KR100611449B1 - Nonaqueous Electrolyte for Battery - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte for batteries comprising an organic solvent and a lithium salt, characterized in that it comprises dichlorobenzene of the formula (1), the battery to which the non-aqueous electrolyte for batteries of the present invention is excellent in charge and discharge life performance at high temperature The increase in thickness is reduced and the capacity storage characteristics at high temperatures have the advantage of being excellent.

[Formula]

Lithium battery, non-aqueous electrolyte, organic solvent, lithium salt, dichlorobenzene, charge and discharge life performance, high temperature stability, thickness increase rate

Description

Nonaqueous Electrolyte for Battery {Nonaqueous Electrolyte for Battery}             

1 is a graph comparing charge and discharge life performance of a battery using a nonaqueous electrolyte according to the present invention and a battery using a conventional nonaqueous electrolyte.

Figure 2 is a graph comparing the increase in thickness with time at a high temperature of 90 ℃ in a state of charge of a battery using a non-aqueous electrolyte according to the present invention and a battery using a conventional non-aqueous electrolyte.

The present invention relates to a non-aqueous electrolyte for batteries, and more particularly, to a non-aqueous electrolyte for lithium batteries comprising an organic solvent and a lithium salt, the dichlorobenzene is included in the thickness increase rate at high temperatures, and the capacity storage characteristics at high temperatures. It relates to this excellent nonaqueous electrolyte solution for batteries.

Lithium secondary batteries have high energy density, low self-discharge rate, and light weight, making them popular as high-performance energy sources for portable electronic devices requiring thin and lightweight notebook computers, camcorders, mobile phones, and digital cameras. Such lithium secondary batteries generally use a lithium metal mixed oxide as a positive electrode active material, and use a carbon material or metal lithium as a negative electrode material. Since a lithium battery is usually designed at high pressure, an organic solvent that can withstand high voltages, that is, a non-aqueous electrolyte, is used as an electrolyte, and a lithium salt dissolved in an organic solvent is mainly used.

In general, the electrolyte used in the battery reacts with the carbon constituting the negative electrode to form a thin film on the surface of the negative electrode, but the type of the formed film is greatly influenced by the solvent and additives used in the electrolyte, which is known to have a great effect on the battery performance. . Therefore, studies for optimizing the composition of the non-aqueous electrolyte are being actively conducted. In particular, the demand for excellent charge and discharge life performance and high temperature stability performance of the battery has recently increased, and in order to satisfy this, technologies for adding a specific compound to the electrolyte have been developed.

As an example of such a prior art, Japanese Patent Application Laid-Open No. 9-63649 discloses a method of improving the charge and discharge life of a battery by preventing decomposition of the electrolyte by adding 1% or more of CO ₂ to the nonaqueous electrolyte and preventing the reaction between the organic solvent and the lithium salt. It is starting. Japanese Patent Laid-Open No. 9-6344 has proposed a method of improving the safety and discharge characteristics of a battery by adding at least 10% by weight of a cyclic cyclic substituted carbonate compound.

On the other hand, Japanese Patent Laid-Open No. 8-236155 proposes a method of improving the charge / discharge life performance of a battery by adding an amine compound to suppress decomposition of the electrolyte. US Patent No. 5,709,968 proposes a technique for suppressing the thermal runaway phenomenon of the battery during overcharge by using a benzene compound substituted with an alkyl group and a halogen group.

However, most of the conventional techniques as described above, in which a specific compound is added to an electrolyte solution to improve battery performance, have the problem of improving the performance of some items of the battery, but rather reducing the performance of other items. For example, when an additive is added to the electrolyte, charge and discharge life performance is improved, but high temperature stability is reduced.

In order to overcome this problem, the present applicant proposes a technique for improving the charge / discharge life performance of a battery without adding a halogenated benzene compound to the non-aqueous electrolyte in the prior patent application No. 99-10777. It was. The present inventors earnestly researched to develop a non-aqueous electrolyte solution which can evenly improve various characteristics of the battery such as the charge / discharge life performance of the battery, stability at high temperature, and the like. The present invention has been completed by discovering the fact that it is possible to greatly improve the life performance and high temperature swelling stability.

One object of the present invention is to provide a novel nonaqueous electrolyte solution for batteries with improved charge and discharge life performance of the battery without degrading the performance of the basic electrolyte solution.

Another object of the present invention is to provide a nonaqueous electrolyte solution for batteries in which the thickness increase rate of the battery is significantly reduced and the capacity storage characteristics at high temperatures are improved in addition to the above object.

That is, the present invention provides a nonaqueous electrolyte solution for a battery comprising 0.1 to 50% by weight of dichlorobenzene in the 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 for lithium batteries of the present invention is characterized in that it contains 0.1 to 50% by weight of dichlorobenzene of the general formula (1) as a non-aqueous electrolyte in which lithium salt is dissolved in an organic solvent.

In the present invention, the dichlorobenzene of Formula 1 is one selected from the group consisting of 1,2-dichlorobenzene, 1,3-dichlorobenzene and 1,4-dichlorobenzene. The amount of dichlorobenzene added in the present invention is 0.1 to 50% by weight, preferably 0.5 to 10% by weight. When the amount of dichlorobenzene added in the present invention is less than 0.1% by weight, the high temperature charge-discharge life performance, high temperature stability, and the effect of decreasing the thickness increase rate at the time of leaving the high temperature, which are intended in the present invention, cannot be sufficiently obtained. If it exceeds, since the effect does not increase proportionally as adding dichlorobenzene, it is not preferable from an economic point of view.

Batteries such as a lithium secondary battery decompose the electrolyte during high temperature storage in a fully charged state, and continuously generate gas, thereby expanding the thickness of the battery. As such, when the thickness of the battery increases, a problem may occur in the mounting of the battery. Therefore, the battery preferably has a small thickness increase rate at high temperature. In the present invention, when dichlorobenzene is added to the basic electrolyte solution in which lithium salt is dissolved in the organic solvent, decomposition of the electrolyte solution is suppressed even at high temperature storage, thereby significantly reducing the thickness increase rate of the battery and at the same time, charging / discharging life performance of the battery and capacity at high temperature. Storage characteristics are also significantly improved.

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. One example of a preferable composition of the nonaqueous electrolyte solution for batteries of the present invention is to contain 0.1 to 50% by weight of dichlorobenzene 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 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 ~ 2M, 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 may be lowered. This may be degraded.

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 that the thickness of the battery expands 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

A solution of 1 M of LiPF ₆ dissolved as a solute in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2 was used as a basic nonaqueous electrolyte, and 1,4-dichlorobenzene was used as the basic nonaqueous electrolyte. 2% by weight of the final nonaqueous electrolyte was obtained. A SLPB 393452 battery was prepared using the nonaqueous electrolyte solution prepared as above, 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. The charging and discharging life performance of the battery thus prepared was evaluated and graphically shown in FIG. 1, and after charging standard to 4.2V, the thickness increase with time at 90 ° C. was shown in FIG. 2.

Comparative Example 1

A battery was prepared using a basic electrolyte solution containing 1 M of LiPF ₆ as a solute in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2 without adding dichlorobenzene. The charge and discharge life performance of the battery obtained and the increase in thickness at 90 ° C. were evaluated in the same manner as in Example 1, and the results are shown together in FIGS. 1 and 2, respectively.

Comparative Example 2

As a comparative example, ethylene carbonate (EC) as a basic non-aqueous electrolyte without addition of dichlorobenzene; Ethyl methyl carbonate (EMC); A battery was prepared in the same manner as in Example 1, except that 1 M of LiPF ₆ was dissolved as a solute in a solvent in which fluorobenzene was mixed at a volume ratio of 4: 5: 1, to thereby obtain a battery. The increase in thickness at 90 ° C. of the battery was evaluated in the same manner as in Example 1, and the results are shown together in FIG. 2.

How to evaluate battery performance

* Charge / discharge life performance : The standard capacity (mAh) of the battery was measured every cycle while the battery was charged from 1 C-mA to 4.2 V and then repeatedly discharged from 1 C-mA to 3.0 V for 200 cycles.

* Thickness increase rate at high temperature: 90 ℃ Temperature increase rate is measured after charging the battery between the gauges for measuring thickness in hot air oven at 90 ℃ after standard charging up to 4.2V. Measured according to.

As can be seen from the graph of FIG. 1, the battery to which the nonaqueous electrolyte solution containing the dichlorobenzene of the present invention is applied has a significant improvement in the charge / discharge life performance of the battery as compared to the battery of the comparative example which does not contain dichlorobenzene. In addition, as can be seen through the graph of Figure 2, the non-aqueous electrolyte of the present invention was significantly reduced in thickness increase at 90 ℃ high temperature when applied to the battery, in particular, the effect of reducing the thickness increase is the case of applying the dichlorobenzene of the present invention It was much better than the case where another halogen compound (fluorobenzene) of Comparative Example 2 was applied.

Examples 2-7

After the amount of ethylene carbonate (EC) was fixed to 40% by weight, the amount of ethyl methyl carbonate (EMC) was changed from 10% to 55% by weight, and the amount of 1,4-dichlorobenzene was added to 5% by weight to 50% by weight. 1 M of LiPF ₆ was dissolved as a solute in a solvent obtained by mixing while changing to a nonaqueous electrolyte. The SLPB 393452 battery was prepared using the nonaqueous electrolytes prepared as described above, but graphite was used as a negative electrode active material 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. The standard capacity of the battery thus prepared and the thickness of the battery after 4 hours at 90 ° C. were evaluated and shown in Table 1 below.

Comparative Example 3

A non-aqueous electrolyte was obtained by dissolving 1 M of LiPF ₆ as a solute in a solvent in which 40 wt% of ethylene carbonate (EC) and 60 wt% of ethyl methyl carbonate (EMC) were mixed without adding dichlorobenzene. After the battery was prepared, the standard capacity of the prepared battery and the thickness after 4 hours at 90 ° C. were evaluated and shown in Table 1 below.

Solvent Composition (wt%) Standard capacity (mA) Thickness increase at high temperature (mm) EC EMC 1,4-dichlorobenzene Comparative Example 3 40 wt% 60 wt% 0 wt% 660 4.90 Example 2 40 wt% 55 wt% 5 wt% 670 4.05 Example 3 40 wt% 50 wt% 10 wt% 665 4.00 Example 4 40 wt% 40 wt% 20 wt% 660 3.98 Example 5 40 wt% 30 wt% 30 wt% 640 3.98 Example 6 40 wt% 20 wt% 40 wt% 625 3.98 Example 7 40 wt% 10 wt% 50 wt% 620 3.98

 The nonaqueous electrolyte solution for batteries according to the present invention has an excellent charge / discharge life performance and remarkably suppresses the increase in thickness at a high temperature, thereby having an excellent high temperature stability.

Claims (4)

An electrolyte solution for lithium secondary batteries that employs a lithium-based active material as a positive electrode and a graphite-based active material as a negative electrode, and at least one cyclic carbonate organic solvent selected from ethylene carbonate and propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, and ethyl methyl. Dichlorobenzene represented by the following Chemical Formula 1 in a solvent in which at least one linear carbonate-based organic solvent selected from carbonate and methylpropyl carbonate is mixed, among 1,2-dichlorobenzene, 1,3-dichlorobenzene and 1,4-dichlorobenzene 1 to 15% by weight of one or more selected, LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiCF ₃ SO _{3 It} comprises at least one lithium salt selected from the group, the concentration is 0.8 to 2M A nonaqueous electrolyte solution for a battery. [Formula 1]

delete The method of claim 1, wherein the organic solvent further comprises one or two or more selected from the group consisting of γ- butyrolactone, methyl acetate, ethyl acetate, propyl acetate, methyl propionic acid and ethyl propionic acid. A nonaqueous electrolyte solution for the battery. delete

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