KR100370389B1 - Non-aqueous electrolyte solution for lithium battery - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte for lithium batteries, and more particularly, to 100 parts by weight of a mixed organic solvent of a cyclic carbonate organic solvent and a linear carbonate organic solvent in which lithium salt is dissolved at 0.8 to 2.0 M. The present invention relates to a nonaqueous electrolyte solution for lithium batteries prepared by adding 0.1 to 5.0 parts by weight of the aluminoxane compound shown. The use of the nonaqueous electrolyte solution for lithium batteries of the present invention can easily produce a lithium battery having excellent charge and discharge cycle life characteristics.

In the above, R is a methyl group, ethyl group, n-propyl group or isopropyl group, n is 5 to 30.

Description

Non-aqueous electrolyte solution for lithium battery

The present invention relates to a non-aqueous electrolyte for lithium batteries, and more particularly, to 100 parts by weight of a mixed organic solvent of a cyclic carbonate organic solvent and a linear carbonate organic solvent in which lithium salt is dissolved at 0.8 to 2.0 M. The present invention relates to a nonaqueous electrolyte solution for lithium batteries prepared by adding 0.1 to 5.0 parts by weight of the aluminoxane compound.

[Formula 1]

In the above, R is a methyl group, ethyl group, n-propyl group or isopropyl group, n is 5 to 30.

The miniaturized and slimmed lithium secondary battery used in notebook computers, camcorders, mobile phones, etc. is a positive electrode active material made of lithium metal mixed oxide capable of detaching and intercalating lithium ions, a negative electrode made of carbon material or metal lithium, and a mixed organic material. It consists of electrolyte solution in which lithium salt was melt | dissolved in the solvent in appropriate quantity. Coins, 18650 cylinders, 063048 squares, and the like are generally used as the lithium battery.

The average discharge voltage of about 3.6 to 3.7 V of the lithium battery is one of the biggest advantages of obtaining high power compared to other alkaline batteries or Ni-MH or Ni-Cd batteries. In order to achieve such a high driving voltage, an electrochemically stable electrolyte composition is required in the charge and discharge voltage range of 0 to 4.2V. Therefore, carbonate organic solvents such as ethylene carbonate (hereinafter referred to as "EC"), dimethyl carbonate (hereinafter referred to as "DMC") and diethyl carbonate (hereinafter referred to as "DEC") are appropriately mixed. It is used as a solvent of electrolyte solution. As the solute of the electrolyte, lithium salts such as LiPF ₆ , LiBF ₄ , and LiClO ₄ are usually used, and these act as a source of lithium ions in the battery to enable basic operation of the lithium battery. However, the non-aqueous electrolyte prepared in this way may have disadvantages in high rate charge and discharge because the conductivity of the nonaqueous electrolyte is significantly lower than that of the aqueous electrolyte used in Ni-MH or Ni-Cd batteries.

The ion conductivity of the electrolyte is an important factor that greatly affects the charge / discharge performance and the rapid discharge performance of the battery. In order for the electrolyte to have high ionic conductivity, the number of free ions must first be high, so the dielectric constant must be high and the viscosity must be low in consideration of the mobility of the free ions. In addition, when the electrolyte is solidified at low temperature, the free ions are restricted and thus the charge and discharge of the battery is impossible. Therefore, the electrolyte should have a low freezing point (see Makoto Ue, Solution Chemistry of Organic Electrolytes, Progress in Battery Materials (1997) Vol. 16).

In order to improve the ionic conductivity of the electrolyte for lithium batteries, various techniques are proposed to improve the electrochemical characteristics of lithium batteries by mixing high dielectric constant solvents and low viscosity solvents, and to improve low temperature performance of lithium batteries by mixing solvents with low freezing points. (US Pat. No. 5639575, US Pat. No. 55,25443). However, the change in the composition of the solvent alone does not improve the conductivity of lithium ions at low temperatures, particularly at about −20 ° C., and therefore, when discharging at a high rate (1 C), the discharge characteristic is rapidly decreased due to a sharp increase in internal resistance.

On the other hand, lithium ions from the lithium metal oxide used as the positive electrode during the initial charging of the lithium battery move to the graphite (crystalline or amorphous) electrode used as the negative electrode, and are inserted between the layers of the graphite electrode. At this time, since lithium has a high reactivity, the electrolyte and the carbon constituting the cathode react on the surface of the graphite anode to generate compounds such as Li ₂ CO ₃ , Li ₂ O, and LiOH. These compounds form a kind of passivation layer on the surface of the graphite cathode, which is called a solid electrolyte interface (SEI) film. Once formed, the SEI film functions as an ion tunnel to pass only lithium ions.

SEI film solvates lithium ions by the effect of this ion tunnel, and organic solvent molecules having a large molecular weight, such as EC, DMC, or DEC, which move together with lithium ions in the electrolyte are inserted together in the graphite cathode ( cointercalation) prevents the structure of graphite cathodes from collapsing. Once the SEI film is formed, lithium ions again do not react sideways with the graphite cathode or other material, and the amount of charge consumed to form the SEI film has a property of not reversibly reacting upon discharge with an irreversible capacity. Accordingly, no further decomposition of the electrolyte occurs and the amount of lithium ions in the electrolyte is reversibly maintained to maintain stable charge and discharge (see J. Power Sources (1994) 51:79 to 104).

The properties of the SEI film depend on the type of solvent or additives contained in the electrolyte, and are known as one of the main factors that affect the performance of the battery by affecting ion and charge transfer (see Shoichiro Mori, Chemical properties of various organic electrolytes for lithium rechargeable batteries, J. Power Source (1997) Vol. 68). Therefore, in order to improve the high-rate discharge characteristics at low temperatures of the lithium ion battery, in addition to the composition of an electrolyte which may have high ionic conductivity even at low temperatures, it is necessary to form an SEI film to which lithium ions can move to reduce the internal resistance of the battery. .

An object of the present invention is to solve the problems of the prior art, by adding an aluminoxane compound to a conventional nonaqueous electrolyte for lithium batteries to realize the formation of a stable SEI film, intercalation of lithium ions into the graphite cathode interlayer. And a novel nonaqueous electrolyte solution for lithium batteries that facilitates deintercalation to reduce internal resistance of the battery.

That is, the present invention is 0.1 to 5.0 weight of the aluminoxane compound represented by the following formula (1) to 100 parts by weight of a mixed organic solvent of a cyclic carbonate organic solvent and a linear carbonate organic solvent in which lithium salt is dissolved at 0.8 to 2.0 M. It provides a nonaqueous electrolyte solution for lithium batteries prepared by addition.

[Formula 1]

In the above, R is a methyl group, ethyl group, n-propyl group or isopropyl group, n is 5 to 30.

Hereinafter, the component of the nonaqueous electrolyte solution for lithium batteries of this invention is demonstrated in detail.

The organic 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 at least one selected from the group consisting of ethylene carbonate and propylene carbonate. A cyclic carbonate organic solvent and two or more linear carbonate organic solvents selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl and ethyl propyl are mixed and used, more preferably carbonic acid. Ethylene, dimethyl carbonate and diethyl carbonate are mixed and used. In addition, one or more types selected from the group consisting of propyl acetate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate and ethyl propionate 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 nonaqueous electrolyte solution for a lithium battery is followed.

On the other hand, as the lithium salt contained in the nonaqueous electrolyte of the present invention, it is preferable to use at least one selected from the group consisting of LiPF ₆ , LiClO ₄ , LiAsF _6, and LiBF ₄ , and more preferably LiPF ₆ . do.

The nonaqueous electrolyte of the present invention is prepared by adding 0.1 to 5.0 parts by weight, preferably 0.5 to 3.0 parts by weight of the aluminoxane compound represented by the following formula (1) to the mixed organic solvent in which lithium salt is dissolved.

[Formula 1]

In the above, R is a methyl group, ethyl group, n-propyl group or isopropyl group, preferably methyl group, n is 5 to 30.

The aluminoxane compound has a very high reactivity with a by-product having a -OH group, for example, LiOH, generated on the surface of the negative electrode as a result of side reactions when charging a lithium battery, and reacts with the negative electrode active material before other components of the electrolyte solution to provide stable Al containing. An electroconductive film, ie, an SEI film, is formed. The SEI film formed as described above allows lithium ions to be easily intercalated and deintercalated into the graphite cathode, thereby reducing the internal resistance of the battery.

The lithium battery can be manufactured according to a conventional method using the nonaqueous electrolyte solution for lithium batteries of the present invention. The lithium battery thus produced has a low internal resistance and an excellent charge / discharge cycle life.

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

5.9% (w / v) methyl in 100 parts by weight of a mixed organic solvent (hereinafter referred to as "basic nonaqueous electrolyte") in which ethylene carbonate: dimethyl carbonate: diethyl carbonate = 1: 1: 1 dissolved in LiPF ₆ was 1.0 M The aluminoxane toluene solution was added so that methyl aluminoxane was 0.5 parts by weight relative to the basic nonaqueous electrolyte, thereby preparing a nonaqueous electrolyte solution for a lithium battery. Using the nonaqueous electrolyte solution thus prepared, an 18650 cylindrical battery was prepared according to a conventional method. In manufacturing the battery, graphite and LiCoO ₂ were used as the negative electrode active material and the positive electrode active material, polyvinylidene fluoride was used as the binder, and acetylene black was used as the conductive agent.

Example 2

A nonaqueous electrolyte solution for a lithium battery was prepared in the same manner as in Example 1, except that 1.0 part by weight of methyl aluminoxane was added, thereby preparing an 18650 cylindrical battery.

Example 3

A non-aqueous electrolyte solution for lithium batteries was prepared in the same manner as in Example 1, except that 2.0 parts by weight of methyl aluminoxane was added, thereby preparing an 18650 cylindrical battery.

Example 4

A non-aqueous electrolyte solution for lithium batteries was prepared in the same manner as in Example 1, except that 3.0 parts by weight of methyl aluminoxane was added, thereby preparing an 18650 cylindrical battery.

Comparative Example 1

An 18650 cylindrical battery was prepared in the same manner as in Example 1, except that a basic nonaqueous electrolyte solution without adding methyl aluminoxane was used.

Each of the 18650 cylindrical batteries obtained from Examples 1 to 4 and Comparative Example 1 was fully charged from 0.2C to 4.2V under a constant temperature of 25 ° C., and then discharged from 0.2C to 2.75V, wherein the volume of gas generated at this time, Internal resistance and initial irreversible capacity were measured and the results are summarized in Table 1 below. The amount of gas generated is shown as a relative value based on the amount of generated in Comparative Example 1.

Gas generation amount Internal resistance (mΩ) Initial irreversible capacity (%) Example 1 0.81 54 9.38 Example 2 0.78 37 6.67 Example 3 1.03 44 7.56 Example 4 1.19 53 8.47 Comparative Example 1 One 62 8.65

As can be seen from Table 1, in the case of the battery using the non-aqueous electrolyte of the present invention, the gas generation amount and the initial irreversible capacity are measured at about the same level as the battery using the conventional basic non-aqueous electrolyte, but the internal resistance is significantly reduced. see.

On the other hand, in order to evaluate the cycle life characteristics of each of the 18650 cylindrical cells obtained from Examples 1 to 4 and Comparative Example 1, each cell was charged under constant current-constant voltage conditions (0.5C, 4.2V) and 2.75 at 0.2C After discharging up to 300 times, the discharge capacity was measured. The measurement results are shown in Table 2 below as relative values based on the discharge capacity of Comparative Example 1.

Discharge capacity Example 1 1.06 Example 2 1.22 Example 3 1.17 Example 4 1.09 Comparative Example 1 One

From the results in Table 2, it can be seen that the battery using the nonaqueous electrolyte of the present invention has improved charge / discharge cycle life as compared to a battery using a conventional basic nonaqueous electrolyte.

As described above in detail, when the nonaqueous electrolyte solution for lithium batteries of the present invention is used, the internal resistance of the battery is reduced, and thus a lithium battery having excellent charge / discharge cycle life characteristics can be easily manufactured.

Claims (4)

It was prepared by adding 0.1 to 5.0 parts by weight of an aluminoxane compound represented by the following formula (1) to 100 parts by weight of a mixed organic solvent of a cyclic carbonate organic solvent and a linear carbonate organic solvent in which a lithium salt was dissolved at 0.8 to 2.0 M. Non-aqueous electrolyte solution for lithium batteries. [Formula 1] In the above, R is a methyl group, ethyl group, n-propyl group or isopropyl group, n is 5 to 30. The method of claim 1, The cyclic carbonate organic solvent is ethylene carbonate, propylene carbonate, or a mixture thereof, and the linear carbonate organic solvent is dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or a mixture thereof. A nonaqueous electrolyte solution for lithium batteries. The method of claim 1, The non-aqueous electrolyte solution for lithium batteries, characterized in that the mixed organic solvent further comprises one or more selected from the group consisting of propyl acetate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate and ethyl propionate. The method of claim 1, The lithium salt is at least one selected from the group consisting of LiPF ₆ , LiClO ₄ , LiAsF _6, and LiBF ₄ , wherein the nonaqueous electrolyte solution for a lithium battery is used.