KR20060041429A - Non-aqueous electrolyte for lithium secondary batteries and lithium secondary batteries containing the same - Google Patents

Abstract

The present invention relates to a nonaqueous electrolyte solution for a lithium secondary battery that does not affect the battery characteristics and does not cause decomposition of the electrolyte during charge and discharge, thereby improving the electromotive force, discharge capacity, and lifespan characteristics of the battery. Disclosed is a nonaqueous electrolyte solution for a lithium secondary battery comprising biscarboxymethyl trithiocarbonate (Bis).

[Formula 1]

Non-Aqueous Electrolyte, Bis (carboxymethyl) trithiocarbonate

Description

Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery comprising same {Non-aqueous electrolyte for Lithium Secondary Batteries and Lithium Secondary Batteries containing the same}

1 is a life characteristics test results of the battery prepared in Examples and Comparative Examples of the present invention.

The present invention relates to a non-aqueous electrolyte for lithium secondary batteries, and more particularly, to non-aqueous electrolyte for lithium secondary batteries, which does not affect battery characteristics and does not cause decomposition of electrolyte during charge and discharge, thereby improving electromotive force, discharge capacity, and lifetime characteristics of the battery. The present invention relates to an electrolyte solution, and to a nonaqueous electrolyte solution for a lithium secondary battery, comprising a non-aqueous organic solvent, a lithium salt, and biscarboxymethyl trithiocarbonate.

The miniaturized and slimmer lithium secondary battery used in notebook computers, camcorders, mobile phones, etc., has a lithium salt in a positive electrode material of a lithium metal mixed oxide, a negative electrode made of a carbon material or a metal lithium, and a mixed organic solvent capable of removing and inserting lithium ions. It consists of an appropriate amount of electrolyte solution dissolved. Coin type, 18650 cylindrical shape, 063048 square shape, and the like are generally used as the lithium secondary battery.

The average discharge voltage of about 3.6 to 3.7 V of the lithium secondary battery is one of the greatest advantages as it can obtain a higher power than other alkaline batteries or Ni-MH or Ni-Cd batteries. In order to exhibit such a high driving voltage, an electrochemically stable electrolyte composition is required in the charge region of 0 to 4.2 V. Therefore, ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate are required. Fluorobenzene (FB) is suitably mixed and used as an electrolyte solvent in order to increase the absorbency with a carbonate organic solvent such as DEC) and a separator.

As the solute of the electrolyte, lithium salts such as LiPF _6, LiBF ₄ , LiClO ₄ , LiN (C ₂ F ₅ SO ₃ ) _2, etc. are commonly used, and these act as a source of lithium ions in the battery, thereby basically operating a lithium secondary battery. To make it possible.

However, the non-aqueous electrolyte prepared as described above may have disadvantages in high rate charging and discharging because the ion conductivity is significantly lower than that of the aqueous electrolyte used in Ni-MH or Ni-Cd batteries.

In the initial charging of a lithium secondary battery, lithium ions derived from a lithium metal composite oxide used as a positive electrode are transferred to a graphite (crystalline or amorphous) electrode used as a negative electrode, and intercalated between the layers of the graphite electrode. At this time, since lithium ions are highly reactive, lithium ions react with carbon constituting the electrolyte and the cathode on the surface of the graphite anode to form 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. The 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 to form a graphite anode. It prevents the structure from collapsing.

Once the SEI film is formed, lithium ions again do not react sideways with the graphite anode or other materials, and the amount of charge consumed to form the SEI film has a property of not reversibly reacting upon discharge with an irreversible capacity. Therefore, no further electrolyte decomposition occurs and the amount of lithium ions in the electrolyte is reversibly maintained to maintain stable charge and discharge (J. Power Sources (1994) 51: 79-104).

In such thin rectangular batteries, the thickness of the battery expands during charging due to gases such as CO, CO ₂ , CH ₄ , and C ₂ H ₆ generated from decomposition of the carbonate-based organic solvent during the above-described SEI formation reaction. (J. Power Sources (1998) 72: 66-70). In this case, the side reaction between the electrode and the electrolyte causes deterioration of life characteristics and a decrease in capacity.

Accordingly, the present invention has been made to solve the above problems of the prior art, does not affect the battery characteristics, does not occur the decomposition of the electrolyte during charging and discharging, non-aqueous electrolyte for lithium secondary battery excellent in electromotive force, discharge capacity and life characteristics The purpose is to provide.

In addition, another object of the present invention is to provide a lithium secondary battery using the non-aqueous electrolyte for lithium secondary battery.

In order to achieve the above object, the present invention is characterized in that it comprises a non-aqueous organic solvent, a lithium salt and biscarboxymethyl trithiocarbonate (Bis (carboxymethyl) trithiocarbonate) of the formula (1).

[Formula 1]

Biscarboxymethyl trithiocarbonate (Bis (carboxymethyl) trithiocarbonate) of Formula 1 is characterized in that the addition of 0.01 to 10% by weight based on the non-aqueous electrolyte.

The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F ₂ x + 1SO ₂ ) (C _y F _2y + 1SO ₂ ) (where x and y are natural numbers), LiCl, and LiI, characterized in that at least one selected from the group consisting of.

The lithium salt is a non-aqueous electrolyte lithium secondary battery, characterized in that used in a concentration of 0.6 to 2 M.

The non-aqueous organic solvent is characterized in that at least one selected from the group consisting of carbonates, esters, ethers and ketones.

The carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC), propylene It is characterized in that at least one selected from the group consisting of carbonate (PC) and butylene carbonate (BC).

The carbonate is characterized in that the mixed solvent of the cyclic carbonate and chain (carbonate).

The non-aqueous organic solvent may be a mixed solvent of a carbonate solvent and an aromatic hydrocarbon organic solvent.

The aromatic hydrocarbon-based organic solvent is characterized in that the aromatic compound of the formula (2).

[Formula 2]

(Wherein R is a halogen or an alkyl group having 1 to 10 carbon atoms and n is an integer of 1 to 5).

The aromatic hydrocarbon-based organic solvent is at least one selected from the group consisting of benzene, fluorobenzene, toluene, fluorotoluene, trifluorotoluene, xylene and mixtures thereof.

The carbonate solvent and the aromatic hydrocarbon organic solvent may be mixed in a volume ratio of 1: 1 to 30: 1.

The ester is a group consisting of butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, n-methylacetate, n-ethyl acetate, and n-propyl acetate It is characterized in that at least one selected from.

In addition, the present invention is the non-aqueous electrolyte; A positive electrode comprising a lithium intercalation compound as a positive electrode active material; And a negative electrode including carbon, a carbon composite, a lithium metal, or a lithium alloy as a negative electrode active material.

The battery is characterized in that a lithium ion battery or a lithium polymer battery.

Hereinafter, a nonaqueous electrolyte and a lithium secondary battery for a lithium secondary battery according to the present invention will be described in detail.

At least one selected from the group consisting of carbonate, ester, ether and ketone is used as the non-aqueous organic solvent used in the preparation of the non-aqueous electrolyte solution for a lithium secondary battery of the present invention.

The carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), At least one selected from the group consisting of propylene carbonate (PC) and butylene carbonate (BC).

In this case, a cyclic carbonate organic solvent and a linear carbonate organic solvent are mixed and used, preferably at least one compound selected from the group of cyclic carbonate organic solvents composed of ethylene carbonate and propylene carbonate, and dimethyl carbonate and diethyl carbonate. And at least one compound selected from the group of linear carbonate organic solvents consisting of ethyl methyl carbonate and methyl propyl carbonate, and more preferably ethylene carbonate and dimethyl carbonate.

When the carbonate is used as the non-aqueous organic solvent, it is used by mixing with an aromatic hydrocarbon organic solvent.

As the aromatic hydrocarbon-based organic solvent, a compound of Formula 2 is used, and preferably at least one selected from the group consisting of benzene, fluorobenzene, toluene, fluorotoluene, trifluorotoluene, and xylene is used. .

[Formula 2]

(Wherein R is a halogen or an alkyl group having 1 to 10 carbon atoms and n is an integer of 1 to 5).

In addition, the carbonate solvent and the aromatic hydrocarbon organic solvent are used by mixing in a volume ratio of 1: 1 to 30: 1. The performance of the electrolyte is preferable when mixed in the above volume ratio.

On the other hand, the ester is composed of butyrolactone, decanolide (decanolide), valerolactone, mevalonolactone, meprolactone (caprolactone), n-methyl acetate, n-ethyl acetate and n-propyl acetate At least one selected from the group.

In addition to the nonaqueous electrolyte of the present invention, at least one compound selected from the group consisting of propyl acetate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, and fluorobenzene may be further included as necessary.

The mixing ratio of the organic solvent selected from each group is not particularly limited as long as the purpose of the present invention is not impaired, and the mixing ratio in the production of a nonaqueous electrolyte solution for a lithium secondary battery is usually used.

Meanwhile, lithium salts included in the nonaqueous electrolyte of the present invention include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , At least one selected from the group consisting of LiAlO ₄ , LiAlCl ₄ , LiN (C _x F ₂ x + 1SO ₂ ) (C _y F _2y + 1SO ₂ ) (where x and y are natural numbers), LiCl, and LiI It is preferable to use one, and more preferably LiPF ₆ is used.

The lithium salt is added at a concentration of 0.6 to 2M.

If the added concentration of the lithium salt is less than 0.6M, there is a problem that the ionic conductivity is lowered, if it exceeds 2M, the viscosity of the electrolyte is increased, there is a problem that the mobility of lithium ions is reduced and low-temperature performance is also reduced.

Biscarboxymethyl trithiocarbonate (Bis (carboxymethyl) trithiocarbonate) contained in the nonaqueous electrolyte of the present invention is 0.01 to 10% by weight, preferably 0.05 to 5% by weight, more preferably 0.1 to 3% by weight, based on the nonaqueous electrolyte Use in%. When the compound is included in less than 0.01% by weight can not be expected to improve the life characteristics of the present patent, if it contains more than 10% by weight thick film is formed on the electrode causes a decrease in battery performance.

The lithium secondary battery may be manufactured according to a conventional method using the nonaqueous electrolyte solution for a lithium secondary battery of the present invention. The lithium secondary battery thus prepared may be formed by gas generation and side reactions inside the battery due to decomposition of the electrolyte during charge and discharge. Since the deterioration of the life characteristics is suppressed, the swelling phenomenon in which the thickness of the battery is expanded is prevented, and the discharge capacity characteristic due to the high voltage charging is also excellent.

Hereinafter, the present invention will be described in more detail with reference to Examples, but these Examples are only for illustrating the present invention and should not be construed as limiting the present invention.

Example 1

1.0 M of LiPF ₆ was dissolved in a solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a ratio of 1: 1: 1, and then vinylene trithiocarbonate (VTTC ) 0.5% by weight of a basic electrolyte solution was prepared.

Graphite was used as the negative electrode active material, LiCoO ₂ as the positive electrode active material, PVDF as the binder, and acetylene black as the conductive agent.

An electrolyte solution in which 0.5 wt% of biscarboxymethyl trithiocarbonate (Bis) was added to the basic electrolyte solution was prepared to prepare a square 423048 battery.

After Mars charge and discharge (0.2C-rate, 4.2 ~ 3.0V), the standard charging and discharging experiment was conducted in the range of 4.2 ~ 3.0V with 1.0C-rate. Charge was made into the constant current-constant voltage conditions, and discharge was made into the constant current conditions.

1 shows the results of comparing the charge and discharge performance (life time) of a battery using a non-aqueous electrolyte solution for a lithium secondary battery containing biscarboxymethyl trithiocarbonate (Bis) according to the present invention.

In addition, Table 1 shows the results of comparing the standard discharge capacity according to the life (unit: mAh).

Example 2

Except for using an electrolyte solution in which 3% by weight of bis carboxymethyl trithiocarbonate (Bis (carboxymethyl) trithiocarbonate) was used, and the same as in Example 1, the results are shown in FIG.

Example 3

Except for using the electrolytic solution with 7% by weight of bis carboxymethyl trithiocarbonate (Bis (carboxymethyl) trithiocarbonate) was the same as in Example 1, the results are shown in FIG.

Comparative Example 1

Except for using the basic electrolyte solution and the same as in Example 1, the results are shown in FIG.

On the other hand, the present invention has been described in detail with reference to the specific embodiment shown in the drawings, but this is only one example and does not limit the protection scope of the present invention, it is common knowledge in the art within the spirit of the present invention Various modifications and equivalent other embodiments are possible by those having the same, and such modifications and equivalent other embodiments belong to the claims appended to the present invention.

As described above, according to the nonaqueous electrolyte solution for lithium secondary batteries according to the present invention, by containing biscarboxymethyl trithiocarbonate (Bis (carboxymethyl) trithiocarbonate), by suppressing decomposition of the electrolyte solution at the charge voltage of 4.2V or more, It is possible to improve the life characteristics of the lithium secondary battery without deterioration of the characteristics.

Claims (14)

A non-aqueous electrolyte solution for a lithium secondary battery, comprising a non-aqueous organic solvent, a lithium salt and biscarboxymethyl trithiocarbonate (1). [Formula 1]

In claim 1, Bis carboxymethyl trithiocarbonate (Bis (carboxymethyl) trithiocarbonate) of the formula (1) based on the non-aqueous electrolyte, non-aqueous electrolyte for a lithium secondary battery, characterized in that the addition of 0.01 to 10% by weight. In claim 1, The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F ₂ x + 1SO ₂ ) (C _y F _2y + 1SO ₂ ) (wherein x and y are natural water), LiCl, and LiI at least one selected from the group consisting of non-aqueous electrolyte for lithium secondary battery. In claim 3, The lithium salt is a non-aqueous electrolyte lithium secondary battery, characterized in that used in a concentration of 0.6 to 2.0M. In claim 1, The non-aqueous organic solvent is at least one selected from the group consisting of carbonates, esters, ethers and ketones. In claim 5, The carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC), propylene Non-aqueous electrolyte for lithium secondary batteries, characterized in that at least one selected from the group consisting of carbonate (PC) and butylene carbonate (BC). In claim 5, The carbonate is a non-aqueous electrolyte for a lithium secondary battery, characterized in that the mixed solvent of the cyclic carbonate and chain (carbonate). In claim 1, The non-aqueous organic solvent is a non-aqueous electrolyte for a lithium secondary battery, characterized in that the mixed solvent of a carbonate solvent and an aromatic hydrocarbon organic solvent. In claim 8, The aromatic hydrocarbon organic solvent is a non-aqueous electrolyte lithium secondary battery, characterized in that the aromatic compound of the formula (2). [Formula 2]

(Wherein R is a halogen or an alkyl group having 1 to 10 carbon atoms and n is an integer of 1 to 5). In claim 9, The aromatic hydrocarbon organic solvent is at least one selected from the group consisting of benzene, fluorobenzene, toluene, fluorotoluene, trifluorotoluene, xylene, and mixtures thereof. In claim 8, The carbonate-based solvent and the aromatic hydrocarbon-based organic solvent is a non-aqueous electrolyte solution for a lithium secondary battery, characterized in that mixed in a volume ratio of 1: 1 to 30: 1. In claim 5, The ester is a group consisting of butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, n-methylacetate, n-ethyl acetate, and n-propyl acetate Non-aqueous electrolyte for a lithium secondary battery, characterized in that at least one selected from. Non-aqueous electrolyte according to any one of claims 1 to 12; A positive electrode comprising a lithium intercalation compound as a positive electrode active material; And a negative electrode including carbon, a carbon composite, a lithium metal, or a lithium alloy as a negative electrode active material. In claim 13, The battery is a lithium ion battery or a lithium polymer battery.

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