KR20070094414A - Nonaqueous electrolyte comprising benzyl phenyl ether derivatives for li-secondary battery - Google Patents

Abstract

A nonaqueous electrolyte solution for a lithium secondary battery, and a lithium secondary battery using the nonaqueous electrolyte solution are provided to prevent the explosion of a battery due to overcharge at a high voltage, thereby improving stability and safety. A nonaqueous electrolyte solution comprises 100 parts by weight of an organic solvent, a lithium salt, and 0.01-10 parts by weight of at least one benzyl phenyl ether represented by the formula 1 or 2 and/or its derivative, wherein R1 and R2 are identical or different each other and are a halogen atom, or a halogenated alkyl group; and m and n are an integer of 0-5. Preferably the organic solvent comprises at least one cyclic carbonate organic solvent selected from ethylene carbonate, propylene carbonate and butylene carbonate, and at least one linear carbonate organic solvent selected from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate and ethylpropyl carbonate, in a ratio of 1:4 to 2:2.

Description

Nonaqueous electrolyte comprising benzyl phenyl ether derivatives for Li-secondary battery

1 shows aluminum (Al) as a positive electrode metal, copper (Cu) as a negative electrode 110 metal, LiCoO ₂ as a positive electrode 100 active material, and carbon (C) as a negative electrode active material. It is a schematic diagram which shows the lithium secondary battery which used this as electrolyte solution.

2 is a graph showing a stability test result in a state in which a voltage of 4.2 V is applied as a charging voltage in a comparative example.

3 to 7 are graphs showing stability test results in a state in which a voltage of 4.2 V was applied as a charging voltage in Examples 1 to 5. FIG.

<Explanation of symbols for main parts of the drawings>

100: positive electrode 110: negative electrode

130: electrolyte solution 140: separator

The present invention relates to a non-aqueous electrolyte for lithium secondary batteries and a lithium secondary battery comprising the same, and more particularly, to a conventional non-aqueous electrolyte for a lithium secondary battery (nonaqueous electrolyte) without affecting the characteristics of the battery It relates to a non-aqueous electrolyte lithium secondary battery comprising a benzyl phenyl ether that can improve the overcharge stability and a lithium secondary battery comprising the same.

Secondary battery is a chemical battery that can be used semi-permanently because it can be recharged unlike a primary battery, and its market size is growing exponentially due to the recent mass distribution of laptops, mobile communication devices, and digital cameras. Recently, it is rapidly growing as one of the three parts industries in the 21st century along with semiconductors and displays.

Secondary batteries include lead-acid batteries, nickel-cadmium (Ni-Cd) batteries, nickel-hydrogen (Ni-MH) batteries, and lithium batteries, depending on the cathode and anode materials. The potential and energy density are determined by Among them, especially lithium secondary batteries are used as a driving power source for portable electronic devices because of their high energy density due to the low redox potential and molecular weight of lithium.

Among such lithium secondary batteries, a lithium secondary battery using a nonaqueous electrolyte, in particular, is coated with a lithium metal mixed oxide as a positive electrode active material on a metal as an anode, and is used as a negative electrode active material on a metal as a cathode. A carbon material or a metal lithium is coated and used, and an electrolyte in which lithium salt is appropriately dissolved in an organic solvent is disposed between these anodes and cathodes.

In brief, the operation principle of the lithium secondary battery, lithium ions (Li ⁺ ) present in an ionic state in the electrolyte are moved from the positive electrode to the negative electrode during charging, and from the negative electrode to the positive electrode during discharging. At the same time, the electrons move along the wire that connects the positive and negative poles to produce lithium.

As described above, in the state of charge of the lithium ion battery, lithium ions (Li ⁺ ) from the lithium metal oxide used as the positive electrode are moved to the carbon electrode used as the negative electrode and intercalated, where lithium ions are highly reactive. As a result, materials such as Li ₂ CO ₃ , LiO, LiOH, etc. are generated on the surface of the negative electrode by reacting with the carbon negative electrode, which forms a film on the surface of the negative electrode.

The film thus produced is called SEI (Solid Electrolyte Interface), and these SEI films serve as a kind of passivation to protect the cathode surface.

That is, the SEI film prevents the reaction between lithium ions and the negative electrode or other materials during charge and discharge, and serves to pass only lithium ions by acting as an ion tunnel.

The ion tunnel effect is characterized in that the organic solvents (e.g., ethylene carbonate, dimethyl carbonate, diethyl carbonate, etc.) of a large molecular weight electrolyte which solvate lithium ions and move together are cointercalated with the negative electrode. It prevents the structure of the negative electrode from collapsing.

Once the SEI film is formed, the lithium ions do not react side-by-side with the negative electrode or any other material, thereby reversibly maintaining the amount of lithium ions.

That is, the carbon material of the negative electrode reacts with the electrolyte during supercharge to form a protective film SEI film on the surface of the negative electrode, thereby maintaining stable charge and discharge without further decomposition of the electrolyte.

However, in the thin rectangular battery of the lithium secondary battery, the thickness of the battery during charging is generated due to generation of gases such as CO, CO ₂ , CH ₄ , and C ₂ H ₆ generated by decomposition of the carbonate-based organic solvent during the SEI formation reaction. Will expand.

In addition, during high temperature storage at full charge (e.g., 100% charged to 4.2V, then left at 85 ° C for 4 days), the protective film gradually collapses due to increased electrochemical and thermal energy over time. This causes side reactions with the exposed negative electrode surface.

Such side reactions cause continuous gas generation, resulting in an increase in the internal pressure of the battery, which may eventually cause the battery to explode.

The technical problem to be achieved by the present invention is to add benzyl phenyl ether which can improve the stability against overcharging of a battery by adding a certain additive to the non-aqueous electrolyte in a lithium secondary battery, especially a lithium secondary battery using a non-aqueous electrolyte. It is to provide a non-aqueous electrolyte solution for a lithium secondary battery containing.

Another object of the present invention is to provide a lithium secondary battery including the non-aqueous electrolyte of the present invention.

Technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

The non-aqueous electrolyte lithium secondary battery according to an embodiment of the present invention for solving the above technical problem is an organic solvent, a lithium salt, and at least one benzyl benzyl ether selected from the group represented by the following formula (1) and (2) And / or derivatives thereof.

(Where R 1 and R 2 are the same or different halogen or halogenated alkyl groups, and m and n are integers from 0 to 5)

Lithium secondary battery according to an embodiment of the present invention for solving the above other technical problem is an electrolytic solution of the present invention, an electrode portion composed of a positive electrode and a negative electrode which are disposed to face each other with the electrolyte therebetween, and the positive electrode and the negative electrode electrically It includes a separator that separates it.

Specific details of other embodiments are included in the detailed description and the accompanying drawings.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, only the present embodiments to make the disclosure of the present invention complete, and common knowledge in the art to which the present invention pertains. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

The non-aqueous electrolyte solution for lithium secondary batteries including benzyl phenyl ether according to the embodiment of the present invention does not contain water (H ₂ O) as it is, and only an organic solvent is used as a solvent.

The organic solvent used at this time includes carbonate-based, ester-based, and aromatic hydrocarbon-based compounds.

Specifically, carbonate organic solvents include cyclic carbonate organic solvents such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and dipropyl. There are linear carbonate organic solvents such as carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and in the present invention, these cyclic carbonates and chain carbonates. Preference is given to using so as to mix.

However, the ratio of the cyclic carbonate organic solvent and the chain carbonate organic solvent is preferably in a ratio of 1: 4 to 2: 2.

Organic solvents used in the non-aqueous electrolyte solution for lithium secondary batteries of the present invention include ester solvents, specifically butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, n-methyl acetate, n-ethyl It may further comprise at least one ester solvent selected from the group consisting of acetate, and n-propyl acetate.

In addition, the organic solvent of the present invention may further include at least one aromatic hydrocarbon compound selected from the group represented by the following formula (4).

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

Specifically, the aromatic hydrocarbon compound is selected from one or more of benzene, fluorobenzene, toluene, fluorotoluene, difluorotoluene, trifluorotoluene, and xylene.

However, in the present invention, when the organic solvent comprises two kinds of carbonate compound and aromatic hydrocarbon compound, it is preferable to mix the volume ratio of carbonate compound: aromatic hydrocarbon compound in the ratio of 1: 1 to 30: 1. .

Lithium salt is used as a solute (salt) in the non-aqueous electrolyte solution for a lithium secondary battery according to an embodiment of the present invention. Specifically, LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + One} or two or more lithium salts selected from ₁ SO ₂ ) (C _y F _{2y + 1} SO ₂ , wherein x and y are natural numbers), LiCl, and LiI are used.

At this time, the amount of the lithium salt is preferably added so that the concentration of the total electrolyte solution is in the range of 0.6 ~ 2.0M, the reason is that when the concentration of the lithium salt is less than 0.6M, the electrolyte performance is lowered by lowering the electrical conductivity of the electrolyte, 2.0 If it exceeds M, it is because there is a problem that the low-temperature performance due to the increase in viscosity at low temperature falls.

In addition to the organic solvent and the lithium salt, the non-aqueous electrolyte lithium secondary battery of the present invention is characterized in that it further comprises benzyl phenyl ether (Benzyl Phenyl Ether) and / or derivatives thereof represented by the formula (1) and (2).

(Where R 1 and R 2 are the same or different halogen or halogenated alkyl groups, and m and n are integers from 0 to 5)

In this case, the amount of benzyl phenyl ether and its derivatives added to the non-aqueous electrolyte of the present invention is preferably added in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the organic solvent described above, and the reason is that If the addition amount of the ton-based compound is 0.01 parts by weight or less, the improvement effect is negligible in solving the technical problem of the present invention. Because it occurs.

The additive used in the present invention is oxidatively decomposed to the positive electrode active material during initial charging of a lithium metal oxide electrode such as LiCoO ₂ to contribute to the formation of a passivation film on the material surface of the positive electrode active material, and is coated with a lithium metal oxide with a passivation film. It has an effect of suppressing oxidative decomposition of electrolyte solution on the surface of the positive electrode without impairing the normal reaction of.

As a result, the positive electrode reacts with the electrolyte during initial charging to form a passivation layer on the surface, thereby maintaining stable charge and discharge without further decomposition of the electrolyte.

In the present invention, the decomposition of the carbonate-based organic solvent is suppressed by oxidative decomposition at the anode during initial charging, which occurs faster than the conventional carbonate-based organic solvent to form a film.

As a result, at room temperature charging and high temperature storage after full charge, and to suppress the thickness expansion of the battery.

The electrolyte of the lithium secondary battery of the present invention is usually stable in the temperature range of -20 ~ 60 ℃ to maintain a stable characteristic even at a voltage of 4V or more to improve the safety and reliability of the lithium secondary battery. The electrolyte solution of the present invention can be applied to all lithium secondary batteries such as lithium ion batteries and lithium polymer batteries.

1 shows that aluminum (Al) is used as the positive electrode 100 metal, copper (Cu) is used as the negative electrode 110 metal, LiCoO ₂ is used as the positive electrode 100 active material, and carbon (C) is used as the negative electrode active material. It is a schematic diagram which shows the lithium secondary battery which used the nonaqueous electrolyte solution as electrolyte solution 130. FIG.

As shown in FIG. 1, a lithium secondary battery according to an exemplary embodiment of the present invention includes a positive electrode 100, a negative electrode 110, an electrolyte 130, and a separator 140.

However, since the electrolyte 130 used in the lithium secondary battery according to the embodiment of the present invention is used, the non-aqueous electrolyte according to the embodiment of the present invention has been described above. .

The positive electrode 100 and the negative electrode 110 are disposed to face each other with the electrolyte 130 interposed therebetween.

The negative electrode 110 is made of crystalline carbon, amorphous carbon, metal lithium, or lithium complex, and the positive electrode 100 is coated with LiCoO ₂ , as an active material on a metal, but LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiN _1-xy Co _x M _y O ₂ (0≤x≤1, 0≤y≤1, 0≤x + y≤1, M is Al, Sr, Mg, La) Or lithium intercalation compounds such as lithium chalcogenide compounds.

The metal used for the positive electrode 100 and the negative electrode 110 is a portion to which a voltage is applied from the outside during charging and supplies a voltage to the outside during discharge, and the separator 140 connects the positive electrode 100 and the negative electrode 110. It is the role of electrical separation.

As the separator 140, one of a single layer separator made of polyethylene or polypropylene, a two layer separator made of polyethylene / polypropylene, a polyethylene / polypropylene / polyethylene, or a three layer separator made of polypropylene / polyethylene / polypropylene is used. do.

Hereinafter, specific embodiments and comparative examples will be described that the stability against overcharging of a lithium secondary battery is improved when the nonaqueous electrolyte solution for a lithium secondary battery according to the embodiments of the present invention is improved. Details not described herein are omitted because they can be sufficiently inferred by those skilled in the art.

Example

<Example 1>

LiPF ₆ was dissolved as a lithium salt in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2 as an organic solvent, thereby preparing a basic electrolyte having a concentration of 1.0 M. 1 part by weight of Benzyl Phenyl Ether was added to 100 parts by weight of the basic electrolyte solution.

In such an electrolyte, polyvinylidene fluoride (PVDF) as a binder in LiCoO ₂ as a cathode active material and acetylene black as a conductive agent were mixed at a weight ratio of 92/4/4, and then dispersed in N-methyl-2-pyrrolidone. A positive electrode slurry was prepared. The slurry was coated on an aluminum foil having a thickness of 20 μm, dried, and rolled to prepare a positive electrode.

As the negative electrode active material, graphite and PVDF as a binder were mixed at a weight ratio of 92/8, and then dispersed in 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, and rolled to prepare a negative electrode.

The prepared electrodes were wound and compressed using a polyethylene separator having a thickness of 16 μm, placed in a rectangular can of 30 mm × 48 mm × 6 mm, and then injected with the electrolyte composition into the electrolyte injection hole of the square can. The rectangular battery was produced by sealing.

<Example 2>

Benzyl Phenyl Ether was prepared in the same manner as in Example 1 except that 1.5 parts by weight of Benzyl Phenyl Ether was added to 100 parts by weight of the basic electrolyte solution.

<Example 3>

Benzyl Phenyl Ether was prepared in the same manner as in Example 1 except that 2.0 parts by weight of Benzyl Phenyl Ether was added to 100 parts by weight of the basic electrolyte solution.

<Example 4>

Benzyl Phenyl Ether was prepared in the same manner as in Example 1 except that 3.0 parts by weight of Benzyl Phenyl Ether was added to 100 parts by weight of the basic electrolyte solution.

Example 5

Benzyl 4-fluoro Phenyl Ether was prepared in the same manner as in Example 1 except that 3.0 parts by weight of the basic electrolyte was added to 100 parts by weight of the additive.

Comparative Example

It was prepared in the same manner as in Example 1 except that only the basic electrolyte solution was prepared without adding an additive.

2. Overcharge evaluation experiment

1C-12V overcharge evaluation experiment after charging the lithium secondary batteries prepared by the above Examples and Comparative Examples under the condition of constant current-to-voltage (CC-CV) at a charging voltage of 4.2V with a current of 0.2C Was carried out.

Table 1 and Figures 2 to 5 show the results of measuring the charge and discharge characteristics and cycle characteristics in the above-described examples and comparative examples prepared as described above.

As shown in Table 1, in the case of Examples 1 to 5 to which benzo phenyl ether and its derivatives were added, it was found that the secondary battery cell was safe without explosion, regardless of the amount of the benzophenyl ether and its derivatives, but without using an additive. In the case of the comparative example it can be seen that the explosion occurs.

FIG. 2 is a graph showing stability test results in a state in which a voltage of 4.2 V is applied as a charging voltage in a comparative example, and FIGS. 3 to 7 show a voltage of 4.2 V as a charging voltage in Examples 1 to 5; This graph shows the stability test results in the applied state.

As shown in FIG. 2, in the case of the comparative example, the stability decreases around 1 hour, whereas in Examples 1 to 5, as shown in FIGS. 3 to 7, 2.5 hours was applied even when the battery was overcharged by applying a high voltage of 4.2V. It can be seen that it shows a very stable voltage distribution.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings and tables, the present invention is not limited to the above embodiments, but may be manufactured in various forms, and common knowledge in the art to which the present invention pertains. Those skilled in the art can understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

According to the non-aqueous electrolyte lithium secondary battery and a lithium secondary battery comprising the same according to an embodiment of the present invention, the side reaction of the battery is suppressed while maintaining the performance of the battery as it is applied at high voltage, greatly improving the stability of the battery and thus overcharging Even there is an advantage that can produce a battery with little risk of explosion.

Claims (11)

A non-aqueous electrolyte solution for a lithium secondary battery comprising an organic solvent, a lithium salt, and at least one benzyl phenyl ether selected from Formulas 1 and 2 and / or derivatives thereof.

(Where R 1 and R 2 are the same or different halogen or halogenated alkyl groups, and m and n are integers from 0 to 5) The method of claim 1, The benzyl phenyl ether or its derivative is added to 0.01 to 10 parts by weight based on 100 parts by weight of the organic solvent, the non-aqueous electrolyte for lithium secondary batteries. The method of claim 1, The organic solvent is one or more of a cyclic carbonate organic solvent of ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), Non-aqueous lithium secondary battery, characterized in that it comprises a linear carbonate organic solvent of at least one of ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC) in a ratio of 1: 4 to 2: 2 Electrolyte solution. The method of claim 3, wherein The organic solvent is at least one ester solvent selected from the group consisting of butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, n-methyl acetate, n-ethyl acetate and n-propyl acetate Non-aqueous electrolyte solution for a lithium secondary battery, characterized in that it further comprises. The method of claim 3, wherein The organic solvent further comprises at least one aromatic hydrocarbon represented by the following formula (3) for a non-aqueous electrolyte lithium secondary battery.

(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 5, The aromatic hydrocarbon compound is at least one of benzene, fluorobenzene, toluene, fluorotoluene, difluorotoluene, trifluorotoluene and xylene, non-aqueous electrolyte for lithium secondary battery. The method of claim 5, The organic solvent is a non-aqueous electrolyte lithium secondary battery, characterized in that the carbonate organic solvent and the aromatic hydrocarbon compound is mixed in a volume ratio of 1: 1 to 30: 1. The method of claim 1, The lithium salt may be LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiN (C ₂ F ₅ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ , wherein x and y are natural numbers), LiCl, and At least one selected from LiI, the concentration is 0.6 to 2.0M in the electrolyte, characterized in that the non-aqueous electrolyte for lithium secondary batteries. The electrolyte of any one of claims 1 to 8; An electrode unit including positive and negative electrodes positioned to face each other with the electrolyte interposed therebetween; And Lithium secondary battery comprising a separator for electrically separating the positive electrode and the negative electrode. The method of claim 9, The positive electrode is formed of LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiN _1-xy Co _x M _y O ₂ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1, M is a lithium secondary battery characterized in that the coating of one active material selected from Al, Sr, Mg, La). The method of claim 9, The negative electrode is a lithium secondary battery, characterized in that the crystalline carbon, amorphous carbon, metal lithium or lithium composite.

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