KR20150026098A - Cathode for lithium-sulfur battery and method of preparing the same - Google Patents

Abstract

The present invention relates to a positive electrode for lithium-sulfur batteries, which includes a porous carbon foam and sulfur wherein the sulfur is included in the porosity of the porous carbon foam, a lithium-sulfur battery including the positive electrode for the lithium-sulfur battery and a manufacturing method of the positive electrode for the lithium-sulfur battery where provided are a positive electrode for a lithium-sulfur battery, which increases sulfur loading amounts because a binder resin is not included and is manufactured in a simple manner, a lithium-sulfur battery including the positive electrode for the lithium-sulfur battery and a manufacturing method of the positive electrode for the lithium-sulfur battery. For this, in the present invention, provided is the positive electrode for a lithium-sulfur battery including a porous carbon foam and sulfur wherein the sulfur is include in the porosity of the porous carbon foam.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode for a lithium-sulfur battery,

This specification relates to a positive electrode for a lithium-sulfur battery and a method of manufacturing the same.

Until recently, the issue of developing a high energy density battery using lithium as a cathode has attracted considerable attention. The lithium metal can be compared with other electrochemical systems having a lithium-inserted carbon anode and a nickel or cadmium electrode, for example, which increases the weight and volume of the anode by the presence of a non-electroactive material to reduce the energy density of the cell Has a low weight and a high energy density, and thus attracts much attention as an anode active material of an electrochemical cell. A negative electrode mainly comprising a lithium metal negative electrode or a lithium metal provides an opportunity to construct a battery which is lighter and has a higher energy density than a battery such as a lithium ion, a nickel metal hydride or a nickel-cadmium battery. These features are highly desirable for batteries for portable electronic devices, such as cell phones and lab-top computers, where premiums are paid at low weights.

Cathode active materials for lithium batteries of this type are known and include sulfur-containing cathode active materials containing sulfur-sulfur bonds and are used for electrochemical cleavage (reduction) and reforming (oxidation) of sulfur- Rechargeability is achieved.

As described above, the lithium-sulfur battery using lithium and alkali metal as the anode active material and sulfur as the cathode active material has a theoretical energy density of 2800 Wh / kg (1675 mAh), much higher than other battery systems, And is attracting attention as a portable electronic device because of its advantage that it is cheap and environmentally friendly material

 However, since sulfur used as a cathode active material of a lithium-sulfur battery is an insulator, it is difficult to transfer electrons generated by an electrochemical reaction. Usually, conductive carbon is added. In order to adhere a cathode active material to an anode current collector, .

 When the amount of the added substance is increased at a limited weight of the anode of the lithium-sulfur battery, the content of sulfur is reduced, so that a structure for maximizing the content of the lithium-sulfur battery at the anode of the lithium- .

Korean Unexamined Patent Application Publication No. 2007-0063185

The present invention relates to a positive electrode for a lithium-sulfur battery which can increase the sulfur loading amount without containing a binder resin and which can be produced by a simple process, a lithium-sulfur battery including the positive electrode for the lithium- And to provide a manufacturing method thereof.

The first embodiment of the present disclosure relates to a porous carbon foam; And sulfur, wherein the sulfur is contained in the pores of the porous carbon foam.

Also, the second embodiment of the present invention relates to a negative electrode comprising: a negative electrode; A positive electrode in the first embodiment; A separator positioned between the anode and the cathode; And an electrolyte impregnated in the negative electrode, the positive electrode, and the separator.

In addition, the third embodiment of the present invention provides a battery module including the lithium-sulfur battery as a unit cell.

In addition, the fourth embodiment of the present invention provides a method for manufacturing a positive electrode for a lithium-sulfur battery including the step of supporting a porous carbon foam in molten sulfur.

The positive electrode for a lithium-sulfur battery and the lithium-sulfur battery provided thereon do not include a binder resin for attaching an active material to a current collector, thereby increasing a sulfur loading amount of the positive electrode, .

Further, in the conventional production process of a positive electrode for a lithium-sulfur battery, a positive electrode for a lithium-sulfur battery can be produced by a simple process in which molten sulfur is supported on a porous carbon foam without a mixing process for forming a composite structure of conductive carbon and sulfur.

FIG. 1 is a graph showing the results of measurement of a lithium-sulfur battery manufactured in Example 1 and Comparative Example 1, when charging / discharging of 0.1 C / 0.1 C charging / discharging 100 cycles was repeated, And the specific capacity of the battery.

The first embodiment of the present invention provides a positive electrode for a lithium-sulfur battery.

In this specification, the porous carbon foam refers to a carbon aggregate having a certain shape and containing a plurality of pores. The porous carbon foam may be TGP-H-030, TGP-H-060 manufactured by Toray, 35 BC, 31BA manufactured by SGL.

The carbon contained in the porous carbon foam may be crystalline or amorphous carbon. The conductive carbon is not limited as long as it is a conductive carbon. Examples of the carbon include graphite, carbon black, activated carbon fiber, inert carbon nanofiber, Fabric or the like.

In one embodiment of the present disclosure, the weight ratio of carbon to sulfur in the anode is greater than or equal to 2: 1 and less than or equal to 1: 4.

In one embodiment of the present invention, the content of carbon in the anode is 10 wt% or more and 50 wt% or less based on the total weight of the anode.

In one embodiment of the present invention, the content of sulfur in the anode is 50 wt% or more and 90 wt% or less based on the total weight of the anode.

In one embodiment of the present disclosure, the pores of the porous carbon foam have an average diameter of 30 탆 or more and 100 탆 or less. When the average diameter of the pores is less than 30 탆, the capacity of the battery is decreased due to a decrease in the amount of sulfur loading. Therefore, when the average diameter of the pores exceeds 100 탆, The utilization of sulfur is lowered and the performance of the battery is reduced.

In one embodiment of the present disclosure, the pores of the porous carbon foam are greater than 50% and less than 99% based on the total volume of the porous carbon foam.

In one embodiment of the present disclosure, the porous carbon foam is a network structure.

When the porous carbon foam has a network structure, pores are formed between the meshes, and the capacity of the cells can be improved by including sulfur in the pores.

The second embodiment of the present invention provides a lithium-sulfur battery.

The description of the positive electrode in the first embodiment can be applied to the positive electrode.

In one embodiment of the present invention, the negative electrode comprises lithium metal or a lithium alloy as the negative electrode active material.

The separator positioned between the positive electrode and the negative electrode separates or insulates the positive electrode and the negative electrode from each other and permits transport of lithium ions between the positive electrode and the negative electrode. The separator may be made of a porous nonconductive or insulating material. Such a separator may be an independent member such as a film, or may be a coating layer added to the anode and / or the cathode.

The material forming the separator includes, but is not limited to, polyolefin such as polyethylene and polypropylene, glass fiber filter paper, and ceramic material. The thickness of the separator is about 5 탆 to about 50 탆, specifically about 5 탆 Can be about 25 [mu] m

The lithium alloy may be an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al and Sn.

In one embodiment of the present specification, the electrolyte comprises a lithium salt and an organic solvent.

The lithium salt is _{LiSCN, LiBr, LiI, LiPF 6} , LiBF 4, LiSO 3 CF 3, LiClO 4, LiSO 3 CH 3, LiB (Ph) 4, LiC (SO 2 CF 3) 3 , and LiN (SO ₂ CF ₃ ) _{2. &} Lt; / RTI >

The concentration of the lithium salt may be in the range of about 0.2 M to about 200 M depending on various factors such as the exact composition of the electrolyte solvent mixture, the solubility of the salt, the conductivity of the dissolved salt, the charging and discharging conditions of the battery, 2.0 < / RTI > M. Lithium salt for example for use in the present disclosure, LiSCN, LiBr, LiI, LiPF 6, LiBF 4, LiSO 3 CF 3, LiClO 4, LiSO 3 CH 3, LiB (Ph) 4, LiC (SO 2 CF 3) 3 and LiN (SO ₂ CF ₃₎ may include one or more from the group consisting of _2.

The organic solvent may be a single solvent or a mixture of two or more organic solvents.

When two or more mixed organic solvents are used, it is preferable to use at least one solvent selected from two or more of the weak polar solvent group, the strong polar solvent group, and the lithium metal protective solvent group.

A weakly polar solvent is defined as a solvent having a dielectric constant of less than 15 which is capable of dissolving a sulfur element among aryl compounds, bicyclic ethers and acyclic carbonates, and the strong polar solvent includes bicyclic carbonates, sulfoxide compounds, lactone compounds, Ketone compounds, ester compounds, sulfate compounds, and sulfite compounds, wherein the lithium metal protective solvent is a saturated ether compound, an unsaturated ether compound, N, O , S or a heterocyclic compound containing a combination of these, is defined as a solvent having a charge / discharge cycle efficiency of 50% or more to form a stable SEI (Solid Electrolyte Interface) on a lithium metal.

Specific examples of the weak polar solvent include xylene, dimethoxyethane, 2-methyltetrahydrofuran, diethyl carbonate, dimethyl carbonate, toluene, dimethyl ether, diethyl ether, diglyme and tetraglyme.

Specific examples of the strong polar solvent include hexamethyl phosphoric triamide,? -Butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl-2-oxazolidone , Dimethylformamide, sulfolane, dimethylacetamide, dimethylsulfoxide, dimethylsulfate, ethylene glycol diacetate, dimethylsulfite, or ethylene glycol sulfite.

Specific examples of the lithium-protecting solvent include tetrahydrofuran, ethylene oxide, dioxolane, 3,5-dimethylisoxazole, furan, 2-methylfuran, 1,4-oxane and 4-methyldioxolane.

The third embodiment of the present disclosure provides a battery module.

The battery module may be specifically used as a power source for an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage device.

The fourth embodiment of the present invention provides a method of manufacturing a positive electrode for a lithium-sulfur battery.

The method for producing the positive electrode for a lithium-sulfur battery can be applied to the description of the positive electrode for a lithium-sulfur battery in the first embodiment.

In the prior art, a carbon-sulfur complex was formed as a positive-electrode sulfur material of a lithium-sulfur battery through a process of mixing carbon and sulfur. However, in this process, a large amount of carbon is required, while sulfur is supported on the porous carbon foam, The positive electrode active material of the lithium-sulfur battery can be formed without addition of additional conductive material such as carbon.

In one embodiment of the present disclosure, the temperature of the molten sulfur is 120 deg. C or higher and 150 deg. C or lower.

Hereinafter, the present invention will be described with reference to Examples. However, the following Examples are intended to illustrate the present invention and the scope of the present invention is not limited thereto.

< Example  1>

SGL Co., Ltd. trade name 35BC (thickness 325 μm, porosity of 80%, the electrical resistance (surface) 15 mΩ · cm ^2, mass per unit area 110 g / m ²⁾ to be melted at 130 ℃ load by supporting the sulfur in the porous carbon foam Lt; ² &gt; / mAh / cm &lt; ² &gt; A lithium foil having a thickness of about 150 micrometers was used as a cathode and dimethoxyethane: dioxolane having 1 M LiN (CF ₃ SO ₂ ) ₂ dissolved therein as an electrolyte were mixed at a volume ratio of 5: 4 to prepare an electrolytic solution. A lithium-sulfur battery was fabricated using a polyolefin of micron thickness.

&Lt; Comparative Example 1 &

8.0 g of a sulfur-carbon active material mixed with carbon: sulfur at a weight ratio of 3: 7, 1.0 g of Super-P as a conductive material and 1.0 g of polyvinylidene difluoride (PVdF) as a binder were dissolved in N -Methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was coated on an aluminum current collector to prepare a sulfur-carbon positive electrode having a loading amount of 5.0 mAh / cm ² . A lithium-sulfur battery was produced in the same manner as in Example 1 except for the production of the positive electrode.

<Experimental Example>

The initial capacity of each cell was measured for each cycle while the lithium-sulfur battery prepared in Example 1 and the lithium-sulfur battery prepared in Comparative Example 1 were repeatedly charged / discharged at 0.1 C / 0.1 C for 100 cycles.

As shown in FIG. 1, the battery of Example 1 according to the present invention had an initial capacity larger than that of the battery of Comparative Example 1, and the cycle characteristics were excellent because the reduction width of the initial capacity was small even if the charge / .

Claims (11)

Porous carbon foam; And sulfur,
Wherein the sulfur is contained in the pores of the porous carbon foam. The positive electrode for a lithium-sulfur battery according to claim 1, wherein the weight ratio of carbon to sulfur in the positive electrode is 1: 2 or more and 1: 4 or less. The positive electrode for a lithium-sulfur battery according to claim 1, wherein the content of carbon in the positive electrode is 10 wt% or more and 50 wt% or less based on the total weight of the positive electrode. The positive electrode for a lithium-sulfur battery according to claim 1, wherein the content of sulfur in the positive electrode is 50 wt% or more and 90 wt% or less based on the total weight of the positive electrode. The positive electrode for a lithium-sulfur battery according to claim 1, wherein the pores of the porous carbon foam have an average diameter of 30 μm or more and 100 μm or less. The positive electrode for a lithium-sulfur battery according to claim 1, wherein the pores of the porous carbon foam are 50% or more and 99% or less based on the total volume of the porous carbon foam. The positive electrode for a lithium-sulfur battery according to claim 1, wherein the porous carbon foam has a network structure. cathode;
A cathode according to any one of claims 1 to 7;
A separator positioned between the anode and the cathode; And
An electrolyte impregnated in the negative electrode, the positive electrode, and the separator;
&Lt; / RTI &gt; A battery module comprising the lithium-sulfur battery of claim 8 as a unit cell. A method for producing a positive electrode for a lithium-sulfur battery, comprising: supporting a porous carbon foam in molten sulfur. The method according to claim 8, wherein the temperature of the molten sulfur is 120 ° C or more and 150 ° C or less.

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