KR20070090852A - Electrochemical device with high safety at high temperature - Google Patents

Abstract

An electrochemical device using a core-shell type composite binder particles is provided to interrupt oxygen from being in contact with the device, to realize early driving of a safety unit under an elevated pressure, and to improve the safety of the device upon an abnormal increase in the internal temperature of the device. An electrochemical device uses a core-shell structured composite particles as a binder, the binder comprising: (a) a core comprising a material that causes a partial or total phase change of a solid or liquid into a gas at a temperature higher than a predetermined temperature; and (b) a polymer shell formed on the surface of the core. The temperature(T) where the core undergoes a phase change into a gas is higher than the normal drive temperature of the electrochemical device.

Description

ELECTROCHEMICAL DEVICE WITH HIGH SAFETY AT HIGH TEMPERATURE

1 is a cross-sectional structural view of a core-shell structural binder according to the present invention.

Figure 2 is a photograph showing the volume change according to the temperature change (25 ℃, 110 ℃) of the core-shell structured binder according to the present invention.

3 is a photograph showing a surface structure after a nail test is performed on the lithium secondary battery of Example 1. FIG.

4 is a graph showing a current change of a battery after inducing an internal short circuit to the lithium secondary battery of Example 1. FIG.

According to the present invention, safety is improved by using a binder which can provide excellent safety even if the internal temperature of the device is abnormally increased due to external or internal factors, and the binder as one component or a coating component of the device element constituting the electrochemical device. An improved electrochemical device.

In general, a lithium secondary battery using a flammable non-aqueous electrolyte may generate short due to dendrites grown by lithium ions at a negative electrode during overcharging. As a result, the internal temperature of the battery rises and the decomposition reaction of the electrolyte may occur. Combustible gas, a flammable gas according to the reaction of the electrolyte and the electrode, there is a problem that explosion or fire occurs due to the generation of oxygen by the decomposition of the anode. In addition, polyethylene used as a separator between the positive electrode and the negative electrode starts to melt in the range of 120 to 130 ° C. when the temperature of the battery rises, and accordingly, the short-circuit occurs due to the contact between the negative electrode and the positive electrode of the corner due to shrinkage of the separator. The heat flows through the current flow, causing the temperature to rise and eventually causing the battery to ignite.

In order to solve this problem, US Patent No. 6,074,776 discloses a method of controlling the flow of current through the increase of electrode resistance by making an insulating layer on the surface of the anode at a high temperature, wherein the aromatic monomer additive introduced is a polymerization reaction in a high voltage state It was used to cause. However, there was still a risk of ignition of the battery due to decomposition of the electrolyte at elevated temperatures.

In Japanese Patent Laid-Open No. 2002-157979, it is excellent in thermal stability and a flame retardant magnesium alloy having a ignition temperature of 550 ° C. or higher is added to a nonaqueous electrolyte to prevent battery from igniting and burning even when the battery temperature rises. The method is disclosed. However, even in this case, even though the magnesium alloy can absorb some heat, it is not possible to absorb all the heat inflows due to the continuous temperature rise, so there is a risk of ignition.

In Japanese Patent Laid-Open No. 194-150975, a method of pressurizing and charging an electrolyte solution with carbon dioxide is used to easily release the electrolyte solution together with carbon dioxide when the temperature of the battery rises abnormally. However, when the electrolyte is sucked into the inner pores of the separator or the inside of the electrode, the gas ignition alone is not easily released to the outside, so the risk of battery ignition due to decomposition of the electrolyte is still not solved.

Japanese Patent Laid-Open No. 1999-317232 proposes a method of flame retarding an electrolyte solution for a lithium secondary battery by adding a phosphate flame retardant such as trialkyl phosphate, trimethyl phosphate, or dimethyl phosphate to the electrolyte solution. However, phosphate-based flame retardants are ignited and melted by their heat, which encapsulates the surface and serves to extinguish the effect of preventing contact with oxygen. Therefore, a large amount of flame retardants must be added to the electrolyte. Therefore, the use of a large amount of phosphate-based flame retardant inevitably leads to deterioration of battery characteristics. In addition, in the case of a highly flammable electrolyte, it is easily propagated once it catches fire, so it is insufficient to be digested only by using a phosphate-based flame retardant.

In view of the above-described problems, the present invention plays the same role as a conventional binder in the normal operating temperature range of the device, but when an abnormal problem occurs due to an external or internal factor and the temperature inside the device rises to an abnormally high temperature, several times to several tens. The volume expansion up to 2 times increases the spacing between the particles of the electrode active material in an instant to suppress the increase of electrode resistance and the large amount of current flow, and / or to open the shell structure at any moment due to the expanded gas. Novel binders were produced which ejected gases that could prevent contact with oxygen, and found that the binder was used as one component of the device element or its coating component, which resulted in excellent safety improvement of the electrochemical device.

Accordingly, an object of the present invention is to provide an electrochemical device having improved safety by providing a binder and the binder which can provide safety by implementing an increase in resistance of the electrode and blocking oxygen contact in the device through volume expansion at a high temperature as described above. It is done.

The present invention provides a composition comprising: (a) a core containing a substance in which part or all of a solid or liquid phase changes into a gas above a certain temperature; And (b) a binder containing composite particles having a core-shell structure comprising a polymer shell formed on the surface of the core, the binder comprising one component of a device element constituting an electrochemical device or a coating component thereof. It provides an electrochemical device, preferably a lithium secondary battery.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is in the solid or liquid phase below a certain temperature and rises above a certain temperature of the solid or liquid, instead of the conventional binder composed of one or more polymers or two or more polymers having different chemical structures even in the core-shell structure. A novel concept of a core-shell structured binder comprising a core material in which part or all of it is phase changed (phase transition) into gas is used as an electrochemical device, preferably a battery binder.

In order to design the new binder, the core material is stably present as a solid or a liquid below a certain temperature, for example, at the normal operating temperature of the device, and when the temperature rises above the normal operating temperature of the device, A portion of the material is pyrolyzed to release the gas, or a portion of the solid or liquid may be vaporized or sublimed to release the gas, and as a shell material, the core is wrapped around the core at the normal operating temperature of the device. While performing the function of a binder, conventional polymers having a glass transition temperature (T _g ) in the vicinity of the gas phase change temperature (T _pc ) of the core material are used, for example, T _pc ≤T _g and T _pc ≥ T _g , respectively. In the case of using the core-shell structured binder having such structural characteristics, the safety improvement effect of the electrochemical device, preferably the lithium secondary battery, is exhibited. Can.

In the present invention, it serves as a binder below a certain temperature, a large amount of gas excluding oxygen (O ₂ ) by a vaporization, sublimation or pyrolysis of the core above a certain temperature, for example, higher than the normal operating temperature range of the electrochemical device. For example, by using a binder that releases an inert gas as one component of a device element or a coating component thereof, it is possible to fundamentally solve the ignition occurrence of the device due to blocking contact with oxygen.

In addition, when the core-shell binder 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 of the binder due to a large amount of gas ejection pressure. Even if an internal short circuit occurs due to the contact of the positive electrode at the edge part due to the shrinkage of the separator, the high current flow can be suppressed through the increase in resistance due to the increase in the distance between the particles of the electrode active material.

In addition, when the temperature of the battery is abnormally increased due to internal or external factors such as high temperature storage or overcharging, the core of the core-shell structure binder used as one component of the device element or coating component thereof is released. By expanding the volume of the gas and increasing the pressure inside the device, it is possible to stop further operation of the device and / or to prematurely activate safety measures that can normally change abnormal conditions inside the device, It is possible to improve the safety of the device by reducing the concentration of the flammable gas and the temperature in the device by discharging the flammable gas and the accumulated heat inside to the outside in advance.

Through such a complex action, it is possible to achieve an excellent safety improvement effect of the electrochemical device.

In the core-shell structured binder according to the present invention, the core material is present as a solid or a liquid, and if a part or all of the solid or liquid can be phase changed to a gas at a temperature higher than a predetermined temperature, There is no special limitation. Phase change here refers to the transition of a substance to another phase or to another transformation, and in the present invention refers to the phase transition of a solid or liquid into the gas phase.

At this time, the temperature at which the core phase changes into a gas is preferably a temperature (T) higher than the normal operating temperature range of an electrochemical device, preferably a lithium secondary battery, and may be in the range of 60 to 200 ° C. have. The component of the gas which the core is phase-changed above a certain temperature and released is also not particularly limited, but if possible, it is preferable that the gas is a gas other than oxygen and / or hydrogen, which is a ignition element. Non-limiting examples thereof include inert gases such as N ₂ , He, Ne, Ar, Kr, and Xe, extinguishing gases such as H ₂ O, CO ₂ , I ₂ , F ₂ , Br ₂ , or mixtures thereof. have.

The substance which is phase-changed into a gas in a solid or liquid state may be (a) a substance which becomes gaseous by vaporization, sublimation or pyrolysis in a temperature range above a certain temperature, or a compound containing the substance which becomes the gaseous state; Restrictive examples include azo (-N = N-)-based compounds, carbonate-based compounds, hydrazide-based compounds, carbazide-based compounds or mixtures thereof. In addition, the content of the core in the core-shell binder is not particularly limited, depending on the type of components of the electrochemical device to which the binder is applied, such as an electrode, a separator, a device case and / or an empty space inside the device, or a device. It can adjust suitably within the range which shows the safety improvement effect of the.

The material constituting the shell of the core-shell binder according to the present invention can be used without limitation any conventional polymer known in the art that can be applied as a conventional battery binder.

The polymer has a glass transition temperature (T _g ) and / or a melting point (T _m ), preferably within 80 to 200 ° C., in which volume expansion occurs in a temperature range similar to the gas phase change temperature (T _pc ) of the core material. It is preferable to have a temperature or melting point, and thermosetting materials may be used, but the present invention is not limited thereto. In this case, the glass transition temperature (T _g ) and / or melting point (T _m ) of the polymer may be larger or smaller than or equal to the gas phase change temperature (T _pc ) of the core material. In addition, polymerized using conventional monomer components known in the art, non-limiting examples of these monomers are acrylate monomers, (meth) acrylic acid ester monomers, vinyl monomers, conjugated dienes Monomers, nitrile group-containing compounds, (meth) acrylamide monomers, unsaturated monocarboxylic acid monomers, styrenes, and mixtures thereof.

Non-limiting examples of the acrylate-based monomers are methacryloxyethyl ethylene urea, β-carboxyethyl acrylate, aliphatic monoacrylate, dipropylene diacrylate, ditrimethyllopropane tetraacrylate, hydroxy Ethylacrylate, dipentaerythriol hexaacrylate, pentaerythriol triacrylate, pentaerythriol tetraacrylate, lauryl acrylate, cetyl acrylate, stearyl acrylate, lauryl methacrylate, cetyl Methacrylate, stearyl methacrylate, or mixtures thereof.

In addition, non-limiting examples of acrylic ester monomers include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate. , n-hexyl acrylate, 2-ethylhexyl acrylate, and the like. Non-limiting examples of methacrylic acid ester monomers include methyl methacrylate, ethyl methacrylate, propyl methacrylate and isopropyl methacrylate. , n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, hydrate Oxypropyl methacrylate or mixtures thereof.

In addition, non-limiting examples of the vinyl monomers include styrene, α-methylstyrene, β-methylstyrene, pt -butylstyrene, divinylbenzene, or mixtures thereof, and the like, and non-limiting examples of the conjugated diene monomers. And 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene or mixtures thereof, and the like, and non-limiting examples of the nitrile group-containing compound include acrylonitrile, Methacrylonitrile or mixtures thereof. Non-limiting examples of the (meth) acrylamide monomers include acrylamide, n-methylol acrylamide, n-butoxymethylacrylamide, methacrylamide or mixtures thereof, and the like. Non-limiting examples include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, metaconic acid, glutaconic acid, tetrahydrophthalic acid, crotonic acid, isocrotonic acid, nadic acid or mixtures thereof.

One or more monomers of the above-described monomer types may be used as constituents, and the type and content of the monomers may be appropriately changed according to the properties and physical properties of each monomer.

The core-shell binder according to the present invention is conventionally polymerized, such as emulsion polymerization, suspension polymerization, dispersion polymerization, seed polymerization, except that a binder is used as the core material. It can be obtained by the method by, but is not limited thereto. At this time, the polymerization temperature and the polymerization time can be arbitrarily selected according to the polymerization method, the raw material to be used, the kind of polymerization initiator, or the like.

The above-described core-shell binder may be applied as long as it is inside the electrochemical device, regardless of its use, location of introduction, and the like, and an empty space inside an electrochemical device such as an electrode, a separator, a device case, or other devices. It may be used as a constituent such as or as a coating component thereof.

When manufacturing an electrochemical device containing a binder having a core-shell structure, four embodiments may be large, but the present invention is not limited thereto.

According to the present invention, a first embodiment of an electrochemical device containing a binder having a core-shell structure is to use a binder having a core-shell structure as one component of an electrode and / or a coating component of a previously manufactured electrode. The method for preparing an electrode including a core-shell binder as a constituent of the electrode is not particularly limited, but a preferred embodiment thereof includes (a) a core-shell binder is used as an electrode material, such as an electrode active material, Preparing an electrode slurry by mixing with a conductive agent, if necessary, and then applying it onto a current collector or coating the prepared electrode surface; And (b) may comprise the step of drying the electrode.

Hereinafter, an example of a method for dispersing the core-shell binder in an electrode will be described in detail.

First, 1) a binder solution is prepared by stirring a core-shell binder in a solvent or a dispersion medium (eg, NMP (N-methyl pyrroridone) at low speed).

In this case, the binder is appropriately added in 0.5 to 50 parts by weight (weight ratio) based on 100 parts by weight of the solvent or dispersion medium, but is not limited thereto. In addition, the solvent or dispersion medium used to prepare the binder solution may be any conventional solvent used in the art, including, but not limited to, N-methylpyrrolidone, acetone, dimethylacetamide, or Organic solvents such as dimethylformaldehyde, inorganic solvents such as water, and mixtures thereof. The amount of the solvent may be sufficient to dissolve and disperse the active material, the conductive agent, the electrode binder, and the adhesion enhancing additive in consideration of the coating thickness of the electrode slurry and the production yield. The solvents are removed by drying after coating the electrode slurry on a current collector.

2) The preparation of the electrode is completed by injecting and mixing the electrode active material into the prepared binder solution, completely dispersing it, and then applying it to a current collector and drying it.

In this way, the electrode active material and the conductive agent are added together to the binder solution containing the binder of the core-shell structure to prepare a slurry for the electrode in the mixer. The electrode drying process may also be carried out according to conventional methods known in the art, and one example may be hot air drying.

The positive electrode active material may be a conventional positive electrode active material that can be used for the positive electrode of the conventional electrochemical device, non-limiting examples thereof LiM _x O _y (M = Co, Ni, Mn, Co _a Ni _b Mn _c ) and Lithium transition metal composite oxides (for example, 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, cobalt of these oxides Substituted with other transition metals or the like or vanadium oxide containing lithium) or chalcogen compounds (for example, manganese dioxide, titanium disulfide, molybdenum disulfide, etc.). 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, 0 <Z <2), LiCoPO ₄ , LiFePO _4, or a mixture thereof is mentioned. More preferably, it is a lithium transition metal composite oxide represented by the following formula (1).

Li _x MO ₂

Wherein M is Ni, Co, or Mn, and x is 0.05 ≦ x ≦ 1.10.

The negative electrode active material may be a conventional negative electrode active material that can be used for the negative electrode of the conventional electrochemical device, non-limiting examples of lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, Lithium adsorbents such as graphite, silicon or other carbons. Non-limiting examples of anode current collectors include foils made by aluminum, nickel, or combinations thereof, and non-limiting examples of cathode current collectors include copper, gold, nickel, or copper alloys, or combinations thereof. By foil.

The conductive agent is not particularly limited as long as it can improve conductivity, and non-limiting examples thereof include acetylene black or graphite.

The weight ratio of the components constituting the electrode of the present invention is not particularly limited, but (a) 80 to 99 parts by weight, preferably 90 to 96 parts by weight of the positive electrode active material or the negative electrode active material; (b) 1 to 15 parts by weight, preferably 1 to 7 parts by weight of the binder of the core-shell structure, and 0.1 to 10 parts by weight of the conductive agent, preferably 1 to 5 parts by weight, for the purpose of increasing the conductivity of the electrode. It may further comprise.

A method of preparing an electrode using the core-shell binder as a coating component of the electrode may also be prepared according to a conventional method known in the art, and for example, a dispersion medium or a solvent may be a core-shell structure. The binder may be dispersed to prepare a binder-containing dispersion liquid having a core-shell structure, and then coated and dried on the prepared electrode surface.

In this case, the coating process may use a general coating method commonly used in the art, for example, solvent evaporation, co-precipitation, precipitation, sol-gel method, post-adsorption filter method, and the like.

As described above, when a binder having a core-shell structure is used as one component of an electrode or a coating component of the electrode, it is usually used as a binder, for example, between the particles of the electrode active material and / or between the electrode active material and the current collector, When the bonding and fixing function is performed and rises above a certain temperature to reach the glass transition temperature or the melting point of the polymer shell, the space between the electrode active material particles in the electrode is partially expanded through the volume expansion of the shell. Subsequently, when the temperature rises, a volume expansion of several times to several tens of times occurs due to gas phase change of the core such as vaporization, sublimation, or thermal decomposition of the core, and the expanded binder pushes the conductive agent and the active material with the expanding force. The flow path of the current formed by the contact between the conductive agent and the electrode active material disappears, thereby greatly increasing the resistance. Therefore, even if an internal short circuit occurs due to the contact of the positive electrode at the edge part due to the shrinkage of the separator due to the rise in temperature, the electrode is expressed by expressing the PTC (positive temperature coefficient) characteristic through the instantaneous increase in the interval between the electrode active material particles in the electrode. It is possible to suppress the increase of the resistance and thereby the rapid high current flow. In addition, due to the large amount of inert gas emitted from the core, it is possible to block oxygen contact in the device, thereby achieving a fundamental safety improvement effect.

According to the present invention, a second embodiment of an electrochemical device containing a core-shell structured binder is used as one component of a battery separator or as a coating component of a conventional battery separator. For example, as known in the art, the polyolefin-based separator substrate may be completed by impregnating a binder-containing coating liquid having a core-shell structure or coating and drying according to a conventional coating method.

In this case, the separator into which the core-shell structure binder may be introduced is not particularly limited as long as it is a porous material that blocks internal short circuits of both electrodes and impregnates the electrolyte, and non-limiting examples thereof include polypropylene. Type, polyethylene, polyolephine-based porous separator or a composite porous separator in which an inorganic material is added to the porous separator.

According to the present invention, a third embodiment of an electrochemical device containing a binder having a core-shell structure is used as a coating component such as a conventional battery case, for example, a can or a pouch. The can can be impregnated into a binder-containing coating liquid of core-shell structure or coated and dried according to a conventional method.

At this time, the shape and components of the battery case in which the core-shell structure binder can be introduced are not particularly limited and may be cylindrical, square, pouch or coin type using cans. In addition, the binder-containing coating liquid of the core-shell structure may be prepared by, for example, dissolving or dispersing the core-shell binder in NMP or water and fixing or changing the temperature, and then dispersing the can using an appropriate tool. It can be completed by applying to the inner wall of the pouch or to the inner surface of the pouch, and then evaporating the solvent or dispersion medium while raising the temperature.

In addition, another embodiment in which the above-described core-shell binder is introduced into an internal empty space of an electrochemical device such as a core and a center pin is possible, and at this time, the same safety effect can be achieved.

According to the present invention, an electrochemical device having a core-shell binder includes (a) first safety means for stopping charging of the device or switching the charging state to a discharge state by detecting a pressure change inside the device, ( b) a second safety means for dissipating heat or gas inside the device by detecting a pressure change inside the device, or both the first safety means and the second means.

Non-limiting examples of first safety means that can be used include pressure sensitive elements such as conventional CIDs known in the art. The pressure sensitive element may be integral, or (i) a pressure sensitive element; (Ii) conducting wires carrying current delivered from said pressure sensitive element; And (iii) a member for stopping charging of the device or switching the charging state to the discharge state in response to the current transmitted through the conductive wire.

At this time, the pressure sensitive element detects the pressure change in the sealed element, that is, the pressure rise, and blocks the current by itself, or generates a current toward the external or control circuit so that the charging of the electrochemical device does not proceed any further. However, it refers to an element that deforms its shape due to pressure and blocks the movement of current, and may be an integral type including both a safety element function and a pressure sensitive element. Also, as described above, the pressure sensitive element and the safety element May be present separately. However, the type or manner thereof is not particularly limited as long as the above operation is performed in a specific pressure range.

Examples of the pressure sensitive element include a crystal having piezoelectricity that senses a pressure change and generates a current. In addition, the pressure range in which the pressure sensitive element operates is not particularly limited so long as it is outside the internal pressure of the conventional element and a range in which no explosion occurs.

Further, the second safety means is not particularly limited as long as it functions to dissipate heat or gas inside the device by detecting a pressure change inside the device, and a non-limiting example thereof may include a pressure release valve such as a vent. .

Electrochemical device equipped with such safety means is the first safety by detecting a change in the internal pressure of the device increased by the gas from the core of the binder contained in the device in the temperature (T) range above the normal operating temperature of the device The means, the second safety means, or the first safety means and the second safety means can be operated early to improve safety.

The electrochemical device of the present invention includes all devices that undergo an electrochemical reaction, and specific examples thereof include all kinds of primary, secondary cells, fuel cells, solar cells, or capacitors. In particular, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery among the secondary batteries is preferable.

The electrochemical device may be manufactured according to a conventional method known in the art, for example, may be manufactured by injecting an electrolyte after assembling a separator between the positive electrode and the negative electrode. In this case, at least one of the electrode, the separator, the case, and the internal space of the device may include a core-shell binder introduced therein.

The battery electrolyte includes conventional electrolyte components known in the art, such as electrolyte salts and organic solvents.

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 ^- is a salt containing an anion ion or a combination thereof, such as. In particular, a lithium salt is preferable.

As the electrolyte solvent, an organic solvent for a battery commonly used in the art, such as cyclic carbonate and / or linear carbonate, may be used. Non-limiting examples thereof include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, die Methoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethylcarbonate (EMC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formic acid , Methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate, butyl propionate or mixtures thereof. Moreover, the halogen derivative of the said organic solvent can be used, and it can also be used for the battery using water.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the following examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

[ Example  1 to 3]

Example  One

(Cathode production)

Carbon powder, PVDF binder, and conductive agent were mixed in a weight ratio of 92: 4: 4, and then dispersed in NMP to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was uniformly coated with a comma gap of 200 μm on a cross section of a Cu foil having a thickness of 10 μm using a negative electrode current collector, and the coating was dried. At this time, the coating speed was 3 m / min.

(Anode manufacturing)

92 parts by weight of lithium cobalt composite oxide, 4 parts by weight of carbon as a conductive agent, and 4 parts by weight of a core-shell acrylate-based binder containing an OBSH-based hydride (containing at 120 to 160 ° C) as a core component NMP as a solvent To a positive electrode mixture slurry was prepared. The positive electrode mixture slurry was applied to an Al thin film of a positive electrode current collector having a thickness of 20 μm. The coating was dried in the same manner as the negative electrode.

(Battery manufacturing)

As a separator, a porous polyethylene film was used, and a jelly roll was manufactured by laminating the strip-shaped cathode and the strip-shaped anode and winding it several times. The length and width were adjusted so that it was properly embedded in a battery can having an outer diameter of 18 mm and a height of 65 mm. The manufactured jelly roll was accommodated in the battery can, and the insulating plates were disposed on both upper and lower surfaces of the electrode element. Thereafter, a negative electrode lead made of nickel was drawn from the current collector and welded to the battery can, and 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 to manufacture a battery. An electrolyte solution was injected into this battery. LiPF ₆ was used as a solvent and an electrolyte in which EC and EMC were mixed in a volume ratio of 1: 2 as an electrolyte.

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

Example  2

A lithium secondary battery was prepared in the same manner as in Example 1, except that 4 parts by weight of a core-shell binder was added instead of PVDF when preparing a negative electrode slurry.

Example  3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 4 parts by weight of a core-shell binder was used to prepare a cathode and an anode slurry.

Comparative example  One

A lithium secondary battery was manufactured in the same manner as in Example 1, except that PVDF-based binders were used as both the positive electrode and the negative electrode slurry binders.

Experimental Example  1. Battery safety evaluation

In order to evaluate the safety of the secondary battery manufactured in the present invention, the following nail penetraion test was performed.

Nail penetration test is a test that observes whether the battery is ignited and exploded after generating a short circuit artificially sticking to the anode and cathode by penetrating the battery at a certain speed using a pointed object.

As a result, it was confirmed that the battery of Comparative Example 1, which used PVDF-based binder as both positive and negative electrode slurry binders, caused ignition and explosion of the battery due to intentional internal short circuit (see Table 1).

On the other hand, the batteries of Examples 1 to 3 using core-shell binders each containing a material that changes phase into a gas at a predetermined temperature or more as a core when preparing a positive electrode and / or negative electrode slurry are intentionally short-circuited. Even if the battery ignition and explosion phenomena were hardly observed (see Table 1). In addition, in the case of the lithium secondary battery manufactured according to the present invention, it was found that the gas was discharged to the outside after the nail test, and a PTC (positive temperature coefficient) effect through the instantaneous increase between the electrode active material particles in the electrode even after an internal short circuit occurred. The increase in resistance and rapid high current flow of the electrode were effectively suppressed and confirmed by the expression (see FIGS. 3 and 4).

In the present invention, the electrode acts as a binder by the polymer shell at the normal operating temperature of the device and increases the resistance of the electrode through the volume expansion by the gas ejection pressure generated from the vaporization of the core material when the temperature rises to an abnormally high temperature, oxygen contact in the device By providing a new concept of core-shell structure binder in the device, which can facilitate the blocking and / or safety measures, it is possible to provide excellent safety even if the temperature inside the device is abnormally increased due to external or internal factors.

Claims (15)

(a) a core containing a substance in which part or all of the solid or liquid phase changes into a gas above a certain temperature; And (b) a polymer shell formed on the surface of the core A binder containing the composite particles of the core-shell structure comprising a. 2. The binder of claim 1 wherein the temperature at which the core phase changes to gas is a temperature T above the normal operating temperature range of the electrochemical device. 3. The binder according to claim 2, wherein the temperature (T) is in the range of 60 to 200 ° C. The binder as claimed in claim 1, wherein the gas is a gas other than oxygen and hydrogen. The binder of claim 1, wherein the gas is at least one selected from the group consisting of N ₂ , He, Ne, Ar, Kr, H ₂ O, Xe, CO ₂ , F _2, and Br ₂ . The method of claim 1, wherein the phase-changing substance from solid or liquid to gas is (a) a substance which becomes gaseous by vaporizing, subliming or pyrolyzing in a temperature range of a predetermined temperature or more, or a compound containing a substance which becomes gaseous. The binder is characterized by. The binder of claim 1, wherein the phase-changing material is a binder selected from the group consisting of azo (-N = N-)-based compounds, carbonate-based compounds, hydrazide-based compounds, and carbazide-based compounds. . The binder of claim 1, wherein the glass transition temperature (T _g ) or melting point (T _m ) of the polymer constituting the shell is greater than, equal to, or less than the gas phase change temperature (T _pc ) of the core material. The polymer according to claim 1, wherein the polymer is an acrylate monomer, a (meth) acrylic acid ester monomer, a vinyl monomer, a conjugated diene monomer, a nitrile group-containing compound, a (meth) acrylamide monomer, and an unsaturated monocarbide. A binder which is polymerized using at least one monomer selected from the group consisting of an acidic monomer. In an electrochemical device comprising an anode, a cathode, a separator, and an electrolyte, the electrochemical device is composed of at least one device element selected from the group consisting of an electrode, a separator, a device case, and a void inside the device, or a coating component thereof. An electrochemical device characterized by using the binder of any one of claims 1 to 9. 11. The method of claim 10, wherein the electrochemical device has a spacing between the electrode active material particles in the electrode through the volume expansion by the gas blowing pressure resulting from the vaporization of the core of the binder present in the electrode at a temperature higher than the operating temperature range of the device An electrochemical device characterized by being expanded. 11. The method of claim 10, wherein the electrochemical device is characterized in that the contact with oxygen is blocked due to a gas other than oxygen generated from the core of the binder contained in the device in the temperature (T) range above the normal operating temperature of the device Chemical element. 11. The device of claim 10, wherein the electrochemical device comprises: (a) first safety means for stopping charging of the device or switching the charging state to a discharge state by detecting a pressure change inside the device, (b) a pressure inside the device And an additional second safety means or both said first and second means for dissipating heat or gas inside the device through change detection. 15. The device of claim 13, wherein the electrochemical device has a first safety means through detecting internal pressure change inside the device increased by a gas generated from a core among binders included in the device in a temperature (T) range above a normal operating temperature of the device. Or a second safety means or both the first safety means and the second safety means are operated. The electrochemical device of claim 10, wherein the electrochemical device is a lithium secondary battery.

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