KR100909289B1 - Electrolyte for lithium secondary battery and lithium secondary battery having same - Google Patents

Abstract

The present invention relates to a lithium secondary battery electrolyte and a lithium secondary battery having the same, and more particularly, to a lithium secondary battery electrolyte containing a lithium salt, an organic solvent, and a cyclic organic compound containing fluorine or phosphorus.

According to the present invention described above, it is possible to provide a lithium secondary battery having excellent flame retardant performance and battery performance maintained or improved.

Lithium Secondary Battery, Flame Retardant Additive, Electrolyte

Description

Electrolyte for lithium secondary battery and lithium secondary battery having same {Electrolyte for Lithium Secondary Battery and Lithium Secondary Battery Having The Same}

The present invention relates to a lithium secondary battery electrolyte and a lithium secondary battery having the same, and more particularly, to a lithium secondary battery electrolyte which can provide a lithium secondary battery with excellent safety.

In line with the rapid development of portable electronic devices, development of high-capacity, high-energy lithium secondary batteries is underway. The lithium secondary battery uses a material capable of intercalations and deintercalation of lithium ions as a negative electrode and a positive electrode, and uses an organic electrolyte or a polymer electrolyte as an electrolyte.

In order to develop a high capacity lithium secondary battery having such a configuration, battery safety is an essential requirement. Lithium secondary batteries have lithium precipitated on the surface of the negative electrode plate as the charge and discharge cycles are repeated, and the lithium is highly reactive with the electrolyte solution, which causes the battery to be subjected to extreme temperatures and pressures such as overcharging, penetration, or compression. There is a risk of explosion due to a sharp rise.

In order to secure the safety of such a lithium secondary battery, research is being conducted in various aspects such as an active material, a separator, a battery system, an electrolyte solution, and the like. Of these, electrolyte additives are expected to have a significant effect with a little investment, and additives with high contribution to safety include overcharge prevention, electrolysis delay, and flame retardant additives. Although the safety of the battery is improving day by day with the development of battery materials and battery management system (BMS), the development of flame retardant additives that can prevent the fire or explosion of the battery, among the above additives, becomes an essential element for the development of large batteries. have.

In this regard, US Pat. No. 5,830,600 discloses an electrolyte solution comprising a flame retardant additive which adds a phosphate-based flame retardant additive and adds a pyrocarbonate-based solvent as a life improvement additive to secure lifespan and safety. However, since the electrolyte solution must include about 50% by volume of a phosphate solvent in order to exhibit a flame retardant effect, there is a problem that the ionic conductivity is lowered and the battery performance is not satisfied.

As such, since a material that satisfies price, flame retardancy, and battery performance has not been developed, development of an electrolyte solution containing a flame retardant additive having low cost and high safety is required.

The present invention is to solve the above problems, to provide a lithium secondary battery electrolyte and a lithium secondary battery having the same to provide a lithium secondary battery having excellent flame retardancy and maintaining or improved battery performance by including a flame retardant additive The purpose.

The present invention for achieving the above object is a lithium salt; solvent; And it provides a lithium secondary battery electrolyte comprising a cyclic (Cyclic) organic compound containing fluorine or phosphorus.

In addition, the cyclic (Cyclic) organic compound provides a lithium secondary battery electrolyte, characterized in that the compound represented by the formula (1).

[Formula 1]

(In Chemical Formula 1, R ₁ , R ₂ And R ₃ are each independently an alkyl group having 1 to 10 carbon atoms, and part or all of hydrogen of the alkyl group may be substituted with fluorine (F).)

In addition, the cyclic organic compound provides a lithium secondary battery electrolyte, characterized in that the compound represented by the formula (2).

[Formula 2]

(In Formula 2, R ₄ , R ₅ , R ₆ are each independently an alkyl group having 1 to 10 carbon atoms, part or all of the hydrogen of the alkyl group may be substituted with fluorine (F).)

In addition, the compound represented by Formula 1 is 2,4,6-tris (trifluoromethyl) -1,3,5-triazine (2,4,6-tris (trifluoromethyl) -1,3,5- triazine; TTFMT) provides a lithium secondary battery electrolyte.

In addition, the compound represented by the formula (2) provides a lithium secondary battery electrolyte, characterized in that tris (2,4,6-trimethoxyphenyl) phosphine (tris (2,4,6-trimethoxyphenyl) phosphine). .

In addition, the cyclic organic compound provides a lithium secondary battery electrolyte, characterized in that contained in 0.1 to 5 parts by weight relative to 100 weight of the electrolyte.

Other embodiments and specific details are included in the detailed description and drawings for carrying out the invention.

According to the present invention described above, it is possible to provide an electrolyte solution and a lithium secondary battery having the same that are excellent in flame retardancy and capable of maintaining or improving battery performance well.

Hereinafter, the electrolyte solution for a lithium secondary battery according to the present invention will be described in more detail. The following detailed description is for the description of one embodiment of the present invention, although not limited to the scope of the claims defined by the claims.

The present invention is a lithium salt; solvent; And a cyclic (Cyclic) organic compound containing fluorine or phosphorus.

As the lithium salt dissolved in the solvent of the electrolyte solution, any one capable of promoting the movement of lithium ions between the positive electrode and the negative electrode can be used, and representative examples thereof include LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₃ , LiBF ₆ or LiClO ₄ .

As the solvent of the electrolyte according to the present invention, cyclic carbonate, linear carbonate, ester, ether or ketone may be used. The ring carbonate may be a ring carbonate selected from the group consisting of ethylene carbonate, propylene carbonate and mixtures thereof, and the linear carbonate is selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate and methylpropyl carbonate. One or more linear carbonates may be used. In addition, the ester may be an ester selected from the group consisting of n-methyl acetate, n-ethyl acetate and n-propyl acetate. As the ketone, polymethyl vinyl ketone may be used.

The electrolyte solution for a lithium secondary battery of the present invention comprises a cyclic organic compound containing fluorine or phosphorus. The cyclic organic compound is preferably included in the range of 0.1 to 5 parts by weight based on 100 parts by weight of the electrolyte. When the amount of the cyclic organic compound is included in an amount greater than 5 parts by weight, the battery performance of the electrolyte is lowered, and when it is included in an amount less than 0.1 parts by weight, the effect on flame retardancy is small.

In the present invention, the cyclic organic compound may be used as long as it is a compound containing fluorine or phosphorus having a flame retardancy while having an organic cyclic structure, and the fluorine or phosphorus may be included or present in one organic material. . Specific examples of the cyclic organic compound containing fluorine or phosphorus include compounds represented by the following general formula (1) or compounds represented by the following general formula (2).

[Formula 1]

[Formula 2]

In Chemical Formula 1, R ₁ , R ₂ And R ₃ are each independently an alkyl group having 1 to 10 carbon atoms, and part or all of hydrogen of the alkyl group may be substituted with fluorine (F). Specific examples of the compound represented by Formula 1 include 2,4,6-tris (trifluoromethyl) -1,3,5-triazine (2,4,6-Tris (trifluoromethyl) -1,3,5 -triazine; TTFMT).

In Formula 2, R ₄ , R ₅ , and R ₆ are each independently an alkyl group having 1 to 10 carbon atoms, and part or all of hydrogen of the alkyl group may be substituted with fluorine (F). Specific examples of the compound represented by Formula 2 include tris (2,4,6-trimethoxyphenyl) phosphine (TTMPP).

Moreover, as long as it does not impair the effect of this invention, the thermosetting initiator etc. which are normally used in this field can also be used together.

When using the electrolyte solution for lithium secondary batteries which concerns on this invention mentioned above, electrochemical stability can be ensured, without deterioration of initial stage discharge capacity, efficiency, etc. That is, safety can be ensured under conditions such as overcharge, external short circuit, compression, and overcharge penetration, and a high capacity battery can be manufactured. In addition, a battery having improved initial charge and discharge cycle life characteristics may be manufactured.

As a cathode active material of a battery using the electrolyte solution of the present invention, all of the transition metal compounds commonly used in lithium secondary batteries may be used, and representative examples thereof include LiCoO ₂ , LiNiO ₂ , and LiNi _x Co _{1- x} M _y O _2. (0.1 <x <1.0, 0 ≦ y <1.0, M is a transition metal), and a transition metal oxide such as LiMnO ₂ , LiMn ₂ O ₄ can be used. A method of manufacturing a cathode using the cathode active material is well known in the battery manufacturing field, and a representative method thereof is a cathode slurry by mixing a cathode active material and a binder such as polyvinylidene fluoride with a solvent such as N-methyl pyrrolidone. After the preparation, the cathode slurry was tape cast on an aluminum foil to prepare a cathode. A conductive agent such as kesene black, carbon black, acetylene black or the like may be further added to the positive electrode slurry. In addition, a cyclic organic compound containing fluorine or phosphorus according to the present invention may be further added to the cathode slurry as a flame retardant additive.

In addition, as the negative electrode active material, all commonly used carbonaceous materials may be used, and representative examples thereof may include crystalline graphite having good dislocation flatness and relatively good reversibility in charge and discharge processes. A method of manufacturing a negative electrode using the negative electrode is also widely known in the battery field, and a representative method thereof is to prepare a negative electrode slurry by mixing a negative electrode active material and a binder such as polyvinylidene fluoride, and then tape the negative electrode slurry on a copper foil. The cathode may be prepared by casting. In the above, a lithium secondary battery may be manufactured by using metal lithium or an alloy-based material as a negative electrode, inserting a separator between the positive electrode and the negative electrode, and injecting an electrolyte solution. The separator serves to block internal short circuits of the two electrodes and impregnate the electrolyte, and materials that may be used as the separator include a polymer, a glass fiber mat, and a kraft paper.

As follows, the present invention will be described in more detail based on examples, but the embodiments of the present invention disclosed below are exemplified to the last, and the scope of the present invention is not limited to these embodiments. The scope of the invention is indicated in the appended claims, and moreover, contains all modifications within the meaning and range equivalent to the claims.

Example 1 Lithium Secondary Battery Using Electrolyte Containing TTFMT

Coin cells were prepared to observe whether the flame retardant performance and battery performance of the cyclic organic compound and TTFMT of the present invention were improved.

The active material used was _{LiMn 1/3 Ni 1/3} Co 1/3 O 2 , and a lithium foil (Li foil) are each used as a material for the positive electrode and the negative electrode, it consisted of a half-cell (half cell) thereof. The manufacturing procedure of the positive electrode plate is as follows.

As the conductive material and the binder, carbon black (Super-P Black) and polyvinylidene fluoride (PVDF) were used. The weight ratio of active material: conductive material: binder was 85: 8: 7. First, the binder is stirred in an appropriate amount of N-methylpyrrolidone (NMP) and a conditioning mixer for 10 minutes, the active material and the conductive material are mixed therein, and then N-methylpyrrolidone (NMP) is added a little more. After addition to adjust the viscosity it was further stirred for 30 minutes. Laminate the aluminum (Al) current collector on a glass plate, cast the slurry prepared on the aluminum (Al) current collector by a doctor blade method, and then dry overnight at 100 ° C. It was. The electrode thus dried was pressed at a compression ratio of 20-25% with a roll press machine at 120 ° C. to complete the electrode.

The coin cell used the 2032 standard, and the electrode manufactured as a positive electrode and the lithium (Li) metal as a negative electrode were used.

As an electrolyte, 1.1 M LiPF ₆ lithium salt, an organic solvent, ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (4: 6 by volume), and a flame retardant additive TTFMT were used. The amount of TTFMT used was 0 parts by weight (not added), 1 part by weight, 3 parts by weight, and 5 parts by weight based on 100 parts by weight of the total electrolyte.

Example 2 Lithium Secondary Battery Using Electrolyte Containing TTMPP

The same operation as in Example 1 was performed except that TTFMT was changed to TTMPP in Example 1.

The results of testing the thermal stability (flame retardant effect) of each electrolyte with different amounts of TTFMT added are shown in FIG. 1, and the results of testing the thermal stability of each electrolyte with different amounts of TTMPP added are shown in FIG. 4. It was. The discharger was tested using a TOOS TOSCAT-3100U model.

The thermal stability test is performed by charging and discharging the prepared coin cell 10 times, recovering the charged positive electrode material and measuring it by differential scanning calorimeter (DSC). In other words, when the temperature rises, the cathode material generates a self-heating phenomenon at a specific temperature. The self-heating phenomenon refers to a phenomenon in which oxygen is released while the cathode active material is decomposed at a temperature of 200 ° C. or higher. This heat generation is a major cause of fire and explosion if the battery is misused or used under conditions other than recommended.

1 is a graph showing a self-exothermic reaction of a positive electrode material using each electrolyte solution prepared in Example 1. FIG. In FIG. 1, the background refers to an electrolyte that does not include an additive, TTFMT. As shown in FIG. 1, 'TTFMT not added', which does not include TTFMT, shows a sharp self-exothermic reaction at around 270 ° C. On the other hand, in the case of the electrolyte solution containing 1, 3, 5 parts by weight of TTFMT, the self-exotherm temperature of the positive electrode material was delayed to about 330 ℃, it is shown that the intensity of the exothermic reaction is also much slowed down.

Figure 2 is a graph showing the results of comparing the life test and capacity of the lithium secondary battery using the respective electrolyte prepared in Example 1. The experiment was repeated while charging and discharging the battery from 4.3V to 2.8V section under the condition of 0.5C, each with a 30-minute pause between charge and discharge. As shown in FIG. 2, when 5 parts by weight of TTFMT was added, it was found that the capacity was slightly improved than when TTFMT was not added except for some cycles. That is, it can be seen that the addition of TTFMT has a flame retardant effect but does not deteriorate battery performance.

Figure 3 is a graph showing the results of the rate characteristic test of the lithium secondary battery using the respective electrolyte solution prepared in Example 1. The cells were charged up to 4.3V each under the conditions of 0.2C, discharged to 2.8V under the conditions of a given discharge current, and experimented with a 30 minute rest time between charging and discharging. As shown in FIG. 3, it can be seen that better rate characteristics are obtained when TTFMT is not added than 'background'.

4 is a graph showing a self-exothermic reaction of a positive electrode material using each electrolyte solution prepared in Example 2. FIG. In FIG. 4, 'background' refers to an electrolyte solution that does not include TTMPP as an additive. As shown in FIG. 4, 'background' without TTMPP shows a sharp self-exothermic reaction at around 270 ° C. On the other hand, in the case of an electrolyte solution in which 1 part by weight of TTMPP is added, the calorific value is largely suppressed, and the amount of suppression is slightly reduced when it is included in 3 parts by weight and 5 parts by weight, but the flame retardant effect is superior to that in the case where TTMPP is not added. Can be.

5 is a graph showing the results of comparing the life test and capacity of the lithium secondary battery using the respective electrolyte prepared in Example 2, Figure 6 is the rate of the lithium secondary battery using the respective electrolyte prepared in Example 2 Graph showing the results of the characteristic experiment. 5 and 6, the cell performance is similar when the TTMPP is included, compared with the case that does not include the TTMPP, it can be seen that the TTMPP has excellent flame retardant effect, but does not inhibit the battery performance.

Therefore, both electrolytes including the cyclic organic compounds TTFMT and TTMPP according to the present invention have excellent flame retardancy and can maintain or improve battery performance well.

1 is a graph showing a self exothermic reaction of a positive electrode material using an electrolyte solution containing TTFMT,

2 is a graph showing the results of comparing the life test and capacity of a lithium secondary battery using an electrolyte containing TTFMT,

3 is a graph showing results of a rate characteristic test of a lithium secondary battery using an electrolyte including TTFMT,

4 is a graph showing a self-exothermic reaction of a positive electrode material using an electrolyte solution containing TTMPP,

5 is a graph showing the results of comparing the life test and capacity of the lithium secondary battery using the electrolyte solution containing TTMPP,

6 is a graph showing results of a rate characteristic test of a lithium secondary battery using an electrolyte solution containing TTMPP.

Claims (7)

Lithium salts; solvent; And An electrolyte solution for a lithium secondary battery comprising a cyclic organic compound represented by Formula 2 below. [Formula 2]

(In Formula 2, R ₄ , R ₅ , R ₆ are each independently an alkyl group having 1 to 10 carbon atoms, part or all of the hydrogen of the alkyl group may be substituted with fluorine (F).) delete delete delete The method of claim 1, wherein the compound represented by Formula 2 is tris (2,4,6-trimethoxyphenyl) phosphine (tris (2,4,6-trimethoxyphenyl) phosphine) for a lithium secondary battery Electrolyte solution. The electrolyte of claim 1, wherein the cyclic organic compound is included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the electrolyte. The lithium secondary battery provided with the electrolyte solution for lithium secondary batteries in any one of Claims 1, 5, and 6.

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