KR20050014426A - The secondary battery with an improved safty - Google Patents

Abstract

PURPOSE: Provided are a battery packaging material which inhibits the generation of heat inside a battery due to the current flowing into the aluminum and copper foils outside a packaging material when an electrically conductive material such as a nail penetrates through a battery, thereby improving the stability of a battery, and a secondary battery packaged with the battery packaging material. CONSTITUTION: The battery packaging material comprises an aluminum laminate film comprising an internal adhesive layer, a middle aluminum layer and an external polymer layer, wherein an electrically conductive metal foil(7) is adhered to at least one surface of upper surface and lower surface of a battery at the outside of the battery packaging material, and the metal foil can be connected with at least one electrode terminal of positive electrode terminal and negative electrode terminal of a battery when the battery is packaged with the battery packaging material. Preferably the metal foil is prepared by using a material selected from the group consisting of a metal, a metal oxide and a metal alloy. Preferably if the metal foil is aluminum, it is connected with a positive electrode terminal, and if copper, it is connected with a negative electrode terminal.

Description

Secondary battery with improved stability {THE SECONDARY BATTERY WITH AN IMPROVED SAFTY}

The present invention relates to a secondary battery packaged with a packaging material of a novel structure with improved stability. In particular, the packaging material of the present invention can be used in lithium secondary batteries, in particular lithium polymer batteries.

Lithium secondary batteries using non-aqueous electrolytes have recently been used as power sources for portable electronic devices due to their high voltage, high capacity, high output, and light weight. However, since such a lithium secondary battery has a safety problem, attempts have been made to solve this problem. When the lithium secondary battery is overcharged, excess lithium comes out from the positive electrode and excess lithium is inserted into the negative electrode, resulting in precipitation of highly reactive lithium metal on the surface of the negative electrode, and the positive electrode also becomes thermally unstable, and the decomposition reaction of the organic solvent used as an electrolyte solution. Sudden exothermic reaction causes safety problems such as battery ignition and explosion.

In addition, when a material having electrical conductivity, such as a nail, penetrates the battery, the electrochemical energy inside the battery is converted into thermal energy, causing rapid heat generation, and the positive or negative electrode material undergoes a chemical reaction by the accompanying heat, causing rapid heat generation. Reaction causes safety problems such as battery ignition and explosion.

In addition, in the case of nail penetration, crimping, impact, and high temperature exposure, a short circuit occurs locally inside the positive electrode and the negative electrode. At this time, locally excessive current flows and heat is generated by this current. Since the magnitude of the short circuit current due to local short circuit is inversely proportional to the resistance, the short circuit current flows to the lower side of the resistor. The current flows through the metal foil mainly used as the current collector, and the heat generation is calculated as shown in FIG. Locally very high heat is generated around the center of the nail.

When heat is generated inside the battery, the positive electrode, the negative electrode, and the electrolyte constituting the inside of the battery react or burn with each other. This reaction is a very large exothermic reaction and eventually ignites or explodes. Therefore, in such a case, it is necessary to prevent rapid generation of heat inside the battery.

In addition, such a safety problem occurs when the battery is pressed by a heavy object, subjected to strong impact, or when the battery is exposed to high temperature. This safety problem becomes more important as the energy density increases as the lithium secondary battery becomes higher in capacity.

In general, a lithium secondary battery uses a lithium-containing transition metal oxide as a positive electrode active material, for example, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO _2, and LiNi _1-X Co _X O ₂ (where 0 <X One or more types are selected from the group which consists of <1). In addition, carbon, lithium metal, or an alloy is used as the negative electrode active material, and other lithium can be occluded and released, and metal oxides such as TiO ₂ and SnO ₂ having a potential of less than ₂ V are also possible. In addition, cyclic carbonate and linear carbonate are used as the nonaqueous electrolyte. The non-aqueous electrolyte includes a lithium salt and is specifically 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 .

In the lithium secondary battery manufactured as described above, the positive or negative electrode and the nonaqueous electrolyte react with each other at a high temperature in a charged state to generate a large reaction heat, and a series of exothermic reactions by such heat causes a safety problem of the battery.

To solve this problem, additives are added to the non-aqueous electrolyte to improve the safety of overcharging.However, additives are added to the non-aqueous electrolyte to secure safety in the aforementioned conditions such as penetration of the nail, pressing, impact, and exposure to high temperature. You can't solve it.

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium secondary battery in which safety is ensured even in situations such as penetration of a nail, compression, impact, exposure to high temperature, etc. in consideration of the problems of the prior art.

In order to achieve the above object, the present inventors anode one or more metal foils having electrical conductivity and / or thermal conductivity, such as aluminum and copper, on the outside of the aluminum layer of aluminum laminate packaging materials which are widely used in lithium secondary batteries, especially lithium polymer batteries. And one or two or more in combination with the negative electrode terminal was connected to allow electricity to flow.

1 is a graph showing the temperature change around the nail penetration portion when the nail penetrates the battery.

2 is a perspective view of a lithium secondary battery packaged by a general packaging material.

3 is a cross-sectional view of a dotted line in FIG. 2.

4 is a perspective view of a lithium secondary battery in which a single metal foil is connected to a battery terminal according to one embodiment of the present invention.

5 is a perspective view of a lithium secondary battery using two metal foils as an embodiment of the present invention, each attached to a lower end of an upper end portion of a battery, and connecting a metal foil to a terminal of the battery.

The present invention provides a secondary battery packaged by a battery packaging material, wherein the battery packaging material is an adhesive layer therein; Aluminum layer in the middle; And an aluminum laminate film including a polymer layer on the outside thereof, wherein an electrically conductive and / or thermally conductive metal foil is attached to one end or both sides of an upper end portion or a lower end portion of the battery outside of the battery packaging material. Or a secondary battery characterized by being connected to both terminals.

Hereinafter, the present invention will be described in detail.

The secondary battery that can be prepared according to the present invention is preferably a lithium secondary battery, the lithium secondary battery includes a positive electrode capable of occluding and releasing lithium ions, a negative electrode capable of occluding and releasing lithium ions, a porous separator and an electrolyte solution.

2 illustrates a lithium secondary battery packaged by a general packaging material, and FIG. 3 is a cross-sectional view of a portion of the packaging material including a dotted line, that is, a cathode / cathode terminal of FIG. 2. In FIG. 3, the packaging material of the aluminum laminate film is composed of an adhesive layer 4 inside, an aluminum layer 5 in the middle, and a polymer layer 6 outside, and the positive terminal 1 or the negative terminal ( 2) is connected to the outside. At this time, the terminal is coated with the terminal film 3.

The terminal film 3 is a special polymer used to improve the adhesiveness between the adhesive layer 4 and the terminals 1, 2. In general, the adhesive layer has excellent adhesive strength between the adhesive layers, but is not excellent in adhesive strength with terminals made of aluminum, nickel, copper, or the like. Therefore, a terminal film is used to improve the adhesive force between the metal terminal and the polymer of the adhesive layer.

The terminal film 3 uses an electrically insulating polymer, and is generally made by mixing an additive with a polyolefin-based polymer used in an adhesive layer.

The adhesive layer 4 serves to bond both sides of the packaging material during battery packaging to prevent external moisture or foreign matter from entering the battery and to prevent leakage of the electrolyte inside the battery to the outside. It is made of a thermoplastic resin so as to adhere well during thermal fusion, and is made of an electrically insulating material. The adhesive layer currently used is mainly manufactured from polyethylene, polypropylene, or a copolymer thereof, which is a polyolefin resin.

The aluminum layer 5 enables the molding when molding the packaging material and serves to prevent the penetration of water, electrolyte, and leakage. The aluminum layer is composed of aluminum metal, which is very good in electrical and thermal conductivity.

The outermost polymer layer (6) enables the outer protection and printing of the battery, and a non-electrically conductive material is used so that the two terminals of the battery are not touched at the same time. Currently used polymers are PET (Poly Ethylene Terephthalate) or nylon.

Therefore, in the conventional battery, the packaging material and the terminal are electrically insulated by the terminal film or the adhesive layer so that no current flows.

In order to ensure the safety of the battery, the present invention attaches an electrically conductive and / or thermally conductive metal foil 7 to the end face (Fig. 4) or both sides (Fig. 5) of the upper end or the lower end of the battery, It is characterized in that it is connected to the positive terminal (1), the negative terminal (2), or both terminals.

According to the present invention, if the metal foil on the outside of the packaging material and the anode terminal is connected so that electricity flows, or the metal foil on the outside of the packaging material and the cathode terminal is connected so that electricity flows, the current in the situation such as nail penetration, etc. Since it flows to the metal foil outside, heat generation occurs in the metal foil outside the packaging material, so that heat generation inside the battery does not occur or heat generation is small.

However, when no special situation such as nail penetration occurs, the current does not flow because the voltage of the metal foil on the outside of the packaging material is the same in any part.

Therefore, when the packaging material is used, current does not flow to the metal foil outside the packaging material, but when a dangerous situation such as nail penetration occurs, the current flows to the metal foil outside the packaging material to suppress the flow of current into the battery and the safety of the battery. Can be secured.

The metal foil outside the packaging material may be used in an exposed state, or may be used surrounded by an electrically insulating polymer layer.

In the present invention, as shown in Figs. 4 and 5, a metal foil having electrical conductivity and / or thermal conductivity is attached to a single metal on one side or both sides of the top and bottom of the battery and connected to the positive or negative terminal. In the case where two or more metals are used in combination, there is a method of inserting a non-conductive material such as a separator between the metals and attaching them to one or both surfaces of the metals and connecting them to the positive or negative terminals. At this time, a non-conductive material such as a separator is inserted between the two foils to serve as a short circuit protection.

Non-limiting examples of how to connect the positive or negative terminal and the metal foil outside the packaging include ultrasonic welding, arc welding and resistance welding.

In addition, it is possible to make the electricity pass by connecting the metal foil outside the terminal and the packaging material in various ways.

As the material of the electrically conductive metal foil usable in the present invention, any metal, metal oxide or alloy thereof having electrical conductivity can be used. For example, aluminum metal, copper metal, nickel metal and the like.

When the metal foil is an aluminum foil, it is preferable that the aluminum foil is connected with the positive electrode terminal, and when the metal foil is a copper foil, it is preferable that the copper foil is connected with the negative electrode terminal.

In addition, the electrically conductive material preferably also has excellent thermal conductivity, in which case the heat inside the battery may be dispersed through a terminal to a thermally conductive metal foil in a normal or special situation.

Non-limiting examples of the non-conductive material used for the separator inserted between the metal foils include polypropylene (PP), polyethylene (PE), and the like, such as a porous separator of a battery, and may be any non-conductive polymer material.

In addition, the present invention is an adhesive layer therein; Aluminum layer in the middle; And an aluminum laminate film including a polymer layer on the outside of the battery packaging material, wherein an electrically conductive metal foil outside the battery packaging material is attached to one end or both sides of an upper end portion or a lower end portion of the battery. The present invention provides a battery packaging material characterized in that the metal foil can be connected to the positive terminal, the negative terminal, or both terminals of the battery when packaging the furnace.

On the other hand, the packaging material of the battery according to the present invention includes an aluminum layer, but a layer made of any material may be substituted for the aluminum layer as long as it is electrically conductive and can impart moldability to the packaging material. Batteries packaged with the packaging material also belong to the equivalent range of the present invention.

Examples of a battery that can use the present invention include: a) a positive electrode capable of storing and releasing lithium ions; b) a negative electrode capable of storing and releasing lithium ions; c) a porous separator; And d) a nonaqueous electrolyte comprising a lithium salt and an electrolyte compound.

The nonaqueous electrolyte includes cyclic carbonate and linear carbonate. Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), gamma butyrolactone (GBL), and the like. For example, at least one selected from the group consisting of diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC) and methyl propyl carbonate (MPC) may be selected.

The 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 .

It is preferable to use carbon, lithium metal, or an alloy as the negative electrode active material. Other metals such as TiO ₂ and SnO ₂ capable of occluding and releasing lithium and having a potential for lithium of less than ₂ V are also possible.

The positive electrode active material is preferably a lithium-containing transition metal oxide, for example, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO _2, and LiNi _1-X Co _X O ₂ (here, 0 <X <1). It is preferable to select at least 1 type from the group. An anode made of a metal oxide such as MnO ₂ or a combination thereof may be used.

In addition, examples of the porous separator is a polyolefin-based porous separator.

The lithium ion secondary battery of the present invention can be prepared by inserting a porous separator between the negative electrode and the positive electrode in a conventional manner, and by adding a non-aqueous electrolyte containing a lithium salt and additives such as LiPF ₆ described above.

The outline of the lithium secondary battery according to the present invention can be used in a pouch type battery made of an aluminum laminate film.

The present invention will be described in more detail with reference to the following examples. However, the examples are only for illustrating the present invention and not for limiting the present invention.

EXAMPLE

Example 1

1M LiPF ₆ solution having a composition of EC: EMC = 1: 2 was used as an electrolyte, artificial graphite was used as the negative electrode, and LiCoO ₂ was used as the positive electrode. Thereafter, a 383562 type lithium polymer battery was manufactured by a conventional method, and the battery was manufactured by packaging using aluminum laminate packaging material, attaching aluminum foil to both sides of the packaging material, and connecting the positive electrode terminal and ultrasonic welding.

Example 2

Prepared in the same manner as in Example 1, but by attaching a copper foil on both sides of the outer packaging material and connected to the negative terminal to prepare a battery.

Example 3

The battery was manufactured in the same manner as in Example 1, except that the aluminum foil and the copper foil were attached together on both sides of the outer packaging material to connect the positive and negative terminals, respectively. At this time, a non-conductive material such as a separator was inserted between the two foils to prevent short circuit.

Comparative Example 1

A battery was manufactured in the same manner as in Example 1, but without attaching a metal foil to the outside of the packaging material.

(Penetration test)

The batteries prepared in Examples 1 to 3 and Comparative Example 1 were prepared in a fully charged state. Using a nail penetration tester, a nail of steel diameter 2.5mm was penetrated to the center of the cell made above.

The safety of the battery varies depending on the penetration speed of the nail, and the nail is allowed to penetrate at a constant speed by using a device capable of adjusting the penetration speed. In order to determine the safety level of the battery, it was tested by varying the penetration rate of the nail. In Comparative Example 1, the battery was ignited even when penetrating the nail at a speed of 10 cm per second, but in Examples 1 to 3, the battery was not ignited even when the nail was penetrated at a speed of 1 cm per second.

The results of the nail penetration test are summarized in Table 1.

Penetration speed of nail (cm per second) Fire or not Comparative Example 1 10 Fire One Fire Example 1 10 Unfired One Unfired Example 2 10 Unfired One Unfired Example 3 10 Unfired One Unfired

As described above, the present invention, through the connection of the aluminum foil and the positive terminal of the outer packaging material, or the connection between the copper foil and the negative electrode terminal of the packaging material, the current flows into the aluminum and copper foil outside the packaging material when the nail penetrates the inside of the battery It is possible to improve the safety of the battery by suppressing the heat generation from. According to the present invention, a lithium ion battery packaged in a battery packaging material having a structure in which a positive electrode terminal or a negative electrode terminal is electrically connected to a metal foil attached to the outside of the packaging material is secured in situations such as nail penetration, crimping, impact, and high temperature exposure. .

Claims (9)

A secondary battery packaged by a battery packaging material, wherein the battery packaging material has an adhesive layer therein; Aluminum layer in the middle; And an aluminum laminate film including a polymer layer on the outside, wherein an electrically conductive metal foil outside the battery packaging material is attached to one or both of the upper and lower ends of the battery, so that the positive electrode terminal, the negative electrode terminal, or both terminals Secondary battery characterized by connected. The secondary battery of claim 1, wherein the metal foil is made of a material selected from the group consisting of an electrically conductive metal, a metal oxide, or an alloy thereof. The secondary battery of claim 1, wherein the metal foil is further thermally conductive. The secondary battery of claim 1, wherein when the metal foil is an aluminum foil, the aluminum foil is connected to a positive electrode terminal. The secondary battery of claim 1, wherein when the metal foil is a copper foil, the copper foil is connected to a negative electrode terminal. The secondary battery of claim 1, wherein when two or more kinds of metal foils are used, a separator made of a non-conductive material is inserted between the metal foils. 7. The method of claim 6, wherein when both aluminum foil and copper foil are used as the metal foil, a separator of non-conductive material is inserted between the two foils, the aluminum foil is connected to the positive terminal, and the copper foil is connected to the negative terminal. Characteristic secondary battery. The secondary battery according to any one of claims 1 to 7, which is a lithium secondary battery. Adhesive layer therein; Aluminum layer in the middle; And an aluminum laminate film comprising a polymer layer on the outside. A battery packaging material in which an electrically conductive metal foil outside the battery packaging material is attached to one end or both surfaces of an upper end portion or a lower end portion of a battery, wherein the metal foil is a positive terminal, a negative terminal, or A battery packaging material which can be connected to both terminals.