KR101891876B1 - Separator of lithium-sulfur battery containing conductive polymer swollen by plasticizer, lithium-sulfur battery comprising the same, and manufacturing method for the same - Google Patents

Abstract

A lithium-sulfur battery separator, wherein the separator comprises a conductive polymer having an anionic functional group; And a plasticizer impregnated in the conductive polymer, wherein the conductive polymer is swollen by the plasticizer.

Description

TECHNICAL FIELD [0001] The present invention relates to a lithium-sulfur battery separator comprising a conductive polymer swollen with a plasticizer, a lithium-sulfur battery including the conductive polymer swollen with plasticizer, and a lithium-sulfur battery including the conductive polymer swollen by plasticizer. method for the same}

The present invention relates to a lithium-sulfur battery separator comprising a conductive polymer swollen with a plasticizer, a lithium-sulfur battery including the same, and a method of manufacturing the same.

Lithium-sulfur secondary batteries are one of the next-generation secondary batteries that can replace lithium-ion batteries because of their high energy density and low active material prices. In addition, lithium-sulfur batteries are increasingly being commercialized in the aviation industry by using high energy density characteristics. However, the lithium-sulfur battery has problems that the polysulfide, which is a positive electrode active material, is eluted into the electrolyte to reduce capacity and shuttle phenomenon. Recently, Nafion polymer was directly coated on the anode surface to solve the polysulfide leaching problem, but the capacity decrease and polysulfide shuttle phenomenon were still observed.

For example, in the prior art ("a positive electrode having a polymer film and a lithium-sulfur battery ", 10-2005-0022616), a polymer is coated on a surface of a positive electrode to dissolve polysulfide to alleviate access to a negative electrode . However, there is a disadvantage in that the technique of coating the anode with a polymer having no ion conductivity does not secure the ion conductivity, and therefore it takes a lot of resistance even if the polysulfide ion elution is suppressed. Therefore, a technique that has the advantage of securing the conductivity of lithium ion and suppressing dissolution of polysulfide ions by lowering the solubility of polysulfide ion thermodynamically has not yet been disclosed.

The object of the present invention is to provide a technique capable of reducing polysulfide ion elution and shuttle phenomenon by controlling the polysulfide distribution.

In order to solve the above problems, the present invention provides a lithium-sulfur battery separator, wherein the separator comprises a conductive polymer having an anionic functional group; And a plasticizer impregnated in the conductive polymer, wherein the conductive polymer is swollen by the plasticizer.

In one embodiment of the present invention, the anion functional group forms a stolen potential to exclude the polysulfide ion as an active material of the positive electrode.

In one embodiment of the present invention, the anionic functional group is at least one selected from the group consisting of sulfonic acid (-SO3-) group, phosphoric acid (-PO4-) group and carboxylate (-COO-) group.

In one embodiment of the present invention, the conductive polymer is a polymer represented by the following formula (1).

(화학식 1)

(Formula 1)

(Wherein x and z represent an integer of 1 to 10, y represents an integer of less than 1000, and A represents any one element selected from H, Li, Na and K.)

In one embodiment of the present invention, the conductive polymer is a polymer represented by the following formula (2).

(화학식 2)

(2)

(Wherein x and y each represent an arbitrary number satisfying 0 <x, y? 1, and B represents any one element selected from the group consisting of H, Li, Na and K)

In one embodiment of the present invention, the separation membrane has a film shape of 1 to 50 μm thick.

In one embodiment of the present invention, the plasticizer is a non-aqueous electrolyte containing no salt, and the nonaqueous electrolyte is selected from the group consisting of N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate , Gamma -butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, tetraglyme, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethyl But are not limited to, formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, At least one selected from the group consisting of propylene carbonate derivatives, tetrahydrofuran derivatives, DEGDME, ether, methyl pyrophosphate, and ethyl propionate.

The present invention provides a lithium-sulfur battery including the above-described lithium-sulfur battery separator.

In one embodiment of the present invention, the lithium-sulfur battery includes a positive electrode; The above-described separation membrane; And a cathode, and the binder of the anode is of the same kind as the conductive polymer of the separator.

The present invention also provides a lithium-sulfur battery system having a bipolar stack structure in which the above-described lithium-sulfur battery is stacked in a unit stack.

In an embodiment of the present invention, there is no additional diaphragm structure between the unit stack and the unit stack.

The present invention also provides a method for preparing a lithium-sulfur battery separator, comprising the steps of: impregnating a conductive polymer having an anionic functional group with a plasticizer; And swelling the conductive polymer. The present invention also provides a method for preparing a lithium-sulfur battery separator.

In one embodiment of the present invention, the plasticizer is a non-aqueous electrolyte containing no salt, and the nonaqueous electrolyte is selected from the group consisting of N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate , Gamma -butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, tetraglyme, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethyl But are not limited to, formamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, At least one selected from the group consisting of propylene carbonate derivatives, tetrahydrofuran derivatives, DEGDME, ether, methyl pyrophosphate, and ethyl propionate.

According to the present invention, a small amount of a plasticizer capable of swelling the polymer separator is impregnated into a polymer electrolyte membrane having a negative charge to improve the ion conductivity of the polymer electrolyte membrane. As a result, ionic conduction occurs, and at the same time, a donnan potential is generated to lower the solubility of the polysulfide (donnan exclusion effect), whereby the polysulfide maintains a high concentration in the anode It is possible to expect a high capacity retention characteristic and an increase in the coulomb efficiency due to the suppression of polysulfide shuttle phenomenon.

Fig. 1 is a model diagram of a hybrid-ion conductor introduced into a lithium-sulfur battery.
FIG. 2 is a table showing ion conductivity and swelling ratio when the single-ion conductive polymer membrane is swollen with various plasticizers.
FIG. 3A is a graph of capacity change and charge-discharge efficiency change after 50 cycles when the hybrid-stage ion conductor system is applied to a lithium-sulfur battery.
FIG. 3B is a graph of change in capacity and charge-discharge efficiency after 50 cycles of a lithium-sulfur battery in a conventional liquid electrolyte system.
FIG. 4 is a model diagram of a hybrid-type ion conductor system applied to a lithium-sulfur battery, in which two cells are connected in series in a bipolar stack structure.

The following embodiments are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention. Therefore, the present invention is not limited to the embodiments described below, but may be embodied in other forms. In the drawings, the width, length, thickness, etc. of constituent elements may be exaggerated for convenience. Like reference numerals designate like elements throughout the specification.

In order to solve the above-mentioned problems, the present invention introduces a polymer having an anionic functional group such as a functional group having a negative charge, for example, a sulfonic acid (-SO 3 -) group, a carboxylate group or a phosphoric acid group as a separator and a binder, The polymer is impregnated with a plasticizer to swell the polymer.

In particular, in order to maximize the theft effect, the present invention can ensure ion conductivity by swelling a single ion conductive polymer (a single ion conductor) with a small amount of a plasticizer without adding a salt, and the system according to the present invention, Therefore, the shunt current can be suppressed when a unit cell is connected in series without an additional diaphragm in the bipolar stack structure.

1 is a schematic diagram of a hybrid ion conductor according to an embodiment of the present invention incorporated in a lithium-sulfur battery. Hybrid mono-ionic conductors herein refer to mono-ionic conductors impregnated with a plasticizer.

Referring to FIG. 1, a separation membrane 100 includes a single ion conductor 120 having a negatively charged functional group and a plasticizer 110. That is, the separator 100 according to an embodiment of the present invention swells the single ion conductor 120 after impregnating the single ion conductor 120 with the plasticizer 110. This maximizes the suppression of the release of polypheide due to the theft effect. In one embodiment of the present invention, the anionic functional group may be at least one selected from the group consisting of sulfonic acid (-SO3-) group, phosphoric acid (-PO4-) group and carboxylate (-COO-) group.

In one embodiment of the present invention, the polymer has a molecular weight of 10,00 to 1,000,000, an equivalent weight of 300 to 1,400, and a Young's modulus of 5 to 400 MPa. It is composed of the above materials.

If the ion equivalent is less than the above range, the physical properties of the polymer are hardened and cracked. When the ion equivalent is more than the above range, the polymer has a low ion conductivity. When the modulus of elasticity is less than the above range, the polymer tends to be hardened and cracked. When the elastic modulus is above the above range, the physical properties of the polymer tends to be poor.

The plasticizer according to an embodiment of the present invention does not include a salt. Thus, the bipolar stack system having a lithium-sulfur battery as a unit (stack) fabricated according to the present invention can provide a shunt current without additional diaphragm structure between unit stacks It has the advantage of being able to suppress.

1, the separator 100 is provided between the anode 300 and the cathode 200. In particular, the anode includes an active material 320, a current collector 330, a single ion conductor of the separator, Ion conductive polymer 340 as a binder.

In the present invention, the swollen polymer separator and the binder material of the positive electrode are used as the single ion conductive polymer in the same manner, so that the lithium ion conduction is smoothly performed at the interface between the separator and the positive electrode.

The mono-ion conductive polymer according to an embodiment of the present invention may include a polymer having the following general formula (1) or (2).

&Lt; Formula 1 >

In Formula 1, x and z represent an integer of 1 to 10, y represents an integer of less than 1000, and A represents H or any one of Li, Na, and K.

(2)

In Formula 2, x and y represent an arbitrary number satisfying 0 <x, y? 1, and B represents one element of H, Li, Na, and K.

In the present invention, by using a single ion conductive polymer membrane swollen with a plasticizer as a separator, the effect of transporting lithium ions from the anode to the anode and the electrical shorting effect are as described above.

In the present invention, the separation membrane 100 has a thickness of between 1 micrometer and 50 micrometer.

In manufacturing the anode 300 of the present invention, a single ion conductive polymer is also used as the binder 340, which not only improves the adhesion between the cathode active materials but also provides an ion conduction path.

In the present invention, the single ion conductive polymeric binder used in the preparation of the anode is dispersed in a single solvent or a mixed solution. The solvent is a single solvent or mixed solution of isopropyl alcohol, distilled water, butyl alcohol, or the like.

In the present invention, the cathode active material 320, the conductive carbon 310, and the single-ion conductive polymeric binder 340 are mixed in a solvent mixture (isopropyl alcohol, distilled water, butyl alcohol) After aligning, cast on the aluminum foil surface and dry.

In the present invention, in order to increase the ionic conductivity of the mono-ion conductive polymer, the Nafion membrane 100 is swollen with the non-aqueous electrolyte solution 110 containing no salt as a plasticizer.

In the present invention, the non-aqueous electrolyte may be at least one selected from the group consisting of N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma- The reaction can be carried out in the presence of a catalyst such as ricci franc, 2-methyltetrahydrofuran, tetraglyme, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, Methylmorpholine, methylene, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, DEGDME ), Ethers, methyl pyrophosphate, and ethyl propionate, or an organic solvent mixed with at least two non-organic monohydric solvents.

A method of manufacturing an anode according to an embodiment of the present invention includes the steps of: preparing a slurry by mixing a single ion conductive polymer mixed in a solvent with an electrode active material and a conductive material; Applying the slurry onto a transfer film; And a drying step of removing the solvent of the applied slurry.

The anode of the lithium-sulfur secondary battery of the present invention comprises a carbon-sulfur complex, a conductive carbon, a single ion conductive polymer, and the content of the ion conductive polymer can be controlled to 10% to 70%.

The manufacturing process of the lithium-sulfur secondary battery of the present invention includes sequentially stacking the prepared anode 300, the single ion conductive separator 100 impregnated with the plasticizer, and the lithium metal 200 in this order.

In order to facilitate a more thorough understanding of the present invention, the present invention will be described in detail through preferred embodiments in which the above manufacturing steps are more specific. It is to be understood, however, that these examples are provided so that the scope of the present invention is not limited thereto.

[Example]

In one embodiment of the present invention, Nafion, which is a single ion conductive polymer containing a sulfonic acid group as an anion, was used as the separator 100 and the positive electrode binder 340. To this end, the Nafion 212 (Dufont) was impregnated with various types of organic solvent plasticizers as shown in FIG. 2, and then the remaining plasticizer remaining on the surface was removed using a desiccant Respectively. At this time, the commercialized Nafion 212 polymer membrane was impregnated with a 2M LiOH solution, and the hydrogen group present at the terminal of the sulfonic acid group was replaced with lithium by stirring at 60 ° C. for 2 hours.

In one embodiment of the present invention, the Nafion 212 used may be replaced by a polymer of Formula I or Formula II.

&Lt; Formula 1 >

In Formula 1, x and z represent an integer of 1 to 10, y represents an integer of less than 1000, and A represents H or any one of Li, Na, and K.

(2)

In Formula 2, x and y represent an arbitrary number satisfying 0 <x, y? 1, and B represents one element of H, Li, Na, and K.

In one embodiment of the present invention, the mono-ion conductive polymer used for the anode is dispersed in a solvent at 5 to 20%. The solvent is a single solvent or mixed solution of isopropyl alcohol, distilled water, butyl alcohol, or the like. Since the commercially available Nafion ionic conductive polymer has a hydrogen group in the sulfonic acid group, it is substituted with a 2M LiOH aqueous solution to replace it with lithium ion.

In one embodiment of the present invention, the non-aqueous electrolyte solution for swelling the single ion conductive polymer is selected from the group consisting of N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, But are not limited to, lactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, tetraglyme, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, But are not limited to, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3- One or two or more aprotic organic solvents selected from the group consisting of tetrahydrofuran derivatives, DEGDME, ether, methyl pyrophosphate, and ethyl propionate, Organic solvent.

In an embodiment of the present invention, when preparing the anode 300, ketjen black and sulfur are mixed in a ratio of 4: 6, and then maintained in a sealed container at 155 DEG C for 12 hours. The prepared KB / S composite and conductive carbon (VGCF) were mixed at a ratio of 2: 1, and a mono-ion conductive polymer solution dispersed in a solvent was added at a mass ratio of 30% to 70% to prepare a slurry. The viscosity of the slurry is adjusted by using the same solvent as the solvent in which the single ion conductive polymer is dispersed.

In an embodiment of the present invention, the slurry thus prepared is cast in an aluminum foil, and then the electrode is dried in a 60 degree oven. Thereafter, the dried electrode is subjected to a pressing process so that the electrode can be extruded up to 60% of the initial electrode thickness using a 150-degree roll press. This is a process for enhancing the ion conduction between the ion conductor polymer and the active material.

In an embodiment of the present invention, the cathode 200 uses lithium metal metal of 450 micrometers in thickness and the anode 300 uses the electrode prepared above. As the separator 100, a Nafion membrane swollen in the plasticizer is used. Put the swollen Nafion membrane between the anode and cathode to remove any residual plasticizer present on the surface before assembling the cell using a desiccant.

FIG. 2 is a table showing ion conductivity and impregnation rate after impregnating a single ion conductive separator into various plasticizers not containing a lithium salt. FIG.

Referring to FIG. 2, when the single ion conductive polymer is impregnated with a plasticizer, the ion conductivity can be increased compared with that before impregnation.

The plasticizer used in this experiment was DOL: 1,3-Dioxolane, DME: 1,2-Dimethoxyethane, DEGDME: Diethylene glycol dimethyl ether, EC: Ethylene carbonate, PC: Propylene carbonate, TEGDME: Tetraethylene glycol dimethyl ether. The comparative example was 1 M LiTFSI, DOL / DME (1: 1, v / v) as a liquid electrolyte containing a salt).

3A is a graph showing the discharge capacity during 50 cycles of charging and discharging at a current density of 0.1 C when a hybrid single ion conductive polymer system is introduced into a lithium-sulfur battery according to an embodiment of the present invention.

Referring to FIG. 3A, it can be seen that a stable discharge capacity is realized for 50 cycles. Also, it can be confirmed that the cullung efficiency is secured at 90% or more. As a result, it can be confirmed that the dissolution of the polysulfide active material is effectively inhibited.

In this experiment, Sulfolane / DEGDME, 1/1, v / v mixed solution was used and the swelling ratio was 60% by volume. Thus, the swelling ratio with the use of the plasticizer according to the present invention is in the range of 10 to 90% of the initial volume.

FIG. 3B is a graph showing a discharge capacity during 50 cycles of charging and discharging at a current density of 0.1 C when a conventional liquid electrolyte system is introduced into a lithium-sulfur battery as a comparative example.

Referring to FIG. 3B, it can be seen that the discharge capacity sharply decreases during 50 cycles. As a result, it can be confirmed that the polysulfide active material elution occurs.

FIG. 4 is a view showing a case where two unit cells are connected in series with a lithium-sulfur battery according to the present invention as a unit cell. The structures and components of the negative electrode, separator, and positive electrode of the unit cell are the same as those of FIG.

Referring to FIG. 4, the bipolar stack according to the present invention is a structure in which a first stack 500 and a second stack 600 are connected in series without an additional diaphragm. In FIG. 4, reference numerals 410 and 710 denote an anode current collector and a cathode current collector, respectively.

The first stack 500 is composed of a cathode made of a lithium metal 530, a hybrid ion-polymer polymer separator 520, and a cathode 510. Similarly, the second stack 600 includes a negative electrode made of lithium metal 630, a hybrid ion-polymer polymer separator 620, and a positive electrode 610. The bipolar stack cell shown in FIG. 2 can remove shunt current between the first stack 500 and the second stack 600 because the liquid electrolyte is impregnated with the polymer and does not contain a lithium salt.

The present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Accordingly, the disclosed embodiments are to be considered in an illustrative rather than a restrictive sense, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

100: Membrane (Hybrid Ion Conducting Polymer)
110: plasticizer
120: Single ion conductive polymer
200: cathode (lithium metal)
300: anode
310: Conductive carbon
320: sulfur
330: Entire house
340: Single ion conductive polymer
400: positive collector
500: First unit cell
510: anode
520: Membrane (Ion Conducting Polymer)
530: cathode (lithium)
610: anode
620: Membrane (Ion Conductive Polymer)
630: cathode (lithium)
700: cathode collector

Claims (13)

As a lithium-sulfur battery separator,
Wherein the separation membrane comprises a conductive polymer having an anionic functional group; And
And a plasticizer impregnated in the conductive polymer,
The conductive polymer is swollen by the plasticizer,
Wherein the plasticizer is a non-aqueous electrolyte containing no salt, and the non-aqueous electrolyte is selected from the group consisting of N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylolactone, , 2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, tetraglyme, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetone But are not limited to, nitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, Wherein the lithium-sulfur battery separator is one or two or more selected from the group consisting of hydrogen fluoride derivatives, DEGDME, ether, methyl pyrophosphate, and ethyl propionate.
The method according to claim 1,
Wherein the anion functional group forms a stolen potential to exclude a polysulfide ion as an active material of the positive electrode.
The method according to claim 1,
Wherein the anionic functional group is at least one selected from the group consisting of a sulfonic acid (-SO3-) group, a phosphoric acid (-PO4-) group and a carboxylate (-COO-) group.
The method of claim 3,
Wherein the conductive polymer is a polymer represented by the following formula (1).

(Formula 1)
(Wherein x and z represent an integer of 1 to 10, y represents an integer of less than 1000, and A represents any one element selected from H, Li, Na and K.)
The method of claim 3,
Wherein the conductive polymer is a polymer represented by the following formula (2).

(2)
(Wherein x and y each represent an arbitrary number satisfying 0 <x, y? 1, and B represents any one element selected from the group consisting of H, Li, Na and K)
The method according to claim 1,
Wherein the separator has a film thickness of 1 to 50 占 퐉.
delete A lithium-sulfur battery including the lithium-sulfur battery separator according to any one of claims 1 to 6.
9. The method of claim 8,
anode; The lithium-sulfur battery separator; And a cathode,
Wherein the binder of the positive electrode is of the same kind as the conductive polymer of the lithium-sulfur battery separating membrane.
13. A lithium-sulfur battery system having a bipolar stack structure in which a lithium-sulfur battery according to claim 9 is laminated in a unit stack.
11. The method of claim 10,
Wherein no additional diaphragm structure is present between the unit stack and the unit stack.
As a method for producing a lithium-sulfur battery separator,
Impregnating the conductive polymer having an anionic functional group with a plasticizer; And
And swelling the conductive polymer,
Wherein the plasticizer is a non-aqueous electrolyte containing no salt, and the non-aqueous electrolyte is selected from the group consisting of N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylolactone, , 2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, tetraglyme, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetone But are not limited to, nitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, A lithium-sulfur battery separator characterized by being at least one member selected from the group consisting of hydrogen fluoride derivatives, DEGDME, ether, methyl pyrophosphate, and ethyl propionate. Joe method. delete

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