-sealing portion of the upper case 143 and the lower case 142 ruptures. Gas is exhausted. Since the heat-sealing sealing portion 150 of the portion where the container 132 of the inert gas carrier 130 is located has a relatively weak bonding force, the container 132 is also broken while the corresponding portion is ruptured when high pressure is generated. Accordingly, the inert gas inside is discharged into the battery due to the breakage of the container 132.

The inert gas introduced into the reactor reduces the concentration of the flammable / volatile gases generated during the decomposition of the electrolyte and prevents it from reaching a concentration capable of causing ignition / explosion.

4 is a schematic view showing a structure in which an inert gas carrier is placed inside a battery pack according to another embodiment of the present invention, and FIG. 5 is a schematic view of a structure in which a container containing the inert gas carrier of FIG. 4 is ruptured. Is shown.

First, referring to FIG. 4, the battery pack 200 has a structure in which a battery cell 220 in which an electrode assembly is embedded in a cell case is mounted inside a predetermined pack case 210, and has an inert gas carrier. 230 is mounted on the outer surface of the battery cell 220, the needle member 240 is provided on the inner surface of the pack case 210 at a position corresponding to the inert gas carrier (230).

In this structure, when the internal pressure of the battery is increased due to gas generation due to abnormal operation inside the battery cell 220 and the battery cell 220 swells as shown in FIG. 5, the needle member 240 is an inert gas carrier 230. The rupture of the container containing the) to discharge the inert gas in the battery pack 200, there is an effect of preventing the heat generation and explosion in the battery pack 200.

FIG. 6 schematically illustrates a structure in which the needle member and the inert gas carrier of FIG. 4 are installed on the outer surface of the battery cell and the inner surface of the pack case, respectively. The battery cell 220 is expanded and inert by the needle member 240. The principle that the container containing the gas carrier 230 is ruptured is the same as described with reference to FIGS. 4 and 5.

4 and 6 show the structure in which the inert gas carrier and the needle member are installed on the outer circumferential surface portion of the battery cell and the inner surface of the pack case corresponding thereto, but the installation positions of the carrier and the needle member are not particularly limited. Bars, for example, may be located on the side of the battery cell and the inner surface of the pack case corresponding thereto.

Although described above with reference to the drawings according to an embodiment of the present invention, those of ordinary skill in the art will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

As described above, the battery cell according to the present invention is an inert gas when the inert gas carrier is damaged when the internal pressure of the battery is increased due to the generation of flammable / volatile gas due to temperature rise due to an abnormal phenomenon inside the battery and decomposition of the electrolyte. As a structure for discharging the gas, the safety of the battery can be greatly improved by reducing the concentration of flammable / volatile gas so as not to reach a concentration capable of causing ignition / explosion.

Claims (15)

A battery cell in which an electrode assembly having a cathode / membrane / cathode structure is built in a cell case, and the inside of the cell case includes an inert gas carrier having a structure for discharging an inert gas under abnormal operating conditions of the battery. The battery cell made of a structure to ensure the safety of the battery by discharging the inert gas while mechanically damaged by the pressure rise inside the battery. The battery cell according to claim 1, wherein the inert gas carrier has a structure in which an inert gas is sealed in a high pressure state in a container capable of rupturing under abnormal operating conditions of the battery. The battery cell of claim 2, wherein the container is a small bag made of a polymer resin. The battery cell of claim 1, wherein the inert gas is at least one gas selected from the group consisting of nitrogen, carbon dioxide, helium, argon, neon, krypton, xenon, and radon. The method of claim 1, wherein the inert gas carrier has a structure in which a material ('gas generator') generating an inert gas by a chemical reaction is sealed in a container which may be damaged under abnormal operating conditions of the battery. Battery cell. The method of claim 5, wherein the gas generating agent is pyrolysis, characterized in that potassium hydrogen carbonate (K ₂ CO ₃ ), sodium hydrogen carbonate (NaHCO ₃ ), or manganese carbonate (MnCO ₃ ) to generate an inert gas carbon dioxide. Battery cell. The battery cell of claim 1, wherein the inert gas carrier has a structure that is damaged by the physical change when the cell case is deformed due to an increase in pressure inside the battery. The battery cell of claim 1, wherein the battery cell has a structure in which the outer circumferential surface of the sheet is heat-sealed and sealed in a state in which an electrode assembly is embedded in a pouch-type cell case of a laminate sheet including a resin layer and a metal layer. . The method of claim 8, wherein the inert gas carrier is located in a portion of the pouch-type battery cell in contact with the heat-sealing sealing portion, the breakage of the heat-sealing sealing portion and at the same time the breakage of the support body is characterized in that the structure to discharge the inert gas Battery cell. 10. The method of claim 9, wherein the electrode assembly is accommodated in a cell case consisting of a case body including a concave shape accommodating portion into which the electrode assembly can be seated, and a lid corresponding to the body, and sealing the edge of the case body and the cover. When the battery cell, characterized in that the inert gas carrier to be part of the structure is engaged with the sealing portion. The battery cell of claim 1, wherein the battery cell has an electrode assembly embedded in a rectangular metal can (cell case), and a safety vent is formed on the outer surface of the metal can to discharge gas when the internal pressure increases abnormally. The inert gas carrier is positioned in contact with the safety vent, and the inert gas carrier is damaged at the same time as the safety vent ruptures, thereby discharging the inert gas. A battery pack in which a battery cell in which an electrode assembly having a cathode / membrane structure / cathode structure is built in a cell case is mounted inside a predetermined pack case. The inside of the pack case is mechanically damaged when the pressure inside the battery increases, and inert gas is removed. A battery pack having a structure including an inert gas carrier having a discharge structure. 13. The battery pack according to claim 12, wherein a needle part for rupturing the support body is installed in the vicinity of the inert gas carrier so that the inert gas can be discharged under abnormal operating conditions of the battery. The method of claim 12, wherein the battery cell is a battery pack, characterized in that the pouch-type battery cell. The method of claim 12, wherein the battery cell is a battery pack, characterized in that the lithium secondary battery having a structure containing a lithium-containing electrolyte in the electrode assembly of the anode / separator / cathode structure.

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