KR20030087311A - An electrolyte for a lithium battery and a lithium battery comprising the same - Google Patents

Abstract

PURPOSE: Provided are an electrolyte for a lithium battery and the lithium battery containing the electrolyte, which is excellent in electrochemical properties, such as capacity property, high discharging property, and low temperature property, and swelling property. CONSTITUTION: The electrolyte for the lithium battery contains: at least one non-aqueous organic solvent selected from the group consisting of carbonate, ester, ether, and ketone; at least one kind of lithium salt selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, and etc.; an additive represented by the formula 1, wherein R1, R2, and R3 are independently selected from the group consisting of alkyl, alkenyl, alkynyl, alkoxy, or aryl, and substituted alkyl, alkenyl, alkynyl, alkoxy, or aryl and at least one of R1, R2, and R3 is aryl. And the lithium battery contains the electrolyte.

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 for improving electrochemical characteristics such as high rate characteristics and low temperature characteristics, and a swelling characteristic of a battery, and a lithium battery comprising 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.

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 electrochemical and swelling characteristics of the battery.

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

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

Figure 2 is a chemical charge and discharge graph of Example 2 according to the present invention.

Figure 3a is a graph showing the low rate charge and discharge characteristics of Example 2 and Comparative Example 2 according to the present invention.

Figure 3b is a graph showing the high rate charge and discharge characteristics of Example 2 and Comparative Example 2 according to the present invention.

4 is a graph showing the life characteristics of Example 2 and Comparative Example 2 according to the present invention.

In order to achieve the above object, the present invention is a non-aqueous organic solvent; Lithium salts; And it provides an electrolyte for a lithium battery that can improve the electrochemical and swelling characteristics of a battery comprising the additive of formula (1).

[Formula 1]

Wherein R ¹ , R ² and R ³ are each independently selected from the group consisting of alkyl, alkenyl, alkynyl, alkoxy, or aryl groups, and substituted alkyl, alkenyl, alkynyl, alkoxy or aryl groups And at least one of R ¹ , R ² and R ³ is an aryl 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 an additive of the following formula (1) in a non-aqueous organic solvent and a lithium salt generally used as an electrolyte for a lithium battery is used as an electrolyte.

[Formula 1]

Wherein R ¹ , R ² and R ³ are each independently selected from the group consisting of alkyl, alkenyl, alkynyl, alkoxy, or aryl groups, and substituted alkyl, alkenyl, alkynyl, alkoxy or aryl groups And at least one of R ¹ , R ² and R ³ is an aryl group.)

Alkyl or alkoxy in the present invention means alkyl or alkoxy having 1 to 10, preferably 1 to 5 carbon atoms, alkenyl or alkynyl is 2 to 10, preferably 2 to 5 carbon atoms Is an alkenyl or alkynyl, and aryl means an aryl having 6 to 24 carbon atoms, preferably 6 to 18 carbon atoms.

Wherein R ¹ , R ² and R ³ are preferably methyl, ethyl, methoxy, ethoxy, or phenyl, at least one of which is phenyl. In addition, R ¹ , R ² and R ³ are preferably substituted alkyl, alkoxy or aryl groups, and the substituent is preferably halogen such as F, Cl, Br, or I, of which Br is most preferred.

Among the additives having Formula 1, an additive which may be preferably used in the present invention may be represented by the following Formula 2.

[Formula 2]

Wherein X is halogen, preferably Br, and l, m and n are in the range of 0 to 5.

In Formula 2, the substitution position of the halogen may be anywhere from 2, 3, or 4, but it is preferable that the halogen is substituted at the 4 position. In the present invention, tris (4-bromophenyl) amine which is a compound having a structure in which Br is substituted at position 4 of the phenyl group may be most preferably used. The chemical structural formula of tris (4-bromophenyl) amine is represented by the following Chemical Formula 3.

[Formula 3]

The electrolyte additive of the present invention increases the capacity of the battery, in particular the charging capacity during formation, can improve high rate and low temperature performance and improve swelling properties. The electrolyte additive is preferably used in an amount of 0.1 to 7% by weight based on the total electrolyte. If the added amount is less than 0.1% by weight, the addition effect is insignificant, and if it exceeds 7% by weight, there is a problem that the battery performance is deteriorated, which is not preferable.

The electrolyte additive is added to the non-aqueous organic solvent containing the 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.

Examples of the lithium salt include 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 , LiN ( C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural numbers), LiCl, and LiI, used in combination of one or two or more selected from the group consisting of It is possible.

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 4 may be used.

[Formula 4]

(Wherein R ⁴ 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 electrolyte of the present invention is prepared by adding the compound of Formula 1 as an electrolyte additive to an organic solvent containing a lithium salt.

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, these are applied to a current collector made of a metal foil or a metal network, and the molded product is used as a positive electrode, a negative electrode active material, a binder, and a conductive agent are mixed as necessary. These were applied to a current collector made of metal foil or metal mesh and molded on 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.

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.

A cross-sectional view of a prismatic lithium battery among lithium batteries manufactured through such a process is shown in FIG. 1.

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 not only has excellent electrochemical characteristics, particularly high rate characteristics and low temperature characteristics, but also has excellent swelling characteristics 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)

1.15 M LiPF ₆ was added to an organic solvent in which ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) was mixed in a volume ratio of 30:30:40, followed by tris (4-bromo) as an electrolyte additive. Electrolyte composition was prepared by adding 3% by weight of phenyl) amine.

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 with a roll press to prepare a positive electrode plate having a width of 4.9 cm and a thickness of 147 μm. Mesocarbon fiber (MCF; Petoca), oxalic acid, and binder (PVDF), a negative electrode active material, were dissolved in NMP in a weight ratio of 89.8: 0.2: 10 to prepare a slurry, and the slurry was applied to a copper current collector, dried, and then By rolling, a negative electrode plate having a width of 5.1 cm and a thickness of 178 μm 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 900 mAh lithium battery.

(Example 2)

Except for using an organic solvent in which ethylene carbonate (EC): ethyl methyl carbonate (EMC): propylene carbonate (PC): fluorobenzene (FB) was mixed in a volume ratio of 30: 55: 5: 10 as an organic solvent for preparing an electrolyte. In the same manner as in Example 1, a rectangular lithium secondary battery was prepared.

(Example 3)

A rectangular lithium secondary battery was prepared in the same manner as in Example 1, except that tris (4-bromophenyl) amine was used in an amount of 5% by weight as an electrolyte additive.

(Example 4)

A rectangular lithium secondary battery was prepared in the same manner as in Example 1, except that tris (4-bromophenyl) amine was used in an amount of 10% by weight as an electrolyte additive.

(Comparative Example 1)

Example 1 except that ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) was mixed with an organic solvent in which a volume ratio of 30:30:40 was added to a solution of 1.15M LiPF ₆ as an electrolyte. In the same manner as in 1, a rectangular lithium secondary battery was prepared.

(Comparative Example 2)

1.15 M LiPF ₆ was added to an organic solvent in which ethylene carbonate (EC): ethyl methyl carbonate (EMC): propylene carbonate (PC): fluorobenzene (FB) was mixed 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 the electrolyte was used as an electrolyte.

In order to evaluate the swelling characteristics of the Examples and Comparative Examples, each of the rectangular lithium secondary batteries of Example 2 and Comparative Example 2 was charged and discharged at 0.2C for 7 hours at a voltage range of 4.2 V to 2.75 V for 7 hours. (formation) was performed. The charge and discharge capacity and the thickness of the battery before and after chemical conversion were measured and the results are shown in Table 1 below. The result of Table 2 measures ten batteries of Example 2 and Comparative Example 2, and describes the average value. In addition, Figure 2 shows the charge and discharge graph of the chemical composition of Example 2.

Evaluation item Example 2 Comparative Example 2 Battery thickness (mm) Hwaseongjeon 4.80 4.80 After Mars 4.86 5.01 Mars Capacity (mAh) Charging capacity 1102 959 Discharge capacity 959 884

As shown in Table 1, the swelling characteristic of Example 2 according to the present invention was found to be superior to Comparative Example 2.

In addition, in the results of Table 1 and FIG. 2, the charge capacity and the discharge capacity of Example 2 were found to be superior to those of Comparative Example 2.

Charge and discharge at low rates by charging the square cells of the above Examples and Comparative Examples to a terminal voltage of 4.2 V at 0.5 C under constant current-constant voltage (CC-CV) conditions and then to a terminal voltage of 2.75 V at 0.2 C under CC conditions. The properties were evaluated. The charge and discharge graphs of Example 2 and Comparative Example 2 are shown in FIG. 3A. Charge-discharge characteristics at high rates by charging the square cells of the above Examples and Comparative Examples to a terminal voltage of 4.2V at 0.5C under constant current-constant voltage (CC-CV) conditions and then to a terminal voltage of 2.75V at 2C under CC conditions Was evaluated. The charge and discharge graphs of Example 2 and Comparative Example 2 are illustrated in FIG. 3B.

As shown in FIGS. 3A and 3B, the charge and discharge characteristics of Example 2 according to the present invention were shown to be much better than those of Comparative Example 2 not only at a low rate but also at a high rate.

In addition, the life characteristics at room temperature were evaluated for the rectangular batteries of Examples and Comparative Examples. The lifetime characteristics were evaluated by charging to the end voltage of 4.2V at 1C under constant current-constant voltage (CC-CV) conditions and then performing 300 discharges to the end voltage of 2.75V at 1C under CC conditions. The lifetime characteristics of Example 2 and Comparative Example 2 are shown in FIG. 4. In the results of Figure 4 it can be seen that the life characteristics of Example 2 according to the present invention is very excellent compared to Comparative Example 2.

The rectangular batteries of Examples and Comparative Examples were charged at 0.2 C in a voltage range of 4.2 V to 2.75 V, and then left at minus 20 ° C. for 4 hours, and then discharged at 0.5 C to measure discharge capacity. The capacity of the battery of Example 2 was 480 mAh, whereas the capacity of the battery of Comparative Example 2 was 360 mAh. From this it can be seen that the battery produced according to the present invention is excellent in low temperature properties.

The lithium battery including the electrolyte of the present invention is excellent in electrochemical and swelling characteristics such as capacity characteristics, high rate characteristics, low temperature characteristics, and the like.

Claims (16)

Non-aqueous organic solvents; Lithium salts; And an electrolyte additive of an electrolyte of Formula 1 below: [Formula 1] Wherein R ¹ , R ² and R ³ are each independently selected from the group consisting of alkyl, alkenyl, alkynyl, alkoxy, or aryl groups, and substituted alkyl, alkenyl, alkynyl, alkoxy or aryl groups And at least one of R ¹ , R ² and R ³ is an aryl group.) The electrolyte for a lithium battery of claim 1, wherein the electrolyte additive is a compound represented by the following Chemical Formula 2: [Formula 2] (Wherein X is halogen and l, m and n are in the range of 0 to 5). The electrolyte for a lithium battery of claim 1, wherein the electrolyte additive is at least one of R ¹ , R ^2, and R ³ being a phenyl group or a substituted phenyl group. The electrolyte of claim 1, wherein the electrolyte additive is tris (4-bromophenyl) amine. The electrolyte of claim 1, wherein the content of the electrolyte additive is 0.1 to 7 wt% based on the 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 , _One or two selected from the group consisting of LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ), wherein x and y are natural numbers, LiCl, and LiI The electrolyte for lithium batteries described above. The electrolyte for a lithium battery of claim 1, wherein the lithium salt is used at a concentration of 0.7 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 Formula 4 below. [Formula 4] (Wherein R ⁴ 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. Non-aqueous organic solvents; Lithium salts; And tris (4-bromophenyl) amine. A lithium battery comprising the electrolyte according to any one of claims 1 to 15.