KR100395818B1 - Organic electrolyte solution and lithium batteries adopting the same - Google Patents

Abstract

The present invention provides an organic electrolyte solution comprising 50 to 99% by weight of a carbonate compound and 0.1 to 5% by weight of carbon disulfide (CS ₂ ).

By adding carbon disulfide to the carbonate compound-based organic electrolyte, in the case of prismatic and polymer lithium ion batteries, the change in battery thickness is reduced by 4% compared to the conventional one, thereby improving reliability of set mountability and improving charge / discharge life characteristics. I could make it.

Description

Organic electrolyte solution and lithium batteries adopting the same

The present invention relates to an organic electrolyte and a lithium battery employing the same, and more particularly, to an organic electrolyte and a lithium battery employing the same, which can reduce the change in battery thickness after full charge and have excellent charge / discharge cycle life.

In general, rechargeable batteries capable of charging and discharging are being actively researched by the development of portable electronic devices such as cellular phones, notebook computers, and computer cam codes. In particular, such a secondary battery is a variety of types such as nickel-cadmium battery, lead-acid battery, nickel-hydrogen battery, lithium ion battery, lithium polymer battery, metal lithium secondary battery, air zinc storage battery. Among the batteries, the lithium secondary battery has an operating voltage of 3.6 V, which is about three times longer than a nickel-cadmium battery or nickel-hydrogen battery, which is widely used as a power source for electronic devices, and has an excellent energy density per unit weight. The demand is growing rapidly.

The lithium secondary battery may be classified into a liquid electrolyte battery and a polymer electrolyte battery according to the type of electrolyte. Generally, a battery using a liquid electrolyte is a lithium ion battery and a battery using a polymer electrolyte is called a lithium polymer battery.

One of the advantages of the lithium ion battery is that the average discharge voltage is about 3.6 to 3.7 V, which is higher than that of other alkaline batteries, Ni-MH, or Ni-Cd batteries. However, in order to produce such a high driving voltage, an electrochemically stable electrolyte composition is required in the charge and discharge voltage range of 0 to 4.2 V. Due to these requirements, EC (Ethylene Carbonate), Di-Methyl Carbonate (DMC), and DEC are required. A mixture consisting of a combination of carbonates such as (Di-Ethyl Carbonate) is used as a solvent. However, the electrolytic solution having such a composition has a lower ionic conductivity than the aqueous electrolytic solution used in Ni-MH or Ni-Cd batteries, and thus, may act as a disadvantage in high rate charge and discharge. LiPF ₆ , LiBF ₄ , LiClO _4, and the like, which are commonly used as the solute of the electrolyte, act as a source of lithium ions in the battery to enable operation of the lithium ion battery.

The electrolyte of such a lithium ion battery is normally stable at a temperature range of -20 ° C to 60 ° C, and must maintain stable characteristics even at a voltage of 4 V region.

During supercharging of lithium ion batteries, lithium ions from lithium metal oxides used as anodes are moved to intercalation by moving to carbon (crystalline or amorphous) electrodes used as cathodes. Reaction with the cathode produces Li ₂ CO ₃ , LiO, LiOH, etc., and these form a film on the surface of the cathode. This film is called SEI (Solid Electrolyte Interface) film.

The SEI film formed during supercharge of a lithium ion battery prevents lithium ions from reacting with a carbon anode or other material during charge and discharge after formation. The film also acts as an ion tunnel, allowing only lithium ions to pass through.

Due to the effect of this ion tunnel, lithium ions are solubilized in the electrolyte solution, thereby preventing the organic solvents having high molecular weight from being cointercalated together on the carbon anode, thereby preventing the carbon cathode structure from collapsing. . Once this film is formed, the lithium ions will no longer react sideways with the carbon anode or other materials, thereby reversibly maintaining the amount of lithium ions. As such, the role of the SEI film is very important in a lithium secondary battery.

That is, the carbon material of the negative electrode reacts with the electrolyte during supercharge to form a passivation layer on the surface of the negative electrode to maintain stable charge and discharge without further decomposition of the electrolyte ( J. Power Sources , 51 (1994) 79-104). At this time, the amount of charge consumed to form the protective film on the surface of the cathode is an irreversible capacity, and has a feature of not reversibly reacting during discharge. For this reason, the lithium ion battery may maintain a stable cycle life after the supercharge reaction without showing any irreversible protective film formation reaction.

However, in the thin rectangular battery, gases such as CO, CO ₂ , CH ₄ , and C ₂ H ₆ generated by decomposition of the carbonate-based organic solvent are generated during the SEI film formation reaction ( J. Power Sources , 72 (1998) 66). As the internal pressure increases, the thickness of the battery expands during charging, resulting in a distortion of the electrode, resulting in a heterogeneous reaction during charging and discharging of the battery, thereby degrading reliability and stability.

In this reaction, in the case of a square battery and a polymer lithium ion (PLI) battery, the thickness of the battery increases, which may cause a problem of making the set itself difficult.

In order to suppress this problem, experiments have been conducted to change the SEI film formation reaction by adding an additive to the electrolyte. For example, Japanese Patent Laid-Open No. 7-176323 discloses a technique of adding CO ₂ to an electrolyte solution. In addition, Japanese Patent Laid-Open No. 7-230825 discloses a nonaqueous electrolyte which contains symmetric sulfone. Japanese Patent Laid-Open No. 8-241732 discloses an electrolytic solution characterized by containing acyclic sulfone. US3907597 discloses a non-aqueous electrolyte consisting of sulfolane and essentially water-free alkyl-substituted sulfolane derivatives, at least one low viscosity organic solvent and ionic solutes. WO 99/19932 discloses a non-aqueous electrolyte comprising one or more fluorinated asymmetric acyclic sulfones having the general formula R—SO ₂ —R ′; Wherein R and R 'are some or all fluorinated linear or branched alkyl groups that are different from each other. US4690877 discloses a non-aqueous electrolyte consisting of only dimethylsulfone and at least one solvent selected from the group consisting of dimethylsulfone and mixtures of other aromatic or aliphatic linear sulfones.

Despite many efforts as described above, the charge and discharge unevenness due to the warpage of the electrode plate due to the expansion of the thickness of the battery during charging, resulting in deterioration of various characteristics and safety of the battery is not completely improved.

Therefore, the technical problem to be achieved by the present invention is to provide an organic electrolyte solution that can solve the above problems.

Another technical problem to be achieved by the present invention is to provide a lithium battery having excellent cycle life characteristics by reducing the thickness change of the battery after full charge by using the electrolyte solution.

Figure 1 shows the voltage profile during chemical charging according to the use of the additive according to the present invention.

2 shows battery life characteristics depending on whether additives are used according to the present invention.

In order to achieve the above object, the present invention provides an organic electrolytic solution comprising 50 to 99% by weight of a carbonate compound and 0.1 to 5% by weight of carbon disulfide (CS ₂ ).

The carbonate compound is preferably at least one selected from the group consisting of EC (Ethylene Carbonate), DMC (Di-Methyl carbonate), and DEC (Di-Ethyl Carbonate).

In order to achieve the above another object, the present invention is a lithium battery comprising a positive electrode, a negative electrode, a separator interposed therebetween, and an electrolyte solution,

The electrolyte provides a lithium battery comprising an organic electrolyte solution containing 50 to 99% by weight of a carbonate compound and 0.1 to 5% by weight of carbon disulfide (CS ₂ ).

The carbonate compound is preferably at least one selected from the group consisting of EC, DMC, and DEC.

The anode preferably comprises at least one lithium metal oxide or lithium metal composite oxide selected from the group consisting of LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiM _x M ' _y O ₂ :

M and M 'each independently represent Co, Mn, or Ni, the range of x is 1 to 0.5, and the range of y is 0.5 to 1, respectively.

The negative electrode preferably includes at least one selected from the group consisting of crystalline or amorphous carbon, graphite and lithium metal.

Hereinafter, an organic electrolyte solution and a method of manufacturing a lithium battery using the same according to the present invention will be described in detail.

The organic electrolytic solution according to the present invention is prepared by adding carbon disulfide to a basic organic electrolytic solution commonly used, that is, carbonate compounds such as EC, DMC, and DEC.

The lithium battery employing the organic electrolyte according to the present invention can be prepared according to a conventional method for producing a lithium battery. That is, the positive electrode plate and the negative electrode plate are each produced in accordance with a conventional method used in manufacturing a lithium battery. In this case, a lithium metal oxide, a lithium metal composite oxide, a transition metal compound, a sulfur compound, or the like may be used as the positive electrode active material, and a crystalline or amorphous carbon material powder, graphite powder, or the like may be used as the negative electrode active material.

Thereafter, a separator is inserted between the positive electrode plate and the negative electrode plate, and the electrode structure is formed by winding or stacking the electrode plate. The separator is assembled into a battery case.

Thereafter, an electrolyte solution containing a carbonate-based organic solvent and a lithium salt containing carbon disulfide according to the present invention is injected into a battery case housed in an electrode structure, and then thermocompression-bonded to complete a lithium battery.

Figure 1 shows the voltage profile of the carbon disulfide, that is, the charge according to the presence or absence of additives. As can be seen in Figure 1, carbon disulfide is decomposed before the carbonate-based organic solvent in the vicinity of 2.3 V, the SEI film formation reaction occurs at this voltage.

At this time, the formed SEI film prevents decomposition of carbonate-based organic solvents such as EC, DMC, and DEC, thereby suppressing gas generation due to decomposition of carbonate-based organic solvents during initial charging in a lithium ion battery or PLI battery, thereby reducing the internal pressure of the battery. And eventually only reduce the thickness of the battery after charging.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

EXAMPLE

<Example 1>

A lithium ion secondary battery was manufactured by the following procedure. 92 parts by weight of LiCoO _{2 as a} positive electrode active material, 4 parts by weight of polyvinylidene fluorite (PVDF) as a binder, and 4 parts by weight of carbon (super-P) as a conductive agent, and 30 parts by weight of N-methyl-2-pyrrolidone Dispersion produced a positive electrode slurry. The slurry was coated on an aluminum foil having a thickness of 20 μm, dried, rolled, and cut into predetermined dimensions to prepare a positive electrode plate.

Crystalline Artificial Graphite (Mesocarbon Fiber: Petoca) 92 parts by weight and 8 parts by weight of PVDF as a binder were dispersed in 40 parts by weight of N-methyl-2-pyrrolidone to prepare a negative electrode slurry. The slurry was coated on a copper foil having a thickness of 15 μm, dried, rolled, and cut into predetermined dimensions to prepare a negative electrode plate.

A separator made of polyethylene (Cellgard) having a thickness of 25 μm was disposed between the positive electrode plate and the negative electrode plate prepared as above, and wound and compressed to insert a 30 mm x 48 mm x 6 mm square can. Then, electrolyte solution was prepared so that LiPF ₆ might be 1.0 M in the solvent of EC: DMC = 5: 5 composition. Carbon disulfide was added to this electrolyte at a ratio of 2.0% by weight, and 2.4 g of the organic electrolyte was injected into the can to complete a lithium battery.

Comparative Example 1

A lithium battery was completed in the same manner as in Example 1 except that the carbon disulfide additive was not added to the organic electrolyte.

For the batteries prepared according to Example 1 and Comparative Example 1, the thickness change test and the charge / discharge life characteristics after full charge were tested. The properties were evaluated according to the following method.

(1) Thickness change test after full charge

The produced batteries were charged under CC-CV conditions at 4.2 V charging voltage with a current of 160 mA, and then discharged to 2.5 V with a current of 160 mA after being left for 1 hour and left for 1 hour. After repeating this process three times, it was charged with 4.2 V charging voltage for 2 hours and 30 minutes at a current of 600 mA. Subsequently, after measuring battery thickness, the thickness change rate of the battery after initial granulation is shown in Table 1.

Thickness change of square cell after full charge Thickness change Comparative Example 1 10.3% Example 1 6.7%

(2) Charge and discharge life test

The battery produced according to Example 1 and Comparative Example 1 was charged with 870 mAh at 4.2 V termination voltage for 2 hours 30 minutes, and the battery life characteristics were evaluated while repeating discharging at 2.75 V 870 mAh. The result is shown in FIG. As can be seen in FIG. 2, in comparison with Comparative Example 1 in which carbon disulfide was not added, in Example 1 in which carbon disulfide was added, the life characteristic slope was significantly reduced.

By adding carbon disulfide to the carbonate compound-based organic electrolyte, in the case of square and polymer lithium ion batteries, the change in battery thickness can be reduced by about 4%, thereby improving the reliability of the set mountability and improving the charge / discharge life characteristics. I was able to.

Claims (6)

An organic electrolytic solution comprising 50 to 99% by weight of a carbonate compound and 0.1 to 5% by weight of carbon disulfide (CS ₂ ). The organic electrolyte of claim 1, wherein the carbonate compound is at least one selected from the group consisting of ethylene carbonate (EC), di-methyl carbonate (DMC), and di-ethyl carbonate (DEC). In a lithium battery comprising a positive electrode, a negative electrode, a separator interposed therebetween, and an electrolyte solution, The electrolyte is a lithium battery, characterized in that consisting of an organic electrolyte containing 50 to 99% by weight of a carbonate compound and 0.1 to 5% by weight of carbon disulfide (CS ₂ ). The lithium battery of claim 3, wherein the carbonate compound is at least one selected from the group consisting of EC, DMC, and DEC. The method according to claim 3 or 4, wherein the anode is at least one lithium metal oxide or lithium metal selected from the group consisting of LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiM _x M ' _y O ₂ A lithium battery comprising a composite oxide: M and M 'each independently represent Co, Mn, or Ni, the range of x is 1 to 0.5, and the range of y is 0.5 to 1, respectively. The lithium battery according to claim 3 or 4, wherein the negative electrode includes at least one selected from the group consisting of crystalline or amorphous carbon, graphite, and lithium metal.