KR20050021131A - Lithium/sulfur secondary batteries with coated separator having improved charge and discharge properties - Google Patents

Abstract

PURPOSE: Provided is a lithium/sulfur secondary battery to prevent the loss of a sulfur electrode due to the dissolution of the sulfur of a positive electrode into a negative electrode and to improve electrical conductivity for reducing the interface resistance of an electrode. CONSTITUTION: The lithium/sulfur secondary battery comprises a positive electrode current collector(11), a positive electrode(12) prepared from a positive electrode active material, a separator(14) where an electrolyte is infiltrated, a negative electrode(15) prepared from a lithium metal or a lithium alloy, and a negative electrode current collector(16) which are layered in turn, wherein the separator where an electrolyte is infiltrated is a polymer layer, and the surface of the separator is uniformly thin film coated with at least one selected from the group consisting of Au, C, Ag, Pt and Cu. Preferably the coating is carried out by plating, sputtering, vapor deposition or vacuum evaporation deposition.

Description

Lithium / sulfur secondary batteries with coated separator having improved charge and discharge properties

The present invention relates to a lithium / sulfur secondary battery capable of improving charge / discharge characteristics of a battery by preventing a loss due to dissolution of sulfur and electrical conductivity coated on a surface of a conductive gold (Au). . More specifically, in order to prevent the loss of the sulfur electrode and improve the electrical conductivity, a separator coated with gold (Au), which is a highly conductive material, is used to prevent the sulfur of the anode from dissolving toward the cathode and to prevent the loss of sulfur. The present invention relates to a lithium / sulfur secondary battery capable of increasing an interfacial resistance of an electrode.

With the rapid development of portable electronic devices, the demand for secondary batteries is increasing, and there is a continuous demand for the emergence of high energy density batteries that can meet the trend of light and small size of portable electronic devices. To this end, there is a need for the development of batteries that satisfy inexpensive, safe and environmentally friendly aspects.

Lithium / Sulfur battery is the most promising in terms of energy density among the batteries developed so far, and the energy density of lithium is 3830 mAh / g and the energy density of sulfur (S ₈ ) is 1675. The active material itself used in mAh / g itself is a cheap and environmentally friendly material, but there are no examples of successful commercialization with this battery system. US Patent No. 5,523,179, US Patent No. 5,814,420, US Patent No. 6,030,720, and Korean Patent No. 316,587 provide technical improvement directions for solving the above problems.

On the other hand, there is a problem in that deterioration of battery life should be solved by using lithium metal as a negative electrode. In other words, when the sulfur dissolves in the electrolyte and moves toward the lithium electrode due to the discharge, the battery capacity decreases due to the corrosion of lithium caused by the reaction between the lithium surface and the electrolyte.

The present invention has been made to solve the above problems, an object of the present invention is to provide sulfur from the sulfur electrode through a metal-coated separator such as gold (Au) to improve the life characteristics of the lithium sulfur secondary battery It is to provide a lithium / sulfur secondary battery that minimizes movement to a lithium electrode and has excellent electrical properties and advantageous in reliability.

The lithium / sulfur secondary battery of the present invention for achieving the above object is a positive electrode made of an active material selected from the group consisting of a positive electrode current collector, a single element sulfur, lithium sulfide and lithium polysulfide, ion transfer It characterized by consisting of a separator, a negative electrode and a negative electrode current collector made of a lithium metal or lithium alloy impregnated with an electrolyte that enables the battery reaction by.

According to the present invention, the positive electrode is formed by selecting at least one active material containing sulfur, for example, from the group consisting of elemental sulfur (S ₈ ), lithium sulfide and polylithium sulfide (Li ₂ S _x , X> 1). A homogeneous slurry prepared from an active material, a conductive material made of carbon or a conductive polymer, a binder such as PVdF, and a solvent such as tetrahydrofuran (THF) is produced in a film form by glass casting.

The active material of the negative electrode is made of a transition metal, for example, Li, Na, Mg or an alloy of transition metal or carbon, and most preferably a lithium metal or a lithium alloy.

The electrolyte which enables the battery reaction by the ion migration is prepared by magnetic stirring by completely dissolving lithium salt in a plasticizer. The plasticizer is polyethylene glycol dimethyl ether (PEGDME), triethylene glycol dimethyl ether (TRGDME), At least one selected from the group consisting of tetraethylene glycol dimethyl ether (TEGDME), ethylene carbonate (EC), propylene carbonate (PC), dioxolane, sulfolane and dimethyl ester (DME) can be used.

According to the present invention, the separator impregnated with the electrolyte has a pore having an average diameter of 0.005 to 50 μm and a porosity of at least 20% by volume or more, and the surface thereof includes gold (Au), carbon (C), and silver ( At least one from the group consisting of Ag), platinum (Pt) and copper (Cu), preferably gold (Au), is homogeneously thinly coated. The coating method for such a separator may be any one of plating, sputtering, vapor phase deposition, and vacuum deposition.

The operation principle of the coated separator is a coating film such as gold (Au) formed on the surface of the separator serves to block the pores of the separator to be able to arbitrarily adjust the size of the pore according to the coating time, the appropriate size of the pores It is free to go in and out, but sulfur is dissolved in electrolyte and it is prevented from moving toward the lithium electrode.

This invention will be described in more detail based on the examples.

Example 1

Preparation of Membrane

The separator is composed of pores with an average diameter of 0.005 to 50 ㎛, porosity is at least 20% by volume or more, it was used made of a polymer having a predetermined composition.

The gold coating of the separator was performed using a DC magnetron sputtering apparatus using gold as a target material, the separator was placed on a substrate, and the membrane surface thin film coating was performed for an arbitrary time. The distance between the substrate and the target was 12 cm and the sputtered angle was kept constant so that the surface of the separator could be uniformly coated with gold.

Figure 2a is a SEM photograph of the gold-coated separator prepared in Example 1.

Positive electrode manufacturing and battery composition

50% sulfur (-200 mesh, ALDRICH Co.) powder as an active material, 30% carbon (<1 μm, acetylene black) as a conductor, 20% PVdF as a binder, were ball milled for 5 minutes, and the powder was evenly distributed. After mixing, 40 ml of a solvent, tetrahydrofuran (THF) was added thereto, and stirred for 1 hour to obtain a homogeneous slurry. The atliter container and the ball were made of stainless steel, the atliter container was 5 cm in diameter and 7 cm in height, and the weight ratio of the ball to the sample was 20: 1 wt%. After ball milling, the state of the sample became a viscous liquid, and the sample was glass cast on a glass plate.

After glass casting, the specimens were dried at room temperature for 24 hours, and vacuum dried (5 × 10 ⁻⁴ Torr) at 60 ° C. for 24 hours. After drying, the sample was formed into a film having a thickness of about 40 μm.

Lithium metal (Cyprus Foote mimeral Co.) was used as the electrode material of the cathode.

As the electrolyte, 1.56 mg of lithium trifluoromethanesulfonate (LiCF 3 SO 3, Aldrich Co.) as a lithium salt and 10 ml of tetra (ethylene glycol) dimethyl ether as a plasticizer were used. The two materials were placed in a Erlenmeyer flask and dissolved by magnetic stirring using a magnetic bar for 3 hours to completely dissolve the lithium salt in the plasticizer.

In the cell assembly, the prepared anode and separator were left in a vacuum oven (60 ° C.) for at least one day, and then moved to a glove box where moisture and oxygen were controlled. The positive electrode plate, the negative electrode plate, and the separator were cut to a predetermined size and stacked using a Swagelok cell in the order of the separator / sulfur electrode impregnated with a lithium / liquid electrolyte as shown in FIG. 1. The prepared battery was repeatedly charged and discharged at a constant current density of 50 mAh / g of sulfur to compare the life characteristics thereof. The results are shown in FIG. 3. Here, the charge and discharge cut-offs were made at 3.5V and 1.7V, respectively.

Comparative Example 1

A lithium / sulfur secondary battery was prepared in the same manner as in Example 1 except that gold was not coated on the separator in Example 1, and the prepared battery was charged and charged at a constant current density of 50 mAh / g of sulfur. The discharge was repeated to compare the life characteristics and the results are shown in FIG. 3. Here, the charge and discharge cut-offs were made at 3.5V and 1.7V, respectively. 2b is a SEM photograph of the membrane not coated with gold.

As shown in FIG. 3, in the case of the lithium / sulfur secondary battery of Example 1 according to the present invention, the rate of decrease in electrical conductivity due to repeated charging and discharging and cycle progress was significantly low, whereas in Comparative Example 1, the electrical conductivity was low. It can be seen that the rate of decrease occurs significantly.

The present invention is intended to minimize the loss of sulfur through the gold (Au) coated separator in order to improve the life characteristics of the lithium / sulfur secondary battery, the gold coated separator is characterized by the electrochemical characteristics, which is a disadvantage of the lithium / sulfur secondary battery As a complementary method, there is an effect of providing a battery which is advantageous for improving the life of the battery.

According to the present invention, the gold-coated separator minimizes that sulfur of the anode dissolves in the electrolyte and escapes from the cathode during charging and discharging of the battery, thereby causing the lithium electrode to corrode by reacting the dissolved sulfur with lithium of the anode. By reducing the electrical conductivity and the growth of dendrite in the lithium electrode formed according to the amount of sulfur loss due to the progress of the cycle to improve the life characteristics of the lithium / sulfur secondary battery, while improving the stability and reliability of the battery It can be effective.

1 is a cross-sectional view of a lithium / sulfur secondary battery according to the present invention.

Figure 2a is a SEM photograph of the gold-coated separator prepared in Example 1 of the present invention.

FIG. 2B is a SEM photograph of the separator not coated with any metal of Comparative Example 1. FIG.

3 is a graph for showing a change in electrical conductivity according to the progress of the cycle of Example 1 and Comparative Example 1.

<Description of the symbols for the main parts of the drawings>

11: positive electrode current collector 12: positive electrode

13 coating layer 14 separator

15: negative electrode 16: negative electrode current collector

Claims (5)

A positive electrode current collector, a positive electrode made of a positive electrode active material, a separator impregnated with an electrolyte that enables battery reaction by ion migration, a negative electrode and a negative electrode current collector made of lithium metal or lithium alloy are laminated in this order. The membrane to be impregnated is a polymer membrane whose surface is homogeneously thin film coated with at least one from the group consisting of gold (Au), carbon (C), silver (Ag), platinum (Pt) and copper (Cu). Lithium / Sulfur Secondary Battery. The method of claim 1, wherein the positive electrode is an active material including carbon selected from at least one selected from the group consisting of sulfur (S ₈ ), lithium sulfide and polylithium sulfide (Li ₂ S _x , X> 1), carbon or A lithium / sulfur secondary battery, which is made of a homogeneous film type prepared from a conductive material made of a conductive polymer, a binder made of a polymer, and a solvent. The lithium / sulfur secondary battery of claim 1, wherein the active material of the negative electrode is made of Li, Na, Mg, or a transition metal alloy or carbon, which is a transition metal. The method of claim 1, wherein the electrolyte that enables the battery reaction by the ion migration is prepared by the magnetic stirring method by completely dissolving a lithium salt in a plasticizer, the plasticizer is polyethylene glycol dimethyl ether (PEGDME), triethylene glycol At least one selected from the group consisting of dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), ethylene carbonate (EC), propylene carbonate (PC), dioxolane, sulfolane and dimethyl ester (DME) Lithium / sulfur secondary battery, characterized in that. The lithium / sulfur secondary battery of claim 1, wherein the coating is performed by any one of plating, sputtering, vapor phase deposition, and vacuum deposition.