KR20060024663A - 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 for lithium secondary batteries that does not affect the battery characteristics and does not cause decomposition of the electrolyte during charge and discharge, thereby improving electromotive force, discharge capacity, and lifespan characteristics. More specifically, the non-aqueous organic solvent and lithium salt And 1,2,4,5-benzenetetracarboxylic dianhydride (1,2,4,5-Benzenetetracarboxylic dianhydride, PMDA) of the formula 1 relates to a non-aqueous electrolyte for a lithium secondary battery.

Lithium Secondary Battery, Non-Aqueous Electrolyte, 1,2,4,5-benzenetetracarboxylic dianhydride (1,2,4,5-Benzenetetracarboxylic dianhydride, PMDA)

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 test result of the life characteristics of the battery prepared in Examples and Comparative Examples of the present invention.

In general, miniaturized and slimmed lithium secondary batteries used in notebook computers, camcorders, mobile phones, etc. are used in cathode materials and mixed organic solvents made of lithium metal mixed oxides, carbon materials, or metallic lithium, which can detach and insert lithium ions. It consists of electrolyte solution in which lithium salt was dissolved in an appropriate amount. 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 secondary 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 exhibit such a high driving voltage, an electrochemically stable electrolyte composition is required at a charge region of 0 to 4.2 V. Therefore, ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (diethyl) are required. Fluorobenzene (FB) is suitably mixed and used as an electrolyte solvent in order to increase the absorbency between the carbonate organic solvent such as carbonate and DEC) and the 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 charge and discharge because the ionic 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. At this time, 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, thereby causing the graphite cathode. Prevents the structure of the collapse.

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 the generation of 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. Power Sources (1998) 72: 66-70). In this case, the side reaction between the electrode and the organic electrolyte causes deterioration of the life characteristics and a decrease in capacity.

In order to solve the above problems, it is an object of the present invention to provide a non-aqueous electrolyte for lithium secondary battery having excellent electromotive force, discharge capacity and lifespan without affecting the battery characteristics, the decomposition of the electrolyte during charging and discharging.

In order to achieve the above object, the present invention provides a non-aqueous organic solvent, a lithium salt and 1,2,4,5-benzenetetracarboxylic dianhydride of the general formula (1,2,4,5-Benzenetetracarboxylic dianhydride, PMDA) Li provides a non-aqueous electrolyte for a secondary battery characterized in that it comprises a).

In another embodiment, the present invention provides a lithium secondary battery using a non-aqueous electrolyte, a lithium intercalation compound as a positive electrode active material, and carbon, a carbon composite, a lithium metal, or a lithium alloy as a negative electrode active material.

The battery may be a lithium secondary battery which is 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), methylethyl carbonate (MEC), 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 one or more selected from the group of cyclic carbonate organic solvents composed of ethylene carbonate and propylene carbonate, and dimethyl carbonate and diethyl. One or more selected from the group of linear carbonate organic solvents consisting of carbonate, ethyl methyl carbonate, and methyl propyl carbonate are used in combination, and more preferably ethylene carbonate and dimethyl carbonate are mixed.

In addition, the non-aqueous organic solvent is used by mixing a carbonate solvent and an aromatic hydrocarbon organic solvent.

In this case, the aromatic hydrocarbon organic solvent is an aromatic compound of the formula (2), preferably the aromatic hydrocarbon organic solvent is benzene, fluorobenzene, toluene, fluorotoluene, trifluoro toluene, xylene and At least one selected from the group consisting of mixtures thereof is used.

(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 butyrolactone, decanolide (decanolide), valerolactone, mevalonolactone, meprolactone (caprolactone), n-methyl acetate, n-ethyl acetate, and n-propyl acetate At least one selected from the group consisting of:

In addition to the nonaqueous electrolyte of the present invention, one or more 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 object 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 LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li (CF3SO2) 2N, LiC4F9SO3, LiAlO4, LiAlCl4, LiN (CxF2x + 1SO2) (CyF2y + 1SO +) 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.

When the concentration of the lithium salt is less than 0.6M, there is a problem that the ion conductivity is lowered. When the lithium salt is more than 2M, the viscosity of the electrolyte is increased, so that mobility of lithium ions is reduced, and low-temperature performance is also reduced.

1,2,4,5-benzenetetracarboxylic dianhydride (PMDA) included in the nonaqueous electrolyte of the present invention is preferably 0.01 to 5% by weight, based on the nonaqueous electrolyte. Is used in an amount of 0.01 to 3 weight ratio, more preferably 0.01 to 2 weight ratio.

 If 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 problem in improving the life characteristics. When the content exceeds 5% by weight, the excessively formed SEI film is inserted / detached Li ion. 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 that the thickness of the battery expands 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 for illustrative purposes only and should not be construed as limiting the present invention.

Example One

After dissolving 1.0 M LiPF6 as a solute in a solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed at a ratio of 1: 1: 1, An electrolyte solution in which 1,2,4,5-benzenetetracarboxylic dianhydride (1,2,4,5-Benzenetetracarboxylic dianhydride, PMDA) (Compound 1) was added at a 0.01 weight ratio 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. The charge was made under the condition of all current-constant voltage, and the discharge was made under the condition of constant current.

Table 1 shows the discharge capacities according to the number of standard charge / discharge cycles, and FIG. 1 shows changes in the discharge capacities according to the number of cycles.

Example 2

Electrolyte solution and the same method as in Example 1 except that an electrolyte solution containing 0.05% by weight of 1,2,4,5-benzenetetracarboxylic dianhydride (1,2,4,5-Benzenetetracarboxylic dianhydride, PMDA) was used. A battery was prepared and a charge / discharge experiment of the battery was performed.

The results are shown in FIG.

Example 3

 The electrolyte solution and the same method as in Example 1, except that an electrolyte solution containing 0.1% by weight of 1,2,4,5-benzenetetracarboxylic dianhydride (1,2,4,5-benzenetetracarboxylic dianhydride, PMDA) was used. A battery was prepared and a charge / discharge experiment of the battery was performed.

The results are shown in FIG.

Example 4

 Electrolyte solution and the same method as in Example 1 except that an electrolyte solution in which 1,2,4,5-benzenetetracarboxylic dianhydride (1,2,4,5-Benzenetetracarboxylic dianhydride, PMDA) was added in an amount of 1% by weight was used. A battery was prepared and a charge / discharge experiment of the battery was performed.

The results are shown in FIG.

Example 5

 Electrolyte solution and the same method as in Example 1 except that an electrolyte solution containing 3% by weight of 1,2,4,5-benzenetetracarboxylic dianhydride (1,2,4,5-Benzenetetracarboxylic dianhydride, PMDA) was used. A battery was prepared and a charge / discharge experiment of the battery was performed.

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 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA) was not added. And the charge and discharge experiment of the battery.

The results are shown in FIG.

1 and Table 1 from the non-aqueous electrolyte containing 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA) of the present invention is characterized in the life characteristics of the lithium secondary battery It can be seen that it improves.

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 appended claims of the present invention.

The nonaqueous electrolyte solution for lithium secondary batteries of the present invention includes 1,2,4,5-benzenetetracarboxylic dianhydride (1,2,4,5-Benzenetetracarboxylic dianhydride, PMDA), and is charged with a charge voltage of 4.2 V or higher. By suppressing the decomposition, the lifetime characteristics of the lithium secondary battery can be improved without deterioration of the battery characteristics.

Claims (16)

Lithium secondary, characterized in that it comprises a non-aqueous organic solvent, a lithium salt and 1,2,4,5-benzenetetracarboxylic dianhydride (1,2,4,5-Benzenetetracarboxylic dianhydride, PMDA) Non-aqueous electrolyte for batteries. [Formula 1]

The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein the non-aqueous organic solvent is at least one selected from the group consisting of carbonate, ester, ether and ketone. The method of claim 2, wherein the carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), Non-aqueous electrolyte for lithium secondary batteries, characterized in that at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC). The non-aqueous electrolyte for lithium secondary batteries according to claim 2, wherein the carbonate is a mixed solvent of a cyclic carbonate and a chain carbonate. 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 solution for lithium secondary batteries according to claim 5, wherein the aromatic hydrocarbon organic solvent is an aromatic compound represented by the following Chemical 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 method of claim 6, wherein 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. Non-aqueous electrolyte for secondary batteries. The nonaqueous electrolyte of claim 5, wherein the carbonate solvent and the aromatic hydrocarbon organic solvent are mixed in a volume ratio of 1: 1 to 30: 1. 3. The ester of claim 2 wherein the ester is butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, n-methyl acetate, n-ethyl acetate, and n Non-aqueous electrolyte solution for lithium secondary batteries, characterized in that at least one selected from the group consisting of propyl acetate. The method of claim 1, wherein the lithium salt is LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li (CF3SO2) 2N, LiC4F9SO3, LiAlO4, LiAlCl4, LiN (CxF2x + 1SO2) (CyF2y + 1SO2) y is a natural water), LiCl, and LiI non-aqueous electrolyte for a lithium secondary battery, characterized in that at least one selected from the group consisting of. The electrolyte of claim 10, wherein the lithium salt is used at a concentration of 0.6 to 2M. The non-aqueous electrolyte for lithium secondary batteries according to claim 1, wherein the compound of Formula 1 is added in an amount of 0.01 to 5 wt% based on the electrolyte. 13. The non-aqueous electrolyte solution for lithium secondary batteries according to claim 12, wherein the compound of Formula 1 is added in an amount of 0.01 to 3 wt% based on the electrolyte. The nonaqueous electrolyte of claim 13, wherein the compound of Formula 1 is added in an amount of 0.1 to 2 wt% based on the electrolyte. Non-aqueous electrolyte according to any one of claims 1 to 14; Lithium intercalation compounds as positive electrode active materials; And A lithium secondary battery comprising carbon, a carbon composite, a lithium metal, or a lithium alloy as a negative electrode active material. The lithium secondary battery according to claim 15, wherein the battery is a lithium secondary battery which is a lithium ion battery or a lithium polymer battery.

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