KR100669315B1 - Polymer electrolyte for lithium-sulfur battery and lithium-sulfur battery comprising same - Google Patents

Abstract

The present invention relates to a polymer electrolyte for lithium-sulfur batteries and a lithium-sulfur battery comprising the same, the electrolyte comprising a monomer comprising a methacrylate group; Peroxides having 6 to 40 carbon atoms; Organic solvents; And an electrolyte containing a lithium salt.

The polymer electrolyte of the present invention can provide a lithium-sulfur battery having improved cycle life characteristics and safety.

Polymer electrolyte, lithium sulfur battery, polyester polyol

Description

Polymer electrolyte for lithium-sulfur battery, and lithium-sulfur battery comprising same TECHNICAL FIELD

1 is a surface photograph of a negative electrode obtained by disassembly after a cycle life test of a lithium-sulfur battery prepared according to Example 1 of the present invention.

2 is a surface photograph of a negative electrode obtained by disassembling after a cycle life test of a lithium-sulfur battery prepared according to Comparative Example 1.

3 is a graph showing the cycle life test results of the lithium-sulfur battery prepared according to Example 1 and Comparative Example 1 of the present invention.

[Industrial use]

The present invention relates to a lithium-sulfur battery polymer electrolyte and a lithium-sulfur battery including the same, and more particularly, a lithium-sulfur battery polymer electrolyte and a lithium-sulfur battery including the same, which can provide a battery having excellent cycle life characteristics. It is about.

[Prior art]

With the development of portable electronic devices, the demand for light and high capacity batteries is increasing. As a secondary battery that satisfies these demands, development of a lithium-sulfur battery using a sulfur-based material as a cathode active material is being actively conducted.

Lithium-sulfur battery uses a sulfur-based compound having a sulfur-sulfur bond as a positive electrode active material, and an alkali metal such as lithium, or a carbon-based material in which insertion / deintercalation of metal ions such as lithium ions occurs It is a secondary battery using as a negative electrode active material. In the reduction reaction (discharged), the SS bond is broken and the oxidation number of S decreases. In the oxidation reaction (charged), the oxidation-reduction reaction of the SS bond is formed by increasing the oxidation number of S and the electrical energy is stored and stored. Create

The lithium-sulfur battery has an energy density of 3830 mAh / g when using lithium metal used as a negative electrode active material, and an energy density of 1675 mAh / g when using sulfur (S ₈ ) used as a positive electrode active material. Among the most promising cells in terms of energy density. In addition, the sulfur-based material used as the positive electrode active material has the advantage that it is cheap and environmentally friendly material.

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

In addition, during the redox reaction, sulfur is leaked into the electrolyte, which deteriorates the battery life, and when the proper electrolyte is not selected, lithium sulfide (Li ₂ S), which is a reducing substance of sulfur, is precipitated and no longer participates in the electrochemical reaction. There is a problem.

In addition, when using a highly reactive lithium metal as a negative electrode active material, when the appropriate electrolyte solution that does not react with the lithium metal is not selected, dendrites of the lithium metal may be generated during charge and discharge may deteriorate cycle life characteristics.

It is expected that the reactivity of the lithium metal and the electrolyte may be reduced in the battery using the polymer solid electrolyte rather than the battery using the liquid electrolyte, but the lithium-sulfur battery has not attempted to use the polymer solid electrolyte. For a general polymer solid electrolyte, US Pat. No. 6,329,103 describes a polymer electrolyte using a polymerizable alkylene oxide polymer, and US Pat. No. 5,925,283 describes at least one halogen-substituted carbonic acid. Ester (bicyclic carbonic-ester) gel polymers are described. However, these conventional studies are limited to lithium-ion batteries only, and their application to lithium-sulfur batteries has not been studied.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a polymer electrolyte for lithium-sulfur battery excellent in lithium protection effect.

Another object of the present invention is to provide a polymer electrolyte for a lithium-sulfur battery that can provide a battery having excellent cycle life characteristics.                         

Still another object of the present invention is to provide a lithium-sulfur battery using the polymer electrolyte.

In order to achieve the above object, the present invention is a monomer containing a methacrylate group; Peroxides having 6 to 40 carbon atoms; Organic solvents; And it provides a polymer electrolyte for a lithium-sulfur battery comprising an electrolyte containing a lithium salt.

The invention also the polymer electrolyte; A positive electrode comprising at least one positive electrode active material selected from the group consisting of elemental sulfur, sulfur compounds and mixtures thereof; And a negative electrode active material selected from the group consisting of a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reacting with lithium ions to form a lithium-containing compound, lithium metal and a lithium alloy. It provides a lithium-sulfur battery comprising a negative electrode comprising.

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

The present invention relates to a polymer electrolyte having low reactivity with lithium metal used as a negative electrode active material in a lithium-sulfur battery. That is, the polymer electrolyte of the present invention can prevent the problem of deterioration in cycle life characteristics due to lithium dendrites generated when lithium metal reacts with the electrolyte solution. The polymer electrolyte of the present invention may be a gel-based physical gel polymer electrolyte in which the polymerization process is performed outside of the battery prior to battery assembly, or may be caused by a polymerization reaction in the battery generated by leaving the polymerization process at about 75 ° C. after battery assembly. The gel may be a chemical gel polymer electrolyte.

The polymer electrolyte of the present invention contains a monomer containing a methacrylate group and an organic peroxide having 6 to 40 carbon atoms, and includes an organic solvent and a lithium salt. In this specification, an organic solvent and a lithium salt are called electrolyte solution.

The monomer including the methacrylate group is a compound having at least one carbon-carbon double bond at the terminal of the monomer, and may be polyfunctional acrylate, poly (ethylene glycol) dimethacrylate, poly (ethylene glycol) diacrylate, poly (Ethylene glycol) divinyl ether ethylene glycol dimethacrylate, ethylene glycol diacrylate, ethylene glycol divinyl ether hexanediol diacrylate, tripropylene glycol diacrylate, tetraethylene glycol monoacrylate, caprolactone acrylate under Those selected from the group consisting of mixtures thereof can be used. Among these, the said polyfunctional acrylate and poly (ethylene glycol) dimethacrylate are preferable, and polyfunctional acrylate is the most preferable. The polyfunctional acrylate is a hydroxyl group of the (polyester) polyol having three or more hydroxyl groups (-OH), some or all of which is substituted with a (meth) acrylic acid ester, and some remaining unsubstituted with a (meth) acrylic acid ester Reactive hydroxyl groups refer to poly (ester) (meth) acrylates substituted with groups that are not radically reactive. Examples of such polyfunctional acrylates include monomers represented by the following formula (1) or (2).

[Formula 1]

[Formula 2]

(In the above formula 1 and 2, R ₁ is H or C ₁ to C ₆ alkyl group, n is an integer of 1 to 100,000, R ₂ is H or C ₁ to C ₆ alkyl group)

In the polymer electrolyte of the present invention, the mixing ratio of the electrolyte solution and the monomer is more than 10, preferably 200 or less: 1, more preferably 40 to 150: 1, and most preferably 60 to 120: 1 in weight ratio.

When the amount of the electrolyte used is less than 10 times the weight of the monomer, it is not preferable because a complete gel is formed in a later polymerization process to form a complete solid electrolyte. Unlike the lithium ion battery, the polymer electrolyte used in the lithium-sulfur battery is preferable to maintain the properties of the liquid electrolyte solution while maintaining the intermediate state between the liquid and the solid, because of excellent battery characteristics. In addition, when the amount of the electrolyte used exceeds 200 times the weight of the polymer, there is a problem that the liquid electrolyte squeezes out of the polymer matrix, which is not preferable.

The electrolyte solution includes an organic solvent and a lithium salt which is an electrolyte salt.

As the organic solvent, a single solvent may be used, or two or more mixed organic solvents may be used. When using two or more mixed organic solvents, it is preferable to use one or more solvents selected from two or more groups among the weak polar solvent group, the strong polar solvent group, and the lithium metal protective solvent group.

Weak polar solvents are defined as those having a dielectric constant of less than 15 that can dissolve elemental sulfur among aryl compounds, bicyclic ethers, and acyclic carbonates; strong polar solvents include acyclic carbonates, sulfoxide compounds, lactone compounds, Among ketone compounds, ester compounds, sulfate compounds, and sulfite compounds, a dielectric constant capable of dissolving lithium polysulfide is defined as greater than 15, and lithium protective solvents are saturated ether compounds, unsaturated ether compounds, N, O, It is defined as a solvent having a charge and discharge cycle efficiency (cycle efficiency) of 50% or more to form a SEI (Solid Electrolyte Interface) film stable on lithium metal, such as a heterocyclic compound containing S or a combination thereof.

 Specific examples of weak polar solvents include xylene, dimethoxyethane, 2-methyltetrahydrofuran, diethyl carbonate, dimethyl carbonate, toluene, dimethyl ether, diethyl ether, diglyme, tetraglyme and the like.

Specific examples of strong polar solvents include hexamethyl phosphoric triamide, gamma-butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl-2-oxazolidone , Dimethyl formamide, sulfolane, dimethyl acetamide or dimethyl sulfoxide, dimethyl sulfate, ethylene glycol diacetate, dimethyl sulfite, ethylene glycol sulfite and the like.

Specific examples of lithium protective solvents include tetrahydrofuran, ethylene oxide, dioxolane, 3,5-dimethyl isoxazole, 2,5-dimethyl furan, furan, 2-methyl furan, 1,4-oxane, 4-methyldioxolane Etc.

As the lithium salt as the electrolytic salt, one or more of lithium trifluoromethanesulfonimide or lithium triflate may be used. At this time, the concentration of the lithium salt is preferably used in the range of 0.6 to 2.0M, more preferably in the range of 0.7 to 1.6M. If the concentration of the lithium salt is less than 0.6M, the conductivity of the electrolyte is lowered, and the electrolyte performance is lowered. If the concentration of the lithium salt is higher than 2.0M, the viscosity of the electrolyte is increased to reduce the mobility of lithium ions.

As in the present invention, in the (polyester) polyol having three or more hydroxyl groups, one or more hydroxyl groups are converted into (meth) acrylic acid esters, and the unreacted hydroxyl groups, which are not substituted with some of the (meth) acrylic acid esters, are radically reactive. By forming a polymer of a poly (ester) (meth) acrylate substituted with a non-acrylate group, an acrylate group not involved in the polymerization reaction remains in the unreacted acrylic group to promote deterioration of low temperature and high rate life characteristics of a lithium-sulfur battery. It can eliminate the factor that causes it.

The polyester polyol having three or more hydroxyl groups may be all synthesized by a method known in the art, for example, hydroxycarboxylic acid condensation polymerization, ring-opening polymerization of lactone, or condensation polymerization of glycol and dicarboxylic acid, Moreover, you may use a commercially available thing. Specific examples of the polyester polyol having three or more hydroxyl groups include trialkylols such as trimethylol, triethylol, and tripropylol, various glycerols, pentaethytitol, and dipenta Erythritol, such as erythritol, etc. are mentioned.

After substituting some or all of the hydroxyl groups of such polyester polyols with (meth) acrylic acid esters, some unreacted hydroxyl groups, which were left unsubstituted, were replaced with groups having no radical reactivity, thereby making the poly (ester) (meth) of the present invention. Prepare acrylates or polymers thereof.

The method of substituting some or all of the hydroxyl groups by the (meth) acrylic acid ester can be carried out under general esterification reaction conditions. For example, the method of condensing polyester polyol and (meth) acrylic acid halide in presence of a base catalyst, and the method of condensing polyester polyol and (meth) acrylic acid in presence of an acid catalyst are mentioned.

First, the method of condensing a polyester polyol and (meth) acrylic-acid halide in presence of a base catalyst is demonstrated.

As the (meth) acrylic acid halide, acrylic acid chloride or (meth) acrylic acid chloride is suitable, and the amount of the (meth) acrylic acid halide is used in an amount of 0.5 to 5 equivalents based on 1 mole of the hydroxyl group of the polyester polyol.

As the base catalyst, organic bases such as triethylamine, pyridine, dimethylaminopyridine and diazabicyclo undecene or inorganic bases such as lithium carbonate, sodium carbonate, potassium carbonate, lithium hydroxide, sodium hydroxide and potassium hydroxide can be used. The base catalyst is suitably used in an amount of 1.0 to 5 equivalents based on the (meth) acrylic acid halide.

The reaction can be carried out in the presence or absence of a solvent. Solvents that can be used include halogenated hydrocarbons such as dichloroethane, chloroform and dichloroethane, aromatic hydrocarbons such as benzene, toluene and xylene, saturated hydrocarbons such as hexane, heptane, decane and cyclohexane, diethyl ether, diisopropyl ether and tetra Ethers, such as hydrofuran, can be used.

The reaction can generally be carried out at -20 to 100 ° C, preferably at -5 to 50 ° C.

In the method of condensing a polyester polyol and (meth) acrylic acid, 0.1-10 mol is suitable for the usage-amount of (meth) acrylic acid with respect to 1 mol of hydroxyl groups of a polyester polyol. As the acid catalyst, sulfuric acid, methanesulfonic acid, p-toluenesulfonic acid, hydrochloric acid, phosphoric acid, phosphotungstic acid salt, phosphomolybdic acid and the like may be used. The amount of acid catalyst used is preferably 0.01 to 10% by weight based on the polyester polyol.

The reaction may use an inert solvent such as aromatic hydrocarbons such as benzene, toluene and xylene, or saturated hydrocarbons such as hexane, heptane, decane and cyclohexane, and it is preferable to azeotropically remove the water produced after the reaction. . The amount of the solvent used is 0.1 to 10 parts by weight based on the polyester polyol. Reaction temperature is 50-200 degreeC, Preferably it is 70-150 degreeC.

In the above-described method, part or all of the hydroxyl groups contained in the polyester polyol are substituted with (meth) acrylic acid esters. Substituted (meth) acrylic acid esters are -OC (= 0) (CH ₂ ) _n OC (= 0) CH = CH ₂ or -OC (CH ₂ ) _n C (CH ₃ ) = CH ₂ (n is from 1 to 20) Is an integer of).

Subsequently, the unreacted hydroxyl group remaining unsubstituted is substituted with a group having no radical reactivity.

The radical non-reactive group is an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 20 carbon atoms, or an ether group having 1 to 20 carbon atoms, and particularly -OC (= O) (CH ₂ ) ₂ CH ₃ ,- O (C═O) Ar, wherein Ar is an unsubstituted or substituted aromatic hydrocarbon group, -OC (═O) (CH ₂ ) _n O (CH ₂ ) _n (CH ₃ ) (n is 1 to 20 ), -O (C = O) (CH ₂ ) _n OC (= O) (CH ₂ ) _n CH ₃ (n is an integer from 1 to 20) or -O (C = O) CH = CH ₂ It is preferable.

As an example of the method, the resulting hydroxyl group is esterified using a compound comprising a group having no radical reactivity equal to or more than the equivalent of the remaining hydroxyl group. The compound containing a group having no radical reactivity may be a carbonyl acid or halogen compound having an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 20 carbon atoms, an ether group having 1 to 20 carbon atoms, or an ester having 1 to 20 carbon atoms. Carbonyl or halogen compounds of the group skeleton can be used. Representative examples of the compound containing a group having no radical reactivity include butylcarboxylic acid.

Alternatively, a modified polyester polyol obtained by ring-opening polymerization of a polyester polyol together with a lactone compound may be used in the esterification step. In the case of using the modified polyester polyol, it is possible to adjust the length of the hydroxyl group acting as a reactor in the molecular backbone, which is effective in changing the physical properties of the electrolyte as a final product. As the lactone compound, ε-caprolactone, γ-caprolactone and the like can be used. The lactone compound can be used in the ratio of arm to the total number of hydroxyl groups of the polyester polyol. Therefore, the amount of the lactone-based compound used in the present invention is not particularly limited, but considering the solubility of the modified polyester polyol in which the lactone-based compound is substituted, the size of the molecule, and the like, it is 1000 mol based on the total hydroxyl groups of the polyester polyol. % Or less, especially 0.01-10 mol is preferable with respect to 1 mol of hydroxyl groups of a polyol.

As the catalyst for promoting the ring-opening polymerization reaction, an organic titanium compound, an organic tin compound, an organic carboxylic acid metal salt of various metals, or the like can be used. Examples of the organic titanium compound include tetrapropyl titanate.

The amount of the catalyst added is preferably 0.001 to 1 parts by weight based on 100 parts by weight of the lactone compound.

In the case of using the modified polyester polyol, an esterification reaction is carried out by adding together acrylic acid and its derivatives and a compound containing a group having no radical reactivity to the modified polyester polyol. By adjusting the molar ratio of the compound containing the acrylic acid and its derivatives and the group having no radical reactivity, some or all of the hydroxyl groups contained in the modified polyester polyol are substituted with (meth) acrylic acid ester, and the remaining part The reactive hydroxyl groups can control the rate at which they are substituted with groups that are not radically reactive.

Some or all of the hydroxyl groups of the polyester polyols are converted into (meth) acrylic acid esters by the above-described method, and the unreacted hydroxyl groups, which are not substituted by the (meth) acrylic acid esters of the remaining unreacted hydroxyl groups, are substituted with groups that are not radically reactive. Poly (ester) (meth) acrylate or its polymer is produced.

Preferred examples of the poly (ester) (meth) acrylate may be represented by the following formula (3).

[Formula 3]

As for the molar ratio of the said (meth) acrylic acid ester and the group which is not radically reactive, 1: 01-1: 100 are preferable. When the molar ratio of the group having no radical reactivity with the (meth) acrylic acid ester is less than 1: 0.01, the degree of crosslinking of the polymer is increased, and the ion conduction property is reduced. It is not desirable to form.

The polymer electrolyte of the present invention also includes a peroxide having 6 to 40 carbon atoms. This peroxide is a substance that initiates the polymerization of the polyester (meth) acrylate polymer, which is a polar portion (hydrophilic portion) -C (= 0) -OOC (= 0) and a nonpolar portion (hydrophobic). Moiety) to an aliphatic or aromatic hydrocarbon group region having 6 to 40 carbon atoms.

In addition, the peroxide having 6 to 40 carbon atoms may be added to the electrolyte instead of nitrogen (N ₂ ), which is an inert gas having no solubility in the electrolyte, which is a polar solvent, as compared to the case of using an azobenzene-based initiator such as 2,2'-azoisobutyronitrile. Since the CO ₂ gas having excellent affinity is generated, the initial charge and discharge efficiency of the lithium battery is improved.

The initial charge and discharge efficiency of a lithium-sulfur battery is closely related to the formation of a film formed on the electrode, particularly a film formed on the surface of the negative electrode. The shape of this film is directly related to the overall performance of the battery. When the surface of the negative electrode plate is observed in the state of charge after the initial charge / discharge cycle has progressed, the surface of the negative electrode plate is uniform if the battery has excellent initial charge and discharge efficiency. In addition, when the initial charge and discharge efficiency is poor, it can be seen that a large amount of lithium is precipitated at various places on the surface of the negative electrode plate.

Specific examples of the peroxide having 6 to 40 carbon atoms include isobutyl peroxide, lauronyl peroxide, benzoyl peroxide, m-toluoyl peroxide, t-butyl peroxy-2-ethyl hexano Eights, t-butyl peroxy bibarate, t-butyloxyneodecanate, diisopropyl peroxy dicarbonate, diethoxy peroxy dicarbonate, bis- (4-t-butylcyclohexyl) peroxy dicarbonate, At least one selected from the group consisting of dimethoxy isopropyl peroxy dicarbonate, dicyclohexylperoxy dicarbonate, and 3,3,5-trimethylhexanoyl peroxide. In particular, lauroyl peroxide or benzoyl peroxide is preferred.

The amount of the peroxide is preferably 0.3 to 5 parts by weight based on 100 parts by weight of the poly (ester) (meth) acrylate. When the amount of the peroxide is less than 0.3 part by weight, the polymerization reactivity is lowered. When the amount of the peroxide is more than 5 parts by weight, the molecular weight of the polymer may be excessively large, resulting in poor mechanical properties as the polymer electrolyte.

It is preferable that the weight average molecular weights of the polymer of the said poly (ester) (meth) acrylate are 300-100,000.

Hereinafter, a method of manufacturing a lithium-sulfur battery using the polymer electrolyte of the present invention will be described.

A monomer having a methacrylate group, an organic peroxide having 6 to 40 carbon atoms, and an electrolyte are mixed to prepare a composition for forming a polymer electrolyte.

The polymer electrolyte in the form of a film may be prepared using the composition for forming a polymer electrolyte, or the polymer composition may be polymerized in a battery after the composition is introduced into a battery case as it is. In the case of manufacturing in the form of a film, it is preferable to have a thickness of 5 to 90 μm because of excellent properties such as ion conductivity of the polymer electrolyte.

The polymer electrolyte in the form of a film is prepared by coating the composition on a supporting substrate, then performing a polymerization reaction by selectively heat treatment or UV irradiation, and peeling off the film produced on the supporting substrate. Here, the heat treatment temperature is different depending on the half-life of the initiator of the radical reaction used, but 40 to 110 ℃ is suitable, but more preferably 60 to 85 ℃. If the temperature of the thermal polymerization is too low, a large amount of unreacted monomer remains or the reaction time becomes long, resulting in the cost of the manufacturing process. In addition, when the reaction temperature is too high, a problem arises in that the amount of decomposition of lithium salts is greatly increased. As such, when the polymer electrolyte in the form of a film is used, a separate separator is not required since the polymer electrolyte also plays a role of a separator in a battery assembly process.

In the case of a chemical gel electrolyte which polymerizes in a battery, a battery is manufactured by inserting a positive electrode, a negative electrode, and an electrode group in which a separator is inserted between the positive electrode and the negative electrode in a battery case, and injecting the polymer electrolyte forming composition. . The battery is left at 70 to 80 ° C. for 2 to 6 hours. At this time, a polymerization reaction of the composition for forming a polymer electrolyte occurs to form a polymer electrolyte. As the separator, a polyethylene separator, a polypropylene separator, a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

In the positive electrode, the positive electrode active material is inorganic sulfur (S ₈ , elemental sulfur), Li ₂ S _n (n ≧ 1), an organic sulfur compound or a carbon-sulfur polymer [(C ₂ S _x ) _n , where x = 2.5- 50, n ≥ 2] can be used. As the negative electrode active material in the negative electrode, a lithium alloy electrode such as a lithium metal or a lithium / aluminum alloy is used.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

(Comparative Preparation Examples 1 to 8)

Poly (ethylene glycol) dimethacrylate (PEGDMA) having an average molecular weight of 330 was added to dimethoxyethane / 1,3-dioxolane (80/20 volume ratio) in which 1M LiN (SO ₂ CF ₃ ) ₂ as an electrolyte was dissolved. Stir for 10 minutes. A small amount of azobisisobutyronitrile (AIBN), an initiator, was added to the mixture and heated at 75 ° C. for gelation reaction for 4 hours. The results are shown in Table 1 below.

Composition ratio (g) Gelation results Electrolyte PEGDMA AIBN Comparative Production Example 1 30 One 0.01 No gelation but increased viscosity Comparative Production Example 2 25 One 0.01 No gelation but increased viscosity Comparative Production Example 3 20 One 0.01 No gelation but increased viscosity Comparative Production Example 4 15 One 0.01 No gelation but increased viscosity Comparative Production Example 5 12.5 One 0.01 Gelled Comparative Production Example 6 10 One 0.01 Gelled Comparative Production Example 7 7.5 One 0.01 Gelled Comparative Production Example 8 5 One 0.01 Gelled

As shown in Table 1, the amount of the electrolyte solution compared to the monomer was gelated at 1250% or less, and the viscosity was increased without gelation at 1500% or more.

The result prepared by the method of Comparative Preparation Example 6 was made into a disk-shaped specimen and bonded with a stainless steel electrode to measure the ionic conductivity at room temperature. The result was an excellent ion conductivity of 2.0 × 10 ⁻³ (S / cm).

(Production Examples 1 to 7)

To a mixture of 1 mol of dipentaerythritol, 2 mol of ε-caprolactone, and toluene solvent, a tetrapropyl titanate catalyst was added in an amount of 0.01% by weight of the dipentaerythritol and reacted at 50 DEG C. A dipentaerytriol monomer was synthesized wherein is substituted with an "ε-caprolactone residue". Subsequently, 4 moles of acrylic acid and 2 moles of butylcarboxylic acid are reacted with 1 mole of the monomer to substitute -OC (= O) (CH ₂ ) ₅ OC (= O) instead of 4 hydroxyl groups (-OH) present at the terminal of the monomer. CH ₂ = CH ₂ is replaced with, the other two hydroxyl groups (-OH) instead of _{-OC (= O) (CH 2} ) 3 CH 3 to obtain a polyester hexa acrylate compound (PEHA) substituted.

The polyester hexaacrylate-based compound was added to dimethoxyethane / 1,3-dioxolane (80/20 vol. Ratio) in which electrolyte solution 1M LiN (SO ₂ CF ₃ ) ₂ was dissolved and stirred for 10 minutes. A small amount of initiator AIBN was added to the mixture and heated at 75 ° C. for gelation reaction for 4 hours. The results are shown in Table 2 below.

Creation costs Gelation results Electrolyte Polyester hexaacrylate compound AIBN Preparation Example 1 60 One 0.01 Gelled but with small amount of leak Preparation Example 2 50 One 0.01 Gelled but with small amount of leak Preparation Example 3 40 One 0.01 Gelled but with small amount of leak Preparation Example 4 30 One 0.01 Gelled Preparation Example 5 20 One 0.01 Gelled Preparation Example 6 10 One 0.01 Gelled Preparation Example 7 5 One 0.01 Gelled

As shown in Table 2, when the amount of the electrolyte solution compared to the monomer is less than 3000%, the gelation is good, so that the phase separation phenomenon from which the electrolyte escapes from the polymer matrix is not observed. Escaped phase separation was observed. That is, a small amount of leakage occurred.

In order to measure the ion conduction characteristics of Preparation Examples 1 and 4, disk-shaped specimens were bonded to a stainless steel electrode, and the ion conductivity at room temperature was measured. As a result, Preparation Example 4 exhibited excellent ion conductivity of 2.5 × 10 ^-3 (S / cm), and Preparation Example 1 of 3.4 × 10 ^-3 (S / cm).

(Comparative Preparation Example 8): When polyethylene glycol divinyl ether (PEGDVE, molecular weight 240) was used as a monomer

In this case, the amount of electrolyte to monomer was varied up to 500-3000% under the same conditions, but gelation did not occur at all composition ratios.

(Comparative Example 1)

A positive electrode active material slurry was prepared by mixing 67.5 wt% elemental sulfur, 11.4 wt% Super-P conductive material, and 21.1 wt% polyethylene oxide binder in an acetonitrile solvent. This slurry was coated on a carbon-coated Al current collector. The coated current collector was rolled to prepare a positive electrode plate. The prepared positive electrode plate was dried at room temperature for at least 2 hours, and then dried at 50 ° C. for at least 12 hours.

The positive plate was placed inside the pouch and the separator was covered on the positive plate. After covering the lithium foil negative electrode on this separator, the pouch was sealed, leaving only the electrolyte injection hole. Dimethoxyethane / 1,3-dioxolane (80/20 vol. Ratio) electrolyte in which 1M LiN (SO ₂ CF ₃ ) ₂ was dissolved was added to the electrolyte inlet. The electrolyte injection port was sealed to prepare a lithium-sulfur battery (design capacity: 838 mAh / g capacity per mass of sulfur).

(Comparative Examples 2 to 7)

Except for injecting the composition for forming the polymer electrolyte into the electrolyte injection hole was carried out in the same manner as in Comparative Example 1. The polymer electrolyte composition was prepared by adding PEGDMA and AIBN to the liquid electrolyte according to the composition shown in Table 3 below. As the liquid electrolyte solution, a dimethoxyethane / 1,3-dioxolane (80/20 volume ratio) solution in which 1M LiN (SO ₂ CF ₃ ) ₂ was dissolved was used.

The battery manufactured by the method of Comparative Examples 1 to 7 was charged and discharged under the following conditions to measure the rate-specific characteristics and the life characteristics. The results are shown in Table 3 below.

0.1C discharge once (final condition 1.5V)

Two 0.2C charges (end condition: 120% of design capacity or 2.8V)

0.1C discharge (end condition 1.5V)

3 times: 0.2C charge (end condition: 120% of design capacity or 2.8V)

0.2C discharge (final condition 1.5V)

4 times (1 life): 0.2C charge (end condition: 120% of design capacity or 2.8V)

0.5C discharge (end condition 1.5V)

5 or more: 4 conditions repeated

Creation costs Rate-specific characteristics (mAh / g) 1 time 0.5C life (mAh / g) 0.5C lifespan 20 times (mAh / g) % Of lifespan Electrolyte PEGDMA AIBN First discharge 0.1C 0.2C 0.5C Comparative Example 1 10 0 0 1522 797 793 804 804 877 109 Comparative Example 2 25 One 0.01 1058 843 709 562 562 473 84 Comparative Example 3 20 One 0.01 1097 835 670 517 517 453 88 Comparative Example 4 15 One 0.01 1099 839 647 500 500 403 81 Comparative Example 5 12 One 0.01 918 750 499 437 437 340 78 Comparative Example 6 10 One 0.01 1004 825 639 495 495 310 62 Comparative Example 7 8 One 0.01 827 820 610 462 462 278 60

In Table 3, compared to the battery of Comparative Example 1 using only the liquid electrolyte, the cells of Comparative Examples 2 to 7 using the chemical gel showed the performance of both the capacity and the life is reduced, the effect on the expected life improvement I couldn't.

(Comparative Examples 8 to 11)

Except for injecting a composition for forming a polymer electrolyte into the electrolyte injection hole was carried out in the same manner as in Comparative Example 1. The polymer electrolyte composition was prepared by adding PEGDMA and AIBN to the liquid electrolyte according to the composition shown in Table 4 below. As the liquid electrolyte solution, a dimethoxyethane / 1,3-dioxolane (80/20 volume ratio) solution in which 1M LiN (SO ₂ CF ₃ ) ₂ was dissolved was used.

The batteries prepared by the methods of Comparative Examples 1 to 4, 6, 8 and 11 were charged 100 times under 0.2C charging (end condition: 120% or 2.8V of design capacity) and 0.5C discharge (end condition 1.5V). After discharging, the battery was dismantled, and then the lithium electrode was exposed to the air, followed by spontaneous ignition. The results are shown in Table 4 below.

Creation costs Gelation results Result of dismantling after life evaluation Electrolyte PEGDMA AIBN Comparative Example 8 30 One 0.01 No gelation but increased viscosity 2-cell ignition Comparative Example 2 25 One 0.01 No gelation but increased viscosity 1 cell ignition Comparative Example 3 20 One 0.01 No gelation but increased viscosity Unfired Comparative Example 4 15 One 0.01 No gelation but increased viscosity Unfired Comparative Example 9 12.5 One 0.01 Gelled Unfired Comparative Example 6 10 One 0.01 Gelled Unfired Comparative Example 10 7.5 One 0.01 Gelled Unfired Comparative Example 11 5 One 0.01 Gelled Unfired Comparative Example 1 10 0 0 Liquid electrolyte 5-cell ignition

It can be seen that the batteries of Comparative Examples 2 to 4, 6, 8 to 11 using the chemical gels were greatly improved in spontaneous ignition phenomenon compared to the batteries of Comparative Example 1 using the liquid electrolyte. This is because the film of the polymer film is formed on the lithium surface to block the contact between the moisture and the lithium surface.

(Examples 1 and 2)

PEHA prepared in Experimental Example 1 was used instead of PEGDMA, and the same procedure as in Comparative Example 2 was conducted except that the amount thereof was changed as shown in Table 5 below.

Charge-discharge was performed in the same manner as the charge-discharge conditions described above for the lithium-sulfur battery prepared by the method of Examples 1 to 2. The results are shown in Table 5 below, and the results of Comparative Example 1 are also shown.

Creation costs Rate-specific characteristics (mAh / g) 1 time 0.5C life (mAh / g) 0.5C lifetime 300 times (mAh / g) % Of lifespan 0.5C lifespan 400 times (mAh / g) % Of lifespan Electrolyte PEHA AIBN First discharge 0.1C 0.2C 0.5C Example 1 60 One 0.01 1347 796 762 708 708 398 56 358 51 Example 2 30 One 0.01 1264 724 651 563 563 Not carried Comparative Example 1 10 0 0 1522 797 793 804 804 313 39

As can be seen in Table 5, the battery of Example 1 has significantly improved the capacity reduction phenomenon according to the charge and discharge cycle compared to Comparative Example 1 using only the liquid electrolyte, that is, the cycle life characteristics are very excellent. Comparing Example 1 and Example 2, it can be seen that Example 1, which has a higher amount of electrolyte, can significantly reduce the capacity reduction phenomenon caused by the charge / discharge cycle compared to Example 2.

Comparing Example 1 with Comparative Example 1, Example 1 showed a capacity almost similar to Comparative Example 1 at 0.1C and 0.2C, and dropped only slightly at 0.5C. However, in the life test, it can be seen that the service life is 17% better than the 39% of Comparative Example 1 from 300 to 56%. In addition, Example 1 shows that the life reduction rate is smaller as the life progresses, showing excellent life characteristics of only 51% at 400 times and a capacity reduction of only 5% at 100 times from 300 to 400 times. This result is judged to be due to the suppression of corrosion of lithium as a negative electrode in a chemical gel battery using a polyester hexaacrylate-based compound, which can be easily considered by looking at the state of the negative electrode dismantled after the end of the life test.

After completion of the cycle life test, the surface photographs of the negative electrodes obtained by disassembling the batteries of Example 1 and Comparative Example 1 are shown in FIGS. 1 and 2, respectively. It can be seen that the negative electrode of Example 1 after 400 times of life is considerably clean (FIG. 1), and that the negative electrode of Comparative Example 1 after 300 times of life is in a state in which lithium is damaged such as dendrite formation (FIG. 2).

(Examples 3 to 6 and Reference Example 1)

PEHA prepared in Experimental Example 1 was used instead of PEGDMA, and the same amount as in Comparative Example 2 was used except that the amount thereof was changed as shown in Table 6 below.

Creation costs Gelation results Results of dismantling after evaluating life Electrolyte Poly (ester) (meth) acrylate AIBN Example 1 60 One 0.01 Gelled but with small amount of leak 1 cell ignition Example 3 50 One 0.01 Gelled but with small amount of leak Unfired Example 4 40 One 0.01 Gelled but with small amount of leak Unfired Example 5 30 One 0.01 Gelled Unfired Example 6 20 One 0.01 Gelled Unfired Example 2 10 One 0.01 Gelled Unfired Reference Example 1 5 One 0.01 Gelled Unfired Comparative Example 1 10 0 0 Liquid electrolyte 5-cell ignition

The spontaneous ignition phenomenon was greatly improved in the batteries of Examples 1 to 6 using the chemical gel compared with the batteries of Comparative Example 1 using the liquid electrolyte. This is because a film of polymer film is formed on the lithium surface to block the contact between moisture and the lithium surface.

In addition, the battery life characteristics of Examples 1 to Comparative Example 1 are shown in Table 6. Charging and discharging conditions were performed 300 times or more by 0.2C charging (end condition: 120% or 2.8V of design capacity) and 0.5C discharge (end condition 1.5V). The results are shown in Table 7 and FIG.

Creation costs Design capacity (mAh / g) 1 capacity (mAh / g) 300 times capacity (mAh / g) % Of design capacity 400 times capacity (mAh / g) % Of design capacity Electrolyte Poly (ester) (meth) acrylate AIBN Example 1 60 One 0.01 838 1215 425 50.7 383.0 45.7 Comparative Example 1 10 0 0 838 1351 313 37.4

The battery of Example 1 using a chemical gel was slightly inferior to the battery of Comparative Example 1 using a liquid electrolyte, but it was found that the life characteristics were much better than that of Comparative Example 1.

This is because the active movement of the electrolyte solvent is greatly suppressed in the chemical gel battery, and thus the polysulfide, which is the positive electrode active material, is largely suppressed from moving out of the positive electrode mixture and moved to the negative electrode, and the electrolyte solvent itself also significantly inhibits lithium corrosion. I think. This can easily be considered by looking at the state of the cathode which disassembled the cell after the end of life.

The polymer electrolyte of the present invention can provide a lithium-sulfur battery with improved cycle life characteristics.

Claims (31)

 Of the hydroxyl groups of the (polyester) polyols having three or more hydroxyl groups (-OH), some or all of them are substituted with (meth) acrylic acid esters, and some unreacted hydroxyl groups not substituted with (meth) acrylic acid esters are radically reactive. Monomers comprising poly (ester) (meth) acrylates substituted with no groups; Peroxides having 6 to 40 carbon atoms; And Electrolyte containing organic solvent and lithium salt Including, The mixing ratio of the electrolyte solution and the monomer is a polymer electrolyte for a lithium-sulfur battery is more than 10, 200 or less in weight ratio: 1. delete delete delete The polymer electrolyte for lithium-sulfur battery according to claim 1, wherein a mixing ratio of the electrolyte solution and the monomer is 40 to 150: 1 by weight. The polymer electrolyte for lithium-sulfur battery according to claim 5, wherein a mixing ratio of the electrolyte solution and the monomer is 60 to 120: 1 by weight. The group according to claim 1, wherein the group having no radical reactivity is a group consisting of an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aromatic hydrocarbon group having 5 to 20 carbon atoms, an ether group having 1 to 20 carbon atoms, and an ester group having 1 to 20 carbon atoms. The polymer electrolyte for lithium-sulfur battery is selected from. 8. The radical non-reactive group of claim 7, wherein the group is free of -OC (= 0) (CH ₂ ) ₃ CH ₃ , -OC (= 0) Ar, wherein Ar is an unsubstituted or substituted aromatic hydrocarbon group, -OC (= O) (CH ₂ ) _n O (CH ₂ ) _n CH ₃ (n is an integer from 1 to 20), -O (C = O) (CH ₂ ) _n OC (= O) (CH ₂ ) _n CH ₃ (n is an integer of 1 to 20) and -O (C = O) CH = CH _{2 It} is selected from the group consisting of a polymer electrolyte for a sulfur-sulfur battery. The method of claim 1, wherein the (meth) acrylic acid ester is -OC (= 0) (CH ₂ ) _n OC (= 0) CH = CH ₂ or -OC (= 0) (CH ₂ ) _n OC (= 0). A polymer electrolyte for a lithium-sulfur battery, wherein C (CH ₃ ) = CH ₂ (n is an integer of 1 to 20). The polymer electrolyte for lithium-sulfur battery according to claim 1, wherein the monomer is a compound having at least one carbon-carbon double bond at the monomer terminal. delete The polymer electrolyte for a lithium-sulfur battery of claim 1, wherein the monomers are represented by the following Chemical Formulas 1-2. [Formula 1]

[Formula 2]

(In the above formula 1 and 2, R ₁ is H or C ₁ to C ₆ alkyl group, n is an integer of 1 to 100,000, R ₂ is H or C ₁ to C ₆ alkyl group) The polymer electrolyte for a lithium-sulfur battery according to claim 1, wherein the molar ratio of the methacrylic acid ester and the group having no radical reactivity is from 1: 0.01 to 1: 100. The method of claim 1, wherein the C 6 -C 40 peroxide isobutyl peroxide, lauroyl peroxide, benzoyl peroxide, m-toluoyl peroxide, t-butyl peroxy-2-ethyl hexanoate, t -Butyl peroxy bibarate, t-butyloxy neodecanoate, diisopropyl peroxy dicarbonate, diethoxy peroxy dicarbonate, bis- (4-t-butylcyclohexyl) peroxy dicarbonate, dimethoxy A polymer electrolyte for a lithium-sulfur battery, wherein the polymer electrolyte is at least one peroxide selected from the group consisting of isopropyl peroxy dacarboxylate, dicyclo hexylperoxy dicarbonate, and 3,3,5-trimethylhexanoyl peroxide. The polymer electrolyte of claim 1, wherein the peroxide is present in an amount of 0.3 to 5 parts by weight based on 100 parts by weight of the monomer. The polymer electrolyte for lithium-sulfur battery according to claim 1, wherein the polyester polyol is at least one polyol selected from the group consisting of trialkylols, glycerols and erythritols. A positive electrode comprising at least one positive electrode active material selected from the group consisting of elemental sulfur, sulfur compounds and mixtures thereof; A material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reacting with lithium ions to form a lithium-containing compound reversibly, and a negative electrode active material selected from the group consisting of lithium metals and lithium alloys Cathode; And  Of the hydroxyl groups of the (polyester) polyols having three or more hydroxyl groups (-OH), some or all of them are substituted with (meth) acrylic acid esters, and some unreacted hydroxyl groups not substituted with (meth) acrylic acid esters are radically reactive. Monomers containing poly (ester) (meth) acrylates substituted with no groups, peroxides of 6 to 40 carbon atoms; And an electrolyte comprising an organic solvent and a lithium salt, wherein the mixing ratio of the electrolyte and the monomer is in a weight ratio of more than 10 and less than or equal to 200: 1 Lithium-sulfur battery comprising a. delete delete The lithium-sulfur battery of claim 15, wherein a mixing ratio of the electrolyte solution and the monomer is 40 to 150: 1 by weight. The lithium-sulfur battery of claim 20, wherein a mixing ratio of the electrolyte solution and the monomer is 60 to 120: 1 by weight. 22. The group according to claim 21, wherein the group having no radical reactivity is composed of an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an aromatic hydrocarbon group having 6 to 20 carbon atoms, an ether group having 1 to 20 carbon atoms, and an ester group having 1 to 20 carbon atoms. Lithium-sulfur battery is selected from. 23. The non-radically reactive group of claim 22, wherein the group is free of -OC (= 0) (CH ₂ ) ₃ CH ₃ , -OC (= 0) Ar, wherein Ar is an unsubstituted or substituted aromatic hydrocarbon group, -OC (= O) (CH ₂ ) _n O (CH ₂ ) _n CH ₃ (n is an integer from 1 to 20), -O (C = O) (CH ₂ ) _n OC (= O) (CH ₂ ) _n CH ₃ (n is an integer of 1 to 20) and -O (C = O) CH = CH ₂ is a lithium-sulfur battery. 18. The method of claim 17, wherein the (meth) acrylic acid ester is -OC (= 0) (CH ₂ ) _n OC (= 0) CH = CH ₂ or -OC (= 0) (CH ₂ ) _n OC (= 0). Li-sulfur battery wherein C (CH ₃ ) = CH ₂ (n is an integer from 1 to 20). delete The lithium-sulfur battery of claim 17, wherein the monomers are represented by Chemical Formulas 1 to 2 below. [Formula 1]

[Formula 2]

(In the above formula 1 and 2, R ₁ is H or C ₁ to C ₆ alkyl group, n is an integer of 1 to 100,000, R ₂ is H or C ₁ to C ₆ alkyl group) 25. The lithium-sulfur battery of claim 24, wherein the molar ratio of the methacrylic acid ester and the group having no radical reactivity is from 1: 0.01 to 1: 100. 18. The method of claim 17, wherein the C 6 -C 40 peroxide isobutyl peroxide, lauroyl peroxide, benzoyl peroxide, m-toluoyl peroxide, t-butyl peroxy-2-ethyl hexanoate, t -Butyl peroxy bibarate, t-butyloxy neodecanoate, diisopropyl peroxy dicarbonate, diethoxy peroxy dicarbonate, bis- (4-t-butylcyclohexyl) peroxy dicarbonate, dimethoxy A lithium-sulfur battery that is at least one peroxide selected from the group consisting of isopropyl peroxy dacarbonate, dicyclo hexylperoxy dicarbonate, and 3,3,5-trimethylhexanoyl peroxide. The lithium-sulfur battery of claim 17, wherein the peroxide is present in an amount of 0.3 to 5 parts by weight based on 100 parts by weight of the monomer. 18. The lithium-sulfur battery of claim 17, wherein said polyester polyol is at least one polyol selected from the group consisting of trialkylols, glycerols and erythritols. 18. The method of claim 17 wherein the positive active material is elemental sulfur, Li ₂ S _n (n ≥1), dissolved in the cache solrayiteu _{(catholyte) Li 2 S n (} n ≥1), organic sulfur compounds, and carbon-sulfur polymer ( (C ₂ S _x ) _n : x-2.5 to 50, n ≥ 2) lithium-sulfur battery which is at least one positive electrode active material selected from the group consisting of.

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