KR100976960B1 - Electrolyte comprising eutectic mixture and lithium secondary battery containing the same - Google Patents

Abstract

The present invention provides a composition comprising (a) an eutectic mixture consisting of an alkoxy alkyl group-containing amide compound having a specific structure and an ionizable lithium salt; And (b) discloses an electrolyte comprising a plurality of fine particles of alumina and a lithium secondary battery having the same.

The eutectic mixtures contained in the electrolyte of the present invention have inherent properties such as excellent thermal stability and chemical stability, and in particular, exhibit high temperature stability and low reduction potential of the electrochemical window. It can be usefully applied as an electrolyte of an electrochemical device to which ash is applied. In addition, since the added alumina improves the ion conductivity of lithium ions, the performance of the lithium secondary battery may be improved.

Description

ELECTROLYTE COMPRISING EUTECTIC MIXTURE AND LITHIUM SECONDARY BATTERY CONTAINING THE SAME}

The present invention relates to an electrolyte comprising a eutectic mixture and a lithium secondary battery having the same.

Electrochemical devices, such as lithium secondary batteries, electrolytic condensers, electric double layer capacitors, electrochromic display devices, and dye-sensitized solar cells, which are being researched for practical use in the future, are widely used in recent years. Various kinds of electrolytes are used in the back, and the importance thereof is increasing day by day.

Currently, the most widely used electrolytes include ionizable salts such as lithium salts such as ethylene carbonate, propylene carbonate, dimethoxy ethane, g-butyl lactone (GBL), N, N It is a non-aqueous electrolyte solution dissolved in an organic solvent such as dimethyl formamide, tetrahydrofurane or acetonitrile.

By the way, the organic solvent used in such a non-aqueous electrolyte solution is not only easy to leak due to the low viscosity, but also highly volatile and may evaporate. It is also highly flammable. Accordingly, the electrochemical device having the same has problems in durability and stability.

In order to solve this problem, a method of using an imidazolium-based and ammonium-based ionic liquid as an electrolyte of a lithium secondary battery has been proposed. However, such an ionic liquid is reduced at a higher voltage than lithium ions at the negative electrode, or imidazolium and ammonium cations are inserted together at the negative electrode together with lithium ions, thereby degrading battery performance.

On the other hand, Korean Patent Registration Publication No. 10-751203, Korean Patent Publication No. 10-2007-85575 and the like have acetamide, urea, methylurea, caprolactam, valerictam, trifluoroacetamide, carbamate, formamide as electrolytes. And the like, and a eutectic mixture of an amide compound represented by a predetermined chemical formula and a lithium salt is disclosed. Since the eutectic mixture exhibits high thermal and chemical stability in addition to a relatively wide electrochemical window, problems such as evaporation and ignition of the electrolyte according to conventional organic solvents are solved.

Accordingly, the development of various eutectic mixtures useful as electrolytes is accelerating, particularly with higher temperature stability and lower electrochemical window lower limits for application to electrochemical devices requiring various electrochemical properties. There is an increasing demand for eutectic mixture electrolytes.

In addition, it is necessary to improve the ion conductivity so that lithium ions can be sufficiently transferred between the electrodes of the lithium secondary battery.

Accordingly, it is an object of the present invention to provide an electrolyte comprising a novel eutectic mixture exhibiting high thermal and chemical stability and an electrochemical device having the same.

In addition, another object of the present invention is to provide an electrolyte and an electrochemical device including the eutectic mixture having a high temperature stability and exhibits a reduction potential of a low electrochemical window, in addition to the above object. .

In addition, another object of the present invention is to provide an electrolyte having improved ion conductivity of lithium ions and a lithium secondary battery having the same, in addition to the above object.

In order to achieve the above object, the electrolyte of the present invention comprises: (a) an eutectic mixture composed of an alkoxy alkyl group-containing amide compound represented by the following formula (1) and an ionizable lithium salt; And (b) a plurality of alumina fine particles.

In Formula 1,

R, R ₁ and R ₂ are each independently selected from hydrogen, halogen and alkyl group having 1 to 20 carbon atoms, alkylamine group, alkenyl group and aryl group, at least one of which is CH _3- (CH ₂ ) alkoxy alkyl group represented by pO (CH ₂ ) q, p is an integer of 0 to 8, q is an integer of 1 to 8,

X is any one selected from the group consisting of carbon, silicon, oxygen, nitrogen, phosphorus, sulfur and hydrogen, i) m is 0 if X is hydrogen, ii) m is 1 if X is oxygen or sulfur, i) M is 2 if X is nitrogen or phosphorus and i) m is 3 if X is carbon or silicon.

In the electrolyte of the present invention, the alkoxy alkyl group-containing amide compound is N-methoxyethyl methyl carbamate, N-methoxyethyl-N-methyl methyl carbamate, N-methoxymethyl-N-methyl methyl carbamate, N , N-dimethyl methoxyethyl carbamate, N-methyl-N-methoxyethyl methoxyethyl carbamate, N-methyl-N-methoxyethyl methoxymethyl carbamate, N-methoxyethylcaprolactam, N- Methoxyethyl oxazolidinones and the like.

Further, in the electrolyte of the present invention, as the lithium salt, the anion is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, ^{_{(CF 3) 2 PF 4 -}} , (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF ^{_{3 CF 2 SO 3 -, (}} CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5 _{^{) 3 C -, (CF 3}} SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN ^- and the like can be given ^{_{-, (CF 3 CF 2 SO}} 2) 2 N.

In the electrolyte of the present invention, the molar ratio of the alkoxy alkyl group-containing amide compound and the lithium salt of the eutectic mixture is preferably 1 to 8: 1.

In the electrolyte of the present invention, the content of the alumina fine particles is preferably 0.1 to 20% by weight based on the total weight of the electrolyte.

In addition, the electrolyte of the present invention further comprises a first compound capable of reducing at a higher potential (Li / Li ⁺ ) than the eutectic mixture to form a passivating film or a second compound having a higher oxidation potential than the anode potential and consuming an overcharge current. It may include.

In addition, the electrolyte of the present invention may be a liquid electrolyte, and may be a polymer electrolyte such as a solid phase or a gel phase of the polymer itself, and the polymer electrolyte may include a monomer capable of forming a polymer by the eutectic mixture and a polymerization reaction. The polymer electrolyte may be a gel-like polymer electrolyte formed by polymerization of a precursor solution containing it, or a polymer electrolyte in a form in which the eutectic mixture is impregnated into a polymer.

The electrolyte of the present invention described above may be usefully applied to an electrochemical device such as a lithium secondary battery.

The electrolyte according to the present invention has the following effects.

First, since the novel eutectic mixture contained in the electrolyte of the present invention exhibits inherent characteristics of the eutectic mixture such as excellent thermal stability and chemical stability, problems such as evaporation, ignition and side reaction of the electrolyte according to the conventional organic solvent are greatly improved. do.

Second, since the eutectic mixture contained in the electrolyte of the present invention exhibits a lower potential of electrochemical window, it can be usefully applied as an electrolyte of an electrochemical device requiring various electrochemical properties.

Third, since the eutectic mixture contained in the electrolyte of the present invention shows more excellent high temperature stability, it contributes to improving the high temperature safety of the electrochemical device.

Fourth, since the ionic conductivity of lithium ions is improved due to the alumina added to the electrolyte of the present invention, it is possible to improve the performance of the lithium secondary battery.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail. Prior to this, terms or words used in the present specification and claims should not be construed as being limited to the common or dictionary meanings, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

The electrolyte of the present invention comprises: (a) an eutectic mixture composed of an alkoxy alkyl group-containing amide compound represented by the following Chemical Formula 1 and an ionizable lithium salt; And (b) a plurality of alumina microparticles simultaneously.

<Formula 1>

In Formula 1,

R, R ₁ and R ₂ are each independently selected from hydrogen, halogen and alkyl group having 1 to 20 carbon atoms, alkylamine group, alkenyl group and aryl group, at least one of which is CH _3- (CH ₂ ) alkoxy alkyl group represented by pO (CH ₂ ) q, p is an integer of 0 to 8, q is an integer of 1 to 8,

X is any one selected from the group consisting of carbon, silicon, oxygen, nitrogen, phosphorus, sulfur and hydrogen, i) m is 0 if X is hydrogen, ii) m is 1 if X is oxygen or sulfur, i) M is 2 if X is nitrogen or phosphorus and i) m is 3 if X is carbon or silicon.

Electrochemical devices have high heat generation and are frequently exposed to high temperatures, so stability at high temperatures is a very important factor.

The present inventors formed an eutectic mixture with a lithium salt using an alkoxy alkyl group-containing amide compound having the above-described structure. Unlike the conventional nonaqueous electrolyte organic solvent, the eutectic mixture has a high thermal and chemical characteristic unique to the eutectic mixture. It shows stability, which shows higher temperature stability than the eutectic mixture of amide-based compounds such as acetamide, methyl carbamate, and lithium salts as disclosed in the prior art. In addition, the eutectic mixture of the alkoxy alkyl group-containing amide compound and the lithium salt of the present invention exhibits a lower limit of the low electrochemical window. Accordingly, the eutectic mixture of the alkoxy alkyl group-containing amide compound and the lithium salt of the present invention not only contributes to improving the high temperature stability of the electrochemical device, but can be usefully applied as an electrolyte of the electrochemical device to which various negative electrode materials are applied.

In the electrolyte of the present invention, the alkoxy alkyl group-containing amide compound constituting the eutectic mixture is N-methoxyethyl methyl carbamate, N-methoxyethyl-N-methyl methyl carbamate, N-methoxymethyl-N-methyl Methyl carbamate, N, N-dimethyl methoxyethyl carbamate, N-methyl-N-methoxyethyl methoxyethyl carbamate, N-methyl-N-methoxyethyl methoxymethyl carbamate, N-methoxyethyl Caprolactam, N-methoxyethyl oxazolidinone, and the like.

In the electrolyte of the present invention, the lithium salt constituting the eutectic mixture together with the alkoxy alkyl group-containing amide compound described above can be represented by Li ⁺ X ^- as an ionizable lithium salt. In this lithium salt anion is not particularly ^{limited, F -, Cl -, Br} -, I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) _{^{2 PF 4 -, (CF 3}} ) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO _{^{3 -, (CF 3 SO 2}} ) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C - _{, (CF 3 SO 2) 3} C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN ^- and the like can be given ^{_{-, (CF 3 CF 2 SO}} 2) 2 N.

The melting temperature of the eutectic mixture of the electrolyte according to the present invention may vary according to R, R ₁ , X, etc. of Formula 1, but is preferably present in a liquid state at room temperature (25 ° C.). In addition, the viscosity (viscosity) of the eutectic mixture is not particularly limited, but 100 cP or less is most suitable for application to the electrochemical device.

The eutectic mixture of the electrolyte according to the present invention may be prepared according to conventional methods known in the art, for example, the above-described alkoxy alkyl group-containing amide compound and lithium salt are mixed at room temperature, and then at an appropriate temperature of 70 ° C. or lower. After the reaction can be prepared by purification. At this time, the molar ratio of the alkoxy alkyl group containing amide compound and lithium salt of the prepared eutectic mixture becomes like this. Preferably it is 1-8: 1, More preferably, it is 2-6: 1.

Since the electrolyte of the present invention includes a eutectic mixture containing lithium ions in itself, even when applied to a lithium secondary battery, a lithium salt may not be added separately, but a salt such as lithium salt may be, for example, 0 to 1 M / L. Of course, the concentration may further include. When further adding a lithium salt to the electrolyte, in order to improve solubility in the electrolyte, it is preferable to use a lithium salt having the same anion as that of the lithium salt constituting the eutectic mixture.

In addition, the electrolyte of the present invention contains a plurality of alumina fine particles. Alumina increases the lithium ion conductivity of electrochemical devices such as lithium secondary batteries. The content of the alumina fine particles is preferably 0.1 to 20% by weight based on the total weight of the electrolyte, and the average particle diameter of the alumina fine particles is preferably 10 to 100 nm, but is not limited thereto. In particular, when the electrolyte of the present invention is a liquid electrolyte, the alumina fine particles having an average particle diameter in the above range can penetrate well into the space between the separator and the electrode.

On the other hand, the electrolyte of the present invention is a first compound that can be reduced at a higher potential (Li / Li ⁺ ) than the above-mentioned eutectic mixture to form a passivation film, a second compound having a higher oxidation potential than the anode potential to consume the overcharge current Or a mixture thereof.

Non-limiting examples of such a first compound include vinylene carbonate, ethylene sulfite, N-acetyl lactam, 12-crown-4, 18-crown-6, catecholcarbonate, methylchloroformate, and the like. Each can be used individually or in mixture of 2 or more types. In addition, non-limiting examples of the second compound include butyl ferrocene, ferrocene derivatives such as 1,1'-dimethyl ferrocene, triazolium salt, imidazolium salt, tricyanobenzene, tetrashinanoquinomimethane, benzene derivative, pyrocarbonate, cyclo Hexyl benzene etc. can be mentioned, These can be used individually or in mixture of 2 or more types, respectively.

In addition, it will be apparent to those skilled in the art that the electrolyte of the present invention may further include various kinds of additives or organic solvents without departing from the object of the present invention.

Regardless of the type of electrolyte, all of the electrolytes of the present invention may be applied. For example, the electrolyte may be used as a liquid electrolyte or a polymer electrolyte such as a solid or gel phase of the polymer itself. When the electrolyte of the present invention is used as a liquid electrolyte, the above eutectic mixtures may be used alone, or may be used by further adding salts, organic solvents, additives and the like. On the other hand, when the electrolyte of the present invention is a polymer electrolyte, the polymer electrolyte is a gel-like polymer by polymerization of a precursor solution containing a eutectic mixture and a monomer capable of forming a polymer by a polymerization reaction, or the eutectic mixture is a solid phase or It may be made of a polymer electrolyte in a form impregnated with a polymer such as gel.

(1) First, the gel polymer electrolyte produced by the polymerization reaction of the precursor solution will be described.

Gel-like polymer electrolyte according to an aspect of the present invention is (i) the eutectic mixture of Formula 1; And (ii) a precursor solution containing a monomer capable of forming a polymer by a polymerization reaction. The alumina fine particles are dispersed in the precursor solution before the polymerization.

As the monomer (monomer) as the polymerization proceeds, all kinds of monomers capable of forming a gel polymer with the eutectic mixture is applicable, non-limiting examples thereof include vinyl monomers. Vinyl monomers have the advantage of very simple polymerization when mixed with eutectic mixtures to form gel polymers.

Non-limiting examples of vinyl monomers that can be used include acrylonitrile, methyl methacrylate, methyl acrylate, methacrylonitrile, methyl styrene, vinyl esters, vinyl chloride, vinylidene chloride, acrylamide, tetrafluoroethylene , Vinyl acetate, vinyl chloride, methyl vinyl ketone, ethylene, styrene, paramethoxy styrene, paracyano styrene, and the like, each of which may be used alone or in combination of two or more thereof.

The precursor solution may additionally include conventional polymerization initiators or photoinitiators, initiators are decomposed by heat or ultraviolet light to form radicals and react with monomers by free radical polymerization to form gel polymer electrolytes. do. Moreover, superposition | polymerization of a monomer can also be advanced, without using an initiator. In general, free radical polymerization is a reaction of initiation where active molecules or active points are formed, a growth reaction in which monomers are added at the end of an active chain to form an active point at the end of a chain, and a chain transfer reaction that moves an active point to other molecules. In addition, the reaction chain undergoes a stop reaction in which the active chain center is destroyed.

Non-limiting examples of thermal initiators that can be used include organic peroxides such as Benzoyl peroxide, Acetyl peroxide, Dilauryl peroxide, Di-tert-butyl peroxide, Cumyl hydroperoxide, and Hydrogen peroxide, and hydroperoxides, 2,2-Azobis (2). azo compounds such as -cyanobutane), 2,2-Azobis (Methylbutyronitrile), AIBN (Azobis (iso-butyronitrile), AMVN (Azobisdimethyl-Valeronitrile), and organic metals such as silver alkylated compounds. Non-limiting examples of photoinitiators formed by radicals include Chloroacetophenone, Diethoxy Acetophenone (DEAP), 1-phenyl-2-hydroxy-2-methyl propaneone (HMPP), 1-Hydroxy cyclrohexyl phenyl ketone, α-Amino Acetophenone, Benzoin Ether, Benzyl Dimethyl ketal, Benzophenone, Thioxanthone and 2-ethylAnthraquinone (2-ETAQ).

In addition to the components described above, the precursor solution of the gel polymer electrolyte according to the present invention may optionally contain other additives and the like known in the art.

Using the precursor solution described above to form a gel polymer electrolyte according to a conventional method known in the art, it is preferable to prepare a gel polymer electrolyte by the In - Situ polymerization reaction in the electrochemical device. In - Situ polymerization can be achieved by heat or UV irradiation. The content ratio of the eutectic mixture and the monomer in the precursor solution is preferably adjusted to 0.5-0.95: 0.05-0.5. Since the degree of polymerization of the gel polymer can be controlled according to the polymerization time, polymerization temperature or light irradiation degree, which are reaction factors, The polymer is superpolymerized without leaking the electrolyte so that the volume does not shrink.

(2) As another method for producing a polymer electrolyte containing a eutectic mixture according to the present invention, a eutectic mixture containing alumina dispersed therein may be injected into a solid polymer or a gel polymer already formed, so that the eutectic mixture is impregnated with the polymer.

Non-limiting examples of the polymers that can be used include polymethyl methacrylate, polyvinylidene difluoride, polyvinyl chloride, polyethylene oxide, polyhydroxyethyl methacrylate, etc., alone or in combination of two or more thereof. have. This method can simplify the manufacturing process compared to the In - Situ method described above.

(3) As another method for producing a polymer electrolyte comprising a eutectic mixture according to the present invention, a method of forming a polymer electrolyte by dissolving the polymer and the eutectic mixture in a solvent, dispersing alumina fine particles and then removing the solvent can be used. have. At this time, the eutectic mixture is in the form contained in the polymer matrix.

The solvent that can be used is not particularly limited, and non-limiting examples thereof include toluene, acetone, acetonitrile, THF, and the like. In addition, the solvent removal method is not particularly limited, and conventional methods such as applying heat may be used.

The electrolyte comprising the eutectic mixture according to the present invention is applicable to conventional electrochemical devices known in the art, where various electrochemical properties are required depending on the purpose of use.

Non-limiting examples of the electrochemical device include all kinds of primary, secondary cells, fuel cells, solar cells, electrochromic devices, electrolytic condenser or capacitor (capacitor), specific examples thereof Lithium secondary batteries, electric double layer capacitors, dye-sensitized solar cells, electrochromic devices and the like.

When applied to a lithium secondary battery, as a negative electrode of a lithium secondary battery, a negative electrode such as a carbon material capable of occluding and releasing lithium ions, a metal alloy, a lithium-containing oxide, or a silicon-containing material capable of bonding with lithium may be used. As the positive electrode, a lithium-containing oxide or the like is usually used.

Any carbon material capable of occluding and releasing lithium ions may be applied as long as it can be used as a carbon material negative electrode of a lithium secondary battery such as low crystalline carbon and high crystalline carbon. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch-based carbon fiber. High temperature calcined carbon such as (mesophase pitch based carbon fiber), meso-carbon microbeads, Mesophase pitches and petroleum or coal tar pitch derived cokes. In this case, the negative electrode may include a binder, and the binder may include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, Polymethylmethacrylate,

Various kinds of binder polymers, such as styrene-butadiene rubber (SBR), may be used.

In addition, a lithium-containing transition metal oxide may be preferably used as the active material of the positive electrode made of lithium-containing oxide, for example, 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 (O≤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 (0 <z <2), LiCoPO 4 and LiFePO any one selected from the group consisting of _4, or to use a mixture of two or more of these Can be.

In addition, a separator may be optionally interposed between the positive electrode and the negative electrode, and conventional porous polymer films conventionally used as separators, for example, ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, and ethylene / hexene copolymer And porous polymer films made of polyolefin-based polymers such as ethylene / methacrylate copolymers may be used alone or in a stack thereof. In addition to the conventional porous non-woven fabric, for example, a non-woven fabric of high melting glass fibers, polyethylene terephthalate fibers and the like can be used, but is not limited thereto.

The external shape of the lithium secondary battery is not particularly limited, but may be cylindrical, square, pouch type or coin type using a can.

Hereinafter, the present invention will be described in detail with reference to Examples. However, embodiments according to the present invention can be modified in many different forms, the scope of the present invention should not be construed as limited to the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Synthetic example  One

5.8 g of N-methoxyethyl-N-methyl methylcarbamate and 2 g of LiPF _{6 were} placed in a round bottom flask and stirred slowly for 2 hours under a nitrogen atmosphere to obtain 7.8 g of the desired eutectic mixture.

Synthetic example  2

5.2 g of N-methoxyethyl methylcarbamate and 2 g of LiPF _{6 were} placed in a round bottom flask, and stirred slowly for 2 hours under a nitrogen atmosphere to obtain 7.2 g of the desired eutectic mixture.

Synthetic example  3

7.5 g of N-methoxyethyl-N-methyl methoxyethyl carbamate and 2 g of LiPF _{6 were} placed in a round bottom flask and stirred slowly for 2 hours under a nitrogen atmosphere to obtain 12 g of the desired eutectic mixture.

Control group 1

4.7 g of purified methyl carbamate and 6 g of LiTFSI were added to a round-bottomed flask and slowly stirred under a nitrogen atmosphere at room temperature for 2 hours to obtain 10.7 g of a eutectic mixture.

Control 2

3.8 g of purified acetamide and 6 g of LiTFSI were placed in a round bottom flask and stirred slowly for 2 hours under a nitrogen atmosphere to obtain 9.8 g of a eutectic mixture.

In order to evaluate the physical properties of the eutectic mixture prepared according to the above-described synthesis examples and controls, it was carried out as follows.

As a sample, the eutectic mixture prepared in Synthesis Example 1 and the eutectic mixtures of the control groups 1 and 2 were used, and the ratio of the eutectic mixtures used was 3: 1 in both amide compound and salt ratios. Viscosity measurements were measured at 25 ° C. using an RS150 viscometer and conductivity was measured using an Inolab 740 instrument. The results are shown in Table 1 below.

Viscosity conductivity A potential window Synthesis Example 1 82 1.2 0.45-4.5 Control group 1 62 1.7 0.6 ~ 4.7 Control 2 100 1.1 0.7-4.9

Evaluation of the ionic conductivity of the electrolyte

Example

A solution in which N, N-dimethoxyethyl-N-methylmethylcarbamate and LiPF ₆ were mixed in a molar ratio 3: 1 was prepared. Polyethylene oxide was dissolved therein in a weight ratio of 30%, and then 2% vinylene carbonate and 10% alumina fine particles (average particle diameter: 50 nm) were mixed with an additive and then gelled to prepare a polymer electrolyte.

Comparative example

A polymer electrolyte was prepared in the same manner as in Example, except that alumina was not added during the preparation of the electrolyte.

Ionic conductivity at various temperatures was measured for the electrolytes of Examples and Comparative Examples described above, and the results are shown in FIG. 1. Referring to FIG. 1, it can be seen that the electrolyte of Example 1 to which alumina was added has superior ion conductivity than the electrolyte of Comparative Example.

Eutectic mixture  High temperature stability evaluation

Production Example

(Anode manufacturing)

LiCoO ₂ as a positive electrode active material, artificial graphite as a conductive material, polyvinylidene fluoride as a binder was mixed in a weight ratio of 94: 3: 3, and N-methylpyrrolidone was added to the resulting mixture to prepare a slurry. The prepared slurry was applied to aluminum foil, and dried at 130 ° C. for 2 hours to prepare a positive electrode.

(Cathode production)

A negative electrode active material, artificial graphite, a conductive material, and a binder were mixed in a weight ratio of 94: 3: 3, and N-methylpyrrolidone was added to prepare a slurry. The prepared slurry was applied to a copper foil and dried at 130 ° C. for 2 hours to prepare a negative electrode.

(Secondary Battery Assembly)

A positive electrode and a negative electrode prepared as described above were prepared in 1 cm ² , and a separator was interposed therebetween. The eutectic mixture prepared in Synthesis Example 1 was injected thereto to complete a secondary battery as shown in FIG. 2. In Fig. 2, reference numeral 1 denotes an anode, 2 a cathode, 3 a separator and an electrolyte, 4 a spacer, 5 a coin can container, 6 a coin can lid, and 7 a seal rubber.

Control group 3

A secondary battery was manufactured in the same manner as in Preparation Example, except that a 1M LiPF ₆ solution having a volume ratio of ethylene carbonate: ethyl methyl carbonate 1: 2 was used instead of the eutectic mixture of Synthesis Example 1 as an electrolyte.

Control 4

A secondary battery was manufactured in the same manner as in Preparation Example, except that the eutectic mixture of Control Group 1 was used instead of the eutectic mixture of Synthesis Example 1 as an electrolyte.

A secondary battery manufactured according to the method 0.5mAcm ^- respectively charged and discharged at a ² to measure the discharge capacity and charge-discharge efficiency of the cycle.

In addition, the secondary battery manufactured according to the above method was charged at 0.5 mAcm ^{- 2} and left at 90 ° C for 4 hours to measure the thickness change of the battery. The experimental results are shown in Table 2.

Initial thickness (mm) Late thickness (mm) % Increase Production Example 3.86 3.90 1.0% Control 4 3.85 4.43 15.0%

Referring to Table 2, it can be seen that the battery of the preparation example using the eutectic mixture of the present invention showed better high temperature stability than the battery of the control 4 using the conventional eutectic mixture.

1 is a graph showing the ion conductivity according to the temperature change of the electrolyte of the Examples and Comparative Examples,

2 is a schematic cross-sectional view of a coin-type secondary battery,

3 is a graph measuring charge and discharge efficiency of a secondary battery according to Preparation Example and Control 3;

Claims (18)

(a) an eutectic mixture composed of an alkoxy alkyl group-containing amide compound represented by the following formula (1) and an ionizable lithium salt; And (b) an electrolyte comprising a plurality of alumina fine particles. <Formula 1>

In Formula 1, R, R ₁ and R ₂ are each independently selected from hydrogen, halogen and alkyl group having 1 to 20 carbon atoms, alkylamine group, alkenyl group and aryl group, at least one of which is CH _3- (CH ₂ ) alkoxy alkyl group represented by pO (CH ₂ ) q, p is an integer of 0 to 8, q is an integer of 1 to 8, X is any one selected from the group consisting of carbon, silicon, oxygen, nitrogen, phosphorus, sulfur and hydrogen, i) m is 0 if X is hydrogen, ii) m is 1 if X is oxygen or sulfur, i) M is 2 if X is nitrogen or phosphorus and i) m is 3 if X is carbon or silicon. The method of claim 1, wherein the alkoxy alkyl group-containing amide compound is N-methoxyethyl methyl carbamate, N-methoxyethyl-N-methyl methyl carbamate, N-methoxymethyl-N-methyl methyl carbamate, N, N-dimethyl methoxy ethyl carbamate, N-methyl-N-methoxyethyl methoxyethyl carbamate, N-methyl-N-methoxyethyl methoxymethyl carbamate, N-methoxyethylcaprolactam and N-meth The electrolyte, characterized in that any one selected from the group consisting of oxyethyl oxazolidinone. The method of claim 1, wherein the lithium salt anion is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) ^{_{2 PF 4 -, (CF 3}} ) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO ^{_{3 -, (CF 3 SO 2}} ) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C - _{, (CF 3 SO 2) 3} C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN ^- and _{(CF 3 CF 2 SO 2)} 2 N - electrolyte, characterized in that at least one selected from the group consisting of. The electrolyte according to claim 1, wherein the eutectic mixture has a molar ratio of the alkoxy alkyl group-containing amide compound and a lithium salt of 1 to 8: 1. The electrolyte of claim 1, wherein the content of the alumina fine particles is 0.1 to 20% by weight based on the total weight of the electrolyte. The electrolyte of claim 1, wherein the average particle diameter of the alumina fine particles is 10 to 100 nm. The method of claim 1, wherein the first compound that can be reduced at a higher potential (Li / Li ⁺ ) than the eutectic mixture to form a passivation film, the second compound having an oxidation potential higher than the anode potential to consume the overcharge current and their The electrolyte further comprises any one selected from the group consisting of a mixture. 8. The compound according to claim 7, wherein the first compound is selected from the group consisting of vinylene carbonate, ethylene sulfite, N-acetyl lactam, 12-crown-4, 18-crown-6, catecholcarbonate and methylchloroformate. An electrolyte characterized by one or a mixture of two or more thereof. The method of claim 7, wherein the second compound is any one selected from the group consisting of ferrocene derivatives, triazolium salts, imidazolium salts, tricyanobenzene, tetrashinanoquinomethane, benzene derivatives, pyrocarbonate and cyclohexylbenzene Electrolyte characterized in that the mixture of two or more kinds. The electrolyte of claim 1, wherein the electrolyte is a polymer electrolyte. The polymer electrolyte according to claim 10, wherein the polymer electrolyte comprises a gel polymer electrolyte formed by polymerization of a precursor solution containing (i) the eutectic mixture and (ii) a monomer capable of forming a polymer by polymerization. Electrolyte characterized in that. 12. The electrolyte of claim 11, wherein said monomer is a vinyl monomer. The method of claim 12, wherein the vinyl monomer is acrylonitrile, methyl methacrylate, menyl acrylate, methacrylonitrile, methyl styrene, vinyl esters, vinyl chloride, vinylidene chloride, acrylamide, tetrafluoroethylene And vinyl acetate, vinyl chromide, methyl vinyl ketone, ethylene, styrene, paramethoxy styrene, and paracyano styrene. Any one or a mixture of two or more thereof. The electrolyte of claim 11, wherein the content ratio of the eutectic mixture and the monomer in the precursor solution is 0.5-0.95: 0.05-0.5. The electrolyte of claim 11, wherein the gel polymer electrolyte is prepared by in-situ polymerization in an electrochemical device. 11. The electrolyte of claim 10 wherein the polymer electrolyte is impregnated with the eutectic mixture in a polymer. 17. The polymer according to claim 16, wherein the polymer is any one selected from the group consisting of polymethylmethacrylate, polyvinylidene difluoride, polyvinyl chloride, polyethylene oxide and polyhydroxyethyl methacrylate or a mixture of two or more thereof. It is an electrolyte characterized by the above-mentioned. In the electrochemical device comprising a positive electrode, a negative electrode and an electrolyte, The electrolyte is a lithium secondary battery, characterized in that the electrolyte of any one of claims 1 to 17.

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