KR20190060184A - Cathode for lithium-sulfur battery, method for preparing the same, and lithium-sulfur battery comprising the same - Google Patents

Abstract

The present invention provides a positive electrode for a lithium-sulfur battery, a method for manufacturing the same, and a battery comprising the same. The positive electrode for a lithium-sulfur battery comprises: a positive electrode active material layer containing sulfur; and a coating layer comprising sulfurized polyacrylonitrile (S-PAN) formed by heat-treating a mixture of sulfur and polyacrylonitrile on all or part of a surface of the positive electrode active material layer.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode for a lithium-sulfur battery, a method for producing the positive electrode, and a lithium-sulfur battery including the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a positive electrode for a lithium-sulfur battery, a method for producing the same, and a lithium-sulfur battery including the same.

As the application fields of energy storage technology extend to mobile phones, tablets, laptops and camcorders, electric vehicles (EV) and hybrid electric vehicles (HEV), research and development of electrochemical devices for energy storage Is increasing.

In particular, the development of secondary batteries such as lithium-sulfur batteries capable of charging and discharging has become a focus of attention. In recent years, research and development on the design of new electrodes and batteries have been carried out in order to improve the capacity density and specific energy of secondary batteries. .

Lithium-sulfur (Li-S) batteries have a high energy density and are becoming popular as next-generation secondary batteries that can replace lithium-ion batteries. In the inside of the lithium-sulfur battery, a reduction reaction of sulfur and an oxidation reaction of lithium metal occur at the discharge. From the S ₈ of the cyclic structure, sulfur has a linear structure of lithium polysulfide (Li ₂ S ₂ , Li ₂ S ₄ , Li ₂ S ₆ , Li ₂ S ₈ ). This lithium-sulfur battery has a characteristic of exhibiting a stepwise discharge voltage until the polysulfide (PS) is completely reduced to Li ₂ S.

However, the lithium-sulfur battery has a large problem that the capacity is reduced due to the polysulfide (PS) shuttling phenomenon at the anode side. That is, since long-chain lithium polysulfide (Li ₂ S ₆ , Li ₂ S ₈ ) has a high solubility in the organic electrolytic solution, it causes PS shuttling toward the negative electrode through the electrolytic solution, A decrease in capacity due to the irreversible loss of the cathode active material, and a reduction in battery life due to the deposition of sulfur particles on the lithium surface.

In order to solve the above problems, various researches such as adding a PS adsorbing material to a positive electrode composite or modifying a separator made of existing PE have been conducted, but a clear solution has not been proposed yet.

Korean Patent Publication No. 10-2016-0141615

Disclosure of the Invention The present invention has been conceived to solve the above-described problems of the prior art, and it is an object of the present invention to provide an electrode in which a coating layer capable of preventing dissolution of lithium polysulfide is formed on the surface of a cathode active material layer containing sulfur, A lithium-sulfur battery anode capable of improving life characteristics, a method for producing the same, and a lithium-sulfur battery including the same.

In order to achieve the above object,

A cathode active material layer containing sulfur; And

(S-PAN) formed by heat-treating a mixture of sulfur and polyacrylonitrile formed on all or a part of the surface of the positive electrode active material layer, and a coating layer comprising lithium sulfide and polyacrylonitrile - Provide a positive electrode for a sulfur battery.

In addition,

(a) preparing a sulfided polyacrylonitrile (S-PAN);

(b) preparing a coating composition comprising the sulfated polyacrylonitrile (S-PAN) of step (a);

(c) applying a cathode active material containing sulfur on the current collector to form a cathode active material layer; And

(d) coating the surface of the cathode active material layer prepared in the step (c) with the coating composition prepared in the step (b) to form a coating layer. ≪ / RTI >

Further, according to the present invention,

A negative electrode comprising lithium metal or a lithium alloy as a negative electrode active material;

A positive electrode for a lithium-sulfur battery according to any one of claims 1 to 9;

A separator provided between the anode and the cathode; And

A lithium-sulfur battery comprising: an electrolyte;

The positive electrode for a lithium-sulfur battery of the present invention is formed by forming a sulfated polyacrylonitrile (S-PAN) coating layer on the surface of a positive electrode active material layer containing sulfur to prevent elution of lithium polysulfide, The present invention provides the effect of greatly improving the performance of the display device.

Further, the lithium-sulfur battery of the present invention is manufactured using the positive electrode for a lithium-sulfur battery, thereby providing greatly improved capacity and life characteristics.

1 is a schematic view showing a conventional electrode (a) for a lithium-sulfur battery and an electrode (b) for a lithium-sulfur battery in which an S-SPAN coating layer according to an embodiment of the present invention is formed.
FIG. 2 is a graph showing the results of a comparison between a conventional lithium-sulfur battery electrode (FIG. 1 (a)) and a lithium-sulfur battery electrode (FIG. 1 (Characteristics before and after use of S-SPAN).

Hereinafter, the present invention will be described in detail.

The present invention relates to a positive electrode active material layer containing sulfur; And a coating layer comprising sulfated polyacrylonitrile (S-PAN) formed by heat-treating a mixture of sulfur and polyacrylonitrile formed on all or part of the surface of the cathode active material layer And a positive electrode for a lithium-sulfur battery.

The coating layer containing the polyacrylonitrile (S-PAN) functions to prevent elution of lithium polysulfide, thereby greatly improving the capacity and life characteristics of the battery.

The sulfided polyacrylonitrile (S-PAN) may be formed by mixing sulfur and polyacrylonitrile in a weight ratio of 1.5 to 6: 1, more preferably 2 to 5: 1. When the composition ratio satisfies the above-mentioned range, the dissolution of lithium polysulfide can be effectively prevented. However, when the weight ratio of sulfur is lower than the above range, the sulfur content of the sulfated polyacrylonitrile (S-PAN) If the weight ratio of sulfur is higher than the above-mentioned range, it is possible to further prevent the residual sulfur which is not reacted with the polyacrylonitrile after the preparation of the sulfurized polyacrylonitrile (S-PAN) May be required.

The coating layer preferably contains 50 to 95% by weight, more preferably 70 to 90% by weight, of sulfated polyacrylonitrile (S-PAN) based on the total weight of the coating layer.

(S-PAN) is contained in the above range, the elution of the lithium polysulfide can be effectively prevented. However, when the weight ratio is lower than the above range, the content of polyacrylonitrile (S-PAN) Can not be effectively prevented from dissolving the lithium polysulfide. If the weight ratio is higher than the above range, a stable coating layer can not be formed due to a decrease in the binder content.

The coating layer may further include at least one selected from the group consisting of a conductive agent, a binder and a dispersing agent.

Examples of the conductive agent include, but are not limited to, graphite based materials such as KS6, conductive materials such as carbon-based materials such as Super-P, denka black and carbon black, and conductive materials such as polyaniline, And conductive polymers such as polyphenylene sulfone, polyphenylene sulfone, polyphenylene sulfone, polyphenylene sulfide, and polyphenylene sulfide.

Examples of the binder include, but are not limited to, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, A copolymer of polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride, Kynar), poly (ethyl acrylate), polytetrafluoroethylene polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylidene fluoride, polystyrene, derivatives thereof, blends, copolymers and the like.

Particularly, it is more preferable to use styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC).

As the dispersing agent, those known in the art may be used. For example, carbon fibers may be used.

The heat treatment may be performed at 280 to 500 ° C.

In the present invention, the cathode active material layer containing sulfur is not particularly limited and those known in the art may be used.

As the form of sulfur contained in the cathode active material layer, there can be used any form known in the art without limitation, but a sulfur-carbon composite form can be more preferably used. As the sulfur-carbon composite, any known in the art can be used without limitation. In one embodiment, the sulfur-carbon composite may be formed by applying sulfur particles to the porous carbon. Also, the sulfur-carbon composite may be formed by melting sulfur particles and mixing them with carbon. The weight ratio of carbon to sulfur in the sulfur-carbon composite may be 1:20 to 1: 1.

The carbon may be crystalline or amorphous carbon, and is not limited as long as it is conductive carbon, and may be, for example, graphite, carbon black, activated carbon fiber, inert carbon nanofiber, carbon nanotube, carbon fabric and the like.

In one embodiment of the present invention, the cathode active material layer further includes at least one additive selected from a transition metal element, a group IIIA element, a group IVA element, a sulfur compound of these elements, and an alloy of these elements and sulfur .

The transition metal element includes at least one element selected from Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Os, Ir, Hg and the like, and the Group IIIA element may include Al, Ga, In, Ti, and the Group IVA element may include Ge, Sn, Pb, and the like.

The cathode active material layer may further include an electrically conductive conductive material for allowing electrons to smoothly move within the anode together with the cathode active material or, optionally, an additive, and a binder for adhering the cathode active material to the current collector.

The conductive material is not particularly limited, but conductive materials such as graphite materials such as KS6, carbon-based materials such as Super-P, denka black and carbon black, and conductive materials such as polyaniline, polythiophene, polyacetylene, and polypyrrole Can be used alone or in combination.

Examples of the binder include poly (vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, alkylated polyethylene oxide, crosslinked polyethylene oxide, polyvinyl ether, poly (methyl methacrylate) (Trade name: Kynar), poly (ethyl acrylate), polytetrafluoroethylene polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, and polyvinylidene fluoride (polyvinylidene fluoride) Polystyrene, derivatives thereof, blends, copolymers and the like can be used.

The content of the binder may be 0.5 wt% or more and 30 wt% or less based on the total weight of the positive electrode active material layer.

The coating layer preferably forms an interlayer between the cathode active material layer and the electrolyte. The interlayer interrupts the migration of lithium polysulfide, thereby improving the capacity and life characteristics of the battery.

In an embodiment of the present invention, the anode for the lithium-sulfur battery may be a plate type or a rod type. In the case of a plate type, the coating layer may be located, for example, in the whole of the surface of the cathode active material layer exposed to the electrolyte, and in the case of a rod type, the coating layer may be formed on the surface of the cathode active material layer Can be located entirely.

The coating layer may be formed to a thickness of 5 to 60 탆, more preferably 10 to 50 탆.

When the thickness of the coating layer is in the above range, the effect of preventing dissolution of lithium polysulfide is excellent. However, if the thickness is less than the above range, the effect of preventing dissolution of lithium polysulfide becomes insufficient, It is undesirable from the viewpoint that there may be a decrease in the energy density of the battery which counteracts the effect of the increase of the discharge capacity due to the coating layer.

In the electrode for a lithium-sulfur battery of the present invention, the amount of the sulfated polyacrylonitrile (S-PAN) contained in the coating layer relative to 100 parts by weight of the positive electrode active material layer is 5 to 50 parts by weight, more preferably 10 to 40 parts by weight It should be included.

When the sulfated polyacrylonitrile (S-PAN) is contained in the above-mentioned range, the effect of preventing dissolution of lithium polysulfide is excellent. However, when the sulfopolyacrylonitrile (S-PAN) is contained in the range below the above range, the effect of preventing dissolution of lithium polysulfide is insufficient , It is undesirable from the viewpoint that there may be a decrease in the energy density of the battery which counteracts the effect of the increase in the discharge capacity due to the coating layer.

In addition,

(a) preparing a sulfided polyacrylonitrile (S-PAN);

(b) preparing a coating composition comprising the sulfated polyacrylonitrile (S-PAN) of step (a);

(c) applying a cathode active material containing sulfur on the current collector to form a cathode active material layer; And

(d) coating the surface of the cathode active material layer prepared in the step (c) with the coating composition prepared in the step (b) to form a coating layer. ≪ / RTI >

The contents described in the electrode for a lithium-sulfur battery can be directly applied to the manufacturing method of the present invention.

The poly-acrylonitrile sulfide (S-PAN) in step (a) may be prepared by mixing polyacrylonitrile and sulfur powder and heat-treating the mixture at 280 to 500 ° C. The heat treatment may be performed in an argon atmosphere for 0.5 to 6 hours.

As described above, the coating composition of the step (b) may further include at least one selected from the group consisting of a dispersant and a conductive agent. The coating composition may further include a solvent capable of dissolving or dispersing the solid content contained in the coating composition.

The coating composition may further comprise 1 to 50% by weight of a binder based on the total weight of the coating composition based on the solid content. The binder may include styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF) , And PTFE (Polytetrafluoroethylene). In particular, it may be more preferable to use styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as binders.

The coating composition comprises 10 to 78% by weight of sulfurized polyacrylonitrile (S-PAN), 0.1 to 10% by weight of a conductive agent, 1 to 50% by weight of a binder, 20 to 80% And may further include a solvent. The coating composition may further comprise 0.1 to 10% by weight of a dispersing agent based on the total weight of the coating composition.

As the above-mentioned solvent, it is possible to dissolve or disperse the solids contained in the coating composition well-known in the art. For example, it is possible to use a solvent such as N-methyl-2-pyrrolidone (NMP), methoxypropylacetate, butyl acetate, glycolic acid esters, butyl esters, butyl glycols, methylalkyl polysiloxanes, alkylbenzenes, propylene glycols, But are not limited to, aralkyl-modified methylalkylpolysiloxanes, polyether-modified dimethylpolysiloxane copolymers, polyether-modified dimethylpolysiloxane copolymers, polyacrylate solutions, alkylbenzenes, diisobutylketones, organomodified polysiloxanes, butanol, isobutanol, modified polyacrylates, A modified polyurethane, and a polysiloxane-modified polymer may be used.

The application of the cathode active material containing sulfur in the step (c) can be carried out by a method commonly used in this field. As the cathode active material containing sulfur in the step (c), known components in this field may be used without limitation, but it is preferable to use a sulfur-carbon composite.

In the production process of the present invention, a cathode for a lithium-sulfur battery can be produced by a method known in the art except for those described above.

In addition,

A negative electrode comprising lithium metal or a lithium alloy as a negative electrode active material;

A positive electrode for a lithium-sulfur battery according to the present invention;

A separator provided between the anode and the cathode; And

And a lithium-sulfur battery including the electrolyte.

As for the positive electrode for a lithium-sulfur battery, the above-described contents can be applied as it is.

As the negative electrode of the lithium-sulfur battery of the present invention, a negative electrode known in the art as a negative electrode containing lithium metal or a lithium alloy as the negative electrode active material can be used without limitation.

As the lithium alloy, lithium and an alloy of a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al and Sn may be used as the negative electrode active material.

The separator positioned between the positive and negative electrodes separates or insulates the positive and negative electrodes from each other and enables lithium ion transport between the positive and negative electrodes. The separator may be made of a porous nonconductive or insulating material, but is not limited thereto, Separators known in the art can be used.

The separator may be an independent member such as a film, or may be a coating layer added to the anode and / or the cathode. The material of the separator includes, for example, a polyolefin such as polyethylene and polypropylene, a glass fiber filter paper, and a ceramic material, but is not limited thereto. The thickness of the separator is about 5 탆 to about 50 탆, Lt; / RTI >

As the electrolyte, those known in the art may be used, and for example, an electrolyte including a lithium salt and an organic solvent may be used. The electrolyte may be impregnated into a negative electrode, a positive electrode and a separator.

As the organic solvent contained in the electrolyte, for example, a single solvent or a mixed organic solvent of two or more may be used. When two or more mixed organic solvents are used, at least one solvent may be selected from two or more of the weak polar solvent group, the strong polar solvent group, and the lithium metal protective solvent group. Wherein said weak polar solvent is defined as a solvent having a dielectric constant of less than 15 that is capable of dissolving a sulfur element in an aryl compound, bicyclic ether, or acyclic carbonate, said strong polar solvent being selected from the group consisting of bicyclic carbonates, sulfoxide compounds, A lithium metal protective solvent is defined as a solvent having a dielectric constant higher than 15 that is capable of dissolving lithium polysulfide in a compound, a ketone compound, an ester compound, a sulfate compound, or a sulfite compound, and the lithium metal protective solvent is a saturated ether compound, an unsaturated ether compound, , A cyclic compound having a cyclic efficiency of not less than 50% to form a stable SEI (Solid Electrolyte Interface) on a lithium metal such as a heterocyclic compound containing O, S, or a combination thereof.

Specific examples of the weak polar solvent include xylene, dimethoxyethane, 2-methyltetrahydrofuran, diethyl carbonate, dimethyl carbonate, toluene, dimethyl ether, diethyl ether, diglyme and tetraglyme. However, the present invention is not limited thereto.

Specific examples of the strong polar solvent include hexamethyl phosphoric triamide,? -Butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl- But are not limited to, zolyidone, dimethylformamide, sulfolane, dimethylacetamide, dimethylsulfoxide, dimethylsulfate, ethylene glycol diacetate, dimethylsulfite, ethylene glycol sulfite and the like.

Specific examples of the lithium protecting solvent include tetrahydrofuran, ethylene oxide, dioxolane, 3,5-dimethylisoxazole, furan, 2-methylfuran, 1,4-oxane and 4-methyldioxolane. But is not limited thereto.

The lithium-sulfur battery may be constructed by applying techniques known in the art, except for the characteristic features of the present invention described above.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as set forth in the appended claims. Such changes and modifications are intended to be within the scope of the appended claims.

Preparation Example 1: Preparation of composition for anode coating

1 g of polyacrylonitrile powder and 6 g of sulfur powder having an average particle size of 5 탆 were mixed and the mixture was transferred to an alumina boat and then purged with argon atmosphere using a tube furnace In a quartz tube at 300 < 0 > C for 2.5 hours to produce S-PAN.

The S-PAN 1.2g of VGCF ^® -H 0.15g, SBR solution of 0.26g (SBR solid content: 40 wt%), 4.1g CMC solution (CMC solids 1.1% by weight) and mixed to prepare a composition for a positive active material coated with the slurry Respectively.

Example 1: Preparation of positive electrode for lithium-sulfur battery

The conductive carbon having electric conductivity and sulfur were mixed at a ratio of 30:70 wt%, and a sulfur-carbon composite was produced through a ball mill process. A composition for forming an active material layer was prepared by mixing 80.0 wt% of a cathode active material containing the sulfur-carbon composite, 10.0 wt% of carbon nanofibers (conductive material), and 10.0 wt% of SBR / CMC (binder) , And 3.6 mg / cm < ² > on the aluminum current collector to prepare a conventional anode.

The slurry for coating prepared in Preparation Example 1 was coated on the above-prepared conventional positive electrode to a thickness of 40 탆 to prepare a positive electrode for a lithium-sulfur battery of the present invention.

Example 2: Preparation of lithium-sulfur battery

A lithium foil having a thickness of about 150㎛ with the above positive electrode prepared in Example 1 as a cathode, and an electrolyte solution used in the ether solvent in an electrolytic solution was added to 1M of LiNO ₃ of LiTFSI and 1% by weight, the separator A 16-micron polyolefin was used to prepare a lithium-sulfur battery. Discharge potentials were applied only to 1.9 V in order to suppress the capacity development from the S-PAN which normally starts the first discharge at a potential of 1.9 V or lower.

Comparative Example 1: Preparation of lithium-sulfur battery

A lithium-sulfur battery was prepared in the same manner as in Example 2 except that the conventional anode prepared in Example 1 (including S-PAN coating ratio) was used.

Test Example 1: Measurement of Charge / Discharge Characteristics by Cycle

The charge and discharge characteristics of the lithium-sulfur battery were measured and the results are shown in FIG.

As shown in FIG. 2, the lithium-sulfur battery of Example 2 to which the S-PAN coating layer was applied had superior charge-discharge capacity characteristics and cycle characteristics as compared with the lithium-sulfur battery of Comparative Example 1 (which did not use the S-PAN coating layer) Respectively.

Claims (17)

A cathode active material layer containing sulfur; And
(S-PAN) formed by heat-treating a mixture of sulfur and polyacrylonitrile formed on all or a part of the surface of the positive electrode active material layer, and a coating layer comprising lithium sulfide and polyacrylonitrile - anode for sulfur battery. The method according to claim 1,
Wherein the sulfided polyacrylonitrile (S-PAN) is formed by mixing sulfur and polyacrylonitrile in a weight ratio of 1.5 to 6: 1. The method according to claim 1,
Wherein the coating layer comprises 50 to 95% by weight of poly (acrylonitrile) sulfide (S-PAN) based on the total weight of the coating layer. The method of claim 3,
Wherein the coating layer further comprises at least one selected from the group consisting of a conductive material, a binder and a dispersing agent. The method according to claim 1,
Wherein the heat treatment is performed at a temperature in the range of 280 to 500 占 폚. The method according to claim 1,
Characterized in that in the cathode active material layer containing sulfur, sulfur is contained in the form of a sulfur-carbon composite. The method according to claim 1,
Wherein the coating layer forms an interlayer between the positive electrode active material layer and the electrolyte. The method according to claim 1,
Wherein the coating layer is formed to a thickness of 5 to 60 [mu] m. The method according to claim 1,
Wherein the sulfated polyacrylonitrile (S-PAN) contained in the coating layer is 5 to 50 parts by weight based on 100 parts by weight of the positive electrode active material layer. (a) preparing a sulfided polyacrylonitrile (S-PAN);
(b) preparing a coating composition comprising the sulfated polyacrylonitrile (S-PAN) of step (a);
(c) applying a cathode active material containing sulfur on the current collector to form a cathode active material layer; And
(d) coating the surface of the cathode active material layer prepared in the step (c) with the coating composition prepared in the step (b) to form a coating layer. Way. 11. The method of claim 10,
Wherein the poly-acrylonitrile sulfide (S-PAN) of step (a) is prepared by mixing polyacrylonitrile powder with sulfur powder and heat-treating the mixture at 280 to 500 ° C. (Preparation method of positive electrode for sulfur battery). 11. The method of claim 10,
Wherein the coating composition of step (b) comprises 10-78 wt% of sulfided polyacrylonitrile (S-PAN), 0.1-10 wt% of a conductive material, 1-50 wt% of a binder, By weight based on the total weight of the lithium-sulfur battery. 13. The method of claim 12,
Wherein the coating composition further comprises 0.1 to 10% by weight of a dispersing agent. 11. The method of claim 10,
Wherein the coating of the cathode active material in step (c) is performed using the cathode active material coating composition comprising the cathode active material, the conductive material, the binder, and the solvent. 11. The method of claim 10,
Wherein the cathode active material containing sulfur in step (c) is a sulfur-carbon composite. A negative electrode comprising lithium metal or a lithium alloy as a negative electrode active material;
A positive electrode for a lithium-sulfur battery according to any one of claims 1 to 9;
A separator provided between the anode and the cathode; And
A lithium-sulfur battery including an electrolyte. 17. The method of claim 16,
Wherein the lithium alloy is 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.

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