KR102071138B1 - Polysulfide infiltrated cathode for lithium-sulfur batteries - Google Patents

Abstract

Herein is a carbon current collector comprising one or more micropores; Anolyte in which lithium polysulfide is dissolved; And a cathode active material adsorbed in pores of the carbon current collector immersed in the anolyte solution, wherein the cathode active material is a sulfur compound including sulfur of lithium polysulfide dissolved in the anolyte solution. Disclosed is a lithium-sulfur secondary battery including a positive electrode and a positive electrode for a lithium-sulfur secondary battery.

Description

 Polysulfide infiltrated cathode for lithium-sulfur batteries}

The present invention relates to a positive electrode for a lithium-sulfur secondary battery in which polysulfide is immersed, and more particularly, to a lithium-sulfur secondary battery in which polysulfide is immersed in a carbon current collector, a lithium-sulfur secondary battery including the positive electrode, and the The present invention relates to an electronic device including a lithium-sulfur secondary battery.

Lithium secondary batteries are commonly used in electronic devices such as mobile phones, laptops and camcorders because of their high energy density and high voltage. Recently, based on the maintenance of cats and related laws on environmental protection, the use of lithium secondary batteries is increasing. For example, a method of using a lithium secondary battery as a storage battery for storing electric power or a use for powering an automobile such as an electric vehicle or a hybrid electric vehicle is considered.

High energy density can be considered as the most important battery characteristic. In order to realize high energy density, development of an electrode active material having a large theoretical capacity is required. However, the transition metal oxide, which is a positive electrode active material for a lithium secondary battery, has a theoretical capacity of only about 250 mAh / g or less, so it is not easy to realize high energy density of a lithium secondary battery including a transition metal oxide.

In order to overcome this problem, development of a lithium-sulfur battery using a sulfur-based compound as a cathode active material is being actively conducted. Lithium-sulfur batteries have a theoretical capacity density of 2,600 mAh / kg, and are known to have capacity characteristics equivalent to 10 times that of conventional transition metal oxides in simple calculations. Therefore, it is expected to be able to implement a higher energy density than the conventional lithium secondary battery, including sulfur as a positive electrode active material. In addition, by using inexpensive sulfur as a main raw material of the secondary battery can reduce the production cost of the secondary battery.

 In general, lithium-sulfur batteries have a structure in which a sulfur-based compound having a disulfide bond is used as a cathode active material and a material containing lithium metal or lithium ions as a cathode active material. Specifically, lithium ions decomposed at the cathode during discharging react with sulfur of the disulfide bond to generate lithium sulfide, and sulfur oxides are reduced by dissociation of the disulfide bond. On the contrary, during charging, the lithium ions are plated on the surface of the negative electrode again, and disulfide bonds are generated to increase the oxidation number of sulfur. That is, electrical energy is stored or released through the above-described redox reaction.

On the other hand, liquid lithium polysulfides (Li ₂ S _x , 4 ≦ _x ≦ 8) and solid insoluble lithium sulfides (Li ₂ S ₂ , Li ₂ S) are formed as discharge products at the anode during discharge, and during charging, A reverse reaction proceeds. In particular, the liquid lithium polysulfide diffuses through the electrolyte in the form of a heavy molecule or an anion. As lithium polysulfide diffuses out of the region of the anode, the amount of sulfur participating in the electrochemical reaction at the anode decreases. The reduction in the amount of sulfur results in a decrease in capacity.

In addition, side reactions of the negative electrode and lithium polysulfide may be further problematic. As the charge and discharge reaction continues, insoluble lithium sulfide (Li ₂ S) is fixed to the cathode and the surface. Insoluble lithium sulfide fixed on the surface lowers the reaction activity of the negative electrode and worsens the overall potential characteristics of the cell.

As a typical approach to solve the above problems, a method of constraining sulfur by using a microstructure of porous and highly conductive carbon has been proposed. However, this method has a problem that the sulfur content per electrode area is very small, and the electrochemically inert carbon support occupies a large part of the electrode.

Korea Patent Registration No. 10-0508920

The present invention has been made in order to solve the above problems, and aims to suppress by-products and shuttleling of lithium sulfide.

The present invention furthermore aims at increasing the capacity per unit area of the positive electrode by eliminating the use of inert carbon supports and improving the loading density of sulfur.

In addition, another object of the present invention is to provide a positive electrode for a lithium-sulfur secondary battery that is easy to mass-produce.

As a means for achieving the above object the present specification is a carbon current collector including one or more micropores; Anolyte in which lithium polysulfide is dissolved; And a positive electrode active material adsorbed in the pores of the carbon current collector immersed in the positive electrode solution, wherein the positive electrode active material is a sulfur compound including sulfur of lithium polysulfide dissolved in the positive electrode solution. It starts.

In each lithium-sulfur secondary battery positive electrode of the present invention, it is preferable that lithium polysulfide of the positive electrode solution is evenly injected into the carbon current collector in the liquid phase.

In each of the positive electrode for a lithium-sulfur secondary battery of the present invention, the carbon current collector includes two or more carbon nanofibers, and the carbon current collector is preferably a carbon cloth in which carbon nanofibers are intertwined.

In each of the positive electrode for lithium-sulfur secondary battery of the present invention, the diameter of the micropores contained in the carbon current collector is preferably 0.5 nm or more and 1.5 nm or less.

In the positive electrode for a lithium-sulfur secondary battery of the present invention, the diameter of the micropores contained in the carbon current collector is preferably 0.7 nm or more and 1.3 nm or less.

In each of the positive electrode for lithium-sulfur secondary battery of the present invention, the diameter of the micropores contained in the carbon current collector is preferably 1.1 nm.

In each of the positive electrode for lithium-sulfur secondary battery of the present invention, it is preferable that sulfur of the positive electrode active material per unit area (cm ² ) of the carbon current collector is adsorbed to the carbon current collector at more than 2 mg and less than 10 mg.

In each of the positive electrode for lithium-sulfur secondary battery of the present invention, it is preferable that sulfur of the positive electrode active material per unit area (cm ² ) of the carbon current collector is adsorbed to the carbon current collector to more than 4 mg and less than 8 mg.

In each of the positive electrode for lithium-sulfur secondary battery of the present invention, it is preferable that 6 mg of sulfur of the positive electrode active material per unit area (cm ² ) of the carbon current collector is adsorbed to the carbon current collector.

In addition, the present specification as a means for achieving the above object is a carbon current collector containing one or more micropores, the anolyte solution in which lithium polysulfide is dissolved, and is adsorbed in the pores of the carbon current collector immersed in the anolyte solution A positive electrode active material, wherein the positive electrode active material is a sulfur compound including sulfur of lithium polysulfide dissolved in an anolyte solution; Lithium, lithium alloy or carbon-based negative electrode; A lithium-sulfur secondary battery comprising a separator is disclosed.

In each lithium-sulfur secondary battery of the present invention, it is preferable that lithium polysulfide of the anolyte is evenly injected into the carbon current collector in the liquid phase.

In each of the lithium-sulfur secondary batteries of the present invention, the carbon current collector includes two or more carbon nanofibers, and the carbon current collector is preferably a carbon cloth in which carbon nanofibers cross each other.

In each lithium-sulfur secondary battery of the present invention, the diameter of the micropores contained in the carbon current collector is preferably 0.5 nm or more and 1.5 nm or less.

In each lithium-sulfur secondary battery of the present invention, the diameter of the micropores contained in the carbon current collector is preferably 0.7 nm or more and 1.3 nm or less.

In each lithium-sulfur secondary battery of the present invention, it is preferable that the diameter of the micropores contained in the carbon current collector is 1.1 nm.

In each lithium-sulfur secondary battery of the present invention, it is preferable that sulfur of the positive electrode active material per unit area (cm ² ) of the carbon current collector is adsorbed to the carbon current collector in excess of 2 mg and less than 10 mg.

In each of the lithium-sulfur secondary batteries of the present invention, it is preferable that sulfur of the positive electrode active material per unit area (cm ² ) of the carbon current collector is adsorbed to the carbon current collector at more than 4 mg and less than 8 mg.

In each lithium-sulfur secondary battery of the present invention, it is preferable that 6 mg of sulfur of the positive electrode active material per unit area (cm ² ) of the carbon current collector is adsorbed onto the carbon current collector.

Herein is a positive electrode for each lithium-sulfur secondary battery of the present invention; Lithium, lithium alloy or carbon-based negative electrode; Disclosed is a lithium-sulfur secondary battery comprising a separator, and further, an electronic device including each lithium-sulfur secondary battery of the present invention.

The present invention provides a lithium-sulfur secondary battery having improved charge / discharge cycle characteristics by suppressing by-products and shuttleling of insoluble lithium sulfide through the above-described configuration.

In addition, the present invention can implement a lithium-sulfur secondary battery having a high energy density per unit area by improving the loading density of sulfur.

In addition, the lithium-sulfur secondary battery of the present invention utilizes a carbon current collector to exclude the inert carbon support, and provides a feature that the lithium-sulfur secondary battery can operate normally regardless of the curvature change.

1 is a CV (Cyclic Voltametry) curve of Example 1 of the present invention.
2A is a CV curve of Comparative Example 1 of the present invention.
2B is a CV curve of Comparative Example 4 of the present invention.
3A is an exploded photograph of each battery after GCPL cycling of a coin-type battery including Example 1 and Comparative Example 4 of the present invention.
3B is a surface photograph of a separator-side carbon current collector after GCPL cycling of a coin-type battery including Comparative Example 4 of the present invention.
3C is a photograph of a lithium negative electrode after GCPL cycling of a coin-type battery including Comparative Example 4 of the present invention.
4 is an EIS spectra graph before and after GCPL cycling of Example 1 of the present invention.
5 is an EIS spectra graph after GCPL cycling of Comparative Example 4 of the present invention.
6 is a graph showing a change in discharge capacity after GCPL cycling in another potential range of Example 1 of the present invention.
7 is a graph showing a change in discharge capacity according to the number of charge / discharge cycles of Example 1 and Comparative Examples 1 to 4 of the present invention.
8 shows each tenth charge / discharge profile of Example 1 and Comparative Examples 1 to 4 of the present invention.
9 is a graph showing the change in area capacity according to the loading (mgS / cm ² ) of the 100th sulfur of the charge / discharge cycle of 0.3C of Example 1, Comparative Examples 1 to 4 of the present invention.
10 is a graph showing the change according to the number of charge / discharge cycles of the coulombic efficiency of Example 1 and Comparative Examples 1 and 4 of the present invention.
11 is a photograph of Embodiment 2 of the present invention.
12 is a schematic diagram of the bending of Embodiment 2 of the present invention.
13 is a graph showing changes in discharge capacity according to the number of charge / discharge cycles of Example 2 and Comparative Examples 5 and 6 of the present invention.

The terminology used herein is for the purpose of describing particular examples only. Thus, for example, singular forms include plural forms unless the context clearly requires them to be singular. In addition, the terms "comprise" or "include" as used in the present application are used to clearly indicate that there exists a feature, step, function, component, or combination thereof described in the specification, and other features. It should be noted that it is not intended to preliminarily exclude the presence of elements, steps, functions, components, or combinations thereof.

On the other hand, unless defined otherwise, all terms used herein are to have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Accordingly, unless specifically defined herein, a particular term should not be construed in an excessively ideal or formal sense.

On the other hand, in this specification will be described as a "Li ₂ S ₆ has infiltrated the carbon current collector" below "CC-S". "The weight Xmg of sulfur adsorbed per unit area (cm <^2> ) of CC-S" is described below as "CC-SX". For example, 'CC-S6' refers to a carbon current collector in which Li ₂ S ₆ having a weight of 6 mg of sulfur adsorbed per unit area (cm ² ) of the carbon current collector is infiltrated.

On the other hand, the expression "entangled" in the present specification is not limited to the dictionary meaning "to be entangled with each other so that threads or strings are difficult to loosen", the synonyms "mixed", "entangled", May be interpreted as "entangled" or the like. In addition, the term "entangled" in the present specification not only includes irregularly arranged threads or strings, but also includes regularly arranged threads or strings. In addition, in the context of the entire specification, it may be expanded in a range that can be clearly understood by those skilled in the art.

On the other hand, "lithium polysulfide" in the present specification implies that it can be dissolved in the anolyte, and "lithium polysulfide" may also be understood as "anode active material" in the context of the entire description. Hereinafter, the problem solving means of the present invention will be described in detail.

<Positive electrode for lithium-sulfur secondary battery of the present invention>

Hereinafter, each component constituting the positive electrode of the positive electrode composition for a lithium-sulfur secondary battery of the present invention will be described in detail.

Anolyte

1. Lithium Polysulfide

In order to evenly inject the lithium polysulfide into the carbon current collector in the liquid phase, sulfur or lithium sulfide is dissolved in the anolyte solution. For example, Li ₂ S _x (4 ≦ x ≦ 8, where x is a positive even number) is preferable. If x is 4 or less, Li ₂ S _x is insoluble and cannot be injected into the liquid phase. If x is 8 or more, Li ₂ S _x is chemically unstable.

Sulfur of lithium polysulfide is adsorbed into the pores of the carbon current collector to be a positive electrode active material, and the positive electrode active material may be a sulfur compound including at least one form selected from the group consisting of elemental sulfur (S ⁰ ), lithium sulfide and lithium polysulfide. have. The positive electrode active material is reduced upon discharge to form soluble lithium polysulfide (Li ₂ S _x (4 ≦ _x ≦ 8)), insoluble lithium disulfide (Li ₂ S ₂ ), and insoluble lithium sulfide (Li ₂ S).

Insoluble lithium sulfide produced by the reduction reaction of the positive electrode active material adsorbed to the pores of the carbon current collector is deposited in the pores of the carbon current collector to form a passivation layer. The passivation layer of the present invention is a layer of insoluble lithium sulfide formed by depositing insoluble lithium sulfide produced by the reduction reaction of the cathode active material in the pores of the carbon current collector, and lithium polysulfide by blocking the pores of the carbon current collector. Suppress Shuttle. The carbon current collector acts as a confining layer of lithium polysulfide produced by the reaction of the battery.

2. Solvent

The solvent of the anolyte solution is sufficient to prevent the shuttle of the lithium polysulfide adsorbed in the carbon current collector pores, but is not particularly limited. The solvent in the anolyte prevents the shuttle of the lithium polysulfide from the carbon current collector due to polarity and / or specific interaction with the dissolved lithium polysulfide. Since lithium polysulfide is easily dissolved in an aqueous solvent as a substance capable of hydrogen bonding, a non-aqueous solvent is an example of a preferred solvent of the present invention.

As an example of the non-aqueous solvent, the ether solvent may be, for example, a non-cyclic ether, a cyclic ether, a polyether, or a mixture thereof. More specifically, the ether solvent is 1,3-dioxolane (DOL), 1,2-dimethoxyethane (1,2-Dimethoxyethane: DME), furan (Furan), 2-methyl Furan (2-Methylfuran), 2,5-dimethylfuran, tetrahydrofuran, ethylene oxide, 1,4-oxane, 1,4-Oxane, 4 -Methyl-1,3-dioxolane (4-Methyl-1,3-Dioxolane), tetraethylene glycol dimethyl ether (TEGDME) or a mixed solvent thereof. Preferably, one selected from linear ether and cyclic ether may be selected and mixed, more preferably 1,3-dioxolane (1,3-Dioxolane: DOL) and 1,2- as in one embodiment of the present invention. Dimethoxyethane (1,2-Dimethoxyethane: DME) by mixing and applying in a predetermined volume ratio, it may be a solution mixed in a volume ratio of 1: 1.

In the non-aqueous solvent for a lithium-sulfur secondary battery of the present invention, the content of the ether solvent in the above example can be adjusted according to the goal of improving the performance of the battery, but within a range of 50 to 95% based on the total volume of the solvent. It is desirable to apply. If less than 50% is used, the desired performance improvement effect is insignificant, and at least 5% is preferably used together with other solvents that can improve battery performance. Examples of the other solvents include sulfonate solvents.

On the other hand, the lithium salt of the present invention is a good material to be dissolved in the non-aqueous solvent, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF _{3 CO 2, LiAsF 6, LiSbF 6} , LiAlCl 4, CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 Nli, chloroborane lithium, lower aliphatic carboxylic acid lithium, phenyl lithium borate, there is LiTFSI And preferably LiTFSI as an example of the present invention.

Carbon collector

The carbon current collector of the present invention has a microporous structure of activated carbon, which is advantageous for physical adsorption of sulfur. Two or more carbon nanofibers constitute a carbon current collector having one or more micropores to which sulfur can be adsorbed. The structure of the carbon nanofibers may be configured to include pores in which lithium polysulfide can sufficiently infiltrate the carbon current collector, and is not particularly limited. However, for example, preferably, the carbon current collector may be a carbon cloth in which carbon nanofibers are intersected and entangled.

On the other hand, when the battery is continuously charged / discharged, the carbon current collector serves as a restraining layer that suppresses the shuttle of lithium polysulfide generated by the reaction of the battery, so that the structure of the carbon current collector forming the positive electrode may be deformed. The performance of the battery may be degraded. Therefore, the carbon nanofibers forming the carbon current collector are preferably physically and chemically stable materials.

As the ratio of the carbon current collector pores, it is preferable that the volume ratio of the pores has a high ratio of about 50% to 95% based on the volume of the entire carbon current collector. For example, when the volume ratio of pores is less than 50%, lithium polysulfide is not sufficiently infiltrated, and thus, lithium-sulfur secondary batteries cannot enjoy improved capacity characteristics and life characteristics. On the contrary, when the volume ratio of the pores is 95% or more, the electrical conductivity of the carbon current collector may decrease, thereby degrading the performance of the battery.

In addition, the pores of the carbon current collector are sufficient as long as sulfur can be adsorbed, and the pore arrangement is not particularly limited. The pores of a general porous carbon material are radially arranged from the outer surface of the carbon material, and if the pores on the outer surface of the carbon material are blocked, the penetration into the inside of all the pores in which the sulfur compound anode active material and lithium cation are arranged radially is costly. The performance of the battery is reduced. On the other hand, as an example of the present invention, the pores of the carbon current collector may be preferably arranged in a line from the outer surface of the carbon current collector to the inside. Even if pores on the outer surface of the carbon current collector are occluded, it is easy to penetrate into the inside of other outer pores where the cathode active material and lithium cation are not occluded, and thus the cathode active material and lithium cation, etc. Penetration of Efficient Efficiently Occurs Efficiently and the Performance of the Battery is Not Degraded

The pores of the carbon current collector may have a diameter of the internal pores that is easy to infiltrate the electrolyte and can suppress the shuttleling of the lithium polysulfide generated by the reaction of the battery, and is not particularly limited. For example, the diameter of the fine pores of the carbon current collector of the present invention is preferably between 0.5nm to 1.5nm. If the diameter of the micropores is less than 0.5 nm, it is inexpensive to penetrate the short chain structure S _2-4 , the electrolyte and the lithium cation into the anode. On the contrary, when the diameter of the fine pores exceeds 1.5 nm, the passivation layer of the insoluble lithium sulfide deposited on the carbon current collector does not sufficiently occlude the pores, thereby preventing the shuttle of the lithium polysulfide. Therefore, when the diameter of the fine pores exceeds 1.5 nm, the cycle characteristics of the battery rapidly decreases.

More preferably, the diameter of the pores in which the lithium cation and the electrolyte are easily moved may be about 0.7 nm to 1.3 nm. The passivation layer of insoluble lithium sulfide deposited on a carbon current collector is easy to penetrate S _2-4 of a short chain structure, S ₈ of a ring structure _{, an} electrolyte and a lithium cation when the diameter of the fine pores is 0.7 nm or more and 1.3 nm or less. The pores are sufficiently occluded to suppress shuttleling of lithium polysulfide efficiently, thereby ensuring excellent cycle characteristics. Even more preferably about 1.1 nm.

Coupling Characteristics and Specific Effects

The combination of the carbon current collector, the anolyte solution, and the positive electrode active material of the present invention suppresses the shuttleting of lithium polysulfide, thereby obtaining a positive electrode for a lithium-sulfur secondary battery having improved life characteristics, cycle characteristics, capacity characteristics, and the like. Hereinafter, the origin of the peculiar effect of the present invention will be described in more detail.

1. Shuttle suppression-charge / discharge cycle characteristics

The carbon current collector of the present invention may be immersed in the anolyte solution in which lithium polysulfide is dissolved. In order to evenly inject the lithium polysulfide into the carbon current collector in the liquid phase, sulfur or lithium sulfide is dissolved in the anolyte solution. _X of the liquid lithium polysulfide (Li ₂ S _x ) may have a range of 4≤x≤8. When the carbon current collector of the present invention is immersed in the anolyte through an electrochemical reaction, the reaction area between the pores of the carbon current collector and the anolyte in which lithium polysulfide is dissolved is maximized.

In addition to the above, since the carbon current collector has a microporous structure, the weight of sulfur adsorbed on the carbon current collector can be easily controlled by simply changing the concentration of the anolyte solution. By controlling the weight of the sulfur, it is possible to control the deposition amount of insoluble lithium sulfide produced by the reduction reaction of the positive electrode active material containing sulfur. Since the insoluble lithium sulfide produced by the reduction reaction of the positive electrode active material adsorbed to the carbon current collector pores inhibits the shuttle of lithium polysulfide as a self-trap, the carbon current collector of the present invention is dependent on the reaction of the battery. It can serve as a confining layer of the produced lithium polysulfide.

On the other hand, when the weight of sulfur adsorbed to the carbon current collector is too small, the amount of insoluble lithium sulfide is not deposited enough to form a passivation layer sufficiently, and when charging / discharging is repeated, the shuttle of lithium polysulfide cannot be suppressed. In addition, when the weight of sulfur is too high, the reduction reaction of the positive electrode active material including sulfur is promoted, thereby rapidly forming irreversibly a passivation layer of insoluble lithium sulfide, thereby deteriorating the characteristics of the battery. On the other hand, when an appropriate amount of insoluble lithium sulfide is deposited in the carbon current collector pores, the deposited insoluble lithium sulfide serves to suppress the shuttle of the lithium polysulfide, but its deposition due to charging / discharging is reversible, resulting in a positive electrode. Its cycle characteristics are excellent.

As an example of the weight (mg) of sulfur adsorbed per unit area (cm ² ) of a carbon current collector capable of depositing an appropriate amount of insoluble lithium sulfide, preferably 2 mg or more and 10 mg or less is mentioned. In 2 mg or less, the amount of insoluble lithium sulfide is too small to inhibit the shuttle of lithium polysulfide, and in the case of 10 mg or more, the amount of positive electrode active material including sulfur adsorbed to the carbon current collector is excessive, so that the reduction reaction is promoted. The passivation layer of sulfide is rapidly formed, and deposition of insoluble lithium polysulfide is irreversibly caused to deteriorate battery characteristics.

The weight (mg) of sulfur adsorbed per unit area (cm ² ) of the carbon current collector is more preferably 4 mg or more and 8 mg or less. Insoluble lithium sulfide starts to form a passivation layer sufficiently from 4 mg or more, thereby inhibiting the shuttle of lithium polysulfide and at the same time having a high loading density of sulfur, thereby having excellent electrode characteristics. From 8 mg or more, the amount of positive electrode active material containing sulfur adsorbed on the carbon current collector is excessive, thereby facilitating a reduction reaction, thereby rapidly forming a passivation layer of insoluble lithium sulfide and irreversible deposition of insoluble lithium polysulfide. Sharply deteriorating properties.

The weight (mg) of sulfur adsorbed per unit area (cm ² ) of the carbon current collector is even more preferably 6 mg. When the weight of sulfur adsorbed is 6 mg, insoluble lithium sulfide sufficiently forms a passivation layer to suppress shuttle of lithium polysulfide and reversible deposition of insoluble lithium sulfide, resulting in excellent cycle characteristics. In addition, sulfur has a high loading density and may have excellent electrode characteristics.

That is, by combining the anolyte and the carbon current collector of the present invention, it is possible to easily control the weight of sulfur adsorbed to the carbon current collector by maximizing the reaction area. By controlling the deposition amount in the pores of insoluble lithium sulfide produced by the reduction reaction of the positive electrode active material, it is possible to enjoy improved battery characteristics due to the prevention of the shuttle of the lithium polysulfide.

2. elasticity and elasticity

As an example of the carbon current collector of the present invention, in the carbon cloth, carbon nanofibers intersect and entangle with each other, and thus have excellent elasticity, elasticity, and flexibility. Specifically, the carbon nanofibers of the present invention can be stretched by 1.25 times or more, and this elasticity can sufficiently accommodate the volume change (80%) during the charge / discharge process without damaging the electrode. In addition, by utilizing the carbon current collector of the present invention, the lithium-sulfur secondary battery of the present invention maintains a constant discharge capacity even after repeated bending. Details thereof will be described later.

3. Energy density

The carbon current collector of the present invention has improved mechanical properties and electrical conductivity as a current collector. Specifically, polysulfide or sulfur is constrained during the charge / discharge process to prevent diffusion. In addition, the capacity of the carbon current collector that may contain an electrolyte is 63 µL / cm ² or more, which is much larger than that of a conventional metal current collector (carbon coated Al, 0.0023 µL / cm ² ). Therefore, the loading density of sulfur can be easily improved by immersing the carbon current collector of the present invention in the anolyte solution.

In addition, the carbon current collector of the present invention has a microporous structure that is advantageous for physical adsorption of sulfur as activated carbon. For example, when calculating the surface area of the carbon current collector and the volume of the fine pores according to the nitrogen adsorption measurement method, the surface area of the carbon current collector per 1 g of the carbon current collector may be approximately 1630 m ² , and the volume of the fine pores may be approximately 0.87 cm ³ days. Can be. Theoretically, the maximum amount of sulfur that can be adsorbed to the micropores of the carbon current collector of the present invention is about 11.5 mg per unit area (cm ² ) of the carbon current collector.

The present specification includes a positive electrode for a lithium-sulfur secondary battery in which a detailed configuration for the carbon current collector, a detailed configuration for the anolyte solution, and a detailed configuration for the positive electrode active material are independently combined with each other as a means for solving the above problems. The present specification also discloses a lithium-sulfur secondary battery including the positive electrode of the present invention and an electronic device including the lithium-sulfur secondary battery.

<Lithium-sulfur secondary battery and electronic device including the positive electrode for lithium-sulfur secondary battery of the present invention>

Lithium-sulfur secondary battery comprising the positive electrode for lithium-sulfur secondary battery of the present invention

The lithium-sulfur secondary battery may be manufactured in various forms such as a coin cell, a beaker cell, a pouch cell, a cylindrical cell, a square cell, and the like. The lithium-sulfur secondary battery of the present invention has physical properties such as elasticity and flexibility by eliminating the use of a sulfur-free carbon support by using a carbon current collector, and on the premise of maintaining the above characteristics, There is no special limitation. However, the pouch cell may be considered as one way to maximize the improved mechanical properties of the carbon current collector.

 The lithium-sulfur secondary battery of the present invention includes the positive electrode, the negative electrode, the separator, and the like of the present invention. It should be noted that the idea of the present invention is not limited by the examples of the negative electrode and the separator described below.

As the negative electrode, a lithium metal or lithium metal alloy thin film may be used as it is. Alternatively, the negative electrode may be used with a lithium metal or lithium metal alloy thin film disposed on a conductive substrate which is a current collector. The lithium metal thin film may be integrated with the current collector. Alternatively, the negative electrode may include a current collector and a negative electrode active material layer disposed on the current collector.

The current collector in the negative electrode may be one selected from the group consisting of stainless steel, copper, nickel, iron and cobalt, but is not necessarily limited thereto, and may be any metal substrate having excellent conductivity that may be used in the art. For example, the current collector may be a conductive oxide substrate, a conductive polymer substrate, or the like. In addition, the current collector may have various structures such as a conductive metal, a conductive metal oxide, and a conductive polymer coated on one surface of the insulating substrate in addition to the structure of the entire substrate. On the other hand, the current collector may be a flexible substrate. In this case, the current collector can be easily bent. In addition, after bending, the current collector may be easily restored to its original form. Therefore, in the pouch cell type lithium-sulfur secondary battery of the present invention, it is preferable to use a flexible substrate as a current collector from the viewpoint that mechanical properties can be actively utilized.

In addition, the negative electrode may further include other negative electrode active materials in addition to the lithium metal or the lithium metal alloy. The negative electrode may be an alloy of lithium metal and another negative electrode active material, a composite of lithium metal and another negative electrode active material, or a mixture of lithium metal and another negative electrode active material. Other negative electrode active materials that may be added to the negative electrode may include, for example, one or more selected from the group consisting of metals capable of alloying with lithium, transition metal oxides, non-transition metal oxides, and carbon-based materials.

For example, the metal alloyable with lithium is Si, Sn, Al, Ge, Pb, Bi, Sb Si-Y alloy (The Y is an alkali metal, alkaline earth metal, Group 13 element, Group 14 element, transition metal, rare earth Element or a combination thereof, not Si), Sn-Y alloy (Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element or combination thereof, and not Sn. ) And the like. As the element Y, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po or a combination thereof.

For example, the transition metal oxide may be lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like, and the non-transition metal oxide may be SnO ₂ , SiO _x (0 <x <2), or the like.

The separator may be used as long as it is commonly used in lithium-sulfur secondary batteries. A low resistance to the ion migration of the electrolyte and excellent in the ability to hydrate the electrolyte can be used. For example, it is selected from glass fiber, polyester, teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of nonwoven or woven fabric. For example, a flexible separator such as polyethylene or polypropylene may be used.

Electronics

Since the lithium-sulfur secondary battery having the positive electrode of the present invention has improved cycle characteristics, physical characteristics, and energy density, it may be used as a power source for various electronic devices. Examples of electronic devices include air conditioners, washing machines, TVs, refrigerators, freezers, air conditioners, laptops, tablets, smartphones, PC keyboards, displays for PCs, desktop PCs, CRT monitors, printers, integrated PCs, mice, and hard disks. , PC peripherals, Iron, Clothes dryer, Window fan, Transceiver, Blower, Ventilation fan, TV, Music recorder, Music player, Oven, Range, Toilet bowl with cleaning function, Warm air heater, Car component, Car navigation , Flashlight, Humidifier, Mobile Karaoke Machine, Ventilation Fan, Dryer, Air Purifier, Mobile Phone, Emergency Light, Game Machine, Sphygmomanometer, Coffee Grinder, Coffee Maker, Kotatsu, Copier, Disc Changer, Radio, Shaver, Juicer, Shredder ), Water purifiers, lighting fixtures, dehumidifiers, dish dryers, rice cookers, stereos, stoves, speakers, trouser presses, vacuum cleaners, body fat scales, scales, household scales, rain Dio player, electric board, rice cooker, electric stand, electric kettle, electronic game machine, portable game machine, electronic dictionary, electronic notebook, microwave oven, electric cooker, electronic calculator, electric cart, electric wheelchair, power tool, electric toothbrush, electric foot Warmer, Barber, Telephone, Clock, Intercom, Air circulator, Electric insecticide, Hot plate, Toaster, Hair dryer, Electric drill, Hot water heater, Panel heater, Grinder, Soldering iron, Video camera, VCR, Facsimile, Food processor, Quilt dryer, Headphones, Microphone, Massager, Mixer, Sewing machine, Rice cake machine, Floor heating panel, Lantern, Remote control, Hot and cold, Water cooler, Cold air conditioner, Word processor, Whisk, Electronic instrument, Motorcycle, Toys, Lawn mower , Fishing bobbers, bicycles, cars, hybrid cars, plug-in hybrid cars, electric cars, railways, ships, airplanes, emergency storage batteries, etc. The.

The lithium-sulfur secondary battery according to the present invention is particularly small electronics such as notebooks, tablets, smartphones, electric carts, integrated mice, game consoles, electronic dictionaries, electronic notebooks, etc., which require improved cycle characteristics, elasticity, and flexibility. It can be used suitably as a power supply of an apparatus etc.

{Example}

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, this is provided to be easily implemented by those of ordinary skill in the art, the present invention can be implemented in a number of different forms, the spirit of the invention is not necessarily limited to the embodiments no.

In addition, in the following examples and comparative examples, in the case of Galvanostatic cycling with potential limitation (GCPL) cycling for analyzing cycle characteristics and rate characteristics, WonATech's equipment was used. In preparation for GCPL cycling, electrolyte and anolyte are injected into the electrode, then the cells are assembled and waited for 6 hours to allow the solution to penetrate into the pores. However, the pouch-type battery including CC-S6 according to Example 2 was subjected to GCPL cycling without the preparation step of 6 hours.

In Example 1 and Comparative Examples 1 to 4, the volume (μl) ratio of the anolyte solution to the weight (mg) of sulfur was set high as about 22 μl / mg. The above condition is to set the volume ratio of the anolyte solution to the sulfur weight higher than that of the conventional lithium-sulfur secondary battery. In general, as the charge / discharge is repeated, the amount of sulfur dissolved in the anolyte decreases as the volume of the anolyte decreases relative to the weight of sulfur. On the other hand, under the above conditions, since the volume of the anolyte is relatively high relative to the weight of sulfur, the amount of sulfur dissolved in the anolyte is maintained relatively well even after repeated charging / discharging. Therefore, when the charging / discharging is repeated under the above conditions, the anode is able to better understand whether the sulfur inhibits the shuttleling of sulfur and whether sulfur is bound to the anode without dissolving in the anolyte solution. That is, by setting the above conditions, it is possible to easily prove the stability of the positive electrode and the cell having stable performance of charge / discharge cycle characteristics.

Example 1 CC-S6

(CF₃SO₂)₂NLi) 1M과 황의 소스인 Li₂S₆를 용해하여 양극액을 준비하였다. 더하여, 본 발명의 탄소집전체를 상기 양극액에 잠입시켜 본 발명의 양극을 제작하였다. 특히, 상기 탄소집전체의 단위 면적(cm²) 당 흡착되는 황의 중량이 6mg이었다.DOL (1,3-Dioxolane) and DME (1,2-Dimethoxyethane) were mixed at a volume ratio of 1: 1 and used as a solvent of the anolyte solution of the present invention. Lithium salt LiTFSI Trifluoromethanesulfonylimide, in the solvent

(CF ₃ SO ₂ ) ₂ NLi) 1M and Li ₂ S ₆ as a source of sulfur were dissolved to prepare an anolyte. In addition, the carbon current collector of the present invention was immersed in the anolyte solution to prepare a positive electrode of the present invention. In particular, the weight of sulfur adsorbed per unit area (cm ² ) of the carbon current collector was 6 mg.

Comparative example  1: CC-S2

Prepared in the same manner as in Example 1, except that Li ₂ S ₆ is ² mg by weight of sulfur adsorbed per unit area (cm ² ) of the immersed carbon current collector.

Comparative example  2: CC-S4

Prepared in the same manner as in Example 1, except that Li ₂ S ₆ is 4 mg by weight of sulfur adsorbed per unit area (cm ² ) of the immersed carbon current collector.

Comparative example  3: CC-S8

Prepared in the same manner as in Example 1, except that Li ₂ S ₆ is 8 mg by weight of sulfur adsorbed per unit area (cm ² ) of the immersed carbon current collector.

Comparative example  4: CC-S10

Prepared in the same manner as in Example 1, except that Li ₂ S ₆ is 10 mg by weight of sulfur adsorbed per unit area (cm ² ) of the immersed carbon current collector.

Example  2 : Pouch type battery containing CC-S6

Example 1 was put into the pouch and a pouch type battery is comprised. The pouch was made of plastic (polyethylene). The carbon current collector (CH900-20, Kuractive) is formed into a rectangular shape having a width of 2 cm and a length of 6 cm to form an electrode, and the carbon current collector is immersed in the anolyte. A blank electrolyte was added to bring the volume sum of the anolyte and the blank electrolyte to 100 μl. The amount of the anolyte is appropriately adjusted so that the weight of sulfur adsorbed per unit area (cm ² ) of the carbon current collector is 6 mg. Next, a pouch type battery was constructed by adding a rectangular separator and a lithium metal negative electrode having the same width and length.

Comparative example  5: containing CC-S6 Coin type  battery

Manufactured in the same manner as in Example 2, except that the carbon current collector (CH900-20m, Kuractive) was formed in a circular shape having a diameter of 14 mm, the electrode was immersed in the anolyte solution, and the circular separator having a diameter of 19 mm was then formed. It is different from a coin-type battery by attaching a lithium metal negative electrode.

Comparative example  6: Banding  Pouch type battery with untested CC-S6

It is manufactured in the same manner as in Example 2, except that the banding test has not been performed.

<Evaluation of Example 1 and Comparative Examples 1 to 4>

Charge / discharge cycle characteristics

1 and 2-Analysis of CV (Cyclic Voltametry) Curve

1 and 2 show 1.0 to 3.0 V vs. In the potential range of Li / Li ⁺ , the potential scanning speed is a CV curve with a charge / discharge cycle of 0.1 mV / s. FIG. 1 is a CV curve of Example 1, and FIGS. 2A and 2B are CV curves of Comparative Examples 1 and 4, respectively. Typically, in lithium-sulfur secondary batteries, two steep reduction peaks and one broad oxidation peak appear due to the typical multistage redox reaction between lithium and sulfur.

More specifically, in the case where the potential of Example 1 is scanned in the reverse direction in FIG. 1, 2.3 V vs. of the soluble lithium polysulfide (Li ₂ S _x (4 ≦ _x ≦ 8)) is formed from sulfur. The first reduction peak was seen in Li / Li ⁺ and was 1.9 V vs. in the formation of insoluble lithium disulfide (Li ₂ S ₂ ) or insoluble lithium sulfide (Li ₂ S). A second reduction peak is seen in Li / Li ⁺ . Subsequently, when the potential of Example 1 is scanned in the forward direction, 2.6 V vs. is due to the continuous oxidation of insoluble lithium sulfide to sulfur. A large oxide peak appears in Li / Li ⁺ . In the case of Example 1 in FIG. 1, when the charge / discharge cycle is repeated, the first reduction peak (2.3 V vs. Li / Li ⁺ ) is slightly decreased, and the second reduction peak (1.9 V vs. Li / Li ⁺ ) is shown. Increases marginally.

On the other hand, in the case of Comparative Example 1 in FIG. 2A, as the number of charge / discharge cycles increased, the current density gradually decreased. This is because sulfur was lost from the carbon current collector through the elution of sulfur.

mA/cm²까지 크게 증가시켰다.In addition, in Comparative Example 4 of FIG. 2B, since the weight of sulfur adsorbed on the carbon current collector is excessive to promote the reduction reaction, the passivation layer of insoluble lithium sulfide is irreversibly formed quickly. As a result, the charge / discharge cycle characteristics were drastically deteriorated, so that the current density was considerably lower than that of the reduction peak of Example 1 shown in FIG. You can check it. In addition, excessively stacked insoluble lithium sulfide induces parasitic reaction of polysulfide remaining in the catholyte to increase the current density of the oxide peak.

It was greatly increased up to mA / cm ² .

From these results, it can be seen that an appropriate amount of insoluble lithium sulfide produced by the reduction reaction is adsorbed into the pores of the carbon current collector to form a passivation layer, thereby delaying the dissolution of the lithium polysulfide adsorbed in the pores of the carbon current collector. . Therefore, in order to implement a high performance electrode, it is necessary to control the deposition amount of insoluble lithium sulfide which contributes to the formation of a passivation layer.

In Example 1, the electrode performance is excellent by controlling the deposition amount of insoluble lithium sulfide, but the current density is maintained almost uniform even if the deposition is reversible and the charge / discharge cycle is repeated, thereby improving the charge / discharge cycle characteristics. outstanding. On the other hand, in Comparative Examples 1 and 4, sulfur was excessively adsorbed or excessively adsorbed, thereby significantly reducing the charge / discharge cycle characteristics.

2. FIGS. 3-6-EIS analysis after Galvanostatic cycling with potential limitation (GCPL) cycling

3A is a photograph of a coin cell including Example 1 and a coin cell including Comparative Example 4 after GCPL cycling according to an assembly sequence. 3B is a surface photograph of a carbon current collector on a side in contact with a separator in a coin cell including Comparative Example 4 after GCPL cycling. 3C is a photograph of a lithium anode in a coin cell including Comparative Example 4 after GCPL cycling.

In Figures 4 to 6 GCPL cycling is 1.8 ~ 2.6 V vs. It was carried out with a constant current of 0.3 C (-500 mA / g sulfur) in the potential range of Li / Li ⁺ . In addition, electrochemical impedance spectroscopy (EIS) was measured by Bio-logic VSP from 300 kHz to 0.05 Hz. If 500 mA / g exceeds the maximum current density and the potential range is slightly narrow to cover the entire redox reaction, the high sulfur load electrodes, such as Example 1 and Comparative Example 4, are liable for shuttleling during GCPL analysis. The ability to prevent shuttles of polysulfides can be evaluated and the cycle characteristics of the CC-S electrodes can be evaluated.

According to FIG. 3, in the coin cell including Comparative Example 4 after GCPL cycling, it was possible to visually confirm that the lithium polysulfide was dissolved into the electrolyte, and (FIG. 3b) to visually fix the Li ₂ S to the surface of the lithium negative electrode. It could be confirmed (Fig. 3c). On the other hand, in contrast, in the coin cell of Example 1, there was no visual indication of dissolution of lithium polysulfide, and it was not visually confirmed that Li ₂ S adhered to the surface of the lithium negative electrode. From these results, it can be seen that the charge / discharge cycle of Example 1 is more stable than that of Comparative Example 4.

In Figures 4 and 5 the change in impedance before and after GCPL cycling was monitored. From the results of FIG. 4, it can be seen that the deposition of insoluble lithium sulfide in Example 1 is very reversible considering that the intermediate frequency semicircle corresponding to the charge transfer resistance is maintained well before and after GCPL cycling. On the other hand, in the comparative example 4 from the results of FIG. 5, the resistance was greatly increased, and it was confirmed that the intermediate frequency semicircle corresponding to the charge transfer resistance was not maintained well. This is because sudden battery damage occurred.

From these results, it can be inferred that deposition of insoluble lithium sulfide is more reversible in Example 1 than in Comparative Example 4. It can be seen that Example 1 has a more stable charge / discharge cycle than Comparative Example 4.

On the other hand, in Figure 6 Example 1 is 1.8 ~ 2.6 V vs .. Li / Li ⁺ potential range, 1.5 to 3.0 V vs. Each was cycled with a constant current of 0.3C (~ 500mA / g sulfur) in the Li / Li ⁺ potential range. According to FIG. 6, it can be seen that discharge capacity is maintained even when GCPL cycling is performed with respect to Example 1 at different potential ranges, so that the charge / discharge cycles of Example 1 are maintained at other potential ranges.

3. FIG. 7-Change of discharge capacity (mAh / cm ² ) according to the number of charge / discharge cycles

7 shows a change in discharge capacity (mAh / cm ² ) according to the number of charge / discharge cycles. In Example 1, the discharge capacity was well maintained at about 3 to 3.3 mAh / cm ² even though the number of charge / discharge cycles was increased. On the other hand, in Comparative Example 1, the discharge capacity is continuously decreased from about 2.3 mAh / cm ² , and in Comparative Example 2, the discharge capacity is well maintained in the range of about 2.5 to 2.7 mAh / cm ² when the number of charge / discharge cycles is 100 or less. However, since the number of charge / discharge cycles exceeded 100, the discharge capacity continuously decreased from about 2.7 mAh / cm ² .

In addition, in Comparative Example 3, the discharge capacity rapidly decreases since the number of charge / discharge cycles exceeds 35, and thus the discharge capacity becomes a dead cell close to the value of 0 mAh / cm ^2. The capacity decreases drastically from the number of charge / discharge cycles exceeding 100, resulting in a dead cell close to the value of 0 mAh / cm ² .

From these results, when the weight of sulfur adsorbed per unit area (cm ² ) of the carbon current collector is 4 mg or more (Comparative Example 2), the passivation layer of insoluble lithium sulfide starts to form and the charge / discharge cycle characteristics are compared to Comparative Example 1. It is excellent compared to, and it can be seen that the charge / discharge cycle characteristics are the most excellent in Example 1. On the other hand, when the weight of sulfur adsorbed is 8 mg and 10 mg (Comparative Examples 3 and 4), the passivation layer of insoluble lithium sulfide is rapidly irreversibly formed and the charge / discharge cycle characteristics rapidly decrease. Able to know.

Capacity characteristics

8-Charge / discharge tenth profile of Example 1, Comparative Examples 1 to 4

FIG. 8 is a charge / discharge tenth profile of Example 1, Comparative Examples 1 to 4, with about 1.5 to 2.7 V vs. It is a graph of the change in capacity in the Li / Li ⁺ interval. Referring to the tenth charge / discharge profile of Example 1 in FIG. 8, in the discharge profile, about 2.3 and 2.0 V vs. Separate flat sections appear in Li / Li ⁺ and 2.1 to 2.6 V vs. In the Li / Li ⁺ interval, the rising interval appears.

Example 1 ranges from 1.5 to 2.7 V vs. sufficient to cover the entire redox reaction. The capacity loss in Li / Li ⁺ is only 0.03%, and the capacity is well maintained as compared with Comparative Examples 1 to 4. The capacitor also ~ 3.3 mAh / cm ² as Comparative Example 1 to each of the capacitance of 4 ~ 2.1mAh / cm ^2, ~ than ^{2.5mAh / cm 2, ~ 1.5mAh /} cm 2, ~ 1.1mAh / cm 2 Was bigger.

2. Fig. 9-100th charge / discharge profile of Example 1 and Comparative Examples 1 to 4

FIG. 9 shows the 0.3C charge / discharge 100th profile of Example 1 and Comparative Examples 1 to 4. FIG. It is a graph showing the change in area capacity (mAh / cm ² ) according to the weight (mg) of sulfur adsorbed per unit area (cm ² ) of the carbon current collector.

In Figure 9,

In Comparative Example 1, the area capacity at the 100th charge / discharge was measured as 1.9 mAh / cm ² .

In Comparative Example 2, the area capacity was measured as 2.7 mAh / cm ² at the 100th charge / discharge.

In the case of Example 1, the area capacity at the 100th charge / discharge was measured as 3.1 mAh / cm ² .

In Comparative Example 3, the area capacity was measured as 0.05 mAh / cm ² at the 100th charge / discharge.

In Comparative Example 4, the area capacity was measured as 0.1 mAh / cm ² at the 100th charge / discharge.

In Comparative Example 1, since the weight (mg) of sulfur adsorbed per unit area (cm ² ) of the carbon current collector is 2 mg, the passivation layer may not be sufficiently formed. Sulfur elution cannot be prevented and therefore, the charge / discharge 100th has a relatively low area capacity value compared to Example 1.

In Comparative Example 2, the weight (mg) of sulfur adsorbed per unit area (cm ² ) of the carbon current collector starts to form a passivation layer with 4 mg. The cycle characteristics are superior to those of Comparative Example 1, and in terms of the capacity characteristics, the area capacity is 2.7 mAh / cm ² even at the 100th charge / discharge, which is similar to that of Example 1.

In Example 1, the passivation layer is suitably formed with a weight of 6 mg of sulfur adsorbed per unit area (cm ² ) of the carbon current collector. The cycle characteristics are the best, and the capacity characteristics of 3.1 mAh / cm ² , which is the highest area capacity value, are maintained well even in the 100th charge / discharge cycle.

In Comparative Example 3, the weight (mg) of sulfur adsorbed per unit area (cm ² ) of the carbon current collector is 8 mg so that the passivation layer is irreversibly formed quickly. Compared to Example 1, the cycle characteristics are sharply lowered, and even in the capacity characteristics, a dead cell has an area capacity value close to zero at the 100th charge / discharge rate.

In Comparative Example 4, the weight (mg) of sulfur adsorbed per unit area (cm ² ) of the carbon current collector is 10 mg, similarly to Comparative Example 3, the passivation layer is irreversibly formed quickly. The cycle characteristics and the capacity characteristics are poor, and the dead cell shows an area capacity value close to zero at the 100th charge / discharge.

3. FIG. 10-Coulomb efficiency change of Example 1 and Comparative Examples 1 and 4

Coulombic efficiency (%) is also called charging and discharging efficiency, it represents the ratio of the discharge capacity (Ah) to the electric charge amount (Ah) as a percentage (%). FIG. 10 is a graph showing a change according to the number of charge / discharge cycles of the coulombic efficiency of Example 1 and Comparative Examples 1 and 4. FIG. Example 1 is well maintained in the range of cycles to 200 cycles without a change in the coulombic efficiency according to the cycle number.

In Comparative Example 1, the coulombic efficiency was maintained well in the range of about 140 cycles, whereas in Comparative Example 4, the coulombic efficiency was not maintained well depending on the number of cycles, and from about 90 cycles or more, a dead cell was observed. Coulomb efficiency is close to zero.

From this result, unlike Example 1, Comparative Example 4, the passivation layer is formed irreversibly fast, the cycle characteristics are bad, it can be seen that if the charge / discharge is repeated more than 90 times becomes a dead cell (dead cell).

4. Comparison of electrode properties between Example 1 and known electrodes without binder

Sample Current
density Areal
capacity Cycle Capacity
degrade sulfur
Loading
amount mA / cm ² mAh / cm ² % mg / cm ² One Carbon cloth-Li ₂ S ₈ / GPE 2.144 4.66 500 0.079 6.4 2 N, S-codoped graphene sponge 1.541 3.77 100 0.287 4.6 3 CNT / S 3.01 2.78 500 0.024 3.7 4 Bottom-up free standing electrode (CNT) 0.528 4.41 150 0.198 6.3 5 CNTs / CC 1.424 1.06 300 0.103 1.7 6 CFC-S 0.303 7.37 42 0.115 6.7 7 AFC-S 0.98 5.33 80 0.274 6.5 8 ACC-Li / S 0.049 7.5 20 1.272 1.27 9 ACC-S / 1M LiNTf ₂ 0.128 1.05 50 1.005 1.27 10 CC-S6 1.005 4.2 60 - 6 11 3.015 3.2 200 0.03 6

Table 1 is a chart comparing the electrode characteristics of Example 1 and a known electrode without a binder. Samples in order from above, Carbon cloth-Li ₂ S ₈ / GPE, N, S -codoped graphene sponge, CNT / S, bottom-up free standing electrode (CNT), CNTs / CC, CFC-S, AFC-S, ACC-Li / S, ACC-S / 1M LiNTf ₂ and Example 1 (CC-S6) may be charged / discharged 60 times and 200 times, respectively. The characteristics of the electrodes to be compared are: current density (mA / cm ² ), capacity (mAh / cm ² ), number of charge / discharge cycles, capacity loss, sulfur load per unit area (cm ² ) of the electrode in order from the top left of the diagram. There is a weight (mg).

According to the table, each of the charge / discharge cycles of Example 1 after 60 cycles and 200 cycles was 4.2 mAh / cm ² and 3.2 mAh / cm ² , which is 4.21 corresponding to the average capacity of the sample except Example 1. The value is similar to mAh / cm ² . However, the capacity loss of Example 1 is 0.03% and corresponds to the lowest value among the samples in the table except for CNT / S. Considering the capacity value and the capacity loss, the capacity characteristics of Example 1 are superior to other samples in the above table.

Configuration of the present invention contributing to charge / discharge cycle characteristics and capacity characteristics

Since the carbon current collector of the present invention has a uniformly developed microporous structure without meso- / macro-pores, the weight of sulfur adsorbed to the carbon current collector can be easily controlled by simply changing the concentration of the anolyte solution. By controlling the weight of the sulfur, it is possible to control the deposition amount of insoluble lithium sulfide produced by the reduction reaction of the cathode active material including sulfur. The deposition amount of insoluble lithium sulfide is a decisive factor in determining charge / discharge cycle characteristics and capacity characteristics.

With regard to the charge / discharge cycle characteristics, when the deposition amount of insoluble lithium sulfide is too small, the shuttle of lithium polysulfide cannot be suppressed. If the deposition amount is too high, the weight of sulfur adsorbed on the carbon current collector is excessive, thereby facilitating a reduction reaction, thereby rapidly forming a passivation layer of insoluble lithium sulfide and irreversible deposition of insoluble lithium polysulfide. Lowers. On the other hand, when an appropriate amount of insoluble lithium sulfide is deposited in the carbon current collector pores, the deposited insoluble lithium sulfide serves to suppress shuttle of the lithium polysulfide, and the deposition due to charge / discharge occurs reversibly, resulting in positive Its cycle characteristics are excellent.

Regarding the capacity characteristics, the capacity characteristics were better when adsorbing an appropriate amount of sulfur for the deposition of a suitable insoluble lithium sulfide. Specifically, in Example 1, the capacity loss is only 0.03%, and the capacity is also larger than the Comparative Examples 1 to 4 in terms of capacity characteristics, so the capacity characteristics are more excellent. Moreover, even when comparing the capacitance characteristic with the other well-known electrode which does not have a binder, it is excellent in capacitance characteristics, such as having high capacitance and low capacitance loss. This is because the capacity of the insoluble lithium sulfide can be reversibly formed when adsorbing an appropriate amount of sulfur, even when charge / discharge continuously occurs.

Therefore, the structure of the carbon current collector of the present invention can easily control the deposition amount of insoluble lithium sulfide, thereby making it possible to easily fabricate a positive electrode having excellent charge / discharge cycle characteristics and capacity characteristics. As a result, the manufacturing process of the lithium-sulfur secondary battery having improved performance may be simplified.

<Battery Performance Evaluation of Example 2>

11 is a photograph of a pouch type battery (Example 2) including Example 1 of the present invention.

12 is a simplified diagram showing a bending condition of Embodiment 2 of the present invention. The battery of Example 2 was folded at 0 mm at a folding diameter of 10 mm and 90 degrees and then unfolded in the reverse order of the previous folding. As described above, when the battery is folded once and extended, it is banding number 1.

FIG. 13 is a graph showing changes in discharge capacity according to the number of charge / discharge cycles of Example 2 and Comparative Examples 5 and 6. FIG.

The battery of Example 2 except for Comparative Examples 5 and 6 in FIG. 13 is folded according to the bending conditions according to FIG. 12. In Figure 13 the cell of Example 2 was bent 150 times prior to GCPL cycling (1 ^st bending), with 1.5-3.0 V vs. current density of 0.1C. After three cycles in the Li / Li ⁺ potential range, it bends again 150 times after the third charge (2 ^nd bending).

Comparative Example 5 which is a coin-type battery in FIG. 13 includes a circular carbon collector in which the weight (mg) of sulfur adsorbed per unit area (cm ² ) of the carbon current collector is 6 mg. As evaluated, the charge / discharge cycle characteristics were excellent and the discharge capacity according to the number of charge / discharge cycles was kept constant at about 4mAh / cm ² .

In addition, Comparative Example 6, which is a pouch-type battery in FIG. 13, includes a carbon current collector having a weight of 6 mg of sulfur adsorbed per unit area (cm ² ) of the carbon current collector which has not been subjected to the bending test. In Comparative Example 6, a carbon current collector was relatively large in a rectangular shape having a width of 2 cm and a length of 6 cm, compared to Comparative Example 5, which was a coin-type battery manufactured in a circular shape having a diameter of 14 mm. Although the battery of Comparative Example 6 was made larger than Comparative Example 5, the battery of Comparative Example 6 was well maintained at a higher discharge capacity of about 6 mAh / cm ² compared to that of Comparative Example 5.

In FIG. 13, the battery of Example 2 includes a carbon current collector having a weight (mg) of 6 mg of sulfur adsorbed per unit area (cm ² ) of the carbon current collector, and thus has excellent charge / discharge cycle characteristics. Example 2 of the cell is the total carbon house width 2cm, length 6cm in spite rectangular relatively production significantly, compared to the comparative example 5 as the comparative example 5, the discharge capacity of 4mAh / discharging capacity than cm ² of 6mAh / cm ² Has a larger discharge capacity. The battery of Example 2 not only has a small battery as in Comparative Example 5, but also has a larger discharge capacity and excellent electric / charging / discharging cycle characteristics even when manufactured larger than that.

Further, the battery of Example 2 in Fig. 13 when the third charge / discharge cycles conducted at 2 ^nd bending Example 2 is bent 150 times, the decrease in the discharge capacity of about 5.7mAh / cm ² to about 4.5mAh / cm ² do. 2 ^nd bending reason for reducing the discharge capacity of the 4-th cycle after the discharge is due to the self (self-discharge) during the time required for the bending test was some occurrence of sulfur is reduced. 2 ^nd bending discharge capacity of Example 2, when the fifth cycle, after is is about 6.1mAh / cm ² returns to the vicinity of the original discharge capacity (about 5.7mAh / cm ²⁾ due to the banding value is decreased by the discharge capacity It can be seen that the discharge capacity is reduced by the self discharge rather than. That is, if the above description is interpreted, the battery of Example 2 can operate normally irrespective of the curvature change, and has a mechanical property that the electrical performance does not change even when the curvature change due to bending.

On the other hand, the carbon current collector of the present invention has elasticity and flexibility and can maintain electrical characteristics even when there is a physical change such as folding or stretching. The carbon current collector of the present invention excludes the use of a separate inert carbon support, and has the advantage that it can operate normally regardless of the curvature change of the battery as in Example 2.

Claims (16)

A carbon current collector including one or more micropores;
Anolyte in which lithium polysulfide is dissolved; And
And a cathode active material adsorbed in pores of the carbon current collector immersed in the anolyte solution.
The positive electrode active material is a sulfur compound containing sulfur of lithium polysulfide dissolved in the anolyte solution,
Sulfur of the positive electrode active material per unit area (cm ² ) of the carbon current collector is adsorbed to the carbon current collector at 6 mg, the positive electrode for a lithium-sulfur secondary battery.
The method of claim 1,
Lithium polysulfide of the positive electrode solution is a lithium-sulfur secondary battery, characterized in that evenly injected into the carbon current collector in the liquid phase.
The method of claim 2,
The carbon current collector includes at least two carbon nanofibers, and the carbon current collector is a carbon cloth in which the carbon nanofibers are intertwined with each other.
The method according to any one of claims 1 to 3,
A positive electrode for a lithium-sulfur secondary battery, characterized in that the diameter of the micropores contained in the carbon current collector is 0.5nm or more and 1.5nm or less.
The method of claim 4, wherein
A lithium-sulfur secondary battery positive electrode, characterized in that the diameter of the micropores contained in the carbon current collector is 0.7nm or more and 1.3nm or less.
The method of claim 5,
A positive electrode for a lithium-sulfur secondary battery, characterized in that the diameter of the micropores contained in the carbon current collector is 1.1nm.
delete delete A carbon current collector including one or more micropores, an anolyte in which lithium polysulfide is dissolved, and a cathode active material immersed in the anode solution and adsorbed in pores of the carbon current collector, and the cathode active material is the anode A positive electrode for a lithium-sulfur secondary battery, characterized in that the sulfur compound containing sulfur of lithium polysulfide dissolved in a liquid;
Lithium, lithium alloy or carbon-based negative electrode; And
A separator;
The sulfur of the positive electrode active material per unit area (cm ² ) of the carbon current collector is lithium-sulfur secondary battery, characterized in that adsorbed at 6 mg in the carbon current collector.
The method of claim 9,
Lithium polysulfide of the anolyte is a lithium-sulfur secondary battery, characterized in that evenly injected into the carbon current collector in the liquid phase.
The method of claim 10,
The carbon current collector includes at least two carbon nanofibers, and the carbon current collector is a carbon cloth in which the carbon nanofibers are intertwined with each other.
The method according to any one of claims 9 to 11,
Lithium-sulfur secondary battery, characterized in that the diameter of the micropores contained in the carbon current collector is 0.5nm or more and 1.5nm or less.
The method of claim 12,
Lithium-sulfur secondary battery, characterized in that the diameter of the micropores contained in the carbon current collector is 0.7nm or more and 1.3nm or less.
The method of claim 13,
Lithium-sulfur secondary battery, characterized in that the diameter of the micropores contained in the carbon current collector is 1.1nm.
delete delete

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