KR101288642B1 - Electrochemical device with high safety at high temperature and impact - Google Patents

Abstract

The present invention is a core (core) containing sodium acetate; And a shell made of a polymer coated on the surface of the core. The present invention also relates to an electrolyte, an electrode and a separator comprising the core-shell structured particles and / or sodium acetate. The present invention also relates to an electrochemical device using the core-shell structure and / or sodium acetate as one component of a device element constituting an electrochemical device or a coating component thereof.

Electrochemical device, secondary battery, electrode, separator, electrolyte, core-shell structure particles, sodium acetate

Description

ELECTROCHEMICAL DEVICE WITH HIGH SAFETY AT HIGH TEMPERATURE AND IMPACT

The present invention relates to particles of a core-shell structure containing sodium acetate in a core so as to provide excellent safety even when the internal temperature of the device is abnormally increased or externally impacted by external or internal factors, and the core-shell structure of the core-shell structure. The present invention relates to an electrochemical device having improved safety by using particles and / or sodium acetate itself as one component of a device element constituting an electrochemical device or a coating component thereof.

Recently, miniaturization and lighter weight of electronic equipment have been realized and use of portable electronic devices has become common, so researches on lithium secondary batteries having high energy density have been actively conducted.

The lithium secondary battery is manufactured by using a material capable of inserting and detaching lithium ions as a negative electrode and a positive electrode, and filling an organic or polymer electrolyte between the positive electrode and the negative electrode, and lithium ions can be inserted and removed from the positive electrode and the negative electrode. Electrical energy is generated by oxidation and reduction reactions.

However, such a lithium secondary battery has safety problems such as ignition and explosion caused by using a nonaqueous electrolyte, and such a problem becomes more serious as the capacity density of the battery increases. Specifically, when the battery is overcharged and the normal operating voltage is exceeded, the positive electrode emits excessive lithium, and the excess lithium generates dendrites on the negative electrode, so that both the positive electrode and the negative electrode are thermally unstable, and thus the electrolyte is released. Rapid exothermic reactions occur such as decomposition. Such exothermic reactions cause ignition and rupture of the battery due to thermal runaway, which is a problem for the safety of the battery.

According to the present invention, when an abnormal problem occurs due to external or internal factors and the temperature inside the device is abnormally high temperature, the core-shell structure collapses, and the material contained in the core is released to the outside of the shell and melted and / or solidified. It is an object to provide a core-shell structured particle that can impart thermal stability.

In addition, the present invention is to provide an element of the electrochemical device comprising the core-shell structure particles and / or sodium acetate and an electrochemical device having improved safety by having the element of such an electrochemical device.

The present invention is a core (core) containing sodium acetate; And

It provides a core-shell structured particles comprising a shell made of a polymer coated on the core surface.

The present invention provides an electrolyte, an electrode, and a separator containing the core-shell structured particles and / or sodium acetate.

In addition, the present invention provides an electrochemical device, preferably a secondary battery, using the core-shell structure and / or sodium acetate as one component of a device element constituting an electrochemical device or a coating component thereof.

Hereinafter, the present invention will be described in detail.

Since the core-shell structured particles according to the present invention contain sodium acetate in the core and the shell is made of a polymer that can be melted at an abnormally high temperature, the shell melts at an abnormally high temperature, thereby causing the core-shell structure to collapse. Sodium acetate can be released to the outside of the shell.

In general, sodium acetate is dissolved in a solvent and easily coagulates even in a small impact in the liquid state. When the sodium acetate is included in a dissolved state in the electrolyte, when the electrochemical device receives an external shock such as a nail or a crimp, solidification of the dissolved sodium acetate may occur to act as a resistance to prevent the movement of lithium ions.

In addition, sodium acetate, which is present in a solidified state in the electrolyte, may cause dissolution accompanied by an endothermic reaction when the temperature of the electrochemical device increases, thereby suppressing the temperature rise.

Therefore, in the present invention, by including sodium acetate having the above-described mechanism of action directly in the electrolyte, the electrode and / or the separator, it is possible to impart the safety of the electrochemical device in the event of external impact or abnormal high temperature phenomenon.

In addition, the present invention provides an electrolytic solution, an electrode and / or a separator by including particles of a core-shell structure in which the structure collapses at an abnormally high temperature so that sodium acetate having the above mechanism of action can be released to the outside of the shell. The sodium acetate released at high temperature can impart the safety of the electrochemical device.

In the core-shell structured particles according to the present invention, the core-shell structure collapses at a temperature higher than the normal operating temperature of a device using the core-shell structured particles, such as an electrochemical device. Can be released. That is, the shell melts at an abnormally high temperature, thereby causing the core-shell structure to collapse, and sodium acetate contained in the core may be released to the outside of the shell. Thus, the polymer constituting the shell may have a melting point (Tm) higher than the normal operating temperature of the device, such as an electrochemical device, using the particles of the core-shell structure, preferably has a melting point (Tm) of 70 Preference is given to polymers which are ˜200 ° C.

The polymer is polymerized using a common monomer component known in the art, for example, (meth) acrylate compound, (meth) acrylonitrile compound, (meth) acrylic acid compound, (meth) Polymers or copolymers polymerized using at least one monomer selected from the group consisting of acrylamide compounds, styrene compounds, vinylidene chloride, vinyl halide compounds, butadiene compounds, ethylene compounds, acetaldehyde and formaldehyde Can be. In this case, the monomer may be used by appropriately changing the type and content according to the properties and physical properties of each monomer.

Examples of the (meth) acrylate-based compound include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, and isobutyl (Meth) acrylate, n-hexyl (meth) acrylate, ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, stearyl ( Meta) acrylate, cyclohexyl (meth) acrylate, butylcyclohexyl (meth) acrylate, benzyl (meth) acrylate, phenylethyl (meth) acrylate, phenylpropyl (meth) acrylate, butanediol di (meth) Acrylate, ethylene glycol di (meth) acrylate, tripropylene glycol tri (meth) acrylate, pentaerythritol tri (meth) acrylate, and the like;

Examples of the (meth) acrylonitrile-based compound include (meth) acrylonitrile;

Examples of the (meth) acrylic acid compound include (meth) acrylic acid, maleic acid, fumaric acid, and the like;

Examples of the (meth) acrylamide compound include (meth) acrylamide, methacrylamide, and the like;

Examples of the styrene-based compound include styrene, α-methylstyrene, β-methylstyrene, p-nitrostyrene, ethylvinylbenzene, divinyl benzene, and the like;

Examples of butadiene compounds include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and the like;

Examples of the ethylene compound include, but are not limited to, ethylene, propylene, 1-butene, 1,1-dichloroethylene, fluoroethylene, 1,1-difluoroethylene, and the like.

In the core-shell structured particle according to the present invention, the sodium acetate may be in a solid state or a liquid state dissolved in a solvent. In this case, the solvent for dissolving the sodium acetate may be water, methyl alcohol, ethyl alcohol, isopropyl alcohol, etc., which can dissolve sodium acetate, but is not limited thereto.

In the core-shell structured particles according to the invention, the core: shell = 5 to 90% by weight: preferably 95 to 10% by weight. If the core is less than 5% by weight, the amount of sodium acetate contained in the core is small, so that the effect of improving the safety of the electrochemical device is insignificant. On the other hand, if the shell is less than 10% by weight, formation of the core-shell structure is difficult.

In addition, the particles of the core-shell structure are not particularly limited in size, but in view of the particle size of the core-shell structure and in consideration of the particle size of the material that can be used together, for example, electrode active material, binder, etc. The particle diameter is 40 to 6000 nm, preferably 100 to 5000 nm.

The core-shell structured particle according to the present invention comprises a first step of forming an inverse emulsion by mixing a polymer forming monomer, sodium acetate and water; And a second step of polymerizing the polymer forming monomer in the inverse emulsion.

In this case, the polymer forming monomer forming the sodium shell and the polymer shell may be prepared in an inverse emulsion of the first step by dissolving in water.

In the first step of forming the inverse emulsion, an inverse emulsion may be further included by including an emulsifier, an initiator for polymerization and / or a pH buffer.

In addition, in the first step, separate organic solvents may be used together. The organic solvent preferably has a hydrophobicity to form an emulsion, the break point is 60 ~ 150 ℃, preferably 60 ~ 120 ℃, more preferably 60 ~ 100 ℃ so that it can be easily removed after the polymerization is completed Can be used. Non-limiting examples of organic solvents include, but are not limited to, toluene, hexane, isooctane, benzene, chloroform, methylisobutyrate, and the like. In addition, these organic solvents can be used individually or in mixture of 2 or more types.

The emulsifiers may be used alone or in combination of two or more kinds of anionic emulsifiers, cationic emulsifiers, nonionic emulsifiers, or reactive emulsifiers copolymerizable with monomers for forming polymers. The amount of emulsifier to be used is determined by the particle size of the final emulsion to be obtained. When not using an organic solvent, 0.05 to 20 parts by weight may be used per 100 parts by weight of the monomer for polymer formation, and when an organic solvent is used, 0.05-20 weight part can be used with respect to 100 weight part of the sum total of the monomer for forming a polymer, and an organic solvent.

Examples of the polymerization initiator include, but are not limited to, an azo initiator, a peroxide initiator, and a redox-based initiator composed of a combination of redox compounds. As another method, UV polymerization, a radiation polymerization method, etc. can be utilized. The amount of the polymerization initiator used varies depending on the molecular weight of the desired polymer, but may be used in an amount of 0.01 to 1.0 parts by weight based on 100 parts by weight of the monomer for polymer formation.

In addition, the pH adjusting buffer may be used a conventional buffer commonly used in the art, such as phosphate-based, carbonate-based, the amount may be used 0.01 to 1.0 parts by weight based on 100 parts by weight of water.

After the second step, a third step of removing water may be further included. When using the organic solvent together in the first step, it may include a third step of removing the organic solvent and water. At this time, the water and the organic solvent can be removed using their boiling point. Examples of the removal method may include, but are not limited to, steam stripping, vacuum distillation, and the like, and may employ process techniques well known in the art.

Electrolytic solution according to the present invention, i) a solvent; ii) electrolyte salts; And

iii) a core containing sodium acetate; And particles of the core-shell structure according to the present invention and / or sodium acetate comprising a shell made of a polymer coated on the core surface.

The solvent is not particularly limited as long as it is usually used as a solvent for an electrolyte solution, preferably a nonaqueous solvent, and cyclic carbonate, linear carbonate, lactone, ether, ester, ketone, or water can be used.

Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of the linear carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC) (DPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC). Examples of the lactone include gamma butyrolactone (GBL), and examples of the ether include dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, and the like. There is this. Examples of the esters include n-methyl acetate, n-ethyl acetate, methyl propionate, methyl pivalate and the like, and the ketone includes polymethyl vinyl ketone. These solvents may be used alone or in combination of two or more.

As for the electrolyte salt contained in electrolyte solution, lithium salt is preferable. Non-limiting examples of lithium salts include LiPF ₆ , LiBF ₄ , LiCl, LiBr, LiI, LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiC (CF ₂ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ), where x and y are natural numbers, LiSO ₃ CF ₃ and the like. These lithium salts can be used individually or in mixture of 2 or more types. In addition, the electrolyte salt may be used in a concentration of 0.8 ~ 2.0 M with respect to the solvent.

In the electrolyte solution of the present invention, the core-shell structure particles and / or sodium acetate of iii) are preferably contained in an amount of 1 to 30% by weight, preferably 10 to 20% by weight in the total electrolyte. When the electrolyte contains less than 1% by weight of core-shell structured particles and / or sodium acetate, the effect of improving the high temperature safety and impact safety of the device due to sodium acetate at an abnormally high temperature of the electrochemical device is minimal, while exceeding 30% by weight. If included, the characteristics of the electrochemical device is lowered, which is not preferable.

Electrode according to the present invention, i) an electrode active material; ii) a current collector; And

iii) a core containing sodium acetate; And particles of the core-shell structure according to the present invention and / or sodium acetate, including a shell made of a polymer coated on the core surface, and may optionally include a binder. The electrode includes an anode and a cathode.

The electrode active material includes a cathode active material and a cathode active material.

The positive electrode active material is an active material capable of inserting and detaching electric charges such as lithium ions, and is not particularly limited as long as it is used as a positive electrode active material for an electrochemical device, preferably a secondary battery, and a lithium transition metal oxide or a chalcogen compound can be used. .

Examples of the lithium transition metal oxide include 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 (where 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 part of manganese, nickel, cobalt of these oxides substituted with another transition metal or the like, or vanadium oxide containing lithium (LiV ₃ O ₈ ). Examples of the chalcogen compound include manganese dioxide, titanium disulfide, molybdenum disulfide, and the like. And these positive electrode active materials can be used individually or in mixture of 2 or more types.

As the negative electrode active material, a carbon material, a lithium metal, or an alloy thereof, which can absorb and release charges such as lithium ions, may be used. Other TiO ₂ and SnO which may occlude and release lithium, and have a potential for lithium less than 2V. Metal oxides such as ₂ may be used. In particular, carbon materials, such as graphite, are preferable.

The current collector is a highly conductive metal, and is a metal to which an electrode active material and a binder can easily adhere, and any current collector can be used as long as it is not reactive in the voltage range of the battery. Representative examples include a mesh, a foil, and the like manufactured by aluminum, copper, gold, nickel or aluminum alloy or a combination thereof.

In the electrode of the present invention, the core-shell structure of the iii) and / or sodium acetate is preferably contained in a ratio of 0.1 to 10 parts by weight, preferably 2 to 5 parts by weight with respect to 100 parts by weight of the electrode active material. When the core-shell structure particles and / or sodium acetate are contained in the electrode at less than 0.1 part by weight relative to 100 parts by weight of the electrode active material, the effect of improving the high temperature safety and impact safety of the device due to sodium acetate at an abnormal high temperature of the electrochemical device is minimal. On the other hand, if it is included in excess of 10 parts by weight, the amount of the electrode active material is relatively small, the reversible capacity may be reduced and the performance of the electrode may be reduced.

The electrode of the present invention can be prepared by conventional methods known in the art. For example, an electrode active material; menstruum; Core-shell structured particles and / or sodium acetate according to the invention; If necessary, a binder, a conductive material, and a dispersant may be mixed and stirred to prepare a slurry for an electrode, and then applied to a current collector of a metal material, compressed, and dried to prepare an electrode.

The binder may be suitably used in an amount of 1 to 10 by weight and the conductive material in an amount of 1 to 30 by weight based on the electrode active material.

The binder performs the adhesive function of connecting and fixing the particles between the electrode active material particles and / or between the electrode active material and the current collector, and is not particularly limited as long as it is usually used as a binder for an electrochemical device, preferably a secondary battery. Do not. Non-limiting examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and the like.

The conductive material included in the slurry for the electrode as needed is not particularly limited as long as it is an electronic conductive material that does not cause chemical change in the operating voltage of the configured electrochemical device electrode. In general, carbon black may be used, and products currently marketed as conductive materials include acetylene black (Chevron Chemical Company or Gulf Oil Company), Ketzen Ketjen Black EC series (Armak Company), Vulcan XC-72 (Cabot Company) and Carbon Super-P (MMM) There is this.

Examples of the solvent include organic solvents such as NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, and dimethylacetamide, and water. These solvents may be used alone or as a mixture of two or more thereof . The amount of the solvent used is sufficient to dissolve and disperse the electrode active material, the binder and the conductive material in consideration of the coating thickness of the slurry and the production yield.

The method of applying the slurry for the electrode to the current collector is also not particularly limited. For example, it can be applied by a method such as doctor blade, dipping, brushing, etc., and the coating amount is not particularly limited, but the thickness of the active material layer formed after removing the solvent or the dispersion medium is usually 0.005-5 mm, preferably 0.05-2 The amount of the range which becomes a mm range is preferable.

The method of removing the solvent or the dispersion medium is not particularly limited, but the solvent or the dispersion medium may be used as quickly as possible within the speed range in which stress concentration occurs and cracks occur in the active material layer or the active material layer does not peel off from the current collector. It is preferable to use a method of adjusting to remove to volatilize. As a non-limiting example it may be dried for 0.5 to 3 days in a vacuum oven at 50 ~ 200 ℃.

The separator according to the present invention comprises a core containing sodium acetate; And particles of the core-shell structure according to the invention and / or sodium acetate comprising a shell made of a polymer coated on the surface of the core, preferably a separator for an electrochemical device, more preferably It is a separator for secondary batteries.

Specifically, the separator according to the present invention uses the core-shell structured particles and / or sodium acetate according to the present invention as one component of the separator or as a coating component of a conventional separator. For example, a polyolefin-based separator may be impregnated with a core-shell structured particle and / or sodium acetate-containing coating solution or coated according to a conventional coating method, as known in the art, followed by hot air or infrared drying. It can be completed by drying in a method.

The coating solution may be prepared by dissolving or dispersing a core of a core-shell structure or sodium acetate in a solvent, such as a non-limiting example of acetone, and stirring by raising the temperature or applying heat.

In this case, the separator in which the core-shell structure and / or sodium acetate may be introduced is not particularly limited as long as it is a porous material that blocks internal short circuits of the positive and negative electrodes and impregnates the electrolyte solution. Polypropylene-based, polyethylene-based, polyolefin-based porous separators or composite porous separators in which inorganic materials are added to the porous separators.

The core-shell structured particles and / or sodium acetate according to the invention can be used as coating components in conventional device cases, preferably battery cases, such as cans or pouches. For example, the battery can can be impregnated with the core-shell structured particles and / or the sodium acetate-containing coating solution or coated and dried according to a conventional method.

At this time, the shape and composition of the device case to which the core-shell structure and / or sodium acetate can be introduced is not particularly limited, and can be cylindrical, square, pouch or coin type using a can Can be. In addition, the core-shell structured particles and / or sodium acetate-containing coating solution may be prepared by, for example, dissolving or dispersing the core-shell structured particles and sodium acetate in NMP or water and fixing or changing the temperature thereafter. The dispersion may be completed by applying an appropriate tool to the inner wall of the can or the inner side of the pouch and then evaporating the solvent or dispersion medium with increasing temperature.

In addition, the present invention is an electrochemical device comprising an anode, a cathode, a separator and an electrolyte,

The at least one device element selected from the group consisting of the positive electrode, the negative electrode, the separator, the electrolyte solution, and the device case may be a particle having a core-shell structure and / or sodium acetate according to the present invention as its component or its coating component. It provides an electrochemical device characterized in.

The electrochemical device of the present invention includes all devices that undergo an electrochemical reaction, and specific examples thereof include all kinds of primary cells, secondary batteries, fuel cells, solar cells, or capacitors. Particularly, 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 above 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 the separator between the positive electrode and the negative electrode. In this case, at least one of the electrode, the separator, and the device case may include particles of the aforementioned core-shell structure and / or sodium acetate.

Hereinafter, the present invention will be described in detail with reference to examples. However, the following examples are only for exemplifying the present invention, and the present invention is not limited by the following examples.

Example 1 Preparation of Particles with a Core-Shell Structure

A solution in which 100 parts by weight of acrylamide and 50 parts by weight of sodium acetate were mixed with 100 parts by weight of water was prepared.

0.5 parts by weight of sodium lauryl sulfate and 100 parts by weight of toluene were added to the solution and mixed. This mixed solution was mixed for 2 minutes at 13000 rpm using Ika Lab. Ultra Turrax T50 to make a crude emulsion.

Next, the inverse miniemulsion was prepared by repeating and homogenizing three times at 5,000 psi using a microfluidizer from Microfluidics.

The inverse miniemulsion thus prepared was placed in a reactor and sealed, and then depressurized while stirring to remove air containing oxygen included in the reaction system, and nitrogen was again adjusted to normal pressure. This process was repeated three times to replace the air of the reaction system with nitrogen, and then, 5 parts by weight of an aqueous solution containing 0.5 parts by weight of ammonium persulfate dissolved at room temperature at a time, and the polymerization reaction was performed for 5 hours by adjusting the temperature of the reaction system to 40 degrees Celsius. Proceeding to prepare a core-shell structured particles.

After the prepared core-shell structured particles were separated, water and toluene inside the prepared particles were removed by heating under reduced pressure, thereby finally preparing core-shell structured particles.

Example 2 Preparation of Electrolytic Solution

Ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: LiPF ₆ was dissolved in a non-aqueous solvent having a composition of 2 (v: v) to a concentration of 1M to prepare a mixed solution, 95% by weight and the mixed solution 5 wt% of the particles of the core-shell structure prepared in Example 1 were mixed to prepare an electrolyte solution.

Example 3 Preparation of Electrolytic Solution

An electrolyte solution was prepared in the same manner as in Example 2, except that 5% by weight of sodium acetate was used instead of 5% by weight of the core-shell structured particle prepared in Example 1.

Example 4 Preparation of Electrolytic Solution

Same as Example 2, except that 2.5% by weight of the core-shell structure prepared in Example 1 and 2.5% by weight of sodium acetate were used instead of 5% by weight of the particle of the core-shell structure prepared in Example 1. An electrolytic solution was prepared by the method.

Example 5 Preparation of Positive Electrode

92% by weight of LiCoO ₂ as a positive electrode active material, 4% by weight of acetylene black as a conductive material, and 4% by weight of particles of the core-shell structure prepared in Example 1 were mixed and mixed with NMP as a solvent to prepare a slurry for the positive electrode. It was. The positive electrode slurry was uniformly coated with a comma gap of 200 μm on an Al thin film having a thickness of 20 μm, coated, and dried to prepare a positive electrode. At this time, the coating speed (coating speed) was 3m / min.

Example 6 Preparation of Anode

94% by weight of graphite as a negative electrode active material, 2% by weight of acetylene black as a conductive material, 4% by weight of particles of the core-shell structure prepared in Example 1 were mixed, and NMP was added as a solvent to prepare a slurry for the negative electrode. In addition, the negative electrode slurry was uniformly coated with a comma gap of 200 μm on a Cu thin film having a thickness of 10 μm, coated, and dried to prepare a negative electrode. At this time, the coating speed (coating speed) was 3m / min.

Example 7 Preparation of Separator

After preparing a slurry coating solution by adding solvent NMP to the core-shell structured particles prepared in Example 1, it was uniformly coated on a porous polyethylene film, coated, and dried to prepare a separator.

Example 8 Fabrication of Battery

94% by weight of LiCoO ₂ as a positive electrode active material, 3% by weight of acetylene black as a conductive material and 3% by weight of PVDF as a binder were mixed and added to NMP (N-methyl-2-pyrrolidone) to prepare a positive electrode slurry. Al) was applied and dried on the current collector to prepare a positive electrode.

95% by weight of artificial graphite and 2% by weight of acetylene black were used as the negative electrode active material, and 3% by weight of PVDF as a binder was added to NMP to prepare a negative electrode slurry, which was then coated on a copper (Cu) current collector. And dried to prepare a negative electrode.

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. Then, the negative electrode lead made of nickel was drawn from the current collector and welded to the battery can. The positive electrode lead made of aluminum was drawn from the positive electrode current collector, and welded to the aluminum pressure release valve mounted on the battery cover. The battery was prepared by injecting an electrolyte solution prepared in.

Example 9 Fabrication of Battery

A battery was manufactured in the same manner as in Example 8, except that the electrolyte prepared in Example 3 was used as the electrolyte.

Example 10 Fabrication of Battery

A battery was manufactured in the same manner as in Example 8, except that the electrolyte prepared in Example 4 was used as the electrolyte.

Example 11 Fabrication of Battery

The electrolyte was prepared by dissolving LiPF ₆ in a non-aqueous solvent having a composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: 2 (v: v) to a concentration of 1 M, and the positive electrode was used in Example 5 Except for using the prepared positive electrode, a battery was prepared in the same manner as in Example 8.

Example 12 Preparation of Battery

The electrolyte was prepared by dissolving LiPF ₆ in a non-aqueous solvent having a composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: 2 (v: v) to a concentration of 1 M, and the negative electrode was Example 6 A battery was manufactured in the same manner as in Example 8, except that the anode prepared in US was used.

Example 13 Fabrication of Battery

The electrolyte was prepared by dissolving LiPF ₆ to 1 M in a nonaqueous solvent having an composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: 2 (v: v), and the separator was used in Example 7. A battery was manufactured in the same manner as in Example 8, except that the prepared separator was used.

Example 14 Preparation of Battery

The electrolyte was prepared by dissolving LiPF ₆ in a non-aqueous solvent having a composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: 2 (v: v) to a concentration of 1 M, and the positive electrode was used in Example 5 A prepared positive electrode was used, and a negative electrode was manufactured in the same manner as in Example 8 except for using the negative electrode prepared in Example 6.

Example 15 Preparation of Battery

The positive electrode was used in the positive electrode prepared in Example 5, the negative electrode was used in the same manner as in Example 8 except for using the negative electrode prepared in Example 6.

Example 16 Preparation of Battery

The positive electrode was used in the positive electrode prepared in Example 5, the negative electrode was used in the negative electrode prepared in Example 6, the separator was the same as in Example 8, except that the separator prepared in Example 7 The battery was prepared.

(Comparative Example 1)

An electrolyte solution was prepared by dissolving LiPF ₆ in a non-aqueous solvent having a composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: 2 (v: v) to a concentration of 1 M, Example 8 In the same manner as the battery was prepared.

Experiment 1: Battery Safety Evaluation

Using the batteries prepared in Examples 8 to 16 and Comparative Example 1, the thermocouple was attached to the battery while evaluating safety by performing nail test that penetrates the battery with nails at a rate of 1 m / min after charging to 4.3V. The temperature rise of the battery was confirmed. The results of each nail test and the maximum rise temperature (only one Paas battery can be measured) of the battery during the test are shown in Table 1 below. In Table 1 below, Pass indicates that there is no ignition and explosion, and Pass / test indicates the number of cells passed / tested.

Experiment Nail test result
(Pass / test) Battery maximum temperature
(Paas one battery) Example 8 2/5 82 ° C Example 9 3/5 78 ℃ Example 10 3/5 80 ℃ Example 11 2/5 88 ℃ Example 12 2/5 86 ℃ Example 13 3/5 84 ℃ Example 14 3/5 78 ℃ Example 15 4/5 75 ℃ Example 16 5/5 72 ℃ Comparative Example 1 0/5 (all fired-fail) Not measurable

In the nail test, the nail penetrates into the cell, tears the separator, shorts the positive and negative electrodes, and when a large amount of current flows, the temperature rises momentarily, causing severe fire or explosion. According to Table 1, the battery prepared in Examples 8 to 16 was reduced in the frequency of ignition and explosion compared to the battery prepared in Comparative Example 1, the maximum temperature of the battery is 72 ~ 88 ℃ normal operation of the battery The temperature rise above the temperature was suppressed. Therefore, the battery according to the present invention was found to improve safety.

Experiment 2: Battery Performance Evaluation

Rate characteristics and cycle characteristics were confirmed to evaluate the performance of the batteries prepared in Examples 8 to 16 and Comparative Example 1, and the results are shown in Table 2 below. Battery 1C capacity was based on 2200mAh.

C-rate characteristics were measured by cycling at a discharge rate of 0.2C, 1.0C, which is shown in Table 2 below.

Cycle characteristics measured the efficiency for the initial capacity after 300 cycles after repeated charge and discharge at 1C, which is shown in Table 2 below.

Experiment 0.2C
(mAh) 1.0C
(mAh) Cycle
(300 cycle,%) Example 8 2240 2213 82% Example 9 2212 2187 75% Example 10 2218 2193 78% Example 11 2196 2188 76% Example 12 2218 2190 77% Example 13 2240 2210 80% Example 14 2174 2154 72% Example 15 2172 2150 70% Example 16 2170 2148 69% Comparative Example 1 2240 2214 82%

According to Table 2, the battery prepared in Examples 8 to 16 was the same or somewhat reduced in the C-rate characteristics and cycle characteristics compared to the battery prepared in Comparative Example 1, but showed a value of the effective range. Therefore, it was found that the battery according to the present invention can improve safety without a large decrease in performance.

Since the core-shell structured particles according to the present invention contain sodium acetate in the core and the shell is made of a polymer that can be melted at a high temperature, the shell melts at an abnormal high temperature, thereby causing the core-shell structure to collapse and sodium acetate. It can be released to the outside of the shell. Electrolyte, electrode, and separator containing particles of core-shell structure and / or sodium acetate according to the present invention are one component of an electrochemical device, and the electrochemical device including them may contain the acetic acid in the event of external impact or abnormal high temperature phenomenon. An increase in electrical resistance due to coagulation / melting of sodium / heat absorption due to an endothermic reaction may occur, thereby improving the safety of the electrochemical device.

Claims (19)

A core containing sodium acetate; And It comprises a shell (shell) made of a polymer coated on the core surface, Particles of the core-shell structure, characterized in that the average particle diameter is 40 ~ 6000nm. The core-shell structure of claim 1, wherein the core-shell structure is collapsed at a temperature higher than the normal operating temperature of the device using the particles of the core-shell structure to release the sodium acetate to the outside of the shell. Particles. The core-shell structured particle of claim 1, wherein the polymer has a melting point (Tm) higher than a normal operating temperature of a device using the core-shell structured particle. The core-shell structured particle according to claim 1, wherein the polymer has a melting point (Tm) of 70 to 200 ° C. The core-shell structured particle of claim 1, wherein the sodium acetate is in a solid state or a liquid state dissolved in a solvent. 6. The core-shell structured particle according to claim 5, wherein the solvent is at least one selected from the group consisting of water, methyl alcohol, ethyl alcohol and isopropyl alcohol. The method of claim 1, wherein the polymer is a (meth) acrylate compound, (meth) acrylonitrile compound, (meth) acrylic acid compound, (meth) acrylamide compound, styrene compound, vinylidene chloride, halogenated Particles of the core-shell structure, characterized in that the polymer or copolymer polymerized using at least one monomer selected from the group consisting of vinyl compounds, butadiene compounds, ethylene compounds, acetaldehyde and formaldehyde. The core-shell structured particle according to claim 1, wherein the core: shell = 5 to 90% by weight: 95 to 10% by weight. delete The method of claim 1, wherein the core-shell structured particle comprises: a first step of mixing an monomer for forming a polymer, sodium acetate, and water to form an inverse emulsion; And a second step of polymerizing the monomer for forming a polymer in the inverse emulsion. The core-shell structure according to claim 10, wherein the inverse emulsion of the first step is formed by using together at least one organic solvent selected from the group consisting of toluene, hexane, isooctane, benzene, chloroform and methylisobutyrate. Particles. The core-shell structured particle of claim 10, wherein the inverse emulsion of the first step further comprises an emulsifier and an initiator for polymerization. i) solvent; ii) electrolyte salts; And iii) An electrolyte solution comprising the core-shell structured particle of claim 1 or the core-shell structured particle of claim 1 and sodium acetate. The electrolyte according to claim 13, wherein iii) the core-shell structured particle of claim 1 or the core-shell structured particle of claim 1 and sodium acetate are included in an amount of 1 to 30% by weight in the total electrolyte. i) an electrode active material; ii) a current collector; And iii) An electrode comprising particles of the core-shell structure of claim 1 or particles of the core-shell structure of claim 1 and sodium acetate. The method according to claim 15, wherein iii) the core-shell structured particle of claim 1 or the core-shell structured particle of claim 1 and sodium acetate are included in an amount of 0.1 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. Electrode. The core-shell structure according to any one of claims 1 to 8 and 10 to 12, or the core-shell structure according to any one of claims 1 to 8 and 10 to 12. A separator comprising particles of sodium acetate. In the electrochemical device comprising a positive electrode, a negative electrode, a separator and an electrolyte solution, At least one device element selected from the group consisting of the anode, the cathode, the separator, the electrolyte, and the device case is any one of claims 1 to 8 and 10 to 12 as its constituents or coating components thereof. An electrochemical device characterized by using the core-shell structured particle of claim, or the core-shell structured particle and sodium acetate. The electrochemical device of claim 18, wherein the electrochemical device is a secondary battery.