KR20040061562A - Nonaqueous Electrolyte for Use in Lithium Battery - Google Patents

Abstract

PURPOSE: A nonaqueous electrolyte solution for a lithium battery is provided, to improve the stabilities to electrochemical degradation and overcharge by using heterocyclic nitrogen compound, thereby allowing an electrode pack to be miniaturized. CONSTITUTION: The nonaqueous electrolyte solution comprises 100 parts by weight of an organic solvent mixture of linear and cyclic carbonate-based organic solvents which contains 0.8-2 M lithium salt; and 0.1-10.0 parts by weight of at least one heterocyclic nitrogen compound selected from the group consisting of a pyridine derivative represented by the formula 1, a pyrimidine derivative represented by the formula 2 and a triazine derivative represented by the formula 3, wherein R is an alkyl or alkoxy group of C0-C12. Preferably the lithium salt is at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, BETI and HQ115; the cyclic carbonate-based organic solvent is at least one selected from the group consisting of ethylene carbonate and propylene carbonate; and the linear carbonate-based organic solvent is at least one selected from the group consisting of carbonate dimethyl, carbonate diethyl, carbonate methylpropyl and carbonate ethylmethyl.

Description

Nonaqueous Electrolyte for Lithium Battery {Nonaqueous Electrolyte for Use in Lithium Battery}

The present invention relates to a non-aqueous electrolyte for lithium batteries, and more particularly, to a new non-aqueous electrolyte containing components which can improve the electrochemical decomposition characteristics of lithium batteries and the safety during overcharging without affecting battery characteristics. will be.

With the rapid miniaturization, light weight, and diversification of public-use mobile phones, portable electronic devices, and portable information terminals, development of secondary batteries that can be charged and discharged for a long period of time with small energy, light weight, high energy density, and the like has been strongly developed. It is required. Non-aqueous electrolyte secondary batteries, such as lithium secondary batteries, are the most promising secondary batteries that can satisfy these demands, and thus researches on them have been actively conducted.

Although the electrolyte for lithium batteries needs to be stable with respect to the lithium anode, there is no known thermodynamically stable solvent for lithium. Actually, the electrolyte is decomposed during initial charging of the battery, and the resulting reaction product is a lithium anode. It is believed that the formation of an ion conductive protective film, ie, a solid electrolyte interface (SEI), on the surface prevents further reaction between the electrode and the electrolyte, thereby stabilizing.

However, in such a nonaqueous electrolyte secondary battery, when the power circuit or the charging device of the electronic device is broken or overcharged, abnormal heat generation occurs in the battery, and in extreme cases, the battery may be damaged or ignite. Therefore, it has become an important issue to effectively suppress heat generation and ensure battery safety so that the battery does not cause thermal runaway.

Currently, as a countermeasure against rupture and ignition of a battery during overcharging, a method of controlling a charging voltage by a charger is most common by providing a protection circuit and a protection device inside the battery. However, at the current state of the art, since the use of the protection circuit and the protection element places great restrictions on the miniaturization and cost reduction of the battery pack, it is desirable to secure the safety of the battery without the protection circuit and the protection element.

In the meantime, efforts have been made to solve such problems, and Japanese Patent Laid-Open No. 7-302614, Japanese Patent Laid-Open No. 9-50822, Japanese Patent Laid-Open No. 9-106835, Japanese Patent No. 2939469, etc. A small amount of aromatics was added to the electrolyte solution to secure the battery against overcharging. Looking at the content and problems of these patents in more detail as follows.

Japanese Patent Application Laid-Open No. 7-302614 and Japanese Patent Application Laid-open No. Hei 9-50822 have an molecular weight of 500 or less as an additive in an electrolyte solution, a reversible redox potential at a positive electrode potential or higher at the time of full charge of a secondary battery, and a π electron orbit. It is proposed to use organic low molecular weight compounds such as anisole, and such additives constitute a protective mechanism capable of consuming overcharge current during overcharging of a secondary battery by an action called redox shuttle. It is describing. However, although it is certain that organic low molecular weight compounds such as anisole used in these patents function as redox shuttles during overcharging, these reactions inevitably have an adverse effect on the charge / discharge cycle characteristics of the battery since they occur in the general battery operating voltage range. It turns out mad.

On the other hand, Japanese Patent Application Laid-open No. Hei 9-106835 proposes the use of an additive which can protect a battery during overcharge by causing a polymerization reaction at a voltage in an overcharge state and acting as a resistor. However, since the additive used in this patent has a low polarity and low solubility in the electrolyte, part of the additive precipitates during low temperature operation, and charge and discharge are repeated up to a voltage upper limit of 4.1 V or long term at a high temperature of 40 ° C. or higher. In the neglected charge-discharge state, the additives tend to decompose to deteriorate the battery characteristics. Further, safety cannot be sufficiently secured when the overcharge test is performed after 300 cycles.

Therefore, the present invention is to solve the problems of the prior art as described above, by adding a heterocyclic nitrogen compound (heterocyclic nitrogen compound) to the conventional non-aqueous electrolyte for lithium batteries is a novel electrochemical degradation characteristics and improved safety when overcharged An object of the present invention is to provide a nonaqueous electrolyte for lithium batteries.

That is, the present invention is a heterocyclic nitrogen compound having the structure of Formulas 1 to 3 to 100 parts by weight of a mixed organic solvent of a cyclic carbonate organic solvent and a linear carbonate organic solvent containing a lithium salt of 0.8 to 2 M To provide a non-aqueous electrolyte for lithium batteries prepared by adding any one of 0.1 to 10.0 parts by weight of ratio:

[Formula 1]

;

[Formula 2]

;

[Formula 3]

(Wherein R is a C ₀ -C ₁₂ alkyl or alkoxy group).

1 is a graph showing the electrochemical decomposition characteristics of the electrolyte solution according to Example 1;

2 is a graph showing the electrochemical decomposition characteristics of the electrolyte solution according to Example 2;

3 is a graph showing the electrochemical decomposition characteristics of the electrolyte solution according to Example 3; And

4 is a graph showing the electrochemical decomposition characteristics of the electrolyte solution according to Comparative Example 1.

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

As a cathode active material of a conventional lithium secondary battery, a layered lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or lithium manganese oxide (LiMn ₂ O ₄ ) is mainly used as a material having a large capacity per unit weight. They are quite unstable because most of lithium ions are in a desorption state in an overcharged state, causing rapid decomposition exothermic reaction with electrolyte or depositing lithium metal on a negative electrode, and in the worst case, may cause battery rupture or ignition. Additives to prevent the need to add to the electrolyte to ensure the safety of the battery overcharge. In the present invention, any one selected from the group consisting of a pyridine derivative having a structure of formula (1), a pyrimidine derivative having a structure of formula (2) and a triazine derivative having a structure of formula (3) as an additive for achieving the above object Species heterocyclic nitrogen compounds are used:

;

;

(Wherein R is a C ₀ -C ₁₂ alkyl or alkoxy group).

The solvent used in the preparation of the nonaqueous electrolyte solution for lithium batteries of the present invention is used by mixing a cyclic carbonate organic solvent and a linear carbonate organic solvent, preferably a group consisting of ethylene carbonate (EC) and propylene carbonate (PC). From at least one cyclic carbonate organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC) One or more selected linear carbonate organic solvents are mixed and used, more preferably, ethylene carbonate and dimethyl carbonate are mixed, or ethylene carbonate, ethyl methyl carbonate and diethyl carbonate are mixed and used. In addition, it consists of propyl acetate (PA), methyl acetate (MA), ethyl acetate (EA), butyl acetate (BA), methyl propionate (MP), ethyl propionate (EP), and fluorobenzene (FB) as needed. One or more organic solvents selected from the group to be added may be further mixed and used. The mixing ratio of the organic solvent selected from the above groups is not particularly limited as long as the object of the present invention is not impaired, and the mixing ratio of the non-aqueous electrolyte for lithium batteries is generally used.

On the other hand, as the lithium salt contained in the non-aqueous electrolyte of the present invention, it is preferable to use one or more selected from the group consisting of LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , BETI, and HQ115, and more preferably. LiPF ₆ is used.

The non-aqueous electrolyte of the present invention is 0.1 to 10.0 parts by weight of the pyridine-, pyrimidine- or triazine-derivative, preferably 100 parts by weight of the basic electrolyte obtained by dissolving the lithium salt in the mixed organic solvent at 0.8 to 2 M. Is prepared by adding in a proportion of 0.1 to 0.5 parts by weight.

The lithium battery can be manufactured according to a conventional method using the nonaqueous electrolyte of the present invention, and the lithium battery thus prepared has higher electrochemical stability than a battery using a conventional nonaqueous electrolyte, and thus has excellent safety during overcharging.

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

1.0 parts by weight of pyridine was added to 100 parts by weight of a basic electrolyte solution in which 1 M of LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC): dimethyl carbonate (DMC) = 1: 1 (v / v). The electrolyte solution was completed.

Subsequently, the 2016 type button battery was manufactured using the nonaqueous electrolyte. At this time, graphite was used as the active material for the anode, PVDF [poly (vinylidene fluoride)] was used as the binder, LiCoO ₂ was used as the active material for the cathode, PVDF was used as the binder, and acetylene black was used as the conductive agent. It was.

The battery thus prepared was evaluated for overcharge characteristics by a 1.0C-rate overcharge experiment (see Table 1), and electrochemical decomposition characteristics were evaluated by LSV (Linear Sweep Voltametry) method (Working electrode: Pt; Reference electrode: Li-metal; Counter electrode: Li-metal; Voltage range: 3 to 0 V; Scan rate: 0.1 mV / s) (see FIG. 1).

Example 2

A nonaqueous electrolyte and a 2016-type button cell were prepared in the same manner as in Example 1, except that pyrimidine was used instead of pyridine. The battery thus prepared was evaluated for overcharging characteristics by a 1.0C-rate overcharging experiment (see Table 1), and the electrochemical decomposition characteristics were evaluated by LSV method (see FIG. 2).

Example 3

A nonaqueous electrolyte and a 2016-type button cell were prepared in the same manner as in Example 1, except that triazine was used instead of pyridine. The battery thus prepared was evaluated for overcharging characteristics by a 1.0C-rate overcharging experiment (see Table 1), and electrochemical decomposition characteristics were evaluated by LSV method (see FIG. 3).

Comparative Example 1

A 2016 type button battery was manufactured in the same manner as in Example 1, using the basic electrolyte solution. The battery thus prepared was evaluated for overcharging characteristics by a 1.0 C-rate overcharging experiment (see Table 1), and the electrochemical decomposition characteristics were evaluated by LSV method (see FIG. 4).

# 12V holding time Example 1 20 hours Example 2 16 hours Example 3 15 hours Comparative Example 1 0 hours

As can be seen in Table 1, the batteries prepared using the non-aqueous electrolyte of the present invention were all maintained at 1.0 C-rate overcharge at 12.0 (V) for more than 15 hours, these results were used in the present invention It is suggested that the heterocyclic nitrogen compound is very effective in preventing overcharging of lithium batteries.

As described in detail above, the non-aqueous electrolyte of the present invention has excellent electrochemical decomposition characteristics and safety against overcharging, and thus, it is possible to miniaturize and reduce the cost of the battery pack without requiring a separate protective circuit and a protective device for preventing overcharging.

Claims (5)

Pyridine derivative of the following formula (1), pyrimidine derivative of the following formula (2) and triazine of the following formula (3) in 100 parts by weight of a mixed organic solvent of a cyclic carbonate organic solvent and a linear carbonate organic solvent containing a lithium salt of 0.8 to 2 M Non-aqueous electrolyte for lithium batteries prepared by adding any one heterocyclic nitrogen compound selected from the group consisting of derivatives in a ratio of 0.1 to 10.0 parts by weight: [Formula 1] ; [Formula 2] ; [Formula 3] (Wherein R is a C ₀ -C ₁₂ alkyl or alkoxy group). The non-aqueous electrolyte solution for lithium batteries according to claim 1, wherein the lithium salt is at least one selected from the group consisting of LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , BETI, and HQ 115. The non-aqueous electrolyte solution for lithium batteries according to claim 1, wherein the cyclic carbonate organic solvent is at least one selected from the group consisting of ethylene carbonate (EC) and propylene carbonate (PC). The group according to claim 1, wherein the linear carbonate organic solvent is composed of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC). Non-aqueous electrolyte solution for lithium batteries, characterized in that at least one selected from. The mixed organic solvent of claim 1, wherein the mixed organic solvent is propyl acetate (PA), methyl acetate (MA), ethyl acetate (EA), butyl acetate (BA), methyl propionate (MP), ethyl propionate (EP), and fluorobenzene. A non-aqueous electrolyte solution for lithium batteries, further comprising at least one selected from the group consisting of (FB).