KR100847214B1 - Electrochemical device with excellent safety in overcharge and high temperature storage - Google Patents

Abstract

The present invention is characterized in that a foaming agent that releases gas other than oxygen at a temperature (T) higher than the normal operating temperature range of the battery is coated on the electrode surface or mixed with an electrode material, and a method for producing the same. And an electrochemical device comprising the same.

In the present invention, by using a blowing agent that releases a large amount of inert gas in a temperature range higher than the normal operating temperature of the battery as a constituent component or a coating component of the electrode, the safety of the battery during overcharging and high- Can be improved.

Foaming agent, electrode, safety, overcharge, azo system, azobiscarboxamide (ADA)

Description

TECHNICAL FIELD [0001] The present invention relates to an electrochemical device having excellent safety in overcharging and high-temperature storage. BACKGROUND OF THE INVENTION [0001]

FIG. 1 is a graph showing changes in resistance of the electrode manufactured in Example 1 and Comparative Example 1 according to temperature changes. FIG.

The present invention relates to an electrode capable of imparting excellent safety even when the internal temperature of the battery rises abnormally due to external or internal factors, and to an electrochemical device having the electrode, and more particularly, Which can prevent explosion and / or ignition during overcharging and high temperature storage by preventing the contact with oxygen required for ignition by blocking the high current flow by increasing the resistance, and a method for producing the same, The present invention relates to an electrochemical device having an electrode and improved safety.

Generally, in a lithium secondary battery using a flammable non-aqueous electrolyte, short-circuiting occurs due to dendrite which is generated by lithium ions in the negative electrode during overcharging. As a result, the internal temperature of the battery rises and the decomposition reaction of the electrolyte, And explosion or fire due to the generation of flammable gas due to the reaction of the electrodes. The polyethylene used as the separator between the anode and the cathode starts to melt in the range of 120 to 130 占 폚 when the temperature of the battery rises. As a result, the cathode and the anode come into contact with each other due to shrinkage of the separator, The heat is generated by the current flow, the temperature rises, and finally, the ignition of the battery occurs.

In order to solve such a problem, U.S. Patent No. 6,074,776 discloses a method of controlling an electric current flow through an increase in electrode resistance by forming an insulating layer on a surface of a positive electrode at a high temperature. In this case, the added aromatic monomer additive is polymerized . However, when the temperature rises, there is still a risk of ignition of the battery due to electrolyte decomposition.

Japanese Unexamined Patent Application, First Publication No. 2002-157979 discloses a flame-retardant magnesium alloy having an excellent thermal stability and an ignition temperature of 550 ° C or higher, which is injected into a non-aqueous electrolyte to prevent the battery from igniting and burning even when the battery temperature rises, / RTI > However, even in this case, even if the magnesium alloy can absorb a certain amount of heat, there is a risk of ignition potentially because it can not absorb the heat inflow due to the continuous temperature increase.

Japanese Patent Application Laid-Open No. 1994-150975 discloses a method in which an electrolytic solution is pressurized and charged with carbon dioxide and the electrolyte is easily released to the outside together with carbon dioxide when the temperature of the battery rises abnormally. However, when the electrolyte is sucked into the internal pores or electrodes of the separator, the gas pressure alone can not be easily released to the outside, so that the risk of battery ignition due to decomposition of the electrolytic solution is still not solved.

Japanese Patent Application Laid-Open No. 1999-317232 discloses a method of flame retarding an electrolyte for a lithium secondary battery by adding a phosphoric acid-based flame retardant such as trialkyl phosphate, trimethyl phosphate, or dimethyl phosphate to the electrolyte solution. However, since the phosphoric acid flame retardant is ignited and melts as the heat, it covers the surface and extinguishes by the effect of preventing contact with oxygen, so a large amount of flame retardant must be injected into the electrolyte solution. Therefore, the use of a large amount of the phosphoric acid-based flame retardant leads to deterioration of the characteristics of the battery. In addition, in the case of an electrolyte having a strong flammability, since it is easily propagated once it has been ignited, it is not enough to extinguish it only by using a phosphoric acid-based flame retardant.

In view of the above-mentioned problems, the present inventors have found that (1) a method of preventing contact with oxygen required for ignition before reaching the ignition point is used and / or (2) Even when a short circuit occurs due to the increase in temperature due to a rise in temperature, the gap between the electrode active material particles is instantaneously widened to suppress an increase in electrode resistance and a large amount of current flow, thereby improving the safety of the battery. For the first time.

In fact, when the foaming agent is used as a constituent component or a coating component of the electrode, a large amount of inert gas is released at a temperature higher than the normal operating temperature of the battery, for example, around 130 DEG C to increase the interval between particles constituting the electrode, Thereby preventing a sudden flow of the current and increasing the internal pressure to open the vent to lower the temperature so as not to reach the ignition and also to prevent the contact with oxygen which is the ignition-inducing element by the discharged inert gas, It was confirmed that the effect of suppressing the ignition of the battery by the gas and the improvement of the safety of the battery by the gas were excellent.

Accordingly, it is an object of the present invention to provide an electrode containing a foaming agent capable of achieving the aforementioned safety improvement effect, a method for producing the electrode, and an electrochemical device including the electrode.

The present invention relates to an electrode characterized in that a foaming agent for discharging gas excluding oxygen at a temperature (T) higher than the normal operating temperature range of the battery is coated on the surface of the electrode or mixed with the electrode material, and an electrochemical Device, preferably a lithium secondary battery.

(A) mixing the foaming agent with an electrode material, coating the foil on the current collector or coating the previously prepared electrode surface; And (b) drying the electrode. The present invention also provides a method of manufacturing an electrode including a foaming agent.

Hereinafter, the present invention will be described in detail.

The present invention is characterized by using a foaming agent, which is not used in a conventional battery, or is supplementarily used for forming a pore structure by thermal decomposition even when applied, as one constituent component or a coating component of an electrode.

Conventional blowing agents have been used for extrusion or injection molding in rubber, polyurethane, EVA or the like to decompose at a processing temperature to release a large amount of gas to form bubbles, thereby being strong against impact or reducing the amount of raw materials used. However, in the present invention, the blowing agent is used for the purpose of instantaneously decomposing in a narrow temperature range to eject a large amount of inert gas and increase the pressure inside the battery.

When the foaming agent having the above-described characteristics is used as a constituent component and / or a coating component of the electrode, the safety of the battery can be improved.

That is, when the temperature of the battery abnormally rises due to internal or external factors such as high-temperature storage or overcharging, due to the decomposition reaction of the electrolytic solution, the generation of flammable gas by the reaction between the electrolyte and the electrode, Resulting in ignition and explosion of the battery. In order to solve such a problem, a monomer additive for forming an insulating layer and an electrolyte additive such as a flame retardant have been used, but the fundamental problem of lowering the safety of the battery has not been solved.

In contrast, in the present invention, by using a foaming agent that releases a large amount of a gas other than oxygen (O ₂ ), for example, an inert gas, which is one of ignition elements at a temperature higher than the normal operating temperature range of the battery, Can be fundamentally solved.

In addition, when the foaming agent is used as one component of the electrode, the gap between the electrode active material particles in the electrode is instantaneously increased due to the volume expansion due to a large amount of gas discharge pressure. Therefore, Even if an internal short circuit due to contact between the two electrodes occurs, the flow of high current can be suppressed by increasing the resistance due to the increase of the distance between the electrode active material particles. In fact, it was confirmed from the present experimental example that the electrode resistance of the foaming agent was significantly increased at a temperature higher than the normal operating temperature range of the battery (see FIG. 1).

Furthermore, since the vent can be operated early due to an increase in gas pressure inside the battery due to a large amount of gas emitted by the foaming agent, heat inside the battery can be dissipated in advance to the outside, thereby reducing the internal temperature.

By the above-described combined action, an excellent safety improvement effect of the battery can be achieved.

A blowing agent capable of achieving the above-mentioned action may be used as a component of the electrode, mixed or used as a coating component of the electrode manufactured. At this time, the foaming agent can be used without limitation any conventional foaming agent known in the art capable of instantly decomposing in a specific temperature range to release a large amount of gas other than oxygen.

The temperature at which the blowing agent decomposes and releases a large amount of gas is not particularly limited as long as the temperature is higher than the normal operating temperature of the battery. In particular, the temperature at which the decomposition reaction of the electrolyte solution A lower temperature range is preferred. In one example, the temperature is in the range of 130 to 150 ° C.

The gas component to be pyrolyzed and released by the blowing agent is not particularly limited as long as it is not oxygen, which is a firing element. However, it is preferably an inert gas such as N ₂ , He, Ne, Ar, Kr, Xe or a mixture thereof Do.

Non-limiting examples of usable foaming agents include azo (-N═N-) -based compounds, and azobiscaroxamide (ADA) -based compounds preferably represented by the following formula (1).

The ADA-based blowing agent rapidly releases a large amount of nitrogen at a rate of 25 to 350 ml / g, preferably 220 ml / g at 130 to 150 ° C, thereby sufficiently satisfying the safety improvement effect of the battery. There are no particular limitations on the components, form and the like of the component as long as it can satisfy the above-described conditions and improve the safety of the battery in addition to the foaming agent of the component.

The amount of the foaming agent to be introduced into the electrode is not particularly limited as long as it exhibits an effect of improving the safety of the battery, but is preferably 0.05 to 10 parts by weight per 100 parts by weight of the electrode active material. When the foaming agent is used in an amount less than 0.05 part by weight, the desired safety improvement effect may be insufficient. When the amount is more than 10 parts by weight, the amount of the electrode active material due to the use of the foaming agent is relatively decreased.

A method for producing an electrode including a foaming agent as a constituent component of the electrode according to the present invention is not particularly limited. For example, the foaming agent may be mixed with an electrode material such as an electrode active material, Or the like to prepare an electrode slurry and then coating the electrode slurry on the collector or coating the prepared electrode surface. And (b) drying the electrode.

Hereinafter, an example of a method of dispersing the foaming agent in the electrode will be described in detail.

First, 1) a binder (for example, PVDF (polyvinylidene fluoride)) is added to a solvent or a dispersion medium (for example, N-methyl pyrrolidone) to prepare a binder solution.

At this time, the binder is suitably added in an amount of 5 to 20 parts by weight (weight ratio) based on 100 parts by weight of the solvent or dispersion medium, but is not limited thereto. The solvent or dispersion medium used for preparing the binder solution may be any conventional solvent used in the art, including, but not limited to, N-methylpyrrolidone, acetone, dimethylacetamide, An organic solvent such as dimethylformaldehyde, an inorganic solvent such as water, or a mixture thereof. The amount of the solvent used is sufficient to dissolve and disperse the active material, the conductive material, the electrode binder, and the adhesion promoting additive in consideration of the coating thickness and the production yield of the electrode slurry. The solvents are removed by drying after coating the electrode slurry on the current collector.

2) The electrode active material and the foaming agent are added to the prepared binder solution, mixed and completely dispersed, and then coated on the current collector and dried to complete the electrode production.

The foaming agent is suitably used in an amount of 0.5 to 50 parts by weight based on the binder, but is not limited thereto. In this way, the electrode active material and the conductive agent are added to the binder solution containing the foaming agent to prepare the electrode slurry in the mixer. The electrode drying process can also be performed according to a conventional method known in the art, and one example can be hot-air dried.

As the cathode active material, a conventional cathode active material which can be used for a cathode of a conventional electrochemical device can be used, and examples thereof include LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) Lithium manganese composite oxides such as LiMn ₂ O ₄ , lithium nickel oxides such as LiNiO ₂ , lithium cobalt oxides such as LiCoO ₂ , and manganese, nickel, and cobalt of these oxides, A vanadium oxide containing lithium, etc.) or a chalcogen compound (e.g., manganese dioxide, titanium disulfide, molybdenum disulfide, etc.), and the like. Preferably _{LiCoO 2, LiNiO 2, LiMnO 2} , LiMn 2 O 4, Li (Ni a Co b Mn c) O 2 (0 <a <1, 0 <b <1, 0 <c <1, a + b _{+ c = 1), LiNi 1} -Y Co Y O 2, LiCo 1-Y Mn Y O 2, LiNi 1-Y Mn Y O 2 ( here, 0≤Y <1), Li ( Ni a Co b Mn _c ) O ₄ (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn _{2 -z} Ni _z O ₄ , LiMn _{2 -z} Co _z O ₄ here, the 0 <Z <2), LiCoPO 4, LiFePO 4 or a mixture thereof. More preferably a lithium-transition metal composite oxide represented by the following formula (2).

Li _x MO ₂

In the above formula, M is Ni, Co, or Mn, and x is 0.05? X? 1.10.

The negative electrode active material can be a conventional negative electrode active material that can be used for a negative electrode of a conventional electrochemical device. Examples of the negative electrode active material include lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, Graphite or other carbon-based lithium-adsorbing materials. Non-limiting examples of the positive current collector include aluminum, nickel, or a combination thereof. Examples of the negative current collector include copper, gold, nickel, or a copper alloy or a combination thereof Foil to be manufactured, and the like.

As binders, conventional binders can be used, and non-limiting examples thereof include polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), Teflon, or a mixture thereof.

The conductive agent is not particularly limited as long as it can improve conductivity, and examples thereof include acetylene black, graphite and the like.

The weight ratio of the components constituting the electrode of the present invention is not particularly limited, but may be (a) 80 to 99 parts by weight, preferably 90 to 96 parts by weight, of the positive electrode active material or negative electrode active material; (b) 1 to 15 parts by weight, preferably 1 to 7 parts by weight of a binder; And (c) 0.05 to 10 parts by weight, preferably 1 to 5 parts by weight, of the foaming agent. In addition, 0.1 to 10 parts by weight, preferably 1 to 5 parts by weight, of the conductive agent may be further added for the purpose of increasing the conductivity of the electrode.

The method of preparing an electrode using the foaming agent as a coating component of the electrode may also be carried out by a conventional method known in the art. For example, a foaming agent may be dispersed in a binder solution or a solvent to prepare a foaming agent- And then coating and drying it on the surface of the prepared electrode.

The present invention provides an electrochemical device comprising a cathode, a cathode, a separator, and an electrolyte, wherein the anode, cathode, or both electrodes are electrodes containing a foaming agent.

The electrochemical device includes all devices that perform an electrochemical reaction, and specific examples thereof include all kinds of primary and secondary batteries, fuel cells, solar cells, and capacitors. In particular, lithium secondary batteries among the secondary batteries are preferable, and examples thereof include lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, and lithium ion polymer secondary batteries.

The electrochemical device of the present invention can be manufactured by putting a porous separator between an anode and a cathode by a conventional method known in the art and injecting the electrolyte.

The electrolyte for a battery includes conventional electrolytic solution components known in the art, such as an electrolyte salt and an organic solvent.

Using the electrolyte salts is A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, K ⁺ comprises an alkaline metal cation or an ion composed of a combination thereof, such as, and B ^- is PF ₆ ^-, BF _{^{4 -, Cl -, Br -}} , I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2) 3 ^- &lt; / RTI &gt; or a combination thereof. In particular, a lithium salt is preferable.

The organic solvent may be a conventional solvent known in the art such as cyclic carbonate and / or linear carbonate, and examples thereof include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC) (DMC), dipropyl carbonate (DPC), dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate, And the like. In addition, halogen derivatives of the above organic solvents can be used, and they can also be used in batteries using water.

The separation membrane is not particularly limited, but a porous separation membrane can be used, and examples thereof include a polypropylene-based, polyethylene-based, and polyolefin-based porous separation membrane.

The outer shape of the electrochemical device manufactured by the above method is not limited, but a cylindrical shape, a coin shape, a square shape, or a pouch shape can be used.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the following examples serve to illustrate the present invention, and the scope of the present invention is not limited thereto.

[Examples 1 to 3]

Example 1

(Cathode manufacture)

A negative electrode mixture slurry was prepared by mixing carbon powder as a negative electrode active material, polyvinylidene fluoride (PVDF) as a binder, a conductive agent, and a foaming agent AMBM in a weight ratio of 91: 4: 4: 1 and then dispersing the mixture in NMP. The anode mixture slurry was applied uniformly to the end face of a Cu foil having a thickness of 10 탆 as a cathode collector with a comma gap of 200 탆 and dried. At this time, the coating speed was 3 m / min. The dried electrode was sampled for stability and the results are shown in Table 1 below.

(Anode manufacture)

The positive electrode mixture slurry was prepared by mixing a lithium cobalt composite oxide as a cathode active material, carbon as a conductive agent, PVDF as a binder, and a blowing agent AMBM in a weight ratio of 92: 4: 3: 1. The anode mixture slurry was applied to an Al thin film of a cathode current collector having a thickness of 20 탆 and coated and dried in the same manner as the cathode.

(Battery manufacturing)

A porous polyethylene film was used as a separator, and a band-shaped negative electrode and a positive electrode were laminated and wound several times to produce a jelly roll. The length and width were adjusted so that it was appropriately embedded in a battery can having an outer diameter of 18 mm and a height of 65 mm. The prepared jelly roll was stored in a battery can, and an insulating plate was disposed on both upper and lower surfaces of the electrode element. Then, a negative electrode lead made of nickel was drawn out from the current collector and welded to the battery can. A positive electrode lead made of aluminum was drawn from the positive electrode current collector and welded to an aluminum pressure release valve mounted on the battery cover. An electrolyte solution was injected into the battery. The electrolyte solution was a mixed solvent of EC and EMC in a volume ratio of 1: 2 and LiPF ₆ solution as an electrolyte.

The battery thus prepared was charged to 4.2 V with a constant current. The standard capacity of the electrolyte secondary battery was 2200 mAh and the efficiency was measured at a rate of 1 C (2200 mA / h) and 0.2C (440 mA / h) at a constant current from 4.2 V to 3 V, .

Example 2

A battery was prepared in the same manner as in Example 1 except that the foaming agent was changed to 3 parts by weight in the preparation of the positive electrode and the negative electrode slurry.

Example 3

A battery was prepared in the same manner as in Example 1 except that the foaming agent was changed to 7 parts by weight in the preparation of the positive electrode and negative electrode slurry.

Comparative Example 1

A battery was prepared in the same manner as in Example 1 except that no foaming agent was added to the positive and negative electrode slurries.

Experimental Example 1. Evaluation of Physical Properties of Electrodes

In order to evaluate the change in resistance of the electrode containing the foaming agent according to the present invention, the following procedure was performed.

In Example 1, an electrode containing a foaming agent was used, and as a control thereof, the electrode of Comparative Example 1 prepared according to a conventional method in the art was used.

Fig. 1 shows the change in resistance of each electrode while increasing the temperature. It can be seen that the resistance of the electrode of Comparative Example 1 containing no foaming agent decreases as the temperature rises. In contrast, the electrode of Example 1 containing a foaming agent started to increase in resistance after 110 ° C and showed a much higher resistance value than the electrode of Comparative Example 1 up to 140 ° C (see FIG. 1). This means that the foaming agent, which is a component of the electrode, increases the resistance of the electrode while discharging a large amount of nitrogen gas.

Therefore, it was confirmed that the electrode containing the foaming agent of the present invention instantly increases the gap between the electrode active material particles in the electrode due to the volume expansion due to a large amount of the gas ejection pressure, thereby suppressing the high current flow through the resistance increase.

Experimental Example 2 Evaluation of safety of a battery

In order to evaluate the safety of a lithium secondary battery having an electrode containing a foaming agent according to the present invention, the following procedure was performed.

The lithium secondary batteries prepared in Examples 1 to 3 were used, and the lithium secondary batteries of Comparative Example 1, which were produced according to a conventional method known in the art, were used as a control group without using a foaming agent.

1-1. Hot box experiment

Each cell was stored at a high temperature of 160 DEG C for 4 hours, and the state of the battery was described in Table 1 below.

As a result of the experiment, in the lithium secondary battery of Comparative Example 1 having electrodes manufactured according to a conventional method without using a foaming agent, the safety of the battery was lowered to about 50%, while the batteries of Examples 1 to 3 containing the foaming agent It was confirmed that the battery of Example 3 produced by using the foaming agent in an amount of 7 parts by weight had an excellent safety improvement effect due to no ignition and explosion at all (see Table 1) .

1-2. Overcharge experiment

Each battery was charged under the condition of 12V / 1C, and the state of the battery thereafter is shown in Table 1 below.

As in the above hot box test results, the batteries of Examples 1 to 3 containing the foaming agent had an excellent safety improvement effect as compared with the lithium secondary battery of Comparative Example 1 having electrodes manufactured by a conventional method without using a foaming agent (See Table 1).

1-3. Penetration experiment

The nail penetration test was performed using each cell, and the state of the battery was described in Table 1 below.

Similar to the results of the hot box test and the overcharge test, the batteries of Examples 1 to 3 containing the foaming agent showed excellent safety compared to the lithium secondary battery of Comparative Example 1 having electrodes manufactured by a conventional method without using a foaming agent (See Table 1).

By using the foaming agent as a coating component or an electrode additive for an electrode, the present invention can remarkably improve the safety pointed out as a problem of the conventional lithium secondary battery.

Claims (14)

A foaming agent which releases at least one inert gas selected from the group consisting of N ₂ , He, Ne, Ar, Kr, and Xe in a temperature range of 130 to 150 ° C. which is higher than the normal operating temperature range of the battery, Or is mixed with an electrode material. The electrode according to claim 1, wherein the temperature (T) is higher than a normal operating temperature of the battery and is lower than a temperature at which a decomposition reaction of the electrolytic solution in the battery occurs. delete delete The electrode according to claim 1, wherein the electrode is in contact with oxygen due to an inert gas generated from the foaming agent in a temperature range (T) higher than a normal operation temperature of the battery. The electrode according to claim 1, wherein the gap between the electrode active material particles in the electrode is expanded by volume expansion due to the gas ejection pressure generated from the foaming agent in a temperature range (T) higher than a normal operation temperature of the battery. The electrode according to claim 1, wherein the electrode operates the vent through an increase in the internal pressure of the battery due to the gas generated from the foaming agent in a temperature range (T) higher than a normal operating temperature of the battery. The electrode according to claim 1, wherein the foaming agent is an azo (-N = N-) -based compound. 9. The electrode according to claim 8, wherein the azo-based compound is a compound represented by the following formula (1). [Chemical Formula 1]

The electrode according to claim 1, wherein the content of the foaming agent is 0.05 to 10 parts by weight per 100 parts by weight of the electrode active material. An electrochemical device comprising an anode, a cathode, a separator, and an electrolyte, wherein the anode, the cathode, or both electrodes are electrodes according to any one of items 1 to 2 and 5 to 10. 12. The electrochemical device according to claim 11, wherein the electrochemical device is a lithium secondary battery. (a) mixing a foaming agent with an electrode material, and then applying the foaming agent on the current collector or coating the electrode surface; And (b) drying the electrode And a foaming agent containing the foaming agent. The manufacturing method according to claim 13, wherein the step (a) of mixing the foaming agent with an electrode material comprises dispersing an electrode active material, a binder, and a foaming agent in a solvent to produce an electrode slurry.

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