KR101251521B1 - Nonaqueous electrolyte for lithium battery - Google Patents

Abstract

The present invention relates to a nonaqueous electrolyte for a lithium secondary battery, and includes tetramethylsulfone (TMS), which is a sulfone-based organic solvent, and an anode film-forming additive in an electrolyte solution containing lithium salt as a carbonate-based solvent and a solute dissolved in the carbonate-based solvent. Providing a non-aqueous electrolyte for lithium batteries, characterized in that 2,5-dihydrofuran (DHF) or gamma butyrolactone (GBL) is added,
By adding a sulfone solvent such as tetramethylsulfone to the basic electrolyte solution and adding 2,5-dihydrofuran (DHF) or gamma butyrolactone (GBL) as an anode film forming additive, the electrolyte solution does not decompose at high potentials, resulting in energy density. It is effective to improve and have excellent charge / discharge cycle characteristics.

Description

Non-aqueous electrolyte for lithium battery {NONAQUEOUS ELECTROLYTE FOR LITHIUM BATTERY}

The present invention relates to a non-aqueous electrolyte for lithium batteries, and more particularly, to an electrolyte at high potential by adding 2,5-dihydrofuran (DHF) or gamma butyrolactone (GBL) as a sulfone solvent and an anode film forming additive to a basic electrolyte solution. The present invention relates to a nonaqueous electrolyte which prevents the decomposition phenomenon.

In general, a secondary battery is a chemical battery that can be recharged and used semi-permanently unlike a primary battery. Recently, the market size of a secondary battery is growing exponentially due to mass distribution of laptops, mobile communication devices, and digital cameras. .

Such secondary batteries include lead-acid batteries, nickel-cadmium (Ni-Cd) batteries, nickel-hydrogen (Ni-MH) batteries, and lithium batteries, depending on the cathode material and the anode material. The intrinsic properties determine the potential and energy density. In particular, lithium batteries have been widely 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 the lithium secondary batteries, a lithium secondary battery using a nonaqueous electrolyte, in particular, is coated with a lithium metal mixed oxide on a metal as an anode, and is coated with a carbon material as a cathode. Between these anodes and cathodes, an electrolytic solution in which lithium salts are appropriately dissolved in an organic solvent is placed.

As the electrolyte solvent of the lithium secondary battery, a nonaqueous carbonate organic solvent such as ethylene carbonate, dimethyl carbonate, diethyl carbonate, or the like is used.

Looking at the operation principle of such a lithium secondary battery, the lithium ion (Li +) present in the ionic state in the electrolyte is moved from the positive electrode to the negative electrode when charged (charge), and from the negative electrode to the positive electrode during discharge (electricity) Generates.

At this time, the electrons move in the same direction as lithium ions along the wire connecting the anode and the cathode.

Currently used lithium secondary batteries can be charged up to 4.2 ~ 4.3V, and more energy can be used by charging more than 4.3V. However, these organic solvents have a problem in that the electrolyte is decomposed when the charge is more than 4.3V causing cycle degradation.

The present invention has been made to solve the above problems, by adding 2,5-dihydrofuran (DHF) or gamma butyrolactone (GBL) as a positive electrode film forming additive to a sulfonic solvent having a high oxidation potential. An object of the present invention is to provide a nonaqueous electrolyte for a lithium battery which suppresses decomposition of an electrolyte and has excellent charge and discharge cycle characteristics.

Embodiment of the present invention for achieving the above object is a non-aqueous electrolyte for a lithium battery, characterized in that the sulfonic acid-based organic solvent is added to an electrolyte solution containing a lithium salt as a carbonate solvent and a solute dissolved in the carbonate solvent. to provide.

Embodiments according to the invention are characterized in that the addition of an anode coating forming additive to the nonaqueous electrolyte.

The sulfone organic solvent of the embodiment according to the present invention is characterized in that tetramethylsulfone (TMS).

The carbonate solvent of the embodiment according to the present invention is at least one cyclic carbonate solvent selected from ethylene carbonate, propylene carbonate, pentylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl It is characterized in that the at least one chain carbonate solvent selected from propyl carbonate.

The lithium salt of the embodiment according to the invention is characterized in that at least one selected from LiPF ₆ or LiTFSI.

The non-aqueous electrolyte of the embodiment according to the present invention is LiPF ₆ 0.8-2 M in which LiPF ₆ is dissolved as a solute in a solvent in which a cyclic carbonate, a chain carbonate, and a sulfone are mixed in a volume ratio of 1: 1 to 7: 1 to 5, respectively. 0.1 to 5 parts by weight of vinyl carbonate (VC) is added to 100 parts by weight of the electrolyte solution.

Embodiment, the non-aqueous electrolyte comprises a cyclic carbonate, chain carbonate, sulfone, each one according to the invention: an electrolytic solution of 1 ~ 5 LiPF ₆ 1M solution dissolving LiPF ₆ as a solute in a solvent mixture in a volume ratio of: 1-7 It is characterized by adding 0.1 to 5 parts by weight and 0.1 to 5 parts by weight of vinyl carbonate (VC) and 2,5-dihydrofuran (DHF), respectively, in 100 parts by weight.

The non-aqueous electrolyte of the embodiment according to the present invention is LiPF in which LiPF ₆ and LiTFSI are dissolved as a solute in a solvent in which a cyclic carbonate, a chain carbonate, and a sulfone are mixed in a volume ratio of 1: 1 to 7: 1 to 5, respectively. ₆ to 5 parts by weight of vinyl carbonate (VC) and 2,5-dihydrofuran (DHF) are added to 100 parts by weight of an electrolyte of 0.8 to 2 M and LiTFSI 0.2 to 1 M, respectively. .

As described above, the present invention adds a sulfone-based solvent such as tetramethylsulfone to the basic electrolyte solution and adds 2,5-dihydrofuran (DHF) or gamma butyrolactone (GBL) as an anode film forming additive, and thus the electrolyte solution at high potential. This is not decomposed to improve the energy density, and has the effect of having excellent charge and discharge cycle characteristics.

1 is a graph of an experimental example for examining the effect of tetramethylsulfone.
Figure 2 is a graph comparing the Example and Comparative Example according to the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention.

Such an embodiment may be embodied in various different forms as one of ordinary skill in the art to which the present invention pertains, and is not limited to the embodiments described herein.

An embodiment according to the present invention is to prevent the decomposition of the solvent at high potential by mixing an organic solvent having a high oxidation potential, and to add a positive electrode film forming additive to form a film on the positive electrode of the lithium battery to prevent decomposition of the electrolyte It is about a nonaqueous electrolyte.

In general, the basic electrolyte solution used in the lithium secondary battery is a non-aqueous organic solvent including at least one solvent selected from the group consisting of a carbonate solvent, an ester solvent, an ether solvent, and a ketone solvent, and the non-aqueous organic solvent. It comprises a lithium salt dissolved in a solvent.

First, an organic solvent having a high oxidation potential to be used in the embodiment according to the present invention should be selected. For this purpose, the experiment was carried out as follows.

Experimental Example 1

1 M nonaqueous electrolyte was prepared by dissolving LiPF ₆ as a solute in a solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC) and glutaronitrile (GLN) were mixed at a ratio of 1: 2: 2.

 Experimental Example 2

LiPF ₆ was dissolved as a solute in a solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), tetramethyl sulfone (TMS), and glutaronitrile (GLN) were mixed at a ratio of 1: 2: 1: 1, and 1M was dissolved as a solute. A nonaqueous electrolyte solution was prepared.

Experimental Example 3

A 1 M nonaqueous electrolyte was prepared by dissolving LiPF ₆ as a solute in a solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and tetramethyl sulfone (TMS) were mixed at a ratio of 1: 2: 2.

In order to measure the electrochemical properties of the electrolyte solutions prepared in Experimental Examples 1 to 3, a graphite-based active material was used as the negative electrode, a LiNi 1/3 Co 1/3 Mn 1/3 O ₂ active material was used as the positive electrode, and Experimental Example 1 as the electrolyte. A coin cell type battery was prepared using the electrolyte of 3 to 3.

In order to evaluate the electrochemical characteristics, the lithium battery having the electrolytes of Experimental Examples 1 to 3 was discharged to 2.5V by a constant current method with a current of 1C, and when reaching a current of 0.02C after charging a constant current to 4.5V with a current of 1C. Charged to constant voltage up to 4.5V.

The results for Experimental Examples 1 to 3 are shown in the graph of FIG. 1.

Looking at Figure 1, it can be seen that the lifetime characteristics in Experimental Example 3 is the best.

That is, tetramethylsulfone (TMS) and glutaronitrile (GLN) are known to be stable solvents at high potentials, but the experimental results show that the electrolyte solution containing glutaronitrile (GLN) did not have good life characteristics, and tetramethylsulfone alone When used, it was found to exhibit better life characteristics.

Accordingly, in the present invention, the tetramethylsulfone was selected as an organic solvent having a high oxidation potential.

In the embodiment according to the present invention, an additive was added to prevent electrolyte decomposition at high potential. Electrolytic decomposition phenomenon refers to the occurrence of the electron transfer from the anode to the electrolyte.

In the embodiment according to the present invention, a cyclic carbonate type, a chain carbonate type, and a sulfone type are used as the solvent of the nonaqueous electrolyte.

The cyclic carbonate-based solvent is typically one or more organic solvents selected from ethylene carbonate, propylene carbonate, pentylene carbonate, and the like as a solvent used in a lithium secondary battery. When the cyclic carbonate type exceeds 30% by volume in the mixed solvent, it is difficult to dissolve. In particular, since ethylene carbonate is present as a solid at room temperature, adding too much may cause problems.

In addition, the chain carbonate-based solvent is also a solvent commonly used in lithium secondary batteries, at least one organic selected from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, etc. Solvent.

In addition, the embodiment according to the present invention used LiPF _6, LiTFSI as the solute of the lithium salt _, but this is not limited to the embodiment according to the present invention, it is used in the lithium secondary battery which is a technical field of the present invention. Any lithium salt may be used as long as it is a lithium salt used as a solute for producing an electrolyte solution that does not impair the technical idea of the present invention.

In the first embodiment according to the present invention, a cyclic carbonate type, a chain carbonate type, and a sulfone type are used as the solvent of the nonaqueous electrolyte. The ratio is prepared by mixing in a volume ratio of 1: 1 to 7: 1 to 5, respectively. At this time, when the amount of the chain carbonate is more than 7, the phenomenon of decomposition at high potential occurs. When the ratio of sulfone is more than 5, the ionic conductivity is lowered, which causes problems in the movement of ions.

In the first embodiment, LiPF ₆ is dissolved as a solute to prepare an electrolyte solution of LiPF ₆ 0.8 to 2 M. When the concentration of LiPF ₆ is less than 0.8 M, the ionic conductivity may be lowered. Decomposition may increase.

In addition, 0.1 to 5 parts by weight of vinyl carbonate (VC) is added to 100 parts by weight of the electrolyte, which is thin when the amount of vinyl carbonate is less than 0.1 parts by weight, and the effect of the present invention cannot be obtained, and 5 parts by weight. This is because when the amount is exceeded, a thick film is formed on the negative electrode to hinder the movement of lithium ions.

In the second embodiment according to the present invention, vinyl carbonate (VC), 2,5-dihydrofuran in 100 parts by weight of the electrolyte of LiPF ₆ 1M prepared by adding LiPF ₆ as a solute to the solvent prepared in the first embodiment. (DHF) is added in an amount of 0.1 to 5 parts by weight, which is thin when the amount of vinyl carbonate and 2,5-dihydrofuran is less than 0.1 parts by weight, and when the amount is greater than 5 parts by weight, a thick film is formed on the cathode. This is because it may interfere with the movement of lithium ions by forming.

In the third embodiment according to the present invention by dissolving LiPF ₆ and LiTFSI as a solute in 100 parts by weight of the electrolyte in the solvent prepared in the first embodiment as a solute of LiPF ₆ 0.8 ~ 2M and LiTFSI 0.2 ~ 1M in 100 parts by weight of vinyl It is prepared by adding 0.1 to 5 parts by weight of carbonate (VC) and 2,5-dihydrofuran (DHF), respectively. The basis for the numerical limitation of LiPF ₆ and LiTFSI is the same as in the first embodiment, and the basis for the numerical limitation of vinyl carbonate (VC) and 2,5-dihydrofuran (DHF) is in the second embodiment. Is the same as

In the fourth embodiment according to the present invention, by dissolving LiPF ₆ and LiTFSI as a solute in the solvent of the first embodiment to prepare an electrolyte of 0.8M, 0.2M, respectively, 100 parts by weight of vinyl carbonate (VC), 2 parts by weight and 0.2 parts by weight of gamma butyrolactone (GBL) were added to prepare a nonaqueous electrolyte for lithium batteries.

In the embodiment according to the present invention, 2,5-dihydrofuran (DHF) or gamma butyrolactone (GBL) was used as an additive for forming a film on the positive electrode. In order to determine the effects of the 2,5-dihydrofuran (DHF) and gamma butyrolactone (GBL) was performed as follows.

[Example 1]

2 weight% of vinyl carbonate (VC) was added to a 1 M electrolyte solution in which ethylene carbonate, ethyl methyl carbonate and tetramethyl sulfone were mixed at a ratio of 1: 2: 2, and a 1 M electrolyte solution in which LiPF ₆ was dissolved as a solute. A battery nonaqueous electrolyte was prepared.

[Example 2]

Vinyl carbonate (VC), 2,5-dihydrofuran (DHF) in a solvent obtained by mixing ethylene carbonate, ethyl methyl carbonate and tetramethyl sulfone in a ratio of 1: 2: 2 and a 1 M electrolyte solution in which LiPF ₆ was dissolved as a solute. ) Was added 2% by weight and 0.2% by weight of the electrolytic solution, respectively, to prepare a non-aqueous electrolyte for lithium batteries.

[Example 3]

Vinyl carbonate (VC) and gamma butyrolactone (GBL) were respectively added to a solvent in which ethylene carbonate, ethyl methyl carbonate, and tetramethyl sulfone were mixed at a ratio of 1: 4: 4, and a 1 M electrolyte solution in which LiPF ₆ was dissolved as a solute. 2% by weight and 1% by weight of the electrolyte was added to prepare a nonaqueous electrolyte for lithium batteries.

Example 4

Ethylene carbonate, ethyl methyl carbonate, and tetramethyl sulfone were mixed in a ratio of 1: 2: 2, and LiPF ₆ and LiTFSI (LiN (C ₂ F 5 SO ₃ ) ₂ ) were dissolved as solutes, respectively, 0.8 M and 0.2 M, respectively. 2 parts by weight and 0.2 parts by weight of vinyl carbonate (VC) and gamma butyrolactone (GBL) were respectively added to 100 parts by weight of the electrolyte solution to prepare a nonaqueous electrolyte for lithium batteries.

[Comparative Example 1]

Non-aqueous electrolyte solution was added with 2% by weight of vinyl carbonate (VC) to 1M electrolyte solution in which LiPF ₆ was dissolved as a solute in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a ratio of 3: 7. Was prepared.

In order to measure the electrochemical characteristics of the electrolyte solutions prepared in Examples 1 to 3 and Comparative Example 1, a graphite-based active material was used as a negative electrode, a LiNi 1/3 Co 1/3 Mn 1/3 O 2 active material was used as the positive electrode, and the electrolyte was used. Coin cell type batteries were prepared using the electrolytes prepared according to Examples 1 to 4 or Comparative Example 1.

In order to evaluate the electrochemical characteristics of the manufactured battery, the battery was discharged to 2.5V with a constant current method at a current of 1C, and the charge was charged at 4.5V until the current reached 0.02C after constant current charging to 4.5V at a current of 1C. Was done.

The experimental results are shown in FIG. 2.

Referring to FIG. 2, when the electrolytes of Examples 1 to 4 were used, good life characteristics were compared with those of Comparative Example 1. In addition, Examples 2 and 4 showed better life characteristics than those of Examples 1 and 3.

As a result, the use of 2,5-dihydrofuran (DHF) as a positive electrode film-forming additive in a sulfone solvent having a high oxidation potential can provide excellent charge / discharge cycle characteristics by suppressing decomposition of the electrolyte at high potentials. Able to know.

In addition, Example 4 showed better life characteristics than Example 2, and as a result, when LiTFSI was mixed with the solute, it was found that a more stable film was formed on the cathode or the anode.

In addition, the capacity retention rate according to the number of cycles of the above experimental results is shown in Table 1 below.

cycle characteristic Example 1 Example 2 Example 3 Example 4 Comparative Example 1 1 time Discharge Capacity (mAh / g) 188 186 187 186 194 90 times Discharge Capacity (mAh / g) 148 154 141 160 109 Capacity retention rate (%) 78.7 82.8 75.4 86.0 56.2

As can be seen in Table 1, when 2,5-dihydrofuran (DHF) is used, the capacity is maintained up to 82.8% even after 90 charges, and an electrolyte is prepared using LiPF ₆ and LiTFSI as a solute. When vinyl carbonate (VC) and gamma butyrolactone (GBL) were added, the capacity was maintained to 86%.

This prevents the solvent from decomposing at high potential using tetramethylsulfone and at the same time adds 2,5-dihydrofuran (DHF) to form a film on the anode, thereby preventing electrons from moving from the anode to the electrolyte to decompose the electrolyte. This is the result of preventing the phenomenon.

Claims (8)

A cyclic carbonate, a chain carbonate, and a sulfone are mixed in a volume ratio of 1: 1 to 7: 1 to 5, respectively, and at least one lithium salt selected from LiPF ₆ or LiTFSI as a solute dissolved in the solvent. 0.1 to 5 parts by weight of vinyl carbonate (VC) is added to 100 parts by weight of the electrolyte,
A non-aqueous electrolyte for lithium batteries, comprising adding 0.1 to 5 parts by weight of 2,5-dihydrofuran (DHF) or gamma butyrolactone (GBL) to 100 parts by weight of the electrolyte to form a positive electrode film. delete The method of claim 1,
The sulfone organic solvent is tetramethyl sulfone (TMS), characterized in that the non-aqueous electrolyte for lithium batteries. The method of claim 1,
The carbonate solvent is one or more cyclic carbonate solvents selected from ethylene carbonate, propylene carbonate, pentylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate. Non-aqueous electrolyte for lithium batteries, characterized in that at least one chain carbonate solvent. delete The method of claim 1,
The electrolyte solution is a lithium battery non-aqueous electrolyte, characterized in that LiPF ₆ 0.8 ~ 2M dissolved LiPF ₆ as a solute. The method of claim 1,
The electrolyte is a lithium battery non-aqueous electrolyte, characterized in that LiPF ₆ 1M dissolved LiPF ₆ as a solute. The method of claim 1,
The electrolytic solution is a non-aqueous electrolyte for lithium batteries, characterized in that LiPF ₆ 0.8 ~ 2M and LiTFSI 0.2 ~ 1M dissolved LiPF ₆ and LiTFSI as a solute.

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