KR100799866B1 - Secondary battery having a high safety - Google Patents

Abstract

The present invention provides a secondary battery in which a heat conductive layer is disposed between an assembly in which electrodes and separators are stacked and a battery packaging material. When the battery is faced with a situation such as internal short circuit breakdown, overcharge or high temperature exposure, the heat conduction layer can effectively dissipate heat generated inside the battery to the outside of the battery, thereby igniting the battery without degrading the performance of the battery. And it can prevent the rupture to improve the safety of the battery.

Secondary Battery, Lithium Secondary Battery, Lithium Polymer Battery, Thermal Conductive Layer, Battery Safety

Description

Secondary battery with excellent safety {SECONDARY BATTERY HAVING A HIGH SAFETY}

1 illustrates a process of assembling an assembly including an electrode and a separator (101: anode, 102: cathode, 103: separator, 104: assembly).

2 shows an example of a lithium polymer battery packaged by a battery packaging material.

FIG. 3 is a cross-sectional view of the dotted line in FIG. 2 (a: positive electrode terminal, b: negative electrode terminal, c: terminal film, d: inner adhesive layer, e: aluminum layer, f: polymer layer).

4 illustrates an example in which a heat conductive layer is formed on an upper surface of an assembly including an electrode and a separator (403: membrane, 405: thermal conductive layer).

5 illustrates an example in which a heat conductive layer is formed on the top and bottom surfaces of an assembly including an electrode and a separator (505: heat conductive layer).

6 is a graph showing the results of the high temperature exposure experiment for the battery of Example 1 (1: battery internal temperature, 2: oven temperature).

7 is a graph showing the results of the high temperature exposure experiment for the battery of Comparative Example 1 (1: battery internal temperature, 2: oven temperature).

The present invention relates to a secondary battery having excellent safety, specifically a secondary battery having excellent safety provided with a heat conductive layer for dissipating heat generated inside the battery to the outside.

In recent years, with the progress of electronic technology, portable electronic devices such as mobile phones and laptop computers have been widely used, and their miniaturization and weight reduction have been achieved. Accordingly, as a driving power source for portable electronic devices as described above, research and development on a battery having a high voltage, a high capacity, and a high output at a light weight are being actively conducted, and among them, the development of a secondary battery capable of charging and discharging has become a focus of interest. .

BACKGROUND ART Secondary batteries using nonaqueous electrolytes have been put into practical use as secondary batteries that meet the above requirements. In particular, lithium secondary batteries developed in the early 1990s among the currently applied secondary batteries have a higher operating voltage and a higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries using an aqueous solution electrolyte. Because of the large advantage, the development of technology for miniaturizing and minimizing it is proceeding rapidly.

However, such lithium secondary batteries have many problems with regard to safety such as nail penetration, overcharge, high temperature exposure, and the like. In particular, in a charged lithium secondary battery, a positive or negative electrode and a nonaqueous electrolyte react with each other at a high temperature to generate a large amount of reaction heat, so that a series of exothermic reactions by heat causes a safety problem of the battery. Specifically, it is as follows.

The lithium secondary battery uses a nonaqueous electrolyte made of a flammable organic solvent. Therefore, when the battery is subjected to an impact or an internal short test through the nail at a constant pressure and speed, the electrochemical energy inside the battery is increased. As the heating energy is converted into a heating energy, a sudden heat generation occurs, and the thermal runaway causes a positive or negative electrode to react with a chemical reaction, which causes a sudden exothermic reaction, resulting in safety problems such as battery ignition and explosion.

On the other hand, when the battery is overcharged, excess lithium comes out of the positive electrode and lithium is inserted into the negative electrode, and lithium metal, which is highly reactive, precipitates on the surface of the negative electrode, resulting in a thermally unstable state, whereby an organic solvent used as an electrolyte undergoes a decomposition reaction. And a sudden exothermic reaction causes safety problems such as battery ignition and explosion.

In addition, when exposing the battery at a high temperature for an appropriate time while heating at a constant speed in an oven capable of convection, the positive electrode active material decomposes and the exothermic reaction by the reaction of the nonaqueous electrolyte and the active material proceeds, thereby causing a local temperature inside the battery. Thermal runaway from the rise leads to ignition and rupture of the battery.

Therefore, various countermeasures have been proposed as a method for solving the above risks. For example, the electrolyte solution may contain additives such as self-extinguishing phosphate esters, phosphate ester compounds substituted with self-extinguishing halogen atoms, or radical scavengers. Techniques for improving safety are disclosed. In addition, techniques for increasing the flash point and securing safety by using a fluorine-substituted compound or a chlorine-substituted compound as the electrolyte itself have been proposed.

However, in the case of adding a self-extinguishing substance or a substance having a high flash point to the electrolyte as in the conventional art, there is a problem in that the ion conductivity of the electrolyte is lowered and the high rate discharge characteristic or the low temperature characteristic of the battery is lowered. In addition, even when using a microcapsule containing a flame retardant or a chemical that causes an electrolyte curing reaction, combustion of the electrolyte is accelerated by oxygen released from the electrode during internal short circuit breakdown or thermal safety test by heating. Because of this, it is also difficult to say that there is sufficient effect in terms of safety.

The present inventors can effectively dissipate the heat generated inside the battery to the outside by disposing a thermal conductive layer between the assembly and the battery packaging material laminated the electrode and separator in the secondary battery, thereby localized short circuit, overcharge or high temperature Even though the exposure occurs, the present invention has been found to minimize the ignition and rupture caused by the temperature increase inside the battery, thereby improving the safety of the battery.

The present invention provides a secondary battery, wherein a heat conductive layer is disposed between an assembly in which electrodes and separators are stacked and a battery packaging material.

Hereinafter, the present invention will be described in more detail.

The secondary battery of the present invention includes an assembly in which electrodes and separators are laminated, a battery packaging material, and a thermally conductive layer disposed therebetween.

In the present invention, by arranging the thermal conductive layer between the assembly and the battery packaging material it is possible to improve the safety of the battery. Specifically, it is as follows.

The battery absorbs / discharges heat generated during internal short circuit breakdown, overcharge or high temperature exposure. As a result, when the internal temperature of the battery reaches a predetermined temperature or more (for example, 160 ° C. or more), oxygen is released due to the collapse of the structure of the positive electrode. The released oxygen accelerates the combustion of the electrolyte, thereby causing thermal runaway, causing the battery to ignite or burst. However, in the present invention, the heat conduction layer disposed between the assembly and the battery packaging material effectively dissipates heat generated during breakdown of the battery, overcharge, or high temperature, by artificially dissipating heat to the outside of the battery. It can suppress and improve the safety of a battery.

In the present invention, any material constituting the heat conductive layer may be used without limitation as long as it is known as a heat conductive material. Specific examples of the thermally conductive material include, but are not limited to, alumina (Al 2 O 3), aluminum hydroxide (AlOH 3), silica, boron, graphite, and the like. Among them, Al-based materials are inexpensive, easy to manufacture into adhesive tapes using UV curing, and have excellent thermal conductivity. Therefore, Al-based materials are more preferably used as the material of the thermally conductive tapes.

Various methods may be used as a method of configuring the thermal conductive layer of the present invention by using the thermal conductive material as described above. For example, the thermally conductive layer of the present invention is formed by attaching an adhesive thermally conductive tape comprising a thermally conductive material to the assembly or battery packaging material or coating a thermally conductive coating composition comprising a thermally conductive material on the assembly or battery packaging material. Can be. Adhesive thermally conductive tapes or thermally conductive coating compositions containing such thermally conductive materials can be readily prepared using methods known in the art. For example, adhesive thermally conductive tapes can be produced by UV curing a photosensitive composition comprising a thermally conductive material. As such an adhesive thermally conductive tape, you may use a commercial item as it is. In addition, the adhesive coating composition can be prepared by dissolving or dispersing the thermally conductive material in a suitable solvent. The method of coating such an adhesive coating composition is also not limited, and conventional methods may be used.

However, since the thermal conductive layer of the present invention preferably does not affect the performance of the battery, it is preferable that the thermal conductive layer made of a thermally conductive tape or a thermally conductive coating composition including the thermally conductive material has chemical resistance to the electrolyte. Do. For this purpose, it is preferable to use an inorganic metal type having chemical resistance as the thermal conductive material. In addition, in the case of a thermally conductive tape, it is preferable to select it after confirming the surface and internal state of the tape after the predetermined time has been impregnated with the electrolyte solution. Most preferred thermally conductive tapes include ceramic fillers containing aluminum particles having excellent thermal conductivity and acrylic polymers having adhesive properties. Specific examples of the adhesive heat conductive tape include 8805, 8810, 9882, etc. of 3M products, but are not limited thereto.

On the other hand, the heat conductive layer is not formed separately from the assembly or the battery packaging material may be composed of a part of the battery packaging material. For example, the heat conductive layer of the present invention may be formed such that the adhesive layer (d) or the polymer layer (f) of the battery packaging material of FIG. 3 is formed as a heat conductive layer so that the heat conductive layer can also function as a heat conductive layer. In this case as well, the effects of the present invention as described above can be achieved. As a method for forming the adhesive layer or the polymer layer of the battery packaging material as a heat conductive layer, a method of coating by adding a thermal conductive material to the original material when forming the adhesive layer or the polymer layer of the battery packaging material may be used.

Although the thickness of the heat conductive layer of the present invention formed as described above is not particularly limited, it is preferable that the thinnest possible thickness is used in consideration of the thickness of the battery packaging material and the size of the battery.

In the present invention, the thermal conductivity of the thermally conductive layer can be further increased by disposing the thermally conductive layer together with the thermally conductive metal. Therefore, in the present invention, the thermally conductive metal may be disposed on one or both surfaces of the thermally conductive layer. Aluminum is most preferred as the thermally conductive metal.

A method of forming an assembly in which the electrode and the separator are stacked is illustrated in FIG. 1. The assembly 104 may be formed by sequentially stacking an anode, a separator, and a cathode such that the separator 103 is positioned between the anode 101 and the cathode 102, and the separator is positioned at the outermost part of the formed assembly. desirable.

When the secondary battery of the present invention is a lithium secondary battery, the positive electrode and the negative electrode should be made of a material capable of occluding and releasing lithium ions. The positive electrode active material includes lithium-containing transition metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO _2, and LiNi _1-X Co _X O ₂ (here, 0 <X <1). It is preferably at least a species, and metal oxides such as MnO ₂ or combinations thereof are also possible. Further, the negative electrode active material is preferably carbon, lithium metal or alloy, and other metal oxides such as TiO ₂ and SnO ₂ capable of occluding and releasing lithium and having a potential for lithium of less than 2V.

In addition, the separator is preferably a porous separator, a specific example is a polyolefin-based porous separator.

2 and 3 illustrate an aluminum laminate film packaging that is an example of a battery packaging that can be used in the secondary battery of the present invention. FIG. 2 illustrates a lithium secondary battery packaged by an aluminum laminate film packaging material, and FIG. 3 is a cross-sectional view of a portion of a packaging material including a dotted line portion, that is, a cathode / cathode terminal, of FIG. 2. As shown in Figure 3, the aluminum laminate film packaging material may be composed of an adhesive layer (d) therein, an aluminum layer (e) in the middle, a polymer layer (f) in the outside, the anode terminal ( a) or the negative terminal b is connected to the outside. At this time, these terminals are apply | coated with the terminal film (c).

The adhesive layer (d) of the battery packaging material serves to bond both sides of the packaging material to the battery assembly when the battery packaging prevents external moisture or foreign substances from entering the battery and prevents leakage of the electrolyte inside the battery to the outside. Therefore, it is preferable that the adhesive layer (d) has durability against organic substances such as electrolyte. In addition, the adhesive layer (d) is preferably made of a thermoplastic resin and an electrically insulating material so as to adhere well during thermal fusion. The material of the adhesive layer that can be used in the present invention includes, but is not limited to, polyethylene, polypropylene, or a copolymer thereof, which is a polyolefin resin.

 The aluminum layer (e) of the battery packaging material enables the molding when molding the packaging material and serves to prevent the penetration or leakage of moisture or electrolyte solution. The aluminum layer is composed of aluminum metal, which is very good in electrical and thermal conductivity.

The polymer layer (f) at the outermost side of the battery packaging material enables battery external protection and printing. It is usually desirable to use a material that is not electrically conductive so that both terminals of the battery do not touch at the same time. Polymer layer materials that can be used in the present invention include PET (Poly Ethylene Terephthalate) or nylon, but is not limited thereto.

In the secondary battery of the present invention, except for forming a thermally conductive layer, a conventional method used for manufacturing a battery, for example, an anode, a separator, and an anode are laminated to prepare an assembly, which is then packaged in a packing material and a nonaqueous electrolyte is added thereto. It can manufacture by a method. The thermally conductive layer of the present invention may be formed on one or both of the top and bottom surfaces of the assembly, or inside the battery packaging material, such as by attaching a thermally conductive tape or coating a thermally conductive composition prior to battery assembly. 4 and 5 show examples of attaching the thermally conductive tapes 405 and 505 to the top surface and to both the top and bottom surfaces of the battery assembly, respectively.                     

In the case of forming the thermal conductive layer as described above, since the thermal conductive layer is in close contact with the assembly and the battery packaging material, the thermal conductive layer is not separated from the assembly or the battery packaging material when the electrolyte is injected after the battery assembly. Therefore, heat generated in the battery can be effectively transferred to the outside along the aluminum layer having excellent thermal conductivity through the adhesive layer of the packaging material through the heat conductive layer.

In the present invention, the heat generated inside the battery by the heat conduction layer can be effectively transferred to the outside to maintain the temperature inside the battery lower than the normal firing temperature (ignition at 160 ℃ or more when the positive electrode active material is LiCoO2). As a result, the temperature inside the battery may be further increased due to thermal decomposition of the active material, the electrolyte, and other materials, and thus explosion and rupture of the battery may be prevented.

Non-aqueous electrolytes that can be used in the secondary battery of the present invention include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), gamma butyrolactone (GBL) and the like, linear carbonates such as diethyl carbonate (DEC), dimethyl Carbonate (DMC), ethylmethyl carbonate (EMC) and methyl propyl carbonate (MPC), although not limited thereto.

Lithium salt contained in the non-aqueous electrolyte is preferably selected from the group consisting of LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , and LiN (CF ₃ SO ₂ ) ₂ , but is not limited thereto. It is not.

It is preferable that the secondary battery manufactured by the present invention is a lithium secondary battery, and the lithium secondary battery of the present invention may be a cylindrical battery or a lithium polymer battery manufactured in a jelly roll shape in which a positive electrode and a negative electrode are disposed to face each other.

The present invention will be described in more detail with reference to the following examples. However, an Example is for illustrating this invention and does not limit this invention.

EXAMPLE

Example 1

As an electrolyte, a 1M LiPF ₆ solution having a composition of EC: PC: DEC = 3: 2: 5 was used, artificial graphite was used as the negative electrode, and LiCoO ₂ was used to prepare a 383562 type lithium polymer battery. It was packaged using an aluminum laminate packaging material, but a battery was manufactured by attaching adhesive heat conductive tapes (3M, 8805) containing a ceramic filler including aluminum particles and an acrylic polymer having adhesive ability to both sides of the packaging material.

Example 2

A battery was prepared in the same manner as in Example 1, except that the adhesive material was attached together with the aluminum foil and the adhesive thermal conductive tapes 3M and 8805 containing the ceramic filler including aluminum particles and the acrylic polymer having the adhesive ability on both sides of the packaging material. Prepared.

Comparative Example 1

A battery was manufactured in the same manner as in Example 1, except that none of the thermal conductive tape and the aluminum foil were attached to the inside of the packaging material.

(High temperature exposure test)

The batteries prepared in Examples 1 and 2 and Comparative Example 1 were prepared in a fully charged state. In the high temperature exposure test, the battery is fired by exposing the fully charged battery for 1 hour at a high temperature of 160 ° C. to 170 ° C. after heating up to 5 ° C. per minute (5 ° C./min) at room temperature in an oven with convection. It was done in a way. In Comparative Example 1, when the temperature was raised at a rate of 5 ° C. per minute, it was ignited at a temperature of 160 ° C., but in Examples 1 and 2, it was not ignited at 160 ° C. when the same conditions were performed. In particular, in the case of Example 2, it was found to have an excellent stability effect that does not ignite even at 170 ℃.

The results of the high temperature exposure test are shown in Table 1.

High Temperature Exposure Temperature (℃) Ignition Comparative Example 1 160 Fire 170 Fire Example 1 160 Unfired Example 2 160 Unfired 170 Unfired

6 and 7 show the results of the high temperature exposure test of Example 1 and Comparative Example 1, respectively. 1 represents the temperature inside the battery, and 2 represents the temperature of the oven. In FIG. 6, the battery did not ignite even at 160 ° C., but in FIG. 7, the battery ignited at 160 ° C. and ruptured.

In the secondary battery of the present invention, since the thermal conductive layer is disposed between the assembly of the electrode and the separator and the battery packaging material, heat generated inside the battery can be effectively dissipated to the outside of the battery in a situation such as an internal short circuit, overcharge or high temperature exposure. As a result, the battery can be prevented from igniting and bursting, thereby improving the safety of the battery without degrading the performance of the battery.

Claims (10)

An electrode assembly in which electrodes connected to electrode terminals and separators are stacked; A battery packaging material disposed on an outer periphery of the electrode assembly and surrounding the electrode assembly; And a heat conductive layer disposed between the electrode assembly and the battery packaging material. A part of the heat conductive layer is in contact with the electrode terminal. The lithium secondary battery of claim 1, wherein the thermally conductive layer comprises at least one thermally conductive material selected from the group consisting of alumina (Al 2 O 3), aluminum hydroxide (AlOH 3), silica, boron, and graphite. . The lithium secondary battery according to claim 1, wherein the thermal conductive layer is formed by attaching a tacky thermal conductive tape to the inside of the battery packaging material or to one or both of the upper and lower surfaces of the assembly. The lithium secondary battery of claim 3, wherein the thermally conductive tape comprises a ceramic filler containing aluminum particles and an acrylic polymer. The lithium secondary battery of claim 1, wherein the thermally conductive layer is formed by coating a coating composition including a thermally conductive material on either or both of the top and bottom surfaces of the battery packaging material or the assembly. The lithium secondary battery according to claim 1, wherein the heat conductive layer is composed of a part of the battery packaging material. The lithium secondary battery according to claim 6, wherein the battery packaging material comprises an adhesive layer, an aluminum layer, and a polymer layer, and the heat conductive layer is composed of an adhesive layer of the battery packaging material. delete The lithium secondary battery according to any one of claims 1 to 7, wherein a thermally conductive metal is disposed on one or both surfaces of the thermally conductive layer. The lithium secondary battery of claim 9, wherein the thermally conductive metal is aluminum.

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