WO2018034501A1

WO2018034501A1 - Multi-layered separator, coated with catalyst layer, for lithium sulfur batteries and lithium sulfur battery using same

Info

Publication number: WO2018034501A1
Application number: PCT/KR2017/008938
Authority: WO
Inventors: 김용태; 최지환
Original assignee: 부산대학교 산학협력단
Priority date: 2016-08-17
Filing date: 2017-08-17
Publication date: 2018-02-22

Abstract

The present invention relates to a lithium sulfur battery comprising: a positive electrode and a negative electrode which are disposed so as to face each other; a separator positioned between the positive electrode and the negative electrode; and an electrolyte, wherein the separator comprises a base substrate layer and a catalyst layer coated on the base substrate layer. Using the separator according to the present invention has the effect of inhibiting such phenomena and allows for the improvement of the capacity and cycle properties of the battery due to a catalyst substance coated on the surface of the separator.

Description

Multilayer Separation Membrane for Lithium Sulfur Battery Coated with Catalyst Layer and Lithium Sulfur Battery Using the Same

The present invention relates to a multilayer structure membrane for a lithium sulfur battery coated with a catalyst layer and a lithium sulfur battery using the same, and more particularly, to inhibit a shuttle phenomenon, a separator for a lithium sulfur battery which can improve capacity and cycle characteristics of the battery and the same. The present invention relates to a lithium sulfur battery used.

Lithium secondary batteries have higher energy density and longer lifespan than nickel cadmium batteries and nickel-hydrogen batteries. They are widely used in various fields such as computers and mobile devices. They are also used as medium and large secondary battery materials for electric vehicles in the future. Is getting.

Separation membrane among the important parts of the lithium secondary battery prevents the short circuit of the positive electrode and the negative electrode of the battery, and the ion transfer is made to have a great effect on the battery stability. Recently, high energy density and lifespan of secondary batteries are required. Accordingly, the separator is also required to have high performance as well as high stability.

On the other hand, in the lithium sulfur battery, the positive electrode contains sulfur and lithium metal is used as the negative electrode.

The lithium sulfur battery is finally Li ₂ S The reduction of sulfur in combination with the lithium ions which have been moved from the cathode in the cathode during discharge ^- involves the reaction for forming a ^{(2Li + + 2e + S ↔} Li 2 S) and 1672 mAh / g) theoretical capacity.

In such a lithium sulfur battery, sulfur forming a positive electrode and LiS, which is a final product of reaction, are electrically non-conductive, and thus an electrolyte having a high dielectric constant is used.

As a result, the soluble polysulfide is dissolved in the electrolyte to reciprocate the positive electrode and the negative electrode, and insoluble Li ₂ S and Li ₂ S ₂ generated in this process accumulate on the surface of the negative electrode and other separators, thereby degrading battery performance. In other words, a shuttle mechanism problem occurs in which a decrease in battery capacity and cycle characteristics occurs.

As a solution to this problem, a method of preventing the elution of sulfur by improving the electrolyte has been developed, but the progress is insignificant.

The problem to be solved by the present invention is to provide a multi-layer separator for a lithium sulfur battery coated with a catalyst layer that can suppress the shuttle phenomenon in a lithium sulfur battery, improve 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 which are not mentioned will be clearly understood by those skilled in the art from the following description.

In order to solve the above problems, the present invention provides a separator for a lithium sulfur battery, wherein the separator provides a separator for a lithium sulfur battery including a base substrate layer and a catalyst layer coated on the base substrate layer.

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

In addition, the present invention provides a separator for a lithium sulfur battery, wherein the separator provides a separator for a lithium sulfur battery comprising a base substrate layer and a mixed layer of a catalyst material and a carbon material coated on the base substrate layer.

In addition, the present invention provides a separator for a lithium sulfur battery, characterized in that the ratio of the catalyst material to the mixed amount 100% of the catalyst material and the carbon material is 10 to 30%.

In addition, the present invention is a lithium sulfur battery separator, wherein the separator is a laminate of a first separator membrane coated with a catalyst layer on top of the first base substrate layer and a second separator membrane coated with a carbon layer on the second base substrate layer. It provides a separator for lithium sulfur battery, characterized in that the form.

In addition, the present invention is a positive electrode and a negative electrode disposed opposite each other; A separator positioned between the anode and the cathode; And an electrolyte, wherein the separator provides a lithium sulfur battery including a base substrate layer and a catalyst layer coated on the base substrate layer.

In addition, the present invention provides a lithium sulfur battery, characterized in that the amount of the catalyst layer is 2 to 4 mg / ㎠ per unit area.

In addition, the present invention is a positive electrode and a negative electrode disposed opposite each other; A separator positioned between the anode and the cathode; And an electrolyte, wherein the separator provides a base material layer and a lithium sulfur battery including 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, characterized in that the ratio of the catalyst material to the mixed amount 100% of the catalyst material and the carbon material is 10 to 30%.

In addition, the present invention is a positive electrode and a negative electrode disposed opposite each other; A separator positioned between the anode and the cathode; And an electrolyte, wherein the separator is formed by stacking a first separator coated with a catalyst layer on the first base substrate layer and a second separator coated with a carbon layer on the second base substrate layer. Provided is a lithium sulfur battery.

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

That is, in the conventional lithium-sulfur battery, polysulfide melts in the sulfur anode during charge and discharge, causing shuttle phenomena to move between the positive electrode and the negative electrode, which causes a big problem in the capacity and cycle characteristics of the battery.

However, the use of the separator according to the present invention acts to suppress such phenomena and improve the capacity and cycle characteristics of the battery by the catalytic material coated on the separator surface.

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

2 is a schematic graph showing an exemplary form of a separator according to the present invention.

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

Figure 4 is a graph showing the capacity characteristics according to the ratio of the catalyst material to the mixed amount of the catalyst material and the carbon material 100%.

5 is a graph comparing the battery performance prepared according to Examples 1 to 3, Comparative Examples.

6 is a graph showing capacity characteristics of a battery according to a change in thickness of a carbon layer.

7 is an electron scanning microscope (SEM) image for comparing the structure of each carbon having a different specific surface area.

8 to 10 are graphs showing changes in charge and discharge curves during a cycle of a lithium sulfur battery according to the experimental example.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the present embodiments are intended to complete the disclosure of the present invention, and the general knowledge in the art to which the present invention pertains. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Regardless of the drawings, the same reference numbers refer to the same components, and “and / or” includes each and every combination of one or more of the items mentioned.

Although the first, second, etc. are used to describe various components, these components are of course not limited by these terms. These terms are only used to distinguish one component from another. Therefore, of course, the first component mentioned below may be a second component within the technical spirit of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In this specification, the singular also includes the plural unless specifically stated otherwise in the phrase. As used herein, "comprises" and / or "comprising" does not exclude the presence or addition of one or more other components in addition to the mentioned components.

Unless otherwise defined, all terms (including technical and scientific terms) used in the present specification may be used in a sense that can be commonly understood by those skilled in the art. In addition, the terms defined in the commonly used dictionaries are not ideally or excessively interpreted unless they are specifically defined clearly.

The spatially relative terms " below ", " beneath ", " lower ", " above ", " upper " It can be used to easily describe a component's correlation with other components. Spatially relative terms are to be understood as including terms in different directions of components in use or operation in addition to the directions shown in the figures. For example, when flipping a component shown in the drawing, a component described as "below" or "beneath" of another component may be placed "above" the other component. Can be. Thus, the exemplary term "below" can encompass both an orientation of above and below. The components can be oriented in other directions as well, so that spatially relative terms can be interpreted according to the orientation.

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

Referring to FIG. 1, a lithium sulfur battery 100 according to the present invention includes a positive electrode 110 and a negative electrode 120 disposed to face each other; A separator 130 positioned between the anode 110 and the cathode 120; And electrolytes (not shown).

More specifically, first, the positive electrode 110 is disposed on the positive electrode current collector 111 and the positive electrode current collector 111 and includes a positive electrode active material layer 112 including a positive electrode active material and optionally a conductive material and a binder. It may include.

In this case, the positive electrode current collector 111 may be any one that can be used as a current collector in the art, and specifically, foamed aluminum, expanded nickel, and the like having excellent conductivity may 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 ≧ 2).

In addition, the conductive material may be used without limitation as long as the conductive material is a conductive material. For example, the conductive material may be a metallic conductive material such as a metal fiber or a metal mesh; Metallic powders such as copper, silver, nickel and aluminum; Or organic conductive materials, such as a polyphenylene derivative, can also be used.

In addition, the conductive material may be a carbon-based material having a porosity, and carbon black, graphite, graphene, activated carbon, carbon fiber, and the like may be used as the carbon-based material.

In this case, the conductive materials may be used alone or mixed, the conductive material is preferably included in 5 to 20% by weight based on the total weight of the positive electrode active material layer.

If the content of the conductive material is less than 5% by weight, other conductivity enhancement effects are insignificant in the use of the conductive material, whereas if the content is more than 20% by weight, the content of the positive electrode active material is relatively small, which may lower the capacity characteristics.

In addition, the binder may include a thermoplastic resin or a thermosetting resin. For example, polyethylene, polypropylene, polytetrafluoro ethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoroalkylvinylether copolymer, vinylidene fluoride-hexa Fluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoro propylene copolymer, propylene-tetrafluoro Low ethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinylether-tetrafluoro ethylene copolymer, ethylene Acrylic acid copolymers may be used alone or in combination, but are not necessarily limited thereto. If that can be used as a binder in the art can be both.

At this time, the positive electrode 110 as described above may be prepared according to a conventional method, specifically, a composition for forming a positive electrode active material layer prepared by mixing a positive electrode active material, a conductive material and a binder on an organic solvent, is applied onto a current collector And it may be dried and optionally produced by compression molding on the current collector for the purpose of improving the electrode density.

In this case, the organic solvent may be uniformly dispersed in the positive electrode active material, the binder, and the conductive material, and it is preferable to use one that is easily evaporated.

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

Next, the negative electrode 120 may be disposed on the negative electrode current collector 121 and the negative electrode current collector 121, and may include a negative electrode active material layer 122 including a negative electrode active material and optionally a conductive material and a binder. have.

In this case, the negative electrode current collector 121 may be any one that can be used as a current collector in the art, and specifically, copper, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. It may be selected from.

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

As a material capable of reversibly intercalating / deintercalating the lithium ion, any carbon-based negative electrode active material generally used in lithium sulfur batteries may be used, and specific examples thereof include crystalline carbon and amorphous materials. Carbon or these can be used together.

In addition, representative examples of the material capable of reacting with the lithium ions to form a lithium-containing compound reversibly include tin oxide (SnO ₂ ), titanium nitrate, silicon (Si), and the like, but are not limited thereto.

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

In this case, the negative electrode 120 may further include a binder selectively with the negative electrode active material.

The binder may act as a paste for the negative electrode active material, mutual adhesion between the active materials, adhesion between the active material and the current collector, and a buffer effect on the expansion and contraction of the active material. Since the same may be the same, a detailed description thereof will be omitted.

On the other hand, the negative electrode 120 may be lithium or lithium alloy. As a non-limiting example, the lithium alloy may be an alloy of lithium with metals such as Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and / or Sn.

In addition, the cathode 120 may be a thin film of lithium metal.

In the process of charging and discharging a lithium sulfur battery, sulfur, which is used as a cathode active material, may be converted into an inert material and adhered to a surface of the anode 120 of lithium or lithium alloy.

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

However, inert sulfur formed on the surface of the lithium negative electrode may serve as a protective layer of the lithium negative electrode, and as a result, lithium metal and inert sulfur formed on the lithium metal, for example, lithium sulfide may be used as the negative electrode.

Subsequently, referring to FIG. 1, as described above, the lithium sulfur battery 100 according to the present invention includes a separator 130 positioned between the positive electrode 110 and the negative electrode 120.

The separator 130 functions to physically separate the anode 110 and the cathode 120, and includes a base base layer 132 and a catalyst layer 131 coated on the base base layer 132. do.

The base substrate layer 132 corresponds to a separator generally used in a conventional lithium sulfur battery, and the base substrate layer 132 may be a porous polymer film. For example, the base substrate layer 132 The porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer may be used alone or in combination thereof. Alternatively, a conventional porous nonwoven fabric, for example, a non-woven fabric made of high melting glass fibers, polyethylene terephthalate fibers, or the like may be used, but is not limited thereto.

In addition, the catalyst layer 131 may include Pt, Ir, Ru, Ni, Mn, Co, Fe, Ti, Re, Nb, V, S, W, Zr, Ta, and Mo metals, oxides, nitrides, and carbides of the metals. It may be made of at least one catalyst selected from the group consisting of phosphide, sulfide, but is not limited to the material of the catalyst layer 131 in the present invention.

At this time, the amount of the catalyst layer according to the present invention is preferably 2 to 4 mg / ㎠ 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 to reciprocate the positive electrode and the negative electrode, and the insoluble Li ₂ S and Li ₂ S ₂ generated in this process are different from the negative electrode surface and the like. Accumulation at the membrane interface leads to a problem of shuttle mechanisms in which battery performance decreases, that is, battery capacity and cycle characteristics decrease.

Therefore, conventionally, as a solution to solve this problem, a method of preventing sulfur elution by improving the electrolyte has been developed, but the progress is insignificant.

However, in the present invention, by coating the catalyst layer 131 on the base substrate layer 132 corresponding to the separator generally used in the conventional lithium sulfur battery, the shuttle phenomenon in the lithium sulfur battery is suppressed, It is possible to improve the capacity and cycle characteristics of the.

On the other hand, the separator according to the present invention can be modified in the following form.

2 is a schematic graph showing an exemplary form of a separator according to the present invention. At this time, Figure 2 shows an exemplary form of the separator in the basic assembly structure of the coin cell, but is not limited to the basic assembly structure of the coin cell in the present invention.

Referring to FIG. 2, the separator according to the present invention may correspond to the form of a separator including a catalyst layer coated on an upper portion of the base substrate layer as in FIG. 1.

In this case, in the case of a separator including a 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 / ㎠ per unit area.

Table 1 is a table showing catalyst loadings per unit area.

구분division	Sample ASample A	Sample BSample B	Sample CSample C	Sample DSample D	Sample ESample E
촉매로딩량Catalyst loading	0mg/㎠0mg / ㎠	2.2mg/㎠2.2mg / ㎠	3.1mg/㎠3.1mg / ㎠	5.8mg/㎠5.8mg / ㎠	7.2mg/㎠7.2mg / ㎠

Referring to FIG. 3, in the case of Sample B having a catalyst loading per unit area of 2.2 mg / cm 2 and Sample C having 3.1 mg / cm 2, the capacity characteristics were improved compared to Sample A having a catalyst loading of 0 mg / cm 2 per unit area. You can check it.

However, in the case of Sample D having a catalyst loading per unit area of 5.8 mg / cm 2 and Sample E having 7.2 mg / cm 2, the capacity characteristics of the catalyst loading per unit area were 0 mg / cm 2. have.

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

Alternatively, referring to FIG. 2, the separator according to the present invention may correspond to a separator coated with a mixed layer in which a catalyst material and a carbon material are mixed on the base substrate layer.

The carbon material may be any one selected from the group consisting of carbon black, carbon nanotubes, graphene, graphite, amorphous carbon, nano graphite, and combinations thereof, and specific products include super P and denka black. It may be (denka black) or ketjen black (ketjen black) and the like, but does not limit the material of the carbon material in the present invention.

In this case, the conductivity may 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 100% of the mixed 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 100% of the mixed amount of the catalyst material and the carbon material. However, in Table 2 below, the mixed amount of the catalyst material and the carbon material except for the binder content was based on 100%.

구분division	Sample ASample A	Sample BSample B	Sample CSample C	Sample DSample D	Sample ESample E
촉매(%)catalyst(%)	00	88	2020	4040	8080
카본(%)Carbon(%)	8080	7272	6060	4040	00
바인더(%)bookbinder(%)	2020	2020	2020	2020	2020
(촉매+카본) 대비촉매비율(%)Catalyst Ratio (%)	00	1010	2525	5050	100100

Referring to FIG. 4, in the case of Sample B having a catalyst ratio of 10% and Sample C having a catalyst ratio of 25%, it can be seen that capacity characteristics are improved compared to Sample A having a catalyst ratio of 0%.

However, in the case of Sample D having a catalyst ratio of 50% and Sample E having a catalyst ratio of 100%, it can be seen that the capacity characteristics are not good compared to Sample A having a catalyst ratio of 0%.

Therefore, in the form of a separator coated with a mixed layer in which the catalyst material and the carbon material are mixed on the base substrate layer, the ratio of the catalyst material to 100% of the mixed amount of the catalyst material and the carbon material is 10 to 30%. desirable.

In addition, referring to FIG. 2, the separation membrane according to the present invention includes a first separation membrane coated with a catalyst layer 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. It may correspond to the stacked form of.

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

In this case, in the present invention, the carbon layer is a thick film, preferably 70 μm to 120 μm, and more preferably, the carbon layer is 75 μm to 110 μm.

When the thickness of the carbon layer is less than 70 μm, there is no effect of improving the capacity of the battery. Further, when the thickness of the carbon layer exceeds 120 μm, the capacity of the battery tends to decrease. In the present invention, the carbon layer is preferably 70㎛ to 120㎛. This will be described later.

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

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

..... Equation (1)

(However, in the formula (1), W ₁ is the initial mass of the coating layer, W ₂ is the mass after the electrolyte is impregnated in the coating layer.)

The electrolyte absorption rate (%) is due to the porous characteristics of the carbon layer, and when the electrolyte absorption rate (%) is less than 40%, the pore amount in the carbon layer is too small to prevent material transfer, thereby reducing battery performance. In addition, when the electrolyte absorption rate (%) exceeds 70%, the carbon layer may not play a role of easily holding the polysulfide described later, the electrolyte absorption rate (%) of the carbon layer is preferably 40 to 70%. Do.

The electrolyte absorption rate will be described later.

In the case of the carbon layer, not only physically catches the polysulfide described above, but also facilitates the movement of electrons.

In addition, the carbon layer has a porosity characteristic, while lithium is plated on the porous carbon layer, the specific surface area of the lithium anode is widened to induce uniform distribution of electrons, thereby inhibiting dendrite growth of lithium metal. And induce stable electrochemical reactions.

Subsequently, referring to FIG. 1, the electrolyte (not shown) of the lithium sulfur battery according to the present invention includes lithium salt dispersed in an organic solvent, and the positive electrode 110, the negative electrode 120, and the It is included in the lithium sulfur battery in a state impregnated with the separator 130.

The lithium salt may be used without particular limitation that is commonly applicable to lithium batteries.

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 ) ₂ It may be one or more compounds selected from the group.

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

As the organic solvent, a single solvent or a mixed solvent of two or more may be used. In the case of using a mixed solvent as the organic solvent, it may be advantageous to express the performance of the battery by selecting one or more solvents from two or more groups among the weak polar solvent group, the strong polar solvent group, and the lithium protective solvent group. .

Wherein the weak polar solvent is a solvent having a dielectric constant of less than 15 among aryl compounds, bicyclic ethers, and acyclic carbonates; The strong polar solvent is a solvent having a dielectric constant of greater than 15 among acyclic carbonate, sulfoxide, lactone, ketone, ester, sulfate, sulfide; The lithium protective solvent refers to a solvent that is stable to 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, tetraglyme, and the like. have.

In addition, the strong polar solvent is hexamethyl phosphoric triamide, gamma-butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl-2-oxazolidone, dimethyl formamide And sulfolane, dimethyl acetamide, dimethyl sulfoxide, dimethyl sulfate, ethylene glycol diacetate, dimethyl sulfite, ethylene glycol sulfite and the like.

In addition, examples of the lithium protective solvent include tetrahydrofuran, ethylene oxide, dioxolane, 3,5-dimethyl isoxazole, furan, 2-methylfuran, 1,4-oxane, 4-methyldioxolane and the like. .

In addition to the electrolyte components, the electrolyte further includes additives (hereinafter, referred to as 'other additives') that can be generally used in the electrolyte for the purpose of improving the life characteristics of the battery, reducing the battery capacity, and improving the discharge capacity of the battery. can do.

Hereinafter, specific experimental examples of the present invention are presented. However, the experimental examples described below are merely to specifically illustrate or explain the present invention, and therefore, the present invention is not limited to the following experimental examples.

Example 1

An elemental sulfur (S): conductor (carbon): binder was mixed at a weight ratio of 75: 20: 5 and ball milled for 1 hour to prepare a cathode active material slurry.

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

After coating the prepared positive electrode slurry on an aluminum foil (Al foil), and dried at 80 ℃ in an oven to prepare a positive electrode.

As the negative electrode, non-oxidized lithium metal foil was used, and a separator was disposed between the prepared positive electrode and the lithium metal foil as a counter electrode, thereby preparing a coin cell evaluation battery.

The separator was prepared by coating a catalyst layer of Pt on top of a base substrate layer made of polyethylene.

Example 2

In the same manner as in Example 1, except that the separator was prepared by coating a mixed layer of a Pt catalyst material and a carbon material of acetylene black (Denka black, Denki Kagaku Kogyo) on top of the base base layer made of polyethylene. Was carried out.

Example 3

As the separator, a carbon layer of acetylene black (Denka black, Denki Kagaku Kogyo) was placed on top of the first separator membrane coated with Pt catalyst layer on the first base substrate layer made of polyethylene and the second base substrate layer made of polyethylene. The same process as in Example 1 was carried out except that the laminate structure of the coated second separator was manufactured.

[Comparative Example]

It carried out similarly to Example 1 except having used the base base material layer which consists of polyethylene as said separator.

Specifically, FIG. 5 (a) is a graph comparing a separator coated with a catalyst material and a general lithium sulfur battery (compare Example 1 with a comparative example), and FIG. 5 (b) shows a mixture of catalyst material and carbon at a predetermined ratio. After that, it is a graph comparing the coated membrane and a typical lithium sulfur battery (comparison of Example 2 and Comparative Example), Figure 5 (c) is a carbon-coated membrane and a catalyst material-coated membrane after the production of each It is a graph which compared the general lithium sulfur battery with what was laminated | stacked (comparison of Example 3 and a comparative example).

Referring to the graphs showing the cycle characteristics of FIG. 5, it can be seen that in Examples 1 to 3, the battery performance is more excellent as compared with the comparative example.

In particular, in the case of Example 3, it can be seen that the discharge capacity is significantly improved compared to the comparative example.

Therefore, in the present invention, by coating the catalyst layer on the base substrate layer, the cycle characteristics of the lithium sulfur battery can be improved, and in particular, in the present invention, the base substrate layer contains a carbon material or the carbon layer together with the catalyst layer. By coating, the cycle characteristic of a lithium sulfur battery can be improved.

Hereinafter, the battery characteristics 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 is better when the carbon layer is included in the catalyst layer (Example 2) than when only the catalyst layer is coated on the base substrate layer (Example 1). Since the battery performance is more excellent in the case of coating the layer (Example 3), the following is to check the battery characteristics according to the coating thickness of the carbon layer of the separator.

[Additional Experimental Example]

The separator was prepared by coating a carbon layer of acetylene black (Denka black, Denki Kagaku Kogyo) on the base base 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.

Referring to FIG. 6, when the thicknesses of the carbon layers are 75 μm, 90 μm, and 110 μm, respectively, it can be seen that the capacity characteristics of the battery are significantly improved compared to those of the 35 μm and 55 μm thicknesses, respectively. .

On the other hand, when the thickness of the carbon layer corresponds to 138㎛, it can be seen that the capacity characteristics of the battery is lower than when the thickness of the carbon layer is 75㎛, 90㎛, 110㎛, respectively.

Therefore, in the present invention, the carbon layer is a thick film, preferably 70 µm to 120 µm, and more preferably, the carbon layer is 75 µm to 110 µm.

In other words, when the thickness of the carbon layer is less than 70 μm, there is no effect of improving the capacity of the battery, and when the thickness of the carbon layer exceeds 120 μm, the capacity of the battery tends to decrease. Therefore, the carbon layer in the present invention is preferably 70㎛ to 120㎛.

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, wherein the electrolyte absorption rate (%) according to Equation (1) of the carbon layer is preferably 40 to 70%.

..... Equation (1)

Applicant compared the characteristics of the battery performance according to the electrolyte absorption rate of the carbon layer according to the present invention through the following experiment.

First, the present inventors experimented by making sheets of acetylene black (Denka black, Denki Kagaku Kogyo) having a large specific surface area and meso carbon micro beads (MCMB, Osaka Gas) having a small specific surface area, respectively.

Electron scanning microscope (SEM) was observed to see the carbon structure of the Denka black and MCMB, and the electrolyte absorption experiment was performed to see the electrolyte absorption rate of each carbon sheet.

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

Referring to FIG. 7, Denka black powder has a constant particle size of about 0.1㎛, while MCMB powder has a particle size of 0.5 to 1㎛, it can be seen that the particle size is larger than denka black.

In this case, when the powder is produced in each sheet, the Denka black sheet has a particle size of less than about 0.1㎛, while maintaining the original particle size and shape, the parts are in the shape of agglomeration with each other.

In addition, the MCMB sheet is crushed particles show a much different particle size and shape than the original powder.

In other words, the MCMB sheet is in the form of aggregates as a whole, despite the use of the same amount of binder as Denka black, it can be seen that the pores are not visible and blocked.

Since MCMB carbon has a larger particle size than Denka black carbon, it is thought that large spherical MCMB carbon particles aggregate together and show no pores.

From the surface shape results of the above-described SEM, each sheet is expected to have a large difference in the pores, and the electrolyte absorption rate of each sheet to determine how much the carbon sheets absorb the electrolyte because the electrolyte absorption rate can be different if the porosity is different. Was measured.

The electrolyte absorption rate was measured by taking out each carbon sheet after being impregnated in the electrolyte for a certain time and weighed, and was calculated by the above Equation (1).

As a result of the experiment, the initial weight of Denka black sheet was 0.0198g and the initial weight of MCMB sheet was 0.0464g. After the impregnation of each carbon sheet in electrolyte, the weight was taken out and 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 absorbency of Denka black-sheet was about 53.73% and the MCMB-sheet was about 3.73%.

From these results, it can be seen that Denka black sheet has about 14 times better electrolyte absorption than MCMB sheet, and MCMB sheet, which appears to have a specific surface area and no pores, does not absorb electrolyte well.

In other words, in order to investigate the characteristics of each carbon sheet, an electrochemical evaluation was performed by making a cell to see how the carbon sheets were applied to the lithium sulfur battery.

At this time, FIG. 8 illustrates a case where the carbon sheet is not included in the separator, FIG. 9 illustrates a case where the Denka black sheet is included in the separator, and FIG. 10 illustrates a case where the MCMB sheet is included in the separator.

First, referring to FIG. 8, when the separator does not contain a carbon sheet, the initial capacity showed a discharge capacity of 1002 mAh / g, which is 59% of the theoretical capacity, and 547 mAh / g, which is 54% of the initial discharge, at 50 cycles. The capacity of

In contrast, referring to FIG. 9, when the separator includes a Denka black sheet, the initial capacity is 1491 mAh / g, which is 89% of the theoretical capacity, and 1062 mAh / g, which is 71% of the initial discharge capacity at 50 cycles. .

Meanwhile, referring to FIG. 10, when the separator includes an MCMB sheet, an initial capacity of 106 mAh / g, which is 6.3% of theoretical capacity, and a discharge capacity of 239 mAh / g, which is higher than the initial discharge capacity, are shown at 50 cycles.

Based on the results of FIGS. 9 and 10, 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, the MCMB sheet may interfere with the movement of lithium ions to react with sulfur. It seems to have had an adverse effect.

As a result, the electrolyte absorption rate (%) is due to the porosity of the carbon layer. In the present invention, when the electrolyte absorption rate (%) is less than 40%, the amount of pores in the carbon layer is so small that material transfer is hindered. When the performance decreases and the electrolyte absorption rate (%) exceeds 70%, the carbon layer cannot play a role of catching polysulfide, so the electrolyte absorption rate (%) of the carbon layer is 40 to 70%. Is preferably.

Although embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. You will understand that. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims

In the separator for lithium sulfur battery,

The separator is a separator for a lithium sulfur battery comprising a base substrate layer and a catalyst layer coated on the base substrate layer.
The method of claim 1,

The amount of the catalyst layer is a lithium sulfur battery separator, characterized in that 2 to 4 mg / ㎠ per unit area.
In the separator for lithium sulfur battery,

The separator is a separator for a lithium sulfur battery comprising a base substrate layer and a mixed layer of a catalyst material and a carbon material coated on the base substrate layer.
The method of claim 3, wherein

Separation membrane for a lithium sulfur battery, characterized in that the ratio of the catalyst material to the mixed amount 100% of the catalyst material and the carbon material is 10 to 30%.
In the separator for lithium sulfur battery,

The separator is a lithium sulfur battery separator, characterized in that the stack of the first separator membrane coated with a catalyst layer on top of the first base substrate layer and the second separator membrane coated with carbon layer on the second base substrate layer.
The method of claim 5, wherein

The thickness of the carbon layer is a lithium sulfur battery separator, characterized in that 70㎛ to 120㎛.
The method of claim 5, wherein

The electrolyte absorption rate (%) according to Equation (1) of the carbon layer is a lithium sulfur battery separator, characterized in that 40 to 70%.

..... Equation (1)

(However, in the formula (1), W 1 is the initial mass of the coating layer, W 2 is the mass after the electrolyte is impregnated in the coating layer.)
An anode and a cathode disposed to face each other;

A separator positioned between the anode and the cathode; And

Includes an electrolyte,

The separator is a lithium sulfur battery comprising a base substrate layer and a catalyst layer coated on the base substrate layer.
The method of claim 8,

The amount of the catalyst layer is a lithium sulfur battery, characterized in that 2 to 4 mg / ㎠ per unit area.
An anode and a cathode disposed to face each other;

A separator positioned between the anode and the cathode; And

Includes an electrolyte,

The separator comprises a base substrate layer and a mixed layer of a catalyst material and a carbon material coated on the base substrate layer.
The method of claim 10,

Lithium sulfur battery, characterized in that the ratio of the catalyst material to the mixed amount 100% of the catalyst material and the carbon material is 10 to 30%.
An anode and a cathode disposed to face each other;

A separator positioned between the anode and the cathode; And

Includes an electrolyte,

The separator is a lithium sulfur battery, characterized in that the stack of the first separator membrane coated with a catalyst layer on top of the first base substrate layer and the second separator membrane coated with carbon layer on the second base substrate layer.
The method of claim 12,

The thickness of the carbon layer is a lithium sulfur battery, characterized in that 70㎛ to 120㎛.
The method of claim 12,

The electrolyte absorption rate (%) according to Equation (1) of the carbon layer is a lithium sulfur battery, characterized in that 40 to 70%.

..... Equation (1)

(However, in the formula (1), W 1 is the initial mass of the coating layer, W 2 is the mass after the electrolyte is impregnated in the coating layer.)