KR20050068665A - Nonaqueous electrolyte for battery - Google Patents

Abstract

The present invention relates to a nonaqueous electrolyte solution for a battery, comprising 0.1 to 20% by weight of an alkene sultone compound represented by the following formula (1) in a nonaqueous electrolyte solution for a lithium battery comprising an organic solvent and a lithium salt. It is possible to suppress the increase in thickness of the battery when stored at a high temperature for a long time without affecting the characteristics, so it has the advantage of excellent high temperature performance and excellent set mounting efficiency.

[Formula 1]

Description

Nonaqueous Electrolyte for Battery {Nonaqueous Electrolyte for Battery}

The present invention relates to a non-aqueous electrolyte for batteries, and more particularly, to increase the thickness of a battery during high temperature storage for a long time, characterized in that it comprises an alkene sultone compound in a non-aqueous electrolyte for lithium batteries consisting of an organic solvent and a lithium salt. The present invention relates to a nonaqueous electrolyte for batteries having improved high temperature performance.

Lithium secondary batteries have high energy density, low self-discharge rate, and light weight, and thus are attracting attention as high-performance energy sources for portable electronic devices requiring thin and lightweight notebook computers, camcorders, and mobile phones. Such lithium secondary batteries include a coin type, a cylindrical shape, a square shape, and the like. Generally, a lithium metal mixed oxide is used as a positive electrode active material, and a carbon material or a lithium metal is used as a negative electrode material. The average discharge voltage of about 3.6 to 3.7V of the lithium battery can obtain a higher power than other alkaline batteries or Ni-MH or Ni-Cd batteries, which is one of the greatest advantages of the lithium battery. In order to exhibit such a high driving voltage, an electrochemically stable electrolyte composition is required at a high voltage of 4V or more. Therefore, lithium batteries are organic solvents such as ethylene carbonate (EC), dimethyl carbonate (DMC), methyl carbonate (MEC), and diethyl carbonate (DEC). Solvents are mixed and used appropriately. As the solute of the electrolyte, lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , and LiN (C ₂ F ₅ SO ₃ ) ₂ are commonly used. They act as a source of lithium ions in the battery, thereby preventing the basic operation of the lithium battery. Make it possible.

However, these nonaqueous electrolytes also have disadvantages in high rate charging and discharging, because their ionic conductivity is significantly lower than the aqueous electrolytes used in Ni-MH or Ni-Cd batteries. In the initial charging of a lithium battery, lithium ions from the lithium metal composite oxide used as the positive electrode move to the graphite (crystalline or amorphous) electrode used as the negative electrode and are intercalated between the layers of the graphite electrode. At this time, since lithium is highly reactive, the electrolyte and the carbon constituting the cathode react on the graphite cathode surface to form compounds such as Li ₂ CO ₃ , Li ₂ O, and LiOH. These compounds form a kind of passivation layer on the surface of the graphite cathode, which is called a solid electrolyte interface (SEI) film. Once formed, the SEI film functions as an ion tunnel to pass only lithium ions. The SEI film solvates lithium ions by the effect of this ion tunnel, and organic solvent molecules having a large molecular weight, such as EC, DMC, or DEC, which move together with lithium ions in the electrolyte are inserted together in the graphite cathode to form a graphite anode. It prevents the structure from breaking down. Once the SEI film is formed, lithium ions again do not react sideways with the graphite cathode or other material, and the amount of charge consumed to form the SEI film has a property of not reversibly reacting upon discharge with an irreversible capacity. Thus, no further electrolyte decomposition occurs and the amount of lithium ions in the electrolyte is reversibly maintained to maintain stable charge and discharge (see J. Power Sources (1994) 51: 79-104).

In the thin square battery, the thickness of the battery is expanded during charging due to the generation of gases such as CO, CO ₂ , CH ₄ , and C ₂ H ₆ generated from decomposition of the carbonate-based organic solvent during the above-described SEI formation reaction. (See J. Power Sources (1998) 72: 66-70). In addition, when stored at high temperature in a fully charged state (for example, left at 85 ° C. for 4 hours after being fully charged to 4.2V), the SEI film is gradually decayed due to increased electrochemical energy and thermal energy. Side reactions continue to occur between the cathode surface and the surrounding electrolyte. In this case, the internal pressure of the battery increases due to the continuous gas generation. As a result, in the case of the square battery and the polymer lithium ion (PLI) battery, the thickness of the battery increases, making it difficult to install the set itself.

The present invention is to overcome the problems of the prior art described above, the object of the present invention is to suppress the decomposition of the electrolyte when applied to the battery, it is possible to suppress the increase in the thickness of the battery when left at high temperature and the capacity at high temperatures of the battery It is to provide a novel nonaqueous electrolyte solution for lithium batteries capable of improving storage characteristics.

That is, the present invention provides a nonaqueous electrolyte solution for a battery comprising 0.1 to 20% by weight of an alkene sultone compound in a nonaqueous electrolyte solution for a lithium battery composed of an organic solvent and a lithium salt.

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

Non-aqueous electrolyte of the present invention is characterized in that it comprises 0.1 to 20% by weight of an alkene sultone compound of the formula (1) in an organic solvent in which lithium salt is dissolved.

Wherein n is an integer between 2 and 5.

Alkene sultone compounds of the present invention include ethylene sultone, propylene sultone, butylene sultone, isobutylene sultone and the like. The addition amount of such an alkene sultone compound is 0.1-20 weight%, Preferably it is 0.1-5 weight%, More preferably, it is 0.1-2 weight%. When the amount of the alkene sultone compound added in the present invention is less than 0.1% by weight, the effect of suppressing the increase in thickness due to the inhibition of the decomposition of the electrolytic solution intended in the present invention is insignificant. Since this reduced problem may occur, the amount of the alkene sultone compound added is preferably within the above range.

In the present invention, a carbonate organic solvent may be used as the electrolyte, and a lithium salt such as LiPF ₆ may be used as the solute. An example of a preferable composition of the battery nonaqueous electrolyte of the present invention is to contain 0.1 to 20% by weight of an alkene sultone compound in a mixed organic solvent such as a cyclic carbonate organic solvent and a linear carbonate organic solvent in which lithium salt is dissolved at 0.8 to 2 M. .

As the organic solvent of the non-aqueous electrolyte which can be used in the present invention, for example, cyclic carbonate compounds (Cyclic carbonate) such as ethylene carbonate, propylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate And linear carbonate compounds such as ethyl methyl carbonate and ethyl propyl carbonate, propyl acetate, methyl acetate, ethyl acetate, butyl acetate, methyl propionic acid, ethyl propionic acid, and the like. In the present invention, the organic solvent is preferably a cyclic carbonate organic solvent (for example, ethylene carbonate and propylene carbonate) and a linear carbonate organic solvent (for example, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl). It is more preferable to mix and use. Examples of preferred organic solvents are a mixture of ethylene carbonate and dimethyl carbonate.

In addition to the above-mentioned organic solvent, one or more selected from the group consisting of propyl acetate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate and the like may be further mixed and used as necessary. The mixing ratio of the organic solvent selected from each group is not particularly limited as long as the object of the present invention is not impaired, and the mixing ratio in the production of a non-aqueous electrolyte for lithium batteries is generally used.

Meanwhile, as the lithium salt contained in the nonaqueous electrolyte of the present invention, one or more selected from the group consisting of LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiN (C ₂ F ₅ SO ₃ ) ₂ , and the like are used. Preferably, LiPF ₆ is used. In the present invention, the concentration of the lithium salt is preferably in the range of 0.8 ~ 2 M, when the concentration of the lithium salt is less than 0.8 M, the conductivity of the electrolyte is lowered, the performance of the electrolyte is lowered, if it exceeds 2 M low temperature performance due to the increase in viscosity at low temperatures Is lowered.

The lithium non-aqueous electrolyte solution of the present invention can be used to manufacture a lithium battery according to a conventional method, and the lithium battery thus prepared is a gas inside the battery due to charge and discharge life performance and decomposition of the electrolyte when left at a high temperature (90 ° C.). Since the occurrence is suppressed, the swelling phenomenon in which the thickness of the battery is expanded is prevented, and the capacity storage characteristic at high temperature is also excellent.

Hereinafter, the present invention will be described in more detail with reference to examples, but these examples are for illustrative purposes only and should not be construed as limiting the present invention.

Example 1-2

1 M of LiPF ₆ dissolved as a solute in a solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a ratio of 1: 1: 1 was used as the basic electrolyte solution. Ethylene sultone was added in the amounts shown in Table 1 below to obtain a final nonaqueous electrolyte. A rectangular battery was prepared using the nonaqueous electrolyte solution prepared in this manner, but graphite was used as a negative electrode active material, and vinylidene fluoride resin (PVDF) was used as a binder. LiCoO ₂ was used as a cathode active material, PVDF was used as a binder, and acetylene black was used as a conductive agent. Thus, the characteristics of the battery prepared as shown in Table 2 below.

Comparative Example 1

A basic electrolyte solution in which 1 M of LiPF ₆ was dissolved as a solute in a solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a ratio of 1: 1: 1 without adding an alkene sultone compound was added. It was used to prepare a battery and to evaluate the characteristics of the battery thus obtained and the results are shown in Table 2 together.

Comparative Example 2

2% by weight of propane sultone was added to a basic electrolyte solution in which 1 M of LiPF ₆ was dissolved as a solute in a solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a ratio of 1: 1: 1. The final non-aqueous electrolyte was added to prepare a battery using the same, and the characteristics of the battery thus obtained were evaluated, and the results are shown in Table 2 together.

Examples 3-7

Except that propylene sultone was added in the amount shown in Table 1 as an alkene sultone compound, the battery was prepared in the same manner as in Example 1, and the characteristics of the battery thus obtained were evaluated. The results are shown in Table 2 together.

Comparative Example 3

The characteristics of the battery obtained as described above were prepared in the same manner as in Example 1 except that propylene sultone was added as an alkene sultone compound but added in an amount of addition (0.01 wt%) outside the range of the present invention. To evaluate the results are shown in Table 2 together.

Examples 8-9

After preparing a battery in the same manner as in Example 1 except that butylene sultone was added in the amount shown in Table 1 as an alkene sultone compound, the characteristics of the battery thus obtained were obtained. The results are shown together in Table 2 below.

additive Added amount (% by weight) Comparative Example 1 - - Comparative Example 2 Propane sultone 2 Comparative Example 3 Propylene sultone 0.01 Example 1 Ethylene sultone One Example 2 Ethylene sultone 2 Example 3 Propylene sultone 0.1 Example 4 Propylene sultone One Example 5 Propylene sultone 2 Example 6 Propylene sultone 10 Example 7 Propylene sultone 20 Example 8 Butylene Sultone One Example 9 Butylene Sultone 2

Battery thickness change at 85 ° C after charging Thickness change after charging (%) Thickness change after 85 ℃ for 4 hours (%) Thickness change after 85 ℃ 96 hours (%) Capacity remaining after 85 ℃ 96 hours (%) Capacity remaining after 300 cycles (%) Comparative Example 1 8.5 22.3 46.8 42.1 52.1 Comparative Example 2 3.5 8.3 19.5 73.2 82.1 Comparative Example 3 7.8 18.3 45.2 43.2 51.7 Example 1 3.9 4.8 7.6 80.4 76.5 Example 2 2.8 4.1 6.9 78.5 73.1 Example 3 4.5 5.7 12.5 56.4 62.3 Example 4 2.8 4.8 6.2 82.5 85.6 Example 5 3.0 3.5 5.3 84.6 82.1 Example 6 2.7 3.2 4.2 76.2 77.3 Example 7 3.1 3.2 4.8 80.3 72.1 Example 8 2.9 3.7 5.2 75.3 72.8 Example 9 3.5 4.6 6.4 77.2 73.4

Battery Characteristic Evaluation Method

* Remaining capacity after 300 cycles: After the battery was charged to 4.2V and discharged as one cycle for 300 cycles, the remaining capacity (mAh) of the battery was measured.

* Thickness change at high temperature: The temperature change at 85 ℃ is measured 4 hours and 96 hours after the battery is fully charged up to 4.2V and the battery is fixed between the thickness measuring gauges in the hot air oven after weighing 300G. It was.

* Current / voltage cyclic polarization (Cyclic Voltametry): In order to evaluate the electrochemical characteristics of the batteries of Example 1 and Comparative Example 1 by applying a voltage to the working electrode by the current / voltage cyclic polarization experiment under the following conditions As the voltage was changed, the current was measured as a function of the voltage, and the results are shown in FIGS. 1A and 1B, respectively. Working electrode: Anode Material (MCF), reference electrode: Li-metal, counter electrode: Li-metal, voltage range: 3.5V to 0V, scan rate: 0.1 mV / s, 3 cycles.

The battery to which the nonaqueous electrolyte solution for a battery of the present invention is applied has an advantage in that the increase in the thickness of the battery is suppressed when stored for a long time at high temperature, thereby having excellent high temperature performance and excellent set mounting efficiency.

Figure 1a is a graph showing the results of the evaluation of the electrochemical characteristics of the battery according to the present invention by the current / voltage cyclic polarization method,

1B is a graph showing the results of evaluating the electrochemical characteristics of the battery according to the comparative example by the current / voltage cyclic polarization method.

Claims (4)

A non-aqueous electrolyte solution for a battery, comprising 0.1 to 20% by weight of an alkene sultone compound represented by Formula 1 in a non-aqueous electrolyte solution for a lithium battery comprising an organic solvent and a lithium salt. [Formula 1] Wherein n is an integer from 2 to 5. The method of claim 1, wherein the solvent of the non-aqueous electrolyte is ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), fluorobenzene (FB) A nonaqueous electrolyte solution for batteries, characterized in that it is one or two or more mixed organic solvents selected from the group consisting of: The method of claim 1, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂₎ is at least one or two selected from the group consisting of _2, the electrolytic solution of the lithium salt concentration in the non-aqueous electrolyte battery, characterized in that 0.8 ~ 2 M. A battery comprising a negative electrode, a positive electrode, and an electrolyte solution, wherein the electrolyte solution is the nonaqueous electrolyte solution of claim 1.