KR102657130B1 - Thermosetting electrolyte composition for lithium-sulfur battery, gel polymer electrolyte perpared therefrom, and lithium-sulfur battery comprising the same - Google Patents

Abstract

The present invention relates to a thermosetting electrolyte composition for a lithium-sulfur battery, a gel polymer electrolyte prepared thereby, and a lithium-sulfur battery containing the same, and specifically relates to a lithium salt; organic solvent; and a polymer or oligomer having a heat-polymerizable functional group and having a weight average molecular weight (Mw) of 130,000 g/mol to 380,000 g/mol.

Description

Thermosetting electrolyte composition for lithium-sulfur batteries, gel polymer electrolyte prepared thereby, and lithium-sulfur batteries comprising the same

The present invention relates to a thermosetting electrolyte composition for lithium-sulfur batteries, a gel polymer electrolyte prepared thereby, and a lithium-sulfur battery containing the same.

Recently, as the need for large-capacity secondary batteries that can be used in electric vehicles or power storage devices has emerged, research on next-generation secondary batteries is being actively conducted around the world.

Lithium-sulfur batteries use sulfur-based compounds containing sulfur-sulfur bonds as the positive electrode active material, and use alkali metals such as lithium, lithium alloys, and lithium-containing titanium composite oxide (LTO), or these and lithium. It is a secondary battery that uses a carbon-based material in which insertion/extraction of metal ions such as ions occurs as a negative electrode active material.

Lithium-sulfur batteries use an oxidation-reduction reaction in which the oxidation number of S decreases as the S-S bond is broken during a reduction reaction (during discharging), and the oxidation number of S increases during an oxidation reaction (during charging) and the S-S bond is formed again. Stores and generates electrical energy. That is, during discharge, an oxidation reaction of lithium occurs at the cathode, and a reduction reaction of sulfur occurs at the anode.

Specifically, the redox reaction of lithium and sulfur in a lithium-sulfur battery can be expressed by the following reaction equation.

2Li + S ₈ (solid) ↔ Li ₂ S ₈ (solution)

2Li + Li ₂ S ₈ (solution) ↔ 2Li ₂ S ₄ (solution)

2Li + Li ₂ S ₄ (solution) ↔ 2Li ₂ S ₂ (solution)

2Li + Li ₂ S ₂ (solution) ↔ 2Li ₂ S (solid precipitate)

The lithium-sulfur battery has an energy density of 3,830 mAh/g of lithium metal used as a negative electrode active material and 1,675 mAh/g of sulfur used as a positive electrode active material. In terms of energy density, it is the most promising among batteries currently being developed. It's battery. Moreover, the sulfur-based material used as the positive electrode active material is inexpensive and environmentally friendly, which can lead to cost savings.

However, the lithium-sulfur battery system has a disadvantage in that it is difficult to commercialize because the utilization rate of sulfur participating in the electrochemical redox reaction in the battery is low compared to the sulfur content used as the positive electrode active material, and unlike the theoretical capacity, the actual battery capacity is extremely low. there is.

Specifically, lithium polysulfide-based compounds such as Li ₂ S ₈ , Li ₂ S ₆ , Li ₂ S ₄ , and Li ₂ S ₂ , which are by-products during discharge, especially Li ₂ S _x (x>4), have an oxidation number of sulfur. High lithium polysulfide compounds are easily soluble in electrolyte solutions. The lithium polysulfide-based compound dissolved in the electrolyte diffuses away from the anode due to the difference in concentration. The lithium polysulfide-based compound eluted from the anode is lost out of the anode reaction area, making step-by-step reduction to a lithium sulfide-based compound such as Li ₂ S impossible. In other words, the lithium polysulfide-based compound that leaves the anode and cathode and exists in a dissolved state in the electrolyte cannot participate in the charging and discharging reaction of the battery, so the capacity of the sulfur material participating in the electrochemical reaction at the anode decreases, ultimately reducing the lithium -Sulfur is a major factor in reducing the charging capacity and energy of batteries.

In addition, the diffused lithium polysulfide compound not only floats or precipitates in the electrolyte solution, but also reacts directly with lithium and adheres to the surface of the negative electrode in the form of Li ₂ S, causing the problem of corrosion of the negative electrode.

Accordingly, when manufacturing lithium-sulfur batteries, there is a need to develop a method that can minimize side reactions between lithium polysulfide-based compounds and electrolyte solutions.

US Patent Publication No. 6,030,720

The present invention seeks to provide a thermosetting electrolyte composition for lithium-sulfur batteries that can prevent side reactions between a lithium polysulfide-based compound eluted from a positive electrode and an electrolyte solution.

In addition, the present invention seeks to provide a gel polymer electrolyte for lithium-sulfur batteries prepared by polymerization of the electrolyte composition.

Additionally, the present invention seeks to provide a lithium-sulfur battery containing the gel polymer electrolyte.

In order to achieve the above object, in one embodiment of the present invention,

lithium salt;

organic solvent; and

It includes a polymer or oligomer containing a unit represented by the following formula (1) having a thermally polymerizable functional group,

A thermosetting electrolyte composition for a lithium-sulfur battery is provided, wherein the polymer or oligomer has a weight average molecular weight (Mw) of 130,000 g/mol to 380,000 g/mol.

(Formula 1)

In Formula 1,

R is substituted or unsubstituted alkylene having 1 to 5 carbon atoms,

where m and n are the number of repeating units,

m is any integer from 10 to 5000,

n is any integer from 10 to 5000.

The unit represented by Formula 1 may be at least one selected from the group consisting of units represented by Formula 1a and Formula 1b below.

[Formula 1a]

In Formula 1a,

where m1 and n1 are the number of repeating units,

m1 is any integer from 10 to 5000,

n1 is any integer from 10 to 5000.

[Formula 1b]

In Formula 1b,

where m2 and n2 are the number of repeating units,

m2 is any integer from 10 to 5000,

n2 is an integer between 10 and 5000.

The weight average molecular weight (Mw) of the polymer or oligomer containing the unit represented by Formula 1 may be 190,000 g/mol to 380,000 g/mol.

In addition, the polymer or oligomer containing the unit represented by Formula 1 may be included in an amount of 1% to 7% by weight, specifically 1% to 5% by weight, based on the total weight of the thermosetting electrolyte composition for a lithium-sulfur battery.

In addition, in one embodiment of the present invention, the thermosetting electrolyte composition for lithium-sulfur batteries is heat-treated to produce a thermosetting electrolyte composition for lithium-sulfur batteries comprising a polymer thermoset by crosslinking or polymerization between polymers or oligomers containing units represented by Formula 1. A gel polymer electrolyte can be provided.

Additionally, in one embodiment of the present invention

(a) inserting an electrode assembly consisting of a positive electrode, a separator, and a negative electrode sequentially stacked into a battery case;

(b) manufacturing a lithium-sulfur battery by injecting the thermosetting electrolyte composition for a lithium-sulfur battery of the present invention into the battery case;

(c) activating the lithium-sulfur battery; and

(d) heat-treating the thermosetting electrolyte composition to form a gel polymer electrolyte in the lithium-sulfur battery.

At this time, the heat treatment step of forming the gel polymer electrolyte may be performed at a temperature of 60°C to 100°C, specifically 60°C to 80°C for approximately 2 minutes to 10 hours.

Additionally, in one embodiment of the present invention, a lithium-sulfur battery containing the gel polymer electrolyte for a lithium-sulfur battery of the present invention can be provided.

According to the present invention, by providing a thermosetting electrolyte composition for a lithium-sulfur battery comprising a polymer or oligomer containing a unit represented by the formula (1) containing a cyano group and a hydroxyl group, which are thermally polymerizable functional groups, at the terminals, the thermosetting electrolyte composition can be used without a polymerization initiator. A gel polymer electrolyte for lithium-sulfur batteries can be produced through polymerization alone. In addition, by including this, a side reaction of the lithium polysulfide-based compound eluted from the positive electrode active material with the electrolyte solution is prevented, thereby making it possible to manufacture a lithium-sulfur secondary battery with improved capacity characteristics.

Hereinafter, the present invention will be described in more detail.

Terms or words used in this specification and claims should not be construed as limited to their common or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It must be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it is.

Meanwhile, in the present specification, the term “alkylene group” refers to a branched or unbranched aliphatic hydrocarbon group or a functional group in which one hydrogen atom is missing from the carbon atoms located at both ends of the aliphatic hydrocarbon group. In one embodiment, the alkylene group may be substituted or unsubstituted. The alkylene group includes, but is not limited to, methylene group, ethylene group, propylene group, isopropylene group, butylene group, isobutylene group, tert-butylene group, pentylene group, 3-pentylene group, etc., each of which It may be optionally substituted in other embodiments.

In addition, in the present invention, unless otherwise specified, “*” refers to parts connected to each other between terminal parts of the same or different atoms or chemical formulas.

In addition, in this specification, "molecular weight" means the weight average molecular weight (Mw), unless otherwise defined, and the weight average molecular weight (Mw) of the polymer or oligomer of the present invention is measured by gel permeation chromatography. : It can be measured using GPC). For example, after preparing a sample of a certain concentration, the GPC measurement system alliance 4 device is stabilized. Once the device is stabilized, a chromatogram can be obtained by injecting the standard sample and sample into the device, and then the molecular weight can be calculated according to the analysis method (system: Alliance 4, column: Agilent PL mixed B, eluent: THF, flow rate) : 0.1 mL/min, temp: 40℃, injection: 100μL)

Additionally, in this specification, “viscosity” can be measured using Brookfield’s LV DV-II + Pro Viscometer (cone-plate type). For example, after dissolving a polymer or oligomer in DMF (dimethyl formamide) at a concentration of 20%, measurement was performed at 25°C. When measuring, the spindle was S40, rpm 15, and the sample loading amount was 1mL.

Thermosetting electrolyte composition

Specifically, in one embodiment of the present invention

lithium salt;

organic solvent; and

It includes a polymer or oligomer containing a unit represented by the following formula (1) having a thermally polymerizable functional group,

A thermosetting electrolyte composition for a lithium-sulfur battery is provided, wherein the polymer or oligomer has a weight average molecular weight (Mw) of 130,000 g/mol to 380,000 g/mol.

(Formula 1)

In Formula 1,

R is substituted or unsubstituted alkylene having 1 to 5 carbon atoms,

where m and n are the number of repeating units,

m is any integer from 10 to 5000, specifically 50 to 2000,

n is an integer from 10 to 5000, specifically 50 to 2000.

(1) Lithium salt

First, the lithium salt can be used without particular restrictions as long as it is a compound that can provide lithium ions used in lithium secondary batteries as well as lithium sulfur batteries. Representative examples include Li ⁺ as a cation and F ^- as an anion. Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , ClO ₄ ^- , BF ₄ ^- , AlO ₄ ^- , AlCl ₄ ^- , PF ₆ ^- , SbF ₆ ^- , AsF ₆ ^- , BF ₂ C ₂ O ₄ ^- , BC ₄ O ₈ ^- _, PO ₂ F ₂ ^- , PF ₄ C ₂ O ₄ ^- , PF ₂ C ₄ O ₈ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , C ₄ F ₉ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , ( CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^-. It can contain one.

The lithium salt may preferably be included at a concentration of 0.6M to 2M in the electrolyte. If the concentration of lithium salt is less than 0.6M, the conductivity of the electrolyte decreases and electrolyte performance deteriorates. If it exceeds 2M, the viscosity of the electrolyte increases and the mobility of lithium ions decreases.

(2) Organic solvent

In addition, the organic solvent can be used without limitation as long as it can minimize decomposition due to oxidation reactions during the charging and discharging process of the secondary battery and can exhibit the desired properties together with additives. A representative ero ester organic solvent can be used. You can.

The ester-based organic solvent may include at least one organic solvent selected from the group consisting of cyclic carbonate-based organic solvents, linear carbonate-based organic solvents, linear ester-based organic solvents, and cyclic ester-based organic solvents.

The cyclic carbonate-based organic solvent is ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2 , 3-pentylene carbonate, vinylene carbonate, and fluoroethylene carbonate (FEC).

In addition, specific examples of the linear carbonate-based organic solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate. There may be at least one selected from the group consisting of.

In addition, specific examples of the linear ester organic solvent include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate. can be mentioned.

In addition, specific examples of the cyclic ester organic solvent include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone. I can hear it.

At this time, among the ester-based organic solvents, a high-viscosity cyclic carbonate-based organic solvent that has a high dielectric constant and easily dissociates the lithium salt in the electrolyte may be used. In addition, when mixing the cyclic carbonate-based organic solvent with at least one organic solvent selected from the group consisting of a linear carbonate-based organic solvent and a linear ester-based organic solvent having low viscosity and low dielectric constant, a thermosetting electrolyte composition having a higher electrical conductivity can be prepared. You can.

Meanwhile, ionic conductivity in the electrolyte solution is generally determined by the mobility of ions in the thermosetting electrolyte composition, and factors affecting this ionic conductivity are the viscosity of the thermosetting electrolyte composition and the ion concentration in the organic solvent. In other words, the lower the viscosity of the organic solvent, the freer the movement of ions within the organic solvent, so ionic conductivity increases. As the concentration of ions in the organic solvent increases, the ionic conductivity increases because the amount of ions that are charge transporters increases. It increases.

The linear ester-based organic solvent reduces the viscosity of the thermosetting electrolyte composition and increases the degree of dissociation of the lithium salt by chelating lithium cations due to the ether symmetry structure. Therefore, when using the ester-based organic solvent, the ionic conductivity of the thermosetting electrolyte composition can be greatly improved. Among these linear ester solvents, ethyl acetate, ethyl propionate, propyl propionate, or butyl propionate can be used more preferably.

The organic solvent may be used by additionally mixing an ether-based solvent in addition to an ester-based organic solvent.

The ether-based solvent may include at least one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether.

(3) Polymer or oligomer having a thermally polymerizable functional group

In addition, the thermosetting electrolyte composition for a lithium-sulfur battery of the present invention may include a polymer or oligomer containing a unit represented by Formula 1 and having a thermopolymerizable functional group such as a cyano group and a hydroxyl group.

The polymer or oligomer containing the unit represented by Formula 1 is a polymerizable polymer or oligomer that can form gelation by forming crosslinks through a thermal polymerization reaction at a temperature of 60°C or higher, even without a polymerization initiator.

At this time, the weight average molecular weight (Mw) of the polymer or oligomer containing the unit represented by Formula 1 is 380,000 g/mol or less, specifically 130,000 g/mol to 380,000 g/mol, more specifically 190,000 g/mol to 380,000. g/mol, and this weight average molecular weight can be adjusted by the number of repeating units.

When the weight average molecular weight of the polymer or oligomer is within the above range, a crosslinking reaction by thermal polymerization can be performed without a polymerization initiator, thereby producing a gel polymer electrolyte with improved mechanical strength and stability. Furthermore, when the weight average molecular weight of the polymer or oligomer is within the above range, the impregnability of the thermosetting electrolyte composition can be improved by controlling the viscosity of the thermosetting electrolyte composition.

If the weight average molecular weight of the polymer or oligomer exceeds 380,000 g/mol, not only is it difficult to perform thermal polymerization without a polymerization initiator, but also the viscosity of the thermosetting electrolyte composition increases due to the high molecular weight. Impregnability may be reduced. Additionally, when the weight average molecular weight of the polymer or oligomer is 130,000 g/mol or more, a gel polymer electrolyte with secured mechanical strength can be produced.

Meanwhile, the weight average molecular weight of the polymer or oligomer may refer to a converted value for standard polystyrene measured by GPC (Gel Permeation Chromatography), and unless specifically specified otherwise, the molecular weight may refer to the weight average molecular weight. there is. For example, in the present invention, measurement is performed using the Agilent 1200 series under GPC conditions, and the column used at this time can be an Agilent PL mixed B column, and the solvent can be THF.

Meanwhile, in the polymer or oligomer containing the unit represented by Formula 1, the molar ratio of the number of repeating units m:n may be 1:1 to 10:1, specifically 1:1 to 7:1.

At this time, if the molar ratio of m to 1 mole of n is less than 1, the crosslinking reaction cannot be performed smoothly because the number of functional groups that can be crosslinked decreases, and if the molar ratio of m to 1 mole of n exceeds 10, the battery As the crosslinking reaction occurs excessively, the mechanical strength of the gel polymer electrolyte can be increased, but there is a disadvantage in that ionic conductivity deteriorates.

Meanwhile, the unit represented by Formula 1 may be at least one selected from the group consisting of units represented by Formula 1a and Formula 1b below.

[Formula 1a]

In Formula 1a,

where m1 and n1 are the number of repeating units,

m1 is any integer from 10 to 5000,

n1 is any integer from 10 to 5000.

[Formula 1b]

In Formula 1b,

where m2 and n2 are the number of repeating units,

m2 is any integer from 10 to 5000,

n2 is an integer between 10 and 5000.

Meanwhile, the viscosity of the polymer or oligomer containing the unit represented by Formula 1 is about 130 cPs to 160 cPs, more specifically, 135 cPs to 155 cPs (DMF, 20%, 25°C). It can be.

At this time, the viscosity can be adjusted by the number of repeating units of the polymer or oligomer containing the unit represented by Formula 1 and the resulting weight average molecular weight. That is, if the weight average molecular weight (Mw) of the polymer or oligomer containing the unit represented by Formula 1 is within 130,000 g/mol to 380,000 g/mol, the above viscosity can be achieved.

Furthermore, when the viscosity of the polymer or oligomer containing the unit represented by Formula 1 is within the above range, the optimal viscosity of the thermosetting electrolyte composition for a lithium-sulfur battery of the present invention containing it is realized, and the impregnation characteristics of the thermosetting electrolyte composition are achieved. can be secured.

For example, when the weight average molecular weight of the polymer or oligomer containing the unit represented by Formula 1 is 380,000 g/mol or less, the viscosity of the thermosetting electrolyte composition is 160 cPs or less, thereby ensuring the impregnability of the thermosetting electrolyte composition. . In addition, when the weight average molecular weight of the polymer or oligomer containing the unit represented by Formula 1 is 130,000 g/mol or more, the viscosity of the thermosetting electrolyte composition becomes 130 cPs or more, so that the lithium polysulfide-based compound is dissolved in the thermosetting electrolyte composition. By preventing this, the movement of the lithium polysulfide-based compound can be suppressed, thereby improving the capacity reduction of the lithium-sulfur battery.

Meanwhile, the viscosity was measured by dissolving a polymer or oligomer containing the unit represented by Formula 1 in DMF (dimethyl formamide) at a concentration of 20% and then using Brookfield's LV DV-II+Pro Viscometer (cone-plate type). It was measured at 25°C, and the spindle at the time of measurement was S40, rpm 15, and the sample loading amount was 1mL.

Meanwhile, the polymer or oligomer containing the unit represented by Formula 1 is 1% by weight to 7% by weight, specifically 1% by weight to 5% by weight, more specifically, based on the total weight of the thermosetting electrolyte composition for a lithium-sulfur battery. It may be included in 2% by weight to 4% by weight.

If the content of the polymer or oligomer containing the unit represented by Formula 1 is 1% by weight or more, the gel reaction formation effect is improved, and not only can sufficient mechanical strength of the gel polymer electrolyte be secured, but also when charging and discharging a lithium-sulfur battery. By effectively controlling the dissolution of the generated lithium polysulfide-based compound in the thermosetting electrolyte composition, capacity reduction of the lithium-sulfur battery can be improved. In addition, if the content of the polymer or oligomer containing the unit represented by Formula 1 is 7% by weight or less, not only can resistance increase and side reactions caused by excess polymer or oligomer be prevented, but also the wetting characteristics of the thermosetting electrolyte composition are improved. You can do it.

The polymer or oligomer containing the unit represented by Formula 1 included in the thermosetting electrolyte composition according to an embodiment of the present invention includes a cyano group (CN) and a hydroxyl group (OH ^- ) as a thermopolymerizable functional group at the terminal, and Therefore, a cross-linking reaction by heat can be performed in the battery without a polymerization initiator. That is, in the case of a low molecular weight polymer containing the unit represented by Formula 1, even if a separate polymerization initiator is not included, the anion (PF ₆ ^- ) generated from the Li salt present in the thermosetting electrolyte composition is used according to the following reaction formula 1 It can be thermally polymerized as follows to form a gel polymer electrolyte. Therefore, it is possible to prevent side reactions that may be caused by the polymerization initiator included when producing a conventional gel polymer electrolyte.

In the case of a gel polymer electrolyte formed by such a thermal polymer, by forming a network structure in the anode pore layer, the lithium polysulfide-based compound eluted from the anode can be suppressed from dissolving or moving in the thermosetting electrolyte composition, so the eluted lithium polysulfide compound Corrosion of the cathode surface caused by side reactions between sulfide compounds and electrolyte can be prevented.

[Scheme 1]

In addition, in one embodiment of the present invention, the thermosetting electrolyte composition for a lithium-sulfur battery is heat-treated in an inert atmosphere to include a polymer thermoset by crosslinking or polymerization between polymers or oligomers containing units represented by Formula 1. A gel polymer electrolyte for a lithium-sulfur battery can be provided.

Lithium-sulfur battery manufacturing method

Additionally, in one embodiment of the present invention

(a) inserting an electrode assembly consisting of a positive electrode, a separator, and a negative electrode sequentially stacked into a battery case;

(b) manufacturing a lithium-sulfur battery by injecting the thermosetting electrolyte composition for a lithium-sulfur battery of the present invention into the battery case;

(c) activating the lithium-sulfur battery; and

(d) heat-treating the thermosetting electrolyte composition to form a gel polymer electrolyte in the lithium-sulfur battery.

At this time, the heat treatment step to form the gel polymer electrolyte takes approximately 2 minutes to 10 hours, specifically 2 minutes to 8 hours, and the thermal polymerization temperature is 60 ℃ to 100 ℃, specifically 60 ℃ to 80 ℃. You can.

At this time, if the heat treatment temperature exceeds 100°C or the heat treatment time exceeds 10 hours, excessive cross-linking reaction is generated, and the mechanical strength of the gel polymer electrolyte may be increased, but there is a disadvantage in that ionic conductivity deteriorates. In addition, when the heat treatment temperature is less than 60°C or the heat treatment time is less than 2 minutes, there is a disadvantage in that it is difficult to produce a gel polymer electrolyte with sufficient mechanical strength because a sufficient crosslinking reaction is difficult to perform.

Meanwhile, the activation step is a step of forming a solid electrolyte interface (SEI) film on the surface of the cathode by partially performing charging and discharging, and can be performed by a conventional method known in the field. For example, charging and discharging can be performed once or repeatedly at a constant current or constant voltage within a certain range. Specifically, charging and discharging can be performed once at a voltage range of 2.5V to 4.8V. Charging for the activation may be performed at a state of charge (SOC) in the range of 30 to 70%.

An aging step may be further included after the activation step.

The aging step is to stabilize the activated battery by leaving it for a certain period of time, and can be carried out at 19°C to 25°C.

lithium-sulfur battery

Meanwhile, in one embodiment of the present invention, a lithium-sulfur battery including the gel polymer electrolyte for a lithium-sulfur battery can be provided.

Specifically, the lithium-sulfur secondary battery of the present invention can be manufactured by injecting the electrolyte composition of the present invention into an electrode assembly consisting of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. At this time, the positive electrode, negative electrode, and separator that make up the electrode assembly can be all those commonly used in manufacturing lithium-sulfur secondary batteries.

The positive electrode and negative electrode constituting the lithium-sulfur secondary battery of the present invention can be manufactured and used by conventional methods.

(1) anode

First, the positive electrode can be manufactured by forming a positive electrode mixture layer on the positive electrode current collector. The positive electrode mixture layer can be formed by coating a positive electrode slurry containing a positive electrode active material, a binder, a conductive material, and a solvent on a positive electrode current collector, followed by drying and rolling.

The positive electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery. For example, it may be preferable to use aluminum foil, foamed aluminum, foamed nickel, etc. with excellent conductivity. .

Additionally, the positive electrode active material layer may include elemental sulfur (S ₈ ), a sulfur-based compound, or a mixture thereof as a positive electrode active material. Specifically, the sulfur-based compound may be Li ₂ S _n (n≥1), an organic sulfur compound, or a carbon-sulfur polymer ((C ₂ S _x ) _n : x=2.5∼50, n≥2). Since these sulfur substances alone do not conduct electricity, it is preferable to use them by forming a complex with a conductive material.

The positive electrode active material may be included in an amount of 70% to 99% by weight, specifically 80% to 95% by weight, based on the total weight of solids in the positive electrode slurry.

The binder is a component that assists in the bonding of the active material and the conductive material and the bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of solids in the positive electrode slurry. If the binder content is less than 1% by weight, the effect of improving the adhesion between the positive electrode active materials or between the positive electrode active material and the current collector due to the use of the binder is minimal. On the other hand, if it exceeds 30% by weight, the content of the positive electrode active material becomes relatively small and conductivity decreases. There is a risk that capacity characteristics may deteriorate.

Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, and tetrafluoride. Roethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, and various copolymers.

The conductive material is typically added in an amount of 1 to 30% by weight based on the total weight of solids in the positive electrode slurry. At this time, if the content of the conductive material is less than 1% by weight, the effect of improving conductivity due to the use of the conductive material is minimal. On the other hand, if it exceeds 30% by weight, the content of the positive electrode active material is relatively small, and there is a risk that the capacity characteristics may deteriorate.

These conductive materials are not particularly limited as long as they have conductivity without causing chemical changes in the battery. For example, graphite; Carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as single-walled or multi-walled carbon nanotubes, carbon fibers, and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

It is preferable to use a solvent that can uniformly disperse the positive electrode active material, binder, and conductive material and that evaporates easily. Specifically, acetonitrile, methanol, ethanol, tetrahydrofuran, water, isopropyl alcohol, etc. can be mentioned, and can be used in an amount that achieves a desirable viscosity when including the positive electrode active material and optionally a binder and a conductive material. For example, the solid content concentration in the slurry containing the positive electrode active material and, optionally, the binder and the conductive material may be 10% by weight to 60% by weight, preferably 20% by weight to 50% by weight.

(2) cathode

Additionally, the negative electrode can be made by laminating lithium metal to a negative electrode current collector or using the lithium metal foil itself.

The negative electrode current collector generally has a thickness of 3 to 500 μm. This negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, like the positive electrode current collector, fine irregularities can be formed on the surface to strengthen the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

In addition to the lithium metal, negative electrode active materials include materials that can reversibly intercalate or deintercalate lithium ions, materials that can reversibly form lithium-containing compounds by reacting with lithium ions, and a group consisting of lithium metal and lithium alloys. It may also contain a negative electrode active material selected from.

The material capable of reversibly intercalating/deintercalating lithium ions is a carbon material. Any carbon-based negative electrode active material commonly used in lithium ion secondary batteries can be used, and a representative example is crystalline carbon. , amorphous carbon, or a combination of these can be used. Additionally, representative examples of materials that can react with lithium ions to reversibly form lithium-containing compounds include tin oxide (SnO ₂ ), titanium nitrate, and silicon (Si), but are not limited thereto. The lithium alloy may be an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn.

Alternatively, an inorganic protective layer, an organic protective layer, or a material laminated thereon on the surface of lithium metal may also be used as a cathode. The inorganic protective film includes Li, P, O, S, N, B, Al, F, Cl, Br, I, As, Sb, Bi, C, Si, Ge, In, Tl, Mg, Ca, It contains one or more elements selected from the group consisting of Sr and Ba. The organic protective film includes polyethylene oxide or polypropylene oxide, or polyethylene glycol diacrylate, polypropylene glycol diacrylate, ethoxylated neopentyl glycol diacrylate, ethoxylated bisphenol A diacrylate, and one or more acrylate monomers selected from the group consisting of toxylated aliphatic urethane acrylates, ethoxylated alkylphenol acrylates, and alkyl acrylates.

Additionally, during the process of charging and discharging a lithium-sulfur battery, sulfur used as a positive electrode active material may be converted into an inert material and adhere to the surface of the lithium negative electrode. As such, inactive sulfur refers to sulfur in a state in which sulfur can no longer participate in the electrochemical reaction of the anode after undergoing various electrochemical or chemical reactions, and the inactive sulfur formed on the surface of the lithium cathode acts as a protective layer of the lithium cathode. It also has the advantage of acting as a Therefore, lithium metal and inert sulfur formed on the lithium metal, such as lithium sulfide, may be used as the cathode.

(3) Separator

In addition, the separator serves to block the internal short circuit of both electrodes and impregnate the electrolyte. A separator composition is prepared by mixing polymer resin, filler, and solvent, and then the separator composition is directly coated and dried on the top of the electrode. A separator film may be formed, or the separator composition may be cast and dried on a support, and then the separator film peeled from the support may be laminated on the top of the electrode.

In addition, in the lithium sulfur battery, the separator is a physical separator that has the function of physically separating the electrodes, and can be used without particular restrictions as long as it is normally used as a separator in a lithium sulfur battery, especially for ion movement of the electrolyte. It is desirable to have low resistance and excellent electrolyte moisture capacity. Specifically, porous polymer films, for example, porous polymer films made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, are used alone. It can be used as or by laminating them, or a typical porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc., can be used, but is not limited thereto.

The pore diameter of the porous separator is generally 0.01 to 50㎛, and the porosity may be 5 to 95%. Additionally, the thickness of the porous separator may generally range from 5 to 300㎛.

There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it can be applied in various shapes such as cylindrical, square, pouch, or coin depending on the purpose. The lithium secondary battery according to an embodiment of the present invention may be a pouch-type secondary battery.

Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described in detail below. Examples of the present invention are provided to more completely explain the present invention to those with average knowledge in the art.

Example

Example 1

(Preparation of curable electrolyte composition)

98 g of an organic solvent in which 1M LiPF ₆ was dissolved (ethylene carbonate (EC): propylene carbonate (PC): propyl propionate (PP) = 3:1:6 volume ratio) was mixed with a polymer containing the unit represented by Formula 1a ( A thermosetting electrolyte composition containing 2 g of weight average molecular weight (Mw) = 200,000, m1:n1 = 75:25) was prepared (see Table 1 below).

(Secondary battery manufacturing)

A support consisting of carbon nanotubes and a binder was first coated and dried on an aluminum current collector to form a web-shaped conductive network. Next, a slurry was prepared by mixing nano-sized sulfur-based positive electrode particles and a polyvinylidene fluoride binder, and then the slurry was applied so that it was 2.5 times the loading of carbon nanotubes and dried to complete the positive electrode for a lithium-sulfur battery. The capacity per area of the manufactured positive electrode was 2 mAh/cm ² .

An electrode assembly was manufactured by sequentially stacking a lithium electrode using the prepared positive plate, a vacuum-dried separator, and a negative electrode, and then inserted into a pouch case.

Next, the electrolyte composition was injected into the pouch, sealed, and stored at room temperature for 2 days to prepare a test cell.

Example 2.

A thermosetting electrolyte composition was prepared in the same manner as in Example 1, except that a polymer containing the unit represented by Formula 1b (weight average molecular weight (Mw) = 200,000, m2:n2 = 85:15) was used to prepare the thermosetting electrolyte composition. and a test cell containing it was assembled (see Table 1 below).

Example 3.

Example 1, except that when preparing the thermosetting electrolyte composition, an electrolyte composition in which 2 g of the polymer containing the unit represented by Formula 1a (weight average molecular weight (Mw) = 130,000, m1:n1 = 50:50) was dissolved was used. The thermosetting electrolyte composition and a test cell containing the same were assembled in the same manner (see Table 1 below).

Example 4.

Example 1, except that when preparing the thermosetting electrolyte composition, an electrolyte composition in which 2 g of a polymer containing the unit represented by Formula 1a (weight average molecular weight (Mw) = 380,000, m1:n1 = 85:15) was dissolved was used. The thermosetting electrolyte composition and a test cell containing the same were assembled in the same manner (see Table 1 below).

Example 5.

A thermosetting electrolyte composition and a test cell containing the same were assembled in the same manner as in Example 1, except that ethyl propionate solvent was used instead of propyl propionate solvent when preparing the thermosetting electrolyte composition (see Table 1 below).

Example 6.

A thermosetting electrolyte composition and a test cell containing the same were assembled in the same manner as in Example 1, except that 4 g of the polymer containing the unit represented by Formula 1a in 96 g of organic solvent was used when preparing the thermosetting electrolyte composition (Table 1 below) reference).

Example 7.

A thermosetting electrolyte composition and a test cell containing the same were assembled in the same manner as in Example 1, except that 1 g of the polymer containing the unit represented by Formula 1a in 99 g of organic solvent was used to prepare the thermosetting electrolyte composition (Table 1 below) reference).

Example 8.

A thermosetting electrolyte composition and a test cell containing the same were assembled in the same manner as in Example 3, except that 7 g of a polymer or oligomer containing the unit represented by Formula 1a in 93 g of an organic solvent was used to prepare the thermosetting electrolyte composition (see below) (see Table 1).

Example 9.

A thermosetting electrolyte composition and a test cell containing the same were assembled in the same manner as in Example 1, except that 0.9 g of a polymer or oligomer containing the unit represented by Formula 1a in 99.01 g of organic solvent was used to prepare the thermosetting electrolyte composition. (See Table 1 below).

Example 10.

A thermosetting electrolyte composition and a test cell containing the same were assembled in the same manner as in Example 3, except that 8 g of a polymer or oligomer containing the unit represented by Formula 1a in 92 g of organic solvent was used to prepare the thermosetting electrolyte composition (see below) (see Table 1).

Comparative Example 1.

When preparing the electrolyte composition, 97.5 g of organic solvent was used, except that 2 g of polymer (weight average molecular weight (Mw) = 200,000) containing the unit represented by the following formula (2) and 0.5 g of polymerization initiator were used. The electrolyte composition and a test cell containing it were assembled in the same manner as in Example 1 (see Table 1 below).

[Formula 2]

(R ₁ is H, R ₂ is an ethyl group, and n is the number of repeating units, which is 50,000.)

Comparative Example 2.

Example 1, except that when preparing the thermosetting electrolyte composition, an electrolyte composition in which 2 g of the polymer containing the unit represented by Formula 1a (weight average molecular weight (Mw) = 400,000, m1:n1 = 75:25) was dissolved was used. The electrolyte composition and a test cell containing it were assembled in the same manner (see Table 1 below).

Comparative Example 3.

Example 1, except that when preparing the thermosetting electrolyte composition, an electrolyte composition in which 2 g of the polymer containing the unit represented by Formula 1a (weight average molecular weight (Mw) = 100,000, m1:n1 = 25:75) was dissolved was used. The electrolyte composition and a test cell containing it were assembled in the same manner (see Table 1 below).

Comparative Example 4.

An electrolyte composition for a lithium-sulfur battery and a test cell containing the same were assembled in the same manner as in Example 1, except that a polymer having a thermally polymerizable functional group was not included when preparing the electrolyte composition (see Table 1 below).

Thermosetting electrolyte composition organic solvent additive Type (volume ratio) Added amount
(g) chemical formula weight average
Molecular weight (Mw) Addition amount (g) Example 1 EC:PC:PP=3:1:6 98 1a 200,000 2 Example 2 EC:PC:PP=3:1:6 98 1b 200,000 2 Example 3 EC:PC:PP=3:1:6 98 1a 130,000 2 Example 4 EC:PC:PP=3:1:6 98 1a 380,000 2 Example 5 EC:PC:EP=3:1:6 98 1a 200,000 2 Example 6 EC:PC:PP=3:1:6 96 1a 200,000 4 Example 7 EC:PC:PP=3:1:6 99 1a 200,000 One Example 8 EC:PC:PP=3:1:6 93 1a 130,000 7 Example 9 EC:PC:PP=3:1:6 99.1 1a 200,000 0.9 Example 10 EC:PC:PP=3:1:6 92 1a 130,000 8 Comparative Example 1 EC:PC:PP=3:1:6 97.5 2 200,000 2 Comparative Example 2 EC:PC:PP=3:1:6 98 1a 400,000 2 Comparative Example 3 EC:PC:PP=3:1:6 98 1a 100,000 2 Comparative Example 4 EC:PC:PP=3:1:6 100 - - -

Experiment example

Experimental Example 1.

The test cells manufactured in Examples 1 to 10 and Comparative Examples 1 to 4 were activated by charging each at 4.3V under 0.1C conditions and then discharging to 4.1V once. Heat treatment was performed at 65°C for 5 hours.

After completion of heat treatment, the test cells of Examples 1 to 10 and Comparative Examples 1 to 4 were disassembled to confirm the presence or absence of gel polymer electrolyte formation.

When the test cell was disassembled, the degree to which the thermosetting electrolyte composition for a lithium-sulfur battery did not gel but remained in a liquid state and had flowability was determined, and is shown in Table 2 below.

Presence or absence of gel polymer electrolyte formation Example 1 O Example 2 O Example 3 O Example 4 O Example 5 O Example 6 O Example 7 O Example 8 O Example 9 O Example 10 O Comparative Example 1 △ Comparative Example 2 △ Comparative Example 3 △ Comparative Example 4 X
O: Almost no flowable thermosetting electrolyte composition (gel polymer electrolyte formation rate of about 98% or more)
△: Some flowable thermosetting electrolyte composition (gel polymer electrolyte formation degree of about 50% to about 97%)
Х: A large amount of flowable thermosetting electrolyte composition remains (gel polymer electrolyte formation is less than 50% or almost not formed)

Referring to Table 2, when the test cells manufactured in Examples 1 to 10 were disassembled, more than 98% of the thermosetting electrolyte composition was converted to a gel polymer electrolyte, and no flowable thermosetting electrolyte composition was observed.

On the other hand, when the test cells of Comparative Examples 1 to 3 were disassembled, it was observed that some of the thermosetting electrolyte composition was not converted to a gel polymer electrolyte and existed in a flowable state.

At this time, in the case of the test cell of Comparative Example 2 equipped with a thermosetting electrolyte composition containing a polymer having a high weight average molecular weight, the degree of flow of the thermosetting electrolyte composition was not high, but due to the high viscosity of the thermosetting electrolyte composition, thermosetting was carried out up to the center of the cell. It can be confirmed that the electrolyte composition is not impregnated.

Meanwhile, in the case of the test cell of Comparative Example 4 equipped with an electrolyte composition that does not contain a polymer having a thermally polymerizable functional group, it can be seen that the electrolyte composition exists in a liquid state.

Experimental Example 2

The test cells manufactured in Examples 1 to 10 and the test cells manufactured in Comparative Examples 1 to 4 were each activated by performing the process of charging at 4.3 V under 0.1C conditions and discharging to 4.1 V once, and then 65 Heat treated for 5 hours at °C.

After heat treatment was completed, the SOC was charged to 30% at a constant current of 0.2C in a temperature environment of 25°C until the voltage reached 4.0V, and then discharged at a constant current of 0.2C until the voltage reached 3.0V. The capacity after the 50 cycles is expressed as a percentage compared to the initial 1 cycle capacity and is listed in Table 3 below.

Capacity maintenance rate after charging and discharging 50 times (%) Example 1 96.2 Example 2 95.8 Example 3 94.6 Example 4 96.7 Example 5 96.4 Example 6 97.1 Example 7 94.2 Example 8 95.5 Example 9 91.8 Example 10 92.3 Comparative Example 1 90.6 Comparative Example 2 67.1 Comparative Example 3 89.6 Comparative Example 4 86.8

Referring to Table 3, the test cells manufactured in Examples 1 to 8 have a capacity retention rate (%) of 94.2% or more, which is significantly improved compared to the test cells manufactured in Comparative Examples 1 to 4. .

That is, in the case of the test cell of Comparative Example 1 equipped with a thermosetting electrolyte composition containing a polymer containing a unit represented by Formula 2, the side reaction inhibition effect of the lithium polysulfide-based compound was insufficient, and the It can be seen that the capacity maintenance rate deteriorates compared to the test cell.

In addition, in the case of the test cell of Comparative Example 2 equipped with a thermosetting electrolyte composition containing a polymer having a high molecular weight, the impregnability of the thermosetting electrolyte composition decreases, and resistance deviation in the plane direction occurs, causing a significant deterioration in the capacity retention rate. You can see that

In addition, in the case of the test cell of Comparative Example 3 provided with a thermosetting electrolyte composition containing a low molecular weight polymer and the test cell of Comparative Example 4 provided with a thermosetting electrolyte composition containing no polymer, the formation of the gel polymer electrolyte was insufficient. Alternatively, it can be seen that because the gel polymer electrolyte is not formed, the effect of suppressing side reactions of the lithium polysulfide-based compound is insufficient, and the capacity retention rate is deteriorated.

Meanwhile, in the case of the test cell manufactured in Example 9 with a low content of polymer or oligomer and the test cell manufactured in Example 10 with an excessive amount of polymer or oligomer, the capacity remaining ratio (%) was 91.8% and 92.3%, respectively. Although it was lowered by a small amount compared to the secondary batteries manufactured in Examples 1 to 8, it can be seen that it was improved compared to the secondary batteries manufactured in Comparative Examples 1 to 4.

Claims (10)

In a lithium-sulfur battery containing a gel polymer electrolyte for a lithium-sulfur battery,
The gel polymer electrolyte for lithium-sulfur batteries includes lithium salt; organic solvent; and a polymer or oligomer containing a unit represented by the following formula (1) having a thermally polymerizable functional group; prepared by heat treating a thermosetting electrolyte composition for a lithium-sulfur battery comprising:
The weight average molecular weight (Mw) of the polymer or oligomer is 130,000 g/mol to 380,000 g/mol,
A lithium-sulfur battery, wherein the thermosetting electrolyte composition for a lithium-sulfur battery has a viscosity of 130 cps to 160 cps:
(Formula 1)

In Formula 1,
R is substituted or unsubstituted alkylene having 1 to 5 carbon atoms,
where m and n are the number of repeating units,
m is any integer from 10 to 5000,
n is any integer from 10 to 5000.
In claim 1,
A lithium-sulfur battery wherein the unit represented by Formula 1 is at least one selected from the group consisting of units represented by Formula 1a and Formula 1b below:
[Formula 1a]

In Formula 1a,
where m1 and n1 are the number of repeating units,
m1 is any integer from 10 to 5000,
n1 is an integer between 10 and 5000,

[Formula 1b]

In Formula 1b,
where m2 and n2 are the number of repeating units,
m2 is any integer from 10 to 5000,
n2 is an integer between 10 and 5000.
In claim 1,
A lithium-sulfur battery wherein the weight average molecular weight (Mw) of the polymer or oligomer is 190,000 g/mol to 380,000 g/mol.
In claim 1,
A lithium-sulfur battery in which the polymer or oligomer containing the unit represented by Formula 1 is contained in an amount of 1% to 7% by weight based on the total weight of the thermosetting electrolyte composition for a lithium-sulfur battery.
In claim 4,
A lithium-sulfur battery in which the polymer or oligomer containing the unit represented by Formula 1 is contained in an amount of 1% to 5% by weight based on the total weight of the thermosetting electrolyte composition for a lithium-sulfur battery.
In claim 5,
A lithium-sulfur battery in which the polymer or oligomer containing the unit represented by Formula 1 is contained in an amount of 2% to 4% by weight based on the total weight of the thermosetting electrolyte composition for a lithium-sulfur battery.
delete (a) inserting an electrode assembly consisting of a positive electrode, a separator, and a negative electrode sequentially stacked into a battery case;
(b) manufacturing a lithium-sulfur battery by injecting a thermosetting electrolyte composition for a lithium-sulfur battery into the battery case;
(c) activating the lithium-sulfur battery; and
(d) heat treating the lithium-sulfur battery to form a gel polymer electrolyte for a lithium-sulfur battery.
In claim 8,
A method of manufacturing a lithium-sulfur battery, wherein the heat treatment step is performed at 60°C to 100°C for 2 minutes to 10 hours. delete