KR20050063915A - Nonaqueous electrolyte for secondary battery and secondary battery comprising the electrolyte - Google Patents

Abstract

The present invention relates to a nonaqueous electrolyte solution for lithium batteries prepared by adding trialkylsilylbenzene borate to a lithium salt-containing mixed organic solution obtained by dissolving a lithium salt in a carbonate mixed organic solvent. It relates to a lithium secondary battery comprising a. The nonaqueous electrolyte solution for lithium batteries according to the present invention shows improved discharge capacity and discharge voltage at a higher rate than the conventional electrolyte solution, thereby ensuring battery performance and excellent charge / discharge cycle characteristics.

Description

Nonaqueous Electrolyte for Secondary Battery and Secondary Battery Containing It {Nonaqueous Electrolyte for Secondary Battery and Secondary Battery comprising the Electrolyte}

The present invention relates to a nonaqueous electrolyte solution for lithium batteries prepared by adding trialkylsilylbenzene borate to a lithium salt-containing mixed organic solution obtained by dissolving a lithium salt in a carbonate mixed organic solvent. It relates to a lithium secondary battery comprising a. More specifically, the present invention provides trialkylsilyl borate in 100 parts by weight of a lithium salt-containing mixed organic solution in which a lithium salt compound is dissolved at 0.8 to 2.0 M in a mixed solvent consisting of a cyclic carbonate organic solvent and a linear carbonate organic solvent. It relates to a non-aqueous electrolyte for lithium batteries prepared by adding 0.1 to 10 parts by weight of a secondary battery including the same.

With the rapid miniaturization and diversification of mobile phones, portable electronic devices, and portable information terminals, the battery, which is a power source, is compact and lightweight, has high energy density, and can be charged and discharged for a long time, and has high rate characteristics. In order to meet these demands, researches on lithium secondary batteries and the like have been made as secondary batteries. Although the electrolyte solution for lithium batteries is required to be stable with respect to a lithium negative electrode, it is known that there is no solvent which is completely thermodynamically stable with respect to lithium. Indeed, in lithium batteries, the electrolyte decomposes on the negative electrode during initial charging, so that the reaction product forms an ion conductive protective film on the surface of the lithium, that is, a solid electrolyte interface (SEI), and suppresses the reaction between the electrode and the electrolyte It is thought to be stabilized. On the other hand, in the case of high rate characteristics, when a lithium battery is used in a mobile phone and a portable electronic device, a difference in performance varies greatly according to the type of battery as a high current flows. Therefore, it has been an important task to develop an electrolyte solution capable of improving the high rate characteristic of a battery so that the phenomenon of deterioration of the battery does not occur even when a high current is used. However, most of the nonaqueous electrolyte solvents have a low withstand voltage, and when an electrolyte solution using a low withstand voltage solvent is used in a secondary battery, when the charge and discharge are repeated, the solvent is decomposed, resulting in gas generation. The internal pressure rises, the product causes a polymerization reaction, or adheres to the electrode surface. For this reason, there arises a problem that the battery charge and discharge efficiency is lowered and the battery life is shortened due to the decrease in battery energy density. Currently, the first attempt to improve the high rate characteristics is the formation of a stable solid electrolyte interface (SEI) on the surface of the electrode is very important, the SEI thus formed has a higher conductivity, the mobility of Li ⁺ ion and It is to improve the charge and discharge characteristics to bring the improvement of life characteristics and high rate characteristics. To this end, attempts have been made to secure high rate characteristics of batteries by adding small amounts of compounds as additives in the electrolyte of lithium secondary batteries. For example, Japanese Patent Application Laid-Open No. 8-22839 discloses using trimethyl phosphate and triethyl phosphate as additives in an electrolyte solution to improve the withstand voltage resistance and to suppress decomposition of the electrolyte solvent by oxidation. The solubility of the electrolyte can be increased, and an electrolyte solution excellent in the electrical conductivity at room temperature and low temperature can be produced. In addition, Japanese Patent Application Laid-open No. Hei 2-10666 uses a solvent of carbonate ester having a high withstand voltage instead of a solvent having a low withstand voltage, thereby suppressing a decrease in battery energy density after repeated charge and discharge, thereby improving life and high rate characteristics. One electrolyte is disclosed. However, according to the researches of the present inventors, the above techniques do not achieve sufficient high rate characteristics and improvement of life characteristics at the same time, and have been shown to adversely affect other characteristics (such as charge and discharge efficiency) of the battery. On the other hand, conventional lithium secondary batteries use a layered lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ) or lithium manganese oxide (LiMn ₂ O ₄ ), etc., having a large capacity per weight as a positive electrode active material. In case of oxides, most of lithium ions are in a desorption state at a high rate, and thus, they are very unstable, and may cause rapid decomposition exothermic reaction by reacting with an electrolyte or lithium metal on a negative electrode, which may cause battery rupture or ignition in the worst case. There is this.

Therefore, there is a need in the art for the development of an electrolyte solution capable of improving high rate discharge characteristics and life characteristics of a battery without affecting other characteristics of the battery in a lithium secondary battery.

The present inventors have diligently studied to solve the above problems, and when trialkylsilyl borate such as trimethylsilyl borate is added to the nonaqueous electrolyte for batteries, the electrolyte is decomposed by unstable lithium ions even at high rate. The exothermic reaction was suppressed to improve the high rate discharge characteristics, the lifetime characteristics, and the like, and was excellent in the charge and discharge cycle characteristics, and in addition, the present invention was confirmed that it did not adversely affect other characteristics of the battery such as battery charge and discharge efficiency.

As a result, the present invention is directed to providing an improved novel nonaqueous electrolyte for lithium batteries without deteriorating battery performance at high rates.

Accordingly, one aspect of the present invention relates to a non-aqueous electrolyte solution for a lithium battery comprising trialkylsilyl borate represented by the following Chemical Formula 1 in a lithium salt-containing organic mixed solution in which lithium salt is dissolved in a carbonate-based organic mixed solvent. :

[Wherein R is an alkyl group having 1 to 4 carbon atoms]

Another aspect of the present invention relates to a lithium secondary battery including the nonaqueous electrolyte.

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

Non-aqueous electrolyte according to the present invention is 0.1 to 10 parts by weight, preferably 1 to 5 parts by weight, more preferably 0.1 to 1 part by weight of the trialkylsilyl borate of the formula (1) to 100 parts by weight of the lithium salt-containing mixed organic solution Most preferably, 0.1 to 0.5 parts by weight. As the trialkyl silyl borate according to the invention, preferably trimethylsilylborate of the formula (II) is used:

In the nonaqueous electrolyte according to the present invention, the lithium salt-containing mixed organic solution, which is a basic electrolyte, is a solution obtained by dissolving a lithium salt compound in a mixture of carbonate organic solvents.

In more detail, the carbonate mixed organic solvent is composed of a cyclic carbonate organic solvent and a linear carbonate organic solvent. Preferably, the cyclic carbonate organic solvent is ethylene carbonate (EC), propylene carbonate (PC) or a mixture thereof. The linear carbonate organic solvent is dimethyl carbonate (DMC). At least one compound selected from the group consisting of diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and methylpropyl carbonate (MPC) is used. For example, a combination of ethylene carbonate and dimethyl carbonate or a combination of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate can be used. The mixed organic solvent is, if necessary, propyl acetate (PA), methyl acetate (MA), ethyl acetate (EA), butyl acetate (BA), methyl propionate (MP), ethyl propionate (EP) and One or two or more compounds selected from the group consisting of fluorobenzene (FB) may be further included in an amount of 1.0 to 10 parts by weight based on 100 parts by weight of the mixed organic solvent. 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 at the time of preparing a nonaqueous electrolyte solution for a lithium battery is followed.

The mixed organic solvent includes a lithium salt compound, examples of the lithium salt include all known lithium salt compounds used in lithium batteries, preferably LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (C ₂ One or two or more compounds selected from the group consisting of F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) _2, and LiN (CF ₃ SO ₂ ) ₂ are used. More preferably LiPF ₆ is used. The lithium salt compound is present in the carbonate-based mixed organic solvent in the range of 0.8 to 2.0M.

By using the nonaqueous electrolyte solution for lithium batteries according to the present invention, a lithium battery can be manufactured according to a conventional method. The lithium battery thus prepared has excellent battery chemistry and improved electrochemical stability even at high rate discharge, Excellent lifespan characteristics at high C-rate

EXAMPLE

Hereinafter, the structure and effect of the present invention will be described in more detail with specific examples and comparative examples, but these examples are only intended to more clearly understand the present invention, and are not intended to limit the scope of the present invention.

Examples 1 to 3

Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a carbonate-based organic solvent mixed in a 1: 1: 1 ratio of a solution of LiPF ₆ dissolved in 1.0 M as a basic electrolyte solution It was. Examples 1 to 3 by adding 1 part by weight (Example 1), 3 parts by weight (Example 2), 5 parts by weight (Example 3) of trimethylsilyl borate, based on 100 parts by weight of the basic electrolyte solution A nonaqueous electrolyte of was prepared:

The prepared electrolyte was applied to a square 423048 cell. At this time, the active material of the used negative electrode was graphite, and PVDF was used as a binder. LiCoO ₂ was used as an active material, PVDF was used as a binder, and acetylene black was used as a conductive material. With the manufactured battery, the discharge characteristics of the different C-rates were evaluated and the results are shown in Table 1. In addition, each of the batteries prepared above was evaluated for the charge-discharge characteristics and the results are shown in Table 2.

Comparative Example 1

A battery was manufactured using only the same basic electrolyte solution as Example 1 without using trimethylsilyl borate. With the manufactured battery, the discharge characteristics of the different C-rates were evaluated and the results are shown in Table 1. In addition, each of the batteries prepared above was evaluated for the charge-discharge characteristics and the results are shown in Table 2.

DOD: Depth of Discharge

From Table 1, it can be seen that the use of the electrolyte according to the present invention is excellent in high rate discharge characteristics, and furthermore, from Table 2, in the case of the electrolyte according to the present invention, compared with the comparative example without the additive, That is, it is understood that there is almost no degradation of other characteristics of the battery).

On the other hand, with a battery using the electrolyte solution according to Example 1 and Comparative Example 1, by performing a high rate charge and discharge of 1.0 C-rate about 170 cycles (cycle) and about 150 cycles to evaluate the life characteristics of the electrolyte solution, Figure 1 Shown in From Figure 1, it can be seen that the battery using the electrolyte according to the present invention exhibits excellent life characteristics at high rates.

As in the present invention, the nonaqueous electrolyte solution for lithium batteries to which trialkylsilyl borate is added has a high discharge capacity and discharge voltage at a higher rate than a conventional electrolyte solution without adversely affecting other battery characteristics in a battery using a nonaqueous electrolyte solution for secondary batteries. This improves, and has excellent characteristics of charge and discharge cycle characteristics. Therefore, it can be usefully used for the production of secondary batteries having improved high rate characteristics and lifetime characteristics.

1 is a view showing the results of comparing the life characteristics at 0.1 C-rate of the secondary battery using the electrolyte according to Example 1 and Comparative Example of the present invention.

Claims (5)

To 100 parts by weight of a lithium salt-containing mixed organic solution in which a lithium salt compound is dissolved at 0.8 to 2.0 M in a mixed solvent consisting of a cyclic carbonate organic solvent and a linear carbonate organic solvent, trialkylsilyl borate represented by the following formula (1) Non-aqueous electrolyte for lithium batteries prepared by adding 0.1 to 10 parts by weight of: [Formula 1] [Wherein R is alkyl of 1 to 4 carbon atoms]. The cyclic carbonate organic solvent is selected from the group consisting of ethylene carbonate, propylene carbonate and a mixture of both. The linear carbonate organic solvent is dimethyl carbonate, diethyl carbobo. Non-aqueous electrolyte solution for lithium batteries, characterized in that it is selected from the group consisting of nate, ethyl methyl carbonate, methyl propyl carbonate and mixtures thereof. The method of claim 1, wherein the mixed solvent further comprises at least one compound selected from the group consisting of propyl acetate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate and fluorobenzene. A nonaqueous electrolyte solution for lithium batteries. The method of claim 1, wherein the lithium salt compound is LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiN (CF ₃ SO ₂ ) ₂ A non-aqueous electrolyte solution for lithium batteries, characterized in that at least one compound selected from the group consisting of. Lithium battery comprising the nonaqueous electrolyte according to claim 1.