KR20180020083A - A carbon coated separator for lithium sulfur batteries - Google Patents

Abstract

The present invention relates to a separation film for a lithium sulfur battery and a lithium sulfur battery including the same. The separation film includes a base substrate layer and a carbon layer coated on the base substrate layer. A thickness of the carbon layer is 70 μm to 120 μm. The separation film suppresses shuttle phenomena to improve a capacity and a cycle feature of the battery.

Description

[0001] The present invention relates to a separator for a lithium sulfur battery having a carbon layer coated thereon and a lithium sulfur battery using the same.

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

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 separator for a lithium sulfur battery, which is coated with a carbon 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 separator.

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.

According to an aspect of the present invention, there is provided a separation membrane for a lithium sulfur battery, the separation membrane including a base substrate layer and a carbon layer coated on the base substrate layer, The present invention provides a separation membrane for a lithium sulfur battery.

The present invention also provides a separation membrane for a lithium sulfur battery, wherein the thickness of the carbon layer is 75 to 110 mu m.

The present invention also provides a separation membrane for a lithium sulfur battery, wherein the carbon layer has an electrolyte absorption rate (%) according to the following equation (1): 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).

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 separator includes a base substrate layer and a carbon layer coated on the base substrate layer, wherein the thickness of the carbon layer is 70 to 120 탆.

Also, the present invention provides a lithium sulfur battery wherein the material of the carbon layer is at least one selected from the group consisting of carbon black, carbon nanotubes, graphene, graphite, amorphous carbon, nanographite, and combinations thereof.

The base material of the base material layer may be 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, or an ethylene / methacrylate copolymer And a lithium sulfur battery using a nonwoven fabric made of glass fiber or polyethylene terephthalate fiber having a high melting point.

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.

1 is a schematic diagram showing a lithium sulfur battery according to the present invention.
Fig. 2 is a graph showing the cycle characteristics of the batteries of Example 1 and Comparative Example 1. Fig.
3 is a graph showing capacity characteristics of batteries of Examples 2 to 4 and Comparative Examples 2 to 4. FIG.
4 is a scanning electron microscope (SEM) image for comparing the structure of each carbon having different specific surface area.
5A to 5C 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 from the cathode 120 and includes a base layer 131 and a carbon layer 132 coated on the base layer 131, .

The base substrate layer 131 may be a porous polymer film. For example, the base substrate layer 131 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 material of the carbon layer 132 may be any one selected from the group consisting of carbon black, carbon nanotubes, graphene, graphite, amorphous carbon, nanographite, and combinations thereof. Specific products include Super P (super P), denka black or ketjen black. However, the material of the carbon layer 132 is not limited in the present invention.

At this time, in the present invention, the carbon layer 132 is preferably a thick film having a thickness of 70 μm to 120 μm, and more preferably, the carbon layer 132 has a thickness of 75 μm to 110 μm .

When the thickness of the carbon layer 132 is less than 70 mu m, the capacity of the battery is not improved. When the thickness of the carbon layer 132 is more than 120 mu m, It is preferable that the carbon layer 132 in the present invention has a thickness of 70 to 120 占 퐉. This will be described later.

Also, the carbon layer 132 corresponds to a porous coating layer.

In this case, the carbon absorption rate (%) of the carbon layer 132 according to the following equation (1) is preferably 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 the battery performance (%) Of the carbon layer 132 is less than 40% because the carbon layer can not smoothly capture the polysulfide described later when the electrolyte absorption rate (%) exceeds 70% To 70%.

Such an electrolyte absorption rate 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 carbon layer 132 is coated on the upper portion of the base material layer 131, 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.

More specifically, the carbon layer not only captures the polysulfide physically described above, but also facilitates electron transfer.

In addition, the carbon layer has porosity characteristics. 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.

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 is impregnated into the anode 110, the cathode 120 and the separator 130, And is included in the lithium sulfur battery.

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 carbon layer of acetylene black (Denka black, Denki Kagaku Kogyo) on the base substrate layer made of polyethylene.

[Comparative Example 1]

In Example 1, a battery was prepared in the same manner as in Example 1, except that a base substrate layer made of polyethylene was used as the separation membrane.

That is, in Comparative Example 1, a carbon layer of acetylene black (Denka black, Denki Kagaku Kogyo) was not coated as a separation membrane.

Fig. 2 is a graph showing the cycle characteristics of the batteries of Example 1 and Comparative Example 1. Fig.

Referring to FIG. 2, in Example 1 in which a carbon layer of acetylene black (Denka black, Denki Kagaku Kogyo) was coated as a separator, a high performance was obtained at a high rate charging / discharging condition (5C) Can be confirmed.

Therefore, in the present invention, by coating the base substrate layer with the carbon layer, 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 separation membrane according to the present invention will be described.

[Example 2]

Example 1 was carried out in the same manner as in Example 1, except that the carbon layer had a thickness of 75 탆.

[Example 3]

Example 1 was carried out in the same manner as in Example 1 except that the carbon layer had a thickness of 90 탆.

[Example 4]

Example 1 was carried out in the same manner as in Example 1, except that the carbon layer had a thickness of 110 탆.

[Comparative Example 2]

Example 1 was carried out in the same manner as in Example 1, except that the carbon layer had a thickness of 35 탆.

[Comparative Example 3]

Example 1 was carried out in the same manner as in Example 1, except that the carbon layer had a thickness of 55 탆.

[Comparative Example 4]

Example 1 was carried out in the same manner as in Example 1 except that the carbon layer had a thickness of 138 탆.

3 is a graph showing capacity characteristics of batteries of Examples 2 to 4 and Comparative Examples 2 to 4. FIG.

Referring to FIG. 3, it can be seen that the capacity characteristics of the battery are greatly improved as compared with the batteries of Comparative Examples 2 and 3 in Examples 2 to 4.

On the other hand, in the case of Comparative Example 4, the thickness of the carbon layer corresponds to 138 탆, but the capacity characteristics of the battery are lower than those of Examples 2 to 4.

Accordingly, in the present invention, it is preferable that the carbon layer 132 is a thick film having a thickness of 70 μm to 120 μm, and more preferably, the carbon layer 132 has a thickness of 75 μm to 110 μm .

That is, when the thickness of the carbon layer 132 is less than 70 mu m, the capacity of the battery is not improved. When the thickness of the carbon layer 132 is more than 120 mu m, Therefore, it is preferable that the carbon layer 132 in the present invention has a thickness of 70 to 120 탆.

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

As described above, the carbon layer 132 of the present invention corresponds to a porous coating layer, and it is preferable that the carbon layer has an electrolyte absorption rate (%) of 40 to 70% according to the following equation (1) .

..... 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.

4 is a scanning electron microscope (SEM) image for comparing the structure of each carbon having different specific surface area. 4 (a) shows Denka black powder, (b) shows MCMB powder, (c) shows Denka black sheet, and (d) shows MCMB sheet.

Referring to FIG. 4, 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.

5A to 5C 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.

5A shows a case where a carbon sheet is not included in a separation membrane, FIG. 5B shows a case where a Denka black sheet is included in a separation membrane, and FIG. 5C shows a case where an MCMB sheet is included in a separation membrane.

Referring to FIG. 5A, when the separator does not include a carbon sheet, the initial discharge capacity was found to be 592 mAh / g, which is 59% of the theoretical discharge capacity. At 50 cycles, the initial discharge capacity was 54% Respectively.

On the other hand, referring to FIG. 5B, when Denka black sheet is included in the separation membrane, 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. 5C, 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. 5B and 5C, the MCMB sheet has a much lower electrolyte absorption rate than the Denka black sheet. Therefore, in the case of the MCMB sheet having a low electrolyte absorption rate, 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, so that the mass transfer It is impossible to smoothly capture the polysulfide which will be described later. Therefore, when the carbon absorption rate (%) of the carbon layer 132 is lower than 70% (%) Is preferably 40 to 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 (8)

In a lithium sulfur battery separator,
Wherein the separation membrane comprises a base substrate layer and a carbon layer coated on the base substrate layer,
Wherein the thickness of the carbon layer is 70 to 120 占 퐉. The method according to claim 1,
Wherein the carbon layer has a thickness of 75 to 110 占 퐉. The method according to claim 1,
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 separation membrane comprises a base substrate layer and a carbon layer coated on the base substrate layer,
Wherein the thickness of the carbon layer is 70 to 120 占 퐉. 5. The method of claim 4,
Wherein the thickness of the carbon layer is 75 to 110 占 퐉. 5. The method of claim 4,
The method according to claim 1,
Wherein the carbon layer has an electrolyte absorption rate (%) according to the following formula (1): 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). 5. The method of claim 4,
Wherein the material of the carbon layer is at least one selected from the group consisting of carbon black, carbon nanotube, graphene, graphite, amorphous carbon, nanographite, and combinations thereof. 5. The method of claim 4,
The base substrate layer may be made 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, A lithium sulfur battery using a nonwoven fabric made of glass fiber or polyethylene terephthalate fiber having a high melting point.

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