KR100639529B1 - Non-aqueous electrolyte for Lithium Secondary Batteries and Lithium Secondary Batteries containing the same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte solution for a lithium secondary battery that does not affect the battery characteristics and does not cause decomposition of the electrolyte during charging and discharging, thereby improving the electromotive force, discharge capacity, and lifespan characteristics of the battery, and more particularly, lithium salt and dimethyl carbonate. Linear carbonate and ethylene carbonate (EC), at least one of (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) and ethylmethyl carbonate (EMC), A vinylene trithiocarbonate (VTTC) derivative of Formula 1 and an ethylene trithiocarbonate (ETTC) derivative of Formula 2 in a non-aqueous organic solvent mixed with at least one cyclic carbonate of propylene carbonate (PC) and butylene carbonate (BC) It relates to a non-aqueous electrolyte for a lithium secondary battery, characterized in that it comprises at least one of 0.1 to 15% by weight of .

[Formula 1]

[Formula 2]

Lithium Secondary Battery, Non-Aqueous Electrolyte, Thiocarbonate

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 1 to 4 of the present invention.

2 is a life test results of the battery prepared in Examples 5 to 8 and Comparative Examples of the present invention.

The present invention relates to a non-aqueous electrolyte solution for a lithium secondary battery, and more particularly, does not affect the battery characteristics, including thiocarbonate of a cyclic structure, and does not cause decomposition of the electrolyte during charging and discharging, thereby improving the electromotive force, discharge capacity and life characteristics of the battery. It relates to a nonaqueous electrolyte solution for a lithium secondary battery characterized by improving.

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, and LiN (C 2 F 5 SO 3) 2 are commonly used, and these act as a source of lithium ions in the battery to enable basic operation of the lithium secondary battery.

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 move to a graphite (crystalline or amorphous) electrode used as a negative electrode, and are intercalated between layers of the graphite electrode. In this case, since lithium ions are highly reactive, lithium ions react with the carbon constituting the electrolyte and the cathode on the surface of the graphite cathode 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 is expanded during charging due to gases such as CO, CO 2, CH 4, and C 2 H 6 generated from decomposition of the carbonate organic solvent during the SEI formation reaction described above (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.

In order to solve the above problems, the present invention does not affect the battery characteristics, including the thiocarbonate of the cyclic structure, and does not cause decomposition of the electrolyte during charging and discharging to improve the electromotive force, discharge capacity and life characteristics of the battery It provides a non-aqueous electrolyte for lithium secondary battery.

Non-aqueous electrolyte for lithium secondary batteries according to the present invention for achieving the above object is lithium salt, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate ( EPC) and a non-aqueous organic solvent mixed with at least one linear carbonate of ethyl methyl carbonate (EMC) and at least one cyclic carbonate among ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC) It provides a non-aqueous electrolyte for lithium secondary battery, characterized in that it comprises 0.1 to 15% by weight of at least one of a vinylene trithiocarbonate (VTTC) derivative and an ethylene trithiocarbonate (ETTC) derivative of formula (2).

[Formula 1]

[Formula 2]

(Where R 1 to R 6 are hydrogen or halogen or an alkyl, allyl or alkoxy group having 1 to 3 carbon atoms, and R 1 to R 6 may be the same or different).

The compound of Formula 1 is preferably vinylene trithiocarbonate (VTTC) of formula (4) or ethylene trithiocarbonate (ETTC) of formula (5).

[Formula 4]

[Formula 5]

Another object of the present invention to provide a lithium secondary battery, characterized in that using the non-aqueous electrolyte.

The battery may be a lithium ion battery or a lithium polymer battery.

Hereinafter, the component of the nonaqueous electrolyte solution for lithium secondary batteries of this invention is demonstrated 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 composed of ethyl methyl carbonate and methyl propyl 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 3 is used, and preferably at least one selected from the group consisting of benzene, fluorobenzene, toluene, fluorotoluene, trifluorotoluene, and xylene is used. .

[Formula 3]

(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-based solvent and the aromatic hydrocarbon-based organic solvent is preferably used by mixing in a volume ratio of 1: 1 to 30: 1. When mixed in the volume ratio, the performance of the electrolyte is more preferable. If the content is greater than 1: 1, the battery characteristics may be deteriorated. If the content is less than 30: 1, the effect of mixing the aromatic hydrocarbon compound may not be expected.

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, Li (CF 3 SO 2) 2 N, LiC 4 F 9 SO 3, LiAlO 4, LiAlCl 4, LiN (CxF 2x + 1SO 2) (CyF 2 y + 1 SO 2) However, it is preferable to use one or more selected from the group consisting of x and y are natural numbers), LiCl, and LiI, and more preferably LiPF6.

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.

Cyclic type thiocarbonates having a cyclic structure included in the nonaqueous electrolyte of the present invention are 0.01 to 15% by weight, preferably 0.1 to 10% by weight, more preferably 0.5 to 5% by weight, based on the nonaqueous electrolyte. use.

When the content is less than 0.01% by weight, the stable SEI film is not sufficiently formed on the surface of the negative electrode, so there is a small effect of improving the life characteristics. When the content exceeds 15% by weight, the excessively formed SEI film is inserted / desorbed of Li ions. There is a problem in that the battery performance, such as high rate characteristics or capacity characteristics is lowered by inhibiting.

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 invention and should not be construed as limiting the present invention.

Example 1

1.0 M LiPF6 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 an electrolyte solution was prepared.

A rectangular 423048 battery was prepared using graphite as a negative electrode active material, LiCoO 2 as a positive electrode active material, PVDF as a binder, and acetylene black as a conductive agent.

After Mars charge and discharge (0.2C-rate, 4.2 ~ 3.0V), the standard charge and discharge 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 and 2 show changes in discharge capacity according to the number of cycles.

Table 1 shows the data showing no deterioration of the characteristics of the battery, that is, the amount of chemical charge and discharge, and the change in internal resistance.

Example 2

An electrolyte solution and a battery were prepared in the same manner as in Example 1, except that 3 wt% of vinylene trithiocarbonate (VTTC) was added.

The results are shown in FIG.

Example 3

An electrolyte solution and a battery were prepared in the same manner as in Example 1, except that 7 wt% of vinylene trithiocarbonate (VTTC) was added.

The results are shown in FIG.

Example 4

An electrolyte solution and a battery were prepared in the same manner as in Example 1, except that 10 wt% of vinylene trithiocarbonate (VTTC) was added, and a charge and discharge test was performed.

The results are shown in FIG.

Example 5

An electrolyte solution and a battery were prepared in the same manner as in Example 1, except that 0.5 wt% of ethylene trithiocarbonate (ETTC) was added.

The results are shown in FIG.

Example 6

An electrolyte solution and a battery were manufactured in the same manner as in Example 1, except that 3 wt% of ethylene trithiocarbonate (ETTC) was added.

The results are shown in FIG.

Example 7

An electrolyte solution and a battery were prepared in the same manner as in Example 1, except that 7 wt% of ethylene trithiocarbonate (ETTC) was added.

The results are shown in FIG.

Example 8

An electrolyte solution and a battery were prepared in the same manner as in Example 1, except that 10 wt% of ethylene trithiocarbonate (ETTC) was added.

The results are shown in FIG.

Comparative Example

An electrolyte solution and a battery were prepared in the same manner as in Example 1, except that vinylene trithiocarbonate (VTTC) was not added.

The results are shown in FIG.

It can be seen from FIGS. 1 and 2 that the non-aqueous electrolyte containing thiocarbonate, ie, vinylene trithiocarbonate (VTTC) or ethylene trithiocarbonate (ETTC) of the present invention, improves the life characteristics of a lithium secondary battery. have.

As described above, according to the nonaqueous electrolyte solution for lithium secondary batteries according to the present invention, by including thiocarbonate having a cyclic structure, the decomposition of the electrolyte solution when charging at a charge voltage of 4.2 V or more is suppressed, and thus the life of the lithium secondary battery without deterioration of battery characteristics. Properties can be improved.

Claims (9)

Linear carbonate and ethylene at least one of lithium salt, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) and ethylmethyl carbonate (EMC) A vinylene trithiocarbonate (VTTC) derivative of formula (1) and ethylene trithio of formula (2) in a non-aqueous organic solvent mixed with at least one cyclic carbonate of carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC) Non-aqueous electrolyte for lithium secondary battery, characterized in that it comprises 0.1 to 15% by weight of at least one of carbonate (ETTC) derivative. [Formula 1]

[Formula 2]

(Where R 1 to R 6 are hydrogen or halogen or an alkyl, allyl or alkoxy group having 1 to 3 carbon atoms, and R 1 to R 6 may be the same or different). The method of claim 1, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _2x + 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 Non-aqueous electrolyte for lithium secondary batteries. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 2, wherein the lithium salt is used at a concentration of 0.6 to 2M. The nonaqueous electrolyte of claim 1, wherein the nonaqueous organic solvent further comprises a solvent which is at least one selected from the group consisting of esters, ethers, and ketones. The nonaqueous electrolyte for lithium secondary batteries according to claim 1, wherein the nonaqueous organic solvent is a mixed solvent of a carbonate solvent and an aromatic hydrocarbon organic solvent. The non-aqueous electrolyte for lithium secondary battery according to claim 1, wherein the compound of Formula 1 is vinylene trithiocarbonate (VTTC) of Formula 4. [Formula 4]

The nonaqueous electrolyte of claim 1, wherein the compound of Formula 2 is ethylene trithiocarbonate (ETTC) of Formula 5. [Formula 5]

delete A lithium secondary battery using the nonaqueous electrolyte according to any one of claims 1 to 7.

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