KR20050048935A - An electrolyte for a lithium battery and a lithium battery comprising the same - Google Patents

Abstract

The present invention relates to a lithium battery electrolyte and a lithium battery comprising the same, wherein the electrolyte is a non-aqueous organic solvent; Lithium salts; And at least one additive selected from the group consisting of compounds represented by Formulas 1 to 3 below.

[Formula 1] [Formula 2] [Formula 3]

(Wherein A ₁ to A ₁₅ are each independently selected from the group consisting of hydrogen, halogen, alkyl, alkoxy, and hydroxy; X and Y are each independently NR (R is hydrogen or alkyl), S, And O, n is an integer of 5, or 6.

The lithium battery including the electrolyte has excellent electrochemical characteristics, particularly capacity characteristics at a high rate, and excellent battery safety, such as overcharging characteristics, to a battery using a conventional non-aqueous 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 comprising the same, and more particularly, to a lithium battery electrolyte and a lithium battery including the same to improve the overcharge safety of the battery.

[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, as the battery becomes more and more high capacity according to the demand of the consumer, it is difficult to satisfy the high level of safety requirements with the overcharge preventing additive as described above. Accordingly, as the demand for higher capacity of batteries increases, there is an urgent demand for the development of new overcharge additives capable of securing their safety.

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 and a method of manufacturing the same that can improve the overcharge safety of the battery.

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

In order to achieve the above object, the present invention is a non-aqueous organic solvent; Lithium salts; And at least one additive selected from the group consisting of compounds represented by Formulas 1 to 3 below.

[Formula 1]

[Formula 2]

[Formula 3]

(Wherein A ₁ to A ₁₅ are each independently selected from the group consisting of hydrogen, halogen, alkyl, alkoxy, and hydroxy; X and Y are each independently NR (R is hydrogen or alkyl), S, And O; n is an integer of 5, or 6.)

The present invention also provides a non-aqueous organic solvent; It provides a method for producing an electrolyte for a lithium battery comprising mixing a lithium salt and at least one additive selected from the group consisting of the compounds of Formulas 1 to 3.

The present invention also provides a lithium battery comprising the electrolyte for lithium batteries.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in 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 formation of overpressure of the battery. 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.

The lithium secondary battery may have a thermal runaway phenomenon in which the temperature of the battery rapidly rises due to overcharge or short circuit due to a design defect of the battery itself due to misuse or failure of a charger. In particular, during overcharging, excess lithium is released from the positive electrode and precipitated on the surface of the negative electrode so that the two electrodes are thermally very unstable, resulting in thermal decomposition of the electrolyte, reaction between the electrolyte and lithium, oxidation of the electrolyte at the positive electrode, and thermal decomposition of the positive active material The exothermic reaction proceeds abruptly by the reaction of oxygen and electrolyte generated by the so-called so-called thermal runaway phenomenon in which the temperature of the battery rises rapidly, leading to the ignition and smoke of the battery exceeding the maximum allowable temperature of the battery.

The present invention provides an electrolyte for a lithium battery that can improve the overcharge safety of the battery by using an additive selected from one or more selected from the group consisting of compounds represented by the following formulas (1) to (3).

[Formula 1]

[Formula 2]

[Formula 3]

(Wherein A ₁ to A ₁₅ are each independently selected from the group consisting of hydrogen, halogen, alkyl, alkoxy, and hydroxy; X and Y are each independently NR (R is hydrogen or alkyl), S, And O; n is an integer of 5, or 6.

The compounds of Formulas 1 to 3 used as an electrolyte additive in the present invention may initiate polymerization at about 4.5 V or more to increase the resistance between the positive electrode and the negative electrode by coating the surface of the electrode plate. In addition, by performing a redox reaction at a voltage of about 4.5V or more to consume the current applied during overcharging to improve the safety of the battery.

Preferred examples of the compound of Formula 1 include [2,2 '] bithiophene ([2,2'] Bithiophene), [2,2 '] bifuran ([2,2'] Bifuran), and 1,1 '-Dimethyl-1H, 1'H- [2,2'] bipyrrole (1,1'-Dimethyl-1H, 1'H- [2,2 '] bipyrrole), and the like Preferred examples include [3,3 '] bithiophene ([3,3'] Bithiophene), [3,3 '] bifuran ([3,3'] Bifuran), and 1,1'-dimethyl-1H, 1'H- [3,3 '] bipyrrole (1,1'-Dimethyl-1H, 1'H- [3,3'] bipyrrole), and the like. Hexylthiophene (3-Cyclohexyl thiophene), 3-cyclopentylthiophene (3-Cyclopentyl thiophene), 3-cyclopentylfuran (3-Cyclopentyl furan) and derivatives thereof can be used. The structural formulas of the compounds described above are summarized in Table 1 below. However, in addition to the compounds listed in Table 1 below, in Formulas 1 to 3, A ₁ to A ₁₅ are each independently selected from the group consisting of halogen, alkyl, alkoxy, and hydroxy; X and Y are each independently selected from the group consisting of NR (R is hydrogen or alkyl), S, and O; n can also be used when it is an integer of 5 or 6.

TABLE 1

Compound example Formula 1 Formula 2 Formula 3

The electrolyte additive is preferably used in an amount of 0.01 to 50% by weight, preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight, based on the total amount of the electrolyte. If the added amount is less than 0.01% by weight, the addition effect is insignificant, and if the amount exceeds 50% by weight, there is a problem that the life characteristics of the battery is lowered, 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 carbonate may be 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 gamma butyrolactone, n-methyl acetate, n-ethyl acetate, n-propyl acetate, or the like. Is dibutyl ether, and the ketone is polymethylvinyl ketone.

In the case of the carbonate-based solvent in the non-aqueous organic solvent, it is preferable to use a mixture of a cyclic carbonate and a 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 4]

Wherein R ₁ is halogen or alkyl of 1 to 10 carbon atoms and n is an integer of 0 to 6;

Specific examples of the aromatic hydrocarbon organic solvent include benzene, fluorobenzene, chlorobenzene, nitrobenzene, 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 a lithium salt and the electrolyte additive to a non-aqueous organic solvent. It is common to add the electrolyte additive to an organic solvent in which lithium salt is dissolved, but the order of addition of lithium salt and electrolyte additive is not important.

In addition, the composition for forming an electrolyte may be prepared by further adding and mixing a compound selected from the group consisting of a polyfunctional acrylate or a polymer thereof and a mixture thereof and an organic peroxide to the electrolyte of the present invention. At this time, the composition for forming an electrolyte may further include a basic catalyst.

Impregnating or coating the prepared electrolyte composition for a current collector to produce a solid polymer electrolyte, and further comprising the step of polymerizing the solid polymer electrolyte by heat treatment or ultraviolet (UV) irradiation (irradiation). Can be.

It is preferable that the said heat processing temperature is 40-110 degreeC. If the heat treatment temperature is less than 40 ℃ polymerization does not occur, if the temperature exceeds 110 ℃ melting of the separator may be started. In addition, there is a risk that bubbles are generated as the evaporation of the electrolyte and other added organic matters is used.

The present invention provides a lithium battery comprising the electrolyte. As a positive electrode active material of a lithium battery, a compound (lithiated intercalation compound) capable of reversible intercalation / deintercalation of lithium may be used. As the negative electrode active material, a lithium metal, a lithium-containing alloy, a material capable of reversibly reacting with lithium to form a lithium-containing compound, or a carbon material capable of reversible intercalation / deintercalation of lithium is used.

The lithium battery of the present invention can be manufactured through the following process.

First, the electrolyte additive is added to a non-aqueous organic solvent containing lithium salt to prepare a composition for forming an electrolyte. A positive electrode and a negative electrode are respectively produced in accordance with conventional methods used in the production of lithium batteries. Then, a separator made of an insulating resin having a mesh structure is inserted between the positive electrode and the negative electrode, and the electrode assembly is formed by winding or stacking the electrode resin, and then putting the separator into a battery case to assemble the battery.

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 lithium battery of the present invention prepared according to the method described above may be both a lithium primary battery and a lithium secondary battery.

The lithium battery including the electrolyte of the present invention is excellent in battery safety, such as overcharging characteristics, 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)

Mixed organic solution 5 in which ethylene carbonate (EC): methylethyl carbonate (MEC): propylene carbonate (PC): fluorobenzene (FB) in which 1.3 M LiPF ₆ is dissolved is mixed in a volume ratio of 30: 55: 5: 10. An electrolyte was prepared by adding 0.25 g of [2,2 ']-bithiophene ([2,2']-bithiophene) as an electrolyte additive.

A slurry was prepared by adding 94 g of LiCoO ₂ (average particle size: 10 μm) as a positive electrode active material, ₃ g of a conductive agent (super P), and 3 g of a binder (PVDF) to N-methylpyrrolidone (NMP). The slurry was applied on an aluminum foil having a width of 4.9 cm and a thickness of 147 μm, dried, rolled, rolled, and cut to prepare a positive electrode plate.

A slurry was prepared by dissolving 89.8 g of mesocarbon fiber (MCF; Petoca Co., Ltd.), 0.2 g of oxalic acid, and 10 g of binder (PVDF) as an anode active material in NMP, and applying the slurry to a copper current collector having a width of 5.1 cm and a thickness of 178 μm. And dried and rolled with a roll press to prepare a negative electrode plate. A separator made of a polyethylene (PE) porous film was inserted between the positive electrode plate and the negative electrode plate, and 2.3 g of the electrolyte was injected to prepare a rectangular lithium secondary battery.

(Comparative Example 1)

A solution in which 1.3M LiPF ₆ was added to a mixed organic solvent in which ethylene carbonate (EC): methylethyl carbonate (MEC): propylene carbonate (PC): fluorobenzene (FB) was mixed 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 was used as an electrolyte.

The square lithium secondary batteries of Example 1 and Comparative Example 1 were charged and discharged at 2C to measure capacities, and are shown in Table 2 below. The overcharge safety characteristics were evaluated by performing overcharge for about 2.5 hours with a charging current of 2 A between the positive and negative terminals of each lithium secondary battery. Overcharge safety is also listed in Table 2 below.

TABLE 2

Standard capacity (mAh) 2C capacity (mAh) Overcharge safety ^* Example 1 841 779 5L0 Comparative Example 1 843 781 5L5

Note) Overcharge safety: The number before L means the number of test cells.

Overcharge safety assessment criteria are as follows:

(L0: good, L1: leakage, L2: flash, L2: flame, L3: smoke, L4: fire, L5: burst)

As shown in Table 2, it can be seen that the battery according to the embodiment of the present invention is superior to the comparative example in terms of overcharge safety without reducing the 2C capacity characteristic.

The cyclic voltammogram was measured about the square cells of Example 1 and Comparative Example 1. The cyclic voltammogram used lithium as a reference electrode and a platinum electrode as a counter electrode and a working electrode. The scanning speed was 10 mV / s and measured at a voltage range of OCV to 6.0V. The cyclic voltammogram measurement results for the batteries of Example 1 and Comparative Example 1 are shown in FIGS. 2A and 2B, respectively. 2a shows that the decomposition peak of the additive appears in the range of 5-6V, which is the decomposition range of the electrolyte, and oxidative decomposition of such additives is thought to contribute to securing the safety of the battery by consuming the charging current during overcharging. do. On the other hand, in Comparative Example 1 (FIG. 2B), only the electrolyte decomposition current appeared and the current density was found to be almost constant according to cycling.

3A is a diagram showing the current and voltage characteristics of the battery when the battery of Example 1 is overcharged with 12V at a current of 2A. As shown in FIG. 3A, the battery of Example 1 of the present invention is suppressed by an overcharge reaction by a shut down phenomenon in which the electrolyte additive increases the temperature of the battery early to uniformly block pores of the separator. see. This is considered to be because the electrolyte additive blocked the flow of current by forming a film on the electrode surface. 3B is a diagram showing current, temperature, and voltage characteristics of a battery when the battery of Comparative Example 1 is overcharged with a current of 2A at 12V. As shown in FIG. 3B, in the case of Comparative Example 1, the temperature of the battery was sharply increased, and the voltage was also increased to about 15V and then dropped to 0V.

The lithium battery including the electrolyte of the present invention not only has excellent electrochemical characteristics, especially capacity characteristics at high rates, but also excellent battery safety, such as overcharging characteristics, in a battery using a conventional non-aqueous electrolyte.

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

Figure 2a and 2b is a view showing a cyclic voltammogram measurement results of Example 1 and Comparative Example 1 according to the present invention, respectively.

3A and 3B are diagrams showing current, voltage, and temperature characteristics during overcharging of Example 1 and Comparative Example 1 according to the present invention, respectively.

Claims (20)

Non-aqueous organic solvents; Lithium salts; And at least one additive selected from the group consisting of compounds represented by Formulas 1 to 3 below. [Formula 1] [Formula 2] [Formula 3] (Wherein A ₁ to A ₁₅ are each independently selected from the group consisting of hydrogen, halogen, alkyl, alkoxy, and hydroxy; X and Y are each independently NR (R is hydrogen or alkyl), S, And O; n is an integer of 5, or 6. The method of claim 1, wherein the electrolyte additive is [2,2 '] bithiophene ([2,2'] Bithiophene), [2,2 '] bifuran ([2,2'] Bifuran), 1,1 '-Dimethyl-1H, 1'H- [2,2'] bipyrrole (1,1'-Dimethyl-1H, 1'H- [2,2 '] bipyrrole), [3,3'] bithiophene ([3,3 '] Bithiophene), [3,3'] bifuran ([3,3 '] Bifuran), 1,1'-dimethyl-1H, 1'H- [3,3'] bipyrrole ( 1,1'-Dimethyl-1H, 1'H- [3,3 '] bipyrrole), 3-cyclohexyl thiophene, 3-cyclopentylthiophene, 3- An electrolyte for a lithium battery, which is at least one compound selected from the group consisting of cyclopentylfuran (3-Cyclopentyl furan), and mixtures thereof. The electrolyte for a lithium battery of claim 1, wherein the content of the electrolyte additive is 0.01 to 50 wt% based on the electrolyte. The electrolyte for a lithium battery of claim 3, wherein the content of the electrolyte additive is 1 to 5 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 , For a lithium battery which is at least one selected from the group consisting of 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 Electrolyte. The electrolyte for a lithium battery of claim 5, wherein the lithium salt is used at a concentration of 0.6 to 2.0M. 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 7, 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 7, 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 10, wherein the aromatic hydrocarbon-based organic solvent is an aromatic compound represented by Formula 4 below. [Formula 4] (Wherein R ₁ is halogen or alkyl of 1 to 10 carbon atoms and n is an integer of 0 to 6). The method of claim 10, wherein the aromatic hydrocarbon organic solvent is at least one selected from the group consisting of benzene, fluorobenzene, chlorobenzene, nitrobenzene, toluene, fluorotoluene, trifluorotoluene, xylene, and mixtures thereof. A lithium battery electrolyte which is a solvent. The electrolyte of claim 10, 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 mixing at least one additive selected from the group consisting of compounds represented by Formulas 1 to 3 below. [Formula 1] [Formula 2] [Formula 3] (Wherein A ₁ to A ₁₅ are each independently selected from the group consisting of hydrogen, halogen, alkyl, alkoxy, and hydroxy; X and Y are each independently NR (R is hydrogen or alkyl), S, And O; n is an integer of 5, or 6. Non-aqueous organic solvents; Lithium salts; And a compound of Formula 1 to Formula 3; A compound selected from the group consisting of polyfunctional acrylates or polymers thereof and mixtures thereof; And preparing a composition for forming an electrolyte comprising an organic peroxide; And Preparing a solid polymer electrolyte by impregnating or coating the current collector-forming composition on a current collector Method for producing a lithium battery electrolyte comprising a. [Formula 1] [Formula 2] [Formula 3] (Wherein A ₁ to A ₁₅ are each independently selected from the group consisting of hydrogen, halogen, alkyl, alkoxy, and hydroxy; X and Y are each independently NR (R is hydrogen or alkyl), S, And O; n is an integer of 5, or 6. The method of claim 15, wherein the composition for forming an electrolyte further comprises a basic catalyst. The method of claim 15, wherein the solid polymer electrolyte is heat-treated or irradiated with ultraviolet (UV) radiation to polymerize the solid polymer electrolyte. Method for producing a lithium battery electrolyte further comprising. 18. The method of claim 17, wherein the heat treatment temperature is 40 to 110 ° C. A lithium battery comprising the electrolyte according to any one of claims 1 to 13. The lithium battery according to claim 19, wherein said lithium battery is a lithium ion battery or a lithium polymer battery.