KR20230139901A - Method of manufacturing vinyl ethyele carbonate compounds, and a electrolyte for lithium secondary battery and a lithium secondary battery including the same - Google Patents

Abstract

According to embodiments of the present invention, after removing alcohol from the reaction mixture of 3,4-butenediol and dialkyl carbonate, dialkyl carbonate is further added and reacted again to obtain vinylethylene carbonate. The above-described manufacturing method can have excellent reaction efficiency and yield, and can improve processability and economic feasibility. Additionally, an electrolyte for a lithium secondary battery containing high purity vinylethylene carbonate can be provided by the above-described manufacturing method. Therefore, a lithium secondary battery containing the above-described electrolyte for a lithium secondary battery and having excellent performance and stability can be provided.

Description

Method for producing vinyl ethylene carbonate, electrolyte for lithium secondary battery, and lithium secondary battery containing same

The present invention relates to a method for producing vinylethylene carbonate, an electrolyte for a lithium secondary battery containing an electrolyte additive prepared therefrom, and a lithium secondary battery containing the same. More specifically, it relates to a method for producing vinylethylene carbonate using a heterogeneous compound, an electrolyte for a lithium secondary battery containing an electrolyte additive prepared therefrom, and a lithium secondary battery containing the same.

The electrolyte solution of a lithium secondary battery may include a lithium salt, a solvent, and additives, and a non-aqueous organic electrolyte solution using an organic solvent as a solvent may be used. Recently, as miniaturization and integration of lithium secondary batteries are required, research on lithium secondary batteries that have high performance and can provide stable power supply is being actively conducted.

The electrolyte used in lithium secondary batteries may react with the negative electrode and positive electrode due to the charging and discharging behavior of the secondary battery. In this case, the electrolyte is consumed and depleted or the negative electrode and positive electrode are oxidized and deformed, reducing the capacity and lifespan of the secondary battery. It can be. Therefore, the electrolyte of a lithium secondary battery is required to have high ionic conductivity and high stability, and for this purpose, various additives can be used in the electrolyte.

For example, carbonate-based compounds can be used as film-forming additives in electrolytes for lithium secondary batteries. An example of a carbonate-based compound is vinylethylene carbonate (VEC). When applied to lithium secondary batteries, vinylethylene carbonate can be used as a film-forming additive with high reaction activity. For example, as vinylethylene carbonate contains a C=C double bond, it can have a high boiling point and a high dielectric constant, and the electrochemical stability of a lithium secondary battery can be improved.

However, vinylethylene carbonate requires high costs and a long process time to manufacture, and can provide low yield compared to the raw materials used, resulting in low economic feasibility and processability.

For example, Korean Patent Publication No. 10-2008-0086638 discloses an electrolyte for lithium secondary batteries containing a carbonate-based compound.

Korean Patent Publication No. 10-2008-0086638

One object of the present invention is to provide a method for producing high purity vinylethylene carbonate.

One object of the present invention is to provide an electrolyte for a lithium secondary battery containing vinylethylene carbonate prepared by the above-described manufacturing method.

One object of the present invention is to provide a lithium secondary battery containing the above-described electrolyte for a lithium secondary battery.

The method for producing vinylethylene carbonate according to exemplary embodiments includes reacting a premixture containing 3,4-butenediol and dialkyl carbonate to prepare a reaction mixture containing vinylethylene carbonate and alcohol, the reaction mixture It may include performing a re-reaction step to form a product mixture, and separating vinylethylene carbonate from the product mixture.

The re-reaction step includes a first reaction step of removing alcohol from the reaction mixture, a second reaction step of preparing a preliminary product mixture by adding a dialkyl carbonate to the reaction mixture from which the alcohol has been removed, and reacting the preliminary product mixture. It may include a third reaction step of preparing a product mixture.

According to exemplary embodiments, the content of dialkyl carbonate in the premix may be 50 to 200 parts by weight based on 100 parts by weight of 3,4-butenediol included in the premix.

According to exemplary embodiments, the dialkyl carbonate may include at least one of dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate.

According to exemplary embodiments, the premix may further include a basic catalyst.

In some embodiments, the basic catalyst may include an alkali metal base or an alkaline earth metal base.

In some embodiments, the content of the basic catalyst in the preliminary mixture may be 0.1 to 10 parts by weight based on 100 parts by weight of 3,4-butenediol included in the preliminary mixture.

According to exemplary embodiments, the re-reaction step may be performed continuously two or more times. For example, the first reaction step, the second reaction step, and the third reaction step may be performed as one cycle and two or more cycles may be performed continuously.

In some embodiments, the first reaction step may be performed at a temperature below the boiling point of vinylethylene carbonate.

In some embodiments, the amount of dialkyl carbonate added in the second reaction step may be 50 to 200 parts by weight based on 100 parts by weight of 3,4-butenediol included in the preliminary mixture.

According to exemplary embodiments, reacting the preliminary mixture and reacting the preliminary mixture may each be performed at a temperature of 50°C to 100°C.

According to exemplary embodiments, the step of separating vinylethylene carbonate from the product mixture includes a first separation step performed at a temperature below the boiling point of vinylethylene carbonate, and a second separation step performed at a temperature above the boiling point of vinylethylene carbonate. May include steps.

In some embodiments, alcohol and dialkyl carbonate may be removed from the product mixture through the first separation step.

In some embodiments, vinylethylene carbonate may be obtained through the second separation step.

Electrolytes for lithium secondary batteries according to exemplary embodiments may include vinylethylene carbonate prepared by the above-described manufacturing method.

Lithium secondary batteries according to exemplary embodiments may include a positive electrode, a negative electrode disposed opposite to the positive electrode, and the above-described electrolyte for a lithium secondary battery that impregnates the positive electrode and the negative electrode.

The method for producing a vinylethylene carbonate compound according to exemplary embodiments may be performed by reacting 3,4-butenediol and dialkyl carbonate. In some embodiments, the production method may be carried out in the presence of a basic catalyst. Therefore, vinylethylene carbonate can be manufactured through a single process without any additional processes.

Additionally, during the manufacturing process, a re-reaction step may be performed in which alcohol is removed and dimethyl carbonate is added again for reaction. In this case, the reaction of 3,4-butenediol and dialkyl carbonate can be promoted while suppressing the decomposition of vinylethylene carbonate by alcohol. Therefore, the conversion rate to vinylethylene carbonate can be improved, and high purity vinylethylene carbonate can be obtained.

Additionally, the re-reaction step may be performed two or more times. Therefore, the reaction rate of 3,4-butenediol can be further improved, and decomposition of vinylethylene carbonate can be suppressed, thereby improving the yield and purity of the process.

Additionally, the resulting mixture containing vinylethylene carbonate can be separated and purified through reduced pressure distillation. Therefore, high purity vinylethylene carbonate can be obtained through a simple and single process, and the economic efficiency and processability of the manufacturing process can be excellent.

1 and 2 are schematic flowcharts illustrating a method for producing vinylethylene carbonate according to exemplary embodiments.

The method for producing vinyl ethylene carbonate (VEC) according to embodiments of the present invention is to prepare alcohol in a reaction mixture of 3,4-butenediol and dialkyl carbonate. After removing, it can be performed by additionally adding dialkyl carbonate and reacting. Accordingly, the productivity, yield, and purity of vinylethylene carbonate can be improved.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings. However, the following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention along with the contents of the above-described invention, so the present invention is described in such drawings. It should not be interpreted as limited to the specifics.

<Method for producing vinyl ethylene carbonate>

1 is a schematic flow chart showing a method for producing vinylethylene carbonate according to exemplary embodiments.

Referring to Figure 1, a preliminary mixture can be prepared by mixing 3,4-butenediol and dialkyl carbonate (for example, step S10).

3,4-Butenediol may be a compound represented by the following formula (1).

[Formula 1]

Afterwards, the preliminary mixture can be reacted to prepare a reaction mixture containing vinylethylene carbonate and alcohol (for example, step S20). For example, the vinylethylene carbonate and alcohol may be reaction products of 3,4-butenediol and dialkyl carbonate.

According to exemplary embodiments, the dialkyl carbonate may have an alkyl group having 1 to 5 carbon atoms. For example, the dialkyl carbonate may include a compound represented by the following formula (2).

[Formula 2]

In Formula 2, R ₁ and R ₂ may each independently be an alkyl group having 1 to 5 carbon atoms.

For example, in step S20, the reaction shown in Scheme 1 below may proceed.

[Scheme 1]

In some embodiments, the dialkyl carbonate may include at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. In this case, the reactivity of 3,4-butenediol and dialkyl carbonate can be improved, and the productivity and yield of vinylethylene carbonate can be increased. Additionally, since the alcohol formed therefrom has a low boiling point, the alcohol can be easily removed by distillation and heating.

Preferably, the dialkyl carbonate may be dimethyl carbonate.

According to exemplary embodiments, the content of dialkyl carbonate in the premix may be 50 to 200 parts by weight based on 100 parts by weight of 3,4-butenediol included in the premix.

If the content of the dialkyl carbonate is less than 50 parts by weight based on 100 parts by weight of 3,4-butenediol, the reactivity of 3,4-butenediol and dialkyl carbonate may decrease, and the production of vinylethylene carbonate may decrease. You can.

If the content of the dialkyl carbonate is more than 200 parts by weight based on 200 parts by weight of 3,4-butenediol, the content of dialkyl carbonate remaining without participating in the reaction may increase, thereby lowering the purity of vinylethylene carbonate, The economics of the manufacturing process may be deteriorated.

Preferably, the content of dialkyl carbonate in the premix may be 80 to 150 parts by weight based on 100 parts by weight of 3,4-butenediol contained in the premix.

The alcohol may be a by-product produced by the reaction of 3,4-butenediol and dialkyl carbonate. For example, when the dialkyl carbonate is dimethyl carbonate, the alcohol may be methanol. For example, when the dialkyl carbonate is diethyl carbonate, the alcohol may be ethanol.

In one embodiment, the boiling point of the alcohol may be lower than the boiling point of vinylethylene carbonate. For example, a dialkyl carbonate that can form an alcohol with a boiling point lower than that of vinylethylene carbonate may be used in the manufacturing process. Therefore, alcohol, a low boiling point substance, can be selectively removed without loss of vinylethylene carbonate.

In one embodiment, the premix may further include a basic catalyst. For example, a preliminary mixture can be prepared by adding 3,4-butenediol, dialkyl carbonate, and a basic catalyst into a reactor and mixing them.

In one embodiment, the basic catalyst may include an alkali metal base or an alkaline earth metal base. Preferably, the basic catalyst may include an alkali metal base. Alkali metal bases have high activity, so the reaction rate and conversion rate to vinylethylene carbonate can be improved.

For example, it may include at least one of the basic catalysts NaOH, KOH, Na ₂ CO ₃ and K ₂ CO ₃ .

In some embodiments, the content of the basic catalyst in the preliminary mixture may be 0.1 to 10 parts by weight based on 100 parts by weight of 3,4-butenediol included in the preliminary mixture.

If the content of the basic catalyst exceeds 10 parts by weight, a side reaction may occur and the yield of vinylethylene carbonate may decrease. For example, an excess of basic catalyst can react with moisture to form hydroxide, and the hydroxide produced from base can react with vinylethylene carbonate to decompose vinylethylene carbonate.

If the content of the basic catalyst is less than 0.1 parts by weight, the reaction activity of 3,4-butenediol and dialkyl carbonate may be reduced, the reaction rate may be lowered, and the yield of vinylethylene carbonate may be reduced.

Preferably, the content of the basic catalyst in the preliminary mixture may be 1 to 8 parts by weight based on 100 parts by weight of 3,4-butenediol contained in the preliminary mixture.

According to exemplary embodiments, reacting the premix may be performed at a temperature of 50°C to 100°C. Within the above range, the reactivity of 3,4-butenediol and dialkyl carbonate can be improved, and the reaction rate can be excellent. Therefore, the yield and productivity of vinylethylene carbonate can be increased.

Preferably, the step of reacting the premix may be performed at a temperature of 70°C to 90°C.

The reaction time of the premix may be 0.5 to 2 hours. Within the above range, the forward reaction of 3,4-butenediol and dialkyl carbonate can be promoted while preventing decomposition of vinylethylene carbonate by alcohol, a reaction by-product.

In one embodiment, the method for producing vinylethylene carbonate may be performed batchwise or continuously. For example, the 3,4-butenediol, dialkyl carbonate, and basic catalyst can be added to the reactor, and then the added reactants can be mixed and heated to react. The reactor may be a batch reactor, continuous reactor, or semi-batch reactor. Preferably, a batch reactor can be used as the reactor. In this case, reactivity and reaction speed can be improved, and the reaction conversion rate to vinylethylene carbonate can be higher.

According to exemplary embodiments, a product mixture may be prepared by performing a re-reaction step on the reaction mixture (eg, step S30).

Through the re-reaction step, alcohol can be removed from the reaction mixture, and the reaction conversion rate of 3,4-butenediol to vinylethylene carbonate can be increased.

Figure 2 is a schematic flow chart showing a re-reaction step (eg, step S30) in the method for producing vinylethylene carbonate according to exemplary embodiments.

Referring to FIG. 2, the re-reaction step includes a first reaction step (e.g., step S31) of removing alcohol from the reaction mixture, and adding dialkyl carbonate to the reaction mixture from which the alcohol has been removed to prepare a preliminary product mixture. It may include a second reaction step (eg, step S32), and a third reaction step (eg, step S33) of reacting the preliminary product mixture to prepare a product mixture.

In some embodiments, the first reaction step of removing the alcohol from the reaction mixture can be performed at a temperature below the boiling point of vinylethylene carbonate. For example, since alcohol has a lower boiling point than vinylethylene carbonate, alcohol can be selectively separated through the first reaction step.

The term “boiling point” used in this specification refers to the temperature at which the vapor pressure of the compound is in equilibrium with the surrounding atmospheric pressure or pressure. For example, the boiling point of a specific compound at a specific stage may be the temperature at which the vapor pressure of the compound is in equilibrium with the atmospheric pressure or pressure of the reactor at that stage.

Therefore, no alcohol or only a trace amount of alcohol may be present in the reaction mixture. In this case, the reverse reaction between alcohol and vinylethylene carbonate, for example, the decomposition reaction of vinylethylene carbonate by alcohol can be suppressed, and the purity and production amount of vinylethylene carbonate can be increased.

In some embodiments, the first reaction step may be performed under reduced pressure conditions. For example, alcohol can be removed from the reaction mixture by a reduced pressure distillation process.

In one embodiment, the first reaction step may be performed at a temperature of 20°C to 100°C. Within the above conditions, alcohol, a low-boiling substance, can be selectively removed from the reaction mixture, and vinylethylene carbonate can be prevented from being removed from the reaction mixture or thermally decomposed.

In one embodiment, dialkyl carbonate remaining in the reaction mixture may be removed through the first reaction step. For example, since the alcohol and dialkyl carbonate form an azeotropic mixture with a low boiling point, the alcohol and dialkyl carbonate can be removed together through the first reaction step.

In some embodiments, the content of dialkyl carbonate added in the second reaction step may be 50 to 200 parts by weight, preferably 80 parts by weight, based on 100 parts by weight of 3,4-butenediol contained in the preliminary mixture. It may be from 150 parts by weight to 150 parts by weight.

Within the above range, the reaction conversion rate to vinylethylene carbonate can be excellent, and the purity of the obtained vinylethylene carbonate can be increased.

Through the third reaction step, vinylethylene carbonate can be formed from 3,4-butenediol and dialkyl carbonate. In one embodiment, alcohol may be formed as a reaction by-product of the third reaction step.

In some embodiments, the third reaction step of reacting the pre-produced mixture may be performed at a temperature of 50°C to 100°C, and preferably may be performed at a temperature of 70°C to 90°C.

Within the above range, the reactivity of 3,4-butenediol and dialkyl carbonate can be improved, and the reaction rate can be excellent. Therefore, the yield and productivity of vinylethylene carbonate can be increased.

In some embodiments, the reaction time of the pre-produced mixture may be 0.5 to 2 hours.

According to exemplary embodiments, the re-reaction step may be performed repeatedly two or more times.

For example, the first reaction step, the second reaction step, and the third reaction step may be performed as one cycle, and two or more cycles may be performed. In this case, the product mixture prepared in the third reaction step of the first cycle can be used as a reaction mixture in the first reaction step of the second cycle that proceeds thereafter.

As the reaction step of 3,4-butenediol and dialkyl carbonate is repeatedly performed two or more times, the reaction conversion rate of 3,4-butenediol and dialkyl carbonate to vinylethylene carbonate can be increased, and the efficiency of the manufacturing process can be increased. and yield can be increased.

In addition, the content of alcohol in the mixture may be lowered and the content of dialkyl carbonate may be increased by the repeatedly performed re-reaction step. Therefore, the forward reaction between 3,4-butenediol and dialkyl carbonate can be promoted, and the reverse reaction between vinylethylene carbonate and alcohol can be suppressed, thereby increasing the purity of vinylethylene carbonate finally obtained.

In some embodiments, the re-reaction step may be performed 1 to 6 times, and preferably 2 times. For example, the first reaction step, the second reaction step, and the third reaction step may be performed as one cycle, and 1 to 6 cycles may be performed, and preferably, 2 cycles may be performed.

Within the above range, the reaction conversion rate of 3,4-butenediol and the purity of the obtained vinylethylene carbonate can be improved, and process costs can be reduced.

Referring to FIG. 1, vinylethylene carbonate can be obtained by selectively separating vinylethylene carbonate from the product mixture (for example, step S40).

For example, vinylethylene carbonate can be separated by heating and distilling the resulting mixture. The heating and distillation steps of the product mixture may be performed stepwise.

In some embodiments, the heating and distillation of the product mixture includes a first separation step of removing alcohol and dialkyl carbonate from the product mixture, and a second step of obtaining vinylethylene carbonate from the product mixture from which the alcohol and dialkyl carbonate have been removed. 2 May include a separation step.

In one embodiment, the first separation step may be performed at a temperature below the boiling point of vinylethylene carbonate. Accordingly, alcohol and dialkyl carbonate remaining in the resulting mixture can be removed.

For example, since the alcohol and dialkyl carbonate form a low-boiling azeotropic mixture, only the alcohol and dialkyl carbonate can be selectively distilled and removed without loss of vinylethylene carbonate through the first separation step.

In one embodiment, the second separation step may be performed at a temperature higher than the boiling point of vinylethylene carbonate. For example, as the second separation step is performed at a temperature above the boiling point of vinylethylene carbonate, vinylethylene carbonate may be evaporated and extracted.

In some embodiments, the first separation step and the second separation step may be performed under reduced pressure conditions. For example, the first separation step and the second separation step may be performed by a reduced pressure heating distillation process.

In this case, the boiling points of reactants and products contained in the product mixture may be lowered. The removal process of alcohol and dialkyl carbonate, and the extraction process of vinylethylene carbonate can be performed at a relatively low temperature, and process time and efficiency can be improved.

In some embodiments, the first separation step and the second separation step may be performed at a temperature of 20°C to 100°C. Within the above conditions, low-boiling substances such as water, alcohol, and dialkyl carbonate can be selectively removed from the resulting mixture, and vinylethylene carbonate can be prevented from being thermally decomposed or removed.

<Lithium secondary battery>

The electrolyte for a lithium secondary battery (hereinafter abbreviated as electrolyte) according to exemplary embodiments may include an organic solvent, a lithium salt, and vinylethylene carbonate prepared by the above-described production method as an electrolyte additive. The electrolyte for the lithium secondary battery may further include other additives to improve lifespan, output characteristics, and high-temperature performance.

The organic solvent provides sufficient solubility for lithium salt, 3,4-butenediol and/or additives, and may include an organic compound that is not reactive in a lithium secondary battery. For example, the organic solvent may have a salt dissociation degree of about 0.5M or more, preferably 2M or more, with respect to the lithium salt.

If the solubility of the lithium salt in the organic solvent is low, the viscosity of the electrolyte may increase and battery performance may deteriorate. Additionally, the lithium salt may not dissolve uniformly and remain in salt form, thereby increasing resistance. In this case, side reactions may occur due to the remaining lithium salt, and detachment and polarization of the electrode may occur.

According to exemplary embodiments, the organic solvent may include a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, or an aprotic solvent. These may be used alone or in combination of two or more.

Examples of the carbonate-based solvent include linear carbonate-based solvents such as dimethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, diethyl carbonate, and dipropyl carbonate, propylene carbonate, ethylene carbonate, and fluoroethylene carbonate. , cyclic carbonate-based solvents such as butylene carbonate, pentylene carbonate, vinylene carbonate, and vinylethylene carbonate.

Examples of the ester solvent include methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methyl propionate, ethyl propionate, gamma-butyrolactone, decanolide, valerolactone, Mevalonolactone, caprolactone, etc. can be mentioned.

Examples of the ether-based organic solvent include dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), and dimethoxy ethane. ), 2-methyltetrahydrofuran, tetrahydrofuran, etc.

An example of the ketone solvent may be cyclohexanone. Examples of the alcohol-based solvent include ethyl alcohol and isopropyl alcohol.

The aprotic solvent may include a nitrile-based solvent, an amide-based solvent such as dimethylformamide, a dioxolane-based solvent such as 1,3-dioxolane, and a sulfolane-based solvent.

Preferably, a carbonate-based solvent may be used as the organic solvent. For example, the organic solvent may include a mixed solvent of a linear carbonate-based solvent and a cyclic carbonate-based solvent.

According to exemplary embodiments, the lithium salt may include a compound ^represented by Li ⁺

Examples of anions (X ^- ) of the lithium salt include F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , SbF ₆ ^- , AsF 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 ^- , (CF ₃ CF ₂ SO ₂ ) ₂ N ^- or PO ₂ F ₂ ^- may be mentioned. The anion may be present alone or in combination of two or more types. Preferably, the lithium salt may include lithium hexafluorophosphate (LiPF ₆ ).

In some embodiments, the lithium salt may be included at a concentration of about 0.5M to 2.0M, preferably about 0.8M to 1.5M, relative to the organic solvent. If the concentration of lithium salt is less than 0.5M, the ionic conductivity of the electrolyte may decrease and electrochemical performance may deteriorate. If the concentration of lithium salt exceeds 2.0M, the viscosity of the electrolyte may increase and the mobility of lithium ions may decrease. Within the above range, the transfer of lithium ions and/or electrons can be promoted when charging and discharging a lithium secondary battery, thereby improving charging and discharging speed and capacity.

As the electrolyte for lithium secondary batteries includes vinylethylene carbonate as an additive, the output characteristics of lithium secondary batteries can be improved. Additionally, the electrochemical stability of the electrolyte can be improved and irreversible decomposition can be prevented, thereby improving the lifespan and cycle characteristics of the lithium secondary battery.

For example, vinylethylene carbonate has a relatively low reduction potential and can cause an electrochemical reduction reaction on the cathode surface ahead of the electrolyte. Therefore, a solid electrolyte interface (SEI) having a stable and dense structure can be formed on the surface of the graphite cathode.

The content of vinylethylene carbonate may be 0.01 to 10% by weight, preferably 0.01 to 5% by weight, and more preferably 0.1 to 1% by weight, based on the total weight of electrolyte for a lithium secondary battery. Within the above range, electrolyte depletion, gas generation, and charge/discharge capacity reduction due to side reactions between the electrolyte and the cathode can be prevented. Therefore, the durability and long-term life characteristics of the lithium secondary battery can be improved.

In some embodiments, the electrolyte may further include additives such as cyclic carbonate-based compounds, sultone-based compounds, cyclic sulfate-based compounds, linear sulfate-based compounds, aromatic phosphate-based compounds, and/or lithium salt-based compounds. .

The additive can form a stable SEI film on the surface of the electrode. Accordingly, the thickness of the secondary battery can be kept constant and electrolyte leakage and depletion can be prevented. In this case, the resistance of the secondary battery can be reduced and an increase in irreversible capacity can be prevented.

Examples of the cyclic carbonate-based compound include vinylene carbonate, fluoroethylene carbonate, or tetrahydrofuro[3,2-b]furan-2,5-dione. -b]furan-2,5-dione), etc.

Examples of the sultone-based compounds include 1,3-propane sultone, 1,3-propene-1,3-sultone, 1, Examples include 4-butane sultone (1,4-butane sultone).

Examples of the cyclic sulfate-based compounds include ethylene sulfate, 1,3-propanediol cyclic sulfate, and 4,4'-bi-1,3,2-di. Oxathiolane, 2,2,2',2'-tetroxide (4,4'-Bi-1,3,2-dioxathiolane, 2,2,2',2'-tetroxide), 2,4,8, 10-Tetraoxa-3,9-dithiaspiro[5,5]undecane (2,4,8,10-Tetraoxa-3,9-dithiaspiro[5.5]undecane), etc.

Examples of the linear sulfate-based compounds include bis(triethylsilyl) sulfate, bis(trimethylsilyl) sulfate, trimethylsilyl ethenesulfonate, and triethylsilyl. Ethenesulfonate (triethylsilyl ethenesulfonate), etc. may be mentioned.

An example of the aromatic phosphate-based compound may be bisphenol A bis (diphenyl phosphate).

The lithium salt-based compound is a compound different from the lithium salt contained in the electrolyte, for example, lithium difluorophosphate, lithium-bis(oxalato)borate, lithium bis. (Lithium bis(fluorosulfonyl)imide), Lithium Difluoro(oxalato)borate, Lithium tetrafluoro oxalate phosphate, Lithium Lithium difluoro bis(oxalato) phosphate, etc. may be mentioned.

The content of the additive may be 0.1 to 10% by weight, preferably 0.1 to 5% by weight, based on the total weight of the electrolyte. If the content of the additive is less than 0.1% by weight, the stability of the film formed on the electrode surface may decrease and high-temperature battery characteristics may deteriorate. If the content of the additive exceeds 10% by weight, the excess additives may not be sufficiently dissolved in the electrolyte and may exist in a precipitated state. In this case, the resistance of the electrolyte may increase and the output characteristics and life characteristics of the secondary battery may deteriorate. there is.

Lithium secondary batteries according to exemplary embodiments may include a positive electrode, a negative electrode, and the above-described electrolyte for a lithium secondary battery that impregnates the positive electrode and the negative electrode.

The positive electrode may include a positive electrode active material layer formed by applying the positive electrode active material to the positive electrode current collector. The positive electrode active material may include a compound capable of reversibly inserting and deintercalating lithium ions.

In exemplary embodiments, the positive electrode active material may include lithium-transition metal oxide. For example, the lithium-transition metal oxide includes nickel (Ni) and may further include at least one of cobalt (Co) or manganese (Mn).

A slurry can be prepared by mixing and stirring the positive electrode active material with a positive electrode binder, a conductive material, and/or a dispersant in a solvent. After coating the slurry on a positive electrode current collector, the positive electrode can be manufactured by compressing and drying.

The positive electrode current collector may include, for example, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably includes aluminum or an aluminum alloy.

The binder for the positive electrode is, for example, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile, polymethyl It may include an organic binder such as methacrylate (polymethylmethacrylate) or an aqueous binder such as styrene-butadiene rubber (SBR), and may be used with a thickener such as carboxymethyl cellulose (CMC).

The conductive material may be included to promote electron transfer between active material particles. For example, the conductive material may be a carbon-based conductive material such as graphite, carbon black, graphene, or carbon nanotubes, and/or a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO ₃ , or LaSrMnO ₃ It may include a metal-based conductive material including the like.

The negative electrode may include a negative electrode current collector and a negative electrode active material layer formed by coating the negative electrode active material on the negative electrode current collector.

According to exemplary embodiments, the negative electrode active material may include amorphous carbon such as hard carbon and soft carbon, crystalline carbon such as natural graphite and artificial graphite, a silicon (Si)-based compound, lithium metal, or a lithium alloy. . In some embodiments, silicon carbide (SiC) or silicon-carbon particles including a carbon core and a silicon coating layer may be used as the negative electrode active material.

The negative electrode current collector may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably includes copper or a copper alloy.

In some embodiments, a slurry may be prepared by mixing and stirring the negative electrode active material with a binder, a conductive material, and/or a dispersant in a solvent. After coating the slurry on a negative electrode current collector, the negative electrode can be manufactured by compressing and drying. Materials that are substantially the same as or similar to the materials described above may be used as the conductive material.

According to exemplary embodiments, materials substantially the same as or similar to the materials described above may be used as the binder for the negative electrode. For example, polyvinylidene fluoride (PVdF) or styrene-butadiene rubber (SBR) can be used as a binder for the negative electrode. In some embodiments, a thickener such as carboxymethyl cellulose (CMC) may be used in conjunction with the binder.

A separator may be interposed between the anode and the cathode. The separator may include a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. The separator may include a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc.

According to exemplary embodiments, an electrode cell is defined by an anode, a cathode, and a separator, and a plurality of electrode cells may be stacked to form an electrode assembly in the form of, for example, a jelly roll. For example, the electrode assembly can be formed through winding, lamination, folding, etc. of the separator.

The electrode assembly may be accommodated together with the above-described electrolyte for a lithium secondary battery in a case to define a lithium secondary battery.

Electrode tabs may be formed from the positive electrode current collector and negative electrode current collector belonging to each electrode cell and extend to one side of the case. The electrode tabs may be fused together with the one side of the case to form an electrode lead that extends or is exposed to the outside of the case.

Lithium secondary batteries can be manufactured, for example, in a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

Hereinafter, experimental examples including specific examples and comparative examples are presented to aid understanding of the present invention, but these are only illustrative of the present invention and do not limit the scope of the appended claims, and do not limit the scope and technical idea of the present invention. It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible within the scope, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

Examples and Comparative Examples: Preparation of vinylethylene carbonate

(1) Example 1

1) Preliminary reaction step: 100 g of 3,4-butenediol, 100 g of dimethyl carbonate, and 5 g of K ₂ CO ₃ were added to a 500 mL reactor and mixed to prepare a preliminary mixture. Afterwards, the preliminary mixture was reacted under heating and reflux conditions at a temperature of 80°C for 1 hour to obtain a reaction solution.

2) Reaction step: The reaction solution was cooled to room temperature and vacuum distilled to remove dimethyl carbonate and methanol. Afterwards, 100 g of dimethyl carbonate was added again, and the mixture was reacted by heating and refluxing at a temperature of 80° C. for 1 hour to prepare a product mixture.

3) Obtaining steps: The resulting mixture was cooled to room temperature and distilled under reduced pressure at room temperature to remove dimethyl carbonate and methanol. Afterwards, the remaining mixture was heated and distilled under reduced pressure to obtain vinylethylene carbonate (115 g, yield 88.5%).

(2) Example 2

Vinylethylene carbonate (112 g, yield 86.1%) was obtained in the same manner as in Example 1, except that the re-reaction step in Example 1 was repeated twice.

(3) Example 3

Vinylethylene carbonate (110 g, yield 84.6%) was obtained in the same manner as in Example 1, except that the re-reaction step in Example 1 was repeated three times.

(4) Comparative Example 1

100 g of 3,4-butenediol, 100 g of dimethyl carbonate, and 5 g of K ₂ CO ₃ were added to a 500 mL reactor and mixed to prepare a preliminary mixture. Afterwards, the premix was reacted under heating and reflux conditions at a temperature of 80°C for 1 hour to obtain a product mixture.

The resulting mixture was cooled to room temperature and distilled under reduced pressure at room temperature to remove dimethyl carbonate and methanol. Afterwards, the remaining mixture was heated and distilled under reduced pressure to obtain vinylethylene carbonate (118 g, yield 90.7%).

(5) Comparative Example 2

100 g of 3,4-butenediol, 1,000 g of dimethyl carbonate, and 5 g of K ₂ CO ₃ were added to a 2L reactor and mixed to prepare a preliminary mixture. Afterwards, the premix was reacted under heating and reflux conditions at a temperature of 80°C for 1 hour to obtain a product mixture.

The resulting mixture was cooled to room temperature and distilled under reduced pressure at room temperature to remove dimethyl carbonate and methanol. Afterwards, the remaining mixture was heated and distilled under reduced pressure to obtain vinylethylene carbonate (120 g, yield 92.3%).

Experimental example: Purity evaluation of vinylethylene carbonate

The purity of vinylethylene carbonate (VEC) obtained in the above examples and comparative examples was measured using gas chromatography (GC).

The purity of vinylethylene carbonate was analyzed by gas chromatography to measure the ratio of 3,4-butenediol and vinylethylene carbonate, and then calculated as a percentage of the measured vinylethylene carbonate ratio.

The evaluation results are shown in Table 1 below.

division GC analysis results VEC's
Purity (%) 3,4-butenediol
ratio VEC's
ratio Example 1 0.5 99.5 99.5 Example 2 0.1 99.9 99.9 Example 3 0 100 100 Comparative Example 1 8 92 92 Comparative Example 2 1.8 98.2 98.2

Referring to Table 1, in the case of the method for producing vinylethylene carbonate according to the exemplary embodiments, vinylethylene carbonate of overall high purity was obtained.

In addition, in the case of Examples 2 and 3 in which the re-reaction step was repeatedly performed two or more times, it can be confirmed that the purity of the obtained vinylethylene carbonate was further improved.

However, in the case of comparative examples in which the re-reaction step was not performed, it can be confirmed that the purity of the obtained vinylethylene carbonate was low as the decomposition reaction of vinylethylene carbonate by methanol occurred.

In the case of Comparative Example 2, in which the amount of dimethyl carbonate was increased 10 times compared to Example 1, it can be confirmed that the purity is relatively low as the re-reaction step is not performed.

It can be confirmed that when the re-reaction step is performed, vinylethylene carbonate of high purity and yield can be obtained even when a small amount of dimethyl carbonate is used. Therefore, the economic efficiency and processability of the vinylethylene carbonate manufacturing process can be improved.

Claims (15)

Preparing a reaction mixture containing vinylethylene carbonate and alcohol by reacting a premixture containing 3,4-butenediol and dialkyl carbonate;
A first reaction step of removing alcohol from the reaction mixture;
A second reaction step of preparing a preliminary mixture by adding dialkyl carbonate to the reaction mixture from which the alcohol has been removed;
A third reaction step of reacting the preliminary product mixture to prepare the product mixture; and
comprising the step of separating vinylethylene carbonate from the product mixture,
A method for producing vinylethylene carbonate, wherein the first reaction step, the second reaction step, and the third reaction step are performed as one cycle and one or more cycles are performed continuously.
The method of claim 1, wherein the content of dialkyl carbonate in the premix is 50 to 200 parts by weight based on 100 parts by weight of 3,4-butenediol contained in the premix.
The method of producing vinylethylene carbonate according to claim 1, wherein the dialkyl carbonate includes at least one of dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate.
The method of producing vinylethylene carbonate according to claim 1, wherein the premix further includes a basic catalyst.
The method of claim 4, wherein the basic catalyst includes an alkali metal base or an alkaline earth metal base.
The method of claim 4, wherein the content of the basic catalyst in the premix is 0.1 to 10 parts by weight based on 100 parts by weight of 3,4-butenediol contained in the premix.
The method of producing vinylethylene carbonate according to claim 1, wherein the first reaction step, the second reaction step, and the third reaction step are performed as one cycle and two or more cycles are performed continuously.
The method of producing vinylethylene carbonate according to claim 1, wherein the first reaction step is performed at a temperature below the boiling point of vinylethylene carbonate.
The method of claim 1, wherein the content of the dialkyl carbonate added in the second reaction step is 50 parts by weight to 200 parts by weight based on 100 parts by weight of 3,4-butenediol contained in the preliminary mixture.
The method of claim 1, wherein the reacting the premix and the reacting the preproduced mixture are each performed at a temperature of 50°C to 100°C.
The method of claim 1, wherein the step of separating vinylethylene carbonate from the product mixture comprises:
A first separation step of removing alcohol and dialkyl carbonate from the product mixture; and
A method for producing vinylethylene carbonate, comprising a second separation step of obtaining vinylethylene carbonate from the product mixture from which the alcohol and dialkyl carbonate have been removed.
The method of claim 11, wherein the first separation step is performed at a temperature below the boiling point of vinylethylene carbonate.
The method of claim 11, wherein the second separation step is performed at a temperature higher than the boiling point of vinylethylene carbonate.
An electrolyte for a lithium secondary battery comprising vinylethylene carbonate produced by the production method of claim 1.
anode;
a cathode disposed opposite to the anode; and
A lithium secondary battery comprising the electrolyte for a lithium secondary battery of claim 14, which impregnates the positive electrode and the negative electrode.