KR20030086664A - Fabrication of a polymer electrolyte for lithium/sulfur battery and room temperature lithium/sulfur battery containing the same with one flat voltage - Google Patents

Abstract

PURPOSE: Provided is a method for preparing a polymer electrolyte for a lithium sulfur battery, which has one flat voltage ranged from 2.1V to 3.0V and discharge capacity of 800 mAh/g(sulfur) or more and excellent ion conductivity. CONSTITUTION: The method for preparing a cold polymer electrolyte is characterized by comprising the steps of: dissolving at least one binder selected from the group consisting of a polyurethane, a polyvinylidene hexafluoropropylene copolymer, a polyvinylidene fluoride, a polyvinyl chloride, a polyacrylonitrile, a polymethylmethacrylate, a polyethylene oxide and a polypropylene oxide, at least one plasticizer selected from the group consisting of tetraethyleneglycol dimethyl ether, ethylene carbonate, propylene carbonate and a mixture thereof, and a lithium salt; and forming the polymer electrolyte into gels by glass casting. Alternatively, the method comprises the steps of: preparing the binders in the form of a porous polymeric film; impregnating the porous polymeric film with the solution containing the plasticizer and a lithium salt; and forming an ion-conductive microporous polymer electrolyte by glass casting.

Description

A method of preparing a polymer electrolyte for a lithium sulfur battery and a room temperature type lithium polymer sulfur battery having a flat voltage including the polymer electrolyte prepared therefrom same with one flat voltage}

The present invention relates to a method for producing a polyelectrolyte for a lithium polymer battery having one flat voltage and to a lithium polymer sulfur battery composed of the room temperature type polymer electrolyte. More specifically, the present invention relates to a method for producing a polymer electrolyte that can facilitate the preparation of an electrolyte, and to improve ion conductivity and battery capacity, and a lithium polymer sulfur battery composed of the polymer electrolyte.

As the miniaturization of electronic products and communication devices is rapidly progressing worldwide, and the necessity of electric vehicles is increasing, the development of secondary batteries used as mobile power sources for these products is actively progressing. There is a great demand. Accordingly, studies on batteries having a large discharge capacity or energy density, which are important factors of secondary battery performance, are being conducted.

As for the electrode, which is a factor that determines the performance of the secondary battery, the electrode material first needs to have a high energy density or discharge capacity per unit mass, and has excellent thermal and chemical stability within a certain temperature range, as well as excellent oxidation / reversibility. It must have a sufficient electrochemical electrical and ionic conductivity. In addition, the electrode material should be non-toxic, inexpensive and readily available. Among them, the most important thing for the performance of the battery is to develop an electrode having a large discharge capacity per unit weight (Ah / kg) in order to develop a secondary battery having excellent performance as an electrode discharge capacity, that is, an energy density.

However, in the case of lead batteries, nickel / cadmium batteries, and nickel hybrid batteries, which are generally used in electric vehicles, there are advantages in that they can be charged and discharged many times without deteriorating performance, but have a relatively low energy density per unit mass. There are disadvantages. In the case of nickel / hydrogen (Ni / MH) batteries, which are generally used secondary batteries, magnesium-type nickel batteries exhibit the highest electrode capacity, which is about 500 mAh / g, and in the case of lithium (Li) batteries, V ₂ O ₅ represents the largest electrode discharge capacity, about 400 mAh / g.

However, sulfur (S) is a very promising material as an electrode material because its atomic weight is relatively small, non-toxic and very low in price. In particular, lithium / sulfur (Li / S) battery pairs have a theoretical energy density of about 2800 Wh / kg (about 1675 mAh / g), which is significantly higher than other battery systems. Therefore, many researchers have attempted to construct lithium secondary batteries using sulfur.

Rauh et al., J. Electrochem. Soc. Used a carbon electrode as a positive electrode and dissolved sulfur in an organic electrolyte to form a battery.Feed and Yamin made a battery by converting an organic solvent at J. Power Sources in 1981. It was. However, a high discharge capacity could not be obtained due to the reaction of the organic solvent with sulfur.

In order to solve the problem of such an organic solvent, a study using a solid polymer electrolyte has been conducted.

In US Pat. No. 5,686,201, Chu et al. Prepared a positive electrode of a lithium battery using 50 wt% sulfur, 16 wt% carbon, and 34 wt% (PEO) 49 LiTFSi to produce up to 1500 mAh / g sulfur at 90 ° C. Energy density of 750 mAh / g anode).

Cainns et al., 430 mAh / g at 23 ° C. using 75% sulfur, 7.5% carbon, 15% PEGDME / LiTFSi (30: 1) and 2.5% PEO by J. Power Sourecs in 2000. A positive electrode (570 mAh / g sulfur) was obtained.

On the other hand, polymers are generally known as insulators that do not transfer electrons or ions. However, by adding additives such as salts and solvents into the polymer system, ion conduction of the polymer is realized. There are several types of polymer media that conduct ions. Polyelectrolyte based on polyethylene oxide (PEO) was proposed in 1978 by Armand et al. Polyether-based polymers such as polyethylene oxide and polypropylene oxide have ion conductivity by dissociating lithium salts due to proper spacing of oxygen atoms and movement of flexible main chains. The ionic polymer dissolved in the medium is called the polymer electrolyte, and the ionic polymer is in the intermediate position of the polymer connected by the coordination bond with the ionic salt. The polymer electrolyte has an advantage that one ion is fixed to the polymer, so that the transport number of the other is almost 1, and thus there is no polarization of ions. However, the polymer electrolyte has low stability at a wide potential. This is limited. The polymer gel electrolyte has a property in the intermediate stage between the liquid electrolyte in which the salt is doped in the liquid and the polymer electrolyte without the solvent, and shows excellent lithium ion conductivity of 1 S / cm ² or more at room temperature. It has both high power and flexible mechanical properties of polymers.

The polymer gel electrolyte has a disadvantage in that the organic solvent slowly leaks out or evaporates because the gel is in a thermodynamically unstable phase. In particular, the disadvantage is that the conductivity decreases due to the loss of the liquid electrolyte due to the synergy of heat and aging.

Therefore, recently, studies have been conducted to add a plasticizer having high ion conductivity to the polymer electrolyte as a method for improving the ionic conductivity of the solid polymer electrolyte.

Thus, the present inventors manufacture a gel electrolyte or a microporous electrolyte by using a plasticizer in a polymer electrolyte, and apply the same to a lithium sulfur battery, thereby allowing a lithium sulfur battery having one flat voltage of 2.1 V to 3.0 V at room temperature. It was developed to lead to the present invention.

An object of the present invention is to provide a method for producing a polymer electrolyte for a lithium sulfur battery having one flat voltage of 2.1 V to 3.0 V during discharge and having a discharge capacity of 800 mAh / g · sulfur or more.

Another object of the present invention is to provide a method for producing a gel-type or microporous polymer electrolyte suitable for lithium sulfur batteries and having high ionic conductivity even at room temperature.

Still another object of the present invention is to provide a polymer electrolyte having excellent ion conductivity and discharge capacity by adjusting the constituents and current density of the plasticizer.

Still another object of the present invention is to provide an electrolyte suitable for sulfur positive electrode, and to be applied to various battery systems using the same.

1 is a graph showing a discharge curve when a lithium polymer sulfur battery is discharged with a gel type PVdF polymer electrolyte according to the present invention.

2 is a graph showing a discharge curve when the lithium polymer sulfur battery is discharged with the gel PMMA polymer electrolyte according to the present invention.

3 is a graph showing a discharge curve when the ratio of the liquid electrolyte TG and EC is 3: 1 in the microporous PVdF polymer electrolyte according to the present invention and discharged with 100mAh / g-sulfur.

The above objects of the present invention may all be achieved by the present invention described below.

The gel polymer electrolyte of the present invention is a binder selected from polyurethane, polyvinylidene hexafluoropropylene copolymer, polyvinylidene fluoride, polyvinylchloride, polyacrylonitrile, polymethyl methacrylate, polyethylene oxide or polypropylene oxide And a glass casting method by dissolving at least one plasticizer selected from the group consisting of tetraethylene glycol dimethyl ether (TG), ethylene carbonate (EC), propylene carbonate (PC) and mixtures thereof in a solvent together with a lithium salt. It is characterized in that the manufacturing using.

In addition, the microporous polymer electrolyte of the present invention is a polyurethane, polyvinylidene hexafluoropropylene copolymer, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, polyethylene oxide or polypropylene A binder selected from oxides is prepared in advance by a porous polymer film, and impregnated into a liquid electrolyte composed of a plasticizer of tetraethylene glycol dimethyl ether, ethylene carbonate, propylene carbonate, and a lithium salt, followed by a glass casting method.

The present invention also provides a lithium sulfur battery comprising a room temperature type polymer electrolyte prepared by the above method, having a flat voltage of 2.1V to 3.0V at room temperature, and having a discharge capacity of 800 mAh / g or more.

According to the present invention, the gel polymer electrolyte is polyurethane (PU), polyvinylidene fluoride-co-hexafluoro propylene (PVdF-co-HFP), polyvinylidene fluoride (polyvinylidene fluoride) : PVdF), polyvinylchloride (PVC), polyacrylonitrile (PAN), polymethlymethacrylate (PMMA), polyethyleneoxide (PEO) or polypropyleneoxide (polypropyleneoxide: PPO) And a plasticizer selected from the group consisting of tetraethyleneglycoldimethylether (TG), ethylene carbonate (EC), propylene carbonate (PC) and mixtures thereof in a solvent together with a lithium salt. Melt is prepared in the form of a film using a glass casting method. In the preparation of the gel electrolyte, an appropriate amount of plasticizer is required because the film form of the electrolyte has similar values to the gel and liquid electrolyte depending on the amount of plasticizer added. It is also possible to add oxides to increase the mechanical strength.

In addition, the microporous polymer electrolyte according to the present invention is prepared by preparing a binder polymer in the gel form in advance into a porous polymer film and impregnating it in a liquid electrolyte composed of the plasticizer and a lithium salt. Unlike the gel type, the amount of plasticizer is small, but when preparing a porous polymer, the pore size and distribution should be appropriate.

The electrolyte according to the present invention has an ion conductivity similar to that of a conventional polymer electrolyte, and in the case of a lithium battery having such an electrolyte, there is one flat voltage region between 2.1 V and 2.8 V at room temperature, and the discharge capacity is 800 mAh / g. It has a high discharge capacity that is above.

The polymer electrolyte according to the present invention can impart mechanical strength by the above-mentioned binder, and the plasticizer is preferably a mixture of TG: EC = 3: 1 or EC: PC = 1: 1 in volume ratio.

In addition, the lithium salt is used to increase the ionic conductivity of the solid polymer electrolyte, and lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium hexafluor phosphate (LiPF ₆ ), lithium tetrafluoro borate (LiBF ₄ ), Lithium perchlorate (LiClO ₄ ), lithium trifluoromethanesulfonateimide (LiTFSI), and the like, of which lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) is particularly preferred.

As the solvent for dissolving the polymer in the present invention, acetonitrile, acetone, tetrahydrofuran (THF) and the like are preferable.

The polymer, the plasticizer, and the lithium salt can be mixed homogeneously by a stirrer, a mixer, a ball mill, an ultrasonic wave, an etitor, or the like.

The polymer electrolyte may further include an inorganic filler as necessary. The type and content of the inorganic filler to be used can be easily determined by those skilled in the art.

A lithium polymer battery consists of a positive electrode, a negative electrode and a system according to the present invention. The positive electrode and the negative electrode can be easily manufactured by those skilled in the art to which the present invention belongs. The preferred negative electrode of the present invention may be composed of a lithium metal, a lithium alloy, etc., and as the positive electrode, sulfur, carbon, polymer, lithium salt, etc. are put in a solvent with a sulfur electrode, stirred, coated on a glass plate, and dried to form a film. Manufactured in the shape.

The invention can be better understood by the following examples, which are intended to illustrate the invention and are not intended to limit the scope of protection defined by the appended claims.

Example 1 Preparation of Gel-Type PVdF Electrolyte

PVdF-co-HFP (5.4% by weight) and THF (82% by weight) were placed in an Erlenmeyer flask and heated to 60 ° C to completely dissolve PVdF. TG (8.7 wt.%), EC (2.9 wt.%), Lithium salt (LiCF ₃ SO ₃ ) (1 wt.%), And THF were mixed, and when EC and lithium salt were completely dissolved, poured into a Erlenmeyer flask with PVdF dissolved and stirred. .

After stirring for 12 hours, the glass-cast polymer electrolyte was dried at room temperature for 48 hours and vacuum for 3 hours. All these processes were performed in the glove box of argon atmosphere.

Example 2 Preparation of Gel-Type PMMA Electrolyte

PMMA (7% by weight), PVC (3% by weight), EC (15% by weight), PC (15% by weight) and THF (60% by weight) were placed in an etitor and ball milled for 10 minutes. At this time, the weight ratio of the ball: powder was 6: 1, and a stainless steel ball having a diameter of 0.53 cm was used. The glass-cast polymer electrolyte was dried at room temperature for 24 hours and in vacuum for 10 hours. All these processes were made in a glove box in an argon atmosphere.

Example 3 Preparation of Microporous PVdF Electrolyte

2 g of PVdF-co-HFP copolymer and non-solvent dibutyl phthalate (DBP) were added to 10 g of acetone solvent, and 400 wt% (8 g or 7.6 ml) of the polymer was dissolved in a solution at 50 ° C. until uniform for 3 hours. Films were prepared by the method of glass casting.

The acetone remaining after the volatilization of the acetone solvent at room temperature was completely removed by drying in an oven at 50 ℃. The film having a thickness of 150 to 300 mu m was washed several times with an extraction solution (ethyl ether, methanol) to remove remaining nonsolvent. The above method was carried out in a general atmosphere.

In order to prevent shrinkage of the polymer film, it was pressed on glass and vacuum dried at 60 ° C.

In addition, the microporous PVdF polymer electrolyte was prepared by immersing the liquid electrolyte prepared by adding 37.5 ml of TG and 12.5 ml of EC to 5.2 g of LiCF ₃ SO ₃ for about 12 hours.

Example 4 Fabrication of Lithium Sulfur Battery Using Gel PVdF Electrolyte

Lithium metal was used as an electrode as an anode, and sulfur was used as an electrode as an anode.

The sulfur electrode was prepared by titrating the sample as 40 wt% sulfur, 30 wt% carbon, 15 wt% polyethylene oxide, and 5 wt% lithium trifluoromethanesulfonate, and putting the solvent in a mixer using acetonitrile for about 48 wt%. After mixing and dissolving for a period of time, it was poured into a glass tube and dried, followed by vacuum drying at 10-3 Torr for 60 hours for 24 hours to prepare a sulfur electrode on the film.

The methods were carried out in normal atmosphere.

A lithium / solid polymer electrolyte / sulfur battery was formed by stacking in the order of the negative electrode, the electrolyte, and the positive electrode in an atmosphere of argon gas. Here, the gel-type PVdF polymer electrolyte prepared in Example 1 was used as the electrolyte, and the cathode was a lithium electrode, and the anode was a sulfur electrode prepared above.

In order to determine the discharge characteristics of the lithium sulfur battery, the discharge capacity was measured using a discharge tester.

The electrode test conditions were to maintain a rest time for 1 hour at room temperature, the discharge current density was 100 mAh / g-sulfur, the termination voltage was 1.8V.

1 is a graph showing a discharge curve when the lithium sulfur battery is discharged with the gel-type PVdF polymer electrolyte according to the present invention. The flat voltage was 2.4V and the discharge capacity was about 654 mAh / g. .

Example 5 Fabrication of Lithium Sulfur Battery Using Gel PMMA Electrolyte

A lithium sulfur battery was manufactured in the same manner as in Example 4, except that the gel PMMA polymer electrolyte prepared in Example 2 was used instead of the gel PVdF polymer electrolyte in Example 4.

In order to determine the discharge characteristics of the lithium sulfur battery, the discharge capacity was measured using a discharge tester.

The electrode test conditions were to maintain the rest time for 1 hour at room temperature, the discharge current density was 100 mAh / g-sulfur, the final voltage was 1.8V.

2 is a graph showing a discharge curve when the lithium sulfur battery is discharged with the gel-type PMMA polymer electrolyte according to the present invention. The flat voltage is 2.5V and the discharge capacity is about 986 mAh / g. .

Example 6 Fabrication of Lithium Sulfur Battery Using Microporous PVdF Electrolyte

A lithium sulfur battery was manufactured in the same manner as in Example 4, except that the microporous PVdF polymer electrolyte prepared in Example 3 was used instead of the gel PVdF polymer electrolyte in Example 4.

In order to determine the discharge characteristics of the lithium sulfur battery, the discharge capacity was measured using a discharge tester.

The electrode test conditions were to maintain the rest time for 1 hour at room temperature, the discharge current density was 100 mAh / g-sulfur, the final voltage was 1.8V.

Figure 3 shows the results of the discharge experiment, the ratio of the liquid electrolyte TG and EC in the microporous PVdF polymer electrolyte according to the present invention is 3: 1, showing a discharge curve when discharged at 100 mAh / g-sulfur As a graph, the flat voltage was 2.6 V and the discharge capacity was about 800 mAh / g.

The present invention can produce a gel-type or microporous polymer electrolyte suitable for lithium sulfur batteries and having high ion conductivity even at room temperature, and prepare a polymer electrolyte having excellent ion conductivity and discharge capacity by controlling the components and current density of the plasticizer. You can do it.

The lithium sulfur battery according to the present invention has an effect of having a flat voltage of 2.1 V to 3.0 V and a discharge capacity of 800 mAh / g sulfur or more by using the solid polymer electrolyte prepared by the above method.

Claims (6)

A binder selected from polyurethane, polyvinylidene hexafluoropropylene copolymer, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, polyethylene oxide or polypropylene oxide, and tetraethylene glycol dimethyl ether And ethylene carbonate, propylene carbonate, and at least one plasticizer selected from the group consisting of a mixture thereof. A binder selected from polyurethane, polyvinylidene hexafluoropropylene copolymer, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, polyethylene oxide or polypropylene oxide is prepared in advance into a porous polymer film. And impregnated into a liquid electrolyte composed of a plasticizer of tetraethylene glycol dimethyl ether, ethylene carbonate, and propylene carbonate and a lithium salt, and then prepared in a microporous manner using a glass casting method. Manufacturing method. The method for producing a polymer electrolyte according to claim 1 or 2, wherein the solvent for dissolving the polymer is selected from acetonitrile, acetone or tetrahydrofuran. The method of claim 1 or 2, wherein the plasticizer is prepared by using a mixture of TG: EC = 3: 1 or EC: PC = 1: 1 by volume. The method according to claim 1 or 2, wherein the lithium salt is selected from LiCF ₃ SO ₃ , LiClO ₄ , LiBF ₄ , LiPF ₆ , or LiTFSI. A lithium sulfur battery comprising a polymer electrolyte prepared by the method according to claim 1, having a flat voltage of 2.1 V to 3.0 V and a discharge capacity of 800 mAh / g or more.