KR20180020096A - separator for lithium sulfur batteries with catalyst coating - Google Patents

Abstract

The present invention relates to a lithium sulfur battery which comprises: an anode and a cathode arranged to face each other; a separation film located between the anode and the cathode; and an electrolyte. The separation film includes a base substrate layer and a catalyst layer coated on the base substrate layer. According to the present invention, if the separation film is used, phenomena thereof are suppressed and a capacity and a cycle feature of the battery can be improved by a catalyst material coated on a separation film surface.

Description

Layer structure separator for a lithium sulfur battery having a catalyst layer coated thereon and a separator for lithium sulfur batteries using the same,

The present invention relates to a multilayer structure separator for a lithium sulfur battery having a catalyst layer coated thereon and a lithium sulfur battery using the same. More particularly, the present invention relates to a separator for a lithium sulfur battery, which can suppress the shuttle phenomenon and improve the capacity and cycle characteristics of the battery, The present invention relates to a lithium sulfur battery.

Lithium secondary battery has higher energy density and longer life than nickel cadmium battery and nickel metal hydride battery and is widely used in various fields such as computers and portable devices in recent years. .

Among the important components of the lithium secondary battery, the separation membrane prevents a short circuit between the positive electrode and the negative electrode of the battery, and the ion transmission is performed well, which greatly affects the stability of the battery. In recent years, high energy density and lifetime of secondary batteries have been demanded, and thus, separation membranes are required to have not only high stability but also excellent performance.

On the other hand, in the lithium sulfur battery, the anode contains sulfur and the cathode uses lithium metal.

In the lithium sulfur battery, the reduced sulfur at the anode during the discharge combines with lithium ions moved from the cathode to finally form Li ₂ S (2Li ⁺ + 2e ^- + S ↔ Li ₂ S), and 1672 mAh / g) < / RTI >

In this lithium sulfur battery, the anode sulfur and the reaction end product LiS have an electrically non-conductive nature and thus use an electrolyte having a high dielectric constant.

As a result, the soluble polysulfide is dissolved in the electrolyte and the positive and negative electrodes are reciprocated. As a result, the insoluble Li ₂ S and Li ₂ S ₂ produced in the process are accumulated on the surface of the negative electrode and other separator, That is, there arises a shuttle mechanism problem in which the capacity of the battery and the cycle characteristics are deteriorated.

As a solution to this problem, there has been developed a method for improving the electrolyte and preventing the sulfur leaching, but the progress is insignificant.

Korean Patent Publication No. 10-2016-0089954

Disclosure of Invention Technical Problem [8] The present invention provides a multilayer structure separator for a lithium sulfur battery, which is coated with a catalyst layer capable of suppressing a shuttle phenomenon in a lithium sulfur battery and improving the capacity and cycle characteristics of the battery, and a lithium sulfur battery using the same .

The objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

In order to solve the above-mentioned problems, the present invention provides a separation membrane for a lithium sulfur battery, wherein the separation membrane comprises a base base layer and a catalyst layer coated on the base base layer.

The present invention also provides a separation membrane for a lithium sulfur battery, wherein the amount of the catalyst layer is 2 to 4 mg / cm 2 per unit area.

Also, the present invention provides a separation membrane for a lithium sulfur battery, wherein the separation membrane comprises a base base layer and a mixed layer of a catalyst material and a carbon material coated on the base base layer.

The present invention also provides a separator for a lithium sulfur battery, wherein the ratio of the catalyst material to the carbon material is 100% to 10% by weight.

In addition, the present invention provides a separator for a lithium sulfur battery, wherein the separator comprises a first separator coated with a catalyst layer on an upper portion of a first base substrate layer, and a second separator coated with a carbon layer on an upper portion of the second base substrate layer A separator for a lithium sulfur battery is provided.

Further, the present invention provides a positive electrode and a negative electrode arranged opposite to each other; A separator disposed between the anode and the cathode; And an electrolyte, wherein the separation membrane comprises a base substrate layer and a catalyst layer coated on the base base layer.

Also, the present invention provides a lithium sulfur battery, wherein the amount of the catalyst layer is 2 to 4 mg / cm 2 per unit area.

Further, the present invention provides a positive electrode and a negative electrode arranged opposite to each other; A separator disposed between the anode and the cathode; And an electrolyte, wherein the separation membrane comprises a base material layer and a mixed layer of a catalyst material and a carbon material coated on the base material layer.

In addition, the present invention provides a lithium sulfur battery wherein the ratio of the catalyst material to the carbon material is 100% to 10% by weight.

Further, the present invention provides a positive electrode and a negative electrode arranged opposite to each other; A separator disposed between the anode and the cathode; And the electrolyte is characterized in that the separation membrane is a laminated structure of a first separation membrane coated with a catalyst layer on the first base substrate layer and a second separation membrane coated with a carbon layer on the second base substrate layer Lithium sulfur battery.

According to the present invention as described above, it is possible to provide a lithium sulfur battery capable of suppressing the shuttle phenomenon in the lithium sulfur battery and improving the capacity and cycle characteristics of the battery.

That is, in the conventional lithium-sulfur battery, polysulfide is melted at the sulfur anode when charging and discharging, and a shuttle phenomenon occurs between the anode and the cathode, which causes a serious problem in the capacity and cycle characteristics of the battery.

However, the use of the separator according to the present invention suppresses such phenomena, and the capacity and cycle characteristics of the battery can be improved by the catalyst material coated on the separator surface.

1 is a schematic diagram showing a lithium sulfur battery according to the present invention.
2A is a schematic graph showing an exemplary form of a separation membrane according to the present invention.
FIG. 2B is a graph showing the capacity characteristics according to the catalyst loading amount per unit area.
FIG. 2C is a graph showing the capacity characteristics according to the ratio of the catalytic material to the mixing amount of 100% of the catalyst material and the carbon material.
3 is a graph comparing cell performances produced according to Examples 1 to 3 and Comparative Examples.
4 is a graph showing the capacity characteristics of the battery according to the thickness variation of the carbon layer.
5 is a scanning electron microscope (SEM) image for comparing the structure of each carbon having a different specific surface area.
6A to 6C are graphs showing changes in charge / discharge curves of a lithium sulfur battery according to an experimental example during a cycle.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. &Quot; and / or "include each and every combination of one or more of the mentioned items. ≪ RTI ID = 0.0 >

Although the first, second, etc. are used to describe various components, it goes without saying that these components are not limited by these terms. These terms are used only to distinguish one component from another. Therefore, it goes without saying that the first component mentioned below may be the second component within the technical scope of the present invention.

The terminology used herein is for the purpose of illustrating embodiments and is not intended to be limiting of the present invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. The terms " comprises "and / or" comprising "used in the specification do not exclude the presence or addition of one or more other elements in addition to the stated element.

Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Also, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise.

The terms spatially relative, "below", "beneath", "lower", "above", "upper" And can be used to easily describe a correlation between an element and other elements. Spatially relative terms should be understood in terms of the directions shown in the drawings, including the different directions of components at the time of use or operation. For example, when inverting an element shown in the figures, an element described as "below" or "beneath" of another element may be placed "above" another element . Thus, the exemplary term "below" can include both downward and upward directions. The components can also be oriented in different directions, so that spatially relative terms can be interpreted according to orientation.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic diagram showing a lithium sulfur battery according to the present invention.

Referring to FIG. 1, a lithium sulfur battery 100 according to the present invention includes a cathode 110 and a cathode 120 disposed opposite to each other; A separation membrane 130 located between the anode 110 and the cathode 120; And an electrolyte (not shown).

More specifically, the anode 110 is disposed on the cathode current collector 111 and the cathode current collector 111, and includes a cathode active material layer 112 and a cathode active material layer 112 including a conductive material and a binder .

At this time, the cathode current collector 111 can be any as long as it can be used as a current collector in the technical field. Specifically, foamed aluminum or foamed nickel having excellent conductivity can be used.

The cathode active material may include elemental sulfur (S ₈ ), a sulfur-based compound, or a mixture thereof.

Specifically, the sulfur-based compound may be Li ₂ Sn (n? 1), an organic sulfur compound or a carbon-sulfur polymer ((C ₂ S _x ) n: x = 2.5 to 50, n?

The conductive material may be any conductive material, and examples of the conductive material include metallic conductive materials such as metal fibers and metal mesh; Metallic powder such as copper, silver, nickel, and aluminum; Or an organic conductive material such as a polyphenylene derivative can also be used.

The conductive material may be a porous carbon-based material. Examples of the carbon-based material include carbon black, graphite, graphene, activated carbon, and carbon fiber.

At this time, the conductive materials may be used singly or in combination, and the conductive material is preferably included in an amount of 5 to 20 wt% based on the total weight of the cathode active material layer.

If the content of the conductive material is less than 5% by weight, the effect of improving the conductivity of the conductive material is insignificant. On the other hand, if it exceeds 20% by weight, the content of the cathode active material is relatively small.

Further, the binder may include a thermoplastic resin or a thermosetting resin. For example, it is possible to use polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride- Vinylidene fluoride-fluorotetrafluoroethylene copolymers, vinylidene fluoride-chlorotrifluoroethylene copolymers, ethylene-tetrafluoroethylene copolymers, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene lower copolymer, propylene-tetrafluoroethylene Ethylene-chlorotrifluoroethylene copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymers, ethylene -Acrylic acid copolymer or the like may be used alone or in combination, but not always limited thereto, If that can be used as a binder in the art can be both.

In this case, the anode 110 may be manufactured according to a conventional method. Specifically, a composition for forming a cathode active material layer, which is prepared by mixing a cathode active material, a conductive material, and a binder in an organic solvent, And drying and optionally compression-molding the current collector to improve the electrode density.

At this time, it is preferable to use the organic solvent which can uniformly disperse the cathode active material, the binder and the conductive material, and is easily evaporated.

Specifically, the organic solvent includes acetonitrile, methanol, ethanol, tetrahydrofuran, water, isopropyl alcohol, and the like.

The cathode 120 may include an anode current collector 121 and an anode active material layer 122 disposed on the anode current collector 121 and including a negative electrode active material and a conductive material and a binder. have.

The negative electrode current collector 121 may be any material that can be used as a current collector in the technical field. Specifically, the negative electrode current collector 121 may be made of copper, stainless steel, titanium, silver, palladium, nickel, alloys thereof, . ≪ / RTI >

In addition, as the negative electrode active material, a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reacting with lithium ions to reversibly form a lithium-containing compound, a lithium metal and a lithium alloy May be selected.

As a material capable of reversibly intercalating / deintercalating lithium ions, any of carbonaceous anode active materials generally used in a lithium sulfur battery can be used as the carbonaceous material. Specific examples thereof include crystalline carbon, amorphous Carbon or a combination thereof.

Typical examples of the material capable of reacting with the lithium ion to form a lithium-containing compound reversibly include tin oxide (SnO ₂ ), titanium nitrate, silicon (Si), and the like, but the present invention is not limited thereto.

The lithium metal alloy may be an alloy of lithium and a metal of Si, Ge, Al, Sn, Pb, Zn, Bi, In, Mg, Ga or Cd.

At this time, the cathode 120 may further include a binder optionally together with the negative electrode active material.

The binder can act as a paste for the anode active material, mutual adhesion between the active materials, adhesion between the active material and the current collector, buffering effect on expansion and contraction of the active material, and the like. The detailed description will be omitted.

Meanwhile, the cathode 120 may be lithium or a lithium alloy. As a non-limiting example, the lithium alloy may be an alloy of lithium and a metal such as Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al and / or Sn.

The cathode 120 may be a thin film of lithium metal.

Generally, in the course of charging / discharging the lithium sulfur battery, sulfur used as a cathode active material may be converted to an inactive material and attached to the surface of the cathode 120 of lithium or a lithium alloy.

Such inactive sulfur is sulfur in which sulfur can no longer participate in the electrochemical reaction of the anode through various electrochemical or chemical reactions.

However, the inert sulfur formed on the surface of the lithium anode may serve as a protective layer of the lithium anode, and as a result, a lithium metal and an inert sulfur formed on the lithium metal, such as lithium sulfide, may be used as the cathode.

1, a lithium sulfur battery 100 according to the present invention includes a separator 130 disposed between the anode 110 and the cathode 120. As shown in FIG.

The separator 130 physically separates the anode 110 and the cathode 120 and includes a base substrate layer 132 and a catalyst layer 131 coated on the base substrate layer 132 do.

The base substrate layer 132 may be a porous polymer film. For example, the base substrate layer 132 may be a porous polymer film, for example, May be used alone or in a laminated form of a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer. Alternatively, a nonwoven fabric made of a conventional porous nonwoven fabric, for example, glass fiber of high melting point, polyethylene terephthalate fiber or the like can be used, but is not limited thereto.

The catalyst layer 131 may be formed of at least one selected from the group consisting of Pt, Ir, Ru, Ni, Mn, Co, Fe, Ti, Re, Nb, V, S, W, Zr, Ta, , Phosphates, and sulfides. However, the material of the catalyst layer 131 is not limited in the present invention.

At this time, the amount of the catalyst layer according to the present invention is preferably 2 to 4 mg / cm 2 per unit area. This will be described later.

As described above, in the case of the conventional lithium sulfur battery, the soluble polysulfide is dissolved in the electrolyte and the positive electrode and the negative electrode are reciprocated, and the insoluble Li ₂ S and Li ₂ S ₂ generated in this process, There arises a shuttle mechanism problem in which the performance of the battery is deteriorated, that is, the capacity and the cycle characteristics of the battery are lowered.

Therefore, in order to solve this problem, there has been developed a method of improving the electrolyte and preventing the sulfur leaching, but the progress thereof is insignificant.

However, in the present invention, the catalyst layer 131 is coated on the upper portion of the base material layer 132, which is a separator commonly used in a conventional lithium sulfur battery, to suppress the shuttle phenomenon in the lithium sulfur battery, The capacity and cycle characteristics of the battery can be improved.

Meanwhile, the separation membrane according to the present invention may be modified in the following manner.

2A is a schematic graph showing an exemplary form of a separation membrane according to the present invention. 2A illustrates an exemplary embodiment of a separation membrane in a basic assembly structure of a coin cell, but does not limit the basic assembly structure of the coin cell in the present invention.

Referring to FIG. 2A, the separation membrane according to the present invention may correspond to a separation membrane including a catalyst layer coated on the base substrate layer as shown in FIG.

At this time, in the case of the separation membrane including the catalyst layer coated on the base substrate layer, the amount of the catalyst layer according to the present invention is preferably 2 to 4 mg / cm 2 per unit area.

Table 1 is a table showing the amount of catalyst loading per unit area.

division Samplee Sample B Sample C Sample D Sample E Catalyst loading amount 0 mg / cm 2 2.2 mg / cm 2 3.1 mg / cm 2 5.8 mg / cm 2 7.2 mg / cm 2

FIG. 2B is a graph showing the capacity characteristics according to the catalyst loading amount per unit area.

Referring to FIG. 2B, Sample B having a catalyst loading amount of 2.2 mg / cm 2 per unit area and Sample C having 3.1 mg / cm 2 had improved capacity characteristics as compared with Sample A having a catalyst loading amount per unit area of 0 mg / cm 2 Can be confirmed.

However, in the case of Sample D having a catalyst loading amount of 5.8 mg / cm 2 per unit area and Sample E having a 7.2 mg / cm 2 per unit area, it was confirmed that the capacity characteristics were not better than Sample A having a catalyst loading amount of 0 mg / cm 2 per unit area have.

Therefore, in the present invention, the amount of the catalyst layer is preferably 2 to 4 mg / cm 2 per unit area.

2A, the separation membrane according to the present invention may correspond to a separation membrane having a mixed layer formed by mixing a catalyst material and a carbon material on a base substrate layer.

The carbon material may be any one selected from the group consisting of carbon black, carbon nanotubes, graphene, graphite, amorphous carbon, nanographite, and combinations thereof. Specific examples of the carbon nanoparticles include super P, denka black or ketjen black. However, the material of the carbon material is not limited in the present invention.

At this time, the conductivity can be improved through the mixed layer in which the catalyst material and the carbon material are mixed, and the ratio of the catalyst material to the catalyst material in 100% of the mixing amount of the catalyst material and the carbon material is preferably 10 to 30%.

Table 2 is a table showing the ratio of the catalyst material to the mixed amount of 100% of the catalyst material and the carbon material. However, in Table 2, the mixing amount of the catalyst material and the carbon material except for the content of the binder is 100%.

division Samplee Sample B Sample C Sample D Sample E catalyst(%) 0 8 20 40 80 Carbon(%) 80 72 60 40 0 bookbinder(%) 20 20 20 20 20 (Catalyst + carbon)
prepare
Catalyst ratio (%) 0 10 25 50 100

FIG. 2C is a graph showing the capacity characteristics according to the ratio of the catalytic material to the mixing amount of 100% of the catalyst material and the carbon material.

Referring to FIG. 2C, Sample B having a catalyst ratio of 10% and Sample C having a catalyst ratio of 25% can be confirmed to have improved capacity characteristics as compared with Sample A having a catalyst ratio of 0%.

However, in Sample E having a catalyst ratio of 50% and Sample E having a catalyst ratio of 100%, it can be confirmed that the capacity characteristics are rather poor as compared with Sample A having a catalyst ratio of 0%.

Therefore, in the form of a separation membrane in which a mixture layer formed by mixing a catalyst material and a carbon material is coated on the base substrate layer, the ratio of the catalyst material to the catalyst material to the mixing amount of 100% of the catalyst material and the carbon material is 10 to 30% desirable.

2A, the separation membrane according to the present invention includes a first separation membrane having a catalyst layer coated on an upper portion of a first base substrate layer, a second separation membrane having a carbon layer coated on an upper portion of the second base substrate layer, As shown in FIG.

The material of the carbon layer may be any one selected from the group consisting of carbon black, carbon nanotubes, graphene, graphite, amorphous carbon, nanographite, and combinations thereof. Specific examples of the super P, Denka black or ketjen black. However, the material of the carbon layer is not limited in the present invention.

At this time, in the present invention, the carbon layer is preferably a thick film having a thickness of 70 to 120 占 퐉, and more preferably, the carbon layer has a thickness of 75 to 110 占 퐉.

When the thickness of the carbon layer is less than 70 mu m, the capacity of the battery is not improved. On the other hand, when the thickness of the carbon layer exceeds 120 mu m, the capacity of the battery tends to decrease. In the present invention, the carbon layer is preferably 70 to 120 mu m. This will be described later.

On the other hand, the carbon layer corresponds to a porous coating layer.

At this time, in the present invention, it is preferable that the electrolyte absorption rate (%) of the carbon layer according to the following formula (1) is 40 to 70%.

..... 수학식 (1)

(1)

(Where W ₁ is the initial mass of the coating layer and W ₂ is the mass of the coating layer after the electrolyte is impregnated).

When the electrolyte absorption rate (%) is less than 40%, the amount of pores in the carbon layer is too small to prevent mass transfer, so that battery performance is reduced, In addition, when the electrolyte absorption rate (%) exceeds 70%, the carbon layer can not smoothly catch the polysulfide described later. Therefore, the electrolyte absorption rate (%) of the carbon layer is preferably 40 to 70% Do.

Such an electrolyte absorption rate will be described later.

In the case of the carbon layer, it not only captures the physically mentioned polysulfide but also facilitates the movement of electrons.

In the case of the carbon layer, the carbon layer has porosity. By plating lithium on the porous carbon layer, the specific surface area of the lithium anode is widened to induce a uniform distribution of electrons, thereby suppressing the growth of dendrites of the lithium metal And a stable electrochemical reaction can be induced.

1, the electrolyte (not shown) of the lithium sulfur battery according to the present invention includes a lithium salt dispersed in an organic solvent. The electrolyte 110, the cathode 120, And is contained in the lithium sulfur battery in a state of being impregnated in the separation membrane 130.

The lithium salt can be used in a lithium battery without any particular limitation.

Specifically, the lithium salt is _{LiSCN, LiBr, LiI, LiNO 3} , LiPF 6, LiBF 4, LiSbF 6, LiAsF 6, LiCH 3 SO 3, LiCF 3 SO 3, LiClO 4, Li (Ph) 4, LiC (CF _{3 SO 2) 3, Li [} N (SO 2 CF 3) 2], LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2 and _{LiN (CF 3 CF 2 SO 2} ) consisting of _two Lt; / RTI > group.

In addition, the concentration of the lithium salt may be determined in consideration of ion conductivity, etc., and may be preferably 0.2 to 4.0 M, or 0.5 to 1.6 M.

As the organic solvent, a single solvent or a mixed solvent of two or more may be used. When a mixed solvent is used as the organic solvent, the use of at least one solvent selected from two or more of the weak polar solvent group, the strong polar solvent group, and the lithium protecting solvent group may be advantageous for the performance of the battery .

Wherein the weak polar solvent is a solvent having a dielectric constant of less than 15 among aryl compounds, bicyclic ethers, and acyclic carbonates; Wherein the strong polar solvent is a solvent having a dielectric constant greater than 15 among acyclic carbonates, sulfoxides, lactones, ketones, esters, sulfates, sulfides; The lithium protecting solvent means a solvent which is stable to a lithium metal and forms a solid electrolyte interface, such as a saturated ester, an unsaturated ester, a heterocyclic compound and the like.

Specifically, examples of the weak polar solvent include xylene, dimethoxyethane, 2-methyltetrahydrofuran, dimethyl carbonate, diethyl carbonate, toluene, dimethyl ether, diethyl ether, diglyme and tetraglyme have.

Examples of the strong polar solvent include hexamethylphosphoric triamide, gamma-butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl-2-oxazolidone, dimethylformamide , Sulfolane, dimethylacetamide, dimethylsulfoxide, dimethylsulfate, ethylene glycol diacetate, dimethylsulfite, ethylene glycol sulfite and the like.

Examples of the lithium protecting solvent include tetrahydrofuran, ethylene oxide, dioxolane, 3,5-dimethylisoxazole, furan, 2-methylfuran, 1,4-oxane and 4-methyldioxolane .

The electrolyte further includes additives (hereinafter, referred to as "other additives") that can be generally used in electrolytes for the purpose of improving lifetime characteristics of the battery, suppressing the battery capacity reduction, and improving the discharge required amount of the battery, in addition to the electrolyte components can do.

Hereinafter, specific examples of the present invention will be described. However, the following experimental examples are intended only to illustrate or explain the present invention. Therefore, the present invention is not limited to the following experimental examples.

[Example 1]

The cathode active material slurry was prepared by mixing the elemental sulfur (S): conductive material (carbon): binder in a weight ratio of 75: 20: 5 and then ball milling for 1 hour.

PVdF and NMP were used as the binder, and the content of PVdF in the binder was 5% by weight based on 100% by weight of the total binder.

The prepared positive electrode slurry was coated on an aluminum foil and then dried in an oven at 80 DEG C to prepare a positive electrode.

A non-oxidized lithium metal foil was used as a negative electrode, and a separator was placed between the prepared positive electrode and a lithium metal foil as a counter electrode to prepare a coin cell evaluation battery.

The separation membrane was prepared by coating a catalyst layer of Pt on the base substrate layer made of polyethylene.

[Example 2]

As in the case of Example 1, except that the separation membrane was prepared by coating a mixed layer of a catalyst material of Pt and a carbon material of acetylene black (Denka black, Denki Kagaku Kogyo) on a base substrate layer made of polyethylene Respectively.

[Example 3]

As the separator, a carbon layer of acetylene black (Denka black, Denki Kagaku Kogyo) was coated on a first separator coated with a catalyst layer of Pt on the first base substrate layer made of polyethylene and a second base substrate layer made of polyethylene Coated second separator was prepared in the same manner as in Example 1,

[Comparative Example]

The procedure of Example 1 was repeated except that a base substrate layer made of polyethylene was used as the separation membrane.

3 is a graph comparing cell performances produced according to Examples 1 to 3 and Comparative Examples.

3 (a) is a graph comparing a separator coated with a catalyst material and a conventional lithium sulfur battery (comparison between Example 1 and Comparative Example), and FIG. 3 (b) FIG. 3 (c) is a graph showing a comparison between a separator coated with a carbon material and a separator coated with a catalyst material, and FIG. 3 (Comparison between Example 3 and Comparative Example). Fig.

Referring to a graph showing the cycle characteristics of FIG. 3, it can be seen that the batteries of Examples 1 to 3 have better battery performance than the comparative examples.

Particularly, in the case of Example 3, it is confirmed that the discharge capacity is remarkably improved as compared with the comparative example.

Therefore, in the present invention, the cycle characteristics of the lithium sulfur battery can be improved by coating the catalyst layer on the base substrate layer. In particular, in the present invention, the carbon material is contained in the base material layer, By coating, the cycle characteristics of the lithium sulfur battery can be improved.

Hereinafter, characteristics of the battery according to the coating thickness of the carbon layer of the separator according to the present invention will be described.

That is, as described above, the battery performance in the case of containing the carbon material in the catalyst layer (Example 2) is superior to that in the case of coating only the catalyst layer on the base material layer (Example 1) Layer coating (Example 3), the characteristics of the battery according to the coating thickness of the carbon layer of the separation membrane will be described below.

[Additional Experimental Example]

The cathode active material slurry was prepared by mixing the elemental sulfur (S): conductive material (carbon): binder in a weight ratio of 75: 20: 5 and then ball milling for 1 hour.

PVdF and NMP were used as the binder, and the content of PVdF in the binder was 5% by weight based on 100% by weight of the total binder.

The prepared positive electrode slurry was coated on an aluminum foil and then dried in an oven at 80 DEG C to prepare a positive electrode.

A non-oxidized lithium metal foil was used as a negative electrode, and a separator was placed between the prepared positive electrode and a lithium metal foil as a counter electrode to prepare a coin cell evaluation battery.

The separation membrane was prepared by coating a carbon layer of acetylene black (Denka black, Denki Kagaku Kogyo) on the base substrate layer made of polyethylene.

At this time, the capacity characteristics of the battery were measured while changing the thickness of the carbon layer to 75 μm, 90 μm, 110 μm, 35 μm, 55 μm and 138 μm, respectively.

4 is a graph showing the capacity characteristics of the battery according to the thickness variation of the carbon layer.

4, when the thicknesses of the carbon layers were 75 μm, 90 μm and 110 μm, respectively, it was confirmed that the capacity characteristics of the battery were greatly improved as compared with the thicknesses of the carbon layers of 35 μm and 55 μm, respectively .

On the other hand, when the thickness of the carbon layer corresponds to 138 占 퐉, it can be seen that the capacity characteristics of the battery are lower than the case where the thicknesses of the carbon layers are 75 占 퐉, 90 占 퐉 and 110 占 퐉, respectively.

Therefore, in the present invention, it is preferable that the carbon layer is a thick film with a thickness of 70 to 120 占 퐉, and more preferably, the carbon layer has a thickness of 75 to 110 占 퐉.

That is, when the thickness of the carbon layer is less than 70 탆, the capacity of the battery is not improved, and when the thickness of the carbon layer exceeds 120 탆, the capacity of the battery tends to decrease. Therefore, the carbon layer in the present invention) is preferably 70 to 120 mu m.

Hereinafter, the electrolyte absorption rate of the carbon layer according to the present invention will be described.

As described above, the carbon layer of the present invention corresponds to a porous coating layer, and it is preferable that the percentage of the electrolyte absorbed by the carbon layer in the following formula (1) is 40 to 70%.

..... 수학식 (1)

(1)

(Where W ₁ is the initial mass of the coating layer and W ₂ is the mass of the coating layer after the electrolyte is impregnated).

The inventors of the present invention compared the characteristics of cell performance according to the electrolyte absorption rate of the carbon layer according to the present invention through the following experiments.

First, Applicants have made a sheet of acetylene black (Denka black, Denki Kagaku Kogyo) with a large specific surface area and meso carbon micro beads (MCMB, Osaka Gas) with a small specific surface area.

To observe the structure of the carbon of Denka black and MCMB, electron microscopy (SEM) was used. Electrolyte absorption experiments were performed to examine the electrolyte uptake of each carbon sheet.

5 is a scanning electron microscope (SEM) image for comparing the structure of each carbon having a different specific surface area. 5 (a) shows Denka black powder, (b) shows MCMB powder, (c) shows Denka black sheet, and (d) shows MCMB sheet.

Referring to FIG. 5, the denka black powder has a uniform particle size of about 0.1 μm, while the MCMB powder has a particle size of 0.5 to 1 μm, which is larger than denka black.

In this case, when the powder is formed into a sheet, the denka black sheet has a particle size of about 0.1 μm or less, and a part of the denka black sheet is formed as a unitary shape while maintaining the original particle size and shape.

In addition, the MCMB sheet shows that the particle size and shape are much different from the original powder because the particles are crushed.

In other words, although the MCMB sheet is formed as a whole, it can be confirmed that the pores are not seen and clogged even though a positive binder such as Denka black is used.

MCMB carbon is larger than Denka black carbon, so it is considered that spherical MCMB carbon particles are aggregated with each other and pores are not seen.

From the results of the surface morphology of the SEM described above, it is believed that there is a large difference in the porosity of the sheets, and since the absorption rate of the electrolyte may be different when the porosity is different, in order to understand how the carbon sheets absorb the electrolyte, Were measured.

The measurement of the absorbency of the electrolyte was carried out by impregnating each carbon sheet into the electrolyte for a certain period of time, measuring the weight of the carbon sheet by taking out the carbon sheet, and calculating by the above-mentioned formula (1).

As a result, the initial weight of Denka black sheet was 0.0198g and the initial weight of MCMB sheet was 0.0464g. After each carbon sheet was impregnated with electrolyte and weighed, the weight of Denka black sheet was 0.0428g, MCMB The weight of the sheet was 0.0482g.

As a result of the calculation according to Equation (1), the absorption rate of Denka black sheet was about 53.73%, and the MCMB-sheet was about 3.73%.

From these results, it can be seen that the Denka black sheet has an electrolyte absorption rate about 14 times higher than that of the MCMB sheet, and the MCMB sheet having a large specific surface area and no pore shape shows that the electrolyte can not be absorbed well.

6A to 6C are graphs showing changes in charge / discharge curves of a lithium sulfur battery according to an experimental example during a cycle.

In other words, in order to investigate the characteristics of each carbon sheet, a cell was made to evaluate the effect of each carbon sheet when it was applied to a lithium sulfur cell, and electrochemical evaluation was performed.

6A shows a case where a carbon sheet is not included in a separation membrane, FIG. 6B shows a case where a Denka black sheet is included in a separation membrane, and FIG. 6C shows a case where an MCMB sheet is included in a separation membrane.

Referring to FIG. 6A, when a carbon sheet is not included in the separator, a discharge capacity of 1002 mAh / g, which is 59% of the theoretical capacity, is shown, and a discharge capacity of 547 mAh / g Respectively.

6B, when the dense black sheet is included in the separator, the initial capacity is 1491 mAh / g, which is 89% of the theoretical capacity, and the capacity is 1062 mAh / g, which is 71% of the initial discharge capacity in 50 cycles .

Referring to FIG. 6C, when the MCMB sheet is included in the separator, the initial capacity is 106 mAh / g, which is 6.3% of the theoretical capacity, and the discharge capacity is 239 mAh / g, which is higher than the initial discharge capacity at 50 cycles.

Based on the results shown in FIGS. 6B and 6C, since the MCMB sheet has a much lower electrolyte absorption rate than the Denka black sheet, the MCMB sheet having a low electrolyte absorption rate interferes with the migration of lithium ions, It seems to have adversely affected the company.

In the present invention, when the electrolyte absorption rate (%) is less than 40%, the amount of pores in the carbon layer is too small to prevent the mass transfer. Therefore, the electrolyte absorption rate (%) depends on the porosity of the carbon layer. (%) Of the carbon layer is in the range of 40 to 70% because the carbon layer can not smoothly capture the polysulfide when the electrolyte absorption rate (%) exceeds 70% .

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (14)

In a lithium sulfur battery separator,
Wherein the separation membrane comprises a base base layer and a catalyst layer coated on the base base layer. The method according to claim 1,
Wherein the amount of the catalyst layer is 2 to 4 mg / cm 2 per unit area. In a lithium sulfur battery separator,
Wherein the separation membrane comprises a base material layer and a mixed layer of a catalyst material and a carbon material coated on the base material layer. The method of claim 3,
Wherein a ratio of a catalyst material to a catalyst material in a mixing amount of 100% of the catalyst material and the carbon material is 10 to 30%. In a lithium sulfur battery separator,
Wherein the separation membrane is a laminated structure of a first separation membrane having a catalyst layer coated on an upper portion of a first base substrate layer and a second separation membrane having a carbon layer coated on an upper portion of a second base substrate layer. 6. The method of claim 5,
Wherein the carbon layer has a thickness of 70 to 120 占 퐉. 6. The method of claim 5,
Wherein an electrolyte absorption rate (%) of the carbon layer according to the following formula (1) is 40 to 70%.

(1)
(Where W ₁ is the initial mass of the coating layer and W ₂ is the mass of the coating layer after the electrolyte is impregnated). An anode and a cathode arranged opposite to each other;
A separator disposed between the anode and the cathode; And
An electrolyte,
Wherein the separator comprises a base substrate layer and a catalyst layer coated on the base substrate layer. 9. The method of claim 8,
Wherein the amount of the catalyst layer is 2 to 4 mg / cm 2 per unit area. An anode and a cathode arranged opposite to each other;
A separator disposed between the anode and the cathode; And
An electrolyte,
The separator includes a base substrate layer and a mixed layer of a catalyst material and a carbon material coated on the base material layer. 11. The method of claim 10,
Wherein the ratio of the catalyst material to the carbon material to the mixed material is 100% to 10% to 30%. An anode and a cathode arranged opposite to each other;
A separator disposed between the anode and the cathode; And
An electrolyte,
Wherein the separation membrane is a laminated structure of a first separation membrane having a catalyst layer coated on an upper portion of a first base substrate layer and a second separation membrane coated with a carbon layer on an upper portion of a second base substrate layer. 13. The method of claim 12,
Wherein the carbon layer has a thickness of 70 to 120 占 퐉. 13. The method of claim 12,
(%) Of the electrolyte layer in the carbon layer according to the following formula (1) is 40 to 70%.

(1)
(Where W ₁ is the initial mass of the coating layer and W ₂ is the mass of the coating layer after the electrolyte is impregnated).

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