KR101179356B1 - Eutectic mixture electrolyte and secondary battery using the same - Google Patents

Abstract

The present invention retains the advantages of the existing eutectic mixture electrolytes (for example, wide electrochemical window, wide temperature range as a liquid, high solvation ability, non-coordinated binding properties, flame retardancy, etc.), but without significant limitations on the type and concentration of lithium salts. The present invention relates to an eutectic mixture electrolyte that can be easily prepared.

Description

Eutectic mixture electrolyte and secondary battery using same {EUTECTIC MIXTURE ELECTROLYTE AND SECONDARY BATTERY USING THE SAME}

The present invention retains the advantages of the existing eutectic mixture electrolytes (for example, wide electrochemical window, wide temperature range as a liquid, high solvation ability, non-coordinated binding properties, flame retardancy, etc.), but without significant limitations on the type and concentration of lithium salts. It relates to a eutectic mixture electrolyte that can be easily prepared.

Recently, interest in energy storage technology is increasing. As the field of application extends to mobile phones, notebook PCs, and even electric vehicles, research and development on energy storage is becoming concrete. In this respect, the most interesting field is an electrochemical device, and among them, a secondary battery capable of charging and discharging has been attracting attention.

Lithium ion batteries, developed in the early 1990s among the secondary batteries currently applied, have been spotlighted due to their high operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead secondary batteries. I am getting it.

In general, a lithium ion battery is manufactured using a lithium metal oxide as a positive electrode, a carbon material or a lithium metal alloy as a negative electrode, and a solution in which electrolyte salt is dissolved in an electrolyte solvent as an electrolyte. At this time, the electrolyte is a medium for transferring ions between the electrodes, it should be able to transfer the ions at a sufficiently high speed, and a stable material in the operating temperature / pressure range of the battery.

However, organic solvents such as carbonate, lactone, ether and the like used as electrolyte solvents are generally highly volatile and highly flammable, causing problems in safety when overcharged, overdischarged, short-circuited and at high temperatures when applied to lithium ion secondary batteries.

In an attempt to solve the above problem, Japanese Patent 2002-110225 discloses a method of using an imidazolium-based and ammonium-based ionic liquid as an electrolyte. However, there is a problem that the ionic liquid is reduced at a higher voltage than lithium ions at the negative electrode, or imidazolium and ammonium cations are inserted into the negative electrode together with the lithium ions. Therefore, the application of the ionic liquid alone as a liquid electrolyte of a lithium secondary battery revealed a problem that the capacity reduction of the secondary battery was very large in the charge-discharge cycle, but rather, the battery performance was deteriorated. In addition, conventional ionic liquids are expensive and complex to synthesize and purify, making them unsuitable for practical application in secondary batteries.

Therefore, in order to improve the performance of the secondary battery, various attempts have been made to modify the electrode material or to improve electrolyte components, or to develop new electrode materials and electrolytes.

The inventors of the present invention provide a mixture of (a) a eutectic mixture composed of two or more amide group-containing compounds in order to broaden the range of eutectic mixture formation and to facilitate the preparation of the eutectic mixture electrolyte; And (b) an ionizable lithium salt, to provide an easy eutectic mixture electrolyte.

The present invention provides a eutectic mixture electrolyte comprising (a) a eutectic mixture composed of two or more amide group-containing compounds, and (b) an ionizable lithium salt; A method of preparing the eutectic mixture electrolyte; And it provides a secondary battery comprising the eutectic mixture electrolyte.

Hereinafter, the present invention will be described in detail.

The eutectic mixture refers to a substance in which two or more substances are mixed to lower the melting temperature, in particular, a mixed salt which is liquid at room temperature. In particular, normal temperature means 100 degreeC in upper limit, and 60 degreeC in some cases.

Electrolytes containing such eutectic mixtures (hereinafter referred to as eutectic mixture electrolytes) have characteristics such as a wide electrochemical window, a wide temperature range as a liquid, high solvation capability, and non-coordination binding properties, thereby improving battery performance and safety. have. In particular, the eutectic mixture electrolyte has no vapor pressure compared to the conventional organic solvent, so there is little concern about evaporation of the electrolyte during high temperature storage and flame retardancy, thereby improving high temperature storage characteristics and safety of the battery.

Such eutectic mixture electrolyte may be prepared by mixing one amide group-containing compound and a lithium salt. In this case, however, the formation of the eutectic mixture electrolyte in the liquid state varies depending on the type of the lithium salt and / or the use ratio of the lithium salt and the amide group-containing compound.

Accordingly, the present invention finds that two or more amide group-containing compounds can form a eutectic mixture, and is characterized by easily preparing a eutectic mixture electrolyte using the same. More specifically, the present invention is a eutectic mixture composed of two or more amide group-containing compounds; And an ionizable lithium salt, characterized in that the eutectic mixture electrolyte can be more easily formed.

The amide group-containing compound has two polar groups, a carbonyl group and an amine group in the molecule. Accordingly, when two or more kinds of the amide group-containing compound are mixed, the crystallinity of the compound may decrease, and a eutectic mixture may be formed. That is, the carbonyl group (-C = O) and the amine group (-NR ₂ ) present in one amide group-containing compound weaken the bond in the other amide group-containing compound, and the melting point of the mixture is lowered, thereby forming a eutectic mixture. Can be.

Therefore, in the present invention, not only the eutectic mixture electrolyte can be prepared, but also the eutectic mixture electrolyte can be produced with a smaller amount of lithium salt without significant limitations on the type, concentration (usage), and the like of the lithium salt to be used. Etc. can be improved.

In addition, since the present invention contains lithium ions in the electrolyte itself, lithium ions may be added as positive electrode active materials. In the case of a lithium secondary battery that needs to be inserted and detached, no additional lithium salt is required, and since only lithium ions (Li ⁺ ) exist as cations in the electrolyte, unlike conventional ionic liquid electrolytes, There is no fear that the negative electrode insertion of lithium ions is prevented by other cations, and thus battery performance can be improved.

In addition, the eutectic mixture electrolyte of the present invention retains the advantages of existing eutectic mixture electrolytes, such as wide electrochemical window, wide temperature range as a liquid, high solvation ability, non-coordinating ability, flame retardancy, and the like, resulting in battery performance and safety. There is also an advantage that can be secured.

The two or more amide group-containing compounds of the present invention are not particularly limited and may be independently primary, secondary or tertiary amide compounds. For example, the amide group-containing compound may be represented by the following Chemical Formula 1 or Chemical Formula 2, and non-limiting examples thereof include acetamide, N-ethylacetamide, urea, methylurea, caprolactam, and N-methylcapro Lactam, N-ethylurethane, N-methyloxazolidinone, N-hexyloxazolidinone, valericam, triloacetamide, methylcarbamate, ethylcarbamate, butylcarbamate, formamide, formate or their Mixtures and the like.

[Formula 1]

In Formula 1, R ₁ , R ₂ and R ₃ are each independently hydrogen, halogen, alkyl group having 1 to 20 carbon atoms, alkylamine group, alkenyl group or aryl group; X is selected from hydrogen, carbon, silicon, oxygen, nitrogen, phosphorus, and sulfur, i) m = 0 for X = H, ii) m = 1 for X = O or S, i) X = N Or in the case of P, m = 2, i) m in the case of X = C or Si, m = 3, and R ₁ at that time are each independently.

[Formula 2]

In Formula 2, R ₄ And R ₅ are each independently hydrogen, an alkyl group having 1 to 20 carbon atoms, an alkylamine group, an alkenyl group, or an aryl group; X is selected from carbon, silicon, oxygen, nitrogen, phosphorus and sulfur, i) m = 0 if X = O or S, ii) m = 1, X) if X = N or P Or in the case of Si, m = 2, and then R ₄ is each independently; n is an integer from 1 to 10.

As salts of the structure, such as ^{anion-lithium} salt is Li ⁺ Y used in the present invention (Y ^-) roneun Although there is no particular limitation, 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 ^- and the like are preferred.

The molar ratio of the two amide group-containing compounds is preferably 1: 1 to 1: 8, more preferably 1: 1 to 1: 4. Since the portion where the amide group-containing compound can be combined with other compounds is limited, it may be difficult to form a eutectic mixture electrolyte in a liquid state outside the above range.

In addition, the eutectic mixture electrolyte of the present invention is (a) a first compound capable of reducing at a higher potential (Li / Li ⁺ ) than the eutectic mixture electrolyte to form a passivation film on the surface of the cathode, and (b) higher oxidation than the anode potential. It may further comprise a second compound, or both, having a potential to consume the overcharge current.

The first compound is a compound that can be reduced at a higher potential (Li / Li ⁺ ) than the eutectic mixture electrolyte of the present invention to form a passivation film on the surface of the negative electrode, thereby preventing side reactions between the negative electrode and the electrolyte to improve battery performance. If it is not particularly limited, non-limiting examples thereof include alkylene compounds such as vinylene carbonate (VC), sulfonate compounds such as 1,3-propane sultone, and lactam compounds such as N-acetyl lactam.

In addition, the second compound is not particularly limited as long as the second compound has a higher oxidation potential than the anode potential and consumes an overcharge current to prevent explosion and / or ignition due to overcharging of the battery, thereby improving safety of the battery. Non-limiting examples thereof include ferrocene derivatives such as butyl ferrocene, 1,1'-dimethyl ferrocene, triazolium salt, imidazolium salt, tricyanobenzene, tetrashinanoquinomimethane, benzene derivative, pyrocarbonate, cyclohexylbenzene, and the like. have.

On the other hand, the viscosity (viscosity) of the eutectic mixture electrolyte is not particularly limited, it may be suitable for the application of the electrochemical device is less than 100 cP.

The eutectic mixture electrolyte of the present invention comprises the steps of: (a) mixing two or more amide group-containing compounds to form a eutectic mixture; And (b) dissolving ionizable lithium salt (salt) in the eutectic mixture.

The step (a) may be by a conventional method known in the art, for example, by mixing two or more of the amide group-containing compound at room temperature or heated (0 ℃ ~ 70 ℃) to react, Eutectic mixtures can be prepared.

<Application Mode of Eutectic Mixture Electrolyte of the Present Invention>

The eutectic mixture electrolyte of the present invention is not particularly limited in form, but may preferably be applied in two forms: liquid electrolyte form or gel polymer electrolyte form.

1) Since the above-mentioned eutectic mixture electrolyte is a liquid at room temperature, in the present invention, the eutectic mixture electrolyte itself can be used as a liquid electrolyte.

2) It may also be in the form of a gel polymer electrolyte comprising the eutectic mixture electrolyte described above. In this case, the monomer is polymerized in the presence of the above-mentioned eutectic mixture electrolyte; Or it can be prepared by impregnating the above-mentioned eutectic mixture electrolyte in the polymer or gel polymer already prepared.

① First, the form of the gel polymer electrolyte manufactured by the polymerization reaction of a monomer is demonstrated.

The gel polymer electrolyte may include (i) a eutectic mixture electrolyte comprising two or more amide group-containing compounds and a lithium salt; And (ii) a monomer capable of forming a gel polymer by a polymerization reaction.

Monomers are applicable to all kinds of monomers capable of forming a gel polymer by a polymerization reaction, and non-limiting examples thereof include vinyl monomers. When the vinyl monomer is mixed with the eutectic mixture electrolyte to form a gel polymer, transparent polymerization is possible and the polymerization conditions are very simple.

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.

In addition, it is preferable that the monomer has a small volume shrinkage during polymerization, and is capable of in-situ polymerization in a battery.

The electrolyte precursor liquid may further include a polymerization initiator or a photoinitiator.

Initiators are decomposed by heat or ultraviolet rays to form radicals, and react with monomers by free radical polymerization to form gel polymer electrolytes. Moreover, superposition | polymerization of a monomer can also be advanced, without using an initiator. In general, free radical polymerization involves initiation reactions in which highly reactive temporary molecules or active sites are formed, growth reactions in which monomers are added at the end of the active chain to form active sites at the end of the chain, and chain transfer to transfer the active sites to other molecules. Reaction, 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).

On the other hand, the mixing ratio of the electrolyte precursor liquid of the present invention is a weight ratio of (eutectic mixture electrolyte) x: (monomer capable of forming a gel polymer by a polymerization reaction) y: (polymerization initiator) z, x is 0.5 ~ 0.95 , y is 0.05-0.5, z is 0.00-0.05 and it is preferable that x + y + z = 1. More preferably, x is 0.7-0.95, y is 0.05-0.3, and z is 0.00-0.01. However, the present invention is not limited thereto.

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

The above-described electrolyte precursor liquid can be used to form a gel polymer electrolyte according to a conventional method known in the art, for example, it can be prepared by the In-Situ polymerization reaction inside the battery. The In-Situ polymerization reaction is possible through heat or ultraviolet irradiation. In this case, the degree of gel polymer electrolyte formation is preferably such that the gel polymer electrolyte does not leak during polymerization, and the electrolyte is not polymerized so that the volume does not shrink, and may be controlled by polymerization time, polymerization temperature, or light irradiation amount. For example, the thermal polymerization temperature may range from 40 to 80 ° C., and the polymerization time may vary depending on the type of initiator and the polymerization temperature, but is preferably about 20 to 60 minutes.

(2) Another type of gel polymer electrolyte of the present invention is an impregnated eutectic mixture electrolyte with an already formed polymer or gel polymer.

Non-limiting examples of polymers that can be used include polymethylmethacrylate, polyvinylidene difluoride, polyvinyl chloride, polyethylene oxide, polyhydroxyethylmethacrylate, and the like. In addition, gel polymers can be used as all conventional gel polymers in the art. In this case, the manufacturing process may be simplified as compared with the aforementioned In-Situ polymerization method.

(3) Another form of gel polymer electrolyte of the present invention is to form a gel polymer electrolyte by dissolving the polymer and the eutectic mixture electrolyte in a solvent and then removing the solvent. In this case, a eutectic mixture electrolyte is contained in the polymer matrix.

The solvent which can be used is not specifically limited, For example, the general organic solvent used for a battery can also be used. Non-limiting examples include Toluene, Acetone, Acetonitrile, THF, Propylene carbonate (PC), Ethylene carbonate (EC), Diethyl carbonate (DEC), Dimethyl carbonate (DMC), Dipropyl carbonate (DPC), Dimethyl sulfoxide, Acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethylcarbonate (EMC), gamma butyrolactone (γ-butyrolactone) or mixtures thereof Etc. Since the organic solvent may impair the safety of the secondary battery due to flammability, it is preferable to use a small amount if possible. In addition, a phosphate ester may be used as a flame retardant additive mainly used in lithium secondary batteries, and non-limiting examples thereof include trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, tripropyl phosphate, tributyl phosphate, and mixtures thereof. .

The solvent removal method is also not particularly limited, and is made through heating according to a conventional method. In the third embodiment, a post-treatment process may be required to remove the solvent when forming the gel polymer electrolyte.

The secondary battery of the present invention is a positive electrode; cathode; Separator; And it may be composed of an electrolyte, wherein the electrolyte is characterized in that it comprises the above-mentioned eutectic mixture electrolyte.

The secondary battery is preferably a lithium secondary battery, and non-limiting examples thereof include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The secondary battery of the present invention may be manufactured according to a conventional method known in the art, for example, after assembling a separator between the negative electrode and the positive electrode, and injecting the above-mentioned eutectic mixture electrolyte It can be manufactured by.

The eutectic mixture electrolyte of the present invention retains the advantages (eg, wide electrochemical window, wide temperature range as a liquid, high solvation ability, non-coordination, flame retardancy, etc.) of the existing eutectic mixture electrolyte, and is a kind and concentration of lithium salt. It can manufacture easily, without big restrictions etc. In particular, in the present invention, a smaller amount of lithium salt can be used, so that the viscosity, ionic conductivity, and further economic efficiency of the electrolyte can be improved.

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

Preparation of Eutectic Mixture Electrolyte

Example 1.

A eutectic mixture was prepared by mixing 7.5 g of methyl carbamate (melting point (mp) 75 ° C.) and 10 g of N-methyloxazolidinone (mp 15 ° C.) in a molar ratio of 1: 1. The melting point of the eutectic mixture was measured using a differential scanning calorimeter (DSC), and the result is shown by the solid line in FIG. 2. At this time, the melting point was -28 ℃.

In addition, 1M LiPF ₆ was further dissolved in the eutectic mixture to prepare a eutectic mixture electrolyte, and the melting point of the eutectic mixture electrolyte was measured, and is indicated by a dotted line in FIG. 2. At this time, the melting point was -60 ^o C or less, from which it could be confirmed that the eutectic mixture electrolyte was prepared.

Example 2.

Instead of 1M LiPF ₆ , a eutectic mixture electrolyte was prepared in the same manner as in Example 1, except that 3 g of Lithium bis (trifluoromethylsulfone) imide (LiTFSI) was used so that the concentration of lithium salt in the electrolyte was 0.2M.

The melting point of the eutectic mixture electrolyte was measured and shown in FIG. 3. At this time, the melting point was -60 ^o C or less, from which it could be confirmed that the eutectic mixture electrolyte was prepared.

Comparative Example 1

Instead of 7.5 g of methyl carbamate and 10 g of N-methyloxazolidinone in Example 2, 15 g of methyl carbamate was mixed with 3 g of LiTFSI and reacted at 70 ° C.

Subsequently, as a result of observing the mixture, a portion of methyl carbamate was precipitated in a solid state. From this, it was confirmed that the eutectic mixture electrolyte was not formed in this case.

<Production of Secondary Battery>

Example 3.

(Anode manufacture)

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)

The negative electrode active material Li _4/3 Ti _5/3 O ₄ , artificial graphite 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. Injecting the eutectic mixture electrolyte prepared in Example 1 here to complete the secondary battery as shown in FIG.

Comparative Example 2

A secondary battery was prepared in the same manner as in Example 3, except that a 1 M LiPF ₆ solution having a volume ratio of ethylene carbonate: ethyl methyl carbonate = 1: 2 was used as a conventional electrolyte instead of the eutectic mixture electrolyte.

Experimental Example 1. Evaluation of room temperature performance of a secondary battery

A secondary battery prepared in Example 3 and Comparative Example 2 0.5mAcm ^- respectively charged and discharged at a ² to measure the discharge capacity and charge-discharge efficiency of the cycle.

As a result, both the cell of Comparative Example 2 using a conventional electrolyte and the cell of Example 3 using the eutectic mixture electrolyte of the present invention showed a discharge capacity of 99% and a charge-discharge efficiency of 99% after the second cycle. (See FIG. 4). From this, it was found that the eutectic mixture electrolyte of the present invention can exhibit performance comparable to the conventional liquid electrolyte at room temperature.

Experimental Example 2 Evaluation of Thermal Stability of Secondary Battery

Secondary batteries were prepared in the same manner as in Example 3 and Comparative Example 2, except that lithium metal was used as the negative electrode, and charged with 4.2 V relative to lithium, followed by thermal stability evaluation for the positive electrode / electrolyte using DSC. . The results are shown in FIGS. 5 (Example 3) and 6 (Comparative Example 2), respectively.

As a result, in the battery of Example 3 including the eutectic mixture electrolyte of the present invention, heat was observed at 100 ° C. and 260 ° C., and the total calorific value was 120 J / g. On the other hand, the battery of Comparative Example 2 containing a conventional electrolyte was observed to generate heat from 170 ^° C., the calorific value was 300 J / g.

The cell containing the eutectic mixture electrolyte of the present invention exhibited a lower calorific value than the cell containing the conventional electrolyte. From this, it can be seen that the eutectic mixture electrolyte of the present invention has excellent thermal stability and can further improve battery safety.

1 is a cross-sectional structural view of a coin type secondary battery.

2 is a DSC result graph of the eutectic mixture prepared in Example 1, and the eutectic mixture electrolyte.

3 is a DSC result graph of the eutectic mixture electrolyte prepared in Example 2. FIG.

4 is a graph showing charge and discharge efficiency of secondary batteries of Example 3 and Comparative Example 2 measured according to Experimental Example 1. FIG. Here, a dotted line shows Example 3, and a solid line shows the comparative example 2. As shown in FIG.

5 is a DSC result graph of the secondary battery of Example 3 measured according to Experimental Example 2. FIG.

6 is a DSC result graph of the secondary battery of Comparative Example 2 measured in accordance with Experimental Example 2. FIG.

Claims (11)

(a) a eutectic mixture composed of two or more amide group-containing compounds; And (b) an ionizable lithium salt. The eutectic mixture electrolyte according to claim 1, wherein the two or more amide group-containing compounds are each independently a compound represented by the following Chemical Formula 1 or 2. [Formula 1]

In Formula 1, R ₁ , R ₂ and R ₃ are each independently hydrogen, halogen, alkyl group having 1 to 20 carbon atoms, alkylamine group, alkenyl group or aryl group; X is selected from hydrogen, carbon, silicon, oxygen, nitrogen, phosphorus, and sulfur, i) m = 0 for X = H, ii) m = 1 for X = O or S, i) X = N Or in the case of P, m = 2, iii) in the case of X = C or Si, m = 3, and then R ₁ is each independently; [Formula 2]

In Formula 2, R ₄ and R ₅ are each independently hydrogen, an alkyl group having 1 to 20 carbon atoms, an alkylamine group, an alkenyl group, or an aryl group; X is selected from carbon, silicon, oxygen, nitrogen, phosphorus and sulfur, i) m = 0 if X = O or S, ii) m = 1, X) if X = N or P Or in the case of Si, m = 2, and then R ₄ is each independently; n is an integer from 1 to 10. The compound according to claim 1, wherein the two or more amide group-containing compounds are each independently acetamide, N-ethylacetamide, urea, methylurea, caprolactam, N-methylcaprolactam, N-ethylurethane, and N-methyloxa. Zolidinone, N-hexyloxazolidinone, valericam, trifluoroacetamide, methyl carbamate, N, N-dimethyl methyl carbamate, N, N-dimethyl ethyl carbamate, ethyl carbamate, butyl carbamate, form A eutectic mixture electrolyte characterized by being selected from the group consisting of amides and formate. 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 - is the eutectic mixture electrolyte characterized selected from the group consisting of. The eutectic mixture electrolyte of claim 1, wherein the molar ratio of the two amide group-containing compounds is 1: 1 to 1: 8. The method of claim 1, (a) a first compound that can be reduced at a higher potential (Li / Li ⁺ ) than the eutectic mixture electrolyte to form a passivating film, (b) has an oxidation potential higher than the anode potential to consume the overcharge current A eutectic mixture electrolyte, characterized in that it further comprises a second compound, or both. The eutectic mixture electrolyte of claim 1, which is in the form of a liquid electrolyte. The eutectic mixture electrolyte of claim 1, which is in the form of a gel polymer electrolyte. As a method for producing a eutectic mixture electrolyte according to any one of claims 1 to 8, (a) mixing two or more amide group-containing compounds to form a eutectic mixture; And (b) dissolving an ionizable lithium salt in the eutectic mixture; Method for producing a eutectic mixture electrolyte comprising a. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, The secondary battery comprises the eutectic mixture electrolyte according to any one of claims 1 to 8. The secondary battery of claim 10, wherein the secondary battery is a lithium secondary battery.

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