KR20220160721A - Lithium-sulfur battery comprising sulfur-free based cathode - Google Patents

Abstract

The present invention provides an active material-separated lithium-sulfur battery including: a sulfur-free-based negative electrode; a lithium metal negative electrode having a negative electrode protective layer including at least one of lithium salt and lithium oxide on the surface thereof; and a porous separator including glass fibers impregnated in a non-aqueous electrolyte including active sulfur.

Description

Lithium-sulfur battery containing a non-sulfur-based positive electrode {LITHIUM-SULFUR BATTERY COMPRISING SULFUR-FREE BASED CATHODE}

The present invention relates to a lithium-sulfur battery including a non-sulfur-based positive electrode. More specifically, the present invention relates to a lithium-sulfur battery comprising a negative electrode protective layer, a non-sulfur-based positive electrode, and a porous separator including glass fibers, and a non-aqueous electrolyte solution containing active sulfur.

The capacity, output, and lifespan of a secondary battery are important factors in determining the performance of a secondary battery, which is basically greatly influenced by the material selection of the anode and cathode. A lithium-sulfur primary battery or a lithium-sulfur secondary battery is operated by lithium ions moving in an electrolyte interposed between an anode and a cathode, similar to the case of a conventional lithium-ion secondary battery. However, unlike conventional lithium-ion secondary batteries in which lithium ions are intercalated into the crystal structure of the electrode active material to modify the electrode structure, lithium-sulfur batteries only perform simple oxidation and reduction reactions between sulfur and lithium ions. Therefore, compared to conventional lithium-ion secondary batteries, there is no significant restriction on the electrode structure, and theoretically, it can have a larger capacity in the same volume. Due to these characteristics, a lithium-sulfur battery having a composition of sulfur as a positive electrode and lithium metal as a negative electrode has a theoretical capacity when it is assumed that monomeric sulfur (S ₈ ) having a ring structure reacts completely to lithium sulfide (Li ₂ S). 1,675 mAh/g, and the theoretical energy density is 2,600 Wh/kg, compared to other existing battery systems (Ni/MH battery: 450 Wh/kg, Li/FeS: 480 Wh/kg, Li/MnO ₂ : 1,000 Wh/kg, Na/S: 800 Wh/kg) has an energy density as high as about 2.6 to 5.6 times.

In addition, in the case of conventional transition metal oxide lithium-ion secondary batteries, oxides of nickel (Ni), cobalt (Co), and manganese (Mn) having a density higher than that of heavy metals of 5 g/mL or more are used in the cathode. The problem of heavy metal contamination can be raised. However, in the case of lithium-sulfur batteries, these contaminants are excluded, and since they are non-toxic materials, they can be said to be eco-friendly. In addition, sulfur, which is a cathode material, has an advantage in that it is abundant in resources and inexpensive in terms of price.

However, lithium-sulfur batteries have not yet been widely used commercially, because they have poor lifespan characteristics and low volume energy density compared to currently commercially available lithium-ion secondary batteries. Lithium metal, an anode of a lithium-sulfur battery, is known to be a material with low electrochemical reversibility and low stability. On the other hand, polysulfide, which is a discharge product of sulfur, moves to the negative electrode and the active material is lost through an irreversible reaction with lithium, reducing battery capacity. Due to these two reasons, it is understood that the lifespan characteristics of lithium-sulfur batteries are not good.

Furthermore, as the sulfur loading per unit area of the cathode of a lithium-sulfur battery increases, the performance of the battery deteriorates, and the sulfur loading that can produce a unit mass capacity of 1,000 mAh/g and a potential plateau in the second stage is There is also a research result that is only about 3 mg / cm 2 (Ke Sun et al., Journal of Electrochemical Energy Conversion and Storage, vol. 13, pp. 021002-1, 021002-5, May 2016.).

Conventionally, in order to increase the capacity of a lithium-sulfur battery, a method of stacking as much sulfur as possible per unit area of a positive electrode by making sulfur thick on an aluminum current collector was used. Some of the sulfur is separated from the surface of the electrode far away from the electrode, which can cause a problem in that the lifespan is shortened or the conductivity is reduced and the output of the battery is reduced because the conductive path is reduced.

In addition, the cathode of a conventional lithium-sulfur battery is prepared by mixing sulfur, a binder, and a carbon conductive material with a solvent to form a slurry and then coating the current collector, or by combining mesoporous carbon with sulfur. This is a problem in which the manufacturing process is complicated, the manufacturing time is lengthened due to the inability to raise the drying temperature sufficiently during electrode manufacturing due to the volatility of sulfur, and the utilization rate of sulfur rapidly decreases as the amount of sulfur loaded per unit area of the anode increases. have.

KR 10-2014-0122886 A

An object of the present invention is to provide a lithium-sulfur battery. Specifically, the present invention is to provide a lithium-sulfur battery characterized by comprising a negative electrode protective layer, a non-sulfur-based positive electrode, and a porous separator including glass fibers, and a non-aqueous electrolyte solution containing active sulfur.

One embodiment of the present invention, a non-sulfur-based anode; A lithium metal negative electrode having a negative electrode protective layer containing at least one of a lithium salt and a lithium oxide on a surface thereof; and a porous separator including glass fibers impregnated in a non-aqueous electrolyte containing active sulfur.

According to the present invention, the active sulfur may be provided in at least one of a solid phase and a liquid phase in the non-aqueous electrolyte.

According to the present invention, the content of the active sulfur may be 0.1M or more and 4M or less with respect to the non-aqueous electrolyte.

According to the present invention, the apparent density of the non-sulfur-based positive electrode may be 0.01 g/cm 3 or more and 1.3 g/cm 3 or less.

According to the present invention, the non-sulfur-based anode may be metal foil, metal foam, metal mesh, carbon fiber felt, or carbon paper.

According to the present invention, the non-sulfur-based anode may be coated with a carbon-based material. Specifically, the non-sulfur-based anode may be metal foil, metal foam, metal mesh, carbon fiber felt, or carbon paper coated with a carbon-based material.

According to the present invention, the negative electrode protective layer may be bonded to the surface of the lithium metal negative electrode in the form of nanoparticles, a coating layer, or a ligand bond.

According to the present invention, the non-aqueous electrolyte is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiN(SO ₂ CF ₃ ) ₂ ,LiNO ₃ , and It may further include one or more lithium salts selected from LiBETI.

According to the present invention, the content of the lithium salt may be 0.1M or more and 3.0M or less with respect to the non-aqueous electrolyte.

According to the present invention, the lithium-sulfur battery may have a bobbin type structure in which the lithium metal negative electrode surrounds the non-sulfur positive electrode impregnated in the non-aqueous electrolyte solution.

According to the present invention, the lithium-sulfur battery may have a spiral type structure in which a sheet including the non-sulfur-based positive electrode, the porous separator, and the lithium metal negative electrode is sequentially wound.

Since the lithium-sulfur battery according to an exemplary embodiment of the present invention includes active sulfur in the non-aqueous electrolyte, an improved unit capacity can be realized by loading a sufficient amount of active sulfur compared to a conventional lithium-sulfur battery. Furthermore, the lithium-sulfur battery according to an exemplary embodiment of the present invention can solve battery performance deterioration caused by separation of sulfur due to an increase in sulfur loading in a conventional lithium-sulfur battery.

Since the lithium-sulfur battery according to an exemplary embodiment of the present invention can be equipped with active sulfur by a simple method of adding sulfur to the electrolyte, there is an advantage in that the manufacturing cost can be lowered. In addition, the lithium-sulfur battery according to an exemplary embodiment of the present invention can omit a manufacturing process such as manufacturing a carbon-sulfur composite in order to provide sulfur to a positive electrode, so manufacturing costs can be reduced.

In addition, the lithium-sulfur battery according to an exemplary embodiment of the present invention can suppress the formation of dendrites due to charging and discharging of the battery due to the negative electrode protective film, and can prevent short circuit due to the dendrites through the glass fiber-based separator. .

1 is a schematic diagram of a lithium-sulfur battery according to an exemplary embodiment of the present invention.
2 is a schematic diagram of a lithium-sulfur battery having a bobbin type structure according to an exemplary embodiment of the present invention.
3 is a schematic diagram of a lithium-sulfur battery having a spiral type structure according to an exemplary embodiment of the present invention.

In the present specification, when a member is said to be located “on” another member, this includes not only a case where a member is in contact with another member, but also a case where another member exists between the two members.

In the present specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated.

In this specification, unless otherwise stated, "unit capacity" may mean a discharge capacity per unit mass of active sulfur loaded in a lithium-sulfur battery.

Hereinafter, a lithium-sulfur battery according to the present invention will be described in detail.

One embodiment of the present invention, a non-sulfur-based anode; A lithium metal negative electrode having a negative electrode protective layer containing at least one of a lithium salt and a lithium oxide on a surface thereof; and a porous separator including glass fibers impregnated in a non-aqueous electrolyte containing active sulfur.

A lithium-sulfur battery according to an exemplary embodiment of the present invention may be used as a primary battery or a secondary battery.

The lithium-sulfur battery according to the present invention is characterized in that it does not include sulfur in the positive electrode and includes a non-sulfur positive electrode like conventional lithium-sulfur batteries. Specifically, the lithium-sulfur battery according to the present invention includes a non-sulfur positive electrode, and active sulfur as a positive electrode active material is included in the non-aqueous electrolyte. That is, the lithium-sulfur battery according to the present invention may be a lithium-sulfur battery in which a positive electrode active material is separated. Since the lithium-sulfur battery according to the present invention can be manufactured by a simple method of injecting sulfur into a non-aqueous electrolyte without manufacturing a carbon-sulfur composite to provide sulfur to the positive electrode, the manufacturing cost can be greatly reduced. There are advantages. Furthermore, since the lithium-sulfur battery according to the present invention adds sulfur to the non-aqueous electrolyte, the loading amount of sulfur can be greatly increased to improve the battery capacity, and furthermore, the discharge capacity per unit mass of sulfur can be improved.

According to an exemplary embodiment of the present invention, the active sulfur may be provided in at least one of a solid phase and a liquid phase in the non-aqueous electrolyte. Specifically, the active sulfur may be dispersed or dissolved in the non-aqueous electrolyte solution. The active sulfur may be provided in a solid and/or liquid state in the non-aqueous electrolyte. When the active sulfur is provided in a liquid state, it may mean that the active sulfur is dissolved or sol-gelated in the non-aqueous electrolyte solution. In addition, when the active sulfur is provided in a solid state, the active sulfur may be present as elemental sulfur without being dissolved in the non-aqueous electrolyte.

The active sulfur may be elemental sulfur and its sulfides. Specifically, the active sulfur may mean elemental sulfur and/or a sulfur-based compound having a sulfur-sulfur bond (SS bonding). The active sulfur can store and generate electrical energy using an oxidation-reduction reaction in which the SS bond is broken during discharge and the oxidation number of S decreases, and the oxidation number of S increases while the SS bond is re-formed during charging. For example, the active sulfur may be at least one of elemental sulfur and lithium sulfide. Specifically, the active sulfur may be monomeric sulfur (S ₈ ) having a ring structure and/or lithium sulfide formed by reacting the monomeric sulfur (S ₈ ) with a lithium salt of the non-aqueous electrolyte. The lithium sulfide may exist in the form of Li ₂ S ₈ , Li ₂ S ₆ , Li ₂ S ₄ and the like. When the lithium-sulfur battery is discharged, sulfur may escape from Li ₂ S ₈ and react, and when completely reacted, it exists in the form of Li ₂ S. Furthermore, when charging the discharged lithium-sulfur battery, the Li ₂ S is converted into Li ₂ S ₄ , Li ₂ S ₆ , Li ₂ S ₈ , and the like, and can be re-discharged.

According to an exemplary embodiment of the present invention, the content of the active sulfur may be 0.1M or more and 4M or less, 0.1M or more and 2M or less, or 0.5M or more and 1.5M or less, about 1.0M with respect to the nonaqueous electrolyte. The active sulfur may be a content of elemental sulfur, specifically S ₈ , added to the non-aqueous electrolyte. That is, the content of the active sulfur may mean the content of solid and liquid active sulfur included in the non-aqueous electrolyte. When the content of the active sulfur is within the above range, the discharge capacity per unit mass of the active sulfur can be maximized. When the content of the active sulfur exceeds the above range, the active sulfur is not sufficiently ionized in the non-aqueous electrolyte solution, and the amount remaining in the solid phase increases, and unit capacity may decrease. Therefore, by properly adjusting the content of the active sulfur within the above range, an efficient reaction of the active sulfur contained in the non-aqueous electrolyte may be induced.

According to one embodiment of the present invention, the non-sulfur-based anode may be metal foil, metal foam, metal mesh, carbon fiber felt, or carbon paper. Specifically, the non-sulfur-based positive electrode does not contain sulfur, and an electrode current collector such as metal foil, metal foam, metal mesh, carbon fiber felt, or carbon paper may be used.

In addition, according to one embodiment of the present invention, the current collector of the non-sulfur-based positive electrode may be a metal foil, metal foam, metal mesh, carbon fiber felt, or carbon paper coated with a carbon-based material. Specifically, the non-sulfur-based positive electrode does not contain sulfur, and may be applied by coating at least a portion of an electrode current collector such as metal foil, metal foam, metal mesh, carbon fiber felt, or carbon paper with a carbon-based material. The carbon-based material may be coated by applying a slurry including the following carbon-based material and a binder on at least one surface of the electrode current collector and then drying the slurry.

According to an exemplary embodiment of the present invention, the carbon-based material may include at least one selected from the group consisting of carbon black, ketjen black, acetylene black, graphite, and graphene. However, it is not limited thereto, and any carbon-based material used as a conductive material in the art can be applied.

That is, according to one embodiment of the present invention, the non-sulfur-based positive electrode may be a positive electrode current collector. In addition, the non-sulfur-based positive electrode may be a positive electrode current collector coated with a carbon-based material.

According to one embodiment of the present invention, the apparent density of the non-sulfur-based positive electrode is 0.01 g/cm 3 or more and 1.3 g/cm 3 or less, 0.01 g/cm 3 or more and 1.0 g/cm 3 or less, 0.1 g/cm 3 or more and 1.3 g/cm 3 or less, It may be 0.1 g/cm 3 or more and 1.0 g/cm 3 or less, or 0.1 g/cm 3 or more and 0.7 g/cm 3 or less. When the apparent density of the non-sulfur-based anode is within the above range, it is easy to permeate the electrolyte, so that a high unit capacity can be realized.

According to an exemplary embodiment of the present invention, the negative electrode protective layer may be bonded to the surface of the lithium metal negative electrode in the form of nanoparticles, a coating layer, or a ligand bond. The lithium oxide of the negative electrode protective layer may be a metal oxide nanoparticle having a lithium end group.

The porous separator may be a porous separator containing glass fibers as a main component. Specifically, the porous separator may include glass fibers and a polymer material for fixing them. The porous separator must be resistant to attack by electrolyte and other cell components under cell potential. In addition, the porous separator may include glass fibers in a polymer separator having a porous or microporous network structure in order to confine the non-aqueous electrolyte. However, it is not limited thereto, and any one commonly used in the art may be applied.

According to an exemplary embodiment of the present invention, the non-aqueous electrolyte may further include a lithium salt. Specifically, the non-aqueous electrolyte may include a lithium salt and the active sulfur.

According to an exemplary embodiment of the present invention, the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiN(SO ₂ CF ₃ ) ₂ ,LiNO ₃ , and It may include one or more selected from LiBETI. The lithium salt may react with the active sulfur in the non-aqueous electrolyte to form lithium sulfide. The lithium sulfide is converted into lithium sulfide containing sulfur with a lower atomic number, and the lithium-sulfur battery can be discharged.

According to an exemplary embodiment of the present invention, the content of the lithium salt may be 0.1M or more and 3.0M or less, 0.1M or more and 2.0M or less, 0.5M or more and 1.5M or less, or about 1.0M with respect to the non-aqueous electrolyte.

Further, according to an exemplary embodiment of the present invention, the molar ratio of the lithium salt and the active sulfur may be 1.5:1 to 1:1.5, specifically about 1:1. When the molar ratio of the lithium salt and the active sulfur is within the above range, the active sulfur can be used in a high ratio in the non-aqueous electrolyte, and through this, the battery capacity per unit mass of the active sulfur can be maximized.

According to an exemplary embodiment of the present invention, the non-aqueous electrolyte solution may include a non-aqueous organic solvent. Specifically, as the non-aqueous organic solvent, 1,3-dioxolane, 2-methyltetrahydrofuran, polyethylene glymedimethyl ether, tetrahydrofuran, and/or ether-based solvents may be used. have. Dibutyl ether, 2-methyltetrahydrofuran, polyethylene glymedimethyl ether, tetrahydrofuran and the like may be used as the non-aqueous organic solvent. Specifically, the non-aqueous organic solvent is dimethoxyethane, diglyme, triglyme, tetraglyme, 1,3-dioxolane, dimethyl ether, diethyl ether, N-methylpyrrolidone, 3-methyl-2-oxazolidone, dimethylformamide, sulfolane, dimethyl acetamide, dimethyl sulfoxide, dimethyl sulfate, It may include one or more selected from the group consisting of ethylene glycol diacetate, dimethyl sulfite, and ethylene glycol sulfite, and when one or more are mixed and used, the mixing ratio may be appropriately adjusted according to the desired battery performance. have.

A schematic diagram of a lithium-sulfur battery according to an exemplary embodiment of the present invention is shown in FIG. 1 . Specifically, according to FIG. 1, a non-sulfur-based positive electrode 10 and a lithium metal negative electrode 20 are provided with a porous separator 30 interposed therebetween, and the porous separator 30 is impregnated with a non-aqueous electrolyte 40, and a non-aqueous The electrolyte solution 40 is positioned between the non-sulfur-based positive electrode 10 and the lithium metal negative electrode 20 . However, the present invention is not limited to the structure of FIG. 1 and may further include additional members.

According to an exemplary embodiment of the present invention, the lithium-sulfur battery may have a bobbin type structure in which the lithium metal negative electrode surrounds the non-sulfur-based positive electrode impregnated with the non-aqueous electrolyte. 2 is a schematic diagram of the lithium-sulfur battery having the bobbin type structure. Specifically, FIG. 2 shows that the non-sulfur-based positive electrode 10 is impregnated with the non-aqueous electrolyte solution 40 in the center, the lithium metal negative electrode 20 is provided on the inner wall surface of the battery case 50, and the non-sulfur-based positive electrode 10 and a lithium-sulfur battery having a bobbin structure having a porous separator 30 between lithium metal negative electrodes 20 and a side cross-sectional view and a planar cross-sectional view.

According to an exemplary embodiment of the present invention, the lithium-sulfur battery may have a spiral type structure in which a sheet including the non-sulfur-based positive electrode, the porous separator, and the lithium metal negative electrode is sequentially wound. 3 is a schematic diagram of the lithium-sulfur battery having the spiral type structure. Specifically, FIG. 3 is a spiral type in which a non-sulfur-based positive electrode 10, a porous separator 30, and a lithium metal negative electrode 20 are sequentially stacked, and the porous separator is impregnated with a non-aqueous electrolyte 40 ( A side cross-sectional view and a planar cross-sectional view of a lithium-sulfur battery having a spiral type structure are shown.

10: non-sulfur anode
20: lithium metal cathode
30: porous separator
40: non-aqueous electrolyte
50: battery case
60: battery header
70: lead
80: insulator

Claims (10)

a non-sulfur anode;
A lithium metal negative electrode having a negative electrode protective layer containing at least one of a lithium salt and a lithium oxide on a surface thereof; and
Impregnated in a non-aqueous electrolyte solution containing active sulfur, a porous separator containing glass fibers;
Active material-separated lithium-sulfur battery. The method of claim 1,
The lithium-sulfur battery, characterized in that the active sulfur is provided in at least one of a solid phase and a liquid phase in the non-aqueous electrolyte. The method of claim 1,
The lithium-sulfur battery, characterized in that the active sulfur content is 0.1M or more and 4M or less with respect to the non-aqueous electrolyte. The method of claim 1,
The lithium-sulfur battery, characterized in that the apparent density of the non-sulfur-based positive electrode is 0.01 g / cm 3 or more and 1.3 g / cm 3 or less. The method of claim 1,
The non-sulfur-based cathode is a lithium-sulfur battery, characterized in that metal foil, metal foam, metal mesh, carbon fiber felt, or carbon paper. The method of claim 1,
The anode protective layer is a lithium-sulfur battery, characterized in that bonded to the surface of the lithium metal anode in the form of nanoparticles, coating layer or ligand bond. The method of claim 1,
The non-aqueous electrolyte is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiN(SO ₂ CF ₃ ) ₂ ,LiNO ₃ , and A lithium-sulfur battery, characterized in that it further comprises one or more lithium salts selected from LiBETI. The method of claim 7,
The lithium-sulfur battery, characterized in that the content of the lithium salt is 0.1M or more and 3.0M or less with respect to the nonaqueous electrolyte. The method of claim 1,
The lithium-sulfur battery has a bobbin type structure in which the lithium metal negative electrode surrounds the non-sulfur positive electrode impregnated in the non-aqueous electrolyte solution. The method of claim 1,
The lithium-sulfur battery is a lithium-sulfur battery, characterized in that the spiral type structure in which a sheet including the non-sulfur positive electrode, the porous separator, and the lithium metal negative electrode are sequentially wound.

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