KR100628629B1 - 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 phenyl carbamate to a lithium salt-containing mixed organic solution obtained by dissolving a lithium salt in a carbonate mixed organic solvent. It relates to a battery. The nonaqueous electrolyte solution for lithium batteries according to the present invention can prevent overcharging at a high rate as compared with a conventional electrolyte solution, thereby ensuring stability without a protection circuit and a protection device.

Description

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

1 is a graph showing the overcharge result of the electrolyte according to an embodiment of the present invention,

2 to 4 are graphs showing the electrochemical characteristics of the electrolyte according to the Examples and Comparative Examples of the present invention.

The present invention relates to a nonaqueous electrolyte solution for lithium batteries prepared by adding a phenyl carbamate compound to a lithium salt-containing mixed organic solution obtained by dissolving a lithium salt in a carbonate mixed organic solvent. It relates to a battery cell. More specifically, the present invention provides a phenylcarbamate compound 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 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, and 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. According to such a demand, there have been many studies on lithium secondary batteries and the like as secondary batteries. Although the electrolyte solution for lithium batteries needs to be stable with respect to a lithium cathode, it is known that there is no solvent which is completely thermodynamically stable with respect to lithium. In the case of a lithium battery, the electrolyte is actually decomposed to the cathode during initial charging so that the reaction product forms an ion conductive protective film, ie, a solid electrolyte interface (SEI), on the surface of the lithium, and suppresses the reaction between the electrode and the electrolyte. It is thought that it is stabilized.

However, the secondary battery of the nonaqueous electrolyte has abnormal heat generation in the battery when the power circuit or the charging device of the electronic device is broken or overcharged, and in extreme cases, the battery may be damaged or ignited. The development of a method to secure the system is required. As a countermeasure to prevent the battery from rupturing or ignition due to overcharging, a method of controlling the charging voltage of the charger is the mainstream, and there may be a method of additionally installing a protection circuit or a protection element. Installation is not a good solution because the burden on the miniaturization and low cost of the battery pack.

In order to solve this problem, there have been attempts to prevent overcharge by adding an additive to an electrolyte of a lithium battery (see Japanese Patent Application Laid-Open No. 7-302614, Hei 9-50822, Hei 9-106835, and Korean Patent No. 2939496). For example, Japanese Patent Laid-Open Nos. 7-302614 and 9-50822 are additives in an electrolyte, having an molecular weight of 500 or less, pi electron orbits, and anisoles having a reversible redox potential greater than or equal to the positive electrode potential during full charge of a secondary battery. It is proposed to add a compound, in which case, the additive acts as a redox shuttle to establish a protective mechanism that consumes the overcharge current during overcharge. On the other hand, Japanese Patent Laid-Open No. 9-106835 discloses a technique in which an additive protects a battery during overcharge by starting a polymerization reaction at a voltage in an overcharge state and acting as a resistor. However, according to the researches of the present inventors, in the case of the prior art, the shuttle action or the polymerization reaction proceeds in the general battery use voltage range adversely affects the cycle characteristics of the discharge capacity.

On the other hand, in the case of a lithium secondary battery according to the prior art, a layered lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ) or lithium manganese oxide (LiMn ₂ O ₄ ) or the like as a positive electrode active material is used. However, these oxides are very unstable because most of the lithium ions are in a desorption state in an overcharged state, and they react with the electrolyte to cause a rapid decomposition exothermic reaction or to deposit lithium metal on the negative electrode, causing the battery to rupture or ignite in the worst case. There is a problem that can cause.

Therefore, there is an urgent need in the art for the development of a technology capable of securing stability against overcharging without adversely affecting other characteristics of the battery.

The present inventors have diligently researched to solve the above problems, and when phenyl carbamate is added to the nonaqueous electrolyte for the battery, the electrochemical stability of the electrolyte may be increased, thereby greatly improving the battery stability during overcharging. At the same time, it was confirmed that the battery had no adverse effect on other characteristics of the battery and led to the present invention.

As a result, the present invention is to provide a novel nonaqueous electrolyte solution for lithium batteries with improved stability upon overcharging while maintaining other battery performance.

Therefore, according to one preferred embodiment of the present invention, at least one cyclic carbonate organic solvent (A) and dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and ethylene carbonate and propylene carbonate Phenyl carbamate represented by the following formula (1) to 100 parts by weight of the mixed organic electrolyte solution in which the lithium salt compound is dissolved at 0.8 to 2 M in a mixed solvent consisting of at least one linear carbonate organic solvent (B) in methylpropyl carbonate A non-aqueous electrolyte for lithium batteries prepared by adding 0.1 to 10 parts by weight is provided:

According to another preferred embodiment of the present invention, a lithium secondary battery including the nonaqueous electrolyte is provided.

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

The nonaqueous electrolyte according to the present invention is prepared by adding 0.1 to 10 parts by weight, preferably 0.1 to 0.5 parts by weight of phenyl carbamate of Formula 1 to 100 parts by weight of a lithium salt-containing mixed organic solution.

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

Using the nonaqueous electrolyte solution for lithium batteries according to the present invention, a lithium battery can be produced according to a conventional method, and the lithium battery thus prepared has excellent battery chemistry and can effectively prevent overcharging of the battery.

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.

Example

A solution in which LiPF ₆ was dissolved in 1.0 M in a carbonate mixed organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a ratio of 3: 7 was used as a basic electrolyte solution. On the basis of 100 parts by weight of the base electrolyte, 1 part by weight of phenylcarbamate was added to prepare a nonaqueous electrolyte of Example.

The prepared electrolyte was applied to the pouch battery. 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 a cathode active material, PVDF was used as a binder, and acetylene black was used as a conductive agent. With the battery prepared, the overcharge experiment was performed for 2 hours under conditions of 12V and 1.0 C-rate, and the results are shown in Table 1. On the other hand, Figure 1 shows a graph of the result of the overcharge of the battery according to this embodiment.

Comparative Examples 1 and 2

An electrolyte was prepared in the same manner as in Example, except that a methyl carbamate (Comparative Example 1) or a methyl-ethyl carbamate (Comparative Example 2) compound was added instead of phenyl carbamate, thereby preparing a battery. The prepared battery was subjected to an overcharge experiment under the same conditions as in Example, and the results are shown in Table 1.

As is apparent from Table 1 and FIG. 1, when the electrolyte solution according to the present invention was used, the battery stability during overcharge was greatly improved, and the overcharge test was passed for 2 hours. However, the battery using the electrolyte solution according to the comparative example had no gas in the overcharge test. Occurred and eventually exploded.

Furthermore, with the electrolyte solution according to the embodiment of the present invention and the electrolyte solution according to the comparative example, the cyclic voltametry (Cyclic Voltametry) is measured under the following conditions, the results are shown in Figure 2 (Example), Figure 3 (Comparative Example) 1) and 4 (Comparative Example 2):

1) working electrode: anode material (MCF)

2) refernece electrode: Li-metal

3) Counter electrode: Li-metal

4) Voltage range: 3.5V ~ 0V

5) Scan Speed: 0.1mV / s, 3 Cycles

From the comparison of Figures 2 to 4, it can be seen that the electrolyte according to the present invention has better electrochemical properties than the electrolyte of the prior art.

As in the present invention, the nonaqueous electrolyte solution for lithium batteries to which phenyl carbamate is added has improved stability during overcharge without adversely affecting other battery characteristics in a battery using a nonaqueous electrolyte solution for secondary batteries, so that overheating and rupture occur due to overcharge. Or it can be usefully used in the manufacture of secondary batteries without the risk of fire.

Claims (5)

One or more cyclic carbonate organic solvents (A) of ethylene carbonate and propylene carbonate and linear carbonate organic of one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methylpropyl carbonate Non-aqueous lithium battery prepared by adding 0.1 to 10 parts by weight of phenyl carbamate represented by the following formula (1) with respect to 100 parts by weight of the mixed organic electrolyte solution in which a lithium salt compound was dissolved at 0.8 to 2 M in a mixed solvent consisting of a solvent (B). Electrolyte: [Formula 1]

. delete 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 , LiAsF ₆ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiN (CF ₃ SO ₂ ) A non-aqueous electrolyte solution for lithium batteries, characterized in that it is at least one compound selected from the group consisting of ₂ . Lithium battery comprising the nonaqueous electrolyte according to claim 1.

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