阅读说明：本技术 具有熔化截止部分的隔膜和包括该隔膜的电化学装置 (Separator having melt shut-off portion and electrochemical device including the same ) 是由 金贞吉 崔正锡 吴松泽 于 2018-10-25 设计创作，主要内容包括：本发明提供了一种构造成在诸如过充电等危急情况下能够预防着火或爆炸的二次电池,以及防止二次电池着火或爆炸的方法。提供了包含低熔点材料的隔膜,使得在电池异常加热时引发内部短路从而在一定温度以上使电极电阻增加以阻断电流,PTC材料在稳定的SoC下工作。因此,可以预防电池的热失控。(The present invention provides a secondary battery configured to be capable of preventing a fire or explosion in case of a critical situation such as overcharge, and a method of preventing the fire or explosion of the secondary battery. A separator including a low melting point material is provided such that an internal short circuit is induced upon abnormal heating of a battery to increase electrode resistance above a certain temperature to block current, and a PTC material operates under a stable SoC. Therefore, thermal runaway of the battery can be prevented.)

1. A secondary battery comprising a positive electrode, a negative electrode and a separator, wherein,

the separator includes constrictions and a melt-down portion, each constriction containing a porous polymer resin and being arranged in a discontinuous manner, the constrictions being configured to contract at an elevated temperature; the melting section is provided to connect the constricted sections to each other, and the melting section contains a low-melting-point material that melts at a high temperature, and

the positive or negative electrode comprises a Positive Temperature Coefficient (PTC) material.

2. The secondary battery according to claim 1, wherein the constriction is connected with the melting portion in a normal temperature range in which the lithium secondary battery operates, and the melting portion is formed to have a lattice shape by which the melting portion surrounds the constriction.

3. The secondary battery according to claim 1, wherein the low melting point material has physical properties required for a separator of the secondary battery in a normal temperature range in which the lithium secondary battery operates, and melts at a temperature higher than the normal temperature range in which the lithium secondary battery operates, so that the constricted portions are disconnected from each other.

4. The secondary battery according to claim 3, wherein the low melting point material is at least one of PEO or polycaprolactone.

5. The secondary battery according to claim 1, wherein each of the constrictions has physical properties required for a separator of the secondary battery in a normal temperature range in which the lithium secondary battery operates, and contracts at a temperature higher than the normal temperature range in which the lithium secondary battery operates.

6. The secondary battery according to claim 5, wherein the porous polymer resin is at least one selected from the group consisting of high density polyethylene, low density polyethylene, linear low density polyethylene, ultra-high molecular weight polyethylene, and polypropylene.

7. The secondary battery according to claim 1, wherein the PTC material exhibits uniform conductivity in a normal temperature range in which the lithium secondary battery operates, and when the temperature of the lithium secondary battery becomes higher than the normal temperature range in which the lithium secondary battery operates, the resistance of the PTC material abruptly increases to interrupt the flow of current in the lithium secondary battery.

8. The secondary battery according to claim 7, wherein the PTC material is manufactured by mixing a polymer material having low conductivity with conductive particles.

9. A method of preventing overcharge of the secondary battery according to any one of claims 1 to 8, the method comprising:

1) a step of melting the melting portion by an increase in temperature of the secondary battery due to overcharge of the secondary battery;

2) contracting the contraction portion;

3) a step of bringing specific regions of the positive electrode and the negative electrode into contact with each other due to deformation of the melting portion and the constricted portion;

4) a step of lowering the voltage of the secondary battery due to contact between the positive electrode and the negative electrode, thereby maintaining a state of charging the secondary battery and thus raising the temperature of the secondary battery; and

5) a step of abruptly increasing the resistance of the secondary battery due to the melting of the PTC material, thereby bringing the voltage of the secondary battery to a charge termination voltage.

10. A battery pack comprising the secondary battery according to any one of claims 1 to 8.

Technical Field

The present invention relates to a separator having a melt-off portion and an electrochemical device including the same, and more particularly, to a separator including a melt portion having a low melting point material and a contraction portion configured to contract at a high temperature, and an electrochemical device including the same.

Background

As the demand for mobile devices increases, the demand for secondary batteries has also sharply increased as an energy source for the mobile devices. The battery may be classified into a cylindrical battery, a prismatic battery, and a pouch-shaped battery, based on the shape of the battery case. The cylindrical battery and the prismatic battery are each a battery configured to have a structure in which an electrode assembly is mounted in a metal can. The pouch-shaped battery is a battery generally constructed in a structure in which an electrode assembly is mounted in a pouch-shaped battery case made of an aluminum laminate sheet. Among these batteries, the pouch-shaped battery, which can be stacked with high integration, has high energy density per weight, is inexpensive, and is easily modified, drawing considerable attention.

One continuing goal of mobile devices is to increase the capacity of a single mobile device while reducing the size of the mobile device. In the case where more energy is densely concentrated in a mobile device having a reduced volume, the security of the mobile device becomes an issue. In particular, it is necessary to first secure the safety of the secondary battery used in the mobile device because the mobile device is very close to the user using the mobile device.

The lithium secondary battery may explode due to various causes, for example, a short circuit in the secondary battery, overcharge of the secondary battery at a current or voltage exceeding an allowable value, exposure of the secondary battery to high temperature, or deformation of the secondary battery due to dropping or external impact. Various attempts have been made to secure the safety of the lithium secondary battery. Mechanical devices that have been mainly used physically cause a short circuit in the secondary battery by the temperature or pressure in the secondary battery.

For example, patent document 1 discloses a battery having a connection breaking means for breaking an electrical connection between an electrode terminal formed at a battery case and a lead wire connecting the terminal to a power storage element, and a pushing means for pushing a cutting means toward the lead wire when a temperature of a hollow portion of the battery case accommodating the connection breaking means reaches a predetermined temperature or more.

Various techniques have been proposed to prevent the short circuit of the secondary battery by improving materials. In the case where a sharp needle-shaped conductor (e.g., a nail) having high conductivity penetrates the electrode assembly, the positive and negative electrodes of the electrode assembly are electrically connected to each other through the needle-shaped conductor, with the result that current flows through the needle-shaped conductor having low resistance. At this time, the electrode penetrated by the needle-shaped conductor is deformed, and high resistance heat is generated due to a conductive current in a contact resistance portion between the positive electrode active material and the negative electrode active material. In the case where the temperature of the electrode assembly exceeds a critical temperature level due to resistance heat, the positive and negative electrodes contact each other due to shrinkage of the separator, with the result that a short circuit occurs. Such a short circuit causes a thermal runaway phenomenon. As a result, the electrode assembly and the secondary battery including the same may catch fire or explode.

In addition, when the electrode active material or the current collector, which is bent by the needle-shaped conductor, comes into contact with the opposite electrode facing the electrode active material or the current collector, heat higher than resistance heat is generated, so that the thermal runaway phenomenon may be further accelerated. These problems may be more serious in a dual cell including a plurality of electrodes and an electrode assembly including the same. In general, PTC material technology is used in an attempt to solve the above problems by appropriately selecting materials.

The Positive Temperature Coefficient (PTC) material contained in the electrode exhibits uniform conductivity in the normal operating temperature range of the battery, and its resistance abruptly increases to interrupt the flow of current when the temperature in the battery increases. In the case where the additional layer made of the PTC material is formed on the electrode, the process of manufacturing the battery is complicated, with the result that the cost of manufacturing the battery is excessively increased. In addition, the adhesion between the PTC material layer and the electrode active material layer is low, and as a result, the PTC material layer and the electrode active material layer may be separated from each other. In order to solve the above problem, patent document 2 proposes a method of manufacturing an electrode using two slurries.

However, in order to interrupt the flow of current with the PTC material, it is necessary to provide a method of stably interrupting the flow of current through a partial intentional short circuit. Before the PTC effect is achieved, a thermal runaway phenomenon occurs due to self-heating above a specific state of charge (SoC). However, no obvious solution to this problem has been proposed.

Patent document 3 is a patent relating to a separator, and filed in the name of the applicant of the present application, which discloses a separator having excellent thermal stability. In the disclosure of patent document 3, a porous inorganic layer is formed on the surface of a porous polymer resin as a base material, whereby various excellent effects such as thermal stability and movement characteristics of an electrolytic solution are obtained.

Patent document 4 discloses a separator which is partially provided in a region defined between a positive electrode plate and a negative electrode plate in a lithium ion capacitor, the separator having a low melting point portion which melts at a lower temperature than other portions.

However, a technology capable of adjusting a stable operation state of the PTC material using other materials in the secondary battery has not been proposed.

Patent document 1: japanese patent application laid-open No.2011-

-patent document 2: korean registered patent No.10-1709569

-patent document 3: korean registered patent No.10-0775310

-patent document 4: japanese patent application laid-open No.2011-192784

Disclosure of Invention

[ problem ] to

An object of the present invention is to use a material in a secondary battery to adjust the operating state of a PTC material contained in an electrode layer. It is another object of the present invention to provide a structure and method capable of inducing an intentional short circuit in a portion of a secondary battery using an internal separator at a high temperature to induce a PTC material to operate, thereby stably terminating an overcharged state of the secondary battery.

[ solution ]

In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a secondary battery including a positive electrode, a negative electrode, and a separator, wherein the separator includes constrictions each including a porous polymer resin, the constrictions are arranged in a discontinuous manner, the constrictions are configured to constrict at a high temperature, a fusing part is provided to connect the constrictions to each other, the fusing part includes a low-melting-point material that fuses at a high temperature, and the positive or negative electrode includes a Positive Temperature Coefficient (PTC) material.

In a normal temperature range in which the lithium secondary battery operates, the constriction may be connected with the melting portion, and the melting portion may be formed to have a lattice shape, whereby the melting portion may surround each constriction. The shape of each constricted portion is not particularly limited. Specifically, each constricted portion may be formed to have a polygonal shape (e.g., a triangle, a quadrangle, or a pentagon) or a circular shape. The constrictions may be formed to have the same shape or different shapes.

However, the constricted portions are characterized in that the constricted portions are separated from each other by the melted portions, thereby arranging the constricted portions in a discontinuous manner. In addition, the constrictions need not be the same size or arranged in a uniformly spaced or uniform manner. In the present invention, the portion of the separator other than the constricted portion may be the melted portion.

Meanwhile, a general separator having neither a constricted portion nor a melted portion may be provided as an integral part of the separator of the present invention. The separator may be a separator containing porous inorganic particles disclosed in patent document 3.

The melted portions are sufficient to connect the respective constricted portions to each other. Therefore, the area of the melting portion may be 5% to 50%, preferably 10% to 40%, more preferably 20% to 30% of the total area of the separator. In the case where the area of the meltdown portion is less than the above range, the meltdown portion may be removed at an early stage in a state where the temperature in the secondary battery is low, so that a short circuit may occur in the secondary battery before the temperature in the secondary battery reaches an abnormal temperature. When the area of the melting portion is larger than the above range, the area of the constricted portion configured to be constricted becomes small, so that a desired short-circuit region is not formed. In addition, the area of the general separator may be less than 40% of the total area of the separator. In the case where the area of the general separator is greater than the above range, it is difficult to obtain the effect of the present invention due to overcharge of the secondary battery. The remainder of the total area of the diaphragm is occupied by the constriction.

The separator of the present invention may be configured such that the unit pattern is repeated or not repeated, depending on the shape of the battery. In the case where the electrode assembly has a continuous shape (e.g., a jelly-roll shape), the separator of the present invention may be configured such that the unit pattern is repeated. In the case where the electrode assembly is configured such that the unit cells are stacked, the separator of the present invention may be configured such that the unit pattern is not repeated.

In a variation of the physical shape of the constrictions and the melt section of the present invention, the melt section may be provided in a discontinuous manner and the constrictions may be provided in a continuous manner.

The low melting point material may have physical properties required for a separator of a secondary battery in a normal temperature range in which the lithium secondary battery operates, and may melt at a temperature higher than the normal temperature range in which the lithium secondary battery operates, so that the respective constricted portions are disconnected from each other. The low melting point material of the present invention may be at least one of PEO or polycaprolactone. The low melting point material may be 50% or more of the total weight of the melting part.

Each of the constrictions may have physical properties required for a separator of the secondary battery in a normal temperature range in which the lithium secondary battery operates, and may be constricted at a temperature higher than the normal temperature range in which the secondary battery operates. The porous polymer resin for each constriction may be a polyolefin-based polymer resin used in a general lithium secondary battery. Specifically, the porous polymer resin may be at least one selected from the group consisting of high density polyethylene, low density polyethylene, linear low density polyethylene, ultra-high molecular weight polyethylene, and polypropylene.

Polyolefin-based separators tend to shrink with increasing temperature. However, even when the temperature is increased, the shape of the separator is maintained since the melting portion is connected to each contraction portion. The melting portion is melted at a high temperature, thereby reducing a coupling force between the contraction portion and the melting portion. Therefore, when the shrinkage portion shrinks due to the shrinkage action based on the temperature, the positive electrode and the negative electrode are in contact with each other via the melting portion and the shrinkage region of the shrinkage portion.

The PTC material of the positive electrode or the negative electrode is a material exhibiting uniform conductivity in a normal temperature range in which the lithium secondary battery operates, and is configured such that the resistance of the PTC material abruptly increases when the temperature of the secondary battery becomes higher than the normal temperature range in which the lithium secondary battery operates, to interrupt the flow of current in the secondary battery.

The principle of the PTC material interrupting the flow of current will be described in detail below. In the case where a polymer material having low conductivity is mixed with the conductive particles, a low-resistance electrical path is formed along the conductive particles. Therefore, in a general state, the electric path formed by the conductive particles maintains uniform conductivity. However, as the temperature increases, the distance between the conductive particles increases due to the expansion of the polymer material and, as the case may be, the movement of the conductive particles. As a result, the resistance of the PTC material abruptly increases, thereby interrupting the flow of current.

The polymer material is not particularly limited as long as the polymer material has low conductivity and expands at a temperature increase to break the electric path or block the hole as an ion moving path in the electrode. For example, the polymeric material may be a thermoplastic polymer.

The thermoplastic polymer may be a semicrystalline material. The reason for this is that PTC characteristics can be obtained more easily from a semi-crystalline material than from a semi-amorphous thermoplastic material. The crystallinity of the semicrystalline thermoplastic material may be 5% or more, specifically 10% or more, more specifically 15% or more. The thermoplastic polymer is not particularly limited as long as the thermoplastic polymer has the above-described properties. For example, the thermoplastic polymer may be one or more selected from the group consisting of: high density polyethylene; linear low density polyethylene; low density polyethylene; medium density polyethylene; maleic anhydride functionalized polyethylene; a maleic anhydride functionalized elastomer; ethylene copolymers (e.g., Exxelor VA1801 or VA1803 manufactured by ExxonMobil); ethylene butene copolymers; an ethylene octene copolymer; ethylene acrylate copolymers such as ethylene methyl acrylate copolymer, ethylene ethyl acrylate copolymer, and ethylene butyl acrylate copolymer; polyethylene (PE), including glycidyl methacrylate modified polyethylene; polypropylene (PP); maleic anhydride functionalized polypropylene; glycidyl methacrylate modified polypropylene; polyvinyl chloride (PVC); polyvinyl acetate; polyvinyl acetyl group; an acrylic resin; syndiotactic polystyrene (sPS); polyamides, including but not limited to PA6, PA66, PA11, PA12, PA6T, or PA 9T; polytetrafluoroethylene (PTFE); polybutylene terephthalate (PBT); polyphenylene Sulfide (PPS); polyamide-imide; a polyimide; polyethylene vinyl acetate (EVA); glycidyl methacrylate modified polyethylene vinyl acetate; polymethyl methacrylate (PMMA); polyisobutylene; polyvinylidene fluoride (PVDF), polymethyl acrylate; polyacrylonitrile; polybutadiene; polyethylene terephthalate (PET); poly-8-aminocaprylic acid; polyvinyl alcohol (PVA); and polycaprolactone.

The above description is merely illustrative, and it is of course possible to use a thermosetting polymer instead of a thermoplastic polymer to manufacture the PTC material.

According to another aspect of the present invention, there is provided a method of preventing overcharge of a secondary battery, the method including:

1) a step of melting the melting portion by an increase in temperature of the secondary battery due to overcharge of the secondary battery;

2) contracting the contraction part;

3) a step of bringing specific regions of the positive electrode and the negative electrode into contact with each other due to deformation of the melting portion and the contraction portion;

4) a step of lowering the voltage of the secondary battery due to contact between the positive electrode and the negative electrode, thereby maintaining a state of charging the secondary battery and thus raising the temperature of the secondary battery; and

5) and a step of abruptly increasing the resistance of the secondary battery due to the melting of the PTC material, thereby bringing the voltage of the secondary battery to a charge termination voltage.

The secondary battery of the present invention may be applied to all batteries used in various ways. The secondary battery of the present invention can be applied to all of cylindrical, prismatic and pouch-shaped batteries. The electrode assembly may be applied to all z-fold, jelly-roll, and stack and fold type electronic devices, each including a cathode, an anode, and a separator.

According to another aspect of the present invention, there is provided a battery pack including the secondary battery of the present invention, the battery pack being configured to prevent overcharge, and a mobile or electric power device including the battery pack.

Drawings

Fig. 1 is a schematic view showing one embodiment of the separator of the present invention.

Fig. 2 is a schematic view showing a state in which the melting portion of the separator of the present invention has melted and the constricted portion of the separator has contracted due to a temperature increase.

Figure 3 is a schematic diagram showing another embodiment of the separator of the present invention.

Fig. 4 is a schematic view showing a thermal runaway phenomenon occurring when a conventional battery is overcharged.

Fig. 5 is a schematic view showing a stable termination phenomenon occurring when a battery including the separator of the present invention is overcharged.

Detailed Description

Now, the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the terms or words used in the present specification and claims should not be construed as having ordinary and dictionary-based meanings, but interpreted as having meanings and concepts consistent with the technical idea of the present invention on the basis of the principle that the inventor can appropriately define the concept of the term to best explain the present invention. Therefore, the embodiments described in this specification are only the most preferred embodiments and do not cover all technical ideas of the present invention, and therefore it should be understood that there may be various equivalents and modifications capable of substituting for these embodiments at the time of filing this application.

FIG. 1 is a schematic diagram showing one embodiment of a diaphragm 100 of the present invention. The separator of the present invention includes a melting portion 110 and a contraction portion 120. In the embodiment of fig. 1, the constrictions 120 each have a rectangular shape and are separated from each other, and the melting section 110 is formed to have a lattice shape, whereby the melting section 110 is shaped to surround the constrictions 120.

Fig. 2 is a schematic view showing a state in which the constricted part 120 of the separator 100 of fig. 1 has been constricted and a state in which the melted part 110 of the separator 100 has been melted due to a temperature increase. The shrinkage rate, short-circuit area, and temperature of the battery may be adjusted by those skilled in the art in consideration of the operating conditions of the battery.

Figure 3 is a schematic diagram showing another embodiment of a septum 200 of the present invention. The constrictions 220 may have various shapes and sizes, and may not be arranged repeatedly.

Fig. 4 is a schematic view showing a time-based thermal runaway phenomenon occurring when a battery including a general separator provided as a comparative example is overcharged. Unlike the separator of the present invention, the common separator is a single component. That is, neither the melting portion nor the constricted portion is provided separately. When a short circuit occurs at a portion of the battery including the general separator at a specific time, the voltage of the battery does not increase due to the short circuit occurring at the portion of the battery even though the battery continues to be charged. However, the temperature of the battery continues to rise, and the temperature of the battery suddenly increases at another specific time, whereby the battery explodes.

In contrast, as can be seen from fig. 5, when a short circuit occurs in a portion of the battery including the separator of the present invention, the voltage of the battery decreases and the temperature of the battery increases. At this time, the melted portion of the separator melts, thereby further short-circuiting another portion of the battery. As the temperature of the battery rises above a predetermined temperature, the voltage of the battery increases due to the operation of a Positive Temperature Coefficient (PTC) material, so that the battery is not charged any more. Therefore, the thermal runaway phenomenon of the battery does not occur.

Examples using the separator of the present invention and comparative examples using a general polyolefin-based separator are shown below.

[ Industrial Applicability ]

The present invention provides a secondary battery configured to prevent ignition or explosion in a critical situation such as overcharge, and a method of preventing ignition or explosion of the secondary battery. Since the separator containing a low melting point material is used, a short circuit occurs in the battery when the battery is abnormally heated, and the resistance of the electrode increases when the temperature of the battery rises above a predetermined temperature. As a result, the Positive Temperature Coefficient (PTC) material operates in a stable state of charge (SoC). Therefore, the occurrence of the thermal runaway phenomenon of the battery can be prevented.

Description of the reference numerals

100. 200 diaphragm

110. 210 melt section

120. 220, a constriction.