KR100551003B1 - Electrolyte for rechargeable lithium battery and rechargeable lithium battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery electrolyte and a lithium secondary battery comprising the same, the electrolyte is an overcharge inhibitor additive of the formula (1); Lithium salts; And non-aqueous organic solvents.

[Formula 1]

(In Formula 1, R ₁ and R ₂ are the same or different, and each independently H, CH ₃ , CH ₂ NH ₂ , CH ₂ COCH ₃ or CH ₂ CHOHCH ₃ )

The battery using the electrolyte solution containing the overcharge inhibiting additive of the present invention exhibits excellent battery safety even when overcharged.

Overcharge, electrolyte, lithium secondary battery, phenazine

Description

ELECTROLYTE FOR RECHARGEABLE LITHIUM BATTERY AND RECHARGEABLE LITHIUM BATTERY}

[Industrial use]

The present invention relates to a lithium secondary battery electrolyte and a lithium secondary battery comprising the same, and more particularly, to a lithium secondary battery electrolyte that can improve battery safety.

[Prior art]

Recently, with the development of the high-tech electronic industry, it is possible to reduce the weight and weight of electronic equipment, thereby increasing the use of portable electronic devices. As a power source for such portable electronic devices, the necessity of a battery having a high energy density has been increased, and research on lithium secondary batteries has been actively conducted.

When the lithium secondary battery is overcharged due to a charger malfunction or the like and the voltage rises rapidly, excess lithium is discharged from the positive electrode according to the state of charge and is deposited on the negative electrode surface. You will be in a very unstable state. As a result, the exothermic reaction rapidly progresses due to thermal decomposition of the electrolyte, reaction between the electrolyte and lithium, oxidation of the electrolyte at the anode, reaction of oxygen and the electrolyte generated by thermal decomposition of the anode oxide, and a sudden increase in battery temperature (thermal runaway). Therefore, the battery's maximum allowable temperature is exceeded, which causes problems such as fire and smoke of the battery.

In order to solve this problem, many attempts have been made to suppress the overcharging of lithium batteries by changing the composition of the electrolyte or adding an additive to the electrolyte. For example, U.S. Patent No. 5,580,684 adds trimethyl phosphate, tri (trifluoroethyl) phosphate, tri (2-chloroethyl) phosphate, etc. to the electrolyte as a phosphate ester substance to increase the self-extinguishing of the electrolyte. In this case, US Pat. No. 5,776,627 adds thiophene, biphenyl, furan, and the like to polymerize the battery when the battery is abnormal, thereby preventing the movement of lithium. A method of increasing the safety of a battery by opening the vent easily is disclosed.

Also similar to the above methods, US Pat. No. 5,763,119, 1,2-dimethoxy-4-bromo-benzene, US Pat. No. 5,709,968, 2-chloro-p-xylene and 4-chloro-anisole, US Pat. 5,858,573 discloses a method for improving battery safety by adding 2,7-diacetyl thianthrene and the like, respectively.

Similarly, Japanese Patent Laid-Open No. 7-302614 discloses a method of protecting a battery by consuming an overcharge current by forming a polymer using a benzene compound.

However, most of the additives can be polymerized under normal operating conditions of the battery or can generate a large amount of gas by oxidative decomposition, thereby increasing the swelling phenomenon of the battery. There are various problems such as deterioration of various characteristics of the product, which has not been put into practical use.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an electrolyte solution for a lithium secondary battery that can improve the safety of the battery.

Another object of the present invention is to provide a lithium secondary battery including the electrolyte.

In order to achieve the above object, the present invention is an overcharge inhibitor additive of the formula (1); Lithium salts; And it provides a lithium secondary battery electrolyte containing a non-aqueous organic solvent.

[Formula 1]

(In Formula 1, R ₁ and R ₂ are the same or different, and each independently H, CH ₃ , CH ₂ NH ₂ , CH ₂ COCH ₃ or CH ₂ CHOHCH ₃ )

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

The present invention relates to an electrolyte for a lithium secondary battery in which a new additive is added to an existing electrolyte composition so as to prevent a problem due to a sudden voltage increase during overcharging.

The additive used in the present invention is a compound represented by the following formula (1).

[Formula 1]

(In Formula 1, R ₁ and R ₂ are the same or different, and each independently H, CH ₃ , CH ₂ NH ₂ , CH ₂ COCH ₃ or CH ₂ CHOHCH ₃ )

When an electrolyte solution containing this compound is used in a battery, when the battery is overcharged and the voltage rises rapidly beyond the full charge voltage, the additive consumes an overcharge current by a redox-shuttle mechanism. . This is because the additive initiates a polymerization reaction at about 4.9V to form a polymerizable film on the electrode plate surface to coat the electrode plate surface. As a result, polymeric coatings that increase resistance between the anode and cathode, and also have some ionic and electrical conductivity, produce a soft short (shuntting) effect at both electrodes, consuming overcharge currents and suppressing potential rises. Thermal runaway can be controlled, resulting in improved battery safety.

The content of the additive in the electrolyte solution of the present invention is preferably 0.5 to 5% by weight, more preferably 1 to 2% by weight of the electrolyte solution. If the content of the additive is less than 0.5 wt% of the weight of the electrolyte, the effect of adding the additive is insignificant, and if it exceeds 5 wt%, there is a problem that the life characteristics are lowered or the discharge characteristics are worsened.

The electrolyte solution of the present invention includes a lithium salt and a non-aqueous organic solvent which are conventional electrolyte solution compositions in addition to the additive.

The lithium salt is dissolved in an organic solvent to serve as a source of lithium ions in the battery to enable operation of the basic lithium secondary battery and to promote the movement of lithium ions between the positive and negative electrodes. Such lithium salts include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (where x and y are natural numbers), LiCl and LiI selected from the group consisting of Include. The concentration of the lithium salt is preferably used within the range of 0.6 to 2.0M. When the concentration of the lithium salt is less than 0.6M, the conductivity of the electrolyte is lowered, the performance of the electrolyte is lowered, and when the lithium salt is more than 2.0M, the viscosity of the electrolyte is increased to reduce the mobility of lithium ions.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the cell can move. The non-aqueous organic solvent may be used one or more selected from the group consisting of carbonates, esters, ethers and ketones. As the carbonate, cyclic carbonate or chain carbonate may be used. The mixing ratio in the case of mixing one or more of the organic solvents can be appropriately adjusted according to the desired battery performance, which can be widely understood by those skilled in the art. The ring carbonate may be a ring carbonate selected from the group consisting of ethylene carbonate, propylene carbonate and mixtures thereof, and the linear carbonate is selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate and methylpropyl carbonate. One or more linear carbonates may be used. In addition, γ-butyrolactone, valerolactone, decanolide, mevalolactone, etc. may be used as the ester. As the ketone, polymethyl vinyl ketone may be used.

The lithium secondary battery including the electrolyte solution of the present invention includes a positive electrode and a negative electrode.

The positive electrode includes a positive electrode active material capable of reversibly intercalating and deintercalating lithium ions. Representative examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , or LiNi _{1- Use a} lithium-transition metal oxide such as _xy Co _x M _y O ₂ (0≤x≤1, 0≤y≤1, 0≤x + y≤1, where M is a metal such as Al, Sr, Mg, La, etc.) do. In addition, it is natural that any compound well known in the art may be used as a cathode active material of a lithium secondary battery.

The negative electrode includes a negative electrode active material capable of intercalating and deintercalating lithium ions, and the negative electrode active material uses a crystalline or amorphous carbon or a carbon-based negative electrode active material of a carbon composite. In addition, it is natural that any compound well known in the art may be used as a negative electrode active material of a lithium secondary battery.

The battery using the electrolyte solution of the present invention is a lithium secondary battery including the positive electrode and the negative electrode as described above, and may be an ion battery having the above-described configuration, or may be formed of a polymer battery when a gel-forming monomer and an initiator are added to the electrolyte solution. have. As the gel-forming monomer and the initiator, any compound used in forming a polymer battery may be used. Representative examples of the gel-forming monomer may include methacrylate, ethylene oxide, and propylene oxide, and as the initiator, azobis Azo compounds, such as isobutyronitrile etc., or organic peroxides, such as isobutyl peroxide and a lauroyl peroxide, are mentioned. It is well known in the art to form a polymer battery by adding a gel forming monomer and an initiator, and thus detailed description thereof will be omitted.

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)

LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (2: 8 volume ratio) at 1 M concentration. N, N-bis- (2-hydroxypropyl) dihydrophenazine was added to the obtained mixture in an amount of 1% by weight of the mixture to prepare an electrolyte solution.

(Comparative Example 1)

LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (2: 8 by volume) at a concentration of 1 M to prepare an electrolyte solution.

Ten batteries each manufactured by the method of Example 1 and Comparative Example 1 were measured at 12C overcharge characteristics at 1C, and the results are shown in Table 1 below.

1C / 12V Overcharge Characteristics Comparative Example 1 8L4, 2L2 Example 1 10L1

In Table 1, L1 is a simple electrolyte leakage, L2 is less than 200 ℃ fume, L4 means ignition and the number before L means the number of batteries. That is, 8L4 means that eight batteries are ignited. Therefore, in Example 1, only 10 batteries were leaked during overcharging, whereas in Comparative Example 1, eight batteries were ignited and two batteries were smoked. Thus, the battery of Example 1 was compared with that of Comparative Example 1. It can be seen that excellent battery stability during overcharging.

The battery using the electrolyte solution containing the overcharge inhibiting additive of the present invention exhibits excellent battery safety even when overcharged.

Claims (10)

Overcharge inhibitor additive of the general formula (1); Lithium salts; And Non-aqueous organic solvent Including; The content of the overcharge inhibitor additive is 0.5 to 5% by weight compared to the non-aqueous organic solvent Electrolyte for lithium secondary battery. [Formula 1]

(In Formula 1, R ₁ and R ₂ are the same or different, and each independently H, CH ₃ , CH ₂ NH ₂ , CH ₂ COCH ₃ or CH ₂ CHOHCH ₃ ) delete The electrolyte of claim 1, wherein the content of the overcharge inhibiting additive is 1 to 2% by weight based on the nonaqueous organic solvent. The method of claim 1, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ Lithium secondary, one or two or more selected from the group consisting of SO ₃ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ), where x and y are natural numbers, LiCl and LiI Battery electrolyte. The electrolyte of claim 1, wherein the non-aqueous organic solvent is selected from the group consisting of carbonates, esters, ethers, and ketones. A positive electrode including a positive electrode active material capable of reversibly intercalating and deintercalating lithium ions; A negative electrode including a negative electrode active material capable of reversibly intercalating and deintercalating lithium ions; An electrolyte comprising a lithium salt, a non-aqueous organic solvent, and an overcharge inhibiting additive of Formula 1, wherein the content of the overcharge inhibiting additive is 0.5 to 5% by weight relative to the nonaqueous organic solvent. Lithium secondary battery comprising a. [Formula 1]

(In Formula 1, R ₁ and R ₂ are the same or different, and each independently H, CH ₃ , CH ₂ NH ₂ , CH ₂ COCH ₃ or CH ₂ CHOHCH ₃ ) delete The lithium secondary battery of claim 6, wherein the content of the overcharge inhibiting additive is 1 to 2 wt% based on the non-aqueous organic solvent. The method of claim 6, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ Lithium secondary, one or two or more selected from the group consisting of SO ₃ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ), where x and y are natural numbers, LiCl and LiI battery. The lithium secondary battery of claim 5, wherein the non-aqueous organic solvent is selected from the group consisting of carbonate, ester, ether, and ketone.