KR20140034087A - Electrolyte for lithium sulfur batteries and lithium sulfur batteries using the same - Google Patents

Abstract

The present invention relates to an electrolyte for a lithium sulfur battery and a lithium sulfur battery using the same. The electrolyte for a lithium sulfur battery of the present invention includes lithium polysulfide in the electrolyte, so as to prevent sulfur compounds from eluting from anode materials including sulfur, and to improve the stability of the electrolyte. As a result, the side effect, caused by the reaction between the eluted sulfur compounds and cathode, is prevented, thereby presenting stable lifespan properties. [Reference numerals] (AA) Example 1-1; (BB) Example 1-2; (CC) Example 1-3; (DD) Example 1-4

Description

ELECTROLYTE FOR LITHIUM SULFUR BATTERIES AND LITHIUM SULFUR BATTERIES USING THE SAME

The present invention relates to a lithium sulfur battery electrolyte and a lithium sulfur battery including the same.

With the rapid development of portable electronic devices, the demand for secondary batteries is increasing. In particular, there is a continuous demand for the emergence of high energy density batteries capable of meeting the trend toward smaller, lighter, thinner and smaller portable electronic devices, and batteries that must satisfy inexpensive, safe and environmentally friendly aspects. It is required.

The lithium-sulfur battery uses a sulfur-based compound having a sulfur-sulfur combination as a cathode active material, and a carbon-based material in which an alkali metal such as lithium or metal ions such as lithium ions are inserted and removed. As a secondary battery used as a negative electrode active material, an oxidation-reduction in which a reduction in the number of oxides of S occurs during the reduction reaction (discharge) and an oxidation-reduction in which the number of oxides of S decreases during the oxidation reaction (charge). Reactions are used to store and generate electrical energy.

However, there are no examples of successful commercialization with lithium-sulfur battery systems. The reason why the lithium-sulfur battery is not commercialized is that when sulfur is used as an active material, the utilization rate indicating the amount of sulfur participating in the electrochemical redox reaction in the battery relative to the amount of sulfur injected is low. Because it represents.

In addition, elemental sulfur is generally an insulator that is not electrically conductive, and therefore, an electroconductive material that can provide a smooth electrochemical reaction site must be used in order for an electrochemical reaction to occur.

The positive electrode structure using elemental sulfur so far known has a structure in which sulfur and a conductive carbon powder are independently present in the positive electrode active material layer (mixture) and are simply mixed as described in US Pat. Nos. 5,523,179 and 5,582,623. However, in such a structure, when sulfur becomes polysulfide and is eluted in the liquid phase in the electrolyte during charging and discharging, the electrode structure collapses and adversely affects the capacity and life characteristics of the lithium-sulfur battery.

In lithium secondary batteries, electrons move from the negative electrode to the positive electrode through an electron conduction path during discharge, and lithium ions (Li ⁺ ) move from the negative electrode to the positive electrode through an electrolytic solution or electrolyte. An ideal cell would only move electrons through the wires and only ions through the electrolyte. In the case of a lithium secondary battery, lithium ions must be able to move in the movement of ions by the electrolyte. Lithium salt-containing organic electrolytes and lithium salt-containing polymer electrolytes (including gel and channel forms) have been used as ion conducting media because they can stabilize ions.

However, in the lithium sulfur secondary battery, there is a problem that the existing organic electrolyte and the polymer electrolyte can easily move not only lithium ions but also other ions. That is, there is a problem that the S _x ^{2 -} ion species reach the negative electrode through the organic electrolyte and the polymer-based electrolyte medium.

In order to solve the above problems, a method of delaying the flow of the positive electrode active material by adding an additive having a property of adsorbing sulfur to the positive electrode active material slurry has been studied. As an adsorbent for this purpose, Japanese Patent Application Laid-Open No. 9-147868 (June 6, 1997) used activated carbon fibers, and US Patent No. 5,919,587 had a high porosity, a highly porous, fibrous shape. and a method of embedding a positive electrode active material between transition metal chalcogenides having an ultra-fine sponge like structure or encapsulating the positive electrode active material therewith.

However, these conventional technologies have a problem in that the capacity characteristics and life characteristics of lithium-sulfur batteries are not significantly improved.

Japanese Patent Laid-Open No. 9-147868 U.S. Patent 5,919,587

The present invention is to solve the problems of the prior art as described above, and an object of the present invention is to provide a new lithium sulfur battery electrolyte and a lithium sulfur battery comprising the same.

The present invention provides an electrolyte containing lithium polysulfide represented by the following formula (1) to solve the above problems.

[Formula 1] Li _x S _y (1≤x≤2, 1≤y≤10)

In the present invention, the concentration of the lithium polysulfide in the electrolyte solution is characterized in that 0.01 to 1.0 M.

The electrolyte according to the present invention includes LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ S0 ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ S0 ₂ ) (COCF ₃ ), LiAsF ₆ And it is characterized in that it further comprises a lithium salt selected from the group consisting of a combination thereof.

In the present invention, the concentration of the lithium salt in the electrolyte is characterized in that 0.01 to 2.0 M.

In the present invention, the molar ratio of the lithium salt and the lithium polysulfide in the electrolyte is 10: 1 to 100: 1.

In the present invention, the electrolyte is characterized in that it comprises a non-aqueous solvent. The non-aqueous solvent serves as a medium through which ions involved in the electrochemical reaction of the cell can move.

As the non-aqueous solvent, a carbonate, ester, ether, ketone, alcohol or aprotic solvent may be used. Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC) and the like can be used, and the ester solvent is methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methyl propionate , Ethyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone and the like may be used. As the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, polyethyleneglymedimethyl ether, tetrahydrofuran, etc. may be used, and as the ketone solvent, cyclo Hexanon and the like can be used. In addition, ethyl alcohol, isopropyl alcohol, and the like may be used as the alcohol solvent, and as the aprotic solvent, R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, Nitriles such as bond aromatic rings or ether bonds), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolane and the like. In the present invention, the non-aqueous solvent is preferably selected from the group consisting of 1,3-dioxolane, sulfolane, and tetraethylene glycol dimethyl ether, wherein the non-aqueous organic solvent is used alone or in combination of one or more. The mixing ratio when used in combination with one or more can be appropriately adjusted according to the desired battery performance, which can be widely understood by those skilled in the art.

In the present invention, the electrolyte including the lithium polysulfide may be a polymer electrolyte.

In the present invention, the polymer electrolyte is characterized in that the filler and Li ₂ S is dispersed in a composite of a polymer and a lithium salt.

The polymers are polyethylene oxide (PEO), polypropylene oxide (PPO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polymethacrylate (PMA), polymethyl methacrylate (PMMA) and It may be selected from the group consisting of a combination of these.

In the present invention, the lithium salt dispersed in the polymer electrolyte may be selected from the group consisting of LiCF ₃ SO ₃ , LiPF ₆ , LiClO ₄ , LiBOB, LiTFSI and combinations thereof.

In the present invention, the filler may be selected from the group consisting of ZrO ₂ , Al ₂ O ₃ , SiO ₂ and combinations thereof, and the average size of the filler may be 10 nm to 20 nm.

In the present invention, the Li ₂ S is contained in a ratio of 1 to 10 parts by weight based on 100 parts by weight of the polymer.

The present invention also relates to

(1) mixing a lithium salt, a polymer, a filler, and Li ₂ S;

(2) hot pressing the mixture to form a polymer matrix; And

(3) immersing the polymer matrix in a solvent including a lithium salt and lithium polysulfide represented by the following Chemical Formula 1;

[Formula 1] Li _x S _y (1≤x≤2, 1≤y≤10)

In the method for producing a polymer electrolyte according to the present invention, the step of hot pressing the mixture to form a polymer matrix

First pressing at 80 ° C. to 90 ° C. for 15 minutes to 20 minutes at a pressure of 0.2 to 1 ton; And

It may include; the second press for 60 minutes to 90 minutes at a pressure of 4 to 5 tons at 80 ℃ to 90 ℃.

In the method for producing a polymer electrolyte according to the present invention, the step of immersing the polymer matrix in a solvent including lithium salt and lithium polysulfide is characterized in that it is carried out for 2 hours or more.

Gel-like polymer electrolyte prepared according to the production process according to the present invention has the advantage that can be operated at a wide range of temperatures without the risk of evaporation of the liquid component.

The present invention also relates to

An anode comprising an electrically active sulfur-containing material;

A negative electrode comprising lithium; And

An electrochemical device comprising an electrolyte containing lithium polysulfide according to the present invention is provided.

In the present invention, the electrochemical device is a lithium sulfur battery.

In the electrochemical cell of the present invention, the positive electrode and the negative electrode are materials that occlude and release lithium, and those generally used in conventional nonaqueous electrolyte secondary batteries may be used, and carbon materials such as lithium metal, lithium alloy, and graphite may be used. Although it can be used, in order to obtain an electrochemical cell having a high energy density, it is preferable to use silicon alloyed with lithium of Korean Application No. 10-2011-0028246 or carbon sulfur composite of Korean Application No. 10-2012-0047023.

The electrolyte according to the present invention includes lithium polysulfide, wherein the lithium polysulfide inhibits the elution of the sulfur compound from the positive electrode material containing sulfur in a lithium sulfur battery, and acts as an active material on the surface of the positive electrode material, and the eluted sulfur compound By suppressing side reactions between the negative electrode and the negative electrode, the lithium sulfur battery including the lithium sulfur battery electrolyte according to the present invention exhibits stable life characteristics and high efficiency.

Figure 1 shows a TEM picture of the hollow carbon ball and hollow carbon sulfur composite obtained in one embodiment of the present invention.
Figure 2 shows the results of measuring the TGA for the hollow carbon sulfur composite obtained in one embodiment of the present invention.
Figure 3 shows the results of measuring the charge and discharge characteristics for the battery made in one embodiment of the present invention.

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited by the following examples.

< Example  1> Lithium polysulfide  Added TEGDME  Preparation of electrolytic solution

Sulfur was dried in a vacuum oven at 60 ° C. for 72 hours, and a lithium piece of 2 mm × 2 mm × 0.1 mm was prepared, and then the lithium piece and the dried sulfur were transferred to a nonaqueous solvent, TEGDME, as shown in Table 1 below. After dissolving, 1 M LiCF ₃ SO ₃ was added to the solution to prepare an electrolyte as shown in Table 1 below.

Lithium polysulfide Concentration of Lithium Polysulfide (M) Example 1-1 Li ₂ S ₈ 0.05 Examples 1-2 Li ₂ S ₈ 0.025 Example 1-3 Li ₂ S ₆ 0.05 Examples 1-4 Li ₂ S ₄ 0.05

< Example  2> Lithium polysulfide  Added Sulfolane ( sulfolane ) Preparation of Electrolyte

Using sulfolane as a non-aqueous solvent and LiCF ₃ SO ₃ as lithium salt Instead of using a concentration of 1M LiTFSI was prepared, the electrolyte solution shown in Table 2 below in the same manner as in Example 1.

Lithium polysulfide Concentration of Lithium Polysulfide (M) Example 2-1 Li ₂ S ₈ 0.01 Example 2-2 Li ₂ S ₈ 0.025 Example 2-3 Li ₂ S ₈ 0.05

< Example  3> Preparation of Polymer Electrolyte

LiCF ₃ SO ₃ , polyethylene oxide, ZrO ₂ And Li ₂ S was hot-pressed to prepare a polymer matrix.

The hot-pressing process was carried out by the first press for 20 minutes at a pressure of 1 ton at 90 ° C, and then the second press for 60 minutes at a pressure of 5 tons at 90 ° C.

The prepared polymer matrix was 0.05 M lithium polysulfide (Li ₂ S ₈ ) and 1M LiCF ₃ SO ₃ It was immersed in the added TEGDME solution for 2 hours or more to complete the polymer electrolyte.

< Example  4> Preparation of Hollow Carbon Sulfur Composite

The hollow carbon sulfur composite was prepared by preparing hollow carbon balls according to the method described in 10-2012-0047023 filed by the inventor on May 3, 2012, and carrying sulfur thereon. First, 100 g of water and 1 g of 3-mercaptopropyltrimethoxysilane were added to a 250 ml beaker and stirred at room temperature for 1 hour, and then 0.1 ml of NH ₄ OH was slowly added to the reactor. It was stirred for 5 hours at the same temperature. After completion of the reaction, the product obtained was dispersed in 50 ml of water, and then sucrose was added, stirred, and transferred to a Teflon vessel, and reacted at 170 ° C. for 5 hours in a hydrothermal reactor. The product was filtered, washed three times with water and ethanol, dried and heat-treated at 1000 ° C. in an Ar atmosphere to prepare silica-carbon balls.

The silica-carbon ball was stirred in an aqueous HF solution for 24 hours, the silica was etched away, and dried at 100 ° C. for 12 hours to prepare a hollow carbon ball.

The hollow carbon ball and sulfur were mixed in a 1: 5 mass ratio, placed in a Y-shaped glass tube, and heat-treated at 600 ° C. for 4 hours in a vacuum state to complete a sulfur sulfur-supported carbon sulfur composite.

< Experimental Example  1> Scanning electron microscope analysis

TEM images of the hollow carbon ball and the hollow carbon sulfur composite obtained in Example 4 are shown in FIGS. 1A and 1B.

As shown in FIG. 1B, it can be seen that the hollow carbon sulfur composite in which sulfur was supported into the hollow carbon ball was produced.

<Experimental Example 2> thermogravimetric analysis (Thermogravimetric Analysis) Analysis

The TGA of the hollow carbon sulfur composite prepared in Example 4 was measured to determine the temperature of the sulfur content and the weight change reduction point included in the hollow carbon sulfur composite. ℃ 10 min under nitrogen ^conditions the temperature was raised at a rate of ¹ was measured TGA, TGA these measurement results the graph is shown in Fig. As shown in FIG. 2, sulfur is supported up to the inside of the hollow carbon sulfur composite, and it can be seen that the entire carbon sulfur composite supports 40 wt% to 50 wt% sulfur.

< Example  5> Fabrication of electrodes and batteries

A hollow carbon sulfur composite prepared in Example 4, a carbon black conductive material, and a polyethylene oxide binder were mixed in an acetonitrile solvent at a ratio of 60:20:20 to prepare a slurry. The slurry was coated on aluminum foil with a thickness of 40 μm, roll-pressed, and dried at 50 ° C. to remove residual solvent, thereby preparing a positive electrode plate.

Lithium-sulfur batteries were prepared by using lithium foil as the positive electrode and the negative electrode, and using the electrolytes prepared in Examples 1 to 3 as the electrolyte.

< Comparative Example  1>

As Comparative Example 1, LiCF ₃ SO ₃ without polysulfide A battery was prepared in the same manner as in Example 5 using the added TEGDME electrolyte solution.

< Comparative Example  2>

As Comparative Example 2, a battery was prepared in the same manner as in Example 5, using a sulfolane electrolyte solution containing only LiTFSI without polysulfide.

< Comparative Example  3>

As Comparative Example 3, LiCF ₃ SO ₃ without polysulfide The battery was prepared in the same manner as in Example 5 using the polymer electrolyte immersed in the TEGDME solution added only.

< Experimental Example  3> Battery life evaluation

The lifespan characteristics of the batteries including the electrolytes of Examples 1 to 3 and Comparative Examples 1 to 3 prepared in Example 5 were evaluated, and the results are shown in Table 3 below.

As shown in Table 3 below, in the case of a battery using a TEGDME electrolyte (Example 1-1) to which 0.05 M Li ₂ S ₈ was added, Li ₂ S ₈ It can be seen that after 80 cycles compared to Comparative Example 1 without the addition of 20% life characteristics are improved.

As shown in Table 3, the capacity retention and the efficiency after 80 cycles were also improved in Example 2 including the addition of polysulfide and the sulfolane solvent as the organic solvent and the polymer electrolyte immersed in the TEGDME solution containing lithium polysulfide. Compared with Comparative Example 2 and Comparative Example 3, respectively, it can be confirmed that the present invention improves the life characteristics and efficiency of the battery using the electrolyte containing polysulfide.

Capacity retention after 80 cycles efficiency
(Ratio of discharge capacity to 80th cycle charge capacity) Example 1-1 68.4% 82.7% Examples 1-2 62.4% 81.9% Example 1-3 58.3% 80.8% Examples 1-4 60.5% 80.9% Example 2-1 61.2% 91.2% Example 2-2 65.3% 93.1% Example 2-3 69.4% 95.9% Example 3 73.1% 94.2% Comparative Example 1 50.4% 60.9% Comparative Example 2 28.4% 87.6% Comparative Example 3 33.5% 73.2%

The lifetime characteristics according to the type and concentration of the lithium polysulfide added through the battery prepared using the electrolytes of Examples 1-1 to 1-4 and the battery of Comparative Example 1 were measured and the results are shown in FIG. 3.

Li ₂ S ₈ in FIG. 3 It can be seen that Example 1-1 to which lithium polysulfide of the form is added has better life characteristics than Example 1-3 to which Li ₂ S ₆ is added and Example 1-4 to which Li ₂ S ₄ is added.

In addition, the service life characteristics were evaluated better than Example 1-2 in which Example 1-1 having a concentration of lithium polysulfide of 0.05 M was 0.025 M.

Claims (20)

An electrolyte containing lithium polysulfide represented by the following formula (1).
[Formula 1] Li _x S _y (1≤x≤2, 1≤y≤10)
The method of claim 1,
The electrolyte is characterized in that the concentration of the lithium polysulfide in the electrolyte is 0.01 to 1.0 M.
The method of claim 1,
The electrolyte includes LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ S0 ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ S0 ₂ ) (COCF ₃ ), LiAsF ₆ And a lithium salt selected from the group consisting of a combination thereof.
The method of claim 3, wherein
The electrolyte of the lithium salt concentration of 0.01 to 2.0 M in the electrolyte.
The method of claim 3, wherein
An electrolyte having a concentration ratio of the lithium salt and the lithium polysulfide in the electrolyte is 10: 1 to 100: 1.
The method of claim 1,
The electrolyte is characterized in that it comprises a non-aqueous solvent.
The method according to claim 6,
The non-aqueous solvent is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC ), Propylene carbonate (PC), butylene carbonate (BC), methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, Decanolide, valerolactone, mevalonolactone, caprolactone, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, polyethylene glyme Dimethyl ether, tetrahydrofuran, cyclohexanone, R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or ether bond) Nitrile dimethylformamide, 1,3-dioxolane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, dioxolane, sulfolane (sulfolane) and an electrolyte, characterized in that selected from the group consisting of a combination thereof.
The method according to claim 6,
The non-aqueous solvent is at least one selected from the group consisting of 1,3-dioxolane, sulfolane and tetraethylene glycol dimethyl ether.
The method of claim 1,
The electrolyte is a polymer electrolyte, characterized in that the polymer electrolyte.
The method of claim 9,
The polymer electrolyte is a polymer electrolyte, characterized in that the filler and Li ₂ S is dispersed in a complex of a polymer and a lithium salt.
11. The method of claim 10,
The polymers are polyethylene oxide (PEO), polypropylene oxide (PPO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polymethacrylate (PMA), polymethyl methacrylate (PMMA) and A polymer electrolyte selected from the group consisting of a combination of these.
11. The method of claim 10,
The lithium salt dispersed in the polymer electrolyte is selected from the group consisting of LiCF ₃ SO ₃ , LiPF ₆ , LiClO ₄ , LiBOB, LiTFSI and combinations thereof.
11. The method of claim 10,
The filler is selected from the group consisting of ZrO ₂ , Al ₂ O ₃ , SiO ₂ and combinations thereof.
11. The method of claim 10,
The average size of the filler is 10 nm to 20 nm polymer electrolyte.
11. The method of claim 10,
The polymer electrolyte of Li ₂ S is included in the ratio of 1 to 10 parts by weight based on 100 parts by weight of the polymer.
(1) mixing a lithium salt, a polymer, a filler, and Li ₂ S;
(2) hot pressing the mixture to form a polymer matrix; And
(3) immersing the polymer matrix in a solvent containing a lithium salt and a lithium polysulfide represented by the following Chemical Formula 1;
[Formula 1] Li _x S _y (1≤x≤2, 1≤y≤10)
17. The method of claim 16,
Hot pressing the mixture to form a polymer matrix
First pressing at 80 ° C. to 90 ° C. for 15 minutes to 20 minutes at a pressure of 0.2 to 1 ton; And
A method for producing a polymer electrolyte comprising the step of secondary pressing at 80 ℃ to 90 ℃ at a pressure of 4 to 5 tons for 60 minutes to 90 minutes.
17. The method of claim 16,
The immersion process of step (3) is a method for producing a polymer electrolyte that is carried out for 2 hours or more.
An anode comprising an electrically active sulfur-containing material;
A negative electrode comprising lithium; And
An electrochemical device comprising the electrolyte of claim 1.
The method of claim 19,
The electrochemical device is an electrochemical device that is a lithium sulfur battery.

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