KR20140133219A - Electrolyte composition having improved high temperature stability and performance comprising additive and electrochemical device comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte composition, which comprises (i) a solvent; (ii) a lithium salt; and (iiI) 0.1-5 weight% of a pullulan-based polymer resin based on the total weight of the electrolyte composition, wherein the pullulan-based polymer resin is a polymer, an oligomer or a mixture thereof containing at least one repeating unit represented by chemical formula 1. The electrolyte composition according to the present invention shows an excellent life time property at room temperature and a high temperature, suppresses gas generation due to the electrolyte decomposition at a high temperature, improves the stability of an electrochemical device, and, thus, can be usefully used in manufacturing an electrochemical device.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte composition having excellent high temperature stability and performance, and an electrochemical device including the same. BACKGROUND ART [0002]

TECHNICAL FIELD The present invention relates to an electrolyte composition having excellent high-temperature stability and performance, which is used in an electrochemical device field such as a lithium secondary battery, a capacitor, a solar cell, and an energy storage device. More particularly, The present invention relates to an electrolyte composition capable of improving the safety of an electrochemical device by suppressing the generation of gas due to decomposition of an electrolyte at a high temperature.

2. Description of the Related Art As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as an energy source. Many researches have been conducted on lithium secondary batteries having high energy density and high discharge voltage among such secondary batteries.

The lithium secondary battery may be classified into a lithium ion battery including an electrolyte solution as it is, a lithium ion polymer battery in which the electrolyte is contained in a gel-like form, and a lithium polymer battery as a solid electrolyte, depending on the type of electrolyte.

A lithium ion battery including a liquid electrolyte has a risk of electrolyte leakage when fabricated in the form of a pouch and has a risk of ignition / explosion when exposed under high temperature and / or high pressure conditions, Even if a large current flows in a short time due to overcharge, external short circuit, nail penetration, local crush, etc., there is a risk of ignition / explosion as the battery is heated by IR heat.

When the temperature of the battery rises, the reaction between the electrolyte and the electrode is promoted. As a result, a reaction heat is generated and the temperature of the battery rises, which accelerates the reaction between the electrolyte and the electrode again. As a result, the temperature of the battery rapidly rises, which again accelerates the reaction between the electrolyte and the electrode. Such a vicious circle causes a thermal runaway phenomenon in which the temperature of the battery rises sharply, and when the temperature rises to a certain level or higher, the battery may ignite. Further, as a result of the reaction between the electrolyte and the electrode, gas is generated and the internal pressure of the battery is increased, and the lithium secondary battery explodes at a certain pressure or higher. Such a risk of ignition / explosion is the most fatal disadvantage of the lithium secondary battery.

Accordingly, the amount of lithium ion polymer battery having an advantage such as low possibility of leakage of electrolyte and high safety, capability of reducing the shape of battery, and the like can be increased. However, a lithium ion polymer battery in which an electrolyte is contained in the form of a gel has a high viscosity of the electrolytic solution, which hinders the movement of lithium ions and lowers the mobility of lithium ions. And has a disadvantage in that the volume energy density is lower than that of the lithium ion battery, and the manufacturing process is relatively complicated and the manufacturing cost is high.

Accordingly, it has been required to develop an electrolyte composition capable of realizing excellent cell performance and safety by controlling generation of gas due to decomposition of an electrolyte at a high temperature while exhibiting excellent lifetime characteristics at room temperature and high temperature.

An object of the present invention is to provide an electrolyte composition which exhibits excellent lifespan characteristics at room temperature and high temperature and can improve the safety of an electrochemical device by suppressing generation of gas due to decomposition of an electrolyte at a high temperature.

It is still another object of the present invention to provide an electrochemical device comprising the electrolyte composition.

In order to achieve the above object,

(i) a solvent;

(ii) a lithium salt; And

(iii) from 0.1 to 5% by weight, based on the total weight of the electrolyte composition, of a pullulan-based polymer resin

Wherein the electrolyte composition comprises:

Wherein the pullulan-based polymer resin is a polymer, an oligomer, or a mixture thereof containing at least one repeating unit represented by the following formula (1): < EMI ID =

In Formula 1,

Each R is independently H or (CH ₂ ) ₁ CN,

and l is an integer of 1 to 10.

The present invention also provides an electrochemical device comprising the electrolyte composition.

The electrolyte composition according to the present invention exhibits excellent lifetime characteristics at room temperature and high temperature and can suppress the generation of gas due to decomposition of the electrolyte at a high temperature to improve the safety of the electrochemical device and thus can be usefully used in the production of electrochemical devices .

1 is a graph showing a discharge capacity of a battery according to a charge-discharge cycle.
2 is a graph showing a change in thickness of a battery in a high-temperature chamber of 80 ° C with time.

The electrolyte composition according to the present invention comprises (i) a solvent; (ii) a lithium salt; And (iii) 0.1 to 5 wt% of a pullulan polymer resin based on the total weight of the electrolyte composition, wherein the pullulan polymer resin comprises at least one repeating unit represented by the following formula (1) Wherein the polymer is an oligomer or a mixture thereof.

[Chemical Formula 1]

In Formula 1,

Each R is independently H or (CH ₂ ) ₁ CN,

and l is an integer of 1 to 10.

The pullulan-based polymer resin may have a weight average molecular weight of 1,000 to 10,000,000. The solvent is not particularly limited as long as it is an organic solvent used as a non-aqueous solvent of a conventional lithium secondary battery. Examples of the solvent include a carbonate compound, a lactone compound, an ether compound, a sulfolane compound, a dioxolane compound, a ketone compound, a nitrile compound, Compounds and the like. More specifically, it includes carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, ethylene glycol dimethyl carbonate, propylene glycol dimethyl carbonate, ethylene glycol diethyl carbonate, vinylene carbonate, lactones such as γ-butyrolactone, ethers such as dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and 1,4-dioxane, sulfolane and 3-methylsulfolane Dioxolanes such as 1,3-dioxolane, ketones such as 4-methyl-2-pentanone, nitriles such as acetonitrile, pyropionitrile, valeronitrile and benzonitrile, 1,2- Halogenated hydrocarbons such as dichloromethane, dichloroethane, and other methyl formates, dimethylformamide, diethylformamide, dimethylsulfoxide, imidazolium salts, quaternary ammonium salts It may be of the ionic liquid or the like. In addition, they may be mixed and used, and preferably, a cyclic carbonate and a linear carbonate may be mixed together and used.

LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₄ , LiBF ₄ , LiBF ₄ , ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower aliphatic carboxylate, lithium tetraphenylborate, have.

The cyano reactant of the pullulan-based polymer resin included in the electrolyte composition of the present invention assists the smooth transfer of lithium ions at the interface with the electrode, and the hydroxy (-OH) Is prevented from being denatured or gas is generated, so that excellent cell performance and safety can be achieved at the same time.

The pullulan-based polymer resin may be contained in an amount of 0.1 to 5% by weight based on the total weight of the electrolytic solution composition, 0.1 to 4% by weight, 0.1 to 3% by weight, 0.1 to 2.5% by weight, 0.2 to 5 wt%, 0.2 to 4 wt%, 0.2 to 3 wt%, 0.2 to 2.5 wt%, 0.2 to 2 wt%, 0.3 to 5 wt%, 0.3 to 4 wt%, 0.3 0.4 to 2 wt%, 0.4 to 5 wt%, 0.4 to 4 wt%, 0.4 to 3 wt%, 0.4 to 2.5 wt%, 0.4 to 2 wt%, 0.5 to 5 wt% 0.5 to 4 wt.%, 0.5 to 3 wt.%, 0.5 to 2.5 wt.%, 0.5 to 2 wt.%.

If the content of the pullulan-based polymer resin is less than 0.1% by weight, it is not preferable because it can not exhibit effects such as promotion of migration of lithium ions and prevention of degeneration of electrolytic solution, and the content of the pullulan-based polymer resin exceeds 5% The viscosity of the electrolytic solution becomes excessively high, and the ionic conductivity of the electrolytic solution drops rapidly, which is disadvantageous in that the output characteristics of the battery are deteriorated when the electrolytic solution is used in a battery.

In addition, the electrolyte composition of the present invention may have a lithium ion transference number of not less than 0.5, preferably not less than 0.6, more preferably not less than 0.7.

The reason why the electrolyte composition of the present invention has a high lithium ion transmission constant value is due to the interaction between the pullulan-based polymer resin contained in the electrolyte composition and lithium ions and anions. For example, when a lithium salt of the electrolyte composition comprising a LiPF _6, the pullulan-based polymer resin and an anion of PF ₆ ^- the higher the activation energy required for the movement to relatively strongly bonded to slow its movement, while the Li ⁺ is The degree of binding is relatively weak, so the activation energy required for migration is low and migration is rapid. This relative speed is represented by the high ion transport constant of lithium ions.

In addition, the electrolyte composition of the present invention may further include an electrolyte additive other than the pullulan-based polymer resin,

The electrolyte additive may be a polymer, an oligomer or a mixture thereof containing at least one repeating unit represented by the following general formula (2).

In Formula 2,

X, Y and Z are each independently H, OH or (CH ₂ ) _n CN,

R 'are each independently H or (CH _{2) o} CN,

M is an integer of 0 to 10, and n and o are each independently an integer of 1 to 10.

When the electrolyte additive is further included, the electrolyte composition of the present invention may cause a physical or chemical gelling reaction at 30 ° C or higher, preferably 30 to 80 ° C, more preferably 45 to 60 ° C.

Also, since the temperature is proportional to the function of time, even when the electrolyte composition further comprising the electrolyte additive is stabilized at a temperature lower than the temperature causing the gelation at 10 to 30 DEG C, preferably 15 to 25 DEG C for a long period of time, Can be induced.

The gelation refers to the change of the electrolyte composition from the liquid state to the gel state through the interaction between the electrolyte additive itself or the electrolyte additive and the solvent.

For example, when the electrolyte additive is a polymer, an oligomer, or a mixture thereof containing at least one of the repeating units represented by the formula 1, the electrolyte composition of the present invention may have a liquid state through the interaction between the electrolyte additive itself or the electrolyte additive and the solvent And the cyano (or nitrile) reactor of the electrolyte additive included in the gelled electrolyte composition may facilitate the lithium ion to move smoothly at the interface with the electrode, ) The reactor prevents the gel state from being destroyed or deformed by strong hydrogen bonding.

Therefore, the electrolyte composition of the present invention, which further comprises the electrolyte additive, can have a high ionic conductivity even after gelation even though it is in a gel state.

The electrolyte additive may be added in an amount of 0.01 to 15 wt%, 0.01 to 10 wt%, 0.1 to 15 wt%, 0.1 to 10 wt%, 0.1 to 5 wt%, and 0.1 to 4 wt% based on the total weight of the electrolytic solution composition. 0.2 to 4% by weight, 0.2 to 3% by weight, 0.2 to 2.5% by weight, 0.2 to 5% by weight, 0.1 to 3% by weight, 0.1 to 2.5% 0.3 to 5 wt%, 0.3 to 5 wt%, 0.3 to 4 wt%, 0.3 to 3 wt%, 0.3 to 2.5 wt%, 0.3 to 2 wt%, 0.4 to 10 wt%, 0.4 to 5 wt% 0.5 to 3 wt%, 0.4 to 4 wt%, 0.4 to 3 wt%, 0.4 to 2.5 wt%, 0.4 to 2 wt%, 0.5 to 10 wt%, 0.5 to 5 wt%, 0.5 to 4 wt% , 0.5 to 2.5 wt%, and 0.5 to 2 wt%.

The electrolyte composition of the present invention can be used in an electrochemical device including a positive electrode and a negative electrode. In the present invention, the electrochemical device includes all devices that perform an electrochemical reaction. For example, the electrochemical device may be any type of primary, secondary, fuel cell, solar cell, capacitor or energy storage device, A capacitor, or a solar cell, and preferably a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery.

In particular, in the case of a lithium secondary battery, the lithium secondary battery is manufactured by injecting the electrolyte composition of the present invention in a liquid state into an electrode structure composed of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The positive electrode, the negative electrode, and the separator forming the electrode structure may be any of those conventionally used for manufacturing a lithium secondary battery.

The positive electrode is prepared by applying a mixture of a positive electrode active material, a conductive material and a binder on a current collector, followed by drying. As the positive electrode active material, a lithium-containing transition metal oxide may be preferably used. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO ₂ ) A layered compound such as lithium nickel oxide (LiNiO ₂ ) or a compound substituted with at least one transition metal; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula LiNi _1-x MxO ₂ (Here, M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide represented by a; Formula _{LiMn 2 - x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like.

The conductive material is typically added in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material and is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. Examples of the conductive material include natural graphite, artificial graphite, black smoke; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the mixture including the cathode active material. Examples of the binder include polyvinylidene fluoride , Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene ter Polymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like can be used.

The negative electrode is manufactured by applying a negative electrode material on the negative electrode collector and drying the same, and if necessary, the above-described components may further be included.

The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery. Examples of the negative electrode current collector include carbon, nickel, titanium, and the like on the surface of copper, stainless steel, aluminum, nickel, titanium, , Silver or the like, an aluminum-cadmium alloy, or the like can be used.

Examples of the negative electrode material include carbon such as hard graphitized carbon and graphite carbon; Sn _x Me _1-x Me _'y O _z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, of the periodic table Group 1, Group 2, Group 3 element, halogens; 0 <x 1? Y? 3; 1? Z? 8); Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, And Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials, and the like.

As the separator, an insulating thin film interposed between the cathode and the cathode and having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m, and the thickness is generally 5 to 300 mu m.

Examples of the separation membrane include olefin-based polymers such as polypropylene having chemical resistance and hydrophobicity; A sheet or nonwoven fabric made of glass fiber, polyethylene, or the like can be used.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but it may have a cylindrical shape, a square shape, a pouch shape, or a coin shape using a can. It may also be a cable-type lithium secondary battery having a structure similar to a linear wire.

Hereinafter, the present invention will be described with reference to the following examples and comparative examples, but the present invention is not limited thereto.

Example

Example 1: Preparation of electrolytic solution

LiPF ₆ was added to the mixture of ethylene carbonate and ethyl methyl carbonate as a cyclic carbonate in a 1: 2 (volume ratio) organic solvent mixture at a concentration of 1 M to prepare a plurane-based polymer resin (R = (CH ₂ ) ₂ CN, weight average molecular weight: 300,000) was added in an amount of 2 wt% based on the total weight of the electrolytic solution to prepare an electrolytic solution.

[Chemical Formula 1]

Example 2: Preparation of lithium secondary battery

95 wt% of LiCoO ₂ , ₂ wt% of Super-P (conductive material) and 3 wt% of PVdF (binder) were added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a positive electrode mixture slurry And coated on both sides of an aluminum foil, dried and pressed to produce a positive electrode.

A negative electrode slurry was prepared by adding 97.5% by weight of natural graphite, 1.5% by weight of SBR (Styrene-Butadiene Rubber, binder) and 1% by weight of CMC (CarboxyMethyl Cellulose, a thickener and a binder) to water as a negative electrode active material, The negative electrode was prepared by coating, drying and pressing on both sides of the foil.

As the separator, an anode assembly and an anode were laminated using NH616 (product name) manufactured by Asahi Co., Ltd., and the electrolyte prepared in Example 1 was injected to prepare a lithium secondary battery.

Comparative Example 1: Preparation of electrolytic solution

An electrolytic solution was prepared in the same manner as in Example 1, except that the polymer resin was not added.

Comparative Example 2: Production of lithium secondary battery

A lithium secondary battery was produced in the same manner as in Example 2, except that the electrolyte prepared in Comparative Example 1 was injected as the electrolyte solution.

Experimental Example 1: Evaluation of Life Characteristic

The batteries prepared in Example 2 and Comparative Example 2 were placed in a chamber at 23 ° C and charged with 740 mA current in a range of 3 to 4.2 V in a constant current / constant voltage (CC / CV) mode using a charge / / Discharge is continuously performed for 300 cycles, which is shown in FIG.

Referring to the graph of FIG. 1, it can be seen that the battery of Example 2 including the electrolytic solution containing the pullulan-based polymer resin has an improved discharge capacity as compared with the battery of Comparative Example 2 which does not contain the pullulan-based polymer resin in the electrolyte I could confirm.

Experimental Example 2: Evaluation of high temperature safety

In order to evaluate the high-temperature stability of the battery, the cells prepared in Example 2 and Comparative Example 2 were charged at 4.2 V, placed in a high-temperature chamber at 80 ° C, and the change in thickness of the battery was observed at intervals of 10 minutes for 3 days. Respectively.

As can be seen from FIG. 2, the battery of Example 2 including the electrolyte according to the present invention showed less increase in thickness than the battery of Comparative Example 2.

Claims (8)

(i) a solvent;
(ii) a lithium salt; And
(iii) from 0.1 to 5% by weight, based on the total weight of the electrolyte composition, of a pullulan-based polymer resin
Wherein the electrolyte composition comprises:
Wherein the pullulan-based polymer resin is a polymer, an oligomer or a mixture thereof comprising at least one repeating unit represented by the following formula (1): &lt; EMI ID =
[Chemical Formula 1]

In Formula 1,
Each R is independently H or (CH ₂ ) ₁ CN,
and l is an integer of 1 to 10.
The method according to claim 1,
Wherein the pullulan-based polymer resin has a weight average molecular weight of 1,000 to 10,000,000.
The method according to claim 1,
Wherein the electrolytic solution composition contains the pullulan-based polymer resin in an amount of 0.5 to 2% by weight based on the total weight of the electrolytic solution composition.
The method according to claim 1,
Wherein the solvent is a nonaqueous solvent comprising a mixture of a linear carbonate compound and a cyclic carbonate compound.
The method according to claim 1,
Wherein the electrolyte composition further comprises an electrolyte additive,
Wherein the electrolyte additive is a polymer, an oligomer or a mixture thereof containing at least one repeating unit represented by the following formula (2): &lt; EMI ID =
(2)

In Formula 2,
X, Y and Z are each independently H, OH or (CH ₂ ) _n CN,
R 'are each independently H or (CH _{2) o} CN,
Herein, m is an integer of 0 to 10, and n and o are each independently an integer of 1 to 10.
6. The method of claim 5,
Wherein the electrolyte composition comprises the electrolyte additive in an amount of 0.01 to 15% by weight based on the total weight of the electrolyte composition.
An electrochemical device comprising the electrolyte composition according to any one of claims 1 to 6.
8. The method of claim 7,
Wherein the electrochemical device is a lithium secondary battery, a capacitor, or a solar cell.

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