KR101500033B1 - Additive for non-aqueous liquid electrolyte, non-aqueous liquid electrolyte and lithium secondary cell comprising the same - Google Patents

Abstract

The present invention provides an electrolyte additive comprising tris (trimethylsilyl) phosphate (TMSP) and vinyl ethylenesulfite.
Further, there is provided a non-aqueous electrolytic solution containing such an electrolyte additive and a lithium secondary battery comprising the same.

Description

TECHNICAL FIELD [0001] The present invention relates to a non-aqueous electrolytic solution containing an additive, a non-aqueous electrolytic solution containing the additive, and a lithium secondary battery. BACKGROUND ART < RTI ID = 0.0 >

The present invention relates to an electrolyte additive comprising a predetermined phosphate compound and vinyl ethylenesulfite, a non-aqueous electrolytic solution containing the electrolyte additive, and a lithium secondary battery comprising 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.

In recent years, technology has been developed not only for power supply for small appliances, but also for power supply for power storage facilities and for medium and large-sized industrial applications as power sources for vehicles.

Lithium metal oxide is used as the positive electrode active material of the lithium secondary battery, and lithium metal, lithium alloy, crystalline or amorphous carbon or carbon composite material is used as the 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.

This lithium secondary battery is charged and discharged while repeating the process of intercalation and deintercalation of lithium ions from the lithium metal oxide of the anode to the graphite electrode of the anode. At this time, lithium reacts strongly with the carbon electrode to form a film on the surface of the negative electrode. This coating is called Solid Electrolyte Interface (SEI) coating. The SEI coating formed at the beginning of charging prevents the reaction between lithium ion and carbon anode or other materials during charging and discharging. It also acts as an ion tunnel, allowing only lithium ions to pass through. This ion tunnel serves to prevent the collapse of the structure of the carbon anode by co-intercalating the organic solvent of the electrolyte having a large molecular weight moving together by solvation of the lithium ion together with the carbon anode.

However, the SEI film may fail to form a continuous protective film as the battery is charged and discharged, and thus the life of the battery may be reduced. In addition, the SEI coating is thermally unstable and may be destroyed by increased electrochemical energy and thermal energy when the cell is operated at high temperature or left at high temperature.

If the SEI coating is not stable, the performance of the battery due to the collapse of the SEI coating is degraded, and the CO ₂ gas is continuously generated due to the decomposition of the electrolyte, thereby increasing the internal pressure and thickness of the battery.

Therefore, in order to improve the performance of the lithium secondary battery, it is important to form a solid SEI film on the electrode of the 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 a high capacity and a high output at a high temperature while having an improved output when an electrolyte additive comprising a predetermined phosphate compound and vinyl ethylenesulfite is used And completed the present invention.

In order to solve the problems to be solved, the present invention provides an electrolyte additive comprising tris (trimethylsilyl) phosphate (TMSP) and vinyl ethylenesulfite.

Further, the present invention relates to an electrolyte additive comprising tris (trimethylsilyl) phosphate (TMSP) and vinyl ethylenesulfite, a non-aqueous organic solvent, and lithium

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The present invention also relates to a positive electrode comprising 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 nonaqueous electrolyte, wherein the positive electrode active material is a manganese- , A lithium metal oxide, or a mixture thereof.

According to the electrolyte additive of the present invention and the nonaqueous electrolytic solution containing the same, it is possible to minimize problems such as accelerated electrolyte decomposition and swelling phenomenon through formation of a stable SEI (Solid Electrolyte Interphase) film, and thus excellent high-temperature cycle characteristics and high- A non-aqueous electrolytic solution and a lithium secondary battery with improved output characteristics can be provided.

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

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 tris (trimethylsilyl) phosphate (TMSP) and vinyl ethylenesulfite.

The SEI film may be degraded in durability during high temperature storage in a fully charged state (e.g., 4 days at 85 < 0 > C after 100% charging at 4.2 V). 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, CH ₄ , C ₃ H ₆ or the like is generated to increase the internal pressure and the thickness of the battery.

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However, by including vinyl ethylene 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 inducing swelling of the battery and electrolyte decomposition reaction High temperature stability can be maintained.

However, the SEI coating can act as a resistance layer for inhibiting the movement of lithium ions, and the output of the lithium secondary battery may be lowered. However, when the tris (trimethylsilyl) phosphate (TMSP) is added according to the present invention, the resistance of the battery is reduced due to the improvement of the interface property between the electrode and the electrolyte, and the output of the lithium secondary battery can be remarkably improved.

Therefore, according to the present invention, the vinyl ethylene sulfite generates a SEI film by a reduction reaction on the electrode surface, thereby maintaining the high capacity and high temperature stability of the lithium secondary battery. At the same time, the phosphate-based compound of tris (trimethylsilyl) phosphate (TMSP) does not participate in the film formation reaction, but reduces the resistance to inhibit the charge transfer reaction of lithium ion during charging and discharging, . That is, the problem of the power drop that can be caused by the SEI coating acting as a resistive layer can be solved by the addition of the phosphate-based compound of tris (trimethylsilyl) phosphate (TMSP).

In one embodiment, it may specifically be tris (trimethylsilyl) phosphate (TMSP).

(TMSP) may be added in an amount of 0.01 to 5% by weight based on the total amount of the electrolytic solution and 0.01 to 2% by weight, based on the total amount of the electrolytic solution, of the tris (trimethylsilyl) phosphate (TMSP) By weight, more preferably from 0.01 to 1% by weight. If the content is less than 0.01% by weight, a sufficient output improvement effect can not be obtained. If the content is more than 5% by weight, the output improvement effect is remarkable but a side reaction which hinders the output and stability of the battery may be caused.

In addition, when vinyl ethylene sulfite is added to the electrolytic solution, the electrolytic solution preferably contains 0.01 to 5% by weight, more preferably 0.2 to 2% by weight based on the total weight of the electrolytic solution. When the content is less than 0.01% by weight, stable SEI coatings are not sufficiently formed. When the content exceeds 5% by weight, the SEI coating becomes thick, and the internal resistance may excessively increase.

On the other hand, the present invention relates to a non-aqueous electrolytic solution comprising an electrolyte additive comprising tris (trimethylsilyl) phosphate (TMSP) and vinyl ethylenesulfite, a non-aqueous organic solvent, and a lithium salt.

The nonaqueous electrolytic solution according to the present invention is characterized by including TMS (trimethylsilyl) phosphate (TMSP) and vinyl ethylene sulfite together as an electrolyte additive, thereby improving the high-temperature cycle characteristics and storage characteristics due to mutual interaction, A lithium secondary battery can be provided.

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The non-aqueous electrolytic solution of the present invention may further include a lithium salt used as the electrolyte additive. As the lithium salt, 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 , LiSO ₃ CF ₃ and LiClO _4. These lithium salts may be used singly or in combination of two or more.

The non-aqueous organic solvent that can be included in the non-aqueous electrolyte solution is not limited as long as it can minimize decomposition due to oxidation reaction during charging and discharging of the battery, For example, cyclic carbonates, linear carbonates, esters, ethers or ketones. These may be used alone or in combination of two or more. (EC), propylene carbonate (PC), and butylene carbonate (BC) are used as the cyclic carbonates, dimethyl carbonate (DMC) is used as the linear carbonate, and ethylene carbonate , Diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC).

In one embodiment, the non-aqueous electrolytic solution may further include at least one additive selected from the group consisting of a carbonate compound, a sulfate compound, and a sulfone compound so that a stable SEI film can be formed on the surface of the electrode.

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

The sulfate compound may be ethylene sulfate. When the sulfate compound is included as an additive in the non-aqueous electrolyte solution, the sulfate compound may be contained in an amount of 0.5 to 1.5% by weight based on the total weight of the electrolyte solution.

The sulfone compound may be 1,3-propane sultone. When the sulfone compound is included as an additive in the non-aqueous electrolyte, the sulfone compound may be contained in an amount of 0.5 to 1% by weight based on the total weight of the electrolyte solution. .

Meanwhile, 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 cathode active material may include a manganese-based 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-based oxide, lithium-nickel-manganese-based oxide, lithium-manganese-cobalt oxide and lithium-nickel-manganese-cobalt oxide, is _{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 ( here, 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 &lt; Z &lt; 2).

On the other hand, as the negative electrode active material, carbon-based negative electrode active materials such as crystalline carbon, amorphous carbon or carbon composite may be used alone or in combination of two or more.

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 1
[Preparation of electrolytic solution]

Based on the total amount of the electrolytic solution, in a mixed solvent comprising an organic solvent having a composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 3: 3: 4 (volume ratio) and 1.0M of LiPF ₆ , 3% by weight of vinylene carbonate (VC) and 1.5% by weight of 1,3-propane sultone were added, and 1% by weight of vinylethylene sulfite and 0.5% by weight of TMSP were further added to prepare a nonaqueous electrolytic solution.

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[Production of lithium secondary battery]

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

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.

The thus prepared positive electrode and negative electrode were fabricated by a conventional method together with a PE separator, and then the non-aqueous electrolyte was injected to complete the production of a lithium secondary battery.

Comparative Example  One

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

Comparative Example  2

A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that vinyl ethylenesulfite was not included as an electrolyte additive and only 0.5 wt% of TMSP was added to prepare an electrolyte solution.

Experimental Example  One

A high-temperature storage test was conducted to measure the discharge capacity over 0 to 11 weeks in order to investigate the capacity characteristics in the temperature environment of 45 ° C against each of the batteries of Example 1 and Comparative Examples 1 and 2. More specifically, the battery was charged at a constant current of 1 C = 800 mA. After the voltage of the battery reached 4.15 V, the battery was charged for the first time until the charging current reached 50 mA at a constant voltage of 4.15 V. Discharge was carried out at a constant current of 1 C until the battery voltage reached 2.75 V to measure the discharge capacity. These tests were performed for each cell at intervals of one week, and the results are shown in FIG.

       Referring to FIG. 1, the battery of Example 1 including vinyl ethylene sulfite and TMSP as an electrolyte additive regardless of the storage period exhibited excellent high-temperature storage characteristics compared with Comparative Examples 1 and 2 .

In particular, in Comparative Example 1 in which Vinyl Ethylene Sulfite and TMSP were not included as an electrolyte additive, it was confirmed that the power output was markedly lowered from the first week to the battery of Example 1. Further, in the case of Comparative Example 2 in which vinylethylene sulfite is not included as an electrolyte additive, it can be seen that the difference in high-temperature storage characteristics is greater than that in Example 1 from five weeks after the storage period.

Experimental Example  2

Each cell of Example 1 and Comparative Examples 1 and 2 was stored at 90 占 폚 for 4 hours in a 4.2 V full charge state, and the change in thickness was measured. The results are shown in Fig.

Referring to FIG. 2, it can be seen that the battery according to Example 1 according to the present invention had a reduced thickness (swelling phenomenon) when it was stored at a high temperature for a long period of time. Compared with Comparative Example 1 And the comparative example 2, the high temperature stability effect is excellent.

Experimental Example  3

Each battery of Example 1 and Comparative Examples 1 and 2 was charged at a constant current of 1 C = 800 mA in a temperature environment of 55 캜. After the battery voltage reached 4.15 V, the charge current value Was charged for 1 time until it reached 50 mA. The discharging was performed at a constant current of 1 C until the battery voltage reached 2.75 V to determine the discharge capacity of the first cycle.

Subsequently, charging and discharging of the batteries of Example 1 and Comparative Examples 1 and 2 were repeated up to 1050 cycles, and the discharging capacity for each cycle was similarly measured and shown in Fig.

Referring to FIG. 3, it can be seen that the battery of Example 1 exhibits excellent high-temperature cycle characteristics as compared with the lithium secondary batteries of Comparative Examples 1 and 2. Particularly, in Comparative Example 2 involving only the TMSP and the electrolyte containing no vinylethylene sulfite, the discharge capacity was drastically reduced at about 900 cycles, and a sharp drop in the discharge capacity was observed in the case of TMSP and vinyl ethylene sulfite It can be confirmed that they are solving through interaction. TMSP and vinyl ethylene sulfite were found to be capable of increasing the capacity of the battery and improving the life characteristics of the battery.

Claims (10)

An electrolyte additive comprising tris (trimethylsilyl) phosphate (TMSP) and vinyl ethylenesulfite.
The method according to claim 1,
Wherein the vinyl ethylene sulfite is contained in an amount of 0.01 to 5% by weight based on the total weight of the electrolytic solution. delete The method according to claim 1,
Wherein the tris (trimethylsilyl) phosphate (TMSP) is contained in an amount of 0.01 to 5% by weight based on the total weight of the electrolytic solution. The method according to claim 1,
Wherein the tris (trimethylsilyl) phosphate (TMSP) is contained in an amount of 0.01 to 2% by weight based on the total weight of the electrolytic solution. An electrolyte additive including tris (trimethylsilyl) phosphate (TMSP) and vinyl ethylenesulfite (Vinyl Ethylene Sulfite)
Non-aqueous organic solvents and
A non-aqueous electrolytic solution comprising a lithium salt. The method according to claim 6,
The lithium salt is _{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 ) 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
And at least one additive selected from the group consisting of 1,3-propane sultone. An anode including a cathode active material,
A negative electrode including a negative electrode active material,
A separator interposed between the anode and the cathode,
A nonaqueous electrolytic solution according to claim 6,
Wherein the cathode active material is a manganese-based spinel active material, a lithium metal oxide, or a mixture thereof. 10. The method of claim 9,
Wherein the lithium metal oxide is selected from the group consisting of a lithium-manganese-based oxide, a lithium-nickel-manganese-based oxide, a lithium-manganese-cobalt oxide, and a lithium-nickel-manganese-cobalt oxide.

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