KR20210010025A - Vanadium oxide-sulfur composite, positive electrode and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a vanadium oxide-sulfur composite, to a positive electrode, and to a lithium secondary battery comprising the same. More specifically, the electrode comprising the vanadium oxide-sulfur composite as an active material has excellent binding power, exhibits high loading characteristics, and can improve the energy density of the lithium secondary battery. In addition, the vanadium oxide-sulfur composite comprises: vanadium oxide; and sulfur.

Description

Vanadium oxide-sulfur composite, positive electrode and lithium secondary battery including the same {VANADIUM OXIDE-SULFUR COMPOSITE, POSITIVE ELECTRODE AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a vanadium oxide-sulfur composite applicable as a positive electrode material of a lithium secondary battery, a positive electrode including the same, and a lithium secondary battery.

Recently, the demand for secondary batteries is increasing with the rapid development of the electronic device field and the electric vehicle field. In particular, according to the trend of miniaturization and weight reduction of portable electronic devices, there is a growing demand for a secondary battery having a high energy density that can meet the trend.

Among secondary batteries, a lithium-sulfur secondary battery uses a sulfur-based compound having a sulfur-sulfur bond as a positive electrode active material, and an alkali metal such as lithium or a carbon-based material in which metal ions such as lithium ions are inserted and deintercalated, or an alloy with lithium It is a secondary battery that uses silicon or tin to form a negative electrode active material. Specifically, electrical energy is stored by using an oxidation-reduction reaction in which sulfur-sulfur bonds are cut off during discharge, which is a reduction reaction, and the oxidation number of sulfur decreases. And create it.

In particular, sulfur, which is used as a positive electrode active material in lithium-sulfur secondary batteries, has a theoretical energy density of 1675 mAh/g, and has a theoretical energy density that is 5 times higher than that of the positive electrode active material used in conventional lithium secondary batteries. It is a battery capable of expressing the density. In addition, sulfur is attracting attention as an energy source for mid- to large-sized devices such as electric vehicles as well as portable electronic devices because of its low cost, rich reserves, easy supply, and environmental friendliness.

However, since sulfur has no conductivity, a porous carbon material and a sulfur-carbon composite are formed and applied as an electrochemical positive electrode active material. In the sulfur-carbon composite applied as a positive electrode active material as described above, sulfur (S) becomes Li ₂ S due to electrons transferred through the carbon in the lead wire and the sulfur-carbon composite, and lithium ions transferred through the electrolyte from the negative electrode. Reduce.

Sulfur in its natural state exists in the form of an S ₈ ring, and in the process of becoming Li ₂ S with the discharge of the battery, Li ₂ S ₈ , Li ₂ S ₆ , Li ₂ S ₄ After passing through the form of the like, and these materials are well soluble in the electrolyte, there is a problem that such lithium-polysulfide is dissolved in the electrolyte and moves to the negative electrode, resulting in a reduction in life (shuttle effect).

In order to improve this problem, a technique of applying a vanadium oxide-sulfur composite as a positive electrode active material instead of a conventional sulfur-carbon composite has been developed.

European Patent Publication No. 3244472 and Chinese Patent Publication No. 105322131 both disclose that a vanadium oxide-sulfur composite can be applied as a cathode active material for a lithium secondary battery, but the vanadium oxide containing V ₂ O ₅ as vanadium oxide. -When the sulfur composite is applied as a positive electrode active material, the binding force between the current collector and the positive electrode is not good, so there is a limit to increasing the content of the active material in the positive electrode.

Accordingly, there is a need to develop a vanadium oxide-composite having physical properties capable of manufacturing a high sulfur content electrode, which is essential for manufacturing a lithium-sulfur secondary battery having a high energy density.

European Patent Publication No. 3244472 Chinese Patent Publication No. 105322131

Accordingly, the present inventors prepared a vanadium oxide-sulfur composite by mixing V ₆ O ₁₃ and sulfur as a vanadium oxide, and when forming a positive electrode active material layer on an aluminum current collector by using the vanadium oxide-sulfur composite as a positive electrode active material, It was confirmed that the binding force between the aluminum current collector and the positive electrode active material layer was high, and it was possible to increase the density of the positive electrode active material layer, thereby improving the energy density of the lithium secondary battery.

Accordingly, an object of the present invention is to provide a vanadium oxide-sulfur composite capable of forming an electrode having a thin thickness by improving the binding force of the electrode.

Another object of the present invention is to provide a positive electrode including the vanadium oxide-sulfur composite.

Another object of the present invention is to provide a lithium secondary battery including the vanadium oxide-sulfur composite.

In order to achieve the above object, the present invention provides a vanadium oxide-sulfur complex comprising vanadium oxide and sulfur represented by the following Formula 1:

[Formula 1]

V _n O _{2n +1}

In Formula 1, n is an integer of 3 to 10.

The present invention also includes a current collector; And a positive electrode active material layer formed on at least one surface of the current collector, wherein the positive electrode active material layer comprises the vanadium oxide-sulfur composite. It provides a positive electrode for a lithium secondary battery.

The present invention also provides a lithium secondary battery comprising a.

Since the vanadium oxide-sulfur composite according to the present invention has excellent binding power to the current collector, it is possible to manufacture a high loading electrode using the vanadium oxide-sulfur composite.

In addition, a lithium secondary battery including a high loading electrode including the vanadium oxide-sulfur composite as a cathode material may exhibit an effect of improving energy density.

1 is a SEM photograph of vanadium oxide (V ₆ O ₁₃ ) used in Example 1.
2 is a SEM photograph of the vanadium oxide-sulfur composite (V ₆ O ₁₃ /S) prepared in Example 1.
3 is a SEM photograph of the surface and side surfaces of anodes prepared in Example 2, Comparative Example 2, and Comparative Example 5, respectively.
4 is a result of a binding force test for the positive electrode prepared in Example 2, Comparative Example 2, and Comparative Example 5, respectively.
5A and 5B are graphs of a first cycle profile and cycle data for lithium-sulfur secondary batteries each prepared in Example 3, Comparative Example 3, and Comparative Example 6, respectively.

Hereinafter, the present invention will be described in more detail.

Vanadium oxide-carbon complex

The present invention relates to a vanadium oxide-sulfur complex comprising vanadium oxide and sulfur.

In the present invention, the vanadium oxide may be represented by the following Formula 1, but is not limited thereto as long as it has a polycationic property that causes strong physical binding with sulfur:

[Formula 1]

V _n O _2n+1

In Formula 1, n is an integer of 3 to 10.

Preferably, the vanadium oxide may be at least one selected from the group consisting of V ₃ O ₇ , V ₄ O ₉ and V ₆ O ₁₃ .

In addition, the vanadium oxide may be 20 to 40% by weight, preferably 20 to 35% by weight, more preferably 20 to 30% by weight based on the total weight of the vanadium oxide-sulfur composite. If the content of the vanadium oxide is less than 20% by weight, the bonding strength with sulfur and the current collector may be reduced, and if it is more than 40% by weight, the battery performance may be reduced.

In the present invention, the sulfur is sulfur (S ₈ ), Li ₂ S _n (n≥1), an organic sulfur compound and a carbon-sulfur polymer [(C ₂ S _x ) _n , x is an integer of 2.5 to 50, n≥ 2] may be one or more selected from the group consisting of.

The sulfur may be included in an amount of 60 to 80% by weight, preferably 65 to 80% by weight, more preferably 70 to 80% by weight, based on the total weight of the vanadium oxide-sulfur composite. If the sulfur content is less than 60% by weight, the sulfur content in the battery decreases and the battery capacity is excessively reduced. If it is more than 80% by weight, the electrical conductivity in the positive electrode is excessively decreased, and the resistance may increase.

Method for preparing vanadium oxide-sulfur composite

In the present invention, the vanadium oxide-sulfur composite may be prepared by physically mixing vanadium oxide and sulfur.

Since the vanadium oxide used in the present invention has a polyvalent cation property that causes strong physical binding with sulfur, a complex can be formed only by physical mixing.

Specific examples of the vanadium oxide and sulfur used in the preparation method and the content in the prepared composite are as described above.

Positive electrode for lithium secondary battery

The present invention also relates to a positive electrode for a lithium secondary battery comprising a vanadium oxide-sulfur composite as described above. In this case, the vanadium oxide-sulfur composite may preferably be included as a positive electrode active material.

The positive electrode for the lithium secondary battery includes a current collector; And a positive active material layer formed on at least one surface of the current collector.

The binding force between the current collector and the positive electrode active material layer may be 30 to 300 kgf/m, and the loading amount of sulfur in the positive electrode may be 4.0 to 10.0 mg/cm 2 per 100 μm thickness of the positive electrode. Such high binding force and loading amount is due to the vanadium oxide-sulfur composite contained in the positive electrode active material. In addition, due to the high binding force and loading amount of the positive electrode for a lithium secondary battery, the energy density of the lithium secondary battery may be improved.

In the present invention, the current collector is a positive electrode current collector, and the positive electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium , Calcined carbon, or a surface-treated aluminum or stainless steel surface with carbon, nickel, titanium, silver or the like may be used. In this case, the positive electrode current collector may be in various forms such as a film, sheet, foil, net, porous material, foam, non-woven fabric having fine irregularities formed on the surface so as to increase adhesion to the positive electrode active material.

In the present invention, the positive electrode active material layer may include a positive electrode active material, a binder, and a conductive material, and may further include a filler, other additives, and the like.

The positive active material may include a vanadium oxide-sulfur composite as described above.

In addition, a lithium-containing transition metal oxide may be used as the positive electrode active material, for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li(Ni _a Co _b Mn _c )O ₂ (0 <a<1, 0<b<1, 0<c<1, a+b+c=1), LiNi _{1 - y} Co _y O ₂ , LiCo _{1 - y} Mn _y O ₂ , LiNi _{1 - y} Mn _y O ₂ (O≤y<1), Li(Ni _a Co _b Mn _c )O ₄ (0<a<2, 0<b<2, 0<c<2, a+b+c=2), LiMn _{2 - z Ni z O 4,} LiMn 2 - z Co z O 4 (0 <z <2), LiCoPO may be used any one or a mixture of two or more of these _four and is selected from the group consisting of LiFePO _4. In addition, in addition to these oxides, sulfide, selenide, and halide may be used.

In addition, as the binder, polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro Ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber, and various copolymers thereof.

Alternatively, the conductive material is used to further improve the conductivity of the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Polyphenylene derivatives and the like can be used.

The filler is selectively used as a component that suppresses the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes to the battery, and examples thereof include olefin-based polymers such as polyethylene and polypropylene; Fibrous materials such as glass fiber and carbon fiber are used.

Lithium secondary battery

The present invention also relates to a lithium secondary battery comprising the vanadium oxide-sulfur composite as described above.

The lithium secondary battery according to the present invention may include a positive electrode, a negative electrode, a separator and an electrolyte interposed therebetween.

In the present invention, the anode may be an anode including the vanadium oxide-sulfur composite as described above.

In the present invention, the negative electrode of the lithium secondary battery may include a negative electrode current collector and a negative electrode active material layer having a negative electrode active material formed on the negative electrode current collector.

As the negative active material, lithium metal or a carbon material through which lithium ions can be occluded and released may be used, such as silicon or tin. Preferably, a carbon material may be used, and both low crystalline carbon and high crystalline carbon may be used as the carbon material. As low crystalline carbon, soft carbon and hard carbon are typical, and high crystalline carbon is natural graphite, kish graphite, pyrolytic carbon, liquid crystal pitch-based carbon fiber (mesophase pitch based carbon fiber), meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbons such as petroleum or coal tar pitch derived cokes are typical. At this time, the negative electrode may include a binder, and as the binder, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, Various types of binder polymers, such as polymethylmethacrylate, may be used.

In addition, the negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. Surface treatment with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode current collector, like the positive electrode current collector, may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric having fine irregularities on the surface thereof.

In this case, the negative active material layer may further include a binder resin, a conductive material, a filler, and other additives.

The binder resin is used for bonding of an electrode active material and a conductive material and bonding to a current collector. Examples of such binder resins include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetra Fluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine rubber, and various copolymers thereof.

The conductive material is used to further improve the conductivity of the electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Polyphenylene derivatives and the like can be used.

The filler is selectively used as a component that suppresses the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing chemical changes to the battery, and examples thereof include olefin-based polymers such as polyethylene and polypropylene; Fibrous materials such as glass fiber and carbon fiber are used.

In the present invention, the separator may be made of a porous substrate, and the porous substrate may be used as long as it is a porous substrate commonly used in an electrochemical device, for example, a polyolefin-based porous membrane or a nonwoven fabric. It can be used, but is not particularly limited thereto.

Examples of the polyolefin-based porous membrane include polyolefin-based polymers such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, polyolefin-based polymers such as polypropylene, polybutylene, and polypentene, respectively, or a mixture of them. There is one membrane.

As the nonwoven fabric, in addition to the polyolefin nonwoven fabric, for example, polyethylene terephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate ), polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalene, respectively, alone or Nonwoven fabrics formed of polymers obtained by mixing them are exemplified. The structure of the nonwoven fabric may be a spunbond nonwoven fabric composed of long fibers or a melt blown nonwoven fabric.

The thickness of the porous substrate is not particularly limited, but is 1 µm to 100 µm, or 5 µm to 50 µm.

The size and porosity of the pores present in the porous substrate are also not particularly limited, but may be 0.001 μm to 50 μm and 10% to 95%, respectively.

In the present invention, the electrolyte may be a nonaqueous electrolyte, and the electrolyte salt contained in the nonaqueous electrolyte is a lithium salt. The lithium salts may be used without limitation, those commonly used in an electrolyte solution for a lithium secondary battery. For example, the lithium salt is LiFSI, LiPF ₆ , 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 , LiPF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, it may be one or more selected from the group consisting of lithium chloroborane and lithium 4-phenyl borate.

As organic solvents included in the above-described non-aqueous electrolyte, those commonly used in electrolytes for lithium secondary batteries can be used without limitation, and for example, ethers, esters, amides, linear carbonates, cyclic carbonates, etc. can be used alone or in two or more types. It can be mixed and used. Among them, representatively, a cyclic carbonate, a linear carbonate, or a carbonate compound that is a slurry thereof may be included.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, Any one selected from the group consisting of 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and halides thereof, or two or more of these slurries. These halides include, for example, fluoroethylene carbonate (FEC), but are not limited thereto.

In addition, a specific example of the linear carbonate compound is any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate, or Two or more of these slurries may be representatively used, but are not limited thereto. In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are organic solvents of high viscosity and have high dielectric constants, so that lithium salts in the electrolyte can be more easily dissociated. If a low viscosity, low dielectric constant linear carbonate is mixed in an appropriate ratio and used, an electrolyte solution having a higher electrical conductivity can be prepared.

In addition, as the ether of the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, and ethylpropyl ether, or two or more types of slurry may be used. , But is not limited thereto.

In addition, esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, Any one selected from the group consisting of σ-valerolactone and ε-caprolactone, or two or more types of slurry may be used, but is not limited thereto.

The injection of the non-aqueous electrolyte may be performed at an appropriate step in the manufacturing process of the electrochemical device, depending on the manufacturing process and required physical properties of the final product. That is, it can be applied before assembling the electrochemical device or at the final stage of assembling the electrochemical device.

In the lithium secondary battery according to the present invention, in addition to winding, which is a general process, lamination and stacking and folding processes of a separator and an electrode are possible.

In addition, the shape of the battery case is not particularly limited, and may be in various shapes such as a cylindrical shape, a stacked type, a square shape, a pouch type, or a coin type. The structure and manufacturing method of these batteries are well known in this field, and thus detailed descriptions are omitted.

In addition, the lithium secondary battery can be classified into various batteries, such as lithium-sulfur secondary batteries, lithium-air batteries, lithium-oxide batteries, and lithium all-solid batteries, depending on the material of the positive electrode/cathode used.

The present invention also provides a battery module including the lithium secondary battery as a unit cell.

The battery module can be used as a power source for medium and large-sized devices that require high temperature stability, long cycle characteristics, and high capacity characteristics.

Examples of the medium and large-sized devices include a power tool that is powered by an omniscient motor and moves; Electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; Electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); Electric golf cart; Power storage systems, etc., but are not limited thereto.

Lithium-sulfur secondary battery

The vanadium oxide-sulfur composite according to the present invention can be applied to a positive electrode of a lithium-sulfur secondary battery, among lithium secondary batteries.

In this case, the lithium-sulfur secondary battery may be a battery including the vanadium oxide-sulfur composite as a positive electrode active material.

The vanadium oxide-sulfur composite has good binding power to the current collector and can form a high-density positive electrode active material layer, thereby improving battery energy density.

Hereinafter, preferred embodiments are presented to aid the understanding of the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. It is natural that changes and modifications fall within the scope of the appended claims.

Example 1: Preparation of vanadium oxide-sulfur composite (V ₆ O ₁₃ /S)

By physically mixing 30% by weight of vanadium oxide (V ₆ O ₁₃ ) and 70% by weight of sulfur (S) powder, a vanadium oxide-sulfur composite (V ₆ O ₁₃ /S) was prepared.

Example 2: Preparation of positive electrode

The vanadium oxide-sulfur composite (V ₆ O ₁₃ /S) prepared in Example 1 as a positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in a weight ratio of 75:15:10. 0.2 g of the mixture was dispersed in 1100 μL of NMP (N-Methyl-2-pyrrolidone) as a solvent to prepare a positive electrode slurry.

Using a doctor blade, the positive electrode slurry was coated on an Al foil (thickness: 20 µm, thickness 0.00635 g) to a thickness of 700 µm and dried to prepare a positive electrode.

Example 3: Preparation of lithium-sulfur secondary battery

A 50 μm-thick lithium foil as a negative electrode, the positive electrode prepared in Example 2, the electrolyte was DOL/DME (1:1, v/v) as a solvent, and a composition containing ₁ M LiTFSI and 0.2 M LiNO ₃ A coin cell type (CR2032) lithium-sulfur secondary battery was manufactured using the prepared electrolyte and a polyolefin separator. At this time, DOL means dioxolane and DME means dimethoxyethane.

Comparative Example 1: Preparation of carbon-sulfur composite (C/S)

Except for using activated carbon (actovated carbon, YP-50, Kuraray Co.) instead of vanadium oxide (V ₆ O ₁₃ ), a carbon-sulfur composite was prepared in the same manner as in Example 1.

Comparative Example 2: Preparation of positive electrode

A positive electrode was manufactured in the same manner as in Example 2, except that the carbon-sulfur composite (C/S) of Comparative Example 1 was used instead of the vanadium oxide-sulfur composite (V ₆ O ₁₃ /S) of Example 1.

Comparative example 3: lithium-sulfur secondary battery

A lithium-sulfur secondary battery was manufactured in the same manner as in Example 3, except that the positive electrode prepared in Comparative Example 2 was used instead of the positive electrode prepared in Example 2.

Comparative Example 4: Preparation of vanadium oxide-sulfur composite (V ₂ O ₅ /S)

Except for using V ₂ O ₅ instead of V ₆ O ₁₃ as a vanadium oxide, a carbon-sulfur composite was prepared in the same manner as in Example 1.

Comparative Example 5: Preparation of positive electrode

Except for using the vanadium oxide-sulfur composite (V ₂ O ₅ /S) of Comparative Example 4 instead of the vanadium oxide-sulfur composite (V ₆ O ₁₃ /S) of Example 1, the positive electrode was used in the same manner as in Example 2 Was prepared.

Comparative Example 6: Lithium-sulfur secondary battery

A lithium-sulfur secondary battery was manufactured in the same manner as in Example 3, except that the positive electrode prepared in Comparative Example 5 was used instead of the positive electrode prepared in Example 2.

Experimental example 1: Measurement of anode loading

For the positive electrodes prepared in Example 2, Comparative Example 2, and Comparative Example 5, the positive electrode active material loading amount, sulfur loading amount, and electrode thickness were measured in the following manner, and the results are shown in Table 1 below.

The positive active material loading amount was calculated by subtracting the weight of the current collector from the weight of the positive electrode.

The sulfur loading amount was calculated by multiplying the sulfur content by the loading amount of the positive electrode active material.

The thickness of the anode was measured with a contact electrode thickness meter (Hitach).

Comparative Example 2 Comparative Example 5 Example 2 Positive electrode active material loading (active loading, mg/㎠) 4.20 4.53 5.16 Sulfur loading (mg/㎠) 2.94 3.17 3.61 Anode thickness (Thickness, ㎛) 108 98.0 81.0 Ratio (anode thickness: sulfur loading) 1:0.0272 1:0.0324 1:0.0446

As a result, as shown in Table 1, in the case of Example 2, it can be seen that the sulfur loading amount compared to the anode thickness is the highest.

Experimental Example 2: Vanadium oxide-sulfur complex (V ₆ O ₁₃ /S) and anode observation

The vanadium oxide (V ₆ O ₁₃ ) used in Example 1 and the vanadium oxide-sulfur composite (V ₆ O ₁₃ /S) were observed using the same. It was observed using a SEM instrument (FE-SEM, JEOL JSM07600F).

1 is a SEM photograph of vanadium oxide (V ₆ O ₁₃ ) used in Example 1.

Referring to FIG. 1, it can be seen that particles at the nanoscale level of 100 to 200 nm are aggregated. Due to the particle shape at the nanoscale level, the specific surface area of the vanadium oxide is increased, thereby improving electrode adhesion, and consequently improving battery performance.

2 is a SEM photograph of the vanadium oxide-sulfur composite (V ₆ O ₁₃ /S) prepared in Example 1.

2, the vanadium oxide-sulfur composite (V ₆ O ₁₃ /S) is a mixture of micron-level sulfur particles and vanadium oxide (V ₆ O ₁₃ ), so that a high-density electrode can be configured. Able to know.

3 is a SEM photograph of the surface and side surfaces of anodes prepared in Example 2, Comparative Example 2, and Comparative Example 5, respectively.

Referring to FIG. 3, it can be seen that the thickness of the anode of Example 1 is the highest and the thickness is thin.

Experimental Example 3: Anode binding force test

A binding force test was performed on the positive electrodes prepared in Example 2, Comparative Example 2, and Comparative Example 5, respectively.

The binding force was measured using a Peel tester (Instron). The Peel tester is a device that measures the force when an adhesive tape is attached to an electrode and then pulled away.

4 is a result of a binding force test for the positive electrode prepared in Example 2, Comparative Example 2, and Comparative Example 5, respectively.

4, the binding force of the aluminum current collector and the positive electrode slurry is 30 to 300 kgf/m in Example 2 (V ₆ O ₁₃ /S), and 20 to 50 kgf in Comparative Example 2 (V ₂ O ₅ /S). It can be seen that /m, Comparative Example 5 (activated carbon, YP-50, C/S) represents a level of 10 to 20 kgf/m.

This is due to the high induced dipole force of V ₆ O ₁₃ and sulfur having a 3D nano or micro structure, and has a structural difference from V ₂ O ₅ (3D micro-bulk) and C (activated carbon, 0D).

In addition, in terms of the density related to the porosity when preparing the cathode slurry, V ₆ O ₁₃ /S (3.91 g/cm 3)> V ₂ O ₅ /S (3.357 g/cm 3)> C/S (2.2 g/cm 3) Shows the shame.

In contrast, the porosity and the positive electrode slurry prepared during the solvent absorption is _{V 6 O 13 / S <V} 2 O 5 / S < a C / S, and then the positive electrode slurry was coated with the same thickness when dry cracking phenomenon is V ₆ O best at ₁₃ / S It can be seen that it is advantageous for energy density and high-loading because it occurs less and the loading per area of sulfur per thickness and each comparative group is most efficient.

Experimental Example 4: Analysis of the performance improvement effect of lithium-sulfur secondary battery

For the lithium-sulfur secondary batteries prepared in Example 3, Comparative Example 3, and Comparative Example 6, respectively, charging/discharging was repeatedly performed at room temperature to conduct a charge/discharge test, and the first discharge was performed at 0.5C and then 0.2C/ Charging/discharging was continuously repeated at 0.2C. Through this, a capacity-voltage graph was obtained at the first discharge to evaluate the initial discharge performance, and a graph of capacity change according to cycle repetition was obtained to evaluate high rate performance (0.2C/0.2C).

5A and 5B are graphs of a first cycle profile and cycle data for lithium-sulfur secondary batteries each prepared in Example 3, Comparative Example 3, and Comparative Example 6, respectively.

5A and 5B, it can be seen that the lithium-sulfur secondary battery of Example 3 has relatively superior battery performance compared to Comparative Examples 3 and 6.

In the above, although the present invention has been described by limited embodiments and drawings, the present invention is not limited thereto, and the technical idea of the present invention and the following description by those of ordinary skill in the art to which the present invention pertains. It goes without saying that various modifications and variations are possible within the equivalent range of the claims to be made.

Claims (8)

A vanadium oxide-sulfur complex comprising vanadium oxide and sulfur represented by the following formula (1):
[Formula 1]
V _n O _{2n +1}
In Formula 1, n is an integer of 3 to 10. The method of claim 1,
Containing 20 to 40% by weight of the vanadium oxide and 60 to 80% by weight of sulfur, vanadium oxide-sulfur composite. The method of claim 1,
The vanadium oxide is V ₃ O ₇ , V ₄ O ₉ And V ₆ O ₁₃ at least one selected from the group consisting of, vanadium oxide-sulfur complex. Current collector; And a positive electrode active material layer formed on at least one surface of the current collector,
The positive electrode active material layer comprises the vanadium oxide-sulfur composite according to any one of claims 1 to 3, wherein the positive electrode for a lithium secondary battery. The method of claim 4,
The binding force between the current collector and the positive active material layer is 30 to 300 kgf / m, the positive electrode for a lithium secondary battery. The method of claim 4,
The sulfur loading amount of the positive electrode is 4.0 to 10.0 mg/cm 2 per 100 μm of the positive electrode thickness, a positive electrode for a lithium secondary battery. A lithium secondary battery comprising the positive electrode of claim 4. The method of claim 7,
The lithium secondary battery is a lithium-sulfur secondary battery, a lithium secondary battery

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