KR20040021393A - An electrolyte for a lithium battery and a lithium battery comprising the same - Google Patents

Abstract

PURPOSE: An electrolyte for a lithium battery and a lithium battery containing the electrolyte are provided, to improve the swelling property and the safety of a lithium battery. CONSTITUTION: The electrolyte comprises a nonaqueous organic solvent; a lithium salt; and 0.0001-10 wt% of a thiol compound represented by R1SH, wherein R1 is a saturated or unsaturated hydrocarbon group of C1-C30, a saturated or unsaturated hydrocarbon group of C1-C30 containing hetero atoms, or a group comprising ether, imide, ethanol or carboxylic group. Preferably the nonaqueous organic solvent is at least one selected from the group consisting of carbonates, esters, ethers and ketones; and the lithium salt is at least one selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO4, LiAlCl4, LiGaCl4, LiN(CxF2x+1SO2)(CyF2y+1SO2) (wherein x and y are a natural number), LiNO3, LiCl and LiI.

Description

TECHNICAL FIELD The electrolyte for a lithium battery, and a lithium battery including the same, include: A ELITROLYTE FOR A LITHIUM BATTERY AND A LITHIUM BATTERY COMPRISING THE SAME

[Industrial use]

The present invention relates to a lithium battery electrolyte and a lithium battery including the same, and more particularly, to a lithium battery electrolyte having excellent swelling properties and safety and a lithium battery including the same.

[Prior art]

Recently, with the trend toward miniaturization and light weight of portable electronic devices, the need for high performance and high capacity of batteries used as power sources for these devices is increasing. Lithium secondary batteries, which are commercially available and currently used, correspond to the heart of the digital era, which is rapidly being applied to portable phones, notebook computers, camcorders, and the like, which have an average discharge potential of 3.7V, that is, 4C.

In addition to improving battery capacity and performance characteristics, studies are being actively conducted to improve safety such as overcharging characteristics. When the battery is overcharged, depending on the state of charge, lithium is excessively precipitated at the positive electrode, lithium is excessively inserted at the negative electrode, and the positive electrode and negative electrode are thermally unstable, causing rapid exothermic reactions such as decomposition of the organic solvent in the electrolyte and thermal runaway. Occurs, a serious problem occurs in the safety of the battery.

In order to solve this problem, a method of adding an aromatic compound as a redox shuttle additive in an electrolyte has been used. For example, U.S. Patent No. 5,709,968 adds a benzene compound such as 2,4-difluoroanisole to prevent overcharge currents and the resulting thermal runaway phenomenon. It is starting. No. 5,879,834 add a small amount of aromatic compounds such as biphenyl, 3-chlorothiophene, furan and the like to electrochemically polymerize at abnormal overvoltage conditions to increase the internal resistance to improve battery safety. A method is described. These redox shuttle additives act to suppress the overcharge reaction by prematurely raising the temperature inside the battery due to the heat generated by the oxidative heating reaction to shut down the pores of the separator quickly and uniformly. In addition, the polymerization reaction of the additive on the surface of the positive electrode during overcharge also functions to protect the battery by consuming the overcharge current.

However, it is not possible to sufficiently remove the overcharge current by the polymerization reaction of the additive, and the gas swelling phenomenon is intensified due to the decomposition of the oxidation reaction. There is a limit to improvement. The swelling phenomenon refers to a phenomenon in which a central portion of a specific surface is deformed, such as a battery swelling in a specific direction. In addition, these additives have a problem that adversely affect the electrochemical properties of the battery, such as high temperature characteristics or life characteristics of the battery.

As a method for solving the swelling phenomenon, there is a method of improving the safety of the secondary battery by installing a vent or a current breaker for ejecting the internal gas when the internal pressure of the battery rises above a certain level. However, this method has a problem of causing a risk of malfunction due to the internal pressure rise.

In addition, in order to improve the swelling characteristic of the battery, a method of heat-treating the electrode plate in the range of 100 to 200 ° C and then cooling it to room temperature is known (Patent Application 1999-10904).

The present invention has been made to solve the above problems, and an object of the present invention is to provide an electrolyte for a lithium battery that can improve the swelling characteristics and safety of the lithium battery.

Another object of the present invention is to provide a lithium battery having excellent swelling characteristics and safety.

1 is a cross-sectional view of a rectangular lithium secondary battery.

In order to achieve the above object, the present invention is a non-aqueous organic solvent; Lithium salts; And lithium salts; And it provides a lithium battery electrolyte comprising a thiol compound of formula (1).

[Formula 1]

R ₁ SH

Wherein R ₁ represents a saturated or unsaturated hydrocarbon group having 1 to 30 carbon atoms, preferably 10 to 20 carbon atoms, or 1 to 30 carbon atoms containing a hetero atom of nitrogen or oxygen, or ether, imide, ethanol, or carboxyl Compound group containing an acid group.)

The present invention also provides a lithium battery containing the electrolyte.

Hereinafter, the present invention will be described in more detail.

The structure of the general non-aqueous lithium secondary battery 1 is as shown in FIG. The battery uses a lithiated intercalation compound as a positive electrode (2) and a negative electrode (4), inserts a separator (6) between the positive electrode (2) and the negative electrode (4) and wound the electrode assembly (8). After forming it is put into the case 10 is manufactured. The top of the cell is sealed with a cap plate 12 and a gasket 14. The cap plate 12 may be provided with a safety vent (16) to prevent the battery from forming overpressure. The positive electrode tab 18 and the negative electrode tab 20 are respectively provided on the positive electrode 2 and the negative electrode 4 and the insulators 22 and 24 are inserted to prevent internal short circuit of the battery. The electrolyte 26 is injected before sealing the cell. The injected electrolyte 26 is impregnated into the separator 6.

In the present invention, a composition containing a thiol compound represented by the following Chemical Formula 1 in a non-aqueous organic solvent and a lithium salt generally used as an electrolyte for lithium batteries is used as an electrolyte.

[Formula 1]

R ₁ SH

Wherein R ₁ represents a saturated or unsaturated hydrocarbon group having 1 to 30 carbon atoms, preferably 10 to 20 carbon atoms, or 1 to 30 carbon atoms containing a hetero atom of nitrogen or oxygen, or ether, imide, ethanol, or carboxyl Compound group containing an acid group.)

R ₁ of Chemical Formula 1 is a C1-30, preferably a C10-C30 saturated or unsaturated hydrocarbon group, C1-30 containing a hetero atom of nitrogen or oxygen, or ether, imide, ethanol, or carbon It is a compound group containing an acidic group. Preferably it is a C10-20 saturated or unsaturated hydrocarbon group, More preferably, it is a C10-20 alkyl group or an alkenyl group.

Preferred examples of the thiol compound of the formula include 1-pentadecanthiol, hexanethiol, methoxybenzenethiol (CH ₃ OC ₆ H ₄ SH), cyclohexyl mercaptan (C ₆ H ₁₁ SH), 4-mercaptophenol ( HSC ₆ H ₄ OH), 3-mercapto-1,2-propanediol (HSCH ₂ CH (OH) CH ₂ OH), 2-mercaptoethyl ether (HSCH ₂ CH ₂ ) ₂ O), 6-mercapto -1-hexanol (HS (CH ₂ ) ₆ OH), dodecanethiol (CH ₃ (CH ₂ ) ₁₁ SH), 11-mercapto-1-undecanol (HS (CH ₂ ) ₁₁ OH), 11- Mercaptodecanoic acid (HS (CH ₂ ) ₁₀ CO ₂ H), 16-mercaptohexanedecanoic acid (HS (CH ₂ ) ₁₅ COOH), 2-mercapto-1-methylimidazole, 2 Mercapto-5-nitrobenzimidazole and the like.

The thiol compound is preferably used in an amount of 0.0001 to 10% by weight, and more preferably in an amount of 0.01 to 2% by weight based on the total electrolyte. If the added amount is less than 0.01% by weight, the addition effect is insignificant, and if it exceeds 2% by weight, there is a problem that the battery performance is deteriorated, which is not preferable.

The thiol compound of Formula 1 includes a sulfur atom in a hydrocarbon compound. Although not wishing to be bound by any particular theory, it is believed that the sulfur atom of the thiol compound has a high adsorption force with the metal and thus a strong adsorption force on the electrode surface. The strong adsorption force of the thiol compound to the electrode of the sulfur atom can suppress generation of gas at high temperature. Therefore, the thiol compound used as the electrolyte additive of the present invention can prevent the swelling phenomenon by suppressing the gas generation of the battery at a high temperature.

The thiol compound is added to a non-aqueous organic solvent containing a lithium salt. Lithium salt acts as a source of lithium ions in the battery to enable the operation of the basic lithium battery, the non-aqueous organic solvent serves as a medium to move the ions involved in the electrochemical reaction of the battery.

The lithium salt may be LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiGaCl ₄ , ₁ or 2 selected from the group consisting of LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ), wherein x and y are natural numbers, LiNO ₃ , LiCl, and LiI It is possible to mix and use species.

The concentration of the lithium salt is preferably used in the range of 0.6 to 2.0M, more preferably in the range of 0.7 to 1.6M. When the concentration of the lithium salt is less than 0.6M, the conductivity of the electrolyte is lowered, and the performance of the electrolyte is lowered. When the concentration of the lithium salt is higher than 2.0M, the viscosity of the electrolyte is increased to reduce the mobility of lithium ions.

As the non-aqueous organic solvent, carbonate, ester, ether or ketone can be used. The carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC), Propylene carbonate (PC), butylene carbonate (BC), and the like may be used, and the ester may be n-methyl acetate, n-ethyl acetate, n-propyl acetate, or the like. Carbonate solvent in the non-aqueous organic solvent. In this case, it is preferable to use a mixture of cyclic carbonate and chain carbonate. In this case, it is preferable to use the cyclic carbonate and the chain carbonate by mixing in a volume ratio of 1: 1 to 1: 9. The performance of the electrolyte is preferable when mixed in the above volume ratio.

In addition, the electrolyte of the present invention may further include an aromatic hydrocarbon organic solvent in the carbonate solvent. As the aromatic hydrocarbon organic solvent, an aromatic hydrocarbon compound represented by Chemical Formula 2 may be used.

[Formula 2]

(Wherein R ₂ is halogen or an alkyl group having 1 to 10 carbon atoms and p is an integer of 0 to 6).

Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, toluene, fluorotoluene, trifluorotoluene, xylene and the like. In the electrolyte containing an aromatic hydrocarbon-based organic solvent, the volume ratio of the carbonate solvent / aromatic hydrocarbon solvent is preferably 1: 1 to 30: 1. The performance of the electrolyte is preferable when mixed in the above volume ratio.

The present invention provides a lithium battery comprising the electrolyte. The lithium battery of the present invention can be manufactured through the following process.

A positive electrode active material, a binder, and a conductive agent are mixed, and these are applied to a current collector made of a metal foil or a metal network and molded into sheets to use as a positive electrode, a negative electrode active material, a binder, and a conductive agent are mixed as necessary. These are applied to a current collector made of a metal foil or a metal net and molded into a sheet to use as a negative electrode.

Inserting a separator made of a porous insulating resin between the positive electrode and the negative electrode prepared as described above, and winding or stacking the separator to form an electrode assembly, and then put it in a battery case to inject the electrolyte of the present invention Assemble the battery. A cross-sectional view of a prismatic lithium battery among lithium batteries manufactured through such a process is shown in FIG. 1.

Examples of the positive electrode active material of a lithium battery include a compound capable of reversible intercalation / deintercalation of lithium (lithiated intercalation compound), or a material capable of forming a lithium-containing compound by reversibly reacting with lithium. This can be used. Specific examples of these materials include complex metal oxides such as LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , V ₂ O ₅ , sulfide compounds such as TiS and MoS, organic disulfide compounds and organic polysulfide compounds.

As the negative electrode active material, lithium metal or a carbonaceous material capable of reversible intercalation / deintercalation of lithium is used. For example, artificial graphite, natural graphite, graphitized carbon fibers, amorphous carbon, etc. may be mentioned. In addition, of course, materials conventionally used as a positive electrode or a negative electrode of a lithium battery may be used.

As the separator, a polyethylene separator, a polypropylene separator, a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

The electrolyte of the present invention can be both a lithium primary battery and a lithium secondary battery.

The lithium battery including the electrolyte of the present invention has superior swelling characteristics and safety compared to a battery using a conventional non-aqueous electrolyte.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

(Example 1)

1.3M LiPF ₆ was added to an organic solvent obtained by mixing ethylene carbonate (EC): ethylmethyl carbonate (EMC): propylene carbonate (PC): fluorobenzene (FB) in a volume ratio of 30: 55: 5: 10. An electrolyte composition was prepared by adding 0.5% by weight of 1-pentadecanthiol.

A slurry was prepared by adding LiCoO ₂ (average particle diameter: 10 μm), a conductive material (super P), and a binder (PVDF) as a positive electrode active material to N-methylpyrrolidone (NMP) at a weight ratio of 94: 3: 3. The slurry was coated on aluminum foil, dried, and rolled using a roll press to prepare a positive electrode plate having a width of 4.9 cm and a thickness of 147 μm. PHS (Nippon Carbon Co., Ltd.), oxalic acid, and binder (PVDF), which are negative electrode active materials, were dissolved in NMP in a weight ratio of 89.8: 0.2: 10 to prepare a slurry. A negative electrode plate with a thickness of 178 μm and 5.1 cm was prepared. A separator made of a polyethylene (PE) porous film (width: 5.35 cm, thickness: 18 μm) was inserted between the positive electrode plate and the negative electrode plate, and 5.6 g of the electrolyte was injected to prepare a rectangular lithium secondary battery.

(Example 2)

1.15 M LiPF ₆ was added to an organic solvent obtained by mixing ethylene carbonate (EC): ethyl methyl carbonate (EMC): propylene carbonate (PC): fluorobenzene (FB) in a volume ratio of 30: 55: 5: 10. A rectangular lithium secondary battery was prepared in the same manner as in Example 1, except that 0.5 wt% of hexanethiol was added to prepare an electrolyte composition.

(Comparative Example 1)

A solution obtained by adding 1.15 M LiPF ₆ to an organic solvent obtained by mixing ethylene carbonate (EC): ethyl methyl carbonate (EMC): propylene carbonate (PC): fluorobenzene (FB) in a volume ratio of 30: 55: 5: 10. A rectangular lithium secondary battery was manufactured in the same manner as in Example 1, except that the electrolyte composition was prepared.

In order to evaluate the swelling characteristics of the Examples and Comparative Examples, each of the square cells of Examples 1, 2 and Comparative Example 1 was charged and discharged at 0.2 C in a voltage range of 0 V to 4.2 V to form ) Was performed. After 4 hours, 24 hours and 48 hours in a high temperature chamber at 90 ° C with a standard charge of 0.5C, the thickest part of the cell was measured and the average value and thickness increment (thickness measurement at initial time-initial thickness measurement) Was calculated. The average value and thickness increment (described in parentheses) of the thickness measurements are shown in Table 1 below.

TABLE 1

Evaluation item Example 1 Comparative Example 1 Battery thickness (mm) Early 3.77 3.77 4 hours later 4.44 (△ 0.67) 4.58 (△ 0.81) 24 hours later 5.15 (△ 1.38) 5.62 (△ 1.85) 48 hours later 8.17 (△ 4.39) 9.30 (△ 5.53)

As shown in Table 1, the battery according to Example 1 according to the present invention was found to have superior swelling characteristics compared to Comparative Example 1.

The lithium battery containing the electrolyte of the present invention is excellent in swelling characteristics and battery safety.

Claims (15)

Non-aqueous organic solvents; Lithium salts; And a thiol compound represented by Chemical Formula 1 below. [Formula 1] R ₁ SH Wherein R ₁ represents a saturated or unsaturated hydrocarbon group having 1 to 30 carbon atoms, preferably 10 to 20 carbon atoms, or 1 to 30 carbon atoms containing a hetero atom of nitrogen or oxygen, or ether, imide, ethanol, or carboxyl Compound group containing an acid group.) The electrolyte for a lithium battery according to claim 1, wherein R ₁ is an alkyl group or alkenyl group having 10 to 20 carbon atoms. The method of claim 1, wherein the thiol compound is 1-pentadecandiol, hexanethiol, methoxybenzenethiol (CH ₃ OC ₆ H ₄ SH), cyclohexyl mercaptan (C ₆ H ₁₁ SH), 4-mercaptophenol (HSC ₆ H ₄ OH), 3-mercapto-1,2-propanediol (HSCH ₂ CH (OH) CH ₂ OH), 2-mercaptoethyl ether (HSCH ₂ CH ₂ ) ₂ O), 6-mer Capto-1-hexanol (HS (CH ₂ ) ₆ OH), dodecanethiol (CH ₃ (CH ₂ ) ₁₁ SH), 11-mercapto-1-undecanol (HS (CH ₂ ) ₁₁ OH), 11 Mercaptodecanoic acid (HS (CH ₂ ) ₁₀ CO ₂ H), 16-mercaptohexanedecanoic acid (HS (CH ₂ ) ₁₅ COOH), 2-mercapto-1-methylimidazole, An electrolyte for lithium batteries, which is at least one compound selected from the group consisting of 2-mercapto-5-nitrobenzimidazole. The electrolyte for a lithium battery of claim 1, wherein the thiol compound is used in an amount of 0.0001 to 10% by weight based on the total electrolyte. The electrolyte for a lithium battery of claim 1, wherein the thiol compound is used in an amount of 0.01 to 2 wt% based on the total electrolyte. The method of claim 1, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiGaCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ), where x and y are natural numbers, LiNO ₃ , LiCl, and LiI 1 or 2 or more types of electrolytes for lithium batteries. The electrolyte for a lithium battery of claim 1, wherein the lithium salt is used at a concentration of 0.6 to 2.0 M. The electrolyte of claim 1, wherein the non-aqueous organic solvent is at least one solvent selected from the group consisting of carbonates, esters, ethers, and ketones. The method of claim 8 wherein the carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene An electrolyte for a lithium battery, which is at least one solvent selected from the group consisting of carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). The electrolyte of claim 8, wherein the carbonate is a mixed solvent of a cyclic carbonate and a chain carbonate. The electrolyte of claim 1, wherein the non-aqueous organic solvent is a mixed solvent of a carbonate solvent and an aromatic hydrocarbon organic solvent. The electrolyte of claim 11, wherein the aromatic hydrocarbon-based organic solvent is an aromatic compound represented by Chemical Formula 2 below. [Formula 2] (Wherein R ₂ is halogen or an alkyl group having 1 to 10 carbon atoms and p is an integer of 0 to 6). The electrolyte of claim 12, wherein the aromatic hydrocarbon organic solvent is at least one solvent selected from the group consisting of benzene, fluorobenzene, toluene, fluorotoluene, trifluorotoluene, xylene, and mixtures thereof. . The electrolyte of claim 12, wherein the carbonate solvent and the aromatic hydrocarbon organic solvent are mixed in a volume ratio of 1: 1 to 30: 1. A lithium battery comprising the electrolyte according to any one of claims 1 to 14.