KR20130122366A - Additive for non-aqueous liquid electrolyte, non-aqueous liquid electrolyte and lithium secondary cell comprising the same - Google Patents

Abstract

Provided is an additive for non-aqueous liquid electrolyte, comprising the following chemical formula 1, and Vinyl ethylene sulfite. [Chemical formula 1] <img id="i0007" he="94" wi="114" file="pat00007.jpg" img-format="jpg" /> (In the chemical formula, a is C or Si, b is H or F, n is 1-5) In addition, a non-aqueous liquid electrolyte comprising the additive above, and a lithium secondary battery comprising the non-aqueous liquid electrolyte are provided. [Reference numerals] (AA) Capacity (mAh);(BB) Comparative example 1;(CC) Comparative example 2;(DD) Example 1;(EE) Storage period (week)

Description

Electrolytic solution additives, non-aqueous electrolyte and lithium secondary battery comprising the additive {ADDITIVE FOR NON-AQUEOUS LIQUID ELECTROLYTE, NON-AQUEOUS LIQUID ELECTROLYTE AND LITHIUM SECONDARY CELL COMPRISING THE SAME}

The present invention relates to an electrolyte additive including a predetermined phosphate compound and vinyl ethylene sulfite, a non-aqueous electrolyte including the electrolyte additive, and a lithium secondary battery including the same. More specifically, the present invention relates to an electrolyte additive for providing a lithium secondary battery having excellent high temperature storage characteristics and cycle characteristics and improved output.

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries having high energy density and voltage have been commercialized and widely used.

Recently, the technology has been developed to be used not only for power supplies for small devices but also for "medium and large size" industries as power storage facility power supplies or vehicle power supplies.

Lithium metal oxide is used as a positive electrode active material of a lithium secondary battery, and lithium metal, a lithium alloy, crystalline or amorphous carbon or a carbon composite material is used as a negative electrode active material. The active material is coated on the current collector with an appropriate thickness and length, or the active material itself is coated in a film form and wrapped or laminated with a separator as an insulator to form an electrode group. The electrode group is then placed in a can or similar container, Thereby manufacturing a secondary battery.

In such a lithium secondary battery, charging and discharging progress while repeating a process of intercalating and deintercalating lithium ions from a lithium metal oxide of a positive electrode to a graphite electrode of a negative electrode. At this time, since lithium is highly reactive, it reacts with the carbon electrode to form a film on the surface of the cathode. Such a coating is called a solid electrolyte interface (SEI) coating, and the SEI coating formed at the beginning of charging prevents a reaction between lithium ions and a carbon negative electrode or other material during charging and discharging. It also acts as an ion tunnel, allowing only lithium ions to pass through. The ion tunnel serves to prevent the organic solvents of the large molecular weight electrolytes that solvate lithium ions and move together to be co-intercalated with the carbon anode to collapse the structure of the carbon anode.

However, the SEI film may not be able to form a continuous protective film as the charge and discharge of the battery proceeds, thereby deteriorating the life of the battery. In addition, the SEI coating is not thermally stable and may collapse due to increased electrochemical and thermal energy when the cell is operated at high temperatures or left at high temperatures.

As such, when the SEI film is not stable, there is a problem in that the internal pressure and thickness of the battery are increased by deterioration of performance due to its collapse, decomposition of the electrolyte, and continuous generation of CO ₂ gas.

Therefore, in order to improve the performance of a lithium secondary battery, it is important to form a firm SEI film on the electrode of a lithium secondary battery.

The present invention aims at solving the technical problems requested from the past as described above.

The inventors of the present application can provide a lithium secondary battery having high capacity and high temperature storage characteristics and improved output when using an electrolyte additive including a predetermined phosphate compound and vinyl ethylene sulfite. Confirmed and completed the present invention.

In order to solve the above problems, the present invention provides an electrolyte additive comprising a compound of Formula 1 and vinyl ethylene sulfite (Vinyl Ethylene Sulfite).

[Formula 1]

(Wherein a is C or Si, b is H or F, n is 1 to 5)

Furthermore, the present invention provides a non-aqueous electrolyte solution including an electrolyte additive, a non-aqueous organic solvent, and a lithium salt including a compound of Formula 1 and vinyl ethylene sulfite.

[Formula 1]

(Wherein a is C or Si, b is H or F, n is 1 to 5)

The present invention also includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte, wherein the positive electrode active material is a manganese spinel active material It provides a lithium secondary battery which is a lithium metal oxide or a mixture thereof.

According to the electrolyte additive of the present invention and the non-aqueous electrolyte including the same, it is possible to minimize problems such as accelerated electrolyte decomposition and swelling through stable SEI (Solid Electrolyte Interphase) film formation, thereby providing excellent high temperature cycling characteristics and high temperature storage characteristics. It is possible to provide a nonaqueous electrolyte solution and a lithium secondary battery having improved output characteristics.

1 is a graph illustrating a result of measuring a discharge capacity according to a storage time after high temperature storage of a secondary battery including an electrolyte additive according to the present invention according to Experimental Example 1. FIG.
2 is a graph showing a result of measuring a thickness change according to a storage time of a secondary battery including the electrolyte solution additive according to Experimental Example 2 according to the present invention.
3 is a graph showing the results of measuring high temperature cycle characteristics of a secondary battery including the electrolyte solution additive according to the present invention according to Experimental Example 3. FIG.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The electrolyte additive according to the present invention may include a compound of Formula 1 and vinyl ethylene sulfite.

[Chemical Formula 1]

(Wherein a is C or Si, b is H or F, n is 1 to 5)

SEI membranes may have poor durability upon high temperature storage in a fully charged state (eg, left at 85 ° C. for 4 days after 100% charge at 4.2V). That is, when the high-temperature storage in the fully charged state the cathode, while the SEI film gradually collapses and exposed with the lapse of time, so that the surface of the exposed anode reacts with an electrolyte around, causing a side reaction continued to CO, CO _2, Gases such as CH ₄ and C ₃ H ₆ are generated, resulting in an increase in battery pressure and thickness.

However, by including vinylethylene sulfite as in the present invention, the capacity can be maintained by minimizing the irreversible capacity of the battery, exhibiting excellent high temperature cycle characteristics, and causing the swelling of the battery and decomposition of the electrolyte during high temperature storage. By preventing, high temperature stability can be maintained.

However, the SEI film may act as a resistance layer that inhibits the movement of lithium ions, which may cause a decrease in output of the lithium secondary battery. However, when the phosphate-based compound of Formula 1 is added according to the present invention, the output of the lithium secondary battery may be remarkably improved by reducing the resistance of the battery due to the improvement of the interface property between the electrode and the electrolyte.

Therefore, according to the present invention, vinyl ethylene sulfite generates an SEI film by a reduction reaction on the electrode surface, thereby maintaining high capacity and high temperature stability of the lithium secondary battery. At the same time, the phosphate-based compound of Formula 1 does not participate in the film formation reaction, but reduces the resistance that inhibits the charge transfer reaction of lithium ions during charge and discharge, thereby enabling a smooth movement of lithium ions. That is, the problem of output reduction that can occur due to the SEI film acting as the resistive layer can be solved by the addition of the phosphate-based compound of formula (1).

In one embodiment, the compound of Formula 1 may be specifically at least one selected from the group consisting of tris (trimethylsilyl) phosphate (TMSP) and tris (2,2,2-trifluoroethyl) phosphate (TFEP). .

In adding the compound of Formula 1 to the electrolyte, the compound of Formula 1 may be included in an amount of 0.01 to 5% by weight based on the total amount of the electrolyte, it is preferable to include 0.01 to 2% by weight based on the total amount of the electrolyte, 0.01 It is more preferable to include from 1% by weight. If the content is less than 0.01% by weight can not produce a sufficient output improvement effect, if the content is more than 5% by weight, the output improvement effect is remarkable, but side reactions that inhibit the output and stability of the battery may be induced.

In addition, in the addition of vinyl ethylene sulfite to the electrolyte, it is preferable to include from 0.01 to 5% by weight, more preferably from 0.2 to 2% by weight based on the total amount of the electrolyte. If the content is less than 0.01% by weight, it is difficult to form a stable SEI film sufficiently, and if the content is more than 5% by weight, the SEI film may be thick and the internal resistance may be excessively increased.

On the other hand, the present invention relates to a non-aqueous electrolyte solution containing an electrolyte additive, a non-aqueous organic solvent, and a lithium salt of the formula (1) and vinyl ethylene sulfite (Vinyl Ethylene Sulfite).

[Chemical Formula 1]

(Wherein a is C or Si, b is H or F, n is 1 to 5)

The non-aqueous electrolyte according to the present invention includes a compound of Formula 1 and vinyl ethylene sulfite together as an electrolyte additive, thereby providing a lithium secondary battery that exhibits an output improvement effect while improving high temperature cycling characteristics and storage characteristics through interaction between them. can do.

The non-aqueous electrolyte solution of the present invention may further include a lithium salt used as the electrolyte additive. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ , LiBF ₆ , LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ Lithium salts commonly used in electrolytes of lithium secondary batteries, such as LiSO ₃ CF ₃ and LiClO ₄ , may be used, and these may be used alone, or two or more thereof may be used in combination.

In addition, as the non-aqueous organic solvent that can be included in the non-aqueous electrolyte, decomposition by the oxidation reaction or the like during the charging and discharging process of the battery can be minimized, there is no limitation as long as it can exhibit the desired characteristics with the additive, For example, cyclic carbonates, linear carbonates, esters, ethers or ketones. These may be used alone, or two or more thereof may be used in combination. Among the organic solvents, in particular, carbonate-based organic solvents may be preferably used, and cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC), and linear carbonates include dimethyl carbonate (DMC). , Diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC) and ethylpropyl carbonate (EPC).

In one embodiment, the non-aqueous electrolyte may further include one or more additives selected from the group consisting of carbonate compounds, sulfate compounds and sultone compounds to form a stable SEI film on the electrode surface.

The carbonate-based compound may be at least one selected from the group consisting of vinylene carbonate and vinylene ethylene carbonate. When the carbonate-based compound is included as an additive of the non-aqueous electrolyte, it may be included in an amount of 1.5 to 3 wt% based on the total amount of the electrolyte.

The sulfate-based compound may be ethylene sulfate, and when the sulfate-based compound is included as an additive of the non-aqueous electrolyte, it may be included in an amount of 0.5 to 1.5 wt% based on the total amount of the electrolyte.

The sultone compound may be 1,3-propane sultone, and when the sultone compound is included as an additive of the non-aqueous electrolyte, it may be included in an amount of 0.5 to 1 wt% based on the total amount of the electrolyte. Can be.

On the other hand, the lithium secondary battery according to an embodiment of the present invention may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode and the non-aqueous electrolyte. The positive electrode and the negative electrode may include a positive electrode active material and a negative electrode active material, respectively.

Here, the positive electrode active material may include a manganese spinel active material, a lithium metal oxide, or a mixture thereof. Further, the lithium metal oxide may be selected from the group consisting of lithium-manganese oxide, lithium-nickel-manganese oxide, lithium-manganese-cobalt oxide, and lithium-nickel-manganese-cobalt oxide, and more specifically, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (where 0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi _{1 - Y} Co _Y O ₂ , LiCo _{1 - Y} Mn _Y O ₂ , LiNi _{1 - Y} Mn _Y O ₂ (where 0 ≦ Y <1), Li (Ni _a Co _{b Mn c) O 4 (0 <} a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn 2 - z Ni z O 4, LiMn 2 -z Co z O 4 (Where 0 <Z <2).

Meanwhile, as the negative electrode active material, a carbon-based negative electrode active material such as crystalline carbon, amorphous carbon, or a carbon composite may be used alone or in combination of two or more thereof.

The separator may be a porous polymer film such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer Or may be a laminate of two or more kinds. In addition, nonwoven fabrics made of conventional porous nonwoven fabrics, for example, glass fibers having a high melting point, polyethylene terephthalate fibers, or the like can be used, but the present invention is not limited thereto.

Example

EXAMPLES The present invention will be further illustrated by the following examples and experimental examples, but the present invention is not limited by these examples and experimental examples.

Example  One

[Preparation of electrolytic solution]

Ethylene carbonate (EC): ethylmethyl carbonate (EMC): dimethyl carbonate (DMC) = 3: 3: 4 (volume ratio) based on the total amount of the electrolytic solution in a mixed solvent containing an organic solvent and 1.0 M LiPF ₆ 3% by weight of vinylene carbonate (VC) and 1.5% by weight of 1,3-propanesultone were added, and 1% by weight of vinylethylene sulfite and 0.5% by weight of TMSP were further added to prepare a non-aqueous electrolyte solution.

[Production of lithium secondary battery]

As a positive electrode active material, a mixture consisting of a manganese spinel active material and a lithium-nickel-manganese-cobalt-based oxide was used, and a positive electrode slurry was prepared by mixing polyvinylidene fluoride (PVdF) as a binder and carbon as a conductive material. The cathode slurry was coated on an aluminum current collector, followed by drying and rolling to prepare a cathode.

Also, a negative electrode slurry was prepared by mixing natural graphite, a PVdF binder and a thickener as an anode active material and dispersing the mixture in water, coating the negative electrode slurry on a copper collector, followed by drying and rolling.

After preparing a battery in a conventional manner with a positive electrode and a negative electrode prepared in this manner with a PE separator, the prepared non-aqueous electrolyte was injected to complete the production of a lithium secondary battery.

Comparative Example  One

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that the electrolyte solution was prepared without containing vinylethylene sulfite and TMSP additive.

Comparative Example  2

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that the electrolyte solution was prepared by adding only 0.5% by weight of TMSP without including vinylethylene sulfite as an electrolyte additive.

Experimental Example  One

In order to examine the capacity characteristics of each of the batteries of Example 1 and Comparative Examples 1 and 2 at a temperature of 45 ° C., a high temperature storage test for measuring discharge capacity over 0 to 11 weeks was conducted. More specifically, the battery was charged at a constant current of 1 C = 800 mA, and after the voltage of the battery became 4.15 V, the first charge was performed at a constant voltage of 4.15 V until the charge current value became 50 mA. The discharged battery was discharged at a constant current of 1C until the battery voltage reached 2.75V, and the discharge capacity was measured for the first charged battery. These tests were performed at weekly intervals for each cell and the results are shown in FIG. 1.

       Referring to FIG. 1, the battery of Example 1 including vinylethylene sulfite and TMSP as an electrolyte additive regardless of the storage period exhibits excellent high temperature storage characteristics compared to Comparative Examples 1 and 2 with little output reduction. It can be seen that.

In particular, in the case of Comparative Example 1, which does not include vinyl ethylene sulfite and TMSP as the electrolyte additive, it can be seen that the reduction in output compared to the battery of Example 1 from the first week. Furthermore, in the case of Comparative Example 2, which does not include vinyl ethylene sulfite as an electrolyte additive, it can be seen that the difference in high temperature storage characteristics is greater than that of the battery of Example 1 from 5 weeks after the storage period.

Experimental Example  2

Each cell of Example 1 and Comparative Examples 1 and 2 was measured at 90 ° C. for 4 hours under 4.2V full charge, and the thickness change was measured. The results are shown in FIG. 2.

2, compared with Comparative Examples 1 and 2, the battery of Example 1 according to the present invention can be confirmed that the increase in thickness (swelling phenomenon) during long-term storage at high temperature is suppressed, the longer the storage time Comparative Example 1 And the difference with the comparative example 2 is large, it can be seen that the excellent high temperature stability effect.

Experimental Example  3

Each battery of Example 1 and Comparative Examples 1 and 2 was charged at a constant current of 1C = 800 mA in a 55 ° C. temperature environment, and after the battery voltage reached 4.15V, the charging current value was measured at a constant voltage of 4.15V. The first charge was performed until it reached 50 kPa. The first charged battery was discharged at a constant current of 1 C until the battery voltage reached 2.75 V to obtain a discharge capacity at the first cycle.

Subsequently, such charging and discharging were repeated for 1050 cycles for each of the batteries of Example 1 and Comparative Examples 1 and 2, and the discharge capacity for each cycle was measured as shown in FIG. 3.

Referring to FIG. 3, it can be seen that the battery of Example 1 exhibits excellent high temperature cycle characteristics compared to the lithium secondary batteries of Comparative Examples 1 and 2. In particular, in Comparative Example 2 regarding the electrolyte solution containing only TMSP but not vinyl ethylene sulfite, the discharge capacity dropped rapidly at about 900 cycles. You can also confirm that the solution is through interaction. It was confirmed that TMSP and vinyl ethylene sulfite can increase the capacity of the battery, as well as improve the life characteristics of the battery.

Claims (10)

An electrolyte additive comprising a compound of Formula 1 and vinyl ethylene sulfite.
[Chemical Formula 1]

(Wherein a is C or Si, b is H or F, n is 1 to 5) The method of claim 1,
The vinyl ethylene sulfite is an electrolyte additive containing 0.01 to 5% by weight based on the total amount of the electrolyte. The method of claim 1,
The compound of Formula 1 is at least one electrolyte additive selected from the group consisting of tris (trimethylsilyl) phosphate (TMSP) and tris (2,2,2-trifluoroethyl) phosphate (TFEP). The method of claim 1,
The compound of Formula 1 is an electrolyte additive containing 0.01 to 5% by weight based on the total amount of the electrolyte. The method of claim 1,
The compound is an electrolyte additive containing 0.01 to 2% by weight based on the total amount of the electrolyte. Electrolyte additive including the compound of Formula 1 and vinyl ethylene sulfite (Vinyl Ethylene Sulfite),
[Chemical Formula 1]

(Wherein a is C or Si, b is H or F, n is 1 to 5)
Non-aqueous organic solvent and
A non-aqueous electrolyte solution containing a lithium salt. The method according to claim 6,
The lithium salt may be LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , CF ₃ SO ₃ Li, LiC (CF ₃ SO ₂ ) A non-aqueous electrolyte solution containing any one selected from the group consisting of ₃ and LiC ₄ BO ₈ or a mixture of two or more thereof. The method according to claim 6,
Vinylene carbonate or vinylene ethylene carbonate,
Ethylene sulfate and
Non-aqueous electrolyte solution further comprises one or more additives selected from the group consisting of 1,3-propane sultone. An anode including a cathode active material,
A negative electrode comprising a negative electrode active material,
A separator interposed between the positive electrode and the negative electrode;
Including the non-aqueous electrolyte of claim 6,
The cathode active material is a manganese spinel active material, lithium metal oxide or a mixture thereof. The method of claim 9,
The lithium metal oxide is a lithium secondary battery selected from the group consisting of lithium-manganese oxide, lithium-nickel-manganese oxide, lithium-manganese-cobalt-based oxide and lithium-nickel-manganese-cobalt-based oxide.

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